View Single Post
  #36   Spotlight this post!  
Unread 07-11-2007, 09:44
JesseK's Avatar
JesseK JesseK is offline
Expert Flybot Crasher
FRC #1885 (ILITE)
Team Role: Mentor
 
Join Date: Mar 2007
Rookie Year: 2005
Location: Reston, VA
Posts: 3,647
JesseK has a reputation beyond reputeJesseK has a reputation beyond reputeJesseK has a reputation beyond reputeJesseK has a reputation beyond reputeJesseK has a reputation beyond reputeJesseK has a reputation beyond reputeJesseK has a reputation beyond reputeJesseK has a reputation beyond reputeJesseK has a reputation beyond reputeJesseK has a reputation beyond reputeJesseK has a reputation beyond repute
Re: Contact Area and its Relation to Friction?

Quote:
Both had two driven wheels, and two casters. One bot had two andymark kit wheels per axle for driving, and the other had only one per axle. I added extra weight on each in order to make the weight exactly equal. I wired both motors to a single battery and switch. Then I put the two drive bases head to head, set so they would drive directly into each other, on an area of FIRST carpet. When turned on, the base with 2 wheels per axle could overcome and outpush the other base every time. We did this 12 times, each time changing to a new, fresh battery.
After a bit more thinking, I do not have the answer to why this particular scenario happened. However, I do have a solution for how to avoid it -- move to 4 driven wheels on your drive train.

Since friction for a given wheel is dependant upon the force of gravity exerted by the mass of your robot, a 2-driven-wheel system needs most, if not all, of its weight centered directly over the drive axle for maximum traction.

Changing to a 4-driven-wheel system spreads out where in your system the center of mass can be and still practically contribute to all of the wheels' traction. Come to think of it, I think someone previously in this thread mentioned it, and most of the drive train guides I've come across have the underlying assumption Center of Mass rests somewhere in between 4 driven wheels.
__________________

Drive Coach, 1885 (2007-present)
CAD Library Updated 5/1/16 - 2016 Curie/Carver Industrial Design Winner
GitHub