Holonomic Drive System Issues, Robot Drives Diagonally...

[omalleyj]

Originally Posted by Ether

Omni vehicle with 45 degree-mounted wheels goes faster in the forward direction than omega*R (R being wheel radius and omega being wheel angular velocity in rad/sec).

A chart comparing omni, mecanum, and standard wheels can be found here.

A force analysis of mec vs omni can be found here. A kinematic analysis can be done using a similar approach.

Ether, I have to go build a robot now, I'll take a look.

[Omgsar]

So, judging by the responses that I have seen so far, the consensus is that it is not a coding problem?

[AllenGregoryIV]

I would say that it is not a problem with the code that you posted here.

It may be a problem with cRIO or the electronics. (Have you updated your cRIO image to the one that was released this week?)

Also you may want to try using mecanumDrive_Cartesian(giving x and y axis instead of magnitude and direction) instead of polar and see if that works better for you.

Have you tested on blocks and seen which wheels spin when you move each joystick axis? When you move the joysticks, do all four wheels ever spin? If you apply full power forward do your Jaguars light up in the way they are supposed to? (two red and two green most likely)

If you are still having this problem at Alamo(I hope you resolve it by than), I'll try and stop by your pit and see what we can do.

[Andrew Schuetze]

Thanks for all the suggestions and looking over the code. Current and most recent "fix" was to broaden the deadbands. It is now driving much more as expected. Possibly the deadband was too narrow and minor off-center stick movements where exagerated when translated into robot movement.

I'd still like to compare robot performance between the Discobots and this omnidrive robots and continue the evolution of our design process.

[AllenGregoryIV]

Yes, hopefully at some point we will be on the same alliance at Alamo. I think we will definitely give the other alliance some problems. They will be trying to figure out which way we are going and only we will know

See you guys in 8 days.

[omalleyj]

Originally Posted by Ether

Joe said "If you mount them parallel to your frames edges,"

He meant mount each one parallel to its respective edge, like the attached image.

Ah! Oops!
My apologies for doubting you, Joe.
Thanks Ether

[Ether]

Originally Posted by Omgsar

We are using the Logitech Attack3 Joysticks, and yes I have tried to read most of the documentation that is already present on this forum. Specifically the posts by "Ether," those posts really helped... The problem exists in the fact that I don't really understand the calculations and diagrams presented in them.

Could you do the following very simple test and post the results? This would help greatly to diagnose the problem:

- put the robot up on blocks

- command pure forward motion and observe and record what each of the four wheels is doing

- do the same for reverse, strafe right, strafe left, rotate clockwise, and rotate counter-clockwise

And one more thing: you don't need to understand all the calculations and diagrams if that is not your area of interest. There are some posts and papers which just show how to program, for example:

http://www.chiefdelphi.com/media/papers/download/2906