Sadbot and Overhaul Go To Comicpalooza: Scale Model Testing Your BattleBots At Full Scale

Just because all this van stuff was going on doesn’t mean I put down the robots last year. Never a dull moment around these parts! Interspersed between the Operation IDIocracy work over the summer and the Econocrane Saga was a heavyweight sportsman-style event held at the Comicpalooza event in Houston, Texas, by the local organization Houston Area Combat Robotics.

Robots in mid-July in Houston sounds like a great way to get heat stroke, but it was a chance to do some shakedowns and validation on Overhaul that we didn’t really get to do at the 2021 BattleBots season. When you’re at the event itself, you’re really just in survival mode; whatever works works, don’t question it. Getting to run the bot at a low-stress show-off event means I can kinda retrace my steps and figure out exactly what was going on.

Anybody who watched the 2021 season probably saw that Overhaul had some… fire issues. I joked it was probably the 2nd most reliable flamethrower at the competition: It would always catch on fire somewhere around 2:15 to 2:30, plus or minus. Midway through the qualifying fights, I threw in the towel and switched the drive controllers from my 12-FET Brushless Rages to …


Disgraceful. Why not just go stick my head in the jaws and hit the go-stick at this rate?

The controller I’d worked for not too long and not very hard on… was just not capable of sustaining heavyweight-tier power reliably. The reasons were many, but centered around the fact that the old SimonK firmware, while dumb-of-ass enough to whip start any motor you want it to, was consequently also dumb enough that it never had any facilities for current control or limiting built in. So while they could overpower smaller motors, using them on anything bigger than, say, a 60mm series outrunner was asking for trouble if the motor stalled or there was a lot of reversing. A current-generation VESC frontend would easily handle the 12 FETs properly and cap the motor at whatever current you set it to.

I dish on VESC a lot for being another wayward open-source project turned product that requires a worldwide community of people shotgunning into the dark to support, much like 3D printers were last decade. But the truth is I basically watched the VESC project grow up and its proprietor Benjamin Vedder become a self-taught motor control engineer. He worked a lot with my buddy Shane who featured abundantly on this very site in yesteryears. I have only the highest respect for his work in development of the VESC bloodline, which started as a personal hobby project much like I never meant to sell Ragebridges.

Exclusive, never-publicly-shown photo of the Even Bigger Brushless Rage I made for Overhaul in 2021. These boards never made it off the bench because I lost motivation.

The thing that always bugged me, though, is the productizing of the hobby and community. A firmware version change might introduce new features but create new bugs and break old features. Dozens of different manufacturers stray from the project definition and controlled documents to implement their own features, some of which make it back upstream into one of said firmware updates but leave others in the lurch. Software UIs which change with every other version, and so on.

And there is, of course, no fixed documentation because it’s always out of date; the best way to get help is simply to wade through dozens or hundreds of forum posts and social media threads (just try setting up a new VESC using a Youtube video from 2017!). Because I always had my somewhat working controllers, I simply never looked in the VESC direction, and only observed the hand wringing coming from others in the community trying to blaze these new trails in the world of robot fighting.

But whatever the case, it was time to acknowledge that the combined autism of dozens of Europeans and hundreds of Chinese people was far more a force for progress than I could ever be alone. Just like how I’ll probably never build another custom hub motor unless it was purely for, uhh, self-enjoyment.

I did pick up two VESC 6 architecture based Trampa ESCs, confusingly called the “VESC 6 MK V”, right before the 2021 season because I had a SNEAKING FEELING they would be needed. And those were the ESCs which got stuffed into Overhaul. Because the C80/100 motors in Overhaul did not have Hall sensors, I had to fiddle the settings to use sensorless mode.

At the time, the sensorless FOC algorithm was pretty flaky and not great with transient loads,but worked fine for its intended purpose of skateboards, bikes, and hoverboard motor. So, I kept it on sensorless BLDC / block commutation mode, with input shaping like ramp-up times activated and the current control loop gains cranked way too high (a necessity at the time; many of these issues have been resolved in the Present Year)

This made the bot driveable but not superb, and I would have to constantly ‘drive the controller’ so to speak, instead of focusing on the bot itself. If Overhaul looked pretty slippery in the Black Dragon fight and the “Chair Fight” with Big Dill, that was why. I signed up for the event because I figured more stick time is a bare minimum even if I make no other meaningful progress on making the bot drive better.

But there was Sadbot too.

Two heavyweight platforms with allegedly identical powertrains I could use to make delta comparisons, and maybe even fight them against each other! Sadbot was in dire need of a renovation anyways, so I took this as an excuse to organize the piles of stuff that had accumulated on top of it and start appraising what needed a lube n’ tune.

I had bought two VESC 4.12 clones from Hobbyking a while back when I first felt like Brushless Rage needed to be phased out. I supplemented these with a few used units I picked up from someone who was upgrading. These 4.12s are roughly as capable as 6-fet Brushless Rage; they’re going to be underpowered driving a 80mm motor each, but the nice thing is they won’t blow up doing so.

The goal here wasn’t try to run Overhaul on these 4.1x units, but that I didn’t want to spend several hundred dollars on a set of 6.0 based ones for Sadbot yet. If these survive the C80/100 drive motors, so much the better.

Sadbot itself had gathered a whole lot of dust, cobwebs, and metal chips in random spots. Its last action was really Robot Ruckus in 2019, and it’s been pushed around the garage since then. I decided a comprehensive teardown and rebuild of the electrical deck and both Overhaul 1 wheel pods was warranted. So, I just dug in and started ripping everything out…

One increment I wanted to make from Overhaul was using the sensor-integrated C80/100 motors, since much of the development effort seems to have focused on perfecting the Field Oriented Control (FOC) algorithm assuming you have Hall sensors or an encoder.

Fair enough – sensorless starting has a lot more math involved in it, needing bigger and faster microcontrollers, and often requires close-in tuning of inductance, flux linkage, etc. quantities on individual motors. This makes it much harder to get right for a general purpose plug-in controller (In the Present Time, High Frequency Injection [HFI] based pole saliency detection has made its way into VESCs with the latest hardware rev)

The spare motors I picked up for Overhaul before the 2021 season did have Hall sensors, so I went ahead and knocked them apart to switch out the custom-made shafts of the older motors.

The drive pods got cleaned up on all fronts with new chains and lube and new threadlocker in the bolt holes. There were a lot of things which were getting loose and jiggly!

I also took apart the lifter pod to take a look at it all, but it did not need any work. Here’s the reassembled drive pods! They’ll go in last since they’ll make it harder to work on the electrical bay. I’ll finish that first by remaking the wiring to accommodate the VESCs.

Oh yeah! I picked up another Harbor Freight rock chisel thing to make a spare poker. The original Long Pink Member from 2019 was straightened out some, but I figured it wouldn’t live very long if it was bent back and forth more..

Most people using VESCs just throw them in with a bunch of foam wrapped in heat shrink or tape. This approach doesn’t sit right with me (Yes, yes, I know, their robots work and mine doesn’t) and I wanted to try and give them more heat sinking. They’ll be operating close to maximum power handling levels for longer periods of time, driving those C80/100 motors. The obvious problem is that the 4.1x VESCs don’t have a good way to mount to anything because they were kind of designed with being stuffed into a wiring harness in mind.

I came up with a clamping aluminum bar mount that will grab them by the FETussy. The back of the board, with the capacitors, will be secured by a zip tie mount.

The aluminum bar gets bolted into the existing big heat sink plate with a dollop of thermal compound in between.

Here’s how that looks! #4-40 long screws capture the VESCs in between them. The FETs get silicone sheet on the top and bottom for insulation. Heat transfer out of the plastic case on these D2PAK-7 packages isn’t great, which is why Brushless Rage and other controllers have always heat sunk through via-forests in a heavy-copper PCB. But it’s better than nothing.

With the mounting solution validated, I went ahead and worked on the heavy power wiring – extending motor wires, making new battery cables, and so on.

My automotive influence is showing here with all the wire loom. The sensor cables and motor phase leads were run separately to keep the motor current from beating the little Hall sensors …. uhh, senseless.

If needed, I was ready to put them in some conductive loom and ground the ends. Luckily, this turned out not to be needed – just keeping them from running next to each other was enough.

For someone whose entire line of work for over a decade and a half is “technology”, I sure hate technology. Specifically, I’m not personally so much a fan of “just configure it in the app”. Yes, you get much more flexibility and room for features if you have an app. But give me a row of DIP switches, blinkenlichten, and trimmer potentiometers any day.

The cool kids set up their VESCs with their phones because you can get them with Bluetooth now. I, meanwhile, could only find 1 short USB cable to do this with, necessitating this comical and totally safe setup. Sadbot, propped up on one half of a moving dolly, with my computer directly in the line of “Welp it hit the ground and kept going”.

The electrical deck is now all buttoned up with everything operational. The drivetrain controllers are set up in BLDC mode using Hall sensors, but the lifter was kept BLDC sensorless because the 6374 motor running it didn’t have them, and it’s geared down so far it didn’t matter.

I didn’t set the drivetrain controllers up in FOC because for one reason or another, I couldn’t get the FOC auto-detection to take. This may be one of those mismatched firmware, hardware, and software 3-way tangles I alluded to earlier. Dumb ol’ BLDC mode worked flawlessly, however.

Up front, I added something Sadbot has never had up to this point and just got away with: A weapon lock!

Yep, it was finally time. A simple 3/4″ hole drilled in 1/4″ thick steel strips will suffice for putting a bigass square lynch pin through.

Weapon lock all welded up in-place.

While Limewelder was warm, I went ahead and welded the poker solid where the striker interfaces with the tube, just like the old one.

With everything installed and tightened again, Sadbot came in at 220 pounds even! This is the weight of a “classic” heavyweight and what I had in mind when originally designing it in 2015 – the thought was maybe I’d head to Robogames which at the time was still running the 220 pound Heavyweight class. The ample weight allows me a lot of room to mod and add things if I wanted to run at 250 pounds.

Here’s the final hero shot of Sadbot, with weapon lock installed. And a low speed drive video!

I tried to not annihilate everything I owned, but did rip it a little harder in the driveway too. The sensored BLDC setup with the innate current-control loop drove great – I could feel the current limited acceleration, but for the most part it handled predictably. A sharp stop (like running into the curb) could trigger an overcurrent condition which needed me to back off the stick and try again. So I had to be mindful of this, but it only happened periodically. I wrote it off to “50A-ish rated controller trying to wag a motor which could easily drink 200 or more amps”.

The Road to Houston

Houston is about a 12 hour drive from Atlanta; while long, it’s certainly nothing I haven’t done many times before with my Boston to Atlanta (18 hour+) runs. For this trip, I chose the competent van because you should only live one meme at a time. This is also why I have never driven cross-country to BattleBots with a meme van: Don’t put your childhood dreams in series or you’ll cry over their shattered remains on the side of the interstate somewhere in New Texahoma. Live them in parallel with impedance matching.

Loading the robots in turned out to be very easy because I already had my equipment for hoisting heavy things around. Just chain them up and sling them in!

Overhaul was basically pulled out of the crate as-is, where-is, no warranty expressed or implied, no questions asked or answered. To be fair, it did leave the 2021 season ready to run because we were supposed to have another fight.

With all the equipment tossed in after it including handling carts, the Overhaul team tool chest, and spare parts, the reasons why I decided to maximize my automotive Asian Dad Energy for a daily consumable car are abundantly clear.

You can barely do this with a mid-size pickup truck (at least I’d need a bed cap) and the tailgate would be already up to my nostrils. One of my favorite activities is just slinging lumber and 4×8 construction panels into this thing at the Home Depot pro parking shack while dudebros hoist things into the 5’5 beds of their emotional support pickup trucks next to me.

The trip down I-10 was terminally uneventful. By the way, if you’re looking for some lizards, hit these people up! It’s been a very long time since I went to Houston – the last time I recall going was to see family friends when I was a wee caterpillar.

I chose I-10 instead of the more inland I-20 (then cutting south after the Texas border past Shreveport) because E A S Y. I got to see the swampworks of America including the Atchawichyaiwannalaya Basin Bridge among others, and traversing the lights and sights of the Houston energy corridor in southeast Texas was also entertaining.

I left Atlanta around 6AM and cruised into my hotel east of Houston around 10PM, managing to not bomb it the entire way but stop to check out some roadside knick-knack stores.

Next morning at load-in, setting Overhaul and friends up for the visiting crowd! A couple of bots were on display, such as Avalanche from Team Toad behind Overhaul there. It was also competing, so I suppose these were just demo models…

The event being one of only a tiny handful of Heavyweight-scale anything out there meant BattleBots Season 7 prospectives from all over the country also showed up. This is an early prototype version of Horizon, which was being bung together (photo captured mid-swing of the hammer) right up to the safety meeting.

Bunny of Malice set up the merch booth, which we all contributed to in order to satisfy the throngs of onlookers once the con opened.

Besides Overhaul and Sadbot, I also brought a con tchotchke in the form Your Waifu is Trash. This stupid thing has probably seen the most physical miles driven of any actual robot I’ve built, having been to almost every convention I have since 2019. I’ve worn through the brushes on at least one motor and changed wheels because they got too small and worn down from driving on concrete/asphalt.

It’s been a hit everywhere it’s gone, because giving people an avenue to depersonalize their insecurities and self-doubt has never been a flawed business model. I drove YWIT around in between fights, when we took breaks, and when the matches were done for the day.

Pit table shot! I kept Sadbot on the handtruck because it conveniently fit between the drive wheels and allowed access to it in all directions.

One other item I “invested” in before this event was a new charger for Overhaul. I wanted the ability to charge up to 12S lithium in a single bloc, as up to that point, Overhaul’s charger has been a set of 8S-limited Turnigy Reaktors. The battery enclosure had no internal wiring and just ran both battery leads out so I could plug both in. At home or if I didn’t give a shit, I just set my adjustable bench power supply to CC at 15 amps and CV at 49.2 volts (give it a bit of safety margin) and went about my day.

This iCharger X12 came to the rescue! It’s a current-generation charger that takes up to 48V in and can consequently poop up to and over 48 volts, handling over 1000 watts with an ability to regeneratively discharge into a master battery bank. The package is scary small for handling that much power, but I believe in modern semiconductors. In fact, it can overwhelm my puny 24 volt power supply instantaneously, so it’s time to upgrade!

Sadbot had an easy and fun time because of the non-spinner nature of the arena, which effectively dated back to the mid ’00s as one of the original Southeast Combat Robotics (SECR) boxes. One of my fights was with Slammo, who was also here to test out some new architectures and drive setups. This match was fun and tossy until Slammo quit working again, as for some reason it does.

Sadbot also had other fights against some more sumo/sportsman’y heavyweights from locals, and a Mild Salsa version of Mad Catter cheekily named Happy Catter.

At last, the meme happened as one of the final exhibition fights. I drove Overhaul while Bunny drove Sadbot. I literally bought a chair from Team Toad for $10 on the spot to use in this fight, where we set it up and I tried to drop Sadbot on it.

The handling difference between the two really motivated me to swap Overhaul to all new sensor-integrated C80s. Sadbot basically drove like it was brushed again, even if the VESCs still had infrequent (but still annoying) overcurrent faults just because of how outclassed they were by the motors. A swift return-stick-to-neutral was enough to overcome that. Overhaul, being still stuck in Sensorless BLDC mode with some tweaking, drove like an unloaded bus on ice in comparison. I had to anticipate when to turn and basically coast into it, or keep moving in one direction without direction changes.

Overhaul’s forks managed to tear up the drive on Sadbot pretty well, including bending both of the little chain-guiding nuggets and making Sadbot lose a drive side. In return, I accidentally drove the head actuator off the end of the screw trying to pick the chair back up, so Overhaul’s head came flopping downwards. Oops.

Unfortunately, the organizers had issues with the stream (found after the fact; they were thinnly manned and needed all the help they could get!) and as a result we don’t really have any good video from the event, especially the Heavyweight fights. They posted basically “raw” box feed videos at this link.

Sadbot appears in the following fights:

There are videos of the beetleweights and other weight classes on the promoter’s Youtube channel, though. Those were run in a separate arena and as a separate stream.

So I came away from Comicpalooza with a lot of good lessons learned and two working robots. Well how about that!? The real champion, though, we all know… is Your Waifu is Trash.

The lessons from this event went straight into Overhaul when I transitioned from Operation IDIocracy to Battlebots Season 7 prep. We changed all the drive motors – in-use and spares – to the sensored C80/100s, and I ordered spares of those.

I also got more VESC6 units from Trampa and set them all up in FOC mode with sensors, using one calibration/detection and propogating all the settings (The motors are all close enough together characteristics-wise that the small differences were not first-order impacts on control loop behavior). Other than that, the bot didn’t see that many changes and optimizations for Season 7. And, despite “Losing” a bunch again, I think Overhaul really had its best reliability and predictability season to date.

By the way, if the trip to Comicpalooza was comically loaded, the return trip was even funnier. I promised to bring Slammo back for Craig, so on top of all my gear, there was now a Slammo, its parts, its tools, and its handling equipment. He journeyed down from North Carolina a week or so later to collect it all.

I was surely running close to GVWR, and I got concerned enough to inflate the rear tires to 50 PSI for the return trip. I headed northwards out of Houston, taking the I-20 route back east because it turns out I-10 is just like the I-95 of the Gulf Coast: Always crowded, always jammed, always under construction, and everyone is out to kill you all of the time.

How Haven’t I Built One of These Yet? The Tale of Melonbike

Little do people know that back in mid-2019, I put together an e-bike to take some miles off Mikuvan when the Ol’ Vape Shop was still a few miles from my apartment (It’s now in Woburn, MA playing with all the other big companies!). This wasn’t a very publicized thing since it was purely utilitarian and consisted mostly of putting things in a box over a day or two, but I did take photos of the process. Hell, I didn’t even give it a smarmy name. It was always “the bike”. For the purposes of discussion, I’ll refer to it as the Untitled E-Bike.

It was an “F4WPEAK” 500W-class e-bike with a geared rear hub motor that I bought barely working. All I really did was swap out the integrated controller for a 350W Jasontroller hot-rodded to around 750W (yes… they’re still the same to this day), then put some used 12S drone batteries in a Pelican case (the stock 18650 brick was well past its prime). It did its job Just Fine™ and was nothing to really holler about.

When I moved, I did some mild upkeep on it including new tires and a quick lube n’ tune. It comes out regularly if I need to grab a thing or two from stores between a half to two or so miles away and don’t feel like booting up a van. It is truly the white 2016 rental-spec Dodge Grand Caravan of bikes.

You know what that means. I need the Spool Bus counterpart – something that’s abjectly ratted up and dirt-floor chop shop grade, and yet disturbingly practical. Melonscooter itself started this way with me basically appending things to a random (was it even motorized to begin with? I genuinely can’t remember) scooter frame but became my “daily driver” on campus for two and some years until it rusted in half.

Through this past decade, I have yet to put one of these C80-class “melon” motors on a bike. I’ve instructed probably dozens of people on how to, but I tended to stick with the scooters and go-karts. Yep, they’re still sold, now by more vendors than Hobbyking – for instance, Overhaul’s motors are from Alien Power and Flipsky. They’re still the “An Motor” of small DIY EVs. They offer you a solid 4-8 mechanical horsepower depending on how you feed them, and are extremely bare-bones otherwise. They’re not the best built things unless you do some aftermarket/homebrew bulletproofing. I’d liken them to the small-block Chevy V8s of random small EVs at this point. The proliferation of easy to use and robust ESCs for them (unlike 10 years ago) is probably like adding a FITech head unit onto your SBC.

Some time in June, 2022

Back in high school I used to make a somewhat regular habit of going to area flea markets (you know, before they all became shitty discount malls) usually hunting for tools and random R/C and electronic bits. At MITland there was no need for that, because I literally had access to more junk than I could possibly absorb. Then I worked at a company comprising several people who brought together all the junk they could possibly absorb. There was NO pressure to accumulate more junk.

I picked the habit back up recently, and I was stochastically wandering around at the Starlight when I saw this complete piece for sale:

I dunno what it was besides one of those chainsaw engine kit bikes, but the guy literally wanted 20 bucks for it. How could I say no to THAT? Just clearing out a side yard, apparently. Fine by me, in putting off rebuilding the 7.3 IDI in Snekvan for several months I was itching for a dumb fast-integration object anyway.

This thing has clearly sat in said yard for several years. The chain was practically rusted solid into an irregular abstract race track shape. Almost all of the socket-head hardware was corroded as well, and the tires… weren’t. It was missing a pedal, and most of the handlebar fittings as well.

At this point I haven’t gone “Full MITERS” in a very, very long time, so it was relaxing to start digging in.

I say “Chainsaw Bike” like these actually use chainsaw engines. They’re fairly specialized now and usually found between 50 and 100cc displacement, and all kinds of aftermarket accessories are available. They use a secondary drive chain that gets added to the spokes on the left hand side of the bike. While I’ve never owned and ridden one, a few had gone through MITERS when I was around.

Someone clearly had a sense of adventure and appended these studs to the fuel tank with blobs of Sugru.

The then-unnamed Melonbike was missing a lot of parts and needed even more replaced. I finally had an excuse to stop by the Bike Graveyard of Atlanta, the Sopo Bike Co-op. I heard about this place but had never Biked enough to stop by.

It’s a great place, and definitely gave me the full MITERS Bike Pile experience. From Sopo I picked up a new (used) handlebar, a use (used) shifter, some new (used) pedals, and assorted random hardware.

And so for a few days, I had An Bicycle.

I sincerely dislike the ergonomics of the cruiser-style handlebars so I got the mountain bike style straight bars. Apparently 6-speed shifters are extremely rare nowadays, so I just pressed a 7-speed into duty and have 2 gears on each end that are very…. ill-defined. I don’t give a damn.

Here’s where we go full BIG CHUCK’S GARAGE. The plan is to take an Overhaul spare drive motor, a C80/100-130kv, and mate it to a spare Chibi-Mikuvan 9 inch angle grinder drive gearbox. Yes, I still have those parts.

The CMV gearbox is 4.1:1, and it should play well with a roughly 2.5:1 chain reduction going to the rear wheel to give a ratio of about 10:1.

You might notice that at 12S (44V – more 46-47 during useful operation) and with those numbers, the top speed of this thing is something like 45 miles an hour. This is fine by me. I don’t care to gear for acceleration so much with a bike because you’ll just fall over backwards anyway, and current-gen ESCs can provide spot-on torque control.

It also has pedals, being a bike and all. Not accelerating fast enough? Well that’s your personal problem!

This is now where we start having fun. I had to somehow mount this CMV angle grinder head to the frame, which is made of a series of tubes with no right angles anywhere.

I began by making a “context model” of that part of the bike frame. This was made with calipers, tape measures, and eyeballs, so it’s far from perfect.

What it allowed me to do was pick up mounting and constraining features, such as the threaded inserts for what would be a water bottle cage or some kind of other lower accessory carrier. Besides that, I could test the viability of mounting to the bottom frame tube or the seat tube.

I’m growing a bracket now using the XY position of the gearbox axis, from its mounting nose all the way to contacting the seat tube.

The big plan here was to use the seat tube’s threaded inserts as two pin joints so I don’t need to rely all on clamping force to prevent the assembly from twisting.

Like so. The slots would allow me to adjust the final motor position up or down depending on what made more sense for the chain run.

The clamp elements for the seat tube are now being lab-grown.

With a little bit of optimization, here’s the main gearbox mounting clamp.

Pictured here is its companion clamp and a moped sprocket I found on Amazon after briefly surveying the space of shitty bike conversion kits. It’s a 22 tooth #415 plate sprocket that’s supposed to go on something that is not an angle grinder.

I bung out a prototype using a fast and dirty mostly-hollow PLA print. This was pretty much ONLY to get a visual on what to do next. I liked the positioning, so I went ahead and committed this part to the Markforged gods.

Next up was the hub for the sprocket. I was going to have to turn a plain steel plate bore into a D-flat bore for the angle grinder shaft, so this implied a small donut of steel to bridge the gap.

Using the angle grinder shaft to test fit the hub. The shaft doesn’t go all the way through – it gets stopped at a shoulder on the backside of the part which will be partially milled out to pass only the double-D flat portion.

Finished hub, test-fitted sprocket, and shaft all together for a family photo.

The reason I couldn’t just use the angle grinder nut to clamp the sprocket is for side to side clearance reasons. The shaft and sprocket would have poked out pretty far. The space constraint basically required using a flush-mounted hub.

I went ahead and cut the end of the angle grinder shaft off and threaded the end for a 5/16-18 retaining bolt.

The part was then set up on the Benchmaster, Master of Benches, and the D-profile milled out. I just used a 1/2″ endmill and went back and forth to expand the bore along the diameter of the D-shaft.

Finished sprocket and hub, ready to weld!

I finished off the retaining washer using the only 1″ diameter piece of steel I had: a chunk of keyed shaft. More awkward than it has to be, but I didn’t have another little steel bar handy.

The torque in this system is ESC-limited, and going through a larger diameter than usual, so I just put eight tack welds around the hub and called it good.

Here’s how the whole retainment setup looks. I was going to trade the hex-head bolt for a flat head one at some point in the future.

The next challenge is to convert the Chibi Mikuvan gearbox input shaft to one that would work with the C80. I made that 12mm shaft a hollow collet to be clamped onto an 8mm shaft but for this application it would need to join with another 12mm shaft directly.

I decided to machine off the split collet portion and extend the shaft with another solid region. I can then use a keyed coupler or something else that attaches to the extension. So the gear stump was first section off the input shaft…

…and then I took a random chunk of used C80 shaft, turned the concave alignment feature in it, and lined them up with some pressure from the tailstock. The big plan was to weld these two halves together as deep as I could (The chamfers on at the seam were made much deeper after this photo, by the way)

There is only 1 240V outlet in the garage, and Limewelder was stretched to the limit on both ends to try and get to Tinylathe.

It worked, though! I emitted steel in a few small increments and rotated the whole assembly by hand a few times to get full coverage.

After turning the region to clean it up, you can barely tell there was a seam here.

Except, you know, for the differently colored areas of metal…. from the likely different alloys used between the C80 shaft and the CMV shaft. I never took intro to metallurgy, see. The less you know…

The coupler is a 1″ aluminum round turned to the correct length, then bored out and keyed for 12mm shafts with a 3mm keyway.

It was going to be keyed only to accept the motor shaft. The “fixed end” as I called it, which was attached to the gear, was to receive a pin joint with a dowel pin. This involved setting things up on Benchmaster, Master of Benches. Then centering and drilling the indicated diameter through the whole thing, in order to use a 1/8″ dowel pin.

After the second attempt, here we are.

I missed the first shot.

By a lot, apparently.

This will be buried under aluminum. nobody will know the shame

Crosspin installed! This “fixed end” shaft is ready to reinstall.

The shaft has now been reunited with the gearbox. It’s a little wobbly because of the single bearing, but that’s why the motor shaft will be on the other side. The plan is to assemble the motor mount plate a little loosely, run the motor to let the system find its preferred barycenter, and then tighten everything down.

(If the grinder had a double bearing setup at the input, I’d just run a spider coupling or other flexible coupling, but alas, it does need the external support.)

With the gearbox assembly finished enough for a test fit, I was able to run the new #415 chain and get a feel for where to move the tensioner. The chain tensioner these kits come with is very rudimentary, and is just a wide flanged plastic roller. The bearings on this one are pretty disintegrated, so I’d need to remake it anyway. This was when I decided to get extra.

This is a Sprocket Churro. It’s a regular ol’ sprocket tooth model that has had the tooth profiles removed, such that only a small circular section remains at the root, and then scaled a little to match the size of the chain side plates. I could then extrude this profile out to make a wide tensioner roller that semi-actively engages the chain profile (and spins the tensioner roller) instead of dragging across it.

It’s a churro because I put an approximately 5 degree helical twist in it. Why? That tensioner bracket mounts to the rear frame tubes… which are not square with the chain. They’re about 5 or so degrees skewed with respect to the chain midplane.

So, with the angular twist, where the chain comes up from the drive sprocket and meets the roller is then going to be perpendicular with respect to the chain’s midplane.

Its sole purpose is to make me feel better – the OEM roller is completely smooth and the chain just drags across it and everyone was none the wiser.

This is the end result after trimming the Sprocket Churro stock and adding my own flanges. The inside pocket is for two regular 608 size skate bearings.

Here’s what the new modified tensioner roller looks in real life! It’s a little larger in diameter to sit lower on the bracket, and helps push the bracket forwards into undamaged metal (the previous owner(s) having somewhat crimped the section of frame tube it was mounted to before)

The motor mounting plate is another Chibi-Mikuvan spare. I made 5 of those for some reason, and this is the 2nd one being used. I had to open up the mounting holes to accept the C80 motor, and I also put in different mounting holes for the ESC…

…which is a Trampa VESC 6 that was stolen from the Overhaul crate.

Truth be told, this VESC 6 class is undersized for the motor, which can handle quite a lot more amps than it can put out on a continuous basis. Realistically, even for Overhaul, to leverage these C80 motors I need the Big Honkin’ VESC size.

That’s why I mentioned earlier that this design will be ESC-limited; even if it’s capable of ripping it to 45mph a lot quicker, the ESC won’t output the current to do so. It’ll be a smooth cruise to my untimely demise.

With the motor mounted, I noticed that the thing sticks out to the right-hand side a lot. The positioning was kind of forced by the chain alignment plane. It’s not as bad when you sit on it, but certainly something to think about.

Wiring this thing up was almost comically easy compared to Overhaul. I dug up a Hall-effect knob throttle from my stash of go-kart parts, which feeds into the multipurpose COMM port’s ADC pin. The motor Hall effect sensors needed an adapter cable to go from the JST-ZH standard R/C motor sensor cable (1.5mm pin pitch) to the JST-PH 2.0mm pitch connectors that VESC standardized on.

Initial commissioning time! I didn’t have any battery power wiring yet, so I did this on a big ol’ Soviet era lab power supply. It doesn’t need to draw a lot of current, just be of the right voltage.

The VESC commissioning is fairly straightforward nowadays with the “wizard” tools. I first used the FOC Wizard to perform the motor identification (resistance, flux linkage, indutances, etc.), and then set up the ADC port as the throttle. No changes were made to the motor tune besides upping the Min/Max motor currents all the way to 150 amps.

After digging up an XT-90 Y-harness cable from the discarded robot wiring pile, I was able to take Melonbike on its maiden voyage around the area. Overall impression? Suspiciously practical. The acceleration is brisk but gentle at the same time, as expected. Also, the old dry-rotted rim brakes do precisely N O T H I N G. To keep the thing pedaling-friendly, I disabled regenerative and idle (neutral) braking in the settings, so I don’t have regen to help this thing stop.

Having the two unused leftover batteries from Overhaul powering this was funny enough to start with, but bungee cords aren’t a long term mounting solution.

I decided to replicate the Pelican case battery enclosure that I made for the Untitled E-Bike. Except this thing doesn’t deserve a real Pelican. Straight to Harbor Freight I go! Also picked up one of the battery key switches to act as a more legitimate on-off solution.

The big key switch will be mounted on the bottom of the case (when it’s mounted in its final position) as a way to keep it weather resistant and casual idiot camouflaged.

I had a rear rack to clamp the case to again, so I freelanced some clamps out of 1/2″ bar stock aluminum. I drilled a cross hole that was the diameter of the wire which made up the rack structure, then bandsawed out the material to make two fingers. One finger is then drilled and threaded, and the other gets a clearance hole. I can then thread a screw in to clamp on whatever is in between. The case will be bolted into another drilled hole with tapped threads

Here’s the assembly in place. Because the rack structure is angled, wherever I drill the holes in the case is basically where it will end up since it can’t slide up and down. For now, I didn’t bother with a 3rd low-mounted block.

The internal wiring is fairly straigthforward. A set of 2×2 (series-paralllel) harnesses will join my four spare 6S 6.0Ah packs into a 12S, 12Ah configuration, which should provide quite a lot of range. I run a set of small cables from the pack to a charge port. Main power is derived from the other side of the battery switch, and all grounds get bolted together in one place and are continuous to each other.

I decided to make a tie rod clamp setup for the batteries. I actually made these two parts from Overhaul 2 remnants – a never-installed battery clamp plate for it and chunks cut out from the Anti-Chomp polycarbonate pauldrons that covered the drive chains.

The polycarb is more flexible than I’d like a clamp strap to be, and may be replaced with an aluminum bar in the future. It got the job done fine, however.

Here are the batteries installed and all the wiring run.

Putting everything in wire loom made it a pretty clean visual integration as well. The open connector on the battery case is for a charge cord.

And here it is, fully completed and posed in front of the derelict Citicars that I HAVE YET TO DO ANYTHING WITH BESIDES TAKE THE WHEELS OFF.

Again, disturbingly practical was an accomplished goal. This thing is quite tame at low speeds because of the controller minding the motor current – it accelerates faster than the Untitled E-Bike but not by that much, and is very pleasant.

However, hold the throttle down and the “Geared for 45 mph” very quickly reveals itself. After 6 to 7 seconds, you realize the old shitty rim brakes no longer have any effect on your speed.

The top speed I recorded on a lunch run to get tacos was 37 miles per hour. It still had more to give – I ran out of courage as well as clear roads with enough line of sight for an imminent collision to hurt slightly less.

Here’s the two of them together! Melonbike lived for about 3 weeks before I blew out the old machined taper lock on that Chibi-Mikuvan angle grinder gearbox, and then stole all of its batteries back for Overhaul. I’ll crack the gearbox open and weld that pinion on at some point.

(The yellow Citicar is in great original shape so it’s under a soft cover and a tarp. The white one marinated outside for 20 years and I will continue letting it marinate; should I get it operational, the moss and lichen paint job shall stay)