Problems turning

[meatmanek]

Originally Posted by Cody Carey

Since surface area has no bearing on friction, I would assume that this would be a bad Idea. By putting the two "sticky" wheels beside each other, you are reducing the amount that the wheel has to be pulled sideways when turning, and increasing the amount that it rolls along the turn. This decreases over all turning friction.

If you were to place them on opposite corners, it would do nothing to the amount that the sticky wheels have to be pulled sideways to follow the circle of your turning radius, and since One wheel has the same amount of friction as two, I wouldn't expect this to solve your problem at all.

Not true. One wheel with 60 pounds on it has the same amount of friction as 2 wheels with 30 pounds each. However, one can assume that the weight of the robot will be approximately equally distributed across the four wheels, or at least the weight on the omnis will be the same as the weight on the traction wheels. Therefore, the traction wheels have only half as much turning friction as they used to.

Another solution would be to move your wheels closer to the middle of your robot. This increases turning capacity without decreasing traction. However, it causes balance problems, as your wheel base is shorter. Add a few trick wheels or casters that hover just above the ground to fix this problem.

[Cody Carey]

Can someone please explain this to me mathematically? I still don't get it.

It takes less force to rotate a wheel along the diameter of the turning circle than to scrub it sideways along the same circle. With the omni wheels in the front (right picture),you are basically applying force tangentially to the circle which you turn on, and with the omni wheels on opposing corners, You are waisting a lot of your force going outward from the turning circle, and scrubbing both traction wheels sideways.

Is it just that having the omnis on opposite corners woud decrease the force required to turn the robot, but not as much as the omnis on front of back would do? A little help would be greatly appreciated.

[Tom Bottiglieri]

Originally Posted by Cody Carey

Is it just that having the omnis on opposite corners woud decrease the force required to turn the robot, but not as much as the omnis on front of back would do? A little help would be greatly appreciated.

Yes.

While the second scenario you illustrated will get you closer to a "zero friction" turn, it also changes your turning radius from dead center in the robot to inside of the axis between your back two wheels.

Putting the omni's in opposite corners still gives you the problem of turning scrub, but it will significantly reduce the problem as half of your total weight is being distrbuted along wheels which experience little to no axial frictional force. For most situations, this should be enough to kill the bouncing robot problem. This also allows you to keep your 0 degree turn radius, and keep a solid wheel on the ground on each side of the bot at all times.

So really, its all up to driver experience and preference. I have been told that drivers who like to use one stick drive will be much better on a "power slide" bot (omnis on same side) and drivers who prefer two stick will be much better with a 0 degree turn radius.

[Bochek]

well today we ordered 3 andy mark 6" omni wheels,

the reson for 3 was incase one breaks.

we will be replacing the 2 rear wheels with the onmi wheels.

does anyone know the difference in weight between the ifi aluminum sprokets and the steel KOP wheels?

- Bochek

[Arefin Bari]

Originally Posted by Bochek

well today we ordered 3 andy mark 6" omni wheels,

the reson for 3 was incase one breaks.

we will be replacing the 2 rear wheels with the onmi wheels.

does anyone know the difference in weight between the ifi aluminum sprokets and the steel KOP wheels?

- Bochek

The KOP wheels weighs .8 lbs. I believe you were trying to ask about the sprocket that was provided in the kit. If you are wondering if it would help you lose weight when you switch those steel sprockets to aluminum ones, yes you are on the right track.

Also, you are already going to lose .6 lbs by planning on swtiching those kop wheels to AM omni wheels. Those AM omni wheels weigh 5 pounds.

If you need help figuring out how to lose more weight and if you have detailed/close up pictures of the robot, feel free to contact me. I will be more than happy to help you guys and give some suggestions.