Drive Backwards Causes A Rotation Movement

[tanogirl]

We are using the Logitech Extreme 30 Pro Joystick to control our mechanum drive base this year. Drive forward works fine and so does strafing. When we drive backwards the robot wants to rotate instead. We used smart dash board to locate the problem. When we pull the joystick backwards the Z axis has an input greater than the Y axis input.

Our Code is:

myRobot.MecanumDrive_Cartesian(stick.GetX(), stick.GetY(), stick.GetTwixt()/3, 0)

We divided the twist input by 3 to try to help with the problem. It helped a little but not much. Any ideas?

[Alan Anderson]

A twist-style joystick seems obvious for controlling a holonomic drivebase, but in practice it's just too easy to twist it by accident. My suggestion is to use a separate joystick for rotation control.

[tanogirl]

The problem is our driver gets confused when using two joysticks and prefers one

[Ether]

Originally Posted by tanogirl

When we pull the joystick backwards the Z axis has an input greater than the Y axis input.

Please run a test and post the Z vs Y pairs for Y=0 to Y=max for several values of Y.

[tanogirl]

Forward=

Y = 1.000
Z = 0.008

Backwards =

Y = -1.000
Z = -0.0062

It's a small difference but it makes the robot rotate.

[Ether]

Originally Posted by tanogirl

Forward=

Y = 1.000
Z = 0.008

Backwards =

Y = -1.000
Z = -0.0062

It's a small difference but it makes the robot rotate.

The above does not agree with your previous post:

When we pull the joystick backwards the Z axis has an input greater than the Y axis input.

[tanogirl]

Yes the Y axis is greater than the Z axis but the robot still rotates when driving backwards.

[Ether]

Originally Posted by tanogirl

Yes the Y axis is greater than the Z axis but the robot still rotates when driving backwards.

Please post results for Y=0, Y=.2, Y=.4, Y=.6, Y=.8;
repeat for negative Y commands.

If all the Z values are within +/-0.0099,

try adding deadband to your code:

if (fabs(Z)<.01) Z=0;

[tanogirl]

Where would you put that in the code?

[Ether]

Originally Posted by tanogirl

Where would you put that in the code?

Right after you read the joystick Z axis (i.e. before you use it).