• Sajiv Shah

FRC #4 Strafe Motor calculation/Reduction

We decided in the last post that we need around 60 lb-inches of torque to strafe on the bar. If we convert this to newton-meters we get 6.78.

Considering design constraints, we want to use the smallest, lightest motor possible. The best option is the NEO 550 brushless motor, a new brushless motor by REV which is by far the lighest motor that performs on the same level as other FRC motors.

Here's a good article if you are wondering what a brushless vs brushed motor is: https://motors.vex.com/brushed-brushless

Looking at the motor curves below, if we want to operate at 20 amps we would output near 9000 RPM's and 0.2 NM of torque. The reason we would operate at 20 amps is because the battery is under worse conditions toward the end of the match, and operates at a lower voltage. If we divide the 6.8 Newton-meters neccesary to strafe in the worse conditions by the 0.2 Newton-meters of torque that is outputted by the motor, we find that we need around a 34:1 reduction.

The 9000 rpms in a 34:1 reduction gives us a geared rpm of 264.7. Dividing that by 60 to give us rotations per second gives us 4.412 rps. Then mutliplying that by the circumference of a 2-7/8" wheel and dividing by 12 to get feet per second, we get around 3.32 feet per second. That is VERY fast. We will likely jerk the robot if we were not to slow to a stop, and this speed is unnecessarily fast. Therefore, we will likely go with a reduction closer to 50:1