4x4 software differential

[archiver]

Posted by James.

Coach on team #21, ComBBAT, from Brevard Community College and Boeing.

Posted on 11/13/2000 6:01 PM MST


In Reply to: 2 powered, steerable wheels posted by Peter VanWylen on 11/10/2000 8:42 PM MST:



: Okay, we did something like this last year. I don't have the code handy, but this is what we did. First, we found that 4 wheel drive is excessive, expecially when you are trying to steer two of them. We made the steering wheels powered, and the other two fixed, but unpowered. You will probably want to put the steerable wheels in the rear of the robot -- this makes sense if you have ever seen a hi-lo / forklift operate. When lining up to pick something up, you want the power steering, and the drive power to be in the back.

: The program was relatively simple:
: leftmotor = p1_y
: rightmotor = p1_y

: then you need a simple feedback loop between potentiometer and motor to get the wheels to turn in response to the p1_x, and then return to center when you let go of the joystick. Also, you could try breaking the steering and speed control into two seperate joysticks -- this worked nicely, and made it easier to drive.

: This really did work well, and I would recommend this drive mainly because it is *very* easy to drive *fast*, and straight, and to line up for picking things up. Then you just need to make a manual override that when you push the trigger button, it would go into regular two joystick drive, one left, one right, as is usually typical.

: Hope you find this helpful and non-cryptic.

We done 2 wheel drive for many years. I agree it is simple. We have drove it tank style for all the years that we have been doing it. 2 wheel drive tank style is good for flat open spaces, but when you add a ramp or puck, that's the trouble. The CG changes when you start climbing. Thus taking some weight off a set of wheels. Putting the drives wheels all the way in the back sounds good, but with interaction with other parts of the robot, it isn't always possable. We have tried 4x4 in the past and we weren't very happy with the results. With the front wheels driven, all you would really be adding is 4 sprockets and 4 universial joints. Why not?