Gearbox -physics related question

[Kevin Sevcik]

As noted, the rotational inertia of most all gearboxes in FIRST are negligible. And if you lightened the gearbox with everything else the same, your max speed would remain the same, though the robot would accelerate slightly faster. The best way to think about it is as a division of kinetic energy. Assuming you have a flywheel attached such that it spins faster the faster your robot moves, the flywheel would store some amount of rotational kinetic energy for every Joule of translational kinetic energy stored by your robot moving forward. With a standard gearbox, it's probably something like .01 J of rotational energy for every 1 J of translational. With a big flywheel, you'd be storing more in the flywheel, and a comparatively smaller amount of every J from your motor would be going towards actually moving the robot forward.

To correct one error I've sen in this thread. The top speed of your robot does not depend on the max RPM of the motor. It depends on the friction in your drivetrain. The friction represents a torque that must be subtracted from the torque developed by the motor before you start firguring the acceleration of the robot. So at some point, the torque put out by the motor equals the friction torque, and your robot stops accelerating. Since the motor is putting out mre than zero torque, this isn't going to be the no-load speed.

[sporno]

ok thanks for all the help

once again this is all just theory, im just trying to find out if what im saying is even ballpark

and this isnt just in relation to the gearboxes , but any rotating object on the bot.

Also , if the drive train is more efficent , less power is lost , and more gets to the wheels , thus some power is picked up .... right

[Alex.Norton]

Originally Posted by Kevin Sevcik

As noted, the rotational inertia of most all gearboxes in FIRST are negligible. And if you lightened the gearbox with everything Since the motor is putting out more than zero torque, this isn't going to be the no-load speed.

This all depends on how you define your motor. Technically no motor has a no load speed since the motor has to spin itself which takes some power input. Since the CIM has a resistance and you have to put power in which means that your producing power somehow. I think you could define the whole drive train as a motor, maybe a linear motor, and then say that the top speed of the robot is the free speed.

A lot of solving a problem in physics is just choosing the correct frame of reference and it might be easier to define the drive train as the motor and just measure its speed. I'm not sure what the use of this is but hey...

Alex