Problem with mecanum wheels

[buchanan]

Check the motion of the wheels when trying to move sideways. One side should be turning inward with the tops moving toward one another and the other outward with the tops moving apart. It is possible to get the symptom you describe by getting various combinations of things crossed up (motor positions, direction of rotation, etc). If they are moving "both inward" or "both outward" it just sits there and chatters against the floor as the two sides work against one another trying to split or compress the robot.

[minee_5]

Originally Posted by Ether

What do you need a Jacobian for?? Inverse kinematics for mecanum is a straightforward calculation.

I am using velocity control, not position. So, Jacobian it is..

Originally Posted by Orion.DeYoe

It really sounds like your motors aren't geared low enough (i.e. you don't have enough torque). It was too fast and we couldn't straif unless we were running close to full power.

Well, my controller does not require the maximum current. The current sent to motors are pretty low. So, I guess it can't be enough torque, no?

The wheels are fine when they're not in contact with ground. (Much faster but fine) When contacted with ground; it can go sideways (two wheels go inward two go outward) but during the motion; it starts chattering which cause vibration.

[Alan Anderson]

Are the mecanum rollers free to, you know, roll?

[Ether]

Originally Posted by minee_5

I am using velocity control, not position. So, Jacobian it is.

If you know the desired translational and rotational velocity of the vehicle, calculating the required wheel speeds to achieve that does not require a Jacobian. So you've got me curious... what exactly are you doing?

[minee_5]

Originally Posted by Ether

If you know the desired translational and rotational velocity of the vehicle, calculating the required wheel speeds to achieve that does not require a Jacobian. So you've got me curious... what exactly are you doing?

Well, my reference to the robot is in Cartesian space. I want to know where the robot goes, I won't be interested in how fast the wheels are turning eventually. For further control algorithms (such as admittance, etc.), I want to use velocity control instead of position. Kinematics also work, you're right but Jacobian for such device is much simpler for this system, no?

[minee_5]

Originally Posted by Alan Anderson

Are the mecanum rollers free to, you know, roll?

Indeed.

[Ether]

Originally Posted by minee_5

I want to know where the robot goes

Are you saying that you are trying to solve the following forward kinematics problem:

Given the speed of each of the four mecanum wheels, predict what the vehicle motion (translational and rotational velocity) will be?

And if so, why did you decide to control the vehicle that way?