Team 1425 Drivebase and Wiring

[Sparks333]

The drivebase was completed not too long ago (a wormscrew powered by two opposite small CIMs... very powerful) and this is Electrical's year to make the wiring neat... I don't think we did too badly.

Sparks

[Greg Needel]

The wiring looks very nice. I have a few questions about the worm gear transmissions.

Have you experienced any problems with motors fighting each other? in this configuration 1 motor is going forward and 1 is going in reverse. I know that it isn't as large as a concern as a few years ago with the drill motors but I am wondering if you have seen/ compensated for the effects?


Do using the worm gears provide any other benefits besides compact gearbox/motor placement? And how did your team weigh the benefits of them vs. the low torque transfer efficiency rating of worm transmissions. ( worm gears are typically 40-70% efficient vs spur gears of 95-98%)

[Jeffrafa]

We haven't gotten to run comprehensive driving tests to see just how well it performs - that'll be sometime this week after programming gets a little time with it. The gears are definitely more difficult to backdrive than a standard spur gear setup, although ours are quad thread worms - which really makes them halfway towards being helical gears (part of why they are still backdrivable).

As far as efficiency is concerned - after some research and calculations its not nearly as bad as you might think, although there are a lot of factors and variables that weigh in. By going with worm gears we are able to get our complete reduction in a single gearing, compared to typical spur gear setups that generally need a pair of gears to get into a reasonable speed range. Also the quad thread makes it significantly more efficient than a single or dual thread worm because you don't have as much sliding friction against the gear face, and the comparatively low reduction for a worm drive also helps. I ran some rough numbers and came out with ~86% efficiency for a setup like we've got. Considering a pair of 95% efficient spur gears would add together to equal about 90% efficient we aren't that far off from more standard solutions.

Also of note for comparison are the planetary CIM gearheads that came in the kit this year. In another thread Joe Johnson estimated them to be about 72% efficient ( 85% per stage ). So if we get anywhere near my calculated efficiency, we'll be at or above what a lot of teams are running this year.

As long as we keep them lubed well enough we shouldn't notice too significant of a loss to the worms. We'll have more real-world experience to report on this by the end of the week, however.

- Jeff

[Gabe]

What's that thing attached to the compressor? It looks like oil trap from an big shop compressor.

[Jeffrafa]

Originally Posted by Gabe

What's that thing attached to the compressor? It looks like oil trap from an big shop compressor.

I wondered if someone would ask about that ...

Its actually our compressor from our first year (recently deceased). The cylinder off the compressor is just an air filter that we had used for no particular reason (it used to go nicely with the processor heatsink we had zip-tied to the top of the compressor when it was overheating, before it was discovered that the pump was being back-driven.)

Mechanical still has this year's compressor boxed up somewhere, and I guess electrical had that one handy for sizing and picture purposes.

[Sparks333]

On the motors:
We've always ran paired motors... we find that it actually helps for redundancy in pushing competitions. If one gets its breaker blown, the entire side doesn't go. As for fighting, we get that question a lot, and the answer is always the same: with properly calibrated victors and a decent deadzone, there is little to no fighting, and we are almost always more than capable of pushing any robot all over the place. We stick with what works well for us.

Sparks