Archive for the 'Candy Paint & Gold Teeth' Category

 

Motorama 2015 Part II: The Pitfalls of Used Überclocker Ownership and Unmodeled Dynamics of Candy Paint & Gold Teeth

Mar 30, 2015 in Candy Paint & Gold Teeth, Events, Überclocker ADVANCE

Let the masses rejoice, for I’ve decided to go ahead and post my Motorama 2015 trip summary, having been satisfied by the newbies, finally *ahem*. I mean, that and the fact that I have backed up way too many other things to talk about waiting on you guys to finish. One of the consequences of writing up an event report a month and a half post facto is that everything I remembered from the event and wanted to talk about really really badly is now… wait, what was I talking about again? See what I’m talking about?!

Additionally, for the past month or three, I’ve been working some black projects which will be excellent once revealed, but I feel like need a little more time to develop before I drop the bass. Rest assured it will not be disappointing.

Anyways, onto the event!

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The Motorama 2015 All-Bots Update: The Revival of Candy Paint & Gold Teeth, Überclocker Advance Inspection

Feb 15, 2015 in Bots, Candy Paint & Gold Teeth, Überclocker ADVANCE

With Boston getting mashed by blizzard after blizzard literally once every weekend for the past month, there’s not much to do save for hunting baby seals for their meat and blubber working on robots! Especially as wave after wave of cancellations hit MIT to the point where I’ve had to reschedule several shop orientations as well as cram 2 days of lecture content into one for a new black project class I’m helping with… but more about that later. And suddenly, Motorama 2015 is but a week away! And Dragon Con 2015 is next Tuesday, clearly.

Contrary to previous years, I have a temporary moratorium on new bot construction, choosing instead to try and make my current fleet a bit less fail before moving on. This was spurred on mostly by Überclocker being basically perfect by placing at the past 3 events: Motorama 2014 and Dragon Con 2013, and finally winning at Dragon Con 2014, for which I redeemed my karma points on the return trip. I thought it only fair to give Candy Paint & Gold Teeth the same treatment this time around. Last year, due to a whole stack of beginning-of-semester shop issues, I only had days to work on it and the whole bot was extremely rushed on the last mechanical details and the entire electrical system. In large part, the internals were held in by hot glue. This year, as I act as mentor to a host of new MIT-area based builders (who I’ll definitely introduce on this site in the event report!), I’m going to integrate the lessons learned (read: all of them) from last Motorama and finish the bot like I intended.

The following work was from maybe Mid-January to about 2 weeks ago…

Step 1? Actually look at the damn thing! I knew it was all hot glue and zip tied by Adam and company last year, but not how badly. And I will just say… my god.

Now, in reality, I think those lipoly packs are more secure in there with their 10 square inches of Velcro, half-dozen zip ties, and generous fillets of hot glue per each, than anything else I can come up with – including the original sheet metal battery cages. But this also makes them utterly irreplaceable, and Candy Paint ended the event with a dead cell, so these had to definitely go.

The placement of the motor controller was also not optimal, and… well, should I really waste time listing everything that’s wrong with an on-the-fly wiring job?

The next course of action, much like pre-NYMF Chibi-Mikuvan, was to rip everything out and start over. This actually took much more effort than it sounded. Recall that both lithium packs were held in by no less than 10 square inches of Velcro. Real 3M-branded Velcro. We might as well have welded them in.

I got as far as heartstoppingly buckling one of the packs in half by a few degrees before trying other solutions.

It’s actually very, very hard to remove sticky-back Velcro of reputable source, such as if real 3M adhesive is behind it. I ended up pouring acetone into the cavity that surrounds the battery and waiting several minutes while slowly applying upward pressure on the battery wires. The acetone slowly damages the adhesive along the peel front, so the whole thing very slowly lurched upwards and eventually gave up.

Extracting the smoked controller to inspect the depth of destruction. Two of the phase wires desoldered themselves, and the 3rd leg was also a total loss. Ouch…

One of the higher priorities for me was rewinding the weapon motor. The original winding had a short-to-core to begin with, which might have contributed to the controller’s untimely death. I couldn’t identify the location exactly, but there are at least 2 spots per phase where I pulled the wire bundle over bare metal, so the chances were good that I would have shorted something a little.

The issue is that I ran out of the specific size of 70mm stator used in the motor. I have a handful of 70mm stators spread across two types – one with a 32mm center bore, and another with a 26mm one. I designed the motor around the 32mm type, and the only ones I had left were damaged salvage cores from copier motors. Due to how much epoxy I poured over the first stator, I decided it was still better to repair the ones with damaged coatings.

Pouring epoxy over the exposed metal is actually a very unreliable fix, because of the way the original coating wraps around and smooths the edges of the steel. Instead, I had something better:

I had these sheets of “electrical grade hard fiber” from McMaster from past projects. It’s also called “fishpaper”, contains no fish nor shellfish, is gluten-free, and is a resin-impregnated heavy cardstock-like material. Laser cuts beautifully into stator-shaped pieces. I used the model of the stator that I measured up to design the motor for the 2D profile, with the arms and tooth ends purposefully thickened a few percent to not leave any metal exposed. This whole sheet was then applied to the cleaned steel surface with epoxy.

Next up was rewinding. My goal was not only to make a clean winding, but also slow the weapon down. Wait, even more?

The two fights Candy Paint got in at Motorama 2014 showed that the weapon already had enough impact power for my liking, and I try to favor reliability over the so-called “brushless penis contest” in the combat robot world of ever-larger motors and spinning weapons, often to impractical proportions. Trust me, I used to be one of the young boisterous men responsible.

Candy Paint’s bar was designed to spin at 180mph. I would be perfectly content with 120 or even 100, with super rapid spin-up time and excellent “upside-down flailing” torque. To get to this point with the same gear ratio meant increasing the turns on the weapon motor’s stator poles by 50%, which entailed going to… oh, six turns per tooth instead of four. Still easy compared to my 36+ turn hub motors! Either way, a new piece of string to measure the wire length needed was test wound around the four teeth of a phase.

The “hobbykinging rig” was, like last time, wrapped 3 times around a set of 10ft-apart table legs to generate 3 parallel bundles of 9 parallel wires. This gave the motor the equivalent of 14 gauge windings, except far, far easier to wind than a single solid 14 gauge bar.

A half hour or so later… a motor appears! See, low turn-count motors are super easy to wind! A custom hub motor often takes me like 2 or more hours each.

The aluminum bearing cap was thoroughly covered in thickened epoxy before I started pulling wires over it. I left roughly 10″ on each winding end and put heat shrink tubing over them to use directly as output wires.

But the next issue was, once again, how to solder bullet connectors to them. Enamel-coated magnet wire is difficult to solder without resorting to disgusting measures, such as dunking in molten sodium hydroxide or highly acidic fluxes. Or torches and mechanical removal (sanding, scraping). Doing that on a 27-strand bundle was out of the question. I did that last time…

I started haunting the Internet for anecdotes of the “Well, my mama told me to use yak milk and that’s never failed me!” nature. Could I get yak milk around here? Probably, if I look hard enough. But one curious substance showed up repeatedly: average automotive brake fluid. Hey, I don’t have a yak, but I have something about yak-sized that needs brake fluid, so I have some bottles of brake fluid!

When I thought about it a little more, it made sense. DOT 3 and 4 brake fluid is made of glycol esters, which are also found in paint strippers. In fact, brake fluid itself often has “do NOT get on your paint, like seriously” written all over it. So when you heat it up, of course it’s going to attack and damage the enamel coating too.

I was fairly certain from MSDS-haunting that burning brake fluid was not acutely toxic, but also sure that it isn’t good for me in any way, so this step was done with plenty of ventilation.

Well I’ll be damned. Dip the end of your magnet wire bundle in a tiny little bit of brake fluid, and using a large iron, solder as normal. I would estimate the solder flowed 1/3rd as fast as it would on a bare wire, but each of these joints was made in under 15 seconds. None of the inconsistent flowing, burning, blobbing up of flux, etc. I’ve experienced in the past.

This has been your “Well, I’d say don’t try this at home, but that defeats the purpose of putting it on the Internet” moment of this post.

Now, it’s important to point out that DOT 5 brake fluid is made of silicone and probably won’t work in this application.

Installing the motor for a quick spin and fit test!

Finally, I folded the sheet aluminum battery retainers. Each battery will still have a few square inches of more reasonably-placed Velcro padding underneath it which should handle the majority of loads, and this cage is just to prevent them from being sucked into the spinning cheese-grating pulley below them!

Before putting the batteries permanently in, I wanted to try and fit the motor controller in the same region as the motor. This is so the wiring was less chaotic up front, and the controller at least had a modicum of convective cooling available.

Keeping the wires down was more of a challenge than packing the ESC in. I made these polycarbonate retaining strips that have their ends heat-bent up into a hook shape, and are quite difficult to remove. I’ll probably back this area up with a cable tie or two to more guarantee the plastic not flying away.

The ESC has been switched to the 150A K-Force since I’m only running 6S in this bot now. There’s no need to specify a high-voltage 12S capable ESC! Architecutrally, it’s identical to the “Sentilon” HV version.

Final installation of the wiring. There’s a sad empty spot to the right that needs filling with some gaudy mood lighting or something…

This isn’t it, however. All of these wires are sort of too tall and interfering with the volume that the drive pulley needs:

For basic flight testing, I stuffed everything in using massive amounts of gaffer’s tape, but this isn’t a permanent solution.

In this configuration, I found out that the bearing block was either milled 1/16″ too deep, or the bearings are collectively 1/16″ shorter than their nominal dimensions. I had to insert 0.06″ of shims into the spindle in order to have it not wobble.

I took the opportunity to swap in one of the spare pulleys I had made, since the first one was showing “bowtieing” on the D-bore due to how loosely it had been mounted before.

To resolve the wire height issue, I finally finished the bottom plate that was supposed to go on originally. To the underside of this plate are glued a succession of rigid foam rubber blocks which keep pressure on the wires, especially near the cheese-grater pulley. Notice the “0.06 of shims” that I wrote to remind myself how many shims to stuff back in…

I need to find a good hiding spot in order to get a good spinup video of this thing, or even better, some actual testing. MIT is in general so space-constrained though it’s difficult to find a location to do this in. The loading dock is all concrete, but too tight. I’d preferably want to be on a different elevation from the blade, and behind a solid concrete object…

Candy Paint on full drive power is fast. Faster than any spinner has any right to be, with a design speed of just under 16mph. I’m hoping that this balance of drivetrain and high-torque and reliable weapon will be a favorable one. It’s also very squirrelly when turning due to how short the wheelbase is, so I’ll be keeping the dual-rates switched on for this one.

One of the details that completely derailed any plans of Candy Paint domination last year was the unmodified blade. I bought this from a builder who made this blade for an invertible bot, which didn’t care which orientation it was in. Candy Paint is non-invertible by design, and the double bevel caused it to “coin” into the air on any non-perpendicular impact (read: like all 3 of them).

Solution? Just grind the bevel off. This step took a while, since the steel is hardened and my angle grinder is small (the Civilization Destroyer is only equipped with a skinny cutting, not grinding blade).

I only ground 1 bevel off on each side, so the blade can currently only “spin” one way – I made sure that this time it was in the tighten direction, instead of last time where the blade slowly worked itself off since the motor torque was trying to un-spin the nut…

Almost armed up fully. Notice how I also stripped all the paint off? This is because…

I HAVE PRIORITIES.

Can’t test it? Might as well paint it. Candy Paint and Gold Teeth is finally getting some of its namesake. The candy paint: A can of fluorescent safety orange applied like 10 layers thick and glossy-clear coated. The gold teeth: Some Rust-Oleum “gold metallic” spraypaint that, to my utter surprise, actually worked okay.

And here it is, all pretty and shiny-like. I was definitely surprised at how well the paint job turned out. Maybe my many minutes of van bodywork, being forced to spraypaint something other people are forced to look at, helped.

Like I said, I’m still searching for an opportunity to whip this thing up to full speed and run into something. It’s probably going to have to be in some deserted basement, at night, on a weekend, peering from around a corner. I’ve driven the bot around plenty, and have whipped it up to maybe 33% speed, but haven’t planted the blade into anything yet.

That’s all for the Candy Paint reboot. Time to move it off the work mat so I can take a look at …

Überclocker Advance

As mentioned originally, Clocker has been steadily growing out of its awkward engineering bug stage, from suffering several issues at Motorama 2013 to almost winning Dragon Con 2013 to almost winning Motorama 2014, to finally winning Dragon Con 2014. Now, with my #1 nemesis for 2 past Motoramas not going to this tournament, and with the Banebots wheel swap being extremely successful at Dragon Con 2014, leads me to believe that Clocker has a fair shot at the 2015 championship.

IF something stupid doesn’t happen.

That’s a well known failure mode with stuff I make. So, as long as I have plenty of time, let’s take the bot apart as much as possible and check for possible impending stupid things. A wire about to become unsoldered, one of the RageBridge FETs about to pop off, the DeWalt gearboxes falling out of gear, etc. Anything at all.

So apart Clocker goes! On deck for a look-over include…

  • All of the lifter drive clutch parts, which involve shaft collars being tightened the right about to slip. Replace the most likely very fatigued screws holding the lift gear to the collar.
  • The clamp actuator has been “underconstrained” for some time – rebuild and take care of it.
  • Inspect ALL of the DeWalt gearboxes for signs of falling out of gear – the current style has an issue with the plastic shift-retaining ring not retaining. A zip tie takes care of it.
  • Inspect the drive motors’ electrical connections
  • Look over all the RageBridge v1s and reinforce large components with some epoxy or rubbery Goop.

Pretty close to maximum entropy here… I also added cleaning and inspecting the chains to the list here, because if these chains cause me one more problem, I’m firing them on the spot and replacing them with… I dunno, kite string.

Breaking down the actuator for a rebuild. The motor was jiggly (the mounting face having been bent), the whole actuator was falling apart, and the shoulder screw holes were beginning to strip.

I cut new side plates according to the current version of the design. However, instead of using the T-nut holes, I just went ahead and drilled and tapped their bottoms (using slightly longer screws to reach). That end of the actuator being reliant on only T-nut clamping pressure was a build oversight.

Other things I did to the actuator include “correcting for” the bent motor faceplate, then integrating a large amount of JB-weld into its remounting. I consider these motors pretty disposable, and I have a spare ready to swap in, so I’m not concerned about never being able to (cleanly, reversibly) remove this motor again.

The motors in question are these IG32 27:1 motors, which I modified to have metal first stages by, uhh, gutting a 3rd motor and transferring its metal gears to the other 2. This means I have a motor which entirely plastic. It’s labeled “TRAP!” in my bin of motors.

Performing the “zip tie insurance” on all of the motors. There have been some reports from DeWut users that the white shifting barrel likes to jump over the small shifting pins, leaving the gearbox halfway between 2 speeds.

Aaaaaaaand mostly back together. Notice how shiny the inter-fork standoffs are? I remade those too, because some of them had gotten unacceptably buckled. The tie rods were also bent, making disassembling the fork quite entertaining.

I’m stopping short of the electronics. Why? To put pressure on myself to finish RageBridge v2, of course!

Maybe this is the stupid thing in question, but I totally want Clocker (and Candy Paint) to run some pre-prod RageBridge v2s, since Motorama is inevitably the best stress test for them. The current electronics stack works fine, so there’s really no reason to shoot myself in the foot. I suppose I will make it a goal to test RB2 by Wednesday, and if there are any hardware bugs, to forego running them at Motorama.

That ends bot work as of like 2 or 3 nights ago. I’ve been working on RageBridge ever since! That adventure is another post.

Motorama 2014: How Candy Paint & Gold Teeth Happened in an Hour; Überclocker Wins 2nd Place in Sportsmans

Feb 22, 2014 in Bots, Candy Paint & Gold Teeth, Events, Project Build Reports, Überclocker ADVANCE

In the spirit of Motorama always landing on or near Valentine’s Day, here’s some robot loving.

That’s Jamisons‘ new somewhat-secret-but-not-really 30lber megatRON.  This bot was finished in the minutes before departure, as Jamison and I both had teaching responsibilities and other factors that somehow all decided to congregate this past week.

I spent much of Friday evening checking over Überclocker and making sure it was in working condition. After last Dragon*Con, the drive completely stopped working (it had gone one-sided in the first 30lber rumble). I hoped that the motors weren’t damaged and that, like at last Motorama, it was a solder joint issue, since the DeWalt motors really have no good place to solder to.

I’ve known this to be a problem, so I bought some 3/16″ flag terminals right after DC to remedy the problem. That’s how you’re supposed to connect to these motors.

A single large zip tie wrapped around the whole can, overlapping the terminals to keep them in, and I should have no more of these issues. The two solder-covered tabs above the insulated flag terminals are where the wires were attached before. This is an insecure location that’s prone to flexing.

Fast forward a few hours to the event! The trip down was “ordinary” – with Mikuvan in good repair after the last-minute alternator save (with a Big Chuck’s Automotive Blog entry to come about that), the only issue was having to slow down when snow hit as we got close to Harrisburg.

Here’s Candy Paint being last minute saved. I foisted this effort off to Adam, and a new tagalong who is a visiting student in one of the labs that operate out of the IDC, Joaquin. Joaquin had started helping out everyone with their builds (he’s from Chile – he’s technically here on summer vacation), and at 11:30PM the night before had decided he wanted to come along.

The setup from the original plan had changed to the following:

  • Instead of running 8S, I brought along two 5000mAh 3S Traxxas packs that were in my post-DARPA stash to run 6S. Unfortunately, one of the cells ended up having a broken inteconnect tab, so it was taken out and then the bot ran on 5S.
  • The 160A dLUX controller seemingly did not want to run my motor at all. Weird, but it’s also a relatively smart controller, so it might have thought my 4 turn Delta-terminated motor was a short. We brought along two spare Sentilon 100A units which are my go-tos for brick-stupid controller that can actually flow some current.

Besides those two hacks, the bot ran everything as intended.

Here’s the MIT conglomeration pit table before everything started becoming scattered and messy.

To finish Candy Paint, some field tactics had to be deployed, such as when swapping the connectors on the batteries…

The bot basically right after it was finally through inspection and ready for first matches. Not bad, eh?

During the first match, the weapon motor controller decided to fail short after a solid impact that also flipped the bot a few times (luckily landing on its wheels). The reasons for the failure are unknown – these ESCs are known to work great, then spontaneously decide to peace on the next power cycle. The pulsed short current caused one of the Traxxas batteries to fuse a cell tab; for the next match, that was cut out.

And it generated this cloud.

No, just kidding. That’s from HyperActive, in what must be one of the most spectacular kills in all of robot-time, in its match against overhead saw bot Gloomy (which looks a lot like megatRON). Here is the video (and another angle).

I have mixed feelings about this match. On the one hand – holy crap. On the other, now every well-meaning but naive member of the “You should put, like, a circular saw on it so it can cut through the other guy!” crowd now actually have a leg to stand on.

The aftermath of that fire. Gloomy’s weapon came straight down on the 1/8″ Lexan top armor, which gave way to the saw quickly – the titanium sparks seen in the video all came off the center weapon pivot. And right under it was the lipoly battery of course…

Clocker suffered a bit of damage in its second fight as the upper clamp actuator decided to disgorge itself. The construction of this actuator didn’t really leave much side support, so if it got pushed or torque sideways, the T-nut joints slipped out, which is what happened here. The real issue was I didn’t retighten all the screws from Dragon*Con. After I retightened everything, I didn’t have another coming-apart problem, though the motor eventually stopped working.

Another problem with Clocker was that I didn’t have spare wheels. In my rush to get Candy Paint ready, I neglected to order a spare pile of McMasterBots wheels, and only had one more spare. The wheel on Clocker that was the worst ended up getting that last spare, and the rest… well, by the end of my 3rd match with Nyx, they were gone.

So out comes the VHB tape. This was an idea cooked up by Dane – VHB double sided tape is anchored down with superglue, then stretched very tightly for multiple wraps, then anchored to itself with more superglue.

Now, I this this is a brilliant idea for smaller bots, or bots with less drive power, but Clocker’s all drivetrain so these tape treads shed within a few seconds of the pushing matches getting heated. For my last matches, it was like driving the bot on ice.

Candy Paint lost its last match when a wire came loose from the very ad-hoc wiring harness and got snipped by the big shredder holes in the pulley. Oops!

Here’s the final damage tally to Clocker after its last finals match (with Upheaval, no less). The amount of bouncing Clocker did broke off one of the end rollers, and the outriggers themselves are also extremely bent up (hard to see here). The clamp motor isn’t responding, but the actuator is still mechanically good. Seems like it’s due for a full overhaul between now and Dragon*Con…

I’m also considering switching the McMasterbots 40A wheels to some Banebots wheels. I can make a quick-change hex hub in the same manner as Candy Paint and make the wheels far easier to swap, and have many spares on hand. Right now, I have to hand-machine and modify each of the wheels, and as this and past tournaments have clearly shown, Clocker blitzes through wheels – rears especially.

I am extremely satisfied with Clocker’s performance this time. Much like Dragon*Con 2013, it came in second place, being out-robotted instead of something completely stupid and negligent happening. I also now have settled the score from that event with Nyx. As usual, it put on a very visually stimulating show.

Here’s the matches:

vs. Knuckle Buster

vs. Piston Wax

vs. Nyx

vs. Upheaval (two matches for the championship)

Candy Paint went 1/2 – I’ve uploaded the matches where something remotely exciting happened.

vs. Hot Fuzz

Next, it fought Cathi (a ring spinner), wherein Joaquin accidently threw the radio’s “Throttle cut” switch so the weapon didn’t spin up, then Magnificent Poncho (a pusher), whereupon it spent most of the match upside down until the blade came off. It turns out that the blade motor was wired to spin in the untighten direction! Oops.

Finally, in a MIT-on-MIT grudge match, it faced the Atomic Bumble Prime.

One additional overlooked issue was that the blade was a double bevel profile (i.e. looks like <         > from the side). Any hit to an off-perpendicular surface will tend to throw the bot upwards, which clearly happened. This could have been taken care of with 5 minutes of grinder hits, but it was just not done.

Candy Paint’s future is a little uncertain right now. The bot is mechanically sound, took no damage past cutting its own wires, and I can easily rewire it to conform to my original expectations. However, outside of Motorama, there isn’t a local event that handles full 30lbers with weapons. I could put a sanding disc on it and bring it to Dragon*Con. Otherwise, Candy Paint will probably remain idled until next Motorama, unless I feel like putting it together properly and going to some basement to grenade a few old TVs and printers.

That does it for this event! Admittedly rushed preparations ended up working out somewhat, and Clocker has proven itself again to be a pretty damn reliable bot. And I’m not broken down somewhere in the middle of New Jersey.

I now turn my attention back to daily operations of the IDC fab space, as well as my new season of 2.00gokart students. Expect some updates on that as the semester progresses! The class is now somewhat legendary among freshmen and sophomores.

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….

Candy Paint and Gold Teeth Might Be A Thing After All

Feb 03, 2014 in Candy Paint & Gold Teeth

And now, back to your regularly scheduled content!

I determined that the next location to practice my back-alley bodywork skills on Mikuvan was Oops! I mean, we interrupt this weekly installment of Big Chuck’s Automotive Blog to bring you ROBOTS!

It’s been a while since the last Candy Paint post, and tons of work have been finished, but there is still a majority to go. I’ve finished most of the small parts and machined assemblies that will go on the bot, but the frame is not yet welded. I hired out the frame welding to my associate Jack at the D-Lab space down the hallway; since I determined that trying to learn aluminum welding and make a critical weld at the same time is best avoided, especially if I don’t get to arbitrarily remake the parts if I mess them up. The flip side is that I may only have the frame in hand by this coming weekend

Which is one week from Motorama. Uh oh.

In the mean time, let’s start with some machining. Rather, the product of someone else’s machining (boy are we off to a good start):

This is the main blade pulley for Candy Paint, sourced from a shady Chinese shop via mfg.com.

Alright, it’s not fair for me to call them ALL shady, since if you can machine a part to a customer’s specified requirements and tolerances, then there’s no arguing really. Here’s some hard data for the curious. I ordered this part in quantity 4 to sweeten up the deal very slightly over a one-off. The cost was $25 per part, single piece machined 6061-T6 aluminum. There was an engineering fee/setup fee of $40 and the shipping came out to $80 because I had asked for an express air service since I needed them quickly.

All up, about $220 for FOUR of these jobbies. These are hard numbers for your amusement, if you choose to have robots machined by proxy. As far as I can tell, the aluminum is legit.  With any dealings with Chinese job shops, always make clear what you need/want and in what timeframe – for instance, I asked the shop explicitly whether or not they could ship before the Chinese lunar new year holidays, which is like right now. Well, they sure as hell did! Last year, I asked the same for the DeWut hardware; that one literally got out the door the day before closing.

The total turnaround time was 3 weeks. One week for the quote to slow-cook on MFG, and two for production and shipment (so really, prod took only a few days from payment because of shipping).

Okay! So, now that the Chinese have beat me to my own game, I’m going to start machining things.

Okay, fine, I’ll get up early to use a nice machine in a nice shop. Here’s the main weapon motor can being carved from a SOLID BILLET OF STEEL. I knew this was going to be tricky going in because of the extremely space-constrained nature of this motor, so one piecing it was preferable over a press fit anything. This is the rotor portion being made, where the magnets will eventually sit.

It took me a while to get used to 1. machining and 2. on something big again. I had forgotten that carbide loves going fast, and it took a tap on the shoulder and a “Dude, you should be running like 500 RPM on that at least” to kick me back in gear.

Much better. Now for the pulley side.

For the close-in pulley groove, I used a straight grooving tool in a cutoff bar holder (for left side clearance), but with the compound slide set to the V-groove half angle, and just fed very gently.

After cleanup of the ‘skirt’ of the rotor, which was unreachable in the first setup, I pitched the thing on an EZ-Trak style 3-axis CNC machine (the things based off Bridgeport mills) and conversationally bored the six rotor holes – conversationally as in WHY IN THE NAME OF BABY ROBOT JESUS HAVE I FORGOTTEN HOW TO USE THESE DAMN THINGS.

The completed rotor, sitting on top of the billet of steel from whence it was cast.

Time to line up the magnets and…. well, shit.

I typically don’t make full-circle magnet rotors unless I had already tried making one and know that the magnets fit. This little 2mm gap in the magnets is entirely made of manufacturing tolerance. The magnets have larger fillets than I expected, so they packed just a little bit closer together. For instance, if I were to make another of these with the same pile of magnets, I would know how much diameter to reduce by to get a clean fit.

Not a disaster, since all this entails is slipping a paper shim between the magnets when gluing.

I’m sick of Hobbyking motors shitting magnets on me like BurnoutChibi’s NTM motors. I know it’s entirely a matter of cheapening out on adhesive quality and magnet & rotor surface preparation since they need to make a zillion of these per day. For my own motor, I can take a little more care.

The stuff in the cup is some Aeromarine brand Epoxy mixed with a handful of colloidal silica filler. I don’t know what the actual amount was, but it looked like what I would have grabbed from the bag, but that stuff is sort of bad to come in contact with, so I used a cup instead. The silica filler increases the volume of the epoxy and makes it into a quasi-composite material for higher strength and space-fill ability. The mixture was made thick, so it won’t sag when I cure it on the radiators.

I laser cut a spacer to keep the first set of magnets in their proper spaces. This motor has 14 magnet poles, but each pole is made of two magnets. Two like-poled magnets really don’t like being next to each other, so I’m calling upon my old hub motor making tactics here. One set of magnets already solidly anchored will allow me to slip the rest in with ease.

What the magnet ring looks like with the spacer attached. I left this to bake on top of one of the radiators in the shop, since it’s still UNACCEPTABLY COLD here outside.

The next day, I came back and shoved the rest of the magnets in. With another little batch of epoxy, I made big filleted ridges on the inside face (closest to the six holes) to prevent the magnets from moving, then shoved and filled in as much of the epoxy as I could into the small gaps on the near side. I hope the combination of this, and gently sanding the faces of the magnets to be glued, will prevent them from falling off. This rotor will be spinning a healthy 12,000 rpm or so.

Left to do on the motor include making the hub that the stator mounts on, as well as winding the motor itself. This is the first motor I will have made with less than 10 turns per tooth….

Next up, drive hubs. I decided to take a super simple modular approach to this and carve them out of some steel hex. Because the elements involved, such as the wheels and sprockets, are all flat, my choice to retain them along the hub is just retaining rings.

Each hub, therefore, just entails 6 grooving and a cutoff operation, plus the center hole drill.

Here’s a completed hub, with the shoulder screw that will serve as the axle.

Soon after this picture was taken, I realized that there was nothing at all that I could tighten the shoulder screw against to keep the axle in the robot itself – recall the slotted axle mounting points. If I can’t tighten the shoulder screw, then the axle will just fall out. Imagine that happening in a match!

Oops – slight design oversight.

The backup plan is to open the hole in the hub to a little over 3/8″, and use a 3/8″ sleeve bearing over the shoulder screw as the spacer. Essentially, keeping the bearing stationary and spinning the wheel around it. There will be a bit more drag, but nothing an overdose of grease won’t overcome.

The plan executed.

I’ve also chamfered the sprocket teeth in this picture. The chamfer makes the tips of the teeth much narrow, such that the chain can stand some amount of misalignment. This is pretty critical to proper operation of chains and sprockets, especially if the tension can’t be guaranteed like the way I have it set up.

With the four wheels done, time to move onto something very exciting!

That started as a 5 foot long straight bar of aluminum.

With a powered roll bender, it becomes a 16″ hoop that goes around a certain not-quite-round robot. To form the hoop, I sized the bar with about 3-4″ of extra room on each end to accommodate the distance between rollers, and pass it back and forth between the rollers while tightening the center one each time. Gradually, the bar turns into a partial hoop.

The finished hoop

And with it stretched around the robot. Pretend-o-bot!

I need to cut off the ends and trim them to be flush next:

So I did it on one of the wimpy little Craftsman bandsaws I maintain in the shop for students to cut things like plastics and wooden dowels on.

Nobody can stand here and tell me one of those bandsaws can’t cut through 2″ of aluminum, because this took less than 15 seconds. It’s entirely about having the right blade, and keeping the cut lubricated. The blade is a variable-tooth 10-to-14 TPI bimetal type, and I kept pressure on the cut while squirting aluminum Tap Magic at it. Worked great!

To trim the rest of the excess, I broke out the spare angle grinder I bought when appraising gear reduction methods for Chibi-Mikuvan. I have fully integrated this into a shop tool, available only to students who pass a battery of “Dear GOD WHY DO YOU ACTUALLY NEED IT?” tests. I had armed it with a set of both steelcutting and nonferrous-metal cutting discs, so I broke one out for this occasion. When in doubt, abrasives backed by gratuitous power tends to cure most ills. I cut vertically, using the face of the 1/8″ top plate as a guide.

A bit of belt sanding to fit the edge and the front plate could fit flush. I might keep sanding this to close the gap between top plate and front plate more, but the “using abrasives on an aluminum guide surface” part took more out of the top plate than I would like. This edge may stay unwelded or be patched with a small round bar.

I bent the front wedge with a standard metal brake.

I moved onto finishing the drive motors. I’m staying with the 12 o’Clocker style “Angerboxen” design, which is a single-stage repackaged drill motor. To get the parts, I needed the following:

  • Two 18v native 550 size drill motors, to be supplied by Harbor Freight drills (Null Hypothesis leftovers)
  • Two 9 tooth pinions from a 36:1 drill gearbox, since the HF drills are 24:1. To be supplied by two random drill gearboxes on standby.

I took apart four drill motors and was amazed that between then were four different grease colors, plastic gear colors, pinion materials, and ring gear styles. Okay, China. Come on.

The gearcases, like on 12 O’Clocker, are made on a Dimension 3D printer out of ABS plastic. I carved off the ring gears on tinylathe.

(Try to tell me that this plastic is somehow worse than the shady nylon-like substance the original gearboxes were made from…)

I recycled the drill spindles into the output shafts. Again, the output sprockets are retained by ….. retaining rings. I love the cutoff bar I bought for Tinylathe because the width of the tool is correct to service the most common snap ring widths I use:  1/2″ and 12mm.

Here, I’ve used a pinion puller (background) to extract the 15 tooth pinions from the Harbor freight motors and replace them with the 9 tooth pinions from the other drills. Gearboxen have also been populated with metal output gears.

And here are the completed drive motors, after the D profile was milled onto the shafts. I have output sprockets, but they were cut improperly; I’ll need to remake them.

At this point, there are only 3 more major things to machine:

  • The big center spindle and bearing holder block
  • The blade spindle itself
  • The motor’s stator hub

Minor things to do include:

  • Make the battery retaining brackets
  • Wind the stator ahead of time

I hope to knock these out during this coming week, such that when the frame gets back to me, I can immediately start dropping components in it!