Archive for February, 2015


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…


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.

The Curious Story of Meloncraft

Feb 04, 2015 in Project Build Reports

As the world might have been reporting nonstop, Boston’s been getting some snow lately. The biggest snowfall of 2 feet or more was forecast for mid-last week, centered around the evening of January 27th, with what ended up being a followup 12-15″ or so over the succeeding weekend. Besides exercising Landbearshark for the first time since last year, there were… other shenanigans.

Seemingly par for the course at MITERS, instead of all escaping home on Monday evening, people instead began showing up and battening down the hatches for the foot-and-a-half forecast for overnight Monday into Tuesday. As I was preparing Landbearshark for deployment – charging the batteries from last year and drowning some rust in WD-40 – I said texted (we ARE millenials after all) the fateful words to my buddy Adam:

Hey, do you still have the parts for melon-backpack?

Did you think I was kidding?


Let’s be clear here. I was thinking of folks at MITERS strapping themselves onto skis and bombing it down Massachusetts Avenue in the Missing Manual Formation (used whenever someone misplaces the CNC mill programming guidebook). The events of that night were to take a turn beyond what anyone could possibly have considered a good idea.

To truthfully capture the events, I have to back up a little bit. Earlier that night, I was sketching lines on a new sheet of 4′ x 8′ x 0.125″ thick polyethylene sheet trying to put a decent sled for LBS together, instead of what literally was just a scrap of said polyethylene sheet and ratchet strap used in the aforementioned video from late 2013.

No – this time, it was going to be a ratchet strap and more than one piece of polyethylene put together. Lest I be ambiguous, there was serious engineering going on here, like spending more time trying to figure out how to split the sheet into 36″ x 24″ laser-cuttable pieces for use on my Epilog 36EXT machine than, like, just taking a jigsaw to my scribble lines. Serious precision sled.

Shortly thereafter, around 9PM, Adam showed up with a clutch of the 80mm-class model airplane motors we call “melons” (due to a now-vintage in-joke that they are the size of small honeydews or cantalopes), 24″ wooden propellers, and a great bunch of “Sand Castle” 160A Hobbyking controllers, so called because they “resemble” Castle Creations controllers of the same class.

It took maybe 30 seconds of discussion, with the ever-battery-endowed Dane also present, to combine the two designs into one, shown here:

This was as far as the engineering ever got, for after confirming the validity of the design, we split our separate ways.

I was to generate the mechanical framework and machine the panels from standby 3/4″ plywood in the shop material pile. Dane went to retrieve battery modules, and Adam began heading up the electrical system assembly. So there you have it – instant startup! We even got a freshman intern or two from MITERS. I never got around to figuring out who was CEO. We will, however, entertain investors.

Here’s the mechanical development end of things. All I knew was that it had to carry two 24″ propellers spaced far enough that differential thrust would be an effective means of steering. I used the floor tiles as a layout guide and ergonomic sanity check, going as far as to have people measure me sitting down on the floor. Of course, with any rideable creation that uses me as the model organism, most everyone else was going to have trouble fitting in it, so I increased all the dimensions a few inches to compensate.

The time was about 9:30PM.

Seen here is the basic outline of the main slab of wood that will mount everything. I made this whole drawing as parametric as possible, in this case meaning that critical dimensions are linked to one another based on ratios and formulas such that I could change the separation distance between propellers, their vertical height from the ground, and the like without having to manually manipulate the overall shape. That’s because while this was being drawn, we were still taking dummy measurements of what the idea seating position would be if you were to precisely place your head between two screaming 24″ propellers.

Hey, engineers just design stuff. We don’t care if it’s a good or bad or horrible idea.

After settling dimensions, I filled the propeller disc back in with a rudimentary grille/guard to ward off most of the death and dismemberment. The smiley face is purely because I said so.

The extent of the design is shown here. After the back plate, it was a relatively simple job of adding two longitudinal beams and two bulkheads in the middle. You sit in the middle section, legs in the forward section , and the battery pack would hang out behind you. Shown on the far side of the device (on the right of the picture) is an anchor for a cut-up bike handlebar, upon which throttle handles were going to be mounted. Speed holes were added because, well, speed.

All I wanted was the 2D profiles of the parts, for it was time to…

…Get routing. The material is 3/4″ birch plywood out of a shop material leftovers pile. The researchers & students who come through here regularly forget leave materials behind, and over time they get consumed by other students and researchers. It’s the world’s most inedible, artificial food chain! Statistically speaking, it was going to become either something like this, or a potentially metaphoric but abstract piece of public art eventually.

But perhaps this, too, is art.

On a CNC router or mill, with a very finite cutter diameter, corner knockouts are necessary to let the tabs and slots fit. Usually, if I’m waterjet cutting a piece, I don’t bother with knocking out the corners because the nozzle diameter is so small.

Sheet one of two with 90% of the parts by area is done.

To cut the material cleanly in one pass, I used a 1-flute “compression” cutter – Onsrud #60-111, a staple for users of this machine. It cuts downward on the top surface, so there is no tearing of the top veneer, and upwards on the lower surface.

While this was occurring, the electrical team was hard at work putting together the relatively simple electronics, but it was a task that required lots of frosh work swapping connectors:

The motor controller of choice was the Turnigy dLux 160A HV,  featured in a handful of projects (including BurnoutChibi) in the MIT-centered electric vehicle building cloud. It’s got a reasonable build quality and features for the size and price. I wouldn’t trust it to 160 amps in a ground vehicle appl… wait, let me rephrase that: in a traction-propelled vehicle application.

For once, we are actually using these damn things to run propellers.

Here it is, the venerable C80-type Melon outrunner motor. These days, they’re getting increasingly hard to find – Adam custom ordered a run  of these from one of the original OEMs – and certainly cost more than $110 now. One place you can still get them is Alien Power Systems.

In the process of tearing all the cut parts out…

Streaming assembly as I pulled parts off the router.

More people came upstairs to help pitch in. By about 1:30AM, the structure’s almost done.

Smashing the bottom skin on was an ordeal that involve a lot of clamps and people keeping their weight on things. The material is high density polyethylene (HDPE). Here, the bottom plate has already been attached and is now being cut to size.

The plastic was cold-bent, so the last few screws on the curved front were a little heartstopping to install. Afterwards, we waved heat guns over the bend area to try and thermally relieve the stress.

After main assembly finished, a moment of zen by muffin.

The vertical handle sticks seen are halves of a bike handlebar. On their ends will be mounted e-bike twist throttles.

Drill contortioning was required to fasten the propeller shroud, which is pretty much the only good idea on this whole build.

Props and motors are mounted! Time to start wiring things up.

You know that generic union labor joke that goes something like “One guy does the work and 3 others watch him”? MITERS works like that too!

Control electronics consisted of two servo testers, one connected up to each hand throttle. The servo testers’ knobs are potentiometers being read as voltage dividers, so it was actually very simple to swap in the voltage output of the active Hall Effect sensor throttles.  The output of the servo testers are pushed to the ESCs immediately.

The ESCs themselves are zip tied to an arm of the propeller grille to receive active cooling airflow. Winter is literally the best possible time to run these things!

The one and only “beauty shot”, for tenuous definitions of beauty, taken at around 4:30AM. The seat cushion is a chunk of found insulation foam.

Not pictured here are the batteries, which was a small (small in airquotes) 10Ah, 10S (37v 10Ah) lithium polymer battery from my Nuclear Arsenal. It was later swapped to a bigger 12S lithium iron phosphate electric car battery module, at 16Ah, for increased run time.

And of course, it’s video time. This is test run #1, occurring around 4:30AM…

Fact #1: Nobody can steer the damn thing.

Fact #2: The right side motor controller was actually a 120A model – but it had the same casing and the only difference was the numbers “120″ in place of “160″. Whoops, must have grabbed this one by mistake. It died not long after the last shot of the video, and testing ended for the night.

We decided to fall over in the shop on whatever vaguely soft and warm surfaces there were, and replace the controller in a couple of hours. By Tuesday afternoon, most of Boston had cracked 2 feet of snowfall. Almost all of the side streets were impassable due to large main streets like Massachusetts Ave. getting plowing priority, so it was very smooth and graded over!

The toasted controller was replaced with equivalent 160A model, and more hilarity ensued.

Fact #3: Still nobody can steer the damn thing. But everyone is getting steadily better at it! A set of skis bolted to the bottom, or even two or more rails of the same plastic, would have helped for sure.

Testing stopped after the evening hours when traffic picked up due to people emerging from their hiding places, and we were running down the batteries again.

And thus ends the story of Meloncraft. Currently sitting intact in an area of the shop that I cannot keep it in for long, it will likely have the valuable parts dismantled and the wooden body posted to the free stuff mailing list for future young endeavoring powersledders. And because nobody could agree on a better name than meloncraft, I’m just going to declare that it be called Meloncraft.

Meloncraft’s Basic Stats

  • Weight: About 60 pounds empty, with battery
  • Thrust: 50+lb static (based on estimation)
  • Top Speed: …
  • Power: ~8000 W peak (based on estimation of how much the motors draw in similar applications)
  • Two 80-100 type brushless motors
  • Two 160 amp model aircraft controllers
  • 24″ x 12″ wooden propellers
  • 38.4v 16Ah battery pack
  • Two electric bike Hall Effect throttle handles
  • Two R/C servo tester boxes
  • A few feet of doubled up 12 gauge wiring
  • 3/4″ birch plywood and 1/8″ HDPE frame