[Gui Cavalcanti]

Alright, so my last big discussion here was linking friction, traction, and torque as applied to drive trains. Here's what I'm confused about now: linking power, speed, and torque together.

Alright, I know the basics. As speed increases, torque decreases, and vice versa. You can use the motor charts to find your speed at a certain torque, you can make a drive train by know the force you want your robot to push with and then porting it through the wheel radius, back through the gearing, to your motor. I've got all that. Now I'm struggling with how power affects FIRST robots.

Power is work over time, I know that. Work is force times distance, I know that. But why do we need this rating? What is power, technically, to FIRST robots?

If I build a pulley system with a motor lifting a 20 some kilogram weight (200 N, for arguments sake), wrapping the rope around a 2 centimeter radius shaft, the torque required for this is 200 Newtons * .02 meters, translating into 4 Newton*meters. I decide that I want my motor to operate at 200 mN*m, so my gear ratio is 4/.2, or 20:1.

Now that I have my gear ratio decided upon and I know how my motor will be acting, I can find the speed. Let's say that, when the motor has a torque of 200 mN*m, it's spinning at 500 rpm. This is transferred through my gear ratio, resulting in 25 rpm in the shaft. 25 rpm, multipled by (1/60) to convert to seconds, and (2*pi*.02 meters) to convert to linear motion, means that the weight is being lifted at around .05 meters/second.

Ok, I know how to do all that. Now the question is, where did power come into play, if at all? There is nowhere in those equations that I found power - I used the motor curves to relate speed to torque, but that's it. What on earth is the power curve used for?

Thanks in advance!