pic: Pod

This is the crab module we used on our drive this year. Using servos for module rotation worked out very well with the low friction field. There was no need for any feedback and we had plenty of torque.

The gears are mcmaster, with metal servos horns attached.

We also used mechanical slip clutches (torque limiters) on the drive. Control your max torque, and you have a very simple and reliable traction control.

Out of our 67 matches this season, we only had to replace four servos, and a bb-motor.

We had a great season this year, and have a new respect for Hitec servos.

Here is the servo assembly.

So did you guys use RS-545 motors on two modules and fisher price motors on the other two?

Exactly, both with bb 25:1 trannies with an extra 2:1 chain run.

I have to say, this was something I never thought these servos could handle. Did you work out any of the math to make sure the servos could handle the load? Did you have any problems with cross talk from your motors messing with your servos?

Surprisingly, from the math, just one servo could handle the regolith with a safety factor of two. Unfortunately, the carpeting required us to move to three.

I’m not sure what you are referring to by cross talk, but we choose to use coarse gears for our drive to account for any servo misalignment. As far as the servos fighting each other, it is very minimal and only towards the limits of their travel.

Very cool, I would be interested in seeing how to work the math for this. (Im a programmer by training so most problems involving the real world are beyond my skills in physics)

By cross talk I am referring to the nasty problem of when the wires from your servo (or sensor) act as an antenna and pick up the magnetic field from the wires on your motors. I recall 2006 when we would turn on the shooter wheels and our camera servos would go crazy.

06 also had the issue of many shooters being Van de Graaf generators. Large static charges make servos a little unhappy.

Very nice! I marveled at your demo-display in Atlanta. I do believe this is deserving of a white paper. Any chance one is forthcoming?

Ironically I saw you guys at 4 competitions and was even in your pit and never noticed this. I saw the display but never had time to actually look, I meant to at MSC but I never got around to it…I’m impressed and by the awards you received for it so were the judges…nice work.