Lara's Lego H-015 Sentry Droid

[kresty]

Considering battery issues, my Shorai aren't designed for deep cycle and don't have the Ah they'd advertised. We've used them in all the droids, so were limping along. (They are too easy to over-discharge, are only 7Ah @ 12V, and the chargers are iffy). So, I'm considering moving to Ryobi 18V as I already have tons of them. And it comes in a 9Ah, so that'd be about twice the Wh! (160ish vs 80ish).

The Pololu 18v7 motor controllers are 18v, so that should be OK. (L3-G0's are 24V, and he's run 24V before, so that should be OK if I move the droids to 18V). Side note: I was double checking that 18V batteries would be OK, since they're way higher than 18V when full. They'll be fine, but I noticed the prices changed. I got my last ones on sale which was maybe 1/2 off list at the time, and now they're 4x what I paid!

The Pololu 37D 30:1 motors, however, are 12V. They have a 24V version with comparable specs at 24V (at half the amps), but if I run them at 18V, the 30:1 will be slower than our current motor. We have plenty of torque now, so I can probably go for a lower gear ratio. Excessive torque may have even killed our couplers. The question is probably whether to go for the 19:1 or 10:1. I'm not quite sure how to do the math.

19:1 has 530RPM (no load) vs the current 330RPM. 10:1 has 1000RPM. But we'll be running below 24V and the speed seems to drop in about a linear fashion. Torque would drop from 14kg*cm to 8.5 or 4.9 - but we seem to have tons of excess torque right now.

I guess 75% of 530RPM would be about 400RPM, which is still faster than our current motors (and he already spins way too fast, though straight line isn't terrible.) 75% of 1000RPM would be 750, which seems pretty insane for our current use (we could always limit it though programmatically). The torque for the 10:1 would be a lot less at 3.8, and even 6.3 is a lot less than our currently spec'd 15. I guess I'm going to have to do math somehow.