Awkward macnum drive issues

[Dustin Shadbolt]

Hello guys I'm stumped about something. We are using a macnum drive with 4 victors controlling the drive. The left side of the drive is outputting roughly 7volts. The right side is outputting about 9volts. The back-left and front-left are the exact same 7volts. The right side is exactly the same 9 volts. At first we thought something programming wise, but I'm not sure what would cause this issue. I believe it's something along the lines of hardware, but I could be wrong. The drive is a direct-drive system with the nano tubes and what not. Could it be an issue of balance? I imagine the balance on the wheels would actually effect the outcome of the system. As you can see, I'm just completely stumped.

[Alan Anderson]

I'd like to understand your system a little better before trying to give advice. There is one thing you should check immediately, though. When you open the 4 Motor Drive in Begin.vi, you can select between Jaguar or Victor speed controllers. Make sure it matches what you are actually using on the robot.

[j.cole]

Have you double checked your victors (swap em with others if possible).
Have you checked your PWM's. (swap them and make sure they are in the correct ports)
Is the wiring correct on the motors.
Like above make sure your code is designated to victors and not jags.
Try using a arcade or tank drive to see if the same thing happens (to be sure if it is a hardware issue or a code issue).
Wire constants to switches to see if it is a joystick problem.
If all that doesn't work I don't know what to tell you.

[Dustin Shadbolt]

All of the programming checks out and the wiring all seems fine. Is there any way possible of stating that motors must all require let's say 9 volts and the motors will change to meet that voltage. That is our problem at the momoent :\.

[j.cole]

Not that I know of maybe someone else knows. Im thinking you might be able to go really deep in the motor VI's and see how to send a voltage to them (which might be dangerous). Aside from that I don't know what to tell you. Maybe try having an area team come and help you I guess.

[Dustin Shadbolt]

Thanks for the suggestion J.Cole. I went this morning before I headed to campus and did some bench testing. The motors all work fine in tank and in holonomic. The problem seems to be when I multiply the joystick inputs by a number to slow the drive this was giving us the major difference in voltages.

[Alan Anderson]

Originally Posted by dShad

ThaThe problem seems to be when I multiply the joystick inputs by a number to slow the drive this was giving us the major difference in voltages.

When you open your 4 Motor Drive in the Begin vi, make sure you select the Victor option from the drop-down menu underneath it. If you leave it as the default Jaguar, the different default neutral PWM values will make Victors run noticeably faster in "slow reverse" than in "slow forward".

[Aren Siekmeier]

To clarify: The 4 Motor Drive Begin block should look the attached image after selecting Victor from the menu shown.

Also, if your center of mass is off center, then you will have more weight on set of wheels, which will definitely affect driving patterns (although I'm not sure where the voltage fed to the motors comes in there). However, it sounds like this isn't the problem.

[Dustin Shadbolt]

I'm positive that we double checked if not triple-checked that to make sure it was set to victor. The victors start becoming uneven in voltage when I do the following thing in the teleop.vi (see attached picture). The purpose of the code is to reduce the speed of the drive system to make it more manageable for our driver. Is this the proper way to do it or is there something I'm missing that would cause the motors to unbalance voltage wise?

[Ether]

Originally Posted by dShad

The purpose of the code is to reduce the speed of the drive system to make it more manageable for our driver. Is this the proper way to do it or is there something I'm missing that would cause the motors to unbalance voltage wise?

I hope you're not planning on leaving that in there for competition.

By limiting your joystick output to +/-0.25 you are severely limiting the output from your motors.

It would be better to gear the motors down some more so they could operate at full voltage.

[billbo911]

Originally Posted by dShad

I'm positive that we double checked if not triple-checked that to make sure it was set to victor. The victors start becoming uneven in voltage when I do the following thing in the teleop.vi (see attached picture). The purpose of the code is to reduce the speed of the drive system to make it more manageable for our driver. Is this the proper way to do it or is there something I'm missing that would cause the motors to unbalance voltage wise?

Without probing the values while running, I can only guess at a cause.
One possibility is that when the joystick is pressed forward along the Y axis, there may be some slight X axis value other than 0 being fed to the Holonomic Drive block. This might cause what you are seeing.

"Run" the program from LV and probe both the multiplied Y and multiplied X lines feeding the Holonomic Drive block. It will give you a real feel for what is happening. If the result you see doesn't explain the issue, you will need to dig deeper.

[Mark McLeod]

Nevermind, I remembered.

You might try wiring a zero in place of the throttle rotation to be sure you aren't imparting a slight twist.

[Dustin Shadbolt]

Originally Posted by Ether

I hope you're not planning on leaving that in there for competition.

By limiting your joystick output to +/-0.25 you are severely limiting the output from your motors.

It would be better to gear the motors down some more so they could operate at full voltage.

It was just there for the build season to help with teaching the freshmen driver on how to drive the robot and what not. It will be removed from the competition code.

Tonight we are going to gear down the drive somewhat and go from there. I also found out the controller does seem to send a slight x value so i'm working on something to fix this now. Thanks guys.

[j.cole]

Here's what I did if you would like to go off of that. I'm sure there is an easier way of doing this but this way works just fine.