I’m willing to try 1 Victor 888, 1 Talon on each side of my drivetrain. I really don’t see a problem in doing it. What kind of measurements should I try and take?
The effect would be neglegible. However, the different handling of motor controllers means that one motor would go through much more abrasion than the other.
While there are safety diodes, one motor may generate enough backflow because of reverse electro-motiv force, to destroy MOSFETs on these motor controllers. However, this is typically negligible!
It’s funny how basic physics can explain so much :D. #ILovePhysics
How would one motor go through much more abrasion?
It won’t be pushing as much, so one motor will have to work harder to speed the other slacker up
Okay, but in this situation the motors are mechanically linked and spinning at the same speed, so how much does this difference in voltage/current cause much more abrasion?
Skidsteer drivetrain, with 2 gearboxes with one Vic and one Talon per gearbox?
Or four gearboxes with one motor per gearbox?
Assuming the former, here are some ideas, in no particular order:
Just drive it around and see if it behaves normally. No weird noises or odd behavior.
If everything seems OK, do hi speed, lo speed, pushing, turning, reverse, fast throttle changes, etc.
Feel both motors on both sides and see if there’s a noticeable difference in temperature (e.g. are both Vic-driven motors hotter than their Talon mates, or vice-versa).
If you can instrument your bot to measure current, that would be excellent, but may be more work than you have time for.
It won’t be pushing as much, so one motor will have to work harder to speed the other slacker up
This happens all the time. All motors are not created equal. Neither are all motor controllers.
Not quite. There are NO DIODES (on the outputs) on the controllers we use. The diodes would waste roughly 10% of the power by dissipating it as heat.
Also, the MOSFETs are set up so that if the robot is off, and you push it along, the power goes back and powers on the robot, no harm done. If you run while pushing the robot, you can get the cRIO to turn on.
We’re planning on a skid steer. 1 gearbox on eachside.
I was thinking the same thing.
The Talon seems to be a bit more efficient (less voltage loss through the controller), providing effectively a higher motor output than the Jaguars do. Also, back current is handled differently if the wheels were manually turned on the drivetrain.
Having said that, there is a slight loss in efficiency overall but its mostly negligible, and certainly not dangerous. I would think the variance in motor performance due to wear/damage and the imperfections in the drivetrain (gear meshing, etc) would outweigh the difference in speed controllers.
To tell you the truth, it really comes to aesthetics, using the same component everywhere, and tidying the code up a bit by using similar code!
Not disagreeing, but I’m wondering what you mean by “seems to be”. What observations gave you that impression?
back current is handled differently
Can you provide a link to the source of this info? I’m wondering if it’s still true for the new Talons (changed switching method).
Having said that, there is a slight loss in efficiency overall but its mostly negligible, and certainly not dangerous. I would think the variance in motor performance due to wear/damage and the imperfections in the drivetrain (gear meshing, etc) would outweigh the difference in speed controllers.
That’s my working hypothesis, until disproven (by hard data or sound theoretical reasoning).
Everyone up to this point hasn’t touched on what I would think is a very important(and not too difficult) solution for any problems this might cause: gyro correction code. As Ether said, not all motors or motor controllers are created equal. In fact, no motors or motor controllers are created equal. There will always be minor differences even between parts of the same model. If you add a gyroscope to your robot, however, along with some code to automatically correct your output voltages if it starts to veer off course, you solve this problem pretty effectively. It allows you to mix and match motor controllers(we try not to, but it’s handy for emergency repairs), and our drivers can always drive in a straight line without having to compensate for any possible difference in the motors.
So now I’m interested: how do other teams feel about this?
Well the original subject was whether or not using a talon and jaguar to drive 2 cims on each side of the drive train (with pparently 1 gearbox on each side) would cause any problems. Then subsequently the OP asked about 1 talon and 1 victor 888 combo.
In this situation the veering you’re talking about wouldn’t be caused by the motor controller combination.
I don’t see why it couldn’t be–your correction code doesn’t care what causes the veering, it just adjusts the magnitudes to compensate.
Well I’m assuming the same motor controller combination on each side(left and right), i.e, 1 talon and 1 jaguar, 1 talon and one victor 888, or 1 victor 888 and 1 talon. Same motors, on each side, same gearbox etc. Then the veering would be cause by variations in individual motor controllers of the same or different make, motors, gearboxes etc. and not really the combination of the two different motor controllers. With the motors mechanically linked they would always spin at the same speed.
That being said I do agree that correcting for veering is useful as I have done this in the past to help correct for the variation that mainly arises after my motor output.
To borrow from Ether, why do you think that it comes down to aesthetics?
I’m interested in this question too. My gut tells me that you might have some programming fun (I don’t know what the controller curves are like), and it would be more work, but you could probably do it. That being said, I can’t say electronics and motors are my forte, so I’ll be looking into it a little bit more as time allows.
We did some low speed maneuvers today with 1 talon and 1 victor 888 on each side of a 2 CIM configuration on the left and right sides. No noticeable problems and neither motor felt warm to the touch despite a loose bolt in one of the wheels grinding on the chassis.
We observed a while ago that running motor open as jaguar would not drive a talon. But opening as a talon would drive a jaguar. Does this make sense?
Tim