Tag: wheelmotor

Random project updates

chorl

I remember two weeks ago when I said that I would build nonstop through the break; anything I could think of, and come up with more things if I ran out. Anyways, that totally went to hell. But progress is slowly coming.

I’m in the process of completely redoing the Snuffles Reloaded wheelmotor. The previous one was okay for getting the concept to materialize into something solid, but was done across 3 different machines and with little regard (or ability) to center the workpiece properly.

There are also some design changes this time around. Most notably, I’m redoing the magnet can out of steel to better fit the very strong magnets that will be used, as well as to simplify things.

The finished product. This was the single most torturous piece I have done yet. Steel of this diameter needs to be turned reeeeeeeally slowly. I mean like 70RPM slowly. It was very hard for me to keep my feedrate down (because I’m used to small aluminum parts), and if I went too fast, I would just be cutting shallow screw threads.

Not to mention that it was a hot-roll steel pipe that I carved this out of, so the steel was total shit and was gummy. The surface finish is horrible, but it’ll live. The perimeter holes were put in on a CNC machine (most awesome thing evar, only matched in awesomenss by a 5-axis abrasivejet. The two combined can carve the laws of physics and grammar such that they can both be most awesome.)

I’ll do the aluminum parts later. I might possibly redesign some of the internals to make the parts less weird.

In TB4.5MCESP1-related news, the arm controller came.

Ooh, shiny. This is a Syren25 single-channel controller from Dimension Engineering. It’s a nice piece of work, and supposedly features regenerative braking. That’s hardcore. So having opponent bots backdrive TB4.5’s lifter could actually be a good thing, but they should do it slowly and gently!

Since I was going to remount the ESC on my own heatsink plate anyway, I decided to take a look at the underside where the driver chips are.

O GOD WAT

NO! NO NO NO NO…. For the love of Robot Jesus Michael Fizgerald Jackson Christ! SO-8 surface mount FETS?!

I am SO GLAD I’m mounting this thing on a plate of aluminum that weighs more than it does.

I hate those tiny SMT FETs. Especially when the manufacturer (generally of brushless controllers) use like 20 in parallel to get a decent amp rating. What money and weight do you save then?

It’s even worse when you listen to the chip maker who says a 25A part is a 25A part. The SMT has absolutely no thermal mass and no capacity to withstand momentary overload. In fighting bots, you NEED THE OVERHEAD. I’m sorry, I will NOT run 25 amps through this thing for any extended length of time, and am very glad the arm is an intermittent duty cycle.

I’m making my own ESCs from now on, or I’m never building another robot of any kind.

Oh, and the heat spreader plate doesn’t contact the driver chips. That’s even less of a 25A ESC. DE might want to consider backing off the pressure a bit on whatever press that is stamping the aluminum sheet.

Anyways, time to actually start building the bot. The carbide teeth on the miter saw’s new blade are slowly subliming, so it’s best to use them while they’re still fresh.

Snuffles Reloaded: Update 6

chorl1 Comment

It’s shiny. Really shiny.

After another day of furious metal shaving, the structure of the motor is mostly complete. Here are some in-process pics.

Motor side plates before length trimming. They were done step-by-step, one then the other, such that I had to move the asstastic tool holder as little as possible. In retrospect this was probably not the best option, since I did not have the luxury of a tailstock center, so the runout from rechucking a few times is probably obscene, but out of retrospect – oh well.

Test fitting a side plate before finishing the holes.

The internals.

Putting the stator together. No, that’s not the final winding. The wire coils are there to hold the individual laminations in-line while I pressed the whole thing onto the mount and while the epoxy hardened.

Threading the holes in the ring. Here’s Critical Design Flaw #1 (you knew it was coming somewhere!). The wall of the ring is too thin for anything other than, say, 2-56 screws. However, the waterjet made the holes bigger than 2-56 clearance-size. Oops. The next option was #3 screws, which are stupid and rarely used. Then #4, which was just on the edge of bursting through the walls of the ring. I risked it anyway, and things turned out okay.

Hey, the internal ferrous magnet ring. This was actually a rolled strip of 1/32″ steel. This is Critical Design Flaw #1.5, because in retrospect it would have been much better and more effective to make the whole ring from a piece of steel. I wouldn’t have to worry about the ring bursting out and implanting itself in my face, and the magnetic flux would have a better path to travel through. The bolt holes wouldn’t be so close to the edge, and the whole thing would be stiffer anyway.

The precarious seam that somehow holds everything together.

Test installation of the guts. Hey, it seems to be working out!

Actually, it doesn’t. The tolerances and machining imperfections disagree with eachother. Normally, this wouldn’t be that much of an issue, but inside the motor, the airgap between the stator and the magnets is tiny by design. Throw in a dubious lathe with no centers, repeated rechucking, transferring work between different machines, and my awesome skillz, and the magnets don’t fit in. A bit of sanding made things slide in, but it’s inconsistent over the course of one revolution.

There’s alot of improvements that could be made before I continue, such as redoing the can out of steel. Everything else seems to be fine – it rolls smoothly and there is indeed clearance for wiring and windings.

I could redo it, or I could hire it out to a machine shop to take my inconsistencies completely out of it. Although it’s fun to DIY, some times you just want things to work.

It’s finals season, so I have other priorities (like TB4.5-SP1!) to worry about before continuing on this. There’s nothing that prevents it from working conceptually, just manufacturing.

So that probably means SR is going to be on hold for a little while. But it’s still REALLY SHINY!