View Single Post
  #22   Spotlight this post!  
Unread 08-05-2011, 13:41
buchanan buchanan is offline
Registered User
FRC #2077 (Laser Robotics)
Team Role: Mentor
 
Join Date: Mar 2009
Rookie Year: 2007
Location: Wales, WI
Posts: 70
buchanan is just really nicebuchanan is just really nicebuchanan is just really nicebuchanan is just really nice
Re: Offseason Project: Holonomic Kiwi Drive Robot

Quote:
... we only had three unused, good motors.The conclusion of three wheeled robot followed pretty easily.
Certainly a good reason; respecting real-world constraints is engineering too . Another reason to start w/ three wheels is that this sort of drive requires traction, and hence normal force (weight) on all driven wheels at all times. With three wheels you get that pretty much for free if you have the COG in the middle. There are ways to deal with it with four or more wheels, but for learning the technology reducing the number of design factors to be managed makes it easier to get started. Besides, three wheelers just look cool. One idea we toyed with last year was using five wheels (maximum legal CIMs) just to get more power on the ground. We decided not to for the reason I just mentioned, but if a three wheeler attracts attention, imagine the looks you'd get with five .

Quote:
... PID is something I hope to learn during this. The integral and differential bits could be more difficult having not taken any calculus yet, but I don't know enough about it to really know.
CAN/PID (closed-loop, encoders directly to Jaguars) was our big learning push this year. We found it not so much a matter of learning math, but of physically configuring the system. It seems quite fussy, and if everything isn't right nothing works - we had wheels turning backwards and other strange phenomena. There are how-tos on tuning the PID parameters. Once we trusted our hardware we just followed one of those and got good results. IMO closed-loop PID and holonomic drive (we used mecanum this year) is a marriage made in heaven.