Drive Train motors are out of sync

[jojoguy10]

Hello!

Our team is having some issues with our drive train motors. Here are the details:
4 CIM motors
2 Sonic Shifters
CAN (not PWM) Jaguars
2 Encoders (not programmed)

Here's what's happening:
We run both sides (tank drive) at full speed (using regular Logitech Attack 3 joysticks), but one side is much more responsive and over faster than the other side. When we measured the output voltage, 3 out of 4 Jaguars were at around 11.90 Volts, but ONE jaguar (remember, this was at 100% power), was at about 12.20 Volts!

We do not have the encoder setup, but we will if it will help fix this issue.

Here's a quick video of the problem: http://www.youtube.com/watch?v=aUeHCK5DEBA&feature=youtu.be

Thanks!

[Kevin Selavko]

Cant you set Jags on can to output a certain voltage, I think you can but I dont specifically know how to. If your using the 2CAN you could also easily see what all the jags are sending to the motors and receiving from the PDB to help you with your troubleshooting.

[jojoguy10]

Cant you set Jags on can to output a certain voltage, I think you can but I dont specifically know how to. If your using the 2CAN you could also easily see what all the jags are sending to the motors and receiving from the PDB to help you with your troubleshooting.

I'll look into that. We ran out of time last night, sadly, but I DO want to make a simple program to see the voltage output and set it precisely.

I'll post back with my findings when I get them (hopefully soon :-/ )

Thanks!

[DonRotolo]

There is a calibration method that may help equalize the output voltages.

You may have mechanical issues that cause one side move slower than the other, or that cause the robot to track not perfectly straight.

Using encoders, you can force the 'faster' side to slow down to match the 'slower' side in software.

[Mark McLeod]

Jaguar Calibration Procedure

1. Hold down the USER switch with a straightened paperclip.
2. After 5 seconds, the LED flashes Red and Green quickly to indicate Calibration mode.
3. Instruct the controller to send a full-forward signal.
4. Instruct the controller to send a full-reverse signal.
5. Instruct the controller to return to a neutral signal.
6. The LED flashes Green and Yellow quickly to indicate a successful calibration. (Red & yellow means failure to calibrate)
7. Release the USER switch.Jaguar Getting Started Guide (http://content.vexrobotics.com/docs/217-3367-VEXpro_Jaguar_GettingStartedGuide_20130215.pdf) page 11

You'll also see some minor voltage differences if a wire run is much shorter (or longer) than the others.

[kbrowncny]

One of the things that our team noticed last year is that that one side would move faster than the others because of the way in which the CIMS are oriented. Inside your motors are wire windings, depending on which direction they are wound gives a mechanical bias in one direction.. Typically on a tank drive your motors are in oriented on the opposite side of the robot, which can cause the motors to have reverse winding directions...

Best way to fix this would be to regulate down the voltage on one side. Hope this helps :)

[jojoguy10]

Jaguar Calibration Procedure

1. Hold down the USER switch with a straightened paperclip.
2. After 5 seconds, the LED flashes Red and Green quickly to indicate Calibration mode.
3. Instruct the controller to send a full-forward signal.
4. Instruct the controller to send a full-reverse signal.
5. Instruct the controller to return to a neutral signal.
6. The LED flashes Green and Yellow quickly to indicate a successful calibration. (Red & yellow means failure to calibrate)
7. Release the USER switch.Jaguar Getting Started Guide (http://content.vexrobotics.com/docs/217-3367-VEXpro_Jaguar_GettingStartedGuide_20130215.pdf) page 11

You'll also see some minor voltage differences if a wire run is much shorter (or longer) than the others.

That part of the Getting Started Guide is for PWMs. WIll it matter if it's CAN instead (which is what we're using)?

[Mark McLeod]

My apologies, the calibration isn't necessary when you're using CAN commands to drive the Jaguar.

[yash101]

Try calibrating your code. Add a multiplier to the speed on one side to make sure each side runs at the same speed!

So when you get the joystick values and input them into the Jaguars, just add: [multiplier]*[input], e.g. .93*spdx.
Until you get your encoders, this is a cheap-and-dirty way to get the motors calibrated! I wish FRC could legalize some brushless motors/ESCs. That would be safer, lower-maintenance, cheaper and more reliable. Brushless motors can be commutated to get an exact output angluar velocity(RPM)!