Return of the Kitmotter

Kitmotter, the concept that never quite was.

Originally, I built Kitmotter 0001 to be used on a little display stand in order to show the concept of laminated (coarsely-layered, anyway) rotors for potential hub motor or custom BLDC motor applications. The concept is a direct knock of the laminated hub motors of B.W.D Scooter which was the first to explore the idea of using waterjet-cut steel rings with magnet “indents” allowing for easy placement and waterjet-cut plastic (or metal) endcaps – basically allowing a brushless motor to be constructed without any intensive machining work. At least, it gets rid of the need for a large machine to turn the steel rotors that my designs all feature – I can make a whole post about all the random workarounds that we’ve tossed around for building whole motors. The same idea has been used on a few vehicles besides B.W.D – the Pneu Scooter and its close design relative picofahrrad, and a non-motor application, just to name some examples.

Kitmotter-on-a-stick lasted for several demo/exhibition type events until I took it to Singapore…


Poor Kitmotter.

The two little necks of 1/4″ acrylic just did not like a kilogram of motor hanging off it as it was bounced around my luggage. And with that, the base was retired and Kitmotter was relegated to a fairly simple life of “static item I would occasionally grab of the table to show people”.

That is until I dropped it one day.

With its main source of attention payments (from curious freshmen and ambitious motor builders) gone, Kitmotter was forced to live in the slums of my multistorey handcart of parts and stuff for many months (picture from before it suffered its unfortunate luggage incident)


Kitmotter could never afford to live in one of those new parts drawers.

As my cleanups and project purges were happening, so the slums were being cleared, demolished to make way for new expensive high-rise plastic sorty-bin developments. The first tenants of the new development were the fasteners, who pretty much lived on a level above the rest of the parts beforehand anyway (literally). Kitmotter was temporarily forced to stay with friends on another shelf in MITERS. The future seemed bleak for Kitmotter – forgotten, broken, and tossed away, an embodiment of ideas whose time had come to pass.

Until today, when I found 3 sheets of almost pristine 6mm acrylic in the laser cutter scraps pile at the Media Lab. Almost, meaning some UROP most likely took 1 part out of one of the corners then left the rest of the material hidden in the pile hoping nobody would find it because he’s too damned lazy to drag it back upstairs. I swear I haven’t done this before during my undergrad adventures, people.

Well, no name means no claim, so I quickly whipped up a new display case design while a job for the lab was processing:


Yes, white on white. I know.

This box gets rid of the mounting ‘stick’ as well as removing a very obvious pinch point in the original design. Instead the motor is first mounted to a reinforcing cross, then screwed to the case. There’s more acrylic to crack… not that it won’t be any harder, since acrylic. The case is also shorter than the first

Here’s the parts of the new box after cutting. I picked some scrap dark green acrylic to make the spacer rings from this time. The “KITMOTTER” is actually vector-etched into the top plate on a setting just fast enough to break the white plastic coating. Normally all of this is peeled off, but the separated letters remained white, making for a good contrast.

But before any exterior remodeling, I first went in and fixed one thing about Kitmotter that has been wrong since the beginning: THE SENSORS ARE IN THE WRONG SLOTS. Actually, even worse – they have been in the wrong slots for every motor I’ve built which has internal sensors.

I have previously put the Hall sensors into the slot between two teeth of the same phase i e.g. between A and a, or b and B. The rationale being that when a magnet transition (edge between N and S poles) happens, that set of teeth will “pull” the magnets above it into direct alignment.

I’m fairly certain this belief was just carried over from 2007-2008 when i was first learning How Moter, and then never validated or refuted. It took several very brain-twisting discussions and whiteboard sessions before I finally saw the fundamental error in judgement. I still can’t quite explain it in diagrams or short technical sentences – this post by Amy might be the closest thing. Bottom line is, the concept is true (magnets being pulled into alignment) but the magnitude of the movement required is 60 electrical degrees, and it is only possible if the Hall sensors are placed between two teeth of DIFFERENT phases (different “letters” in the conventional notation). It is still possible to find a ‘combination’ of sensor and phase connections which resulted in cyclic commutation, but the timing would always be too far advanced by 30 degrees (or too far retarded). Either way, not good, and it explained why 1. Kitmotter always sounded like a moped engine, and 2. why Tinytroller had issues with running it because it had no ability to compensate for sensor timing.

The fix involved just shifting the sensors over one slot. Because Kitmotter was never built to be actually used in a vehicle, I just heat-gunned the hot-glue-retained sensors and squished them down over another slot. I placed them between the ab, BC, and Ca teeth this time, like I was supposed to.

With its new green trim rings (for green energy and transportation!!!)*, I closed Kitmotter back up again, with fresh and unbent bolts too.

*shoots self

The new case completed. The large hole on the top plate is designed to clear the motor wires, and the motor itself is mounted only to the cross.

Replacing the motor controller was a straightforward deal since the wiring remained the same – another example of my project “case mods” this summer, I suppose. The controller is a sensored Jasontroller – this one I actually bought from Jason himself in Singapore last January. These are, unlike the eBay controllers, sensored-only.

I can already tell that the sensors are actually correct this time – Kitmotter no longer runs shittily in both directions! It’s much smoother, and the current draw is lower at 36 volts. Previously I was getting 4-5 amps of current draw, which I attributed to the bearings (huge and greased) dragging it down…all, you know, 160W of it. The no-load current has now decreased to only 1.3 amps at 36 volts, which makes way more sense. The minimum loaded motor speed before it starts ‘bouncing’ due to the timing error is also eliminated – switching too soon would cause the motor to jump back and forth as it doesn’t quite have enough torque to overcome the load before the phases switch again.

With this new discovery, I now trust sensored commutation a little more again. And all this time I thought it was just sensored being terrible.

Here’s a short video of the new home of Kitmotter 0001!

But wait, that’s not all.

son of kitmotter

Everyone wants their offspring to have a better life than they do, and Kitmotter is no different.

To fit a hub motor in a wheel, the wheel must not have a center. One of the issues that caused the project to stall out initially was the lack of a “ring tire” or definitive way of turning a stock wheel into one. We bounced all kinds of ideas around, such as wrapping urethane tread around the steel can like B.W.D (later attempted by Jedboard), but decided it was very troublesome and difficult to reproduce. The compromise idea seems to be Pneu Scooter’s “sidemotor” arrangement where the hub motor isn’t concentric exactly with the wheel, but offset from it in order to use its existing bearings.

It’s difficult to explain how some times solutions to problems seem to pop up with no warning in your head. I had originally thought of using a hole saw to clear out the center of a wheel a long time ago, but I quickly scrubbed the idea because how the hell are you going to keep it centered without a mill?

What I had forgotten back then was that hole saws generally have pilot drills in the center. I’m used to seeing hole saws being used in strange milling machine fixtures to make “fishmouth” joints for future welded tube frames. In this case, the pilot drill is not used.

It was during a conversation with Jamison about his latest sidemotor build that the thought of using a reduced-shank pilot to use the existing wheel bearings of a caster wheel as the centering mechanism suddenly dawned upon me. Now that I have hindsight, duh, it was so obvious. It doesn’t even need to be a drill bit – there’s nothing to drill. It literally can be a pin that is 1/4″ in diameter on one end, since most hole saw arbors take 1/4″ pilot drills.

Buying a 1/4″ reduced-shank drill on Mcmaster-Carr, though, was the quickest solution.

So here’s everything. Most of the skate and scooter wheels that I deal with have an 8mm bearing. 5/16″ is literally a hair smaller than 8mm – 0.3125 vs. 0.3149 (for normal hairs measuring about 0.0025″ diameter). It would be terrible if it were the other way around. You can reasonably use a 5/16″ rod as an 8mm axle – which is exactly the intention here. The drill bit would not have a very exciting existence during this operation, since it would just be spinning inside a bearing.

The inside “corable” diameter of the 125mm skate wheels I use (“YAK” type 12-spoke wheels) is about 3.25″ or 82.5mm. This is conveniently a size for which they make hole saws.

I replaced the pilot drill with the 5/16″ reduce-to-1/4″-shank drill bit. The alignment seems to be spot on here. Because the pilot drill needs to go past the wheel’s bottom, I elevated the whole thing on a piece of scrap wood. I clamped the edges of the wheel through to the workbench to stabilize it – a similar procedure will probably need to be done for drill press jobs. I’m actually not sure why I went for the hand drill this time – probably due to torque concerns from the ~1HP DeWalt drill versus a wimpy 1/3HP drill press motor, but the alignment and precise feed control could have made alot of difference.

Alot of positive feedback induced jamming later (note to self: drill press.), and  it worked!

After vacuuming out the swarf, the result is quite splendid indeed. The interior finish is clearly not as refined and clean-shaven as a lathe boring job, but who cares?

Basically, my assessment of this process is that one of the last missing pieces of a fully-accessible Kitmotter has been realized. I’m now really kicking myself for not having thought of this earlier. The major problems with Kitmotter were the lack of consistent stators (an issue that is solved by consistent copiers and laser printers), stator-to-bore adapter solutions (solved by 3d printable nylon hubs you can get from Shapeways or other 3DRP vendors), and… tires.

The same type of 12-spoke YAK wheels also comes in 100/110mm size which I’ve confirmed to be borable out to about 2.375 (2 3/8″, or 60mm). Guess what – they make hole saws for that size too. This can get exciting.

The hole saws actually appear to cut a little oversize. There’s two contributions to this (rather massive) overcut. First, the saws themselves are a little bigger than nominal dimension, and second, I could not hold this thing straight at all manually. It seems like a drill press is pretty much mandatory. Each time I twisted the saw, it would take a bigger bite out of one side. It tended to jam on the thin plastic spokes (a finer tooth saw would also mitigate this), so some times the twisting was fairly severe.

However, taking into account a straight cut, the diameter is probably going to be still 3.26″ to 3.27″ anyway – which is pretty much 83mm even. Sloppily using an Inch tool to make a metric dimension….

So, what’s the next step? I need to reduce Kitmotter 0001’s 3.5″ outer diameter down another 1/4″. This is much more difficult than it sounds, because the magnets need to come down in thickness (probably to 1/8″) and the can must get substantially thinner radially, and I could run into trouble with the case fastening screws. The screws will most likely need to be moved ‘external’ to the steel ring, sitting in circular grooves.

Alright, enough of this “future talk”, here is Kitmotter 0002, coming soon to a…nother demo stand? near you.

So what’s going on here?

  • The 7 #4 bolts have been turned into 14 #2 threaded studs. This diameter change was absolutely necessary to thin the can down down to 3.25″ – there was no other way.
  • The radial grooves seat the screws and secure the layered can, while the endcaps have fully enclosed holes to keep the studs on-dimension
  • The magnet thickness is 1/8″ instead of 1/4″, again to bring down the diameter. I’ll definitely lose a little torque from this.
  • The bigger endcap has a flange that is supposed to be used as a guide to drill into the wheel, in order to retain it. I might add more holes for more strength since the threads will be in soft gooey scooter plastic.
  • The axle is a stock 5/8″ keyed shaft of a 3″ stub length that McMaster sells directly. The hub to the stator is 3d printed. All other trimmings are left up to the user.

I’m going to build a prototype of Kitmotter 0002 in the next 2 weeks to validate this model, and I consider it right now to be prime Instructables fodder if it ends up working out. Essentially the last missing link in an “accessible” hub motor vehicle has been solved – where accessible means hypothetically buildable without access to heavy machinery like lathes and mills.

All Good (And Poorly-Maintained) Things Must Come To An End: The Great Project Purge of 2012

i swear to god i will fix this later

At some point, I need to stop telling myself that. It’s well known that my stuff isn’t exactly world-class in terms of reliability and Six Sigma class in quality, but even I can get sick enough of it to declare it a loss and start over. Over the past few months (and years) of neglect, quite a few of the robots and silly vehicles have become damaged and non-operational. I kept Swearing That I’ll Fix It Soon, Guys, but my shelf of stuff is long past overflowing with parts and project detritus and some of them contain good parts that I don’t want to keep buying. With my general shift of operations towards the newly opened IDC space just up the Z-axis from MITERS, tearing down some of the old derelicts and returning their parts to the Earth (/my storage bins) became more appealing – especially as I started collecting more stuff, most of it landing on my fresh new corner desk.

So it is with great sadness (and hidden catharsis) that I must announce the decomissioning of…

Cold Arbor

Cold Arbor never really worked – the frame was too flexible to accommodate the huge teeth of the saw. After Motorama 2010 and Dragon*Con’s Robot Battles ’10, CA pretty much only ventured off my shelf for the occasional demo – it illustrated, visually, what a “combat robot” was very well. Pretty much everyone’s first reaction at the word “Battlebot” is “You should put a saw on it to cut through the other robot!”, and CA is…. well, pretty much a saw. It never really stopped driving, but then the saw actuator broke so it couldn’t do the extending thing any more. Arbor, being the biggest lead weight I had on my shelf, was therefore the first to go.

But before I tore it totally down, I decided to use it still-functional and very smooth drive base as a test dummy.

Last year in the Austrailian robot fighting circle (did you know that Australia has a very active robot combat scene too?), one of the builders began to modify Hobbyking brushless controllers to act as H-bridges for DC drive motors, utilizing 2 of the 3 half-bridges available on the average BLDC controller. I’ve been advocating something like this for a while – use the cheap hardware base that is Chinese brushless motor controllers instead of custom-developing an expensive niche robot controller solution. The choices in robot controllers these days are either said niche and expensive but generally reliable controllers, or these one-tiny-FET-per-leg overfeatured doodads that I’ve literally had zero success rate with. Or you straight build your own and have them work, but I’ve also not successfully managed that yet. There’s nothing on the market right now which is just a bucket of large FETs like the old Victor 883s (which you can still buy, but they’re now a design so old it can almost drive).

That aside, I have also never bothered to schematic-trace the brushless ESC boards or learn & put up with enough raw Atmel C to reflash the microcontrollers (though I suppose I could have flashed Arduino onto them…). So, a ton of hot air rage on my end, but lots of action in the 40+page thread over on the Robowars forum, which has seen all of the cheap common ESCs reverse engineered and firmware implemented for – up to and including its own confusing beepy configuration menu.

They’ve now started selling them (when I say ‘they’, I really mean like one dude), and I took the chance to get some modified “85A” units based off this Hobbyking ESC.

First, I had to remove most of Arbor’s existing electronics. Okay, so my success rate with the Sabertooth controllers isn’t zero – Arbor runs two of the closely related SyRen controllers, but $75 for 25 amps is stupid these days, and I’m also royally undersizing their loads – one is running a little Speed 400 class motor and the other is running a drill type 550 motor which sees about a 10% duty cycle on raising and lowering the saw.

Way cleaner wiring and layout with the ESCheap85 in – I could easily see a robot with a whole rack of these next to eachother. The massive spam of SMT FETs technique used to great success by cheap Chinese controllers is an acceptable compromise, in  my opinion, between one-tiny-SMT-FET per leg used by the Sabertooth and Roboclaw and other most-likely-designed-by-newly-graduated-college-students controllers, and the one-huge-nice-FET approach I usually take. It keeps the board size down, too.

After hooking this up, Arbor was taken on several somewhat strenuous (and absurd) test drives.

None of it was very scientific, nor was there really enough space to seriously stress the bot out. I’m going to have to use these in battle myself before I’m fully sold on the idea, but based on the reports of the substantial number of Australian users, they’re pretty bulletproof, and a few American users have already run 18v DeWalt drills in drivetrains using them (the same motors that Clocker uses). The 85A type has been praised as a “Victor replacement”, but its more limited voltage range (30V fets and 35v capacitors) doesn’t quite convince me it can be swapped directly into a native 24v (up to 28v fully charged and more during dynamic braking) system. I fully agree with the concept, though, and for about $1 per amp I don’t have any complaints past my own reservations.

That doesn’t mean I’m no longer going to attempt my own controllers – I have yet to successfully execute a small current-controlled vehicle H-bridge, of which robot controller is a simpler subset. But that’s for another post.

At the end of it all, here’s Arbor mid-scrapping:

Scrapping is such a negative word. It took me a while to crack open that weapon drive gearbox, since I sealed it up so well at the start – and some of the bolts were bent.

Here’s everything I ended up keeping from Arbor. All of the motors, pretty much all of the drive mechanics (especially those delicious custom gearboxes, which were one of my first good ones), and of course the saw and worm drive in case I rebuild it all. The VictorHVs and Sabertooth controllers were also kept and filed in my robot controllers bin.

prospect for rebuilding: slim

Arbor was a very complicated robot with lots of moving parts – it’s something which is more difficult to get right, and it’s usually more disappointing (to watch as well as to operate) when it doesn’t work. Arbor’s build was rather rushed and many details weren’t completely thought out. I’m more likely to build a 30lb bot that is either more plainly functional or spend alot more time to build a complex but well-designed and tested robot before trying to compete with it.

Going down the line, next I pulled out…

nuclear kitten 5

NK5 was heavily damaged last Robot Battles, and ever since then has been sitting on the shelf. However, the disc motor still works great – and I can make spare discs, so that’s definitely being reused on something. The controllers and motors were also potential salvage items.

NK5 was the last robot I built before I converted fully over to “T-nut” style construction, visible in pretty much all my stuff from 2009 onwards. The design actually dates from late 2008 – my first major t-nutted endeavor was the ill-fated 2.007 robot. The frame has these wonderful corner bars that I machined for this application, but it seems like now you can buy everywhere. I really liked these, so I went ahead and saved them. Tapping into real metal is way better than t-nuts at any rate.

Here’s NK’s remnants pile. The frame materials were just not worth keeping, but I kept the motors – the gearboxes are not stripped, but one of the pinions fell off (but is intact). They might become donor parts for future gearboxes. I am a fan of these little 25mm metal gearboxen: while they are not planetary, they’re big and chunky inside to make up for it, and fairly cheap at $10-15 each.

prospect for rebuilding: hell yeah

I can’t guarantee when, but D*C 2012 is likely because I pretty much have everything-minus-frame. The disc is up for some revision, though. Big tall vertical disc spinners are no longer in vogue, being replaced by small, low bricky drum things with built-in motors (of which there are now like 50).

Next up is my pride and joy,

test bot 4.5 MCE

Really? The bot that made it to real-deal-Battlebots-IQ, then Motorama 2008 and back? The first thing I ever worked on at MITERS? Yep, since its default parking spot since Moto 2008 has been in Clocker’s lifter when it’s not doing other things.

TB certainly has the most grime of any of the bots, and the lifter was pretty much utterly trashed – it took a direct from the vertical disc bot Igoo at Motorama 2008 (that video is slightly painful to watch).

This is one of my first drill motor hacks. I did a few in 2006 for the original TB version 4, but they were either terrible or dismantled very quickly. This thing predates my entire website, pretty much. The extension shaft with the pinion was added when I redesigned the lifter for Moto 2008. It had an additional outboard support, but since it was made of UHMW, the whole gearbox still flexed too much to keep the gears in mesh, and so the pinion stripped very quickly in battle.

After I took the damaged arm parts off, I realized that TB’s drive base was actually in very good mechanical shape. I still love those gearboxes, too: they are super special 12:1 drill box hacks that I made with mating the salvaged 18 tooth planet gear and 9 tooth pinion gear of the first stage of a drill motor with an intact output stage. Coupled with the extremely overvolted 9.6v drill motors, this made the bot have a rather zippy top speed of 14mph. The first version of this gearbox predates the website (again) – this version at least had the luck of being milled, so things actually lined up!

I briefly entertained throwing the BotBitz ESCs in the frame just to drive it around again, but decided against it for the time being. It’s sure been a long time since I’ve had a 4WD drill-powered box.

So I closed it right back up again. Only the damaged arm and wedge parts were scrapped – otherwise, I think I can put something interesting in this bot again, or at least give it a better sendoff at a serious combat event later on, as the most honorable fate for a combat bot is still, in my opinion, being thoroughly vaporized into a cloud of small particles.

prospect for rebuilding: not for Robot Battles

TB4’s design was optimized for “arena” combat which has more guaranteed smooth floors and a more pressing need for huge, thick angled armor. The RB stage is purposefully left fallow to discourage pure wedges – a passive aggressive attempt at encouraging more robot creativity, which I contend has been successful in the past few years even though it kind of locks me out from competing in 12lbers again there with this design. Maybe Motorama 2013….

Finally, a project that I hate to see get tossed so early, but…

razer revolution

It’s lived a decadent life of being a demo attention whore as well as occasionally coming in handy when Melonscooter was on blocks, and has seen 4 different motor controllers (Double DEC’er, Melontroller, Tinytroller, and Jasontroller!), but recently RazEr Rev has become kind of a wreck.

I donated the front end to another MITERS scooter effort after the new battery got 2 dead cells after only a few weeks – definitely a case of bad initial conditions. Since then, it’s been sort of chilling in a corner, slowly being eroded away by the tides of cruft and dead power supplies that ebbs and floes around the shop.

The Jasontroller works great, the battery can be surgically corrected (I’m literally going to scalpel/X-acto knife the dead cells out and make it into a 10S pack), and the Dual Non-Interleaved Razermotor is a little rattly in the bearings but otherwise functional.

So that’s pretty much all I kept. Oh, and the extra heavy duty generation 2 Razor handlebar, after they moved away from welded-to-frame folding joint but before cost cutting made the joint like 24 gauge steel. This front hinge is massive – the steel is something like 0.13″ thick.

The reason I decided to scrap RREV now is because I’ve become dissatisfied with the frame design. It uses a design which I now consider inferior to other similar scooters in the way it’s put together. Starting over with the frame will be a great way to optimize the design towards less material use (like giant plates of 1/4″ aluminum) and make it simpler to assemble in addition to making dedicated space for the battery and Jasontroller, both of which were “aftermarket” additions. It should end up lighter for the same performance, but I don’t see it getting any smaller. Sorry Jamo, but Razor Wind is a little on the small side for my tastes now.

All this talk of what I’m gonna do means the

prospect for rebuilding: immediate

I already ordered some more giant aluminum plates (…sigh) and will probably be redesigning the frame this week. I’ve already got the changes planned out – they’ll just need execution. Like NK5, it will just be a matter of moving old parts over to a new chassis – there’s otherwise not much about RREV that I’m unhappy about. It’s definitely going to get a stock fender.

other stuff

I didn’t take any pictures, but all the Chuckranoplans have been parted out and recycled too. I’m probably not going to be touching this for a while until I stop being afraid of foam so I can build meaningful scale models. 3D printer models were fun for design practice, but are too heavy to work.

Alright, now that I’ve eaten half my offspring, I can start considering rebirthing them again!