Localization of A Omni-Directional Robot

[Ether]

Originally Posted by cad321

What about 2 omni wheels placed perpendicular to each other that drag along the floor. As the one in the y axis moves, it gives you your position in the y axis

That's true only if there is no vehicle rotation. If there is going to be vehicle rotation, you need either a) a gyro, or b) a third follower wheel... and you'll need to integrate (vector sum) the vehicle movements.

You might find this post of interest (and also the rest of the post in that thread).

[cad321]

Originally Posted by Ether

That's true only if there is no vehicle rotation. If there is going to be vehicle rotation, you need either a) a gyro, or b) a third follower wheel... and you'll need to integrate (vector sum) the vehicle movements.

You might find this post of interest (and also the rest of the post in that thread).

I corrected my post to include the gyro. I was thinking of it in my head but forgot to add it in. The third follower wheel for rotation is a good idea as well.

[vrcprogrammer]

This all looks great, how would you recommend using a gyro with the three follower wheels.
Thanks

[AlexanderTheOK]

Originally Posted by vrcprogrammer

This all looks great, how would you recommend using a gyro with the three follower wheels.
Thanks

Well first of all, what is your issue with simply putting encoders on all four of your wheels? If you are going for the X/killough/omni/whateveryouwishtocalllit drive you already have TWO sets of "mouse wheels". Theyre your drive wheels! Even without the gyro you can get rotational odometry. (I have tried this when we were prototyping swerve code on a vex base and it wasn't all too terrible. A gyro is still better, but odometry can determine your angle)

Ether's papers on controlling an omnidirectional drive apply in the reverse direction in order to find your movement based on encoders.

[cad321]

Originally Posted by AlexanderTheOK

Well first of all, what is your issue with simply putting encoders on all four of your wheels?

The biggest issue with this method is wheel slippage. Say I accelerate to quickly, or I get into a pushing match and my wheels start to spin because they lost traction. All of a sudden my robot thinks it's 5 feet further forward than it actually is. By getting feedback from unpowered wheels or a laser, you know that whatever movement you detect should in theory be the exact actual movement of your robot.

[vrcprogrammer]

Originally Posted by "cad321"

The biggest issue with this method is wheel slippage. Say I accelerate to quickly, or I get into a pushing match and my wheels start to spin because they lost traction. All of a sudden my robot thinks it's 5 feet further forward than it actually is. By getting feedback from unpowered wheels or a laser, you know that whatever movement you detect should in theory be the exact actual movement of your robot.

This is the exact reason I am trying to use the follower wheels, but I would like a way to use the gyro/ultrasonics, to check the data, is this needed, or are the followers accurate enough?