Chief Delphi - Can Victor and Jaguar motors work together on a single gearbox?

Chief Delphi (http://www.chiefdelphi.com/forums/index.php)

- Motors (http://www.chiefdelphi.com/forums/forumdisplay.php?f=52)

- - Can Victor and Jaguar motors work together on a single gearbox? (http://www.chiefdelphi.com/forums/showthread.php?t=124585)

AdamWiwc

13-01-2014 16:08

Can Victor and Jaguar motors work together on a single gearbox?

We have three Victor motor controllers and two Jaguar motor controlers, can we put those together on a single gearbox so that we have two motors on each side of the robot totaling of four motors? Is it a better idea to use one of each type on either side or two Jaguars on one side and two Victors on the other?

Thanks for your time.
Team 5185
The dial up grizzlys

apalrd

13-01-2014 16:10

Re: Can Victor and Jaguar motors work together on a single gearbox?

It's not really recommended to do anything but all the same controllers for the drive motors.

If I was in your case, I would put a Victor and a Jaguar on each side. While this could lead to unequal loading of the two CIMs at any part load point, IMHO it's better than the robot drifting to one side because of controller difference.

Jon Stratis

13-01-2014 16:10

Re: Can Victor and Jaguar motors work together on a single gearbox?

The Victors, Jaguars, and Talons all have different response curves - meaning if you told them all to go the same speed in the code, the actual results would be a little different. Thus, it's not recommended that you use different speed controllers with the same gear box. Also, for good control of your robot I would make sure all the speed controllers on the drive train are the same!

Domtech

13-01-2014 16:15

Re: Can Victor and Jaguar motors work together on a single gearbox?

Generally no, the pwm rates for Victors and Jaguars are different, so they would not work off a splitter. Additionally they provide different powers at the same joystick position unless you do a bunch of fancy programming to equalize the 2.(I have not heard of anyone attempting this)

It is recommended to always use the same controllers for multi-motor gearboxes.

Ether

13-01-2014 17:11

Re: Can Victor and Jaguar motors work together on a single gearbox?

Quote:

Originally Posted by Domtech (Post 1326593)

Generally no, the pwm rates for Victors and Jaguars are different, so they would not work off a splitter.

Yes they would. Both Vics and Jags will operate properly with PWM period ranging from 5m to 20ms.

Quote:

Additionally they provide different powers at the same joystick position unless you do a bunch of fancy programming

True for the Vic884, not so much for the Vic888. Even so, all it means is that one motor is carrying more load than the other.

Seth Mallory

16-01-2014 23:35

Re: Can Victor and Jaguar motors work together on a single gearbox?

You have a lot of teams in Calgary and you can possibly trade with one of them. It could be quicker and if you are on a budget you can save the purchase price. Teams in our area have loaned and traded parts for years when needed.

Mr. Lim

17-01-2014 07:01

Quote:

Originally Posted by AdamWiwc (Post 1326587)

We mixed jaguars and victors on our 6 motor drivetrain last year. 2 Victor 888s and 1 jaguar per side.

While it works, we noticed the jaguar motors working much harder than the Victor ones, and had to write some code to rebalance everything. The jaguar motors were heating up while the Victor motors weren't.

DonRotolo

18-01-2014 20:44

Re: Can Victor and Jaguar motors work together on a single gearbox?

Precisely.

The answer to the OP is "yes". But: Some motors will work harder than others, because the curves for the controllers are different.

Ether

18-01-2014 21:11

Re: Can Victor and Jaguar motors work together on a single gearbox?

Quote:

Originally Posted by Mr. Lim (Post 1328409)

we noticed the jaguar motors working much harder than the Victor ones ... The jaguar motors were heating up while the Victor motors weren't.

OK CD community: What's the underlying physical explanation for why this happens?

@Mr Lim: Just to eliminate one possibility: Are you certain the brake/coast settings were identical on all controllers?

Richard Wallace

18-01-2014 21:17

Re: Can Victor and Jaguar motors work together on a single gearbox?

Quote:

Originally Posted by Ether (Post 1329058)

OK CD community: What's the underlying physical explanation for why this happens?

When a Jag and a Vic are shown the same PWM signal, which develops more voltage at its motor terminals?

Ether

18-01-2014 21:20

Re: Can Victor and Jaguar motors work together on a single gearbox?

Quote:

Originally Posted by Richard Wallace (Post 1329060)

When a Jag and a Vic are shown the same PWM signal, which develops more voltage at its motor terminals?

RMS or arithmetic average ?

Richard Wallace

18-01-2014 21:32

Re: Can Victor and Jaguar motors work together on a single gearbox?

Quote:

Originally Posted by Ether (Post 1329062)

RMS or arithmetic average ?

Let's go with arithmetic average for now. ;)

Mr. Lim

18-01-2014 21:33

Re: Can Victor and Jaguar motors work together on a single gearbox?

Quote:

Originally Posted by Ether (Post 1329058)

I'd like to hear an explanation for this one. Although I'd have to check the PWM / Voltage curves more carefully, my guess is because the Jags have a more linear response, in general for any given PWM signal they would produce a higher (magnitude) voltage than a Victor, except for at the extremes, where they would be the same (Vbatt).

Yes, I am certain both would have been on coast.

Our drivetrain runs open loop most of the time, and we do check that all speed controllers on it are specifically set to coast.

Mr. Lim

18-01-2014 21:34

Re: Can Victor and Jaguar motors work together on a single gearbox?

Quote:

Originally Posted by Ether (Post 1329062)

RMS or arithmetic average ?

RMS, assuming we drive both forwards and backwards... or turn!

Ether

18-01-2014 22:05

Re: Can Victor and Jaguar motors work together on a single gearbox?

Quote:

Originally Posted by Mr. Lim (Post 1329066)

Yes, I am certain both would have been on coast.

Are you also certain that:

all the controllers were properly calibrated

and

your code was using the appropriate input pulse width range for the Jags and the 888s?

Ether

18-01-2014 22:07

Re: Can Victor and Jaguar motors work together on a single gearbox?

Quote:

Originally Posted by Mr. Lim (Post 1329066)

I'd like to hear an explanation for this one.

Do you still have last year's bot?

Could you bring it back to life and run a few quick tests?

1) wheels up (bot on blocks): test voltage* at Jag's and 888's motor outputs at several throttle settings

2) bot pushing against a wall: carefully repeat above test with low throttle settings (to avoid overheating)

* measure both true RMS and arithmetic average. true RMS requires a voltmeter that specifically has that capability.

Ether

18-01-2014 22:42

Re: Can Victor and Jaguar motors work together on a single gearbox?

Quote:

Originally Posted by Ether (Post 1329079)

Are you also certain that:

all the controllers were properly calibrated

and

your code was using the appropriate input pulse width range for the Jags and the 888s?

Quote:

Originally Posted by Ether (Post 1329081)

Do you still have last year's bot?

Could you bring it back to life and run a few quick tests?

Pending answers to the open questions and results from any testing Mr Lim (or anyone else) is able/willing to do, my working hypothesis is that the answer lies somewhere in this code:

Code:



/**

 * Common initialization code called by all constructors.

 */

void Jaguar::InitJaguar()

{

        /*

         * Input profile defined by Luminary Micro.

         * 

         * Full reverse ranges from 0.671325ms to 0.6972211ms

         * Proportional reverse ranges from 0.6972211ms to 1.4482078ms

         * Neutral ranges from 1.4482078ms to 1.5517922ms

         * Proportional forward ranges from 1.5517922ms to 2.3027789ms

         * Full forward ranges from 2.3027789ms to 2.328675ms

         * TODO: compute the appropriate values based on digital loop timing

         */

        SetBounds(251, 135, 128, 120, 4);

        SetPeriodMultiplier(kPeriodMultiplier_1X);

        SetRaw(m_centerPwm);



        nUsageReporting::report(nUsageReporting::kResourceType_Jaguar, GetChannel(), GetModuleNumber() - 1);

}











/**

 * Common initialization code called by all constructors.

 * 

 * Note that the Victor uses the following bounds for PWM values.  These values were determined

 * empirically through experimentation during the 2008 beta testing of the new control system.

 * Testing during the beta period revealed a significant amount of variation between Victors.

 * The values below are chosen to ensure that teams using the default values should be able to

 * get "full power" with the maximum and minimum values.  For better performance, teams may wish

 * to measure these values on their own Victors and set the bounds to the particular values

 * measured for the actual Victors they were be using. 

 *   - 210 = full "forward"

 *   - 138 = the "high end" of the deadband range

 *   - 132 = center of the deadband range (off)

 *   - 126 = the "low end" of the deadband range

 *   - 56 = full "reverse"

 */

void Victor::InitVictor()

{

        // TODO: compute the appropriate values based on digital loop timing

        SetBounds(210, 138, 132, 126, 56);

        SetPeriodMultiplier(kPeriodMultiplier_2X);

        SetRaw(m_centerPwm);



        nUsageReporting::report(nUsageReporting::kResourceType_Victor, GetChannel(), GetModuleNumber() - 1);

}





/**

 * Set the bounds on the PWM values.

 * This sets the bounds on the PWM values for a particular each type of controller. The values

 * determine the upper and lower speeds as well as the deadband bracket.

 * @param max The Minimum pwm value

 * @param deadbandMax The high end of the deadband range

 * @param center The center speed (off)

 * @param deadbandMin The low end of the deadband range

 * @param min The minimum pwm value

 */

void PWM::SetBounds(INT32 max, INT32 deadbandMax, INT32 center, INT32 deadbandMin, INT32 min)

{

        if (StatusIsFatal()) return;

        m_maxPwm = max;

        m_deadbandMaxPwm = deadbandMax;

        m_centerPwm = center;

        m_deadbandMinPwm = deadbandMin;

        m_minPwm = min;

}

Mr. Lim

18-01-2014 23:27

Re: Can Victor and Jaguar motors work together on a single gearbox?

They were Jags and Victor 888s.

The Jags were not calibrated, as we found they came out of the box with acceptable centring, and consistent extremes.

The Victors we did calibrate. We noticed that uncalibrated, the problem was even worse. Calibrating them helped slightly, but did not solve the issue entirely.

We program in Java, and instantiated the proper object classes for everything, so the pulse widths should have been proper for each.

Unfortunately, we don't have the time to take out last year's robot right now. It was involved in the 2015 Alpha Testing, and has been significantly re-wired and re-programmed as a result.

Tem1514 Mentor

19-01-2014 10:15

Re: Can Victor and Jaguar motors work together on a single gearbox?

The quick answer is one motor is being run as a generator due to the difference is applied voltage/current/duration (it is a chopper drive circuit).

An application of this is the tread mill drive clean test for cars. aka dyno

Ether

19-01-2014 15:15

Re: Can Victor and Jaguar motors work together on a single gearbox?

Quote:

Originally Posted by Tem1514 Mentor (Post 1329257)

The quick answer is one motor is being run as a generator

That quick answer is not true.

The difference in voltage would have to be so large that the higher-voltage motor was driving the system at a speed exceeding the lower-voltage motor's free speed*. Not likely.

What actually happens is that the higher-voltage motor carries more of the load. It supplies more torque and power. So it tends to get hotter.

The lower-voltage motor is still generating torque and supplying power to the load as long as the speed is lower that that motor's free speed at that voltage.

* at its lower voltage

Richard Wallace

19-01-2014 15:24

Re: Can Victor and Jaguar motors work together on a single gearbox?

Quote:

Originally Posted by Ether (Post 1329362)

... What actually happens is that the higher-voltage motor carries more of the load. It supplies more torque and power. So it tends to get hotter.

Ether's right, as usual.

The 2015 PDB with its datalogging feature will make it easier for more teams to see this effect directly.

dsirovica

19-01-2014 17:21

Re: Can Victor and Jaguar motors work together on a single gearbox?

To conclude:
Different controllers is not recommended, but if needed can be used. The only negative result may be that one motor works harder than the other and will get hotter.

On a related topic: what do people think are the issues with using different motors on the same gearbox (with same controllers). Eg. A CIM and a mini-CIM? My gut level tells me that is perfectly fine, but a soon-to-be Mech Engineer told me that there will be a "torque fight" and that we should adjust each motors' power via a lookup table that we should develop by actual measurements of each of the motors.

Ether

19-01-2014 17:27

Re: Can Victor and Jaguar motors work together on a single gearbox?

1 Attachment(s)

Quote:

Originally Posted by dsirovica (Post 1329411)

On a related topic: what do people think are the issues with using different motors on the same gearbox (with same controllers). Eg. A CIM and a mini-CIM? My gut level tells me that is perfectly fine, but a soon-to-be Mech Engineer told me that there will be a "torque fight" and that we should adjust each motors' power via a lookup table that we should develop by actual measurements of each of the motors.

There's no "torque fight" until you reach the free speed of the motor with the lower free speed (the CIM in this case). Above that speed, the CIM acts as a generator (causing negative torque). However, you'll likely not reach that speed in a typical FRC application (e.g. drivetrain).

You can't adjust the motor's power without knowing the motor's speed. But if you want to assume a given operating speed, you can adjust the motor commands to match power or current.

Ether

19-01-2014 17:42

Re: Can Victor and Jaguar motors work together on a single gearbox?

Quote:

Originally Posted by dsirovica (Post 1329411)

To conclude:
Different controllers is not recommended

I would make a distinction between

a) I recommend that you not do that

and

b) I don't recommend that you do that (but I don't say not to either). In other words, the jury is still out.

I'm in the (b) camp.

Quote:

The only negative result may be that one motor works harder than the other and will get hotter.

We don't know for sure yet that's the only negative result, but it seems to be the case. In any event, two things appear to be true:

1) one motor working harder than the other happens all the time even with the same model motors and motor controllers, albeit on a smaller scale, due to manufacturing tolerances and wear.

2) it can be mitigated in code by running the joystick outputs through a simple LUT or polynomial.

Mr. Lim

19-01-2014 17:56

Re: Can Victor and Jaguar motors work together on a single gearbox?

Okay, I'll chime in with my conclusion:

Yes, a Victor and a Jaguar can work together on a single gearbox.

BUT,

It won't work well unless you code something to compensate for the unbalanced load sharing between the two different types.

dsirovica

19-01-2014 19:00

Re: Can Victor and Jaguar motors work together on a single gearbox?

Thanks Ether for your thorough post (as always!)

I realize this is not quite the correct thread for different motors with same controllers on one gearbox. But to close on that one. Based on your posted Torque/RPM charts, in most properly sized applications one is not likely to run anywhere near the free running speed of the slower motor.

On the correct thread, I do think one needs to be careful when mixing motor controllers. The easiest way would be to check the current into each motor with a DC Amp Clampmeter and make sure they are reasonably close. The power dissipation in the motor is roughly I^2R*, so any difference in I(A) will cause an exponential difference in Power per motor. To fix it you can use a LUP (as mentioned before) but given all the hassle - I would just avoid it - its bad practice anyway.

*R is a fusion of restive R and back-emf, but since they should be nearly the same for same motors its a fair assumption (I see a sledge hammer coming down on me from Ether on this one? ::ouch:: )

Ether

19-01-2014 19:24

Re: Can Victor and Jaguar motors work together on a single gearbox?

Quote:

Originally Posted by dsirovica (Post 1329446)

...The power dissipation in the motor is roughly I^2R*...

*R is a fusion of restive R and back-emf, but since they should be nearly the same for same motors its a fair assumption (I see a sledge hammer coming down on me from Ether on this one? ::ouch:: )

OK, here comes the hammer:

The "R" in I²R is resistance, and has nothing to do with back-emf.

(The "I" is RMS current)

dsirovica

19-01-2014 19:40

Re: Can Victor and Jaguar motors work together on a single gearbox?

True (hm - that is a redundant statement for characterizing Ether's posts),

what I meant to say was this:

P(motor heating)=I^2R
But I is not purely Vbatt/Rmotor, it is:
I= (Vbatt-Vback-emf)/Rmotor

Therefore each motor will have its own R and its own Back-emf characteristics. If they are the same model and same vintage these characteristics are likely very close to each other.

Ether

19-01-2014 19:46

Re: Can Victor and Jaguar motors work together on a single gearbox?

Quote:

Originally Posted by dsirovica (Post 1329454)

I meant to say was this:

P(motor heating)=I^2R
But I is not purely Vbatt/Rmotor, it is:
I= (Vbatt-Vback-emf)/Rmotor
.

That's closer. "Vbatt" should be Vmco (motor controller output). But depending on the motor's inductance and the motor controller's switching frequency, there may be ripple current. That causes extra motor heating and power loss. (That's why I said "I is RMS current").

AdamWiwc

20-01-2014 15:50

Re: Can Victor and Jaguar motors work together on a single gearbox?

Thank you everyone for your help and support. We have the situation all sorted out now and all of us at Team 5185 appreciate it immensely.

Team 5185
Dial Up Grizzlies

Seth Mallory

21-01-2014 08:48

Re: Can Victor and Jaguar motors work together on a single gearbox?

What was your final solution?

All times are GMT -5. The time now is 05:36.