Archive for the 'Bots' Category

 

Dragon Con 2018: Postmodern Robotics Comes Home With a Vengeance

Nov 08, 2018 in Bots, Dragon Con, Roll Cake

Coming hot off my end-of-July trip to the mountain range I keep seeing next to I-81, and aiming to complete my original intended run down to Atlanta via the Blue Ridge Parkway, I decided to do Dragon Con a little differently this year.

Normally I’d be transporting down a whole production of robots from everybody and myself. Life, it seems, hits everyone eventually in the most inconvenient of ways, and a lot of my usual crew couldn’t make it (it seems startups are the robots and elaborate cosplays du jour).  And so this time, I decided early on to stop any plans for developing the next Überclocker /30-haul during the 3 or so weeks of August I had, and only bring Overhaul for display and what of Roll Cake I could get together. I wouldn’t even pack a Markforged printer this time! Imagine that.

So really this was one of the lightest loadouts I’ve done for Dragon Con, ever.  This was actually going to be different for me, and I wasn’t quite sure how to feel about it: Taking an eternity to get down there, actually maybe doing con stuff for once, and only whipping out a robot when convenient. Who the hell would ever do THAT? Go to an entire 100,000+ attendance convention to do stuff that’s not build robots!?

I did a speed-run departing Monday night before the con (Now featuring actual speed!) down to the area of Fancy Gap, VA where, the next day, I jumped onto the Blue Ridge Parkway. I was more interested in the mountainous portions in North Carolina, more so than the scenery itself, so I elected to skip the portion in Virginia as well as not run the Skyline Drive park again. There were plenty of opportunities to take Vans Next to Nature photos.

This was somewhere in Western North Carolina. Where? Hell if I know. The group of motorcyclists in this same parking area didn’t seem to know either. It seems you’re not supposed to know, or pay attention, or care at all; just disappear into the woods and assume you’ll pop out the other side at some point.

I get it. Not as much as someone who actually likes Naturing would, but I do understand.

As night descended on Tuesday, I decided to call a stopping point in Little Swaziland Switzerland, a mountain resort town. This region is very popular with motorcycle tours, as can be seen with Mikuvan’s new and temporary friends here. When you need the size of a van with the cargo capacity of a motorcycle…. Polaris Slingshot. By the way, the NC222A loop around this area is absolutely fantastic. I’m sure it gets tiring if you have to drive it every day to go to work.

I lied. While I didn’t bring along a Markforged printer, I sure as hell did bring a printer in general! I grabbed my “derpy van of 3D printers” Flashforge to make some parts for…. something, on the way down. Yes, I ran it overnight in a hotel room. I ended up having to build a pillow fort around it so I could actually sleep.

By mid-afternoon Wednesday, I’d reached the outer limits of Asheville and….. decided to tap out.

Keep in mind the Blue Ridge Parkway are all very winding, slow 2-lane roads, and that’s no way to cover distance effectively. At some point, I actually had to reach Atlanta and check into my AirCNC.

I decided to express the rest of the way after a harrowing foot-to-the-floor 55mph 4000RPM, 3rd gear climb up the side of Mount Mitchell for what felt like 10 minutes straight. If there was one moment that I was going to blow up my freshly rebuilt engine, I felt like it was going to be right there, but it would have been worth it. Worse, I was low on fuel at that point – there are no gas stations on the BRP – and feared that the straight uphill pull was going to get cut short. I basically coasted down the rest of the way into Asheville to try and conserve fuel.

From Asheville, I took I-40 west until US-74, then followed that down to US-23 – a well known historical path of mine, which I followed to basically outside my old front door…..

 

…step? Nah, in the intervening year, my parents sold the house. I instinctively glided into my favorite gas station from throughout high school and visits during my years at MIT, on Exit 111 on I-85, but realized I had no more business there afterwards. That was a strange moment indeed.

So, onwards we go to my aircnc house in downtown Atlanta. My local chariot was awaiting as soon as I got there! How positively quaint. There’s been a ton of fuss around Atlanta about scooter rentals lately. I mean, my whole goal of getting a place this close to the convention – right over the Downtown Connector in the “Most Boston part of Atlanta”, the Old Fourth Ward, was so I could just (as we memed it) “Millennial my way over” – whether that means rideshare app or silly scooter rental.

To be entirely based: I completely support silly scooter rentals. The only reason, in my mind, that they don’t work is because governments have outdated patchworks of laws regarding vehicular traffic that isn’t private passenger cars – our current society arguably came of age with the expansion of suburbs centered around the private car, and legislation has ossified around this concept to the point of being cancerous, just like infrastructure spending that is continually strongly biased towards private passenger car use. Much of the battle over scooter rentals is what kind of vehicle to tax, title, insure, and operate them as, and the context of legislative preference for FMVSS-certified normal people cars is unavoidable.

Fight me – I own several shitty cars and several more shitty scooters.

It would also help if people didn’t throw them in rivers.

 

Hi. (灬♥ω♥灬)

Who I think were the owners of this Model 3 were watching me very intently from a restaurant outdoor seat, so I didn’t get any closer. I was otherwise going to get within an inch for this photo op.

Thursday Funday is over – onto the con!

Overhaul was going to live in the Robotics track room for the whole weekend, so I did that unloading Thursday night when everyone was getting in the area, so I had backup. It would be rolled out for the Battlebots-related panels and otherwise hidden under a tablecloth. It was part of the Battlebots watch party and the “How to Get on BattleBots” Q&A session.

So, how do you get on Battlebots? Well, hell if I know. It’s clear your robot doesn’t have to be good.

 

That night, I finished the last print at my AirCNC house (whose host said “Would the neighbors mind if I ran a 3D printer all night?” was the weirdest request he’d gotten). And what I’ve been printing all along were in fact parts for my Overhaul cosplay.

It’s a little known fact that Haru-chan, like all good characters, has a male analogue. We actually have a rough sketch of what I call “Haru-dude” made by Cynthia (Lushanarts) from after the rework of Haru-chan:

But he’s too hot for me to pull off, so I simply used it as a design guide and changed up a few things (and also making it more realistic to put together). The “Overhaul head scythe” would obviously not be happening for Dragon Con, but I’ll consider it for something in the future.

I basically modeled and printed the whole thing on the fly, literally during the trip down and on site. I brought a handful of things I figured would be helpful, such as Velcro straps and hot glue and the like. Most parts were not actually modified from the CAD models of Overhaul parts, but made from scratch to exaggerate certain features that would appear too small if I just printed wheel_hub_assy.iam.

3D printing: Replacing the time-honored artform of hand-crafting costume pieces with on-demand kitted disposable bullshit, as-a-service, just like every good millennial trend!

So here we are.

Oddly enough, I was once again behind the camera 99% of the time and only really got this one photo taken of me (credit to Aaron Fan). Oh well, it was the prototype anyway. I actually don’t know of any full-body photos at the moment.

Besides the wrist shanks, I got a gray utility vest and added button snaps to reflect the staggered bolt pattern on the frame rails. I made two “edgelord belt chains”, one out of actual number #40H roller chain from Sadbot’s pokey stick) and one with orange wire loom wrapped around it.

I also made some cartoony wheel sprockets (which are hijacked #80 sprocket models, because again, teeth that are realistic can’t be seen in real life) to clip onto my repurposed motorcycle boots which I used for “dude-Ruby”. I had a few different shades of blue going on, which I’d like to fix for a future more proper rendition.

 

Saturday night robots with a few more of the crew. A couple of AirBnB houses around the area definitely suffered some robot building shenanigans. This was primarily to finish the 30lber seen on the right, but also to work on beetleweights because Sunday SUNDAY SUNDAY is the Robot Microbattles!

Likewise, after I got done working on other peoples’ robots, I put the last few solder joints in on Roll Cake, then test drove it in the hallway (“Do you mind if I test robots indoors?”). It’s quick, but controllably so, and I was fairly comfortable handling it after a few minutes. I like this new drivetrain a whole lot – the slight lag and torque ceiling of the hub motors is completely gone. It’s almost too twitchy now, and I know for a fact the drive motor size can come down to the next smaller outrunner class and be fine – this will be on the docket for a revision.

Now, back to the post title. I said there was a lot of postmodernism in the robots this year. What do I mean by that as applied to robots?

Postmodernism, broadly speaking, encompasses schools of thought which criticize traditional rationality and notions of objectiveness, calling into question the nature of what we call objective truth. In its basest form it often revolves around the ironic deconstruction and decontextualization of something in a disseminable media format, whether it be visual, text, audio, etc.. In a postmodern reading of something, then, nothing is considered “sacred” or free from reproach, and ideas are stripped down to their essence, lampooned and prodded, and then promptly bolted to the front of your robot.

Stance Stance Revolution is an instantiation of postmodernism in robot fighting: from a vertical spinner foundation, the discs are rotated to lie at angles to create an entirely new robot concept. It simultaneously derives from yet rejects the notions of the traditional vertical disc spinner, and is a complete eyesore while doing so. It raises questions at once of why the epistemological fuck would you do that and huh, I never would have thought of that. That’s kind of cool. I guess.

i am the department head of the school of postmodern robotics. don’t question me.

In short, it seemed to me like more robots than usual this year were doing away with, or severely reinterpreting “being competitive”. For instance, this….

….is quite the expression of postmodern robotics. Elements from a proven topology – a 2WD vertical “eggbeater” style drum – are seen as the foundation, but it destroys all notions of being outwardly serious and competitive by the fully functional LED-lit rubber duck mounted to it.

The duck is a liability. It’s a target for opponents. It prevents any form of operating upside down or self-righting. It might fall off and end the match right then… because all the electronics were stuffed inside it.

But it is the central statement of the bot, at the end of the day. This is truly the beauty of Postmodern Robotics.

¯\_(ツ)_/¯

From another branch of Postmodern Robotics, this robot is simply a knife with wheels. Why? Fuck you. It’s a knife with wheels. Are you really going to argue?

 

Roll Cake after the battles were all done. It gave some damage, and took some damage. But most importantly, it moved! And spun! And flipped things, mostly itself!

Full Disclosure: I actually slept through half of MicroBattles. ggwp. I showed up in time to watch a few more matches and participate in two rumbles at the end. Overall, I’m content with how the bot handled itself in the arena. One of the drive motor pinions ended up letting go and I was down one drive side for much of the first rumble, but used the gyroscopic forces of the drum to hobble around and make a few more hits.

One thing I ended up discovering was that the flipper arm wasn’t aggressive enough, due to the more conservative linkage travels I designed in. If your flywheel doesn’t slow down much per use, it’s oversized for the load power. I can probably make the linkage fan out more and trade some more efficiency points for a higher travel.

I ended up not really having time to recharge the battery for the second rumble, so it was running out of power around the middle. Overall, not a very competitive outing, but it showed me the drivetrain idea was sound now and the weapon drive system is fairly flexible in terms of actual layout. I’ll design up another version which is more Roll Cake 3.1 than 4.0 with some changes, but in the back of my mind is also a flipper-focused (non-exposed drum/flywheel) version, more like Magneato of NERC 30lb Sportsmans which Überclocker has fought a few times.

Now, we move onto Monday and the full-size Robot Battles. Remember when I said something about bad ideas just being bolted to your robot? Well some times it’s not even with threaded hardware….

That’s…. an interesting approach. Why so many ducks? Well, why not!? Better yet, they’re all squeak toys. Whenever this robot landed off the stage, it usually let out a protracted squeal sound from one OR MORE! of the ducks deflating.

It was otherwise a nondescript 4-drill-drive pusher bot. Postmodernism!

This is a robot which solely used a pool noodle for a weapon.

Appropriately named “Eyesore”, a newbie team (yay!) with a love for fluorescent paint.

 

nice bite force

 

Now we’re getting extra weird here. What do the ladybug balloons do on this robot? Nothing in particular. Yes, it fought every match with them!

There were not one, but two mildly-modified Roombas (and Roomba clones, as seen above) with things appended to them. One was in fact still “autonomous”, as autonomous as a Roomba can be, and was simply set loose on the stage.

This is a….

You know what? This isn’t even postmodernism any more. An entry with a FULLY FUNCTIONAL, ALL 3D-PRINTED tower crane on top of it? Now you could say we’re hitting on the territory of…

poststructuralism.

Get it? It’s a crane. Structures. Hhhhueuheue

This little saw-bot returns from previous years with an overpowering serving of new incongruently-themed stickers.

(Saws on an open stage?! I always take the time to explain that all freely-spinning appendages of robots are limited to 20ft per second tip speed in the Robot Battles rules, in case the message doesn’t carry through on first glance).

And finally, the robot I was helping work on, Skuld! Built by Leanne from Valkyrie, it’s a 30lber that has a very competently-powerd hammer with a 63mm-class outrunner. This thing could hit hard if it needed! It also had brushless drive with some highly geared inrunners.

That’s not a safety cover on the hammer arm end. That is the hammer arm end: One of several interchangeable plushies.

r/PostmodernRoboticsInAction

 

This is what the ideal robot fight looks like. You may not like it, but this is peak performance.

I don’t even know what the snout-on-a-piece-of-wood is from, but it paired with a powerful drive base is surprisingly effective.

Look! I entered a robot this year! It’s only 217 pounds overweight, no biggie.

On a last minute whim before the 12lb 30lb rumbles, we decided to heave Overhaul on stage to act as an arena hazard (it’s not running since I haven’t repaired the ESC damage from #season3 yet). It added an interesting play element: Suddenly, there was something to drive around and play hide-and-seek behind. People used Overhaul immediately to their advantage this way, skulking around looking for easy openings. Bots with giant wheels could escape by just driving up and over the forks. At one point, 3 or 4 30lbers teamed up to try and push Overhaul – they got a few inches in before the party got violent and broke out into fighting.

Probably one of the best rumbles I’ve ever witnessed come out of this event. It really makes me want to add a terrain element to the MassDestruction arena even more, in order to change up the small-bot game.

And this concludes your introductory lecture to Postmodern Robotics! I took a while to meander back north afterwards. Overall, I can say this Dragon Con was way more stress-free than any previous one. I was happy to see the competitive edge coming off of Robot Battles again, because a few years ago, when I and Jamison and many others were in (or around) colleges, we went through what I call the Tryhard Era of Robot Battles where the matches were becoming just as intense as any of the NERC parties and newbies were getting shut out or demolished. With the return of the TV shows, a lot more folks are cutting their teeth (metaphotical, drum, or otherwise) at these events, and I’ll happily step aside (or sleep through) them to let the interesting unjaded, sacrilegious designs fluorish.

On deck for the immediate arrival of fall is a lot of company-related pregaming before winter really sets in, so I’ll probably have limited content again for a little while. I’ll be slowly picking at 30haul, Overhaul, and the silly van nation in the mean time, but probably aren’t going to do any intense building until well after the new year.

Roll Cake 3: The Build!

Oct 09, 2018 in Bots, Roll Cake

It’s time to put a robot together! This post covers the entire fabrication of Roll Cake 3 in the week or so before Dragon Con. The goal of the bot was primarily to try and drive better with an indirect drive brushless setup and also further refine the packaging and action of the flipper linkage. Will it do anything?! Hell if I know, that’s the fun part to discover!

Even as I was finishing up the design the weeks prior, I was pregaming getting parts. Basically as soon as I determined the C2028 motor would fit in the triangle behind the wheels, I went ahead and ordered 3 more since I only had 1 to start with.

I also ordered these OMG THE MOST ADORABLE LITTLE 0.8 MODULE PINIONS EVER THAT COST WAY TOO MUCH MONEY from SDP-SI. I had to go solely by what they sold for 2mm bores in these gears. I wanted an 8-tooth gear to achieve the 8:1 reduction I wanted to get with the wheel gears, but they only sold the 8-tooth with a 3mm bore. So my drivetrain reduction is going to end up more like 10.6:1, which is fine by me – the bot will be too fast no matter what.

The problem with these tiny gears? The 2mm bores were slip-fit, not press-fit! Certainly irritating, but not the end of the world. Already noted for a revision in the future is maybe transitioning to R/C model pinions, such as R/C car transmissions. Those typically come in 3mm or 1/8″ bores.

I used Loctite 609 to stuff the pinions onto the motors in the end – I tried to silver solder one of them to little success – while I’ve managed to solder or braze pinions before, it seems that the steel they used in this motor shaft is an unusually high chromium grade which didn’t want to take with any flux I had on hand.

That was before I melted the pinion completely. Ah well.

Completed drive motors refitted with their shafts, which was a minor press fit job. I also replaced the stock stainless steel prop-saver screws with drilled-out and re-tapped #4-40 set screws. Another minor point of trouble with these motors is that due to their length and the small shaft diameter, it was hard to get these things to spin entirely true again after resintalling the shaft. A shorter motor (more pancakey) will resolve this.

I put the gearbox parts on print in Onyx as soon as I finished the bot design. The two ring gears and main cam linkage (sticking off to the left) have hoops of carbon fiber; everything else just derives strength from a bunch of perimeters. On the very left are the two connecting links between the cam link and the arm. I also made two first-pass prints of the drive wheels, seen here with O-rings.

Frame parts freshly done and needing cleaning. I’d say this is the only irritating part of doing unibody bots for me – picking the support out of difficult crevices. There’s certainly orientations that I can print in for minimal support, but they sacrifice immense strength in the part itself.  Both of these frame halves were printed in the orientation shown to give continuous loops in the XY (flat) plane.

In Roll Cakes past, I’ve actually taken to making fiber laps around the frame in this orientation, but with the more recent-ish changes to Eiger, you can change the perimeter and fill with more flexibility such that I just stack on the perimeters.

Otherwise, pull out some injection-molded part design – relatively constant wall thickness and smooth transitions if you can manage it, using ribs and cavities versus just solid massive areas, etc. However, my habit with 3D printed frames is leaving a few bulky areas up front such that they remain somewhat hollow – this acts as a very effective energy absorbing medium. For instance, basically the front inch or so if this bot is solid in the model, which means it’s perimeter plus non-solid infill in real life.

 

Drive motor installed with some test fitting done on the wheels here. Most of the hardware on Roll Cake 3 is specified as plastic or metal threadforming screws. If you get really fancy, people like using heat-set or tanged flanged inserts in MarkForged prints. However, I like my expediency, so some fat #10 tri-lobe threads will do to hold the wheels on.

Here’s the final drive fitup. The 0.8 Mod (32-ish DP) gears printed perfectly fine. In my experience, this is about as small as you can print reliably because the nozzle diameter still is small enough to go in and out of tooth tips profiles.

 

Both sides now fitted with drives. The front binding screw is shown sticking out here.

…and now joined together. Already, this thing is way more rigid than last time side to side. Hell, I might as well just ditch the flipper and make it a pure drum :v

The screw length needed to do this assembly were compromises with what I had on hand, so the bot dimensions shifted a little to accommodate them. Roll Cake is in fact not a perfect circle, but slightly squished inwards to yield the rough double-D-flat shape.

I slid in the trigger piece (which has a cutout for the servo arm) first, then I slid the servo into the DMs.

Alrighty, all the easy 3D printed stuff is assembled now. I still have to make a drum and motor, so off to Taki-chan we go!

(Also, check out the waterjet-cut feeder wedges made from leftover Hardox 450 from Overhaul!)

First order of business: separate the motor magnet ring so I can stuff it inside the drum. This can’t always happen cleanly, depending on the motor’s construction. The Donkeys have a single-piece stamped steel rotor, so I simply chucked the shaft in and very carefully parted at the outside corner where the magnet ring area joins the endcap.

With a motor that has an aluminum endcap, it’s often scarier since the parts can separate and self-destruct.  Luckily, this operation went very smoothly with higher speed and gentler feed to keep the forces on the rotor low.

Next up is to rough the drum shape. Most of this was easy, but I had to make the dual-disk shape, so I had to cut a valley in the middle. I just went with multiple staggered parting tool cuts to nearly the right shape, then very very carefully and gently made really shallow passes side to side to clean the profile up. Very gentle. These insert tools really should not be taking any side forces. To do this without wallhacking, I’d have gotten a single wider custom-ground HSS tool or something.

 

Then I bored the drum interior. There’s three stepped diameters – one for the ring bearing, then the magnet ring of the motor, then the “doesn’t matter” internal diameter. For the output side “bearing-stem-gear” I just did a straight drill to 12.0mm since it did not have to be that precise.

Next up: stator holder.

With the aluminum parts roughed out, I decided to make the one odd piece, which is the gear-on-a-stick that will carry the drum energy into the gearbox. This was a pretty easy turning job, but remember, it’s also the other bearing of the whole drum. The center bore, then, had to be 1. a clearance, but not by much, and 2. very clean and precise.

I actually went out and bought a 8mm-plus-0.001″ …. yes, this exists in America…. reamer to make this bore. You read that correctly – it’s a 0.3159″ reamer.

The gear gets a cylindrical boss on both ends eventually. After I finished both sides, I actually had to take a wire brush on an angle grinder to it in order to deburr the gear tooth edges – there were many little burrs and swarf hanging on which would have prevented the gear mate from working.

Parts in the midst of preparation! The stator bore has been drilled and the stem gear keyed on the top surface seen.

Throwing it together for a quick test fit! Here’s where it’s clearly visible that the stem gear skewers the cam ring gear and the cam linkage.

The next task was to drill the tooth holes in the aluminum drum body. I no longer have my old indexing head that made guest appearances in many of my undergrad builds, since I donated it to MITERS years ago. So to make sure I’m able to place the teeth 180 degrees apart, I milled a very shallow flat, then rotated it to sit on that flat, then milled another one.

This ensured I can drill and tap both sides with relatively equal precision. The teeth are just 3/8″-16 alloy cap screws, so they thread right in.

After the drum body was fully fnished, I broached it for a 3mm key – the stem gear is shown here mated to it. The magnet ring pressed into position without much trouble.

Unfortunately, I didn’t have time to make a new set of cluster gears, so I had to take them out of Roll Cake 2. Sad, since I wanted to keep that bot fully operational if I could!

The thought has crossed my mind of hiring out a whole basket of little cluster gears to be made if I’m going to keep evolving this bot.

The catch with these compound planetary cluster-fuck gears is that they have to be assembled at specific angle, or phasing, since there’s a hard relationship between the number of gears and the relative tooth counts. I scratched alignment marks into them when I first put them together for Roll Cake 1, and still use them for reference.

The gray goop I have dripped all over the assembly is liquid bike chain wax. I’ve been avoiding using petroleum-based lubricants like common greases because I don’t want to risk damaging the nylon-based Onyx material from the solvent action. Grease would also add immensely to the no-load drag of the gearbox, which is already a lot happening for a weapon drive.

The planet carrier installs easily after the gears are properly phased in place. It looks from here that there’s a ton of stuff going on, but I guarantee you this is not the case :v

As I mentioned in the design post, this carrier now has its own bearing to support itself. This is a pretty odd (but still apparently some kind of standard) 8mm bore, 14mm OD bearing – very low profile.

The drum drops into place from the front. The service order of this thing is a little suboptimal – to service the drum, I have to disconnect it from the folding linkage, but the central pivot bolt doesn’t rise up out of the body’s central cavity…. so really I have to undo the bottom linkage anchor (those three screws in a row from the CAD model) first, then remove the arm hinge. At least I made sure to make it all serviceable with at most 2 tools this time!

After the drum and arm are mounted, it was time for electrical dressup.

Along with the feeder claws, I cut another insectweight top plate set out of this piece of 1/32″ blue spring steel shim. I bought like 10 feet of this shim some time during undergrad, and have slowly been generating robots out of it since. This thing made its first appearance all the way back in 2009 with Pop Quiz’s rebuild! I’m now on the very last 8-10″ of it after Roll Cake’s parts are accounted for!

For better or worse, picking the parts out of the mother material was one of the last things I did before absconding on  3-day long slow meander down to Atlanta for Dragon Con. On the way, I hit up the Blue Ridge Parkway, like I promised myself I’d do. I only brought Roll Cake and its suite of service tools and a box of parts I think I’d need (mostly electronics), and Overhaul for display. This Dragon Con was going to be a pretty clean show instead of scrambling to take care of a few robots – the reason for this is I was pretty much solo this time, as there was a lot of bad timing involved for the various startups and schemes my friends and I are all involved in.

So what’s better than finishing your bot in the airBnB room when you got into town? Not all that much. I pre-gamed some of the electronics wiring (like battery leads and the like) before I left, so installing the two drive ESCs (AfroESC 12A) and weapon ESC (Spider ZTW 40A with SimonK) was a quick affair. I was able to drive Roll Cake around on the floor to get a gauge for its handling – which is much, MUCH improved over the hub motor drive version.

It’s very quick, but much more maneuverably so than Roll Cake 2, which tended to twitch everywhere. I swear the twitching is better than it was! At least now I could predictably send the bot places, which is an improvement over before!

The flipper geartrain was very tight, though, because I hadn’t had the chance to run it fully in up until that point. It would take several minutes of just running the drum at maximum speed and also a while of keeping the linkage engaged to wear everything in.

Here’s Roll Cake 3 fully buttoned up!

And shown with the flipper linkage at full height. In the next episode, hopefully you’ll get to hear about what it did, if anything!

The Roll Cake that Won’t Die: Roll Cake 3.0

Oct 03, 2018 in Bots, Roll Cake

I still like to pretend that I build robots here on this website! So in preparation for the fall round of events I like to go to (Dragon Con, Franklin, and any MassDestructions we try to hold) I decided in August to try and keep making progress on my recent persistent itch – Roll Cake.

Roll Cake had never “done well” – really done much of anything – at a competition since my main focus each and every time is kind of getting the vision of the bot finally in physical form. Remember its origin story and how I’ve been meaning to build a kinetic flipper for years, but never quite gotten around to it. It’s a robot built around a vision of a exterior shape and layout I came up with more than a decade ago, so it’s almost suboptimal on purpose.

Roll Cake 1 was sort of the grand puking of the idea in which nothing really worked. Roll Cake 2 made the mechanism shine, but still had a deficient drive due to sacrificing drivability for space conservation. My goal with Roll Cake 3 was to improve its driveability while making the weapon much more aggressive; Roll Cake 2 had a rather light drum/flywheel being belt-driven by an undersized motor that frequently overheated or shed belts.

The story of Roll Cake 3 actually dates back to not long after the previous Franklin Institute event, to which I brought it in order to talk about Alternative Flippers with a few other builders – it didn’t compete.

After mulling life on the return trip, I began the design by throwing some parts at the version 2 frame CAD and seeing what stuck. The principal design goals for V3 were:

  1. Moving to indirect drive on the wheels – the direct drive, while workable, was obviously still not very controllable. I figured a very small motor could tuck in the wasted volume (there’s a lot of wasted volume on Roll Cake) behind the wheels and could get me a considerable reduction just with open spur gears alone.
  2. Moving, on the contrary, to DIRECT drive on the weapon. The little 22mm outrunner just wasn’t enough to drive the whole geartrain continuously while also spinning a weapon. I could, with the increased drum interior volume, actually have a beetle-class weapon (so, you know, if the flipper plan just falls off a quarry cliff and explodes, it will at least be just a spinner)
  3. And lastly, moving to a dead shaft instead of V2′s live weapon shaft. This was more or less driven by going to a hub motor weapon. I’ll talk more about the Implications of this design change a little further down.

I had a Turnigy  C2028 motor model already, so I used it as a modeling guide for the positioning of the motor. I placed a Stance Stance Revolution motor, a Multistar pancake outrunner, in as a placeholder for the drum motor, though I wasn’t keen on using it. A motor that was a little more primitive seemed a better fit for the weapon.

To explore the space, I ordered some of the cheapest, shittiest motors you could buy on Hobbyking in the 35 to 45mm size range:

I love Hobbyking for having the sheer gall to sell you a motor that doesn’t have bearings. The Donkey line has bronze bushings and is seemingly made precisely to be the parts-recycling minimum viable products they are. A lot of builders have used them as foundations for their own weapon drives, and so will I!

I miss making motors, so this will be a fun distraction too.

I ended up selecting the Donkey 3511 motor for its stator size, but more importantly, the 12mm stator bore. The blue and silver “DT700″ motor had a thicker stator that I liked, but sadly only had an 8mm bore.

Why the bigger bore? I said earlier I was intending to move to a dead shaft for this iteration. Roll Cake historically has been rather tenuously held together side to side, with relatively small cross sections of material in the center due to the need to fit the flipper linkage. Moving to a dead shaft design allows me to use the shaft as an additional structural member of sorts up front.

The downside is I’d have to make a stator hub that the shaft presses into, and to do that, the stator needs to have a larger hole in the middle. I was intending on keeping the 8mm steel shaft that Roll Cakes have used for time immemorial (as in, literally the same one from v1 and v2), so that meant the stator needed at minimum, say, a 10mm center hole.

I pulled my usual motor designing tricks of making a hub for the stator to mount on, upon which a tpye 68xx ring bearing fits over. I sized this for a 6806 bearing, which has a 30mm bore. It’s a design balance between clearing shaft and wires versus simply being overly large and heavier.

I next generated a rough drum weapon shape that’s hollowed out in the middle. All of the dimensions and spacings were adjustable at this point – the final weapon would be a different width entierly. This just gets me something to start throwing into the CAD model so I can do the fitment of the gearset.

The teeth are, in typical beetle fashion, some big countersunk alloy steel cap screws.

With an eye for weight, I made some parametric adjustable cuts into the drum to turn it into more of a ‘dual disc’ configuration not unlike Witch Doctor and Hypershock. The final drum weight is tuned by just making the cuts smaller or larger.

Next up was the magical Roll Cake gearbox. I made some design changes to make it up to 1/4″ narrower to make the weapon itself occupy more of the front width. The clutch ring now has a single tooth and no longer its own outer support bearing – instead, it simply has a smooth shoulder inside to gently ride on the planet carrier. The carrier itself will have a 8mm thin-section bearing bored into it instead. There will be some extra friction from the technically bearing-less clutch ring, but the much more OP drum should more than make up for it.  I also got rid of an equivalent support bearing on the offset cam ring and it now only has a single bearing also in the center.

To pass power from the drum into the gearbox via the now dead shaft, I had to do something rather unconventional. There is now a lot of stuff going on here, so bear with me….

The distal endcap of the drum (opposite the motor end) is bored out to 12mm and has a key broached in it. A stem gear with a 8mm clearance bore has a keyway milled in one end and is inserted into the drum endcap with a key. The gear’s stem is 12mm OD and passes through the 12mm support bearing of the offset cam ring, and both transmits rotational torque and supports impact loads from the drum.

There is no “bearing” inside the stem gear in the conventional sense – there is only reamed steel on polished hardened steel with some oil in between.  Hey, if there’s one thing I learned from begrudgingly rebuilding an engine, it’s that steel on steel with a bit of oil in between is how every car works. What could go wrong!?

I knew going in I was betting a lot on this… technically a fluid bearing, but whatever…. working out. The friction would be higher than a ball bearing by far, but I was going to bank on the length of engagement making up for it with a light pressure resulting from the contact area.

Anyways, the gear end of the stem gear interfaces with the existing split-planetary gearbox and makes the thing go up and down.

One of the biggest challenges of Roll Cake has always been where to put the battery. When you scale robots down, you inevitably hit a “component Planck Length” of sorts – essentially, at some scale of robotting, the parts stop getting usably smaller. For me, the prismatic battery has always been troublesome for packaging inside a wedge-shaped robot. I played around with several methods, such as this one placing the battery forward and vertical…

…and including the unpalatable approach of splitting the battery up into two smaller ones. I really didn’t want to deal with the extra wiring and now squeezing on space for other components.

But one night I had a moment of come-to-Plastic-Jesus clarity – perhaps it is a reasonable compromise (it is – there ain’t no Perhaps, I’m just stubborn) to ditch the notion that the flipper has to span the whole width of the bot. At this point in the bot’s evolution, I should be thinking in terms of what makes the design work and what it actually needs, versus still trying to stick to my vision of “robot go flap-flap”.

In mulling over the compromise for the arm design, I also included a mockup of the new wheels, which will have a spur gear included on them to mate with a pinion on the motor.  I ended up just rolling with the C2028 motor and ordered a few from Hobbyking. Optimal? Maybe not. Fits back there and in stock? Hell yeah!

I decided to keep the battery arrangement shown – where the battery is placed widthwise in the bot, leaving the left half or so open to be used for the flipper linkage. This suddenly freed up a WHOLE LOT of volume inside the bot, and it was honestly a relief.

Before I went further with that design, I actually backed up and basically started over on another thought in my head about the design. There’s technically nothing stating Roll Cake had to be round. In fact, V1 was not round. Having the corners back could result in the difference between fitting in the battery vertically versus not, so I tried generating a square (chamfered octagon, I suppose) version of the frame to see if that was profitable.

Admittedly I did get pretty far along here – I found a vertical cavity for the battery and even was able to make space for mounting the drum motor. There wasn’t really anything preventing me from going with this design.

What swung me back the other direction was actually the sheer amount of usable space opened by repositioning the battery in the round design. I did want a Roll Cake in which trying to injection-mold ESCs and hyraulic press wires inside wasn’t even going to be an issue. From there, with an ideally working bot, I would make space optimizations as needed.

Well that does it for me. I returned to the round design and began cutting out cavities for everything. There’s gratuitous volume now to put things, and almost makes me wonder if Roll Cake could be a little smaller. However, for now, the final diameter was driven by giving the most space to the drive wheels and batteries while retaining an acceptable arm width that didn’t reduce it to just a stick.

Adding internal boss features to support the drum hub and drive motors now. I also made a crossing retainer for the battery – it sits in a neat little cavity and is prevented from bouncing around by the low wall and the eventual top plate. The geometry for the trigger pin is also taking shape.

Inside the left half of the bot, I made more space-filling features to mount the trigger servo. The dimensions did require cutting a hole of sorts in the underside to clear the servo cable. I moved the servo up as far as I thought was reasonable while still keeping the trigger pin on a radial path into the clutch ring gear.

Smaller but important features are now rolled up including the integrated wheel pegs and the arm pivot. The wheel pegs were going to be a machined piece, but gradually became so short there was no point in machining a part and using a mechanical attachment method. Instead, just printing the peg would do!

Notice how the bottom of the peg has a flat on it – to counteract the messy nature of homogenous-material support lattices in 3D printing which never really prints bottom-sides cleanly, I just made the peg a D-flat to give a single flat surface for the support to finish and the part to build. The eccentricity potential of the wheel from the bearing being on an incomplete circle is going to be negligible; worst case I’ll stuff a shim into the gap.

I put the arm pivot at the very front tip of the bot to make the arm as long as possible in order to get free height at the flipping end. This constraint would drive the arm shape and the placement of the linkages.

I made a first approximation of the arm after that. It had to start out higher than the bot’s upper slope surface in order to clear the cam and ring gears, which is why there’s a mild kink in it. You can see the cam ring passing through the arm here – I used this as a guide to make a cut that was just barely enough to clear it.

From there, it was relatively easy to make the linkage by fixing the cam linkage centered in the bot and fixing the arm in the lowered position. The lower anchor is a simple pin joint I modeled on the backside of the center crossing span of the bot, so all I really needed to do is adjust lengths and the position of the pin joint on the arm itself.

I tuned the linkage lengths to give me in the end around 4″ of rise. The end driving constraint was not hitting the crossing span in the middle when extended, but also when folded, not closing more than about 60 included degrees (or 30 per side measured from the centered cam link as a baseline).

At that point, which is my mental cutoff for “sensible linkage”, the orthogonal loading force from pulling the linkage open is twice the actual opening force, and just gets worse as you collapse the linkage more.

(This, kids, is why your elaborate scissor lifts never work in 2.007…. wait until you take 2.12 and understand the Jacobian matrix)

 

Here is that “JUST BARELY” cut I talked about – when the cam’s coming up, there’s only a few thousands of an inch of clearance as the arm goes up.

In real life, as I found out, the slop in the system actually made it such that the cam lifting shoved the arm upwards, helping the linkage get started out of the folded position. Sci………ence?

As a matter of habit when designing the smaller bots, I began adding hardware to make things more realistic for weight. On a bot that’s tight in space selectively like Roll Cake, I also wanted a sense of where fastener heads were going to go. So it turns out McMaster actually has intricately-cut models of their shitty sheet metal screws for download. I didn’t even know shitty sheet metal screws were 3D modeled, really. Either way, it was handy to see how much fastener head you actually need to clear.

The arm and linkages also get their dose of “Real-ification” by the addition of shoulder screws and properly sized counterbores, thru-holes, and tapped holes.

The linkage length allowed me to finally add one feature that Roll Cakes Past have never ever had: a rear structural link. There was enough leftover space to put a crossing span in the back with a bolt to tie it together! This might be the most structurally sound Roll Cake yet.

Space was tight enough that I needed to put the bolt model in and make sure I could still tighten a nut. The length of the righthand cavity was adjusted a little bit to be just barely longer than the bolt, so I can, you know, actually install it.

The three holes in a row above the rear crossing span? It’s a removable piece, serviced from the rear of the bot, so I can install and uninstall the arm linkage.

It’s a little hard to see what’s going on here. This is a counterbored, hidden cross screw which holds the front half of the bot together. It’s installable from the outside by squishing it past the O-rings in the wheels. You’d otherwise barely know it’s there!

This might be a better view of where it goes. It is sunk about an inch into the right hand (here, left side) half of the bot before the thread diameter begins, in order to put that much plastic in compression first.

I moved onto making some kibbles and bits for the bot – here are two little feeder fangs to try and get under someone and make sure the drum gets first punch. They’ll be waterjet-cut from some kind of leftover steel.

We’re getting awfully close with the CAD now. I took care of some more last details, such as the tiny half-round ears for if the bot gets flipped over to prevent the drum from hitting the ground. While Roll Cake can obviously drive upside down, the double-sided flipper was deprecated post v1, so it still has an “up” side. Maybe one day I will try bringing the double-sided flipper back.

I then made wire passthroughs and filleted corners and broke edges. This is the now-complete “unibody” frame.

I took snapshots of the side cavities and traced them in order to generate conforming top plates. The hole locations were patterned where I could and kind of freelanced where I couldn’t, at a fixed distance from the nearest profile curve.

To actually make the bot, the monolithic model had to split into three pieces – the two halves, plus a drum axle retainer for the non-motor side. I generated cutting surfaces for this operation. The split is not linear, but has a jog in the middle to accommodate convenient locations to begin and end the frame profile.

The cover plates are modeled from the sketch drawings individually. I suppressed the monolithic body and  imported all of the cut pieces and properly constrained them in order to yield the multi-piece modeled frame.

So that does it for Roll Cake 3′s design. In the next episode, I have to actually build the damn thing!

The Overhaul Design and Build Series, Part 5: “Don’t you have to ship this on Wednesday, dude?”

May 31, 2018 in BattleBots 2018, Bots, Events, Overhaul 2

Yes, yes I do. STOP REMINDING ME OR YOU’RE HELPING MACHINE THINGS.

Well here we are, after the airing of the Overhaul vs. Sawblaze fight which will be on Science Channel’s website and other streaming service soon! I have a full writeup I need to do on the lead-in and post-match analysis for that one! That will come after the conclusion of the build series in this post.

We rejoin our heroe…. dumbasses in the 2nd-into-3rd week of March. March 21st was the latest ship date available for east coast teams in order for everything to make it there on time (or so we were told!?). Luckily, Overhaul was actually not in a bad position, at least compared to Season 2 when the extra long days really started kicking in. All I really had to do at this point was a final assembly, then work on remaining spare assemblies.

After the Week of #WeldingGoneWild, it was actually very easy to do a fitting of the whole front of the bot.

That’s about it. The only thing which wasn’t added in this photo was the clamp actuator itself.

I’m much more a fan of this design already. Once the whole thing is loosely assembled, there is a degree of “elastic averaging” *ahem* that goes on as all the bolts get tightened down, but after that, the arms are rock solid.

The drivetrain is being assembled more now. Check out the Markforged nylon engine timing chain style guides! The front chain was still a bit loose after this so (at the event) I ended up making a different set, to be shown.

The one on the right between the two motors is a little ridiculous. We were running so tight on time that I wasn’t going to get the #35 half-links of chain in on time, or at least too close to risk not being able to drive test. So I invented the stupidest possible chain -pincher for the intermediate drive chain – it was gonna wear out very fast with its profile, but would at least let me get some test driving in.

Closing up the other drive side. The design for serviceability that I did 2 years ago is really coming back to help me here. Remember, my team this year is scattered – Paige is working a real job across the country, Cynthia is occupied full-time and could only help on a limited basis with set-up operations, and I only had Allen’s help briefly with welding too. Most of the photos taken in this build series was work done by myself solely.

Here’s the first test-fitment of the entire bot with all hardware installed. I’m really liking all the design changes to the steel parts. In person, the new clamp and forks look better proportioned to the bot. At least to me, way better than OH2 for 2016.

(Fun game: See how many dumb project artifacts you can spot in the background of this and other photos. Chibi-Mikuvan currently resides under my desk.)

 

I spent an evening just pounding out spare parts for the incipient shipment. For one, I was short on drive motors now, but with a shipment of new HobbyKing Sk3 6374-192s waiting, I needed to key the shafts and secure the hardware. It was easier to pop the shafts out en masse and set up the mill properly.

This and more! I went through….. zero 2mm endmills, somehow. Still a harrowing operation.

It was now the weekend before, and I realized that I wasn’t going to be able to get my last round of waterjet-cut parts in time. These days, I get to be in the back of the line for MIT shop waterjetting – which I think is a very reasonable voluntary position to be in, as I have no official involvement any more with the institute. But dangit Sawblaze, you guys still do!

The electrical deck could conceivably just be drilled from a plate of aluminum, so that is what I ended up having to do. Out comes the TERRORISM. I just cut a chunk of 1/4″ aluminum plate out and started marking holes like high school Charles would have done, and he is always right.

Please do not ever, ever, ever do this. This is how you die. This photo is for illustrative purposes only and should never be attempted, building a robot is dangerous, etc. If you do, use the finest tooth blade you can get and have someone else pump WD-40 or cutting fluid constantly. Or you will die.

 

In the middle of the process. All the small holes are #4-40 tapped for Brushless Rages. Notice how I put six holes in some positions? This will be important later.

 

I’m loading up the bot with electrical deck hardware and wiring now. The shock mounts are in (and secured from the bottom) and some of the battery harness is visible.

The wiring for Overhaul this time was…… ad hoc, to say the least. I said I would dispense with the carefully cultivated greenhouse of busbars. The fanout occurs at the master switch terminals this time, with 8 gauge main leads splitting into multiple 12-gauge intermediate cables to the Brushless Rages. Single 6-AWG conductors handle the “fan-in” from the 4 batteries to the master switches.

The octopus taking shape, with ESCs installed.

Remember those 6-hole patterns? I had to temporarily use the 6-FET models for drive, keeping the 12-FETs for lifting and clamping.

What, are they magic or something? In actuality far underrated from their published specs?!

No, but I accidentally sold my entire product line – which is great – leaving ME with no remaining 12-FET units – which isn’t great. I had to dig into all my pre-production units here to even complete Overhaul at all. What is stock tracking even??

I wasn’t running off a cliff without a drone backpack, by the way. A month earlier, I had placed the assembly order for a new batch of Brushless Rages, but they wouldn’t get in until the Monday of the ship week and I was not taking any chances.

With the octopus wired in, the drive base is live for the first time. Check out the motor-on-a-stick I used to simulate having a clamp motor.

 

Overhaul prior to its first indoor test drive! At this point, I’d fight in 20 minutes if I had to. I think I was actually ahead of the curve here by a distressing amount.

 

I cleaned up and routed more wires into loom in order to un-nest the wiring some. This is inconceivably ugly to me, like a steaming fresh pile of partly-regurgitated dog squeeze smeared across a sidewalk by multiple unassuming passerby. I would never ship this in a consulting project. Yet some of y’all at the event said this was the cleanest wiring in a bot ever? What the actual hell is wrong with you?

(After seeing inside everyone’s bots, I’m not inclined to disagree. Sorry not sorry.)

 

Monday came, and hey! Look what’s here! More Brushless RageBridge units for all! I’d end up assembling 25 12-FET units and packing them with me to the event (not including my own spares, which were 4x for drive plus another 4x for spare overhead)

One of the put-off things was welding the wedges together beyond just tacking, so I spent much of Tuesday doing this. The plan was to take the tacked units to MIT to use one of the MIG welders I have access to and really smash them out quickly.  Using the bot itself as a welding jig made for expedient alignment of all my wooden dinosaur puzzle pieces.

DETHPLOW ™ was tacked together in the same fashion, by actually mounting all the pieces to the bot and locally squeezing with clamps.

For completion purposes, I fully TIG welded one set of pointy-wedges and mounted them on the bot in their final positions. TIG welding is truly the wrong technique to use for bitey pointy robot parts, in my opinion, since it takes so much time compared to MIG in an application where the sensitivity is not really reflected in the end product.

As I mentioned previously, it ended up pissing us off so much we immediately bought a MIG welder after we all got back from the event.

This, for instance, is DETHPLOW all MIG-welded together, a process which took only 15 minutes or so once it was jigged up. I designed all these pieces to be MIG-filled anyway. Here I am doing some TIG touchup on areas which I fell a little short with the wirefeed or missed, or had a gap that I couldn’t bridge as the fitup wasn’t 100% perfect. This is a fine state of affairs for me – blitzing and then fine tuning if needed.

One thing which occurred over the weekend was crate setup. I decided to just spent money this time to get an elegant and reusable SINGLE. PALLET. solution. As someone who’s had two double-pallet crates wrecked over two BattleBots seasons for reasons unknown, I decided I was much better off with a tall single pallet. U-Line came to the rescue with this 4′ x 4′ x 6′ tall snap-together crate,which I modified by adding some removable side-in shelving levels. The bot with its lift table and large tool chests/boxes was to fill the bottom floor, and more containerized accessory suitcases in the middle, along with the pictured Markforged gear – Markforged went ahead and lent me a 2nd printer for the event.

The top level would contain the loose large parts such as the frame rails and spare welded assemblies.

You know all those spare-everythings I was cutting and machining? They ended up in a tote which contained all the important mechanical bits of the bot. I’d prepped a full set of drive and lift motor spares, along with a few mor prepared motors. There was also enough cut tube sections to weld up a new clamp at the event if it came to be.

 

And here it is, Overhaul and all of its support equipment and tools plus spare parts, all ready to load up into….

 

Vantruck??????????????

 

THE PLOT THICKENS! During the week prior to shipment, a few of us NE builders came together to ally ourselves against the forces of time.

You see, Team Forge & Farm was planning to road trip across the country with their bot in tow. For a nominal fee of a few spare RageBridges, they were willing to also bring Overhaul along.

This effectively bought me an extra 4 days to work on the bot – in fact, the electrical work and spare welding photos you see were done after the 21st. On the Monday following shipdate, I picked up HUGE along the way and ended up in southern New Jersey.

 

…where, under the cover of darkness, we packed Earl’s truck up with our bots and his alike.

So… what’s in the crate? Well, there was still the lift cart and all of the already-completed spares, the printer, the mechanical tote, and other support equipment like the battery chargers and power supplies, and a few doen Ragebridges of various flavors. I handed off the radio suitcase and both of my event toolboxes off with the robot.

 

There were still a few kibbles I had to take care of after the bot went out but before I did. So, how do you jig up pieces for welding with you don’t have a robot???

You 3D print an imitation of the robot! This is an Onyx print with the same hole spacings and offsets as an Overhaul front frame rail. I used it to tack the pieces together quickly (as to not melt anything) before removing them.

And with that, the build of Overhaul 2 for the new BattleBots concludes. To be entirely honest, I found this build season pretty stress-free, largely because I didn’t have to build a new bot from scratch and was making only well-scoped changes I had anticipated in advance. In the position I am in now working on a new company with my friends, I don’t think I could have pulled off the record build of OH2 for Season 2 in 2016. My (and my friends’) experiences in this build and competition season of BB – without going into NDA details of the show – has really shown me that I have to move back to a “When it’s ready” format like I had to do during my busiest times at MIT trying to vaguely graduate on time. I have a lot of thoughts on the show as a whole and the direction I’d like to move in (and the show should/shouldn’t move in) that are much better reserved until after the entire show airs.

But for now, hang out here a bit for the event report and a SawBlaze vs. Overhaul post-match!

And now a word from our sponsors!

HobbyKing – Somehow still loves me and enthusiastically supportive of my efforts to abuse R/C model parts for unintended applications! I’m running a HobbyKing radio (9XR Pro) and batteries (Graphene 6000 65C 6S packs, times 4), motors (SK3 63-series), BECs, and a whole lot of wiring and connectors. Not to mention the Reaktor battery chargers and who knows what other HK kibbles have made it into my tools and accessories. I like to think that I had a large role to play in the commoditization of silly electric vehicles using R/C parts also.

MarkForged – from the days when I knew 50% of the company to today when half the new marketing and sales staff go “Who is…. Professor Charles?”, they’ve provided me with high-strength printed parts for a lot of different projects, both on this site and off. Introducing them to the robot fighting community via Jamison’s and my efforts pretty much made MarkForged printed-unibodies the competitive standard in the 1 and 3lb classes, and trying to find new niches in the bigger weight classes is one of my goals. This time, Overhaul’s drive wheel hubs and casting molds are printed from Onyx, and there are also plenty of smaller chain glides and tensioners and accessory parts.

SSAB – I find it interesting that the company’s full name is SSAB AB – Svenskt Stål AB AB, or Swedish Steel Company Company, but these days the lettering is the whole company name so that’s actually not true. This year, I’m working with one of their North America regional distributors and all of the armor steel on Overhaul – including the entire clamp arm, top plates, and new wedgelets and DETHPLOW™ are Hardox 450. Hardox is the easily-obtained ARx00 of Europe and other regions worldwide, and bots overseas have used it for years, but it’s not really had a foothold here in our scene compared to the number of AR-spec steel products in the US. So hopefully I can help with advancing that brand too!

BaneBots – I was called an edgelord for even thinking about using P80 gearboxes in a modern Battlebot. I always thought they were under-loved after the FIRST Robotics Competition quality issues of the late noughties, and had used them otherwise in several projects including consulting projects before shoving shorty Ampflow motors into them for Overhaul 1 in 2015. And you know what!? They’re great! Overhaul 2 ran them exclusively for Season 2, and now for Season 3, OH is sporting the new BB220 series with much stronger planetary output stages for the lifter.

Equals Zero Designs – Yeah, umm, I don’t know much about those assclowns.

The Overhaul Design & Build Series, Part 4: Do You Want to be Gooey?

May 13, 2018 in BattleBots 2018, Bots, Events, Overhaul 2

Wasn’t that an insane season premier episode!? If you missed it, it even seems like they’re distributing the episodes in more creative ways this time, up and including Prime Video. That’s good news, including for me, who can’t be buttsed to TV like 99.5% of people near my age group and lower, and so can barely watch his own damn TV show. I’m fairly confident Overhaul will first be on the 3rd episode, so I think it will time well with the conclusion of this series.

The bulk of the physical construction took place around the first and second weeks of March. Actually, let me rewind the clocker just a little bit, back to the last weekend of February.

I got another shipment of stuff from Markforged, which is returning this season as one of the team sponsors. First, a bunch of Onyx filament to print wheel hubs with, as well as two large molds made on the Mark X series machines which have a bigger build volume. The Mark Two is limited to around 5″ in the width dimension, and guess what has 5″ wheels?! I printed a pair of 3″ front wheel molds in-house from Nylon, since that’s much smaller than the build volume limit.

Printing each pair of large wheel cores actually takes an entire day (22 hours, anyway) so it’s kind of a long process to make a dozen wheels. However, it was easy to pipeline everything once I got the prints going, as the polyurethane also happens to want about a day before demolding.

The resin of choice was Smooth-On Reoflex 60. I had plenty of good experiences with Reoflex 50 in Überclocker, but thought it wore a little fast and that Overhaul’s overpowered drivetrain would make that worse. So I elected to move up on the durometer rating, and 60A is similar to Colson wheels.  I got a small pack from the local distributor around here, Reynolds, to test my process and also the amount of liquid pigment needed. See, the native color of the Reoflex resin is a pleasant poop brown color, which is actually too dark to turn MIKU BLUE. So whatever, black wheels it is.

I’ve gotten a lot of questions on how the hell these wheels are supposed to demold. The molds are one-piece with zero draft, so it should be some kind of physical impossibility…. but then you realize that is what the screwy tread profile does!

I went light on the mold release here, and subsequent wheels actually popped out easier than that. Have I mentioned it’s also awkward trying to hold a camera at the same time as keeping yourself upright AND applying several Torques to something? At least a few torques.

They didn’t all work out though. The first center wheel mold I got from Markforged seemed to have some extrusion problems for the exposed surfaces, leaving them porous. We figured I’d just try slathering on the mold release as they reprinted it.

Nah, this one was stuck for good. Later on, I actually cut this mold open and discovered the resin had seeped entirely down through the floor of the mold and even through the inner walls due to its porosity… Yup, not unscrewing this one.

The reprinted mold was fine.

The problem with a robot with much larger wheels…. is that little sample pack pretty much only lasted those three initial wheels. So guess who now owns an entire gallon of goo? There is no intemediate size between the small trial-size and the full gallon.

These buckets are kind of crappy to use without dispensing equipment setup, but luckily I managed to get the workflow down for pouring them, and only got everything slightly gooey.

All of the frame rails now have brace plate holes-to-be-tapped drilled into them, so frame reassembly can begin in parallel with the remaining operations on new drivetrain and clamp/fork parts.

The first things to go back together are the liftgear and new lift motors.

One assembled front 3″ wheel… I’m liking these already.  The tread adhesion is outstanding – I can’t begin to tear the sidewall away from the face of the wheel. That and the mechanical over-molded interface means short of getting these things cut off, I’m not going to lose the tread.

A little bit more progress on reassembly, now with added drive motors.

Going on in parallel with the wheel casting and reassembly was lots and lots of welding. This damn thing almost has too much welding on it. I also know that I only say that because during this build, we didn’t have a MIG welder, only a TIG.

Here’s why – TIG welding is a very slow, methodical process which gives the welder maximum control over the weld composition. For the things we’ve been doing for “work” and consulting projects, this has been great! What it’s not good at is making large amounts of obnoxious fat welds quickly, for things which are only meant to run into each other over and over. Really, a lot of what you’ll see in the arms was designed for MIG welding, but I couldn’t gain access to my usual one back at MIT until nearly the very end of the build season. Putting Overhaul’s arms together, and Brutus’ wedges and plows, were processes which took up an entire day, or days.

The combined builds of Brutus and Overhaul made us go out and buy a MIG welder because of how bad it was. So that obviously won’t be a problem again, since now we have a Millermatic 211 in the arsenal.

However, I will begin with pointing out that a TIG welder is great for performing an act of terror I learned during my MIT career: TIG bending. Hey, it creates a highly localized heat region! By gliding the torch over a line scribed into some metal, you can very easily get it up to formability temperature. The upside is also a smaller HAZ than (in my experience) with an oxy-acetylene torch.

To make these bends in Overhaul’s future ears, I simply dumped 200 amps of TIG into them for a minute or so and then quickly threw them in the brake press. The welded-like appearance is actually very superficial and was a result of the metal surface liquefying somewhat.

The clamp side plates required some cleaning and standoff tubes machined. I actually didn’t have to buy any new tubing for this clamp design – all of it was either from some other tubular object on Overhaul, or could be slightly machined to the needed diameter. The machined tubes were advantageous since I could control the width of the assembly precisely using the turned shoulder.

SSAB’s Hardox comes with a paint-like coating instead of the heavy hot-rolled mill scale that I see a lot on generic AR grade steel. It comes off very quickly with a flap disc, whereas last season involved several hours of grinding with a solid wheel to get the material to clean weldable state.

Other weld prep included fitting the new lift hub pieces together – some diameters had to be cleaned up and shoulders turned once again.

I had to do a rather hilarious setup on the ears which connect to the clamp actuator in order to clean up the internal bore. Yep, that’s 4 out of 6 jaws.

Here I am doing the first assembly tacks on the lift hub. I have a very strange welding habit: I like doing my setup with the TIG welder, then switching to MIG to finish out. This is solely because I have no patience whatsoever for TIG.

Remember those little flats that were cut into the actuator ears and endcaps? Check out the parallels on the bottom – they help align everything so there is no complex fixturing needed.

Blah blah blah… welder and paint, grinder I ain’t, etc.

Because the clamp arm’s aluminum pivot rings still need to go over these, I had to clean the endcap welds up on the lathe afterwards.

A finished lift hub with endcaps threaded and with bearings made of oil impregnated nylon. I actually found a blank that I had machined most of to the correct dimensions, so making more was easy. I had more unfinished blanks which I machined new arm bushings for from also.

It was now Pi day, and New England greeted us with like the 3rd winter storm in 3 weeks. But the build must go on! Never give up, never surrender (seriously kids, don’t ever move up here. it’s not worth it. it’s expensive, shitty, and cold). I set out to Mid-City Steel which was able to quickly supply plasma-cut Hardox 450 parts on short notice and for very low ruble. Combined in this order are more parts for Brutus.

With this order came the first DETHPLOW (out of 2 – I entered a 2nd supplementary order for more spares) and all the arm parts too.

Plot twist: The arms are mild steel.

Yes, yes, finally obtain mythical Hardox sponsorship, end up making lifter forks from goopy mild. I was ready to design the arms to be made from HX450 also, but couldn’t help thinking if the arms were extremely rigid, that something happening to them would just take out everything upstream – the lift hub, main shaft, etc. which are decided not very Hardy or Ox-y.

Therefore, mild steel arms it is. Depending on how they perform in the season, this might be changed down the line.

Setting up the arms for welding was a similar process to everything else – chop and turn some tubes, and clamp it all together. I for one don’t mind if we bought a CNC plasma cutter. Before these industrial processes (which themselves are rather “old school” and established) were “discovered” by the robot community, welding a frame together was a much bigger deal and required much more setup and skill. This was the environment I grew up in, so that’s why it took me so long to learn and appreciate welding.

Here I am putting the arms together with our Miller 200 amp TIG in the foreground.

Hey, wait… That’s not actually me! That’s…

Allen, a new team mate for this season, who is a ‘graduated duckling’ of my involvement with New York Maker Faire and the Power Racing Series. These days, he’s a mechanical engineering student at Stony Brook. I stole him for their spring break and basically trained him from-scratch on TIG welding, upon which he somehow dumped the entire tank of argon over the course of the week.

First of all, it was a lot of welding, if I haven’t made myself clear on this front. But I do think the regulator was set up for too much gas in general, since at one point the flowmeter had something heavy run into it and did not work properly, and we set it up by listening to it. Sigmas! We have none!

(We do now have a new flowmeter)

 

Allen put together essentially everything you see in this build report that wasn’t the lift hub. This is a photo of the two Overhaul heads under construction. It was jigged up using the lift hub on one end and the spacers for the tooth on the other.

Your Godfather horse-head moment for this build.

Connecting all of the welded bits together was actually very painless this time. Think this means I’m getting better at design-for-welding! This is a test-fitted complete lifter assembly. Not pictured are the spare set of long arms and pair of finished short T-Rex arms. And the other lift hub. And D E T H P L O W.

Mechanical re-integration of the bot progressed quickly from this point. Check back in next week for more original content!