help, our wheels dont spin at the same speed
 

We are using two similer cim motors and two toughboxes in order to move our robot. While testing the robot (wheels in the air) we saw that one of the wheels moves at a noticable different speed. The problem is coming from the gearboxes or the motors (we think). Has anyone else encountered this problem? Is there any way to fix it other than programing the robot to adjust to the problem?

Thank you

Re: help, our wheels dont spin at the same speed
 

make sure your wiring is good.

make sure your drivetrain is good. if you have chains, make sure the are lined up right. make sure your axles are straight (if you bot is a non-kit frame)

Re: help, our wheels dont spin at the same speed
 

Have you tried calibrating your jaguars? I'm making the assumption that you're using jags. In 2009, I found a pdf titled, JaguarGettingStarted. It or a newer version is probably still online somewhere.

Re: help, our wheels dont spin at the same speed
 

If you can rule out programming and electrical, and can verify that your axles aren't bent, your chains are straight and of equal tension, etc, consider this:

Are both gearboxes greased? Were they both run a while to let everything seat well? We've found a noticable difference in performance between well-run and barely-run toughboxes, with well-run boxes being much smoother than their counterpart. (Just hook 'em to a battery and let 'em run for 20 minutes or so.)

Re: help, our wheels dont spin at the same speed
 

There are a few reasons that robots don't run straight or differ in speed side to side..
1. Significantly more wire feeding the motor(s) on one side of the robot due to asymmetrical placement of electrical components.
2. Speed controllers not calibrated by procedure or software.
3. Mechanical issues such as bent shafts, dragging chains, excessive loading on shafts or excessive grease in one transmission.
4. Although CIM motors have a small directional bias most motors naturally run faster in one direction than the other due to the design.

The mechanical issues can usually be deduced by rotating the wheels by hand and looking for a difference from side to side. Your robot is trying to talk to you, all you have to do is listen.

Re: help, our wheels dont spin at the same speed
 

With power off, and the battery removed from the robot, try turning both wheels by hand. Is it easier to turn one side, compared to the other? this will help you figure out if it's a mechanical or electric problem.

Re: help, our wheels dont spin at the same speed
 

Make sure your program is being told whether you're using Victor or Jaguar speed controllers. If the motor control code thinks it's controlling the wrong kind, you'll have a built-in discrepancy between forward and reverse speeds. I assume your motors are mounted so that the ones on the left side of the robot turn in the opposite direction from the ones on the right side of the robot, and at low speeds that would definitely show the symptom you describe.

What language are you using to program in?

Re: help, our wheels dont spin at the same speed
 

You do have the same sprockets installed on the wheels . . . right? You don't have say . . 22 tooth on one and 24 tooth on the other?

I mean, no team has EVER made that mistake. :rolleyes:

Re: help, our wheels dont spin at the same speed
 

we are progremming with lab-view and no all the sprockets are the same we're new but still got some knowlege ;)

thank you all we are gussing the problem is caming from the motor spinig in different directions is there any way to fix it mechanicly or only through progreming?

Re: help, our wheels dont spin at the same speed
 

I've always seen our robots favor one side over the other (which we fix with code/calibrating). But what your saying sounds to be more of a major difference. Make sure all your gears are set right in your gearbox. I remember a couple of years ago, someone else on our team put together our toughboxes. One of them was good, but he had a couple of the gears in the other flipped (so the lip on the center hole was on the wrong side) and the gears were rubbing ever so slightly on something (don't remember if it was the side of the toughbox or if it was the other gears). Also, make sure you're lubricating the gearboxes and chains. I've seen pictures of teams holding a pile of metal dust that used to be the teeth on the gears in their gear boxes. This is caused bay lack of lubrication.

Re: help, our wheels dont spin at the same speed
 

To fix it mechanically, you'd probably need to figure out how to mount the motors so they both face the same direction (that is have the output shafts both pointing to the same side of the robot), or else figure out how to add an idler gear to one side so that one is reversed.. Might be more trouble to do this than it would to play with the programming....

Re: help, our wheels dont spin at the same speed
 

You shouldn't need to do this with the CIMs. They are within 100 RPM of balanced, which shouldn't affect anything that much with a gear reduction.

Re: help, our wheels dont spin at the same speed
 

Yup, operating the robot under load, instead of sitting off the floor, might fix the problem....