View Single Post
  #21   Spotlight this post!  
Unread 13-07-2007, 03:48
AdamHeard's Avatar
AdamHeard AdamHeard is offline
Lead Mentor
FRC #0973 (Greybots)
Team Role: Mentor
 
Join Date: Oct 2004
Rookie Year: 2004
Location: Atascadero
Posts: 5,526
AdamHeard has a reputation beyond reputeAdamHeard has a reputation beyond reputeAdamHeard has a reputation beyond reputeAdamHeard has a reputation beyond reputeAdamHeard has a reputation beyond reputeAdamHeard has a reputation beyond reputeAdamHeard has a reputation beyond reputeAdamHeard has a reputation beyond reputeAdamHeard has a reputation beyond reputeAdamHeard has a reputation beyond reputeAdamHeard has a reputation beyond repute
Send a message via AIM to AdamHeard
Re: what motor did you use(arm)

Quote:
Originally Posted by Doug G View Post
I can't emphasize this enough. Over design the power transmission on the arm. If calculations show that you need 30 ft-lbs of torque to lift the arm and object at the end of the arm, then design a motor/transmission combination that can supply that while drawing < 10 Amps! (somewhat dependant on the motor choice)

If you need 30 ft-lbs, then stall torque should be at least 120-150!! Also this way, you can throw in some feedback and PID will have lots of headroom for tuning and working correctly.

In the 7 years of doing FIRST ... In my opinion the ratio of "under-designed arms" to "over-designed (or simply well-designed) arms" is at least 25 to 1.
Exactly... definately a lesson learned there....

Another interesting tidbit I forgot to mention. Our original system w/ FPs wasn't geared low enough and was a pain to tune in PID because it was sooooo fast. The new system with the CIMs (not that the motors make a difference, there were other reasons for the change in motor type) was much slower and torqu-ier so we were able to tune a two jointed arm w/ straight P control in 15 minutes at a San Diego with even better accuracy the the original.