Archive for the 'BattleBots 2018' Category

 

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!

The Overhaul 2018 Design and Build Series, Part 3: When Your Supply Chain is Missing a Half-Link

May 04, 2018 in BattleBots 2018, Bots, Events, Overhaul 2

It’s fab time! The following story takes place in the last week of February to the first week of March – yep, that’s just over 3 weeks, reaching into 2 weeks, until the bot had to be in the crate! In fact, a lot of the earlier photos here were concurrent with finishing out the drivetrain changes and electronics module, since the mechanical modifications were first priority.

Alright, the first thing to do after two years of stagnation and one entire shop move is to take inventory. Some of Overhaul’s parts had wandered off into other projects or been repurposed, and others had been sold to needy builders elsewhere. Oh, and some things instead were to be deprecated and thrown out.

I was first out to ascertain how many good drive motors I had remaining. I originally built a whole bunch of spares and only ended up using two or three. But the lift motors at the time were low on stock at Hobbyking, so I only had four lift motors total – one of which was burnt out and the other had a severely damaged gearbox from (likely) the rumble and post-season shenanigans.

There were also other parts being counted – sprockets and drive hubs, and hardware relevant to the liftgear which I only had a few of to begin with.

By the end of the day, I had a good idea of what needed to be ordered from McMaster the following Monday, as well as what parts to ask HobbyKing for!

 

I began the stripping down of the bot during this process. Poor Overhaul – it’s mostly been living on a lift cart behind my work area, usually causing me to run into it in some way on a regular basis, causing a pattern of injuries on my leg which would have been highly suspicious during high school.

Breaking the bot down was important since I would want to start over with all new fasteners and ascertain the status of all of the parts, such as where a frame rail might need to get cleaned up or if this or that drive hub was about to let go anyway. There were also quite a few parts which were going to receive lightening in my efforts to make weight for DETHPLOW. Basically everything above in blue is being replaced completely, and a lot of parts which went into the now-previous design head will have to be deprecated.

 

Ah, the sad electrical box. Overhaul hasn’t been operational since a year and a half ago when I sold the DLUX 250 reflashed ESCs to Ellis for Robot Wars. To my surprise, this damn thing still powered on. There is a single brushed RageBridge inside to run the former clamp motor, an A23-150 sized Ampflow motor, as well as a BEC module.

Oh well – everything which caught fire is considered automatically sketchy in my book, and this box had an entire unassembled spare if I somehow needed another one – so I salvaged the bus bars and some intact wiring harness parts and unceremoniously chucked the rest.

Overhaul is probably my current masterpiece in terms of design-for-assembly and design-for-service. I put more thought into how things go in and out into this bot than probably every other project I’ve ever made, combined. It’s actually very easy to knock down as one person, since the majority of the bot is supposed to be serviceable by 2 people in under 5 minutes. It takes on average only 2 minutes to release a set of drive motors and under 60 seconds to separate the upper and lower halves of the bot at the arm towers, after which the set of lift motors comes out with only 4 bolts.

The revisions will see some of this go away – for instance, the frame rail brace plate would add a dozen bolts and a different tool to the process. However, I was fine with this – at BattleBots with the current format, you usually have several hours of notice before fighting, if not days. It gets tighter around the playoffs and finals obviously, but the quickest turnaround I’ve witnessed was still on the order of 2-3 hours. If I was scrambling to replace frame rails that hard, it means I’m doing pretty damn well.

On the plus side, the actuator and upper clamp retainment strategies have been changed to be more easy to service.

Well, when you get down to the basics, Overhaul is just a series of gears.

 

All said and done – this is what my table and bench area looks like. I sorted the remaining spare frame rails by type, since each type needed a different kind of surgery or modification.

Chibikart makes a cameo in this photo.

There was about 8 pounds to lose in the frame, spread across a few parts. Overhaul weighed in at 247.0 on the event scale during Season 2, so I used that as a cross-reference to the CAD weight of 240 pounds. To make sure DETHPLOW took me up to the same physical end weight in replacing the separate heavy wedges, and also taking into account the new frame brace plates, I had to get the bot down to around 230 pounds. The rest of the ‘missing weight’ was to be made up in the battery and ESC assembly being smaller and lighter.

Above, I use an annular cutter (also some times called trepanning cutters) to empty out some of the interior of the Epic Lift Gear. If you’ve never used these before, they’re like specialized high-precision hole saws for metal, and can cut a large hole very cleanly and quickly. They used to be very expensive and specialized, but you can find Chinesium sets now that work fine for under $100.  This one was driven in low-gear on Bridget.

The arm towers themselves also lose a bit of meat, with each side getting 1/4″ removed. In a mild perversion of their use, I actually used the same 2″ diameter annular cutter to make the circular boss by simply leaving the interior portion and machining the rest away.

It was now the first week of March, and life suddenly got much more exciting.

I had been scouring the country for a more consistent source of the 4mm AR400 steel that makes up Overhaul’s clamp and fork profiles. Basically, the material seems to come and go at McMaster, who also seems to source it from the depths of a tropical rainforest as all of the AR grade steel I’ve ever gotten from them has been covered in rust and not a single one has really been straight.

Through a lot of calling around local steel companies, I was given an inside sales contact at SSAB – the international manufacturer of the UK/Europe robot fighting circle’s preferred armor steel, Hardox. The gist of the conversation was essentially “Hold on, what did you say you guys were building? Let me talk to the sales manager and we will see what we can do”.

Only afterwards did I do some research and found that SSAB was essentially the U.S. Steel of Sweden. To be fair, I’m not sure what I was expecting, since it’s not like some small mom-and-pop operation produces 8 million tons of high strength steel alloys a year.

So there we go – I’d like to formally welcome SSAB Americas as a sponsor of Overhaul this season! This explains the big Hardox logo on the Equals Zero Robotics Facebook page now.

They not only straight up sent me a diced up 4′ x 8′ plate of 4mm Hardox 450, but also helped find a local steel distributor who had a fast-turnaround plasma cutting service for even more Hardox. This will come into play just a little later.

Alright, presented with several hundred pounds of steel, I will obviously go waterjet. I paid some hush money to the MIT Edgerton Center and popped out a few parts on the Omax 5555 in an evening. I started with 2 full “heads” for Overhaul and basically all of the kibbles which go into the new lift hub design, as well as one set of titanium brace plates.

Here’s the finished parts in the middle of some post-machining.

Back at my shop, I cleaned up the actuator-mounting bore on the clamp side plates. The actuator trunions will ride directly in these holes, so I wanted a not-sandpaper finish here. I didn’t have a carbide boring bar that fit my old boring head, so I reground the old HSS lathe rool I used in there and just ran it very slowly and gently to scrape the little bit of Hardox off.

Harder steels might be horrifying to machine, but they do leave wonderful finishes if you know their weaknesses.

I made a design change to the lift clutch which entailed cutting out some new parts. I wanted to increase the clamping pressure significantly because Overhaul had a lot of trouble actually hauling stuff over during Season 2. To do this, I made new thicker pressure plates such that the tightening nut could exert a lot more force without causing bowing and decreasing of the contact area. I also switched to a higher-friction clutch material (what McMaster calls their high-coefficient of friction), from a medium one.

Additionally, I made over a half pound back here by machining down the Epic Lift Pinion and clutch gear! Technically, that shaft also never ever had to be made of steel – 7075 aluminum would have been highly reasonabel… but I already had slugs of steel sitting around in the right size back then…

Just a couple of days later, the new actuator bodies arrived from my Chinese CM.

Oh. My. Baby robot Jesus.

Probably the most gorgeous assemblies I myself have ever designed and carried to fruition (if I do say so myself). The story of the gear-nut is a tragedy upon itself. I originally threw it at my Chinese shop along with the billet halves, expecting them to basically tell me to quit it with my English Acme thread in the middle of a gear nonsense.  I was fully expecting to just buy two bronze nuts and shove machined stock catalog gears around them.

The problem is then they asked me for a sample of the 1″-4 leadscrew, which is obviously not easy to get in China, as an assembly fitment. They already made one. What?

Absent the ability to mail a chunk of leadscrew (which I didn’t even order yet) in a timely fashion, we settled on the next best thing: I would send them a 3D model of the leadscrew, and they will SLA resin print it and use it as a fitment test. These gearnuts have less slop in the Acme thread than my Bridgeport does.

In the end, it was worth it! The gearnuts are probably the highlight of this whole operation – on almost every project and bot, I have something I call the “penising piece”, referencing the unfortunate tendency for us guys to put a lot of effort into something very showy and impractical for the sake of one-upping each other.

You know what I’m talking about. Don’t deny it. Think about what sport this is.

Too many parts and assemblies like that and your whole project becomes very out-of-scope quickly. Trust me on this, I used to do entire projects that way.

That is not industry terminology. Do not dare try to make it standardized.

There was only one “quality control” problem, and it wasn’t the Chinese’s fault. You see, the thrust bearings I specified on McMaster had a nominal outer diameter, which I designed the pocket for. It in fact was a full 0.02″ larger in real life.

I’m technically not even mad – it’s a thrust bearing. What kind of dumbass tries to make a radially tight-tolerenced fit on something like that?!

The outer shell of those bearings is just a stamped piece of steel – it doesn’t acually Bearing anything, it just vaguely holds the upper and lower races together so you don’t sprinkle the rollers everywhere.

Sadly, I had to bore out my beautiful Chinesium to accommodate the ingrates.

Here is how things fit together. The big thrust bearings sit directly on the face of the gear. The pinion shaft is retained via snap ring and has another bearing that carries it, located in the half not shown here.

And this is how it fits together. I’m quite thrilled with this unit! It ended up weighing about 1lb less than the fiasco I designed last time around, is much smaller and also capable of much heavier loads due to the large trunnion diameter and thicker leadscrew.  The rod end is threaded into the leadscrew and retained with two cross-drilled 1/8″ roll pins each.

Next time on Overhaulin‘ – lots of welding. so much welding.

The Overhaul 2018 Design and Build Series, Part 2: Where Everything Gets Easier

Apr 23, 2018 in BattleBots 2018, Bots, Events, Overhaul 2

Hey! There’s a robot-related TV show premiering on May 11th you might be interested in. There are robots on it, and they do stuff. They might even tell you about how the robots were made or about who made them! I might even be on it occasionally (But for sure not the first episode: The new format of the show was filmed in fairly cleanly episode-divided chunks, and I’m not quite at liberty to say which episode(s) Overhaul stars in)

Guess what? It’s finally after BattleBots. This means my life has finally returned to roughly normal (whatever that…. is), and most importantly, I can actually finish these damn build reports. Remember back in the day when this site was more hardcore, where I posted basically daily about what I made that day? It turns out “real life” is a class you can’t skip too many times a week. Build everything in college and ditch your classes, kids! I mean, uhh, be a responsible young adult and remain engaged in your education. Yeah. That’s the right message to send! Something something public facing role model…

We return to the design stage of Overhaul by picking up after the most imperative task – redoing the steel frontal parts of the bot – was finished. In fact, I left this post half-finished before I dove into making sure everything was done and had spares, etc.

Everything else honestly seemed easy by comparison, because I already determined what was going on with the other aspects of the bot beforehand, and it really only needed to be pounded through. The next two priorities after the new forks and clamp actuator were to finish designing the drive wheels so I could immediately start 3D printing cores and molds for production, and retrofitting the bot with Brushless Rages.

 

The wheel technology I wanted to use on the bot was pretty well developed by prototyping it with Überclocker last year for the Franklin and Motorama events. I essentially just scaled it up and kept the “scooter wheel” style molding features.

 

Something cool you can do with 3D printing easily is make fully interior voids that have no opening to the outside world. I didn’t want to waste material and time by printing a huge wheel which is mostly hollow anyway, and wanted more material perimeters near the highly-stressed hub area. But a fully spoked design would have been extra fragile in my mind.

Solution? I enclosed the spokes with endcaps that have 45-degree chamfered lead-ins so it can print without support. This way, I get the concentrated materal perimeter in the center and the outer regions, as well as two relatively solid endcaps. You can’t see these from the outside at all – they look like blank wheels.

The molds are constructed the exact same as Überclocker’s, too. I’m hurrying on the wheels first because I wanted to test the viability of the “twist to unlock” demolding strategy that I piloted with the smaller wheels. As you can see, I designed in giant wrench flats (or perhaps vising flats) so I can hold the mold in something. Up until this point, I was completely unsure if twist-to-unlock was even going to begin to work!

Parametric generation made designing the 3″ front wheels super easy! To really do parametric modeling well, you have to pay a lot of attention to the order that your features were made in. I’ve practiced using parametric-CAD for its actual parametric properties more in the past few years with consulting jobs, and Überclocker’s wheels were the first multi-variant parametric part of this complexity I’ve done and had gotten it to generate correctly on the first try. I haven’t even dared touch fully parametric assemblies.

The parameters were essentially related to wheel diameter/feature thicknesses, number of thru-slots, and suppression of the interior spokes of the larger one.

(Useful side note – the continuation of that article series about horizontal modeling is something that experienced CAD users all do subconsciously. I learned it the hard way through many of my models exploding, and watching friends with bad CAD habits having entire assemblies made of parts that are exploding. If you look back through how I generate Overhaul’s relatively complex wedge facets, that’s probably the best example I have visible of horizontal modeling concepts)

I imported the wheel assemblies and also added new 12-tooth drive sprockets. I’ve described many times how Overhaul was very under-geared with a design top speed of 18-19mph and could not use nearly all of its velocity space in the arena, coupled with limited traction (hopefully less an issue this time). My experiences with Clocker at Motorama with its new 10mph top speed showed that it felt a lot less squirrely and linear to drive despite not having the best traction.

Going to 12-tooth motor sprockets from the 15 tooth ones would bring that down to 14mph, which was historically a “sweet spot” speed for the 48ft BattleBox.

The liftgear remains pretty much the exact same as last time, but the gearboxes are now the BaneBots BB220 series. I got to test drive these in some of my recent consulting projects after talking with BaneBots post-Season 2. The problem with the P80s was the Double-D coupling inside starting to round off under high-torque loads. The BB220 shares a gear pitch with the P80s, so all my spare purchased gearsets are still useable, but have output stage carriers that are twice as thick and connected using a 12mm hex bore and not a 10mm DD.

I only had to design a different mounting plate to adapt these – the ratios are otherwise the same. BaneBots only sells 4:1 stages for this gearbox right now, but with the ring gear being the same gear pitch and tooth counts as the P80, you COULD fiddle a 3:1 stage anywhere but the output.

Next item on my agenda was the “Anti-Cobalting System” for the outer frame rails. I stewed pretty hard on how to implement these. The ideal solution would have been to box off the top and bottom of the rails with an intermediate tying member, or try to do it Clocker style with a thicker single spanning piece.

Problem is, there is a lot going on in that area – on one side, all the liftgear intermediate bearings are built into the frame rail, and the front drive chain also snakes around there. There’s also not much space to attach an upper brace plate on the inside frame rails without making it fully service-dependent on removing the arm towers (and hence the top half of the bot) for any kind of access to the drivetrain from the top.

I didn’t want to sacrifice that serviceability, and I was also much LESS concerned about “Cobalting” the rails save for a direct side hit because of DETHPLOW now tying both sides together with wubbie isolation. So the ACS became a single bridge plate which spanned the entire unsupported length between the center and front axles. I decided to make it from left over 4mm titanium stitched in through its entire length by 1/4-20 Grade 8 screws.

In a realistic direct hit to the frame side, that plate is still going to buckle and likely pop a few screws. Generally though, it takes transferring a relatively minusule amount of energy to the inner frame rail to prevent buckling. If I had more material and time, I would actually have made an entire width-of-bot bridging piece to act as a huge gusset for this whole area.

But I don’t! So here we are.

That’s actually….. it. There’s not much else going on in this bot which is substantially different this year. Electrically, though, it’s a different story. I decided to drastically refactor and simplify the electrical deck. Last season’s mantra was designing the E-deck and battery as two modules which are replaced wholesale in event of failure, then we figure out what’s wrong with the broken one later.

I really consider that system over-engineered now, and especially with DETHPLOW mode, I needed a lot of that weight back first. With the ESC choice being standardized, there wasn’t a need to make a whole rack of them removable at a time.

I also thought about the number of times I swapped a battery out to charge it and replaced it with a freshly charged one: 0

Every lithium battery worth using in a robot nowadays can charge at 2-5C rates. That means a full charge in 30 minutes or less, and matches at BattleBots will not occur that quickly. Overhaul is also not a bot which is so strenous on batteries that it will roll through an entire charge in one match – Overhaul 1 took up about half of is battery nominal capacity, and OH2 was even worse at like 1/3rd per match.

Therefore, I settled for keeping the Brushless Rages on a single plate accessible from the top for individual removal if needed, and batteries considered now non-removable and better armored within the bot.

So here’s what’s going on! My HobbyKing sponsorship was renewed around now, and they finally had the high C-rating Graphene packs in stock and ready to fire (heh) over to me. I was interested in these last season, but they had been very recently introduced then and the larger sizes were not yet in production.

I am not going to harp on the potential upsides and/or downsides of graphene battery marketing (bad sponsoree…. bad!), but 65C lipos are 65C lipos. Technically Overhaul would be just fine running 2 of them, but I had space for all 4.

The batteries form a single layer in the bot instead of being double-stacked near the back now.

A little hole-patterning later, and the new e-deck unit is basically done. The whole assembly is now wubbie-suspended within the bot, with the batteries (in real life) double-sided taped together into a brick and then sandwiched between the aluminum plate and a lower either-metal-or-Garolite plate, depending on available weight.

This is the assembly by itself. I found some space to squeeze in the 7th Brushless Rage to handle the clamp drive. This whole stack is around 3.5″ tall, so it leaves about 1/2 of air gap between the top plate and my ESCs. That miiiiiiiiiiiiiight be enough?

Seen in faint outline in the e-deck installation photo is a new top plate. I decided to do away with all the fancy cutouts and vents since the ESCs have a giant heat sink for a home. It will exist in two versions – a titanium 4mm one for DETHPLOW mode which trades about 3 pounds I can use, and one made of 4mm AR400/500 steel that weighs more for wedge fight mode (which is looking more and more like it’ll need ballasting)

Finally, the completing modification….. is moving the master switches to somewhere else that isn’t directly accessible on the top of the bot by wayward hammers. Hey, if someone reaches all the way back there (last season), we’re fucked anyway, right? Well guess what – someone did reach all the way there, and we were fucked.

The new location is accessible with the same tool, and with the activator still standing off to the side. The switches face 45-degrees upward directly under the arm tubes and sunk into the frame rail cubby – formerly occupied by Overhaul’s well-meaning but ineffective server fan exhaust port.

So here we go! The two master configurations for Overhaul this time:

General purpose match mode -wedge fights and vertical type weapons alike get the long arms and Limited Liability wedges, with exact positioning depending on who. The heavy top plate is in play. The configuration weight here is 230 pounds only, so I have a lot of wiggle room for silly accessories, minibots, and customized countermeasures.

The anti-KE DETHPLOW mode is specifically for horizontal bar and disc spinners. This mode is actually questionable against higher-hitting bar weapons like Icewave, but I’ve also not had to face such a thing yet, so hell if I know what happens!

And that’s it! The fabrication of everything obviously had to move quickly, so the build reports for Overhaul this year will be a little short. Stay tuned!

The Overhaul 2018 Design & Build Series, Part 1: Because of The Implications

Mar 23, 2018 in BattleBots 2018, Bots, Overhaul 2

Here we go! This post is all about design and redesign. What I’ve decided to do is instead of making a master post of all of Overhaul’s problems and issues I wanted to address, I’ll just stream it as I go. This stems from sitting down to write such a post and then realizing that okay, I actually have a problem with damn near everything. I was 2000 words in and hadn’t even gotten out of the discussion of shortcomings.

One of the most important things you can learn as an engineer is proper project scoping, whether your own or on a team with others, and how to spot and pre-empt scope creep. Well if that’s the case, I just watched my oscilloscope grow legs and bail out of a window, which is a shame, since it cost a lot of money.

Yeah, there’s 1001 things I want to change about Overhaul, but I obviously don’t have the time-money product factor to make it all happen. So I whittled the list down to some of the topics I covered previously, as well as new ones that came about from observing Motorama.

There were both easy to execute changes such as simple part replacements, and also more involved design…… overhauls….. which needed my attention more from the start.

The easy stuff included

  • Higher gearing for less top speed and more control over its own inertia, experimeted on with Clocker.
  • Getting rid of the “rocker” drive configuration by using a smaller center wheel – I want all 6 wheels on the ground at all times if I can manage it, especially with the added torque of a higher gear ratio.

More difficult and needing frame mods and new subassemblies, we have

  • Moving to all Brushless Rages for controllers! This basically meant throwing out the whole electrical deck, which I felt was too over-engineered for Season 2 anyway with its full polycarbonate enclosure.
  • Changing the lift gearboxes to the BaneBots BB220 line, which I had used in a few consulting projects between 2016 and now and which was better suited for high-torque loads. Luckily, this is easy since they are the same physical size.
  • Designing up a bracing system for the frame rails where they are current unsupported between the center and front wheels
  • As seen previously on the first design post, moving to the new actuator design which is more compact and should be much more durable.

And finally, what needed comprehensive redesign:

  • A new clamp body (the Overhaul anteater-dolphin-horsecatbearpig-raptor head) to accommodate the new actuator design
  • Changing the arm and lift hub such that the arms are universal, not mirrored weldments. This wasn’t a problem during Season 2 so much as I wanted to maximize the swappability of parts – if I had to replace a left arm twice, I’d be out of those but not Rights. If the arms were simple flat weldments, they could stand in for each other.
  • Changing the armored wedge design to be more effective – and since Motorama, optimizing for a wedge-fight mode versus a spinner-mode
  • For the latter spinner fight mode, going to a full front-spanning plow arrangement.

Since I was already starting off on the actuator, I decided to move onto the next most logical place first, which is the things that actuator mounts to. When you’re doing almost completely freeform design, you have to anchor it some place. When I taught the EV design class, I called it “grounding” the design – basically, you have to start somewhere, so just pick one and come back to it later as the design evolves.

I had a few concepts sketched for the new lift hub. It basically had to be compatible with the existing arm and gear bolt pattern and be the correct width, so actually designing it was a matter of picking a fastening method which made sense and trying to get it lighter. By “making sense” I meant moving away from the engine head studs holding the previous setup together, one which I no longer favored.

Basically, the longer the threaded stud, the more you have to torque it down for overall rigidity in the things being fastened. I also couldn’t locate an easy source of replacement studs in a higher strength grade than approximately Gr. 5 in the 2 different lengths needed, whereas I could easily find very high strength bolts. Recall that the arms had to be flat now as a design goal, so the whole lift hub is wider anyway, so the bolts may be rather short (well, 3″ and 4″ versus 6-7″ of stud length)

So I made the decision to abandon modifying or adding spacers to the existing lift hub – more spacers, more places for preload loss – and make a whole new hub.

This is the object that resulted. It keeps the profile and spacings of the current hub, but becomes a steel tube weldment with threaded 3/8″ thick endcaps. The length of the barrels on each former arm is just added to the length of the hub, keeping the whole liftgear the same width.

Since I would most likely be the one welding all this up, I could add stupid shortcuts that real welders would probably shun me for.  That’s the reason for those weird little tabs on the bottom, so I can fixture the holes relative to each other easily!

After shadowing Overhaul 2′s principal welder Skunkadelia , and having done more welding in general for work related projects, I’m now more confident enough having picked up my welding skills again to design around it more. I used to despise welding, and still kind of do, but hey, somehow this robot is 50% welded steel shapes so I might as well learn to maintain it.

I kept mulling over the arm design as I decided to whip up a temporary Überclocker-esque wedge shape. Notice the lack of side-wubbie engagement at this point? I was thinking I could get away without them, but Motorama showed me quickly they were probably necessary – as many wubbies on deck as possible.

I included the sidebar in this screenshot to show the process of generating the surfaces and planes needed to define the completely-lacking-in-perpendicular-features wedges.

Adding the backstop plate in a similar fashion to what I was planning for Clocker. After raw sketch lines, I generate surfaces using the sketch profiles.

I then use a Thicken operation on each surface in turn to make them into solid “plates”. At this point, there’s no joinery, because I was just interested in pounding out the shape.

In continuing the “nearly a visual mockup” theme, I then moved onto the fork arms themselves. I decided to dispense with the “tube skeleton and welded plates” method for not really being beneficial over just being made of plate weldments. The tube cuts were always less precise than the waterjet- and laser-cut plates anyway, and part of the reason Overhaul 2 was missing the inter-fork bracing standoffs Clocker had was because none of the holes ended up lining up.

I also committed to having all of the new steel parts made of commonly-found 1/4″, 3/8″, and 1/2″ steel plate. High strength steels like AR400 are far harder to find in thicknesses thinner than that. I had a lead on 3/16″ material fine, but sourcing the 4mm plate last season for the fork and clamp sides was an adventure. Very few steel companies list it as a product, because who needs a 1/8″ thick dumptruck body or mining shovel? It also gave me the option of making things from normie steel (mild/hot and cold roll low carbon) to just use geometry over sheer material strength as a design rule.

 

 

The forkss are now fully made from interleaved plates. Here I’m playing “connect the dots” with tube bosses and gusset plates. I made this plate adaptive so I could still change the  sizes slightly and not have to manually regenerate it.

Here is where I decided to make the forks from plain mild steel. I had the opportunity and supply chain to use AR steel for them as well, but decided against it. Essentially, if the forks were very rigid, they had the potential to easily wreck everything upstream (the lift shaft and hub, the towers, etc.) if somethng hit them directly. With a few geometry changes, I could get the forks to be rigid enough to take the potential downward force from the clamp.

Again, with the basic shape of things established, I went onto the next piece.

I started thinking about “Limited Liability wedges” for Overhaul about the same time as when I cooked up the idea for Clocker. Overhaul’s front is a slightly different shape than Clocker. The chamfer that forms the sloping face is smaller and so the frame rails of the bot extend further forward.

This means there was only so much liability I could limit if I kept the tall rubber wubbies, since by design, they kept the old style wedges flush with the forks. While I probably could have hard-mounted them to keep everything low-profile, I wanted to keep that level of shock isolation and break-away behavior provided by the wubbies in case an attack on  a vertical weapon goes wrong.

I therefore switched the design to a shorter wubbie style , which through the angle of the sloped front, set the ‘intersection line’ of the slope with the ground back a good 3 inches or so. This finally let me have enough fork prominence to make it worthwhile.

Above is the quickly thought up revision 1 of the design, which was basically “make slope piece, add pokey thing”. The idea was fine, but obviously that pokey wasn’t going to last long as a piece single-supported from a plate.

I extended the slope and front vertical pieces off the edge and extended the “pokey thing” as a gusset piece. Now this looks better topologically.

With basically all the elements of the bot that I wanted to redesign in place, I mirrored things and imported the Season 2 clamp to get a first visual.

ADD SAW TEETH AND SPIKES AND HOOKS TO MAKE IT EDGIER

This let me have a sense of which components needed to be bumped and shifted. Overall, the forks are 1″ longer than they were in Season 2. I wanted more prominence in general in order to attack with them first. These wedges are there only to help stablize the bot in most lift instances.

My goal for the clamp profile was to shift it forward more and also make it a little lower profile. Overhaul’s Season 2 clamp design was almost exclusively to house the huge actuator, and it actually looked a little ungainly to me. Plus, the taller the clamp, the more likely it is to get stuck sideways (which the ears are actually placed to prevent).

I simply exported a copy of the clamp profile and ripped most of the features out of it, including the awkward bump of motor-saving.  The hole positions shifted around a lot with the geometry changes, of course, so they had to come and go as I needed them.

After a few tries, I found a near perfect alignment of holes that actually let me mount the actuator in a position I long wrote off – with the motor pointed forwards. This configuration was modified slightly to adjust the motor spacing. It allowed the use of a very short leadscrew to achieve the range of motion desired, so I was much less concerned now about leadscrew rigidity.

Now with 100% more ear. I re-imported and adjusted the ear model, keeping it as a folded single piece. The plan was still to make the clamp sides from 4mm AR steel. I also added an alignment tab for welding. This was the extent of the work I did before Motorama.

One of the first things I did after Motorama was go back and edit the heavy anti-spinner wedges. Clocker doesn’t have the two front wubbies, nor the two sides, and I became even more convinced that Overhaul’s triple-plane constraint was a good design choice. Future Überclocker will have a more design-true layout rather than being a cartoony model.

I made a multi-faceted edge that was just a flat plate where the side wubbies are mounted. Recall that Overhaul’s season 2 wedge pods had fully angled sides, and I had an interior gusset piece which mounted to the side wubbies. I decided to flatten this area out in order to give even less things to grab onto – the prominent gusseted back edge was pretty much an invitation to getting the whole thing ripped off forwards if I miss an approach. Reinforcement of the area would be taken care of by a cross piece (green outline near the front wubbies) and a flat lower gusset.

This was the result. I rather like it – it adds to the new edgier aesthetic of the bot and is much lower profile and less bulky looking than the Season 2 wedges. The 2nd-angle transition to the pointed backstop plates is also much sharper, hopefully adding a stronge upward vector to someone’s deflected shot.

At this point I started becoming weight-paranoid, and so I just rage-added every remaining major part of the bot I could think of. What’s not shown is a pattern of several dozen (if not over a hundred) socket cap screws that make up the frame hardware.

There was also beginning to be a large weight difference on the order of 7-8 pounds between the heavy anti-KE configuration and the lighter wedge-match and vertical weapons configuration. I was just going to let this play out, since I could always add some kind of ballast if needed or make a smarmy lawn-care attachment to fight Hypershock with, but I wanted to leave a healthy margin for the improtant parts.

Notice something about the pointy wedges? I swapped their sides on the bot design! This obviously also works in real life, and is partly the reason I chose the design I did. I could even go in lopsided if I mounted two left or two right ones. An “arms close” configuration like this is that I would imagine doing for a fight against another lifter/flipper, whereas forks apart are what I would take on vertical weapons with since I can try to make close flanking passes and try to get under one of their corners.

Finally, we get to the crux of my Motorama ruminations.

I pulled the CAD back up one day afterwards and went alright, that’s it… this is happening and I will make weight for it no matter what

Basically I took the existing heavy wedge design just completed and bridged the two halves with a single U-shaped front plate. Reinforcing features have not yet been added underneath, but they will be.

This added about 8lb to the front – a little less worse than I thought, really, and that was without selective weight reduction cutouts. I like this already.

As I said from my Motorama conclusion posts, having a full-span front wedge probably could have turned my tournament around. On Overhaul, it is also wubbie-supported in all 3 coordinate planes in both compression and tension as opposed to just a flat plane of wubbies. It would take a lot of me fucking up in order to lose this thing in battle. The team started nicknaming it the “dethplow”, so Dethplow it is.

The plow also allows me to address another Motorama quibble, which was having to back up and attempt to bring the fork down. I made another configuration which I termed “T-rex arms” since they are half the length of the full length forks.

They fit fully behind the plow when stowed, but if I have someone trapped, I no longer have to back up, but can clamp and lift as normal.

rawr i am oversaur-cathorsedolphin-shark…..bearpig

The clamped-opponent orientation does change a little since the tooth now has significant overbite, but whatever – spinner matches are a matter of survival, not looking good.

I tabbed everything together and added five longitudinal gussets and one transverse rail to brace up the front and underside. The total weight of the dethplow is around 30 pounds!

Next up on how to CAD an Overhaul: Moving through the other systems making the revisions I wanted to do.

My Life is Ruined Again: BattleBots Season 3 and the Triumphant Return (?) of Overhaul

Feb 21, 2018 in BattleBots 2018, Overhaul 2

> mfw season 3 announcement

The rumors began shortly after July, when Science Channel announced it was going to pick up BattleBots after ABC unceremoniously shat us out in favor of a …. boy band show? Well fuck me sideways with a fracking well, look at how that turned out for you guys! The rumors intensified in November as discussions and negotiations were clearly under way, and reached a crescendo in January, each week leaving us wondering if “next week” was going to be it.

Well, now they announced it. Crap. Now I actually have to finish something!

Overhaul’s upgrades have been in in the works – albeit slowly. After season 2, I had a whole list of changes I wanted to make and “design regrets” resulting from the extremely fast build season and required turnaround time I wanted to address. Really, I (and a lot of other builders) see #season3 as a chance to do Season 2 “correctly”, addressing things that didn’t go the way we want or designs that could have been done better. And frankly, anybody trying to build from scratch for the season now is either a dumbass or more of a man than I


that apparently ain’t hard

So that’s where we are now. The story of Overhaul upgrades actually goes back to right after Season 2 ended, and starts with what is basically the last large mechanical assembly that was designed, the clamp actuator…. meaning it was the most rushed and horrifying.

Ball screws were a bad idea. I was attracted too much to the promise of 90+ percent transmission efficiency, but they ended up being too fragile and also had the nasty habit of backdriving – made most obvious in my match against Beta. During the following 3-bot rumble with Sawblaze and Road Rash, the ball screw stripped out almost completely and began acting like an Acme leadscrew anyway.

Trust me, that hurts me viscerally to look at.

There was also a confounding problem with the actuator design and the clamp arm. In general, the actuator ended up too bulky to hide effectively without making the head ungainly. Because of the positioning of the motor and the bulkiness of the ball screw, I chose to simply add a little ‘horn’ to the clamp arm (the protrusion close to the pivot point) in order to protect the actuator motor from being landed on if Overhaul got flipped over.

In order to get the clamp running again quickly in case Season 3 happened relatively soon (*ahem*) and to explore the large Acme threaded rod market, I actually designed and machined up a retrofit using 7/8″ Acme screws and nuts – the odd size was for the easiest fitment to the existing actuator bearings, since the root of the 7/8″ Acme thread form required minimal machining to fit.

Also, I found the nuts on sale on eBay for like $20. There’s an engineering justification for every spur of the moment purchasing decision.

I wanted to redesign the whole upper half with a new acme screw based actuator to solve this. Furthermore, I wanted to move from a live-screw design to a dead screw one, where the actuator contains the mating nut within large carrier bearings and simply rides up and down a stationary screw, which is the design I’ve historically used for Überclocker.

The premise went from using the higher efficiency transmission option to the more durable and simple one and just overpowering the everloving fuck out of it to get my desired closing forces. As a large portion of combat robots revolves around the latter, it was clearly the way to go.

I cloned the Overhaul 2 CAD model into a new directory so I can start messing with everything. Here we go!

This is the actuator in its current position in the bot.

I wanted to try and see if I could move to a pull-stroke closing like Überclocker has been running. In general, the answer is “not really” due to how far the actuator will stick out into the ‘grabby zone’. In Überclocker, I sacrifice a whole lot of leverage to position the actuator almost vertically so it’s much more out of the way. I wanted to not make that sacrifice for Overhaul unless I had to, or if it were super convenient. functional requirement: be lazy

I also investigated the idea of flipping the thing upside down. In this configuration, if the trunnion tube is made non-offset (inline with the leadscrew) the motor will unfortunately hang down very low into the ‘grabby zone’ and be vulnerable.

All of this position testing though was enough knowledge for me to begin hashing out the next part of the design.

For now, I just imported the model of the P90X gearbox which was never quite implemented. Into the same model, I imported a bearing I bought on McMaster-Carr which I got curious about while specifying new thrust bearings for the this thing.

These are “one piece” ball and tapered-roller thrust bearings, so-called since McMaster usually sells thrust bearings in little kits of 2 washers and a basket of round things. Don’t be fooled, though… the “one piece” part is just a stamped sheet steel shell that holds the two bearing halves vaguely together.

The one on the right is a ball bearing based one, and the left one is a tapered roller bearing which is basically tapered the ‘wrong’ way compared to a normal one. This means it can support almost no radial load but a ton (or approximately 7 tons) of thrust load!

I found the tapered roller bearing one a little janky, though. The full roller complement meant it had quite a lot of drag when rotating, and the packaging was a good 3/4″ thick. There’s also no way I can reasonably use its 14,000 pound rating …. and that’s an industrial rating, mind you, meaning it will happily do that for thousands of hours and not just 3 minutes. So I chose to move along (for now) using the ball version, which only has a …. 7,000 pound dynamic load rating, but was thinner and lighter.

 

The brown object in the middle is a stock round Acme 1″-4 nut that will either be machined as a gear (quick modeled as teeth here) or have a machined ring gear shoved around it with a thermally-enhanced intereference fit (LN2 the nut, bake the gear, shove them together and run away fast)

You might be wondering what the plan for radial loads is, since ostensibly I have two thrust-only bearings designed into the thing so far. The fake answer is that the leadscrew nut, being bronze, will just ride in the stationary bore of the thrust bearings, since the magnitude of thrust loads will be much higher than potential radial loads on a stationary leadscrew.

The real answer is “yolo”.

Here I am playing with actuator positions again. The “pull-to-close” position in this photo mimics that of Überclocker.  I still felt that the important parts were too exposed here.

Another attempt just flips the actuator upside-down and exposes pretty much only the leadscrew. This was at least tolerable in conception – something being mashed into the leadscrew (which could also be shielded) might still leave me enough travel to get a good grab.

Okay, but what else did I learn from Season 2!? That if you leave something important exposed…. say, a master power switch or similar, and run on the assumption that the chances of something getting into there and causing damage are very low, then it will happen to you 100% of the time.

So I gave up the “pull to close” actuator position in favor of just trying to keep the leadscrew short and fat in order to maximize its column rigidity.  The bonus upside is it woud let me keep the existing center hub between the two arms if need be.

This positioning candidate was actually pretty favorable. I could see how the clamp arm geometry might be changed slightly to better accommodate it, and also permit it to use a relatively short leadscrew

Using the geometric constraints put forth by the toy component placement,  I basically wrapped an aluminum chunk around it. The cavities are for the gears and bearings.

I changed the design to an “embedded P80″ to save length. The clamp motor is being moved to brushless, meaning Overhaul will be completely powered by questionable Chinesium. This time, since the Acme screw will not backdrive, I don’t have to hold the stick to apply pressure to the clamp arm any more, making it more Clocker-like in driving. Furthermore, this also affords me the opportunity to overpower the actuator while keeping a high gear ratio for force application. Überclocker’s current actuator is a regular 36:1 geared 550-class drill motor run at over 2x nominal voltage for moar powar – the short duty cycle of a grab and lift haven’t caused motor burnout problems.

A couple of different brushless motors could fit on this gearbox – right now, the SK3-6374 motor is in for modeling purposes.

Adding more parts and thinking about how to interface to the rest of the bot. The large rod-end is a convenient way to join to the wrist pin in the lift hub.

The design is more or less finished here. Those 4 square holes in the side are actually on a 2.25″ bolt circle, so four 3/8″ screws on each side will fasten the actuator to machined trunnion plates. I may end up making 2 of them dowel pins for shear strength and leaving only 2 as threaded holes.

With the new much more compact design, I was able to get a happy result for placing the actuator within the head. This was a good state to reach – I now have a solution where the trunnion bolt holes line up with the circular arc containing the patterned circular cutouts which Overhaul is known for. As a result, I can just hijack one of those holes (appropriately repositioned) as a trunnion axis, much like it is now.

All of this work occurred in the late December to mid January timeframe. I receive the new actuator billets and custom leadscrew nut back from my Chinese contract manufacturer this week.

In the next episode of Overhaul’s Improbable Overhaul Makeover?, I travel to Motorama 2018 with Überclocker in order to practice driving and strategy – and learn some disturbing new information which might disrupt my #season3 ambitions…