Drive Mobility System

Hey Guys, my team is having problems figuring out what motors to use for the drive system and should the drive system be 2 wheel drive or 4 wheel drive. We are planning on going up the ramp to the other platform. Anyone have any advice???

If your using the Kit Transmission/Gearbox then use the Smaller Cim Motors to drive. Other than that, make sure you have the ground clearance to get onto the ramp easily and without bottoming out ect. Because of the ramp, 4 wheel or 6 wheel drive would probably be ideal.

The kit boxes with two CIMs served us well last year. If you are planning on getting up the ramp, then 4-wheel would be easier to do it with, plus it would give you better traction for pushing matches :slight_smile:

Be very careful with four wheel drive, as it is unbelievably easy to make it unable to turn. Last year this happened to us and we had to put epoxy clay in the treads of our front wheels to allow “real” turning. It actually did turn without it since the drivetrain’s torque would twist the chassis so we’d lose some of or an entire contact patch letting it rotate until the chassis flexed back. Don’t let this happen to you.

You could very well use the kit gearboxes with the small CIMs. Four wheel drive is a good idea if you are planning to go up the ramp, and u need 4’’ off the floor clearance to climb the ramp. If you are using the wheels from the kit, it is a good idea to cover it with tread(at least two) because if u get into pushing contests(likely to happen), the wheels will have no traction and your robot will be pushed around.

actually, 4 wheel drive could be worse for getting on the ramp than 6 wheel drive. Depending on how you mount your wheels, the point at which you’d normally bottom out would be occupied by the middle wheels on the robot, whereas if you had a 4 wheel drive robot you’d get stuck.

No, the original question asked for 4 wheel vs. 2 wheel drive. Four would be better than two, though six is the best (of the three, no 8 wheel drives…). However, some teams may choose not to build a six wheel drive because of the greater resources required. Also, this year, it really doesn’t matter if you bottom out on the ramp; you would probably be off the carpet by that time.

Very true. For the past two days straight (and probably for one more), we have carefully been considering this. For a traditional 6wd skid steer (tank steer) robot to make it up the ramp effectively, the end of it that goes up the ramp first must be much heavier so that when the middle wheels reach the edge between incline and horizontal, gravity pulls the “front” right down on top of the horizontal platform. If this is how it’s done, and the wheels are the front-most and back-most thing on your robot (no frame rails in front of them) then it is possible to have an incredibly low frame (1/4" off the ground) If the “back” of the robot is much heavier, you will either tip over or get hung up on the frame between the middle wheels and the back wheels.

In a six wheeled robot, when the middle wheels get on that edge where the ramp ends and the platform begins, there is a bit of a shaky transition because the robot is sort of like a teeter totter. For some brief moment in time, the robot will only be on it’s two center wheels.

For a traditional 4 wheeled robot, the transition from incline to horizontal surface is quite pleasant, and all 4 wheels remain on the ground at all times. There is no teeter tottering going on at all. However, you will need clearance under the center of your frame.

And then there is the question of long vs wide. For turning’s sake, you’ll probably want 6wd for a long robot (or 4wd with a couple low friction or omni wheels) where 4wd would be just fine for a wide robot. But a wide robot may tip going up that ramp whereas a long robot may not. The it presents the question if you want a wide robot, how do you keep from tipping. Wheelie bar? Extending frame?

So many questions and so little time to answer them all.