Archive for the 'In Progress' Category

 

Candy Paint and the Hail Mary Finish: Last Update before Motorama

Feb 14, 2014 in Bots, Candy Paint & Gold Teeth, In Progress, Project Build Reports

Over the past few weeks, I was supposed to complete Candy Paint & Gold Teeth – especially taking this past week to do so. However, real life has a way of trying to happen all at once to me instead of in reasonably scheduled chunks. This often manifests itself in trivial instances such as a delivery guy showing up with a pallet jack at the same time I’m trying to answer a student question about machining, all the while my phone starts ringing. During all other times, I am a lazy bum.

This past week, it manifested itself in the entire shop being room-swapped, almost like out of some bad redecorating show:

Yes, that is the Shopbot, in all its 5 x 10 foot glory, mounted on a pallet jack and a trash can rolley base. With zip ties.

Oddly enough, I didn’t think this one up.

The former EE/laser cutter room was turned into the combination fab shop and Shopbot room…

..and the former shop had all of the EE equipment, rapid prototyping tools, and 3D printers stuffed into it!

Overall, it’s much more cozy instead of being a big patch of empty space. We did this to consolidate shop space in order to free up the massive area formerly occupied by the Shopbot for more researchers to have space. It was completely necessary, and (of course) this past weekend was the only window of opportunity: any later in the term and it would interfere with classes, and start of summer is too late because of the space needs of new researchers.

Besides that, the following also happened:

  • 2.00gokart Season 3 has started! This warrants its own post, but right after the shop was moved, I had to give orientations/machine training sessions to all of the 20 BRAND! NEW! excited students.
  • the Department of Facilities insisted that this week was exactly when they needed to wax the floors, so many of these things (but THANK ROBOT JESUS NOT THE SHOPBOT) had to be temporarily moved back out.
  • Mikuvan ate an alternator on Monday. This is reserved for another episode of Big Chuck’s Automove Blog, but this was a several-hours repair job yesterday after waiting for parts.
  • I had to teach a main-2.007 Solidworks lecture on short notice, which was a few hours of preparation.

What does this mean? Well, for one, I have almost nothing penciled in for next week right now, so I should just be able to sleep the whole time!

This post will recap Candy Paint’s progress up until last night. It’ll be short but pictureful. As it stands, there is a slim chance of the bot being completed right before check-in and inspections begin, so I’m just rolling triage – what can be done will be done.

First, the welded frame:

Hot. Damn.

I passed this welding job onto my friend Jack, who is the shopmaster of the D-LAB facility across the hallway. I wouldn’t have stood a chance – my only experiences with welding aluminum have always ended up in puddles.

This frame taught a lot of lessons – namely, I’m never going to do it again. I expected some “taco” deformation of the whole thing, but it was actually quite straight. What I found out later on was that many internal features had moved or warped out of place seemingly magically, and almost nothing fit the way it was supposed to. There was to be much Dremelling in my future.  I’m actually not sure why I wanted to go welded-frame in the first place… something about trying out new techniques. The frame was suboptimally designed to be welded – tight corners, very mismatched material thicknesses, and holes very close to edges, since my experience in design-for-welding is slight at best.

One of the first things I did was grind off some of those strength-giving fillets because the top of the bot needed to be flush – again, a design-for-not-welding guy trying to do design-for-welding. This will weaken all the joints, so I’m hoping the underside fillets and tab/slot mates make up for it.

A rough grit zirconia flap wheel made short work of the aluminum.

The finished result. I then took this downstairs to the giant 20 ton hydraulic press for some gentle frame straightening, using the bar that I messed up on the rolling machine as a flat jig. With this done, the next step was to post-process the holes:

One thing I am now aware of that is done is weld a blank frame first, then post-machine everything from a single datum. All of my features ended up moving around or warping – the big center hole’s bolt circle somehow shrunk almost .02″, necessitating Dremelling to remedy. I’m glad I invested in those carbide burrs.

With the frame ready – or almost, with an hour’s more Dremelling than I had intended – for drivetrain and other parts installation, it was time to make those other parts.

The center spindle is made from a single piece of 4340 steel. I single-point machined the giant 1″-14 threads.

I machined the giant center block from a 2 x 4″ brick of billet using the EZ-TRAK CNC mill in the auto shop. Here it is completed with one of the tapered roller bearings and spindle installed!

Waterjetting is easy, but billets are satisfying.

Stator and partially completed stator hub. The stator is a copier motor pull unit I had, the same size as the one in Kitmotter and one of the Razermotors. I’ll be rewinding this with only a few turns of ungodly huge wire.

It took a while to install the wheels, because all of the slots had shifted a little, warped a little, or shrunk a little. But this is what the bot looks like with all 4 wheels!

This is remarkably straight and level – there’s a tiny gap under one wheel. Oh well – after the first hit, I’m sure nothing will be straight ever again.

Installing the big center spindle block. This is a pretty integral portion of the bot, and it fastens onto all three major frame rails inside.

The little offset pocket is a zeroing error on the CNC.

Pretend-o-bot #1! The spindle isn’t constrained here, it’s just sitting in one bearing. This thing spins for a minute if I whip it up to speed…

I stripped all the windings off the motor and used a string to measure the length of new winding needed.

This motor will be spinning north of 15,000 RPM to drive the weapon bar at around 2500. To get this speed, I needed to make a very hot winding – I calculated that 4 turns, Delta-terminated, will be sufficient.

To make 4 turns and not waste all the copper space, I had to resort to very weird measures:

This is my “9x Hobbykinging Rig” from building the Chibikart motors. It places 9 strands of #28 magnet wire in parallel to simulate an easier-to-deal-with 18 gauge winding. “Hobbykinging” refers to the tactic employed on most Chinese r/c motors of using many parallel strands of fine wire to wind motors, as it’s easier on workers than trying to bend thick wire and fit it properly. Done right, it can achieve a higher copper fill than a single thick wire, but there is a diminishing returns point if the individual wires are too thin (such that the enamel insulation starts making up a sigificant portion of total cross sectional area)

To make the windings I needed, I calculated I had more than enough space for four runs of this. So, I wrapped the Hobbykinging rig 4 times around a 12 foot long table to yield 36 parallel strands of #28 – roughly equivalent to a 12 gauge winding.

This is what the winding looks like.

I actually enjoyed winding this motor immensely. It was so easy! Just sling the giant bundle into the teeth and pull. And only for 4 turns instead of 30-40 like the hub motors!

I wanna go work for Hobbyking!

The completed winding.

The  next step was to terminate the motor in Delta by bunching a start and adjacent end of another phase together (e.g. Start of A phase, end of B phase get bound together). I just ran the bundle out using heat shrink, then torched the ends to destroy the enamel coating, then used my Battery Abuser to tin the ends.

After this, I potted the bundles in epoxy to secure the windings.

Moving on to mechanical work again, it was time to assemble the drivetrain.

The sprockets were cut out a while back with the waterjet load. Here they are installed on the motors – and after some manual chamfer-filing while the motors were run under load.

A good amount of Dremelling and hammering was needed to move the mounting surfaces back to where they were supposed to be. The motors will hopefully be secure with their front and rear mounting brackets!

One side’s drive installed. Check out my little chain tensioner blocks – these are made from Delrin and are pushed into the chain with a set screw drilled into the frame.

Each side, after installation, got a 20 minute long run-in so the chain could carve its own path into some of the weld fillets. I came around and cranked the tensioner screw down little by little as time went on.

Now with both sides!

Most of the remaining work on this bot is just putting things in. I have to machine a (simple) shaft for the weapon motor, then it can be test spun. Electronics and batteries will most likely be installed ad-hoc.

I’ll leave the updates to Clocker to another post – so this will be the last one before Motorama. Now, back to the shop….

Returning to the Game With a New 30lb Featherweight: Candy Paint and Gold Teeth

Jan 19, 2014 in Bots, Candy Paint & Gold Teeth, In Progress, Project Build Reports

My mental design-year can be broken up into roughly two halves: Dragon*Con season, which spans from roughly March to August, and Motorama season, which is basically September through the next February. Of course, the observant would notice that these things seemingly coincide with robot tournaments.

But that’s kind of how it works. After each big event, I start thinking about what I want to do for the next. Robot fighting is a game which I do not foresee getting old for me for a very long time to come. And why should it? Of all the things I ever became involved in, besides being the first one over 12 years ago (…) , it’s the most freeform and unburdened by pages and pages of rules and procedures. Run what you brought, not what the organizers say you have to bring. It’s very much a high-energy (… literally…), destructive, and kind of redneck sport, and there’s no whitepaper to write at the end. I have literal dozens of sketched out designs that will likely never see the light of the day unless I drop everything and become a professional robot cockfighter, which I would love to do. Here’s just one.

 

Someone get on that right now. Build it so I can live vicariously through you!

But I digress. It’s been Motorama season for a while, and so my off-duty mental cycles have been devoted to engineering the latest entry in the Imperial Carolingian Robot Army’s Register. May I present CANDY PAINT & GOLD TEETH:

 

Wait a minute. Hold on, trap. That’s a giant spinning weapon, not a fancy multi-axis grabby thing. The hell is wrong with you?

I’ve  been out of the high-energy spinner game for quite a few years. My last “large” kinetic weapon was Trial Bot, all the way back from 2005-2006. That design wasn’t very effective, so it was retired after only one event. I’ve built quite a few successful weaponed 3lbers such as Nuclear Kitten (and its earlier versions), plus Pop Quiz which was successful Back In The Day. Overall, I haven’t been enamored by the big spinning chunk of steel like many competitors have been, choosing instead to focus on drivetrains and manipulator type weapons like lifting and grabbing weapons.

With the flooding of the hobby R/C marketplace by Chinese components some time in 2004-2005, the spinner game began getting ridiculous, with each wave of new bots combining a larger brushless motor with a larger hardened steel weapon of some sort. The arms race began being lambasted as the “brushless penis race” as most of the competitors were young men, and most of the successful designs were the same in concept and execution, only differing by how big the spinning toothed drum or bar was.  It got to the point where many matches were just a minute of robots hovering around each other, each aiming to deliver the match-ending hit, and finally a weapon-to-weapon hit that destroyed both robots or left them totally disabled to the point of only being to crawl around on one wheel.

It was, to borrow a previously used analogy of mine, like we were all dubstep groupies waiting for The Drop… or in this case, The One Hit. The only other bots that could survive were armored bricks which kept running into the spinner until something, one or the other, broke. I did not find this game very interesting, and ultimtely neither did quite a few builders, who began exiting the game after their last bots were exhausted, because it was getting expensive to rebuild over and over robots which were good for only a handful of matches, or even just one. I in fact retired Test Bot out of the 12lb class after it was “penised” at Motorama 2008. That year also saw the first Überclocker.

Several efforts sprung up to counter this, including the Sportsmans’ Class which I found as slightly reactive but ultimately aligned with my own goals of repopulating the ‘middle of the spectrum’. Back in the very old Battlebots days, the power to weight ratios of entries was so low that matches were more determined by driving skill, strategy, and reliability, than dancing around gyroscopically waiting for the right impact to land. This greatly contributed to the corpus of weird or interesting designs (check out the old Team Nightmare event pictures). In the current Sportsman’s class, flippers, hammers, and the odd clamp-and-lift or two (ahem) have all returned. The matches tend to go the full length and feature a lot of action and driving, with the added bonus that you could generally return home with something that did not require a dustpan to pick up.

It’s been a while, however. I miss the feeling of beating something with a chunk of steel. That’s where this design comes in.

There’s been relatively few successful overhead-bar spinners, known in the vernacular as “Hazard-style” after the multi-time Middleweight Battlebots champion. This type of design is hard to get ‘right’ because the blade tends to destabilize the robot if it’s too long or heavy, and then it’s more difficult to self-right if it does go over. Pop Quiz and Trial Bot are both this style of bot, so I have a historical attachment to this design too. Other examples of this design are Brutality

and Tornado Mer, which early versions of this design resembled the most.

Note that all these videos are from quite a long time ago.

I wanted to try making a bot that wasn’t square. Using a continuous round tube for the outer armor was appealing because it presents no obvious weak spots, unlike a square corner (or the backside of Brutality’s front wedge). I fixed the blade size at 2 foot span, 3″ wide, and 1/2″ thick, a relatively solid dimension that ended up being  almost exactly 10 pounds in steel. This dimension has been my ‘default’ go-to for a weapon of this size. A chunk of S7 tool steel typically costs about $100 in this size. All things considered, this thing was basically a small Tornado Mer.

The design goals for this bot were basically:

  • Be round.
  • Be reliable, over packing sheer energy

I started with the “doodle assembly” in which I haphazardly make parts and outline sketches.

 

 The size of the bot was dictated primarily by what size giant tube I could easily find and purchase. Yarde Metals had a few promising candidates in the form of 15″ and 16″ tubing, so I started with 15.  The rectangles represent the outlines of components I wanted to use. At this point, the choice of drive motor was a set of Banebots P60s with some 500-class DC motors. Fairly vanilla, and would give this bot an average drivetrain power for a heavy weaponed 30lber.

I experimented with several different possible heights, shooting for a 1.9″ blade height: 1.5″ wheels, 3/16″ ground clearance, and then a little over that to make sure I don’t whack myself. I’m used to sacrificing COTS parts for smaller packaging – Pop Quiz is still one of the lowest blade height antweights extant and for a while was the absolute lowest, and Trial Bot also had a blade height of 2.2″ using 2″ wheels.

The robot height decision was tied in with what I wanted to drive the weapon. Initially, I was inclined to make a super-wide custom direct-drive motor for the weapon – which would turn this bot into a giant Pop Quiz. One plan was to start from a chopped quadrotor motor on Hobbyking, except add external ring bearings (or metabearings – support rollers) to make it stiffer. I also took apart the 8-FUN motor again to measure the stator and considered using the motor inside as-is.

Further thinking and discussion led me to go for a brushless scooter style high-reduction indirect drive. I figured this bot was going to spend a lot of time upside-down and possibly crammed into a corner. A direct drive motor wouldn’t be as deterministic in such a scenario unless I also ran a sensored controller and used Hall sensors, which I didn’t want to do for reliability’s sake – one more part to jostle loose or break off its solder joints. The first image still shows a pretty insane and almost impossible (due to lack of tooth engagement or minimum pulley radii) and unnecessary 10:1 reduction. I put in a ~85mm motor diameter as a placeholder, since it was pretty clear that this had to be a custom job.

More components have been added here, including the outline of a Ragebridge as well as batteries. Height was the most important criterion when choosing batteries for this thing, since I would only have about 1.25″ of space to put them in. I elected to run an 8S power system with two 4S packs wired in series. My voltage philosophy is generally to run as high of a voltage as I can reasonably do so to minimize current draw and wire size; 8S was about as big as I could get without dangerously overvolting the average 12-18v RS550 motor. This high voltage would allow me maximum flexibility in choosing the weapon motor winding to best match it with the physical gear reduction.

I ended up deciding not to spend another $100-150 on batteries, but to use up more of my Nuclear Arsenal. I was going to split up two Thunder Power 7S 4.4Ah packs to make two 4S ones – two of them have dead cells, so they are not useful by themselves any more. 4 cells from those packs gives me a pack 30mm tall, or pretty much my maximum allowed height, as well as a great deal of battery energy for match length and number-of-spinups overhead.

The reduction is still shown as a slightly less ridiculous 8:1. I was also settling on what kind of power transmission to use:

  • It needs to not stretch – or at least do so minimally, for consistent power transmission properties
  • It should be rubbery, ruling out chain drive. A metal to metal coupling would be kind of asking for breakage.
  • It shouldn’t have teeth, because the high ratio I needed implied a small pulley, tight wrap, and therefore high tension in the belt; plus extreme impact loads.

I decided to give good ol’ V-belts a shot. V-belts often get written off as old technology, but they have favorable properties for this sort of thing – they allow some innate slippage due to the lack of teeth and do have tension members (they’re not just loops of rubber). The “L” series of belts (2L, 3L…) held promise for me since they’re designed to be small and flexible. A 3L belt seemed the best candidate here – 2L belts are tiny (1/4″ wide and 1/8″ thick!) and 5L is getting on up in huge. A 3L belt is 3/8″ wide and a little over 1/4″ thick, and the empirical smallest-pulley in use seems to be around 1.25″. Many larger bots have (and still do) use them for weapon drive, but they are not common in the little bots usually because of the minimum pulley diameter and thickness.

So naturally the next thing to get modeled is the Epic Drive Pulley. This shows the next weird thing on this robot that’s been getting me some stares. I’m electing to go for a live (rotating) axle suspended in dual tapered roller bearings rather than putting a hub and bearings on the blade, and only having a solid pole on the robot.

The latter is a mechanically simpler system, but in my opinion a live axle in this case saves both weight and height. With a hub and bearings that stick up above the blade, the center of impact force reaction is far up the shaft, which needs to be large in diameter and mounted solidly in the center of the bot to handle it. If I’m going to have a big solid block in the center, then I can put bearings in it instead, and move the center of impact much lower as a result. I also lower the blade height substantially doing so.

The big pulley is actually going to take up a substantial portion of the underbody real estate of the bot, since it’s on the other side of the bearings (to save, again, blade height). A lot of components need to fit under it, which ties into the 1.25″ of available workspace issue I raised earlier. This is what the blade spindle assembly looks like, in section; excuse the CAD-ahead going on:

Note the presence of Belleville washers on the top and bottom. These are often used to preload tapered roller bearings for zero-slop operation. In this case, I’m using the bottom washer for bearing preload (it pushes the bearings together, against the shoulder at the top) and the top big washer is only to keep the blade on. This keeps the bearing preload nominally separate from the preload of the blade. The idea is that the preload force has to be overcome before any of these parts even think of moving, and with (hopefully) most of the impact forces being side loads, it should prevent “blade wobble” from shaft compliance.

Now, in a good hit, everything will probably just munge together, but hey.

Back to the proper CAD order:

The internal frame rails were made using a “master sketch” that I reference all the solid models from. At this point, I didn’t know what any of the spacings or sizes needed to be, so I could just adjust the master sketch and the rails would resize to fit. The first time I did this, I made a sketch in the assembly; turns out Inventor doesn’t allow those kinds of references.

So I had to start over and make this sketch in a separate part and the insert the part into the assembly, letting other parts become Adaptive off of it. End random Autodesk Inventor tip.

Whoa, getting a little ahead of myself here.

After liking where the rectangles ended up, I began importing parts from previous robots and inserting them. The P60s are shown, as is the drive wheel solution: Banebots wheels on custom hex hubs, running on shoulder screw dead axles. I’ve never used Banebots wheels before, but they seem to be solid for a lot of other builders. The available of a hex bore was the swaying decision here, since it reduced the “hub” to a chunk of hex steel with a few retaining ring grooves cut into it.

To get power from the offset motors to the wheels, I have one stage of very short chain joining the motors to the rear wheels, and then another 1:1 stage from the rear wheels to the front wheels.

At this point, the protoform of the weapon motor has also been modeled for visual fitting.

This is the motor in a more complete form, though still showing the unrealistically sized 0.9″ pulley. Basically a one-sided hub motor with an integrated pulley, I’m going to blast it out from a solid round. No, not a two-piece welded assembly, nor a stack of waterjet-cut rings. I have a 3.5″ steel billet that’s been sitting around for far too long.

The magnets are the same ones used on the first iterations of Razermotor, sourced from Supermagnetman. The stator is also a leftover from the RazErmotor days, a 70mm copier stator that’s 15mm thick.

It sits on a 8mm shaft that rides in conventional 608 skate bearings. The very short load-to-bearing distance makes me confident that a good quality 8mm shaft (read: not made of the bullshit I make standoffs from, but real shaft steel) is sufficient for this motor; it’s also going to be hitting 12 to 15,000 RPM, and a bigger bearing would suffer.

A pizza appears.

The motor mount has a gratuitous number of slotted holes to let me adjust the belt tension if needed, but also maintain rigidity in the area.

This bot is of an ‘upside down’ construction. The top plate is rigid and integrated into the one-piece frame, and there’s only a bottom ‘dust cover’ which will be made from 1/16″ FR-4 (Garolite) laminate for the electronics. The batteries will have a bracket to retain them, but this is not shown yet. Basically, not a good idea in the old Battlebots days of floor-mounted hazards. I went this way because I didn’t want to have to remove the blade over and over to do maintenance. Everything in this bot drops in from the bottom and is bolted in place.

I also went to ‘duallie’ Banebots wheels because the single 0.4″ wide wheel seemed too fragile. These wheels have a thin web portion before they fatten up for the hub again. The chances of the bot landing on one side (or one corner, hence on the wheel) and breaking that off seemed fairly high. What I’ll likely do is put the two wheels side by side with filled epoxy in the middle to fuse them permanently into one.

A view from the top with the top plate made transparent. Buttonhead screws are shown, though for blade clearance issues, these must necessarily be flatheads in real life.

The design stood like this for a few days. I was satisfied with the roundness, but did not like how much wasted space there was inside. I needed to match the largely rectangular parts inside with a circle on the outside. I guess that’s just a trait of round robots.

After a while, though, I decided to refactor the design into one that was more practical. The roundness makes the bot more visually cohesive, but it is not very practical. I wouldn’t be able to push very well as a last-ditch backup, and being fully round is counterproductive for self-righting – a lot of it depends on luck and physics from jouncing around on-edge. A fully circular bot like Tornado Mer tends to “coin” around (though in that match it didn’t help that the weapon motor contactor locked on…)

I started playing with adding indentations or other features to the design:

Attempt number one: Cut off a chunk of the circle and append a polygonal wedge to it. Simple enough, and it would get the job done, but I didn’t like the fact that the two end corners were exposed. Sharp internal corners on this design would present an unnecessary vulnerability to opponent weaponry, since it would otherwise tend to bounce off the round sides or up the sloped wedge surface.

So I tried a ‘wraparound’ wedge instead. The wedge is not formed to the rounded surface at the corners, but is just tangential to it for a duration. This seam will be welded shut so it will resist peeling.

I liked this design a whole lot more, so I went with it:

Five front gussets support the wedge. I had to rebuild most of what was the rear end, including new cover plate shapes and motor locations. The battery cage has also been modeled – it comprises two 1/16″ aluminum folded sheet metal assemblies that each trap one modified 4S battery pack.

I decided to change out the motors entirely. Previously, I was planning on running a single-stage 5:1 P60 gearbox; however, their length and mass became issues. Plus, I’d have to buy them. Taking a page from 12 o’clocker’s “Angerboxes“, I modified the design to mount from the top down. The drill gearbox is a 6:1, yielding me a little reduction, so I could back down on the need to externally reduce from the intermediate chain stage. The simpler design saves a few ounces per side. Even though they’re plastic-cased, I think a well-supported motor (see the black rear mount) and use of the material in bulk will be sufficient.

The drivetrain is designed to hit 15mph, which is pretty zippy for a heavy weaponed bot.

A size comparison next to Überclocker, which it would bang up pretty badly. Clocker is a pretty good example of a design with too many pointy bits to survive in a big-weapons environment. At the very least, the clamp arm would have needed to be more vestigial to allow weight for a big armored plow in the back.

Physical progress-wise, I’ve accumulated the majority of parts for the bot, and more are on the way. First, a few weeks ago, I snagged these old weapon blades from a lightweight (60lb) bot which were reused in a 30lber years ago. They are…. 24″ long, 3″ wide, and 1/2″ thick, heat treated S7 tool steel with 1 inch bores. Exactly what I was designing! Well, that pretty much seals the blade decision.

The bottom one is solid, weighing 10.2 pounds exactly as it should, and the top has been weight-reduced to around 8 pounds.

I should be able to run the solid one; as-designed, the robot weight is 27.6 pounds, not counting some small hardware and wiring (which always adds up).

Most of the frame parts cut out of 1/8″ and 1/4″ aluminum. Caveat: I’ve only welded aluminum once and it didn’t go over too well. This will surely end well.

A few pieces are missing, so I can’t start just yet; I’m hoping to wander into the machine again this coming week with more parts for other bots.

However, I did sand and fit the rest of the pieces together. Pretend-o-bot #1 is complete!

I’m hoping to be able to roll the big outer hoop this week from barstock. I purchased two 1.75″ wide, 1/2″ thick 5 foot extrusions to make the hoop – only one is needed, but it was cheap and I’m most likely going to bang it up at least once.

I’ve been probing the local peer cloud to see if there are any skilled aluminum welders willing to take this job up. As much as I would like to learn on this bot, I also kind of don’t want to have it shatter on the first hit! If not, or if I’ll have to pay an absurd amount to get it done, well… here goes nothing in particular.

I’ve also gotten:

  • The first boatload of McMaster hardware
  • Motor magnets
  • A pile of Banebots wheels, since a full set of wheels plus spares on this thing is like 16 wheels.

Parts that are already on-hand and just need to be modified or pressed into service:

  • Ryobi drill motors. I purchased these from a parts distributor (p/n 984572-001) on the recommendation of a few veterans of the community. These are basically Harbor Freight drills but much higher quality.
  • The 7S 4.4Ah Thunder Power packs with dead cells, to be reworked into 4S packs
  • The copier motor stator

I’ll still need to machine:

  • The one-piece rotor for the weapon motor
  • The stator mount for the weapon motor
  • The epic block of bearing-holding at the center of the robot

As for the giant output pulley, I did a make-or-buy study as soon as the design was finalized: I threw it on MFG.com, my go-to for hiring shady Chinese job shops to machine things for me (things made through them include all of the DeWut gear and my small run of hub motor parts). I will hopefully have the finished result back by the end of February – but if shit goes down, I’m going to cut out a circle from 1/2″ plate, stick it on a mandrel, and go to town.

In the next episode of Big Chuck’s Automotive Blog…

 

Introducing Überclocker Advance!

Dec 21, 2012 in Bots, In Progress, Project Build Reports, Überclocker ADVANCE

I’ve been in hiding for the past few days out of fear for my life EVERYBODY IS IN FINAL PROJECT DOOMSDAY MODE!!!! PANIC!!! since I’m a TA/lab instructor for the Media Lab’s famed MAS.863 How to Make (a Huge Mess) out of (Almost) Anything class as well as 16.842, a systems design class based on the DARPA Model Based Amphibious Racing competition (MBARC). I have rants prepared summarizing my experiences in both of those, but that’s for another day.

What’s on deck right now is a brand new version of Überclocker, my ‘flagship’ combat robot (flagbot?), which has been out for retirement since at least 2010 or something. It’s what I have been slowly hammering away at for said past few days, stretching sporadically into the last two weeks or so. I’ve realized that it’s rare to see a explain-the-CAD-image on this site any more, which makes me a little disappointed since so much of the idea synthesis that ultimately determines the fate of a build is contained in the design period, and perhaps my thought processes can help in the design work of others. So in an attempt to go Back to My Roots, I’m going to have an explain-the-CAD picture post summarizing the status of this Überclocker build, now entitled Überclocker ADVANCE! for reasons that are difficult to explain using words.

Let’s face it – Clocker has been a little slow-moving compared to most of my past robots and current vehicle-like things. In 2008, it was completely terrible because I basically square-wave stepped into infinite machining and fabrication resources from almost none, without the attendant knowledge and theoretical foundations to use them. In 2009, I rebuilt it using “every trick in the engineering textbook”, and t-nuts, to wholly unsurprising consequences. 2010 and 2011 were marked by dismal failures brought on mostly from a lack of true concern, since at the time I was well-distracted by the aforementioned vehicle projects, and didn’t really take upgrading and repairing the bot seriously. Finally, in 2012, I stepped back and really upgraded the robot, and it did well consider how terribly I ended up operating the damn thing.

The design of this bot actually has a year and a half of history, at least. My first inklings of a desire to totally start from scratch basically started after Dragon*Con 2011 with this concept solid model, made in a few hours.

It got the basic point across – I was tired of having low ground clearance and tiny wheels with their traction limitations (hence the big wheels). Clocker’s broadside attack weakness (since it’s so damned long, at 27″) was fresh in my mind, so I wanted to make the sides rounded in order to give me some complementary leverage in a pushing match. The legs, while they worked reasonably well, were bulky and some times caught on the stage edges and elements, so I wanted to replace the rollers with a ball shape. All of these things were on track for  addressing in version three. But, that model lasted about as long as I spent designing it.

The next burst of inspiration built off this sketch-model in later 2011. It was on the flight back from my most recent Singapore trip that I went through like all 3 of my spare laptop batteries on the plane and followed up on the sketch-model’s selling points. The end result was this.

My god, it’s round. It’s so round. And it was even mostly circular! Did I mention round? Curvilinear?

This was a very strong candidate for the design at the time. It would still involve a fair bit of waterjetting magic, but the frame was out to become much simpler than Überclocker Remix’s original 2009 frame. I actually spent some serious time making the circular edges as … well, circular as I could.

Sadly, I just straight up forgot about this for a long time after landing. Some part of me still said that the shape was impractical, that I wouldn’t have far to tilt before I lost traction, or that the waterjet puzzle was too complicated to be robust. But damn does it look good.

Fast forward another year, and I’ve basically had enough of this thing. Yeah, it was round. But my reservations were correct in every way I cared about. Überclocker original (2008) and Überclocker Remix (2009) both had very distinct and unique shapes – very flat and sleek, with angular elements everywhere that were neither positively contributory nor very easy to make. My recent Great Awakening with Null Hypothesis, a desire to return to the ugly square drivetrain-dominant bot that just worked more than anything else, pushed me strongly towards ditching the desire to be circular. In the modern Battlebot match, the giant brushless spinning weapon staying alive and driving is, in my opinion, something like 75% of the game. So long as you keep rushing at the other guy, strategically or haphazardly, you’re more likely to curry favor from the judges if you last. In the recent past, Clocker has had… well known issues… with that.

The new idea floating in my head was to make the thing bone simple, at least a simple as a 4-actuator 4-wheel drive bot can get. The frame needed to be just big straight rails. The dual-motor setup for the lifter had to go (because ultimately, one motor jamming or stopping will cause the whole thing to quit functioning), the whole thing needed to get smaller or at least get no bigger, and I really needed more ground clearance.

Images in my mind began forming of basically shoving the fork and clamp assembly onto Null Hypothesis. That bot was fast, had infinite traction from it’s 40A durometer 2″ wide “McMasterBots” wheels, and almost unlimited traction-positive angles because of the big overhung wheels. What it translated into in real life was a bunch of bad whiteboard sketches, including…

Yeah, what?

That looks like a combination of Omegaforce, the Wubba-wubba-Bot that never was, and some agricultural implement. It lasted as long as it took for me to sketch it out.

With the final project blitz happening to every lab class on campus including the two I was involved with, I hunkered down in my stuffnest and began creating geometry in Autodesk Inventor, for realsies (but interrupted roughly every 5 minutes with a different variant of “Do you think using a ____ on my _____ is a good idea? Is there one in the shop?”).

Yup, that it’s. That’s the whole robot.

I’ll admit that my reasons for creating DeWut!? were mostly self-serving. I needed to get away from two things:

  1. Using sketchy-ass 18 volt Chinese cordless drills in anything. Null Hypothesis basically ditches a motor every match. While these drills may have been better in the past, modern product design committees have cut so many corners out of them that they’re pretty well rounded off … literally. The cases have gotten curvier and prettier, but the material quality has really been shat out and redigested. I think they’re still fine for 12lbers, and 30s if they are not overdriven at all, but NH clearly pushed them too far.
  2. Repacking the guts of non-sketchy 18 volt American cordless drills (the DeWalts, which are made in China anyway) into my very sketchily-made aluminum gearcases. You can buy this for $200 already, it’s better than my version, but they’re never in stock.

Hence, if I could get the DeWuts made as a stock solution, then I can design everything around them. And soon, everybody can!

With that model in mind, I quickly started jotting down the geometric outline:

It’s still round.

I just can’t let that go. Cold Arbor was kind of round, and it looked great (but that saw is something I will be ashamed of forever), so I threw it in. The base form is that of Clocker as it exists now – two “pods” on the sides and a simple box frame in the middle, and the fork out front. In this picture, I was trying out Null Hypothesis’ 2″ wide giant caster wheels for looks. While I liked it, it would have caused the bot to be almost 2 feet wide, so they were not the final choice.

The hardest part about starting a new build is usually anchoring the design. Where the hell do you start, and what part do you start with? I found that making the outline made the choice much easier since it was then easy to see right in front of you what is holding the bot together.

After Clocker’s 2012 adventures, I tacked on some more items onto my list of grand design intents. The full rundown was now:

  1. More practical and easy to build, as previously described
  2. Higher ground clearance and increased maneuverability, as previously described
  3. The ability to resist or defend against broadside attacks, because round
  4. Making the legs actually useful.
  5. Making the clamping action much quicker

Here’s what I mean by all that.

Making the legs actually useful

Clocker’s “reactive outriggers’ are probably its best feature. The idea is when a 30lb opponent is lifted, the weight shifts forward and the robot gets up on two wheels and the rollers at the end of the outriggers. Hence, the robot still maintains traction and can move while carrying an opponent without hoisting it up all the way. Many historical clamp type weapons like Darkangel and Complete Control (both Clocker inspirations!) have static outriggers that function only to prevent tipping.

Here’s a picture all the way back from clocker 1 in 2008 that shows the principle.

That’s where the fun begins. The idea is basically to spin the opponent in a circle and then let go – not causing damage per se, but it looks intense. Some times it backfires. Other times it’s a big hit at the event.

The problem is that it really only works for a limited range of opponents because of how short the legs on the original Clocker and Remix (2009-current version) were. A little too chunky and Clocker would just faceplant. If they were too small or compact, then I don’t really get enough displacement to break rear traction. If the ratio of leg length to wheelbase were higher, then the range of spinnable opponents would also increase because it would both let me tilt forward with less weight and be more stable in that configuration.

Next, the “doubly supported” legs of the original bot, and Remix as a consequence, were a severe pain to remove if the drivetrain needed servicing (and my goodness did it need servicing…). It used a different hex wrench diameter than the rest of the stuff on the side, and there were 2 screws and 2 washers to line up correctly to remount them.

Some times, a single big chunk of metal is warranted over a creatively sculpted series of smaller chunks. I wanted this build to use a single, thicker ‘leg’ per side that could easily be removed and swapped if needed, from one side of the bot.

Making the clamping action quicker

Unlike many clampbots of smaller weight classes that use R/C servos or larger weight classes that use pneumatics, Clocker has an electric linear actuator to reduce complexity while still offering good grip strength – an R/C servo of this size class exists, but all I know about it is that it’sreally expensive. So, the clamping action is admittedly a little slow. This has resulted in a quite a few missed grip chances in the past.

This particular grievance isn’t a major design element, since Clocker’s clamp actuator was pulled from Cold Arbor and can be customized in several ways. I’m thinking of either switching up the leadscrew from a 10 TPI to an 8tpi fast-travel screw (with 2 starts, so effectively 4 TPI), which would make for a 2.5x increase in tip speed. Else, I can remove a whole stage of gearing from the chopped 36:1 drill gearbox that runs the actuator in order to effect a 6x increase in speed.

It’s a little hard to decide, since I’d have to weight the costs and benefits – namely, how much clamping pressure do I really need? If I could get 6x more speed and not really sacrifice how hard I can hang onto the opponent, then it’s worthwhile. Alternatively, I’ve used the clamp as an emergency lifting arm in the past, so maybe I don’t want to sacrifice so much torque.

Oh, wait, I forgot one thing…

Not needing 3 different sizes of hex wrench, 2 of which must be ball ended, and 20 minutes in order to fix anything.

Probably the worst thing about Clocker is how hard it was to pull anything. At D*C2012, I had to take out the lifter gearbox in order to remove one gear stage from it that had stripped out and binded up the whole thing. It took pretty much exactly 20 minutes to take the robot apart and put it back together, just as I had experienced in the shop. This design goal kind of goes with the simpler and more practical frame design.

Now, where was I? Onto the actual evolution of the design.

I very rarely use an outline of the bot as a design guide, but this time I founded it immensely helpful to visualize how all the parts will interact, roughly, before committing a part file to it. Above is shown an arrangement of the parts as conceived fairly early on, including the Third DeWut that will run the big fork. That’s right – no more weird dual-motor gearbox.

I was fighting back and forth about whether to do direct-drive to one wheel and chain/belt to the other (per side) or an indirect drive to both wheels with the motor in the middle somewhere. It was primarily finding a balance between 3 variables – whether or not the bot needed more ground clearance, the kind of speeds I could get with either method, and where I had to stuff everything else.

If the rear drive wheel were mounted in-line with the motors, then I would be limited to a maximum theoretical ground clearance (i.e. without any type of bottom armor) of 0.75″ with 4″ wheels. If I designed Clocker solely for smooth-arena combat, the ground clearance would be only 0.25″ at most using 3″ wheels, but this is not the case, so 4″ is pretty much required. 0.75″ clearance is what Null Hypothesis and the latest Überclocker all run with, and it seems to be fine for the stage combat scenario of Robot Battles. It would limit me to three speed ranges dictated by which gear I put the DeWalt geaboxes in – they have a 450, 1450, and 2000 RPM ranges (at stock voltage, rated by the company).

Now, I’m dead set on overvolting 18v motors to 24v at least (or rather, 25.6v for 8S A123 cells), because it’s a glaring sign of n00b to run motors at their rated voltage. At the very least, 7S must be used to be comparable in drive power to the current version of Clocker. This depended on how creative I could get with placing the battery itself. At 8S, I would see a (theoretical) top speed of 24mph in the middle gear. Yikes… that’s pretty high. But the alternative, 8mph, in low gear, is really really slow. At 18 volts or 6S A123 cells, the top speed would be a more tame 17mph, more to my liking but a little on the high side. So, wheel-on-motor would be a good choice if I was satisfied with 18 volt electrical systems and 0.75″ ground clearance.

However, if the wheels were not directly in line, I have more options. I could run 3″ wheels at below motor center line to retain the same level of ground clearance , but more manageable speeds. The motor location would be significantly more flexible. It’s wholly possible to run a 1:1 using chain or belts and with the motor not directly connected to either wheel – in this arrangement, my speed at 24v would be still 18mph, which is excellent.

The next variable to consider is how much tractive authority I wanted. By this, I mean how far can the robot be tilted or rolled without losing tractive authority? This would dictate my ability to escape from bad situations – the speed might be enough to avoid them, but if I ever got in one with a low clearance bot with little stubby wheels, it could be worse. Bigger wheels will always help with this problem.

I decided it was worth trying a 1″ ground clearance experiment using 4″ wheels. It would be a new design direction for me, since I have classically favored flat robots. Ideally this would make Clocker virtually impossible to wedge under because it would take incredible effort to break its traction fully. I wanted to leave space for the option of 8S packs, even though it meant a mid-20s top speed, because I could always back down from there and save some weight if that was warranted. A greater tractive authority combined with high speeds makes a bot much harder to catch.

The culmination of all this reasoning and pulling tradeoffs back and forth is many hours of positioning components and thinking of what parts go with the configuration, and roughly how fast it would go. Some times, a good arrangement existed for battery and motor placement, but there was not really space left for the Ragebridges. I made configurations with one Ragebridge per side (instead of 2 stacked on top), the battery in the front (not optimal for center of gravity), and even offset motors.

Ultimately, here’s what it came down to:

I had to release one constraint to settle upon this, and that’s the bot’s width. Clocker is already huge for a 30lber, covering a 18 x 27″ footprint. That’s bigger than some former 60lb Battlebots lightweights. Part of it’s unavoidable with this kind of design, where I have to contain a majority of another opponent.

Only by letting myself build a 19″ wide bot could I fit an up-to-8S pack in the rear along with the ragebridges. The motors and battery pack were now all rear-biased, which was favorable for CG reasons.

The observant would notice that I went back to the 1″ wide wheels after the previous shot. There were 2 primary reasons for that move. First, I really wanted doubly-supported wheels with static (standoff-like) axles. This increases the rigidity of the frame over a single supported wheel, and also lets the outer frame rails act as wheel armor. And second, those 2″ wide wheels would have pushed the bot width dangerously close to 2 feet.

After this part of the design was roughed out, everything else began falling in place. There’s really only one place to put the clamp and fork, really.

The next big challenge was how to mount the fork assembly. Clocker’s current configuration is a little “torsionally unsound” in that the force of a 30lb opponent capture in the fork is reacted entirely by the front frame cross-members twisting. Said front cross-members are also just flat plates, which are known to be very poor in torsional loads. Without the top and bottom plating to support them, the whole thing just lurches back and forth if any load is applied to the fork. While the latter configuration is acceptable (loaded top and bottom armor), I don’t like it as much because it depends on a material much less stiff than the aluminum (i.e. sketchy McMaster FR4 garolite plates) to handle the loads – I’d rather have a more “atomic” structure.

In the above image I’ve whipped up a pretty simple first-pass attempt at the clamp motor and pivot mounting structure. At this point, I was still relatively unsure about how to attach the whole thing to the frame.  The two big top-level choices were a CRJW style standoff tower (preloaded like mad) or just two crossing trussed-out 2.5″ tall aluminum flat plate members, separated a few inches. CRJW’s build style worked out very well with respect to overall stiffness, so I initially favored it.

I was also split between chains or gears for the main lifting drive. The first Clocker used #25 chain, the second used giant custom spur gears. At first, I figured chain would be easier to make an assembly with  because it was narrower yet more flexible (in terms of positioning the components). Hence, at this point, I still had a narrow assembly set up for a #35 chain (for more durability over #25) assuming I’d drop a sprocket in there.

However, what I eventually realized is that chains need space to exist, and I’d need to cut huge gaps out of the frame to pass the chain through. A sprocket combination that got me the needed external reduction in other to not make the fork a fucking hammer meant the large sprocket was almost approaching 6″ across!

I could more easily get 5 or 6:1 in a set of spur gears, whereas the same ratio in a chain necessitated a 9 or 10 tooth sprocket, known to be extremely weak and highly stressing on the chain. So with my brief excursion into the dreamland of chain drive complete, I returned to modeling the assembly to favor a set of big custom 12 pitch spur gears. The assembly would have to get much wider, of course, but this was a minor adjustment.

Here’s a random picture of a gear.

Needing a bit of mental break, I decided to get really creative with a spur gear and embedded the “overclocked” Doomsday Clock motif that appears in every Überclocker. About 3 people will ever get it, and it doesn’t actually make sense to put on the bot. But hey, it’ll look pretty in the model!

I went through an entire round of parts arrangement with the standoffs-style structure that involved lots of shifting the motor and gear around. I wanted the ability to use all 4 corner holes for fastening, else the continuous structural loop would be sacrificed, reducing stiffness. But this generally involved crossing a spur gear (or a chain sprocket), so the gear had to be moved or the fastening hole had to be moved. Keeping the standoffs spaced as far apart as possible maximizes the stiffness of the assembly, but that was of course in direct conflict with whether or not I could stuff a motor and gearing into the same projected space.

After a while, I began realizing that the conflicting goals were pretty much irreconcilable given my choice of constraints and the desired size and aesthetics of the bot. Taking apart a bunch of standoffs would also be a serious maintenance problem (I’d need a clear, straight-shot space across the bot to pull a threaded rod out of). Maybe some crossing spans weren’t so bad after all?

They weren’t. Making the pivot axis of the fork directly over the motor (as opposed to offset in front of it) meant that I didn’t have to make as large of a cutout in the frame rails as I had expected. This allowed the condensation of the assembly to only 3.5″ wide – basically, just enough to contain the motor itself.

In this arrangement if I torqued the pivot axis hard (like hanging a 30lb opponent a foot away) the twisting load is taken up by shearing 4 2.5″ wide bars across their width, basically. Much better than twisting the same bars about their own center axes. This is incredibly difficult to explain in more detail without a thousand more words dedicated to it, or a cute drawing/diagram.

I’ve closed off the structural loop around the fork motor now, and am pretty satisfied with how this turned out.

I try to not optimize anything too hard until the whole system has materialized to some degree, so I moved on immediately towards filling out the less critical parts of the bot, like the fork tines. These were laid out using the outline as a guide, but not for dimensional accuracy. Check out the fish hooks on the end – I’m gonna keep them in “production” just because they look pretty cool (uh oh…), and I also foresee them aiding in sliding under someone’s side armor and catching them. Worst case, I’ll sand them off, so who cares?!

I added the top clamp from Clocker’s 2012 incarnation, which was a newly built assembly, to see how it looks. I’m going to keep this clamp because it’s already built to work with the geometry of taller robots. The pretend-o-bot is starting to form. At this point, I’ve gone back and diddled with the geometry of the motor mount some more in order to get a more favorable “angle of decent” of the fork. As it turned out, a totally centerline pivot point forced the descending part of the fork to be very shallow, which made the ‘active’ part shorter but also let the fork swing down lower (before it hit the motor mount). Here, there was a tradeoff of “do I really want Clocker to lift it self off the ground?” – while it seemed advantageous for making sure I win the wedge war, it would be a disaster for expedient driving and maneuvering since the bot would be effectively high centering itself.

So, in the end, a steeper angle won out since I could hard-stop the fork just barely above the ground. I’ll deal with wedges as they come.

I’ll be reusing the clamp actuator too. Some time was spent playing the Geometry Game (midway down in this post) trying to maximize the range of travel without having the motor impact anything. This time, the components played out in my favor and made a little corner that the motor could stick into without running into the pivot shaft, as well as being protected on most sides by the bot structure!

A geometric example of a new leg has been added, too. The new design calls for this to be machined from solid 3/4″ aluminum. Chunky? Yeah, definitely. But, I need the stiffness if it’s going to be single-supported and stick out that far.

Here’s a bit of SCIENCE!! which I used to sanity check myself when designing the leg. I basically took a reasonable guess at how much instantaneous force the leg will see if Clocker just ran into a wall for no reason – say 1500 lb-force, applied directly to the big roller screw. Then I assumed the bot was infinitely stiff and could hold the leg still at the rear where it is attached. Then I told Inventor to pull some magic and tell me how much it deforms. Result: Probably about .25″ in compression and bending, and I’m more likely than not going to bend the roller screw.

That’s okay, I’ll make spares. A 0.5″ wide leg made Inventor yell at me for large displacements – that indicated some degree of hopelessness.

Realistically, a static FEA calculation isn’t going to capture the whole picture. The bot is not infinitely stiff – if it dives into a wall, the frame will most likely bend significantly at the mounting point, too, absorbing some of the hit energy. The suspension spring could also take up some of that force. The only question, really, is if the whole thing will just stay bent after it, which could be found out with More Analysis I’m not currently in the mood for. Just ship it.

At this point, I was starting to look at just making small refinements. I’ve taken the liberty of shortening the bot a little closer to original dimensions. This was accomplished by swapping spaces with one of the chain tensioners – before, I was limited in how far back I could move the fork pivot axis by how close I could move the tensioner to the main drive sprocket.

Well why not just swap them then?

I threw the current version of clocker in just for a size comparison. As can be observed, the ratio of robot to fork has decreased somewhat, and the ratio of leg length to wheelbase has increased. The frame itself is a tad shorter, but wider. And much taller. Overall,  Clocker ADVANCE occupies a bigger bounding box, but most of it is pretty spindly and empty.

When I was happy with the placement of parts, I began the t-nutting.

Now, I promised to not t-nut so prolifically any more, but this situation warrants it, I swear! The little gussets and brackets will double both as frame binding elements as well as top and bottom plate mounting points. The difference in this case being the top and bottom plates are made no longer structural – just to hold the guts in, not to take loading (short of direct impacts, which will be guarded from with piles of ablative material). These are far less egregious than Clocker Remix’s frame.

Additionally, the presence of the U-shaped gussets in the motor mount strengths that region from twisting even more.

The best part? The lifter motor pops out after undoing 4 screws accessible from the front. It drops out the bottom and can be immediately replaced. The drive motors will take a little more thought.

One issue I ran into was how to retain the gussets from moving in the Z-axis. The last picture showed pretty well an underconstrained joint – i.e. in the absence of friction, it could still slide out the top or bottom. Only friction retains it in real life.

By insetting the fingers fully into slots, I capture them in the Z direction, too. The downside is making the left and right chassis rails 0.125″ taller per side. I found this inconsequential because INFINITE GROUND CLEARANCE. Now, with these captured slots, there is also a clear assembly order for the bot – everything in the middle first, side plates go on last.

I turned my attention to the legs now, and devising a real mounting solution for them. They pivot directly on the front drive wheel’s axis, on a shoulder screw (which also anchors down the front drive axle standoff itself. I devised entirely new shock absorber things for this build, because I need to go up in spring stiffness to counteract the longer lever arm. The basic principle is still the same, however. Waterjetted from the same chunk of metal I will presumably make the legs from, then secondary machined.

I’m considering making a little extension to the frame to put these parts in “double shear” mode which will once again increase their stiffness. I decided to leave this until after the rest of the bot was modeled, since by this point I was getting close on weight.

Notice the blue string running around the model sprockets? I decided to try out Inventor’s chain drive designer for realsies this time. Prior to this, I’d only used it to generate sprocket profiles for machining. But as it turns out, it will tell you exactly how many links you need and whether or not you have enough tensioner travel to last the life of the chain, because chains stretch a few % with age (The answer for me was no, not for 10,000 hours anyway). You select existing cylindrical axes and tell it how big each sprocket is. You can even say a certain axis has an allowable amount of wobble (to make cam style tensioners) or can move in the XY plane a certain amount (for linear sliding tensioners). Then it will update whenever the sprockets are moved, and yell at you if you move them to an impossible position or you need to adjust your tensioners.

Wow. Computers are pretty damn cool.

In seeking more structure for the outer side plate, I decided to extend said tensioners to become standoffs in their own right. These have off-center holes so I can rotate them and then tighten down the long screw that binds the two plates together.

I added simulated top and bottom plates for the final almost-finished look.

At this point, the bot “weighed” 31.0 pounds. Uh oh… All that solid metal has to go. I want it to weigh 28 pounds or so in order to include overhead from wiring and screws I did not yet model (most of the big bolts were put in already).

Clocker Remix is very much “gothic cathedral’d out”, my term for making structures sparse and spindly to reduce weight, like… gothic cathedrals. I’m sure those guys did it less for weight and more because they were badasses, but whatever. However, it was done rather haphazardly – I have truss elements that really don’t do much and could have been totally absent (Did you know that trusses triangles are ideally all equilateral?)

And that’s it.

After selectively trussing out most of the plates and adjusting the height of others, the bot is now at 28.6 pounds as-modeled (with more big screws added, too). The side plates have gotten much lower (and name-emblazoned), which saved a ton of weight. I added one more standoff to raise the stiffness of that outer rail some more. The lowered sides also makes the motor mounting screws that much more easier to access. The only plate not hollowed out right now is the very back, which I’ve decided to keep solid because the bot otherwise has no rear armoring.

And the back shot.

in conclusion,

this is the longest post ever on my website at about 5500 words! I keep upping this number for some reason. It’s been a long time since a pure CAD-based brain-dump post, and I must say it was rather refreshing. Airing out decisions that you have made, makes you think about them more and critique them a little more impartially.

Construction on Clocker will commence as soon as everything opens up again after the Christmas-New-Years-What-Have-You holiday season. The target is Motorama 2013 (more strictly Robot Conflict @ Motorama 2013), an event I haven’t been to since Clocker and Arbor’s collective dismal losses in 2010!

 

Make-a-Segbearshark: Random Updates

Jan 04, 2011 in Done!, In Progress, Land-Bear-Shark, Make-a-Bot, Project Build Reports, SEGFAULT

With the holiday and end-of-year business shutdowns finally ending, the steady trickle of parts shipments for Landmelonsharkpigbeartankboard is flowing once again. I’ve finally gotten my trippy PCBs in for Make-a-Bot too, but haven’t gotten the chance to make the heat spreading plate and test it yet. Otherwise, I got Segfault running once again, now with its own enormously overkill battery.

Overall not much to say, so let’s just start with the grocery list.

landbearshark

LBS is still a pile of parts that has been steadily increasing in size. The materials needed to start the entire project off are the aluminum plates, which have yet to arrive. Otherwise, I have essentially everything – motors, motor-side sprockets, chains and links, the four shock bodies, a whole mess of stainless steel hardware, most other drive components, and this cute little contactor.

Here’s what the whole mess looks like right now…

Still on the way for whatever reason are three 24″ x 24″ x 1/4″ aluminum slabs. Other frame materials are used in small enough quantities to just be scrounged.

The design has been filled out with the requisite t-nuts needed to hold the panels together.

Some minor touches are missing, including places to mount the rider-sensing switches. The contactor and other major electrical components are also homeless at the moment. I also need to make the “second deck” of electronics which will handle tasks other than motor control. I did collect a model of the Giant Red Key Switch, and it hangs out in the back.

If I’m lucky, the metal will arrive tomorrow and the frame can be cut out by the weekend. That’s really the only hard part.

(Okay, minus the electronics…)

make-a-bot

At last, the trippy PCB heaters!

Trriiiippy.

I made one change from the version I keep linking to – there’s a center hole in the board so I can wedge a thermistor between it and the aluminum heat spreader. You know, so I can actually find out the temperature of the working surface. Otherwise, the trace resistance checks out (the squiggles on the bottom side in the design were put there in case they did not…) I’ll need to cut a single square of aluminum for the heat spreader. The aluminum will then be thermal-epoxied (not bolted or sandwiched) to the top of the board.

I got two boards, but will only prepare one of them for now.

segfault

Poor Segfault.

No, I haven’t completely trashed it yet again. It’s been working, but always became weak after 30 minutes or so because all I had in it were two of Überclocker’s packs. It would usually just fall over after an hour. So after the term ended, I swore I would make a new battery just for it such that I can reliably bring it out for demos. Naturally, with the ennui of the break, I felt unmotivated to do anything. Additionally, during an unfortunate scooter-organizing incident, the cable leading to the control knobs was sheared off, so it was just one more impediment and grunt-work repair job I had to tackle before it could even work again.

So maybe I did completely trash it. Either way, I guess it counts as New Year’s resolution to repair Segfault? I’m not sure.

Here’s where it starts.

Ah, another brick of A123 26650 lithium nanophosphate cells; here, being prepared and tinned.

Segfault’s completely empty right side was just begging for a brutally large battery. I measured everything out and found that I could easily fit a 5 x 7 cell array. Since Segfault already demonstrated operation on 7S (about 23 volts), I’d have to make a pack that had 5 cells in parallel. This is more or less a 146% \m/etalpaKkK. With 5 2.2 amp-hour cells in parallel, the total watthours count of this pack comes out to be around 250. It ought to be enough to keep Segfault running for two hours or more.

The enormous \m/etalbraid makes a return on this pack. Grounding braid is now my staple “battery bar”, as shown by the \m/etalpaxXx themselves and RazEr rEVolution’s pack (and the Clockerpacks, and the monstrosity I made for Cold Arbor). Segfault will never draw enough current to overload these busbars, but hey – maybe one day this thing will be repurposed. Have to plan ahead, you know.

Soldering is discouraged on cells like this because of the risk of melting the polymer separator close to the terminal, which results in bad. If you’re very fast and have a soldering iron with a large tip (high thermal mass, effective thermal bath), it’s definitely possible. I stuck to my 3-second rule here – once the joint starts melting, I count 3 seconds to smash it down and add more solder. Once that time is up, I immediately move on to another cell, and don’t return to that one until I’ve visited the rest of the pack.

It’s probably not very legit, but I haven’t overheated a cell yet…

After the whole pack got busbraided, it was time to add the wires. There’s three heavy-gauge wire pairs coming out of the pack this time. The two off to the right interface with the existing double battery connector in Segfault. There’s no reason to have a double connector in the thing, but it’s the way I originally made it to accept the robot batteries.

The single cable to the left is only used for charging. But I guess it could be a third discharge port if needed.

I ordered JST-XH connectors in several different sizes from Digi-key, so I was actually able to make a legitimate balancing harness.

Now the fun part begins: Packaging the whole thing.

MAGIC!!!!

So there’s no soda bottle big enough in this world (please prove me wrong) to swallow up 5 cell wide rows. The \m/etalpaxXx required a 3-liter soda bottle, and they were only 4-parallel groups. And while I could have planned ahead and ordered wide heatshrink tubing, that just doesn’t work with how I like to build these things – i.e. right now.

I did, however, buy a six inch wide roll of Kapton (Crapton, since it was from a Chinese ebay seller, and doubtlessly not real DuPont polyimide film) for Make-A-Bot’s future build surface. So I decided to just give it a try with finishing the packs up. With some cut up sheets of adhesive-backed foam rubber fitted on the cells for shock isolation, I wrapped the Giant Crapton around the whole pack several times in two separate loops. I think it came out great. The tape doesn’t really stretch, so it doesn’t look as “heat-shrinky”, and I wouldn’t say it’s waterproof. But it got the job done.

After a brief interlude to reconnect six little wires, Segfault is now once again attempting to kill innocent riders.