RC-Monster Forums - View Single Post - Higher pinions = safer MMM's? Or no? Someone's lying....

Thomas · 10.06.2009, 04:48 PM

Reading all this makes me want to waste some time posting.

1. Do you really think these Savages reach 63 mph just bashing around? I can imagine that with the 20t pinion, you have a good chance of reaching the same or higher speeds in most gravel pits, compared to running overgeared with a 25t pinion. This because of
a) less acceleration with the taller gearing, but limited space -> less top speed.
b) more current draw -> more voltage drop (even more with poor batteries) -> lower motor RPM.

2. The stopping distance is not constant. You should be more concerned about power than energy. Power = Force * Velocity. With shorter gearing, the stopping distance is shorter (motor torque * gear ratio = torque at the wheels). I would say it's even disproportionately shorter.

3. Assuming both motors are the same, they can provide the same (braking) torque. With the higher motor RPM (because of 1.b) and assuming limited space, also 1.a)) in the 20t pinion setup, the recuperated power is larger because of Power = Torque * Speed.

Conclusion:
If applying full brakes at full speed is killing the ESC, then the 25t pinion is better because the motor RPM is lower.

Anybody care to smash my assumptions?

	(#115)
Thomas RC-Monster Carbon Fiber Offline Posts: 84 Join Date: Apr 2009 Location: Switzerland	10.06.2009, 04:48 PM Reading all this makes me want to waste some time posting. 1. Do you really think these Savages reach 63 mph just bashing around? I can imagine that with the 20t pinion, you have a good chance of reaching the same or higher speeds in most gravel pits, compared to running overgeared with a 25t pinion. This because of a) less acceleration with the taller gearing, but limited space -> less top speed. b) more current draw -> more voltage drop (even more with poor batteries) -> lower motor RPM. 2. The stopping distance is not constant. You should be more concerned about power than energy. Power = Force * Velocity. With shorter gearing, the stopping distance is shorter (motor torque * gear ratio = torque at the wheels). I would say it's even disproportionately shorter. 3. Assuming both motors are the same, they can provide the same (braking) torque. With the higher motor RPM (because of 1.b) and assuming limited space, also 1.a)) in the 20t pinion setup, the recuperated power is larger because of Power = Torque * Speed. Conclusion: If applying full brakes at full speed is killing the ESC, then the 25t pinion is better because the motor RPM is lower. Anybody care to smash my assumptions?