Quote:
Originally Posted by ttldomination
Hello Everyone,
A while back, I read on these forums that adding a 1:1 reduction in a gearbox is a hardware solution to prevent the robot from veering to one side.
I was wondering if anyone could explain this.
Appreciate it,
Sunny G.
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Elaborating on what Jared said...
The old Drill Motors were biased to run faster forwards than in reverse. A typical skid-steer drivetrain with 1 of these motors on each side would be built such that to drive forward these motors would be spinning in opposite directions. The motor bias would then cause the robot to veer to one side (since one side of the drive is running faster than the other).
A way to counter-act this, is to add another 1:1 gear stage inside one side of the drivetrain. Spur gears reverse the direction of motion. So if you add one additional stage to one side, you reverse the direction of motion. This would serve to ensure that both motors are running in the same direction, and eliminates any worry about motor bias. (Of course you make it a 1:1 stage, because you don't want to change the overall gear ratio for this gearbox).
Back in the day, this wasn't a huge issue since there was no autonomous mode. Drivers typically just "dealt with it." In 2003 and 2004 (the 2 years involving both Autonomous mode AND drill motors) many teams came up with different solutions to make their robots track a little straighter. Some teams simply dealt with it by adding a voltage bias to their drivetrain (i.e. applying slightly less voltage to the "fast" side of the drive). Other teams implemented a mechanical solution similar to the one you described. Still other teams implemented some "go straight" code which utilized sensor feedback from the wheels to ensure they are spinning the same speed.
Now-a-days in the "modern era of the CIM motor" we don't really need to worry about motor bias, since CIMs are neutrally biased (they spin about the same forward & reverse).
People still implement go-straight code, but not for the reason described above. The "additional 1:1 reduction" mechanical solution will NOT help a robot with CIM motors drive straight.
-John