Category: Test Bot 4.5 SP1

Stronger, faster, harder, better….

TB4.5MCESP1 Update 8

chorl

I guess I’ll count the wheelmotor co-updates for TB4.5 also. With Motorama now only 3.5 weeks (!!!?) away, it’s time to get crankin’ on SP1.

Some revision work on the “EBays” was needed since I wasn’t going to use the Dimension Engineering ESC for drive any more. Unfortunately, that meant going back to the 883s or spending hectobucks on another controller solution (brewing in-house was another option, but I didn’t quite work up enough balls to do it. Plus the 883s have real transistors anyway). With some wrangling and wiggling of components, I was able to fit all the control electronics on one side – finally, a true electronics bay. The arm controller has to stand vertically, but that isn’t an issue. The other E-Bay contains the battery, power distribution, and master power switch.

The shovage of components on the left side is incredibly tight. Tight enough such that I tried using the wire and cable routing feature of Inventor to see if I can fit all the connections. It should be fine, but I’ll have to build it IRL anyway. Plenty of space for disaster!

Here are the frame rails cut out and positioned, with various components in place. I hadn’t “precision miter-sawed” in a long time, so it took a few practice cuts before I was able to get things within .005 on the first try again. Also, the saw fence seems to be losing some accuracy near the blade, as a few cuts were a bit warped. The gears were rather noisy.
Shortened lifespan. That’s what I get for royally abusing a tool (it’s launched its fair share of stock across the garage). I didn’t get a chance to repair stuff before I left for MITland again, though. It’ll be fine for 2x4s.

Frame rails marked out with calipers and sharpie. UHMW drills, threads, and generally machines very quickly, so I anticipate that this assembly will be done with half a day’s work. Problem: Getting all that Sharpie…errr, layout fluid… off the UHMW. It’s set for a few days, so rubbing alcohol doesn’t affect it any more. I’d use acetone, but the last time I did that, it left the sharpied areas with a pink hue.

So, either pink splotches or random-ass sharpie splotches… Hmm. I’ll figure something out. I could just color the whole bot black with sharpie and have one hell of a solvent trip in the process.

Tomorrow: Working on the arm gearbox, getting some of those components done. Order some aluminum plate, get on the waterjet and GIANT LAZER at the Media Lab and cut out the redesigned EBay plates and the top and bottom chassis covers.

Bot forth!

OMG LÉ WHEELMOTEUR

chorl

It’s done! Structurally, anyways. And it’s really shiny. Besides being shiny, it actually stands a chance of working.

…because I’m fairly certain it has the same center of rotation throughout. If it does not, the discrepancy is too small to see or feel. The outer holes will be countersunk when I can get a sample of a 4-40 flathead cap screw.

Outer plates of 6061 aluminum, can of steel.

The insides. Getting the stator onto the internal hub was a bit of an adventure, and it got a bit mangled in the process. If I were to do this again with appropriate funding, the stator will be a professionally made part. I bet that even if it works, the efficiency will be horrendous since the stator laminations are “insulated” with wood lacquer and made of hot rolled sheet steel, the stuff usually used for odd sculptures, not the cores of high performance electric motors.

With a wheel. The only thing that wobbles now is this wheel, which is most likely a quality issue. The wobble isn’t much at all – a hundredth or two at most. What sort of annoys me is that the tire profile is so tall, which means the motor has to have a relatively small diameter compared to the whole wheel. If I could go completely balls-out custom on this, the motor would be much larger and the tire custom-cast from urethane with a lower profile.

The downside to a lower profile tire is less shock absorbtion, which could impact motor lifetime. That’s a matter of IRL testing.

The magnets and magnet wire are still back in my dorm room, so I’ll finish this motor up when I return.

I also took the opportunity to trim down this gear for TB4.5’s arm geartrain. It will drive the rear link through a pin.

Since I’ll be back on campus on Wednesday, I’m going to order some materials that will have parts cut out of them with various large machines. Some half-inch aluminum for the arm and frame bits, some quater-inch aluminum sheet for the wedges, Garolite for the top and bottom plates, and polycarbonate for the internal EBay components.