Re: New Talon Speed Controller
 

Updated: added linearity tests with load and the Victor looks much better. The Victor 888's should be here Thursday or Friday, so we hope to get results for them out this weekend.

Re: New Talon Speed Controller
 

How did you measure voltage? Output of speed controllers is pulsed:

http://www.chiefdelphi.com/forums/sh...64&postcount=9

Any chance of measuring loaded rpm for the speed controllers?

Re: New Talon Speed Controller
 

That's a good question for the unloaded measurements that were initially made. However, once you hook the speed controllers up to a motor, the motor essentially averages out the pulses for you. Last year we went to show the team how the speed controllers work by hooking up the output to our oscilloscope. At the time, the motors were still connected, which caused no end of confusion for me... I was expecting to see a waveform, and got a solid line at what looked like the average voltage you would expect! After the big "aha!" moment (more of a forehead slap and calling myself an idiot a few times), we unplugged the motors and saw the expected pulsed waveform.

Re: New Talon Speed Controller
 

Many DC voltmeters can read the RMS of a pulsed waveform.


Measuring loaded RPM is in their test plan. (The test plan is linked in Tom's signature)

Read Tom's most recent post in this thread. They re-ran it loaded and measured motor voltage. Motor voltage data should be similar to motor speed data, but I agree it would still be useful to compare the two.

Re: New Talon Speed Controller
 

Tom,
Just to be sure, your load in these tests is the window motor?

Re: New Talon Speed Controller
 

The way I read it Al, the window motor was the powered motor, and the load was the friction of the belt trying to drive an immobilized device:

I believe the output would have been even more linear had they used a different motor with a heavier load.

Re: New Talon Speed Controller
 

That is correct. The window motor is connected via a vacuum drive belt to a 3/8 inch steel roller. We locked the steel roller in place so that the vacuum belt was slipping. That provided a constant load on the window motor.

Re: New Talon Speed Controller
 

Tom,

For each motor controller, how long did it take to run the test and record the data?

Also, did you record the motor current (a measure of torque load) ?

Re: New Talon Speed Controller
 

Tom and Ether,
I was just trying to equalize our previous discussions with regard to motor inductance and controller type. The window motor having different inductance than that of the CIM or larger Banebot types.

Re: New Talon Speed Controller
 

I'd like to see motor inductance and rotor inertia specs for all the FRC motors. I can dream, can't I? :-)

Re: New Talon Speed Controller
 

Perhaps we can convince Rich to make that in his spare time.

Re: New Talon Speed Controller
 

Al, would using a motor with a larger inductance considerably change our results? We didn't have a ready-made clutch mechanism that would provide constant torque back to a CIM, which is why we went with the window motor setup (it was how our ball-magnet worked in 2010).

Ether - the tests were performed quickly, within a span of about 5 minutes - one person ramping the PWM value in labview, another measuring, and a third inputting into excel. We measured the battery voltage before and after and did not see significant change.

Re: New Talon Speed Controller
 

If you ran a CIM at 25% of stall torque I think you'd see a noticeably more linear curve.

I asked about the current not because of concern about battery voltage, but because current is an indication of motor load -- which affects linearity.

Re: New Talon Speed Controller
 

Yes, significantly. The non-linearity is from when the current ripple exceeds the average current. Doubling the inductance cuts the ripple in half, which in turn cuts the critical average current number by half as well.

Re: New Talon Speed Controller
 

I see. We may go back later and look at linearity when hooked to a cim. I think we want to move on and hit our other tests, then circle back around. One last question. Would holding the cim shaft completely stationary then applying different motor voltages result essentially the 'best case' for linearity from the victor? I supposed that's something we could do fairly easily. We'd just have to do it for very short periods of time to prevent breaker-popping.