pic: Average 2014 Chassis

[Ian Curtis]

Originally Posted by Richard Wallace

We measured about 17 Amperes free current using the stock AM gears, and about 10 Amperes free current after replacing with VexPro gears. Gears were well greased for both tests, and the results were repeatable.

AM steel gears appear rougher, while VexPro 7075 gears have smoother finish. Also, VexPro gears are AGMA 11 -- closer tolerances, better fit.

The free current really tells the story, though. Lower friction, less power wasted.

Wow! That is a big difference. For those of us that don't know much about gears/wear-in/etc. would the AndyMark gears improve over time as the surface finish improves? I think I remember someone (971?) ran their gearboxes on a test stand prior to mounting them on their robot and found it wasn't really worth it. A 50% reduction in free current sounds like something that would be worth it though.

[Richard Wallace]

Originally Posted by Ian Curtis

Wow! That is a big difference. For those of us that don't know much about gears/wear-in/etc. would the AndyMark gears improve over time as the surface finish improves? I think I remember someone (971?) ran their gearboxes on a test stand prior to mounting them on their robot and found it wasn't really worth it. A 50% reduction in free current sounds like something that would be worth it though.

Free current has two main factors: (1) internal rotating losses in the CIMs, about 2.5 Ampere per motor so 7.5 Ampere for three motors, and (2) mechanical drag in the rest of the drivetrain. So the reduction we saw using VexPro gears is really about a factor of four; i.e., 9.5 Ampere reduced to 2.5 Ampere. That is about 85 extra Watts of mechanical power per side. Not chump change.