Build Day 45

Boy, it’s been a while since I made an update. But a lot has happened.

A lot of time was spent finishing the drive system. We finished machining down the wheel hubs, then stuck the hub and the axle in the milling machine to drill through them both. We then tapped one end of the hole for an 8-32 screw, and screwed them together. This is a nice, tight fit, better than you could get with a set screw. Then as for the motor shaft, we drilled a 6mm hole in the end of the shaft and stuck it back in the milling machine to mill for a set screw. Because the motor shaft has a flat, the set screw would work for this. Finally, I drilled in the other end of the shaft and tapped it for an 8-32 screw. This was my dad’s brilliant idea, and in retrospect, it really was a great idea. Basically, for dis-assembly, I can thread a screw into that hole and pull the shaft out. Otherwise, there’s no way I’d get it out.

So that was all assembled, and the bearing block plates were glued in place. In the end, we doubled them up for strength, and because of their relative position with the opening in the bottom of the foot.

I decided then was a good time to put R5 together, even with the shoulder hub positioning problem. So I ran wires to the motors, but not as a final assembly. I see now how difficult it’ll be to run the wires through the slots in the foot/ankle, so I’ll wait until final assembly. But I had those run, made up the jumpers to go from my receiver to the Pololu TReX Jr, and brought everything upstairs. I get it all together, hook up the electronics, and it works!! Almost. I hadn’t bothered to make the ankle lock pieces. Apparently, those are kinda important, because R5’s feet would flop around when he would roll.

So the next day, I made them. When I screwed them in place, I accounted for the thickness of the .04″ skins that would go in place, even though I haven’t dome anything with them yet. For now, I’m using simple shim pieces. So I get those in place, and this time he actually works!! R5 could drive around!! I was thrilled. I was only annoyed with the speed. He didn’t seem to be going as fast as he should have. One test with the meter, and I see the motors are only getting 8.5 volts at full power. I run a simple calibration of my TReX Jr, and now they run at full voltage. He will go a little faster than he does now, but that’s because my battery is weak.

I thought this was a pretty good milestone. I was satisfied with this. Of course, I don’t have the wheel for the dome motor yet. If I had that in place, that would be even better. Especially considering that the TRex Jr has a third motor output.

Okay, almost caught up here. So after all that, it was time to break R5 down to fix the shoulder hub problem. I got the body up, and had a surprise about the glue I used. It’s strong!! After trying to pry apart the body, I can appreciate just how well that glue works. But I got it apart.

After some careful-ish measuring/guesstimating, I found that I needed to shim the pieces .22″. This was achieved by gluing layers of thin scraps I had from cutting everything. So I glued in the wad of scraps, then glued the hub mounts back in place. I was not entirely sure about their parallel-ness, but I think it’ll be fine.

Now, I could move onto the body. I taped up the inner skins, which fit well now with the shoulder hubs. They were taped, then glued from the inside. Success! Then, I spent a day or so cleaning up the outer skins. From cutting out the pieces, the inside corners all ended up rounded because of the cutter I used and because of limitations of the software. I made them nice and square. I then glued them on. It looks fantastic!! I have some gaps at the seams, but that was to be expected. It will be fixed later on when I prep for paint. Then this morning, I began cleaning and gluing a couple of the inset panels.

That is where I am now. I have exactly a week until I go back to college, so progress will be slowing. It’s unavoidable, and I knew this when I jumped into this project. But all in all, this was a good way to spend my summer.

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