Category: derpy vehicles

anything silly and rideable.

The Pre-Maker Faire Madness of Chibikart

chorl

Along with most of the rest of MITERS, I’ll be party vanning down to the New York Maker Faire on…. well, now. It’s this weekend.

Like last year, I’m hauling an immense pile of MITERS cargo in addition to a few hapless freshmen and sophmores (who I think count as cargo anyway?). Last time, I brought Landbearshark. This time, I’ll be bringing something about equal in mass but a little more fun: Double Chibis! Tagging along also because they fill space efficiently will be RazEr REV2 and Kitmotter Display Stand.

There go any chance of flying down the hillsides at the NY Hall of Science though.

The Chibikarts, unlike most of everything I build, have been working rather reliably. Chibikart 1 suffered 2 broken motors when MITERS used it for Orientation activities – I’m not really sure went on, but the front two motors were just totally unresponsibe – but the controllers were fine. However, Chibikart 1 still worked with the 2 rear motors, so that’s been its demo state for most of this month.

Last week I decided to crack them open in anticipation of repairs for the NYMF.

Well damn. It looks like my somewhat hastily-soldered phase star-point connections exploded. The solder joints became little balls of solder – indicative of a serious current overload or something. Either way, the damage to both of the motors was similar, so I just re-terminated them. I coated the windings in a thick layer of polyurethane varnish that the high-voltage crew at MITERS like to seal their Tesla Coil secondaries with.

A few days ago, Chibikart1 was involved in a…. “filming accident”.

While I was in the middle of the Poorly Coordinated Death Spiral, the right front motor lost power and started smelling real funny. Upon opening the motor again, I discovered that the windings were actually not burnt – but just shorted. As I unwound the stator,huge chunks of the magnet wire insulation were flaking off and coming apart. I was literally pulling lengths of bare wire from the stator.

My suspicion is that the urethane varnish damaged the insulation of the wire either by being too tenacious (typical cheap magnet wire with sub-300 celsius insulation rating are coated with polyurethane-based enamels) which caused the insulation to prefer the urethane coat instead of the wire, or the solvent was too strong and dissolved or damaged the insulation chemically.

Bottom line is, don’t seal your motor with urethane if it has wires made of urethane. On a similar note, titanium screws in titanium threads will degenerate into the slightly less useful case of a solid blob of titanium.

What was worse, actually, was that the urethane sealed the whole stator into a solid mass of wires. I could not hope to ever unwind this without baking or chemically destroying the urethane in some way. The magnet wire strands just broke off as I tried to pull on them.

I had to rewind both of the front motors, which didn’t take that long since I was used to it:

To give the wires one more layer of protection, this time I insulated the crossing strands with some Kapton layers.

Completed rewind. I decided to group the star point connections into one termination this time instead of attempting to solder a ring of wire around the outside of the windings. The whole mess was coated in epoxy (like I should have done to start with…), and Chibikart 1 is now kicking again.

Chibikart2/DPRC has received no mechanical mods or upgrades, but I did jump the shunt on the 350W Jasontrollers a bit to give it some more punch. Because of the ~25A constant current limit of the Jasontrollers, DPRC is actually a little anemic despite having higher potential power. To really use those motors, I’d need some sensor boards (hmm, I wonder where I could get some) and use higher-current Kelly controllers.

Come see Chibikart and DPRC (and RazEr & co.) at the MITERS display area in the Hackerspaces area (Zone B) at NYMF!

Oh yes, a preview of things to come:

 

RazEr REV2: Mostly there

chorl3 Comments

Over the past few days I’ve been mostly hanging out at the Georgia Tech Invention Studio. I was nominally there as “guest lecturer”, but I don’t quite think their own 2.00EV is organized yet to the point where I can feel comfortable with that title. All the ‘students’ are actually lab instructors (similar to our MITERS keyholders), so there wasn’t that much ‘teaching’ to do. I did hold some impromptu lecture-like things and generally advised people on their builds where needed (and fixed the waterjet?). Regardless, some… interesting products are coming out of it:


It’s literally twice as long as some of the other scooters.

I’m back now, and one of the first things on the agenda is getting the half-assembled repackage of RazEr up and running. I sort of left this in the middle of construction when I zipped off to Atlanta for the weekend. I had the frame ‘box’ assembled to test fits, but I pretty much had to take it apart again to actually install stuff. My direction was essentially assemble the major subassemblies first (make the fender, reinstall the motor, attach the front end) and then lob the electroncis back in as-is, since it worked fine before.

Here’s the fender in place with its leaf spring installed.The ‘sheet metal work’ was done on a vise, then fitted in place using just tightening screw pressure. 5052 aluminum bends very easily, especially in 1/16″ thickness, so I was literally just leaning on the part to get the bends I wanted. To do the large radius sweep at the top, I bent little by little in ‘facets’ which weren’t drastic enough to be seen as disrete (though you can kind of see it).

Now that I’m a little more comfortable with making sheet metal geometries compatible with other 3d solid parts, I might incorporate it into more builds in the future.

The fender is just mounted on a chunk of 1/4″ threaded rod. Nothing fancy at all this time – no spacers, even. The pressure of the leaf spring alone is enough to keep it in place reasonably.

More progress has been made on frame assembly, with the folding joint  reattached now. I traded the former front end for a new A3 type front that was part of the leftovers from my 2.00EV. It’s substantially less beat to shit and doesn’t wobble as much, and I swear it’s a little taller than the one I had before.

I had a left over new fork from building Straight RazEr (whose wreckage has since been donated to Kramniklabs) which I dug out for this build.

I forgot to take a picture of what’s going on with the 5″ colson wheel, but there is actually a type 1614 bearing bored into each stock Delrin bushing. The Colson comes with a 5/8″ bore bushing  that has a 30mm OD (which presses in to the 30mm bore of the wheel itself). I tried to find a > 30mm bearing that wasn’t of a ridiculous axle diameter so I could bore it into the wheel directly, but gave up and went the other direction instead.

A ‘stock check’ of bearings I had turned up some R8 type and 1614 type bearings. Both were 1 1/8″ outer diameter, which I could bore into the Delrin bushing, but I settled on the 1614 bearing since I easily located a stock 3/8″ bolt to serve as the axle pin.

The job itself was done on tinylathe, which is probably one of the handiest tools I’ve ever worked with.

Moving on to the electronics deck now, I put together the ‘switch panel’ which holds the charge and controller ports as well as the annoyingly bright blue LED endowed power switch. The idea is to have BAT and PWR jumped externally with a Deans ‘patch cable’ so I could jack in a flow-through measuremen device like a Wattmeter if needed. Else, the switch is to serve as the primary turn-on mechanism.

It’s better than the yank-the-battery-connector setup RazEr Rev has used since forever, but I’m wondering how long until this switch falls victim to no-precharge arcing damage like the very first switch arrangement.

The interesting part is on the back. Instead of connecting the switch’s built-in LED to ground directly, I threw a 100 ohm resistor on it. This should prevent the light from exploding right away, as it happens when you try running 12v rated switches on 36 volts… Otherwise, there are just a few select wire jumps which bridge the two Deans ports through the power switch. Note the back-to-back soldered Deans connectors on the right…

With the switch panel done, it’s time to load all the electronics back in. The same shell-less Jasontroller appears, bolted to the aluminum frame directly for some heat sinking. There’s a bit more space for batteries this time, since they can reach all the way under the folding joint, but unfortunately it isn’t enough to actually add more cells – just maybe some padding. If I wanted more battery energy about the only good option is moving to prismatic cells.

With everything wired back to the way it was, I shoved the 3d-printed front endcap on. This was one of those pieces made on the Lab Replicator™.

And the repackaged shot. Unfortunately I gave away my only other black Colson wheel, so it’s gray for now. When I get another one (or get it back), the bearings are transferrable.

This frame rides significantly lower than RazEr Rev – too low, actually. This is likely due to a difference in head tube length between the A3 I got like 5 years ago (for the original RazEr!) and now. RazEr Rev rode slightly ‘nose up’, but this one is definitely nose down. The clearance at the front is about 3/4″, decreasing to less than 1/2″ when I’m actually riding it and the rubber block is compressed.

Not going to work. I’ll compensate by making the two wheel fork sides a little longer. In the mean time, it is rideable, and handles just like it used to except with more stopping. And less exposed wires – check out the 3d printed wire guide at the lower right.