My team has a turning problem and we are looking for a quick fix that we can do before the championship rounds begin. We have four wheel drive, one kit CIM and transmission per side, a very wide wheel base (all most as wide as the frame which is the max 46"); we are using four of the kit of parts wheels. We have geared the motors down considerable so that the robot moves at the same speed as a quick walk at full speed. We have decided that replacing two wheels with Omni wheels will be the easiest way to go so we ordered two 6" Omni-wheels rush delivery.
What I am wondering is if I can replace the two wheels that are in opposite corners. This way we will rotate around the center of mass and if we get hit from the side we won’t slide as much as two Omni wheels on the front or back.
If anyone has tried to do this or knows if it will solve my turning problem I would love to know.
Putting omni’s on the corners will do a little, but you will still be loading up your motors, and I don’t know if it’ll relieve your traction enough for the robot to turn freely. You are probably better putting Omni’s on the front (pivoting on the back) or the back (pivoting on the front) depending on the strategy your team is trying to accomplish.
Without actually seeing the robot, I cannot help you much more.
Questions that need to be answered is:
How much is ‘geared down considerably’? 12:1? 16:1?
Whats the coefficient of friction of the tires on carpet?
(Assuming skid steer) whats the distance center-to-center of your tires front-to-back?
That being said i feel that you will be better off placing the omnis in front, shifting your pivot point compleatly instead of just reducing half of your scrub as you would by placing them in opposite corners.
Thanks for the feedback. Only thing I am worried about with replaceing the front or back wheels is that when we get hit from the side we will slide sideways. I am going to talk to the rest of my team to see if they want to risk replacing the opposite wheels and have it turn out that it doesn’t fix the problem.
– We have used omni wheels in the front, and it turns easily, but subject to side defense as well, as you pointed out. Since the wheels should be interchangeable, try your idea on opposite corners. You may reduce drag enough for the CIMS to work. If not, than you can change it during practice rounds on thurs to just the fronts configuration(or rear). Maneuverability and quick scoring is key. It’s hard to defend if you’re behind. --.
494 & 70 did have an issue last year with to much traction and the solution was exactly what you are purposing, omni wheels on the diagonal corners of the robot, it worked well. I am against having two omni wheels on the front or back because your robot will be easily pushed around (your correct). You will have to test it on your robot, I would start with the diagonal placement, and if that does not work, as a last resort you can always put them on the front (I hurts to even type that). Good luck.
I think that is a good idea Teced3 i think we will go with your plan. i hope that changing those two wheels will reduce the drag enough so that we can turn more easily. If not, we will have to move the omnnis to the front or rear. Thanks for the help. And thanks to Pat Major and Don Right for the positive feedback it gives me more faith to go with the opposite corner set up.
I would think that it should work very well if you are hit from a particular point against the non-moving wheels. But when hit against the omni wheels, you might just spin. The tough part is you are going to be making the robot react in a way that your driver hasn’t practiced with. This generally is difficult to overcome in just one weekend. I would recommend practice like crazy.
Correct me if I am wrong but isn’t “wheelbase” defined as the distance between your two front wheels and your two rear wheels? That’s how i always thought of it.
When buying a luxury car sometimes, one has the option of choosing between a short wheelbase and a long wheelbase. Usually the car with the long wheelbase is anywhere between 6 in. to a foot longer, because the distance between the front wheels and the rear axel is longer.
I never thought of wheelbase in terms of wide or narrow. Maybe it has a double meaning. Can it also describe the distance between the two front wheels and/or the distance between the two rear wheels?
Your robot will act as you designed it, instead of something you didn’t intend to. What i mean is you designed it as a 4WD to pivot around teh center of the robot. If you switch to 2 omnis on one side you will throw the pivot to one side of the robot. I think you will like the results you get from the omnis in the corners.
– We have used omni wheels in the front, and it turns easily, but subject to side defense as well, as you pointed out. Since the wheels should be interchangeable, try your idea on opposite corners. You may reduce drag enough for the CIMS to work. If not, than you can change it during practice rounds on thurs to just the fronts configuration(or rear). Maneuverability and quick scoring is key. It’s hard to defend if you’re behind. --.