Thread: Motor Info
View Single Post
  #2   Spotlight this post!  
Unread 03-08-2004, 00:00
Andy Baker's Avatar Woodie Flowers Award
Andy Baker Andy Baker is offline
President, AndyMark, Inc.
FRC #3940 (CyberTooth)
Team Role: Engineer
  
Join Date: May 2001
Rookie Year: 1998
Location: Kokomo, Indiana
Posts: 3,412
Andy Baker has a reputation beyond reputeAndy Baker has a reputation beyond reputeAndy Baker has a reputation beyond reputeAndy Baker has a reputation beyond reputeAndy Baker has a reputation beyond reputeAndy Baker has a reputation beyond reputeAndy Baker has a reputation beyond reputeAndy Baker has a reputation beyond reputeAndy Baker has a reputation beyond reputeAndy Baker has a reputation beyond reputeAndy Baker has a reputation beyond repute
Send a message via AIM to Andy Baker
Re: Motor Info
Adam,

This is a good question. For most motors we use in FIRST, the max efficiency is at about 1/2 of the free speed. With this in mind, some designers size their reductions for this speed and have a robot that drives well.

For instance, they gear their 'bot to run at top speed when getting an input speed from the CIM motor at about 2800 rpm, or about 1/2 of the 5500 free speed rpm. Then these teams make their robot, get their drivetrain as efficient as possible, with little friction, and it drives too fast. The top end is too out of control, tripping circuit breakers and the low end is not torquey enough. Usually, they end up gearing down their robot, slowing it down so it is more controllable and doesn't trip the circuit breakers after running at top speed for more than 5 seconds.

From my experience, I use a "working rpm" top speed of about 75% of the motor's free speed rpm. For instance, when designing drive trains with the CIM motor, I assume that I can get 4000 rpm (again, 5500 is the free speed) at the robot's top speed. This difference of free speed and working speed is because of efficiency losses in the drivetrain and rolling friction losses of the robot.

Have fun,
Andy B.