View Single Post
  #19   Spotlight this post!  
Unread 07-01-2009, 14:13
Matt H. Matt H. is offline
Long Distance Mentor
FRC #1726 (N.E.R.D.S.)
Team Role: Alumni
 
Join Date: May 2006
Rookie Year: 2007
Location: Sierra Vista, AZ
Posts: 238
Matt H. has a reputation beyond reputeMatt H. has a reputation beyond reputeMatt H. has a reputation beyond reputeMatt H. has a reputation beyond reputeMatt H. has a reputation beyond reputeMatt H. has a reputation beyond reputeMatt H. has a reputation beyond reputeMatt H. has a reputation beyond reputeMatt H. has a reputation beyond reputeMatt H. has a reputation beyond reputeMatt H. has a reputation beyond repute
Re: Our Team Needs Help on the Drive!

Quote:
Originally Posted by ExarKun666 View Post
Well throwing another question out there that I have, for crab drive, I have never really seen one so I am not sure how they work or how to set it up. From my understanding this is what it would look like (correct me if I'm wrong)
|\--------/|
|--|----|--|
|=|----|=|
|--|----|--|
|---\__/---|
|-----------|
|oo------oo|
_________

(This is not to scale, (-) is just a space so ignore them)
The circles (o) would be the wheels powered, and pointed to the front of the bot, the (=) would be wheels facing <- at a 90 degree angle, and powered. Is my interpretation of crab drive front wheels correct?
Not quite, but close
If the front two wheels are in a crab modules then they are free to rotate as directed by separate motors. i.e. when turning the crab wheels (=) would be exactly as depicted above, but when moving in a straight line the wheels would be parallel to the rear wheels. The wheels can be turned at a whim using two additional motors. Each crab module consists of a drive motor (generally a CIM) and a turning motor which turns the module.
Here are some threads and images better explaining crab drive:
http://www.chiefdelphi.com/forums/sh...ad.php?t=55454
http://www.chiefdelphi.com/media/papers/1836 (he calls crab swerve, but they are very similar)

Crab drives are a challenge to build, but can dominate if correctly implemented.