Mecanum Trouble

[Dawg2T4]

The wheels are arranged in the proper X as viewed from the top of the bot, as I believe they should be. Right now, sending a pure forward, backward, left, or right signal has the bot going in the right direction. The rotate, however, has all of the wheels going outward from each other (the two front go forward while the two back go backward) or all inward (front go backward, back go forward).

[Ether]

Originally Posted by Dawg2T4

The rotate, however, has all of the wheels going outward from each other (the two front go forward while the two back go backward) or all inward (front go backward, back go forward).

Which rotate command direction (clockwise or counterclockwise) corresponds to which behavior (all outward or all inward)?

[Ether]

Originally Posted by Ether

Which rotate command direction (clockwise or counterclockwise) corresponds to which behavior (all outward or all inward)?

If a rotate clockwise command causes all the wheels to run outward you need to swap the FrontRight and BackLeft motor commands.

If a rotate clockwise command causes all the wheels to run inward you need to swap the FrontLeft and BackRight motor comands.

Others here can advise you how to do that in the software, or you can swap the appropriate motor wires.

[Levansic]

Outward or inward is a bit confusing, try looking directly at the wheels from the outside of the robot, while the robot is elevated and not touching the floor. If you crank the joystick clockwise, all of the wheels should appear to turn counter-clockwise, when viewed from the outside. Take note of the ones that are going clockwise.

Go into begin.vi, and right-click on the terminal on the left side of the 4-motor drive open vi, that matches the inversion for the motors which spin clockwise. Click on the new boolean constant to turn it from false to true. Do this for all motors that are turning the wrong way.

If you have trouble finding the motor inversion terminals (which likely are unconnected), use Control-H to bring up the context-sensitive help, and mouse over the drive open vi.

All of this assumes that your motors are called in the correct position. In most cases, you will likely have to invert two of the four motors.

[Ether]

Originally Posted by Levansic

Outward or inward is a bit confusing

He defined exactly what he meant by those terms in his earlier post:

Originally Posted by Dawg2T4

The rotate, however, has all of the wheels going outward from each other (the two front go forward while the two back go backward) or all inward (front go backward, back go forward).

... but he didn't clearly specify which rotate command (clockwise or counterclockwise) was causing which wheel motion ("outward" or "inward").

Originally Posted by Levansic

If you crank the joystick clockwise, all of the wheels should appear to turn counter-clockwise, when viewed from the outside. Take note of the ones that are going clockwise.

Go into begin.vi, and right-click on the terminal on the left side of the 4-motor drive open vi, that matches the inversion for the motors which spin clockwise. Click on the new boolean constant to turn it from false to true. Do this for all motors that are turning the wrong way.

If he does what you recommended above, it will fix the rotate problem, but break the forward/reverse and strafe right/left motions which are presently working correctly.

What he needs to do is swap the FrontRight and BackLeft motor commands (if the rotate clockwise command is causing the wheels to turn "outward") or swap the FrontLeft and BackRight motor commands (if the rotate clockwise command is causing the wheels to turn "inward").

All of this assumes that your motors are called in the correct position.

They are not. That's the problem.

[Ether]

Originally Posted by Ether

What he needs to do is swap the FrontRight and BackLeft motor commands (if the rotate clockwise command is causing the wheels to turn "outward") or swap the FrontLeft and BackRight motor commands (if the rotate clockwise command is causing the wheels to turn "inward").

The attached chart shows the situation if OP meant to say that a rotate clockwise command
caused the front wheels to rotate forward and the back wheels to rotate backward.

• Green means wheel rotation forward
• Red means wheel rotation backward
• Columns B D F H J L show what it should be
• Columns labeled "?" show what it is actually doing (per OP's testing)

As you can see, swapping the FrontRight and BackLeft motor commands will correct the problem:

• the RCW and RCC will be corrected, and
• the already correct FWD, REV, STR, & STL will be unaffected

[Dawg2T4]

Just for some clarification, when you say swap the Front Right and Back Left motors, do you mean within the HolonomicDrive.vi, or is there a place within the teleop.vi to do that? Our Build session starts in about half an hour, so we can tell how well it worked then.

[Ether]

Originally Posted by Dawg2T4

Just for some clarification, when you say swap the Front Right and Back Left motors...

Just to be clear, I said swap the motor commands, not the motors. This can be accomplished in software, or in hardware by swapping the motor wires (while leaving the motors themselves unmoved). Swapping the physical motors themselves would serve no purpose here.

do you mean within the HolonomicDrive.vi, or is there a place within the teleop.vi to do that? Our Build session starts in about half an hour, so we can tell how well it worked then.

I don't do LabVIEW. Do whatever you have to do so that the motor commands are swapped. What that means is this:

• the command that presently is going to the FrontRight motor should be sent instead to the BackLeft motor, and
  
  
• the command that presently is going to the BackLeft motor should be sent instead to the FrontRight motor

I think that can be accomplished in the Begin vi, wherever you assign the CAN addresses for the 4 motor locations. If there are any LabVIEW gurus reading, please chime in here.


PS: you never did answer this post. It's important; it determines which motor commands should be swapped.

[Dawg2T4]

Sending the robot a clockwise signal makes all of the wheels turn inward towards each other. When we made the change for the motor commands all it did was changed the strafing to the all in/out command and changed what we wanted the rotation to be to strafing.

[Dawg2T4]

Here's a screenshot of our code, just to reiterate, this is the code that has forward, backward, and strafing correct but has a problem with rotating. When we try to rotate clockwise the robots wheels all run inward (meaning, the two front wheel go backward and the two back wheels go forward) and when we try to rotate counterclockwise the wheels go outward (the two front go forward and the two back go backward).

Begin

[IMG][/IMG]

Holonomic

[IMG][/IMG]

Teleop

[IMG][/IMG]

[Ether]

Originally Posted by Dawg2T4

Sending the robot a clockwise signal makes all of the wheels turn inward towards each other.

If that's the case, the change you should have made, according to previous posts, is to swap the FrontLeft and BackRight motor commands. Is that what you did?

If not, undo what you did and make the correct change.

Originally Posted by Ether

PS: you never did answer this post. It's important; it determines which motor commands should be swapped.

Originally Posted by Ether

What he needs to do is swap the FrontRight and BackLeft motor commands (if the rotate clockwise command is causing the wheels to turn "outward") or swap the FrontLeft and BackRight motor commands (if the rotate clockwise command is causing the wheels to turn "inward").

Originally Posted by Ether

If a rotate clockwise command causes all the wheels to run outward you need to swap the FrontRight and BackLeft motor commands.

If a rotate clockwise command causes all the wheels to run inward you need to swap the FrontLeft and BackRight motor commands.

[REDBARON]

Originally Posted by Ether

If that's the case, the change you should have made, according to previous posts, is to swap the FrontLeft and BackRight motor commands. Is that what you did?

Yes that is what we have done, we have tried it swapped and not swapped and neither ways work, when swapped if we give a pure clockwise command both sides run inward, sorry if I am repeating things, I just want to make sure everything is clear,
-Jack

[Ether]

Originally Posted by Dawg2T4

Sending the robot a clockwise signal makes all of the wheels turn inward towards each other. When we made the change for the motor commands all it did was changed the strafing to the all in/out command and changed what we wanted the rotation to be to strafing.

What change did you make?

Looks like the change was not done properly.

Please post LabVIEW png snippet of before & after code.

[REDBARON]

Originally Posted by Ether

What change did you make?

Looks like the change was not done properly.

Please post LabVIEW png snippet of before & after code.

Before:
http://s278.photobucket.com/user/Daw...tml?sort=3&o=1

After:
http://s278.photobucket.com/user/Daw...tml?sort=3&o=0

[Ether]

Originally Posted by Dawg2T4

Sending the robot a clockwise signal makes all of the wheels turn inward towards each other. When we made the change for the motor commands all it did was changed the strafing to the all in/out command and changed what we wanted the rotation to be to strafing.

I don't know what change you made, but it didn't swap the suggested motor commands. The behavior described above is not consistent with the change suggested.

Swapping the FL&BR motor commands should have had no impact at all on the strafe command. And it should have corrected the rotate behavior.

This is assuming that you have provided accurate test data about wheel direction in response to fwd/rev and strafe left/right as shown in the attached chart.

Would you please post the before and after code as a LabVIEW PNG snippet as an attachment here on CD.