paper: Talon, Victor884, Victor888, and Jaguar speed vs torque tests

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Talon, Victor884, Victor888, and Jaguar speed vs torque tests
by: Ether

Test conducted at Whirlpool motor lab, Oct31 & Nov01

Test conducted at Whirlpool motor lab, Oct31 & Nov01

dynamometer brake: Magtrol model HD705, with moment of inertia 15 kg-cm^2.

dynamometer controller: Magtrol model DSP6001

dynamometer data collecting software: Magtrol M-test.

UPDATED VERSIONS ARE AT THE BOTTOM OF THE LIST BELOW

Motor Controller Speed vs Torque tests.pdf (760 KB)
Motor Controller Speed vs Torque tests revA.pdf (812 KB)
Motor Controller Speed vs Torque tests revB.pdf (1.71 MB)
RPM vs Nm raw data.zip (77.8 KB)

That’s great.

Could you use the same axis settings for all graphs, to make it easier to compare?

How were the PWM pulse widths chosen?

Ether did these tests in my lab. The PWM pulse widths were selected to provide a range, in 50 us increments, that fully exercised each controller; i.e., we increased the pulse width until further increases did not yield increased speed. This limit was different for each controller.

I see what you mean about the axis settings – while they are all the same physical size, the torque axis tick labels and gridlines for the Victor 888 do not include odd multiples of 0.1 N-m, as the other do. However, if you blink between the graphs for different controllers there is no shift in scale or origin, so they are actually quite easy to compare.

Ether, if I examine the graph for the CIM with the Victor 884, it shows that at the top PWM setting, the Victor gives significantly less power than any other of the motor controlers. Di you simply not go to the top PWM setting for that motor controler? Is the 884 truely weaker?

Also, your results seem to show that the motor curves, even at full power, are slightly diferent across motor controlers. Is this an artifact of the testing? If it has to do with the electronic characteristics of the motor controlers, could you elaborate on the design implications?

It was an oversight. I have the data but it did not make it into the graph. I will post an update later this evening.

…your results seem to show that the motor curves, even at full power, are slightly diferent across motor controlers. Is this an artifact of the testing? If it has to do with the electronic characteristics of the motor controlers, could you elaborate on the design implications?

The switching method, output PWM frequency, parts selection, and circuit design of a controller can affect the motor performance.

Nice work, very useful.
Could we get the raw data in a spreadsheet, CSV or txt file format so we can import for use in other analysis programs? Thanks.

Thank you for the update.

I was wondering more about the possability of diferent motor controlers being slightly more optimal for diferent applications. For example, the Talon appears to have slightly more power at high load compared to a Jaguar. Does this mean that it would be better for an application where spikes into high load are expected, such as an elevator? Or is this just another artifact of testing and graphing?

Also, to give more concrete numbers it would be nice if you could upload the Excel files you used for the graphs. I always find a table easier to use for motor curves.

*RevA has been posted. It includes 2.00 and 2.10 ms curves for the 884 graph. Also the tic marks on the 888 torque axis were changed to match the other graphs.

The graphs were created with gnuplot, and the raw data does not contain metadata identifying the plots. I’ll work on that after I finish processing and posting the results of the inrush current tests.

Nice work Ether,

if its not too hard to do, it would be great to see a plot taken all the way to stall and show the Current drawn for Highest PWM, for the FRC approved speed controllers.

I suspect many/most robots are not designed to operate in the optimal range, but are driven to operate in the extreme regions, so it would be a great teaching tool to show the inefficiency when operating in the extreme, and therefore the importance of good design.

This would also show the Jag cutting out way before a Vic does. Though the 2013 Jags apparently will not have a current limit?

Dean

*Updated revB posted. Four graphs were added to present the same data as a family of RPM vs PWM curves at constant torque.

OK guys. The raw data has been posted. Knock yourselves out. :slight_smile:

Also, the inrush current test results have now been posted. You can find them here.

Give me some love.

Does the 888 have the same ~50Hz update rate that its predecessor did? What is the frequency of the modulated output?

I’ve been told by a very reliable source that the output PWM frequency is 1000Hz. That’s responsible for the reduction in current ripple and the improved linearity.

I think the input PWM signal period remains at 17ms since I’ve not heard otherwise.

For reference, what are the output PWM frequencies of the 884, Talon, and Jaguar?

Output PWM frequency:

884…150 Hz

888…1 KHz

Jaguar…15 KHz

Talon…15 KHz

Input PWM signal period:

884…10ms WPILib driver (default value)*****

888…no WPILib driver yet

Jaguar…5ms WPILib driver (default value)*****

Talon…no WPILib driver yet

all the motor controllers are capable of periods of 5ms or less

***** this is info I’ve picked up from CD. I’ve not personally vetted it.

There seems to be some confusion regarding the input PWM signal period that VEX Robotics published. The 17ms input signal period in our documentation for the Victor 884 was the typical number used on the old IFI control system.

Both the Victor 884 and 888 can support (and has been tested to support) down to 2.1ms.

Sorry for the confusion.

Paul

*Thanks for the info Paul. For completeness, do you know the minimum period that the Jag can support?

Unless Paul’s team have changed it, the minimum PWM period for Jaguars is 5 ms (i.e. 200 Hz). This coincides with the cRIO capabilities. Jaguar was designed to work specifically with the cRIO for FIRST.

A period faster than 5 ms is great, but doesn’t provide any benefit for FRC applications (unless jhersh updated the FPGA and I didn’t get the memo).

-Scott

Scott,

We did not change it. It is still 5ms.

All,

To be clear, we did not do anything new with regards to the PWM input on the Victor 888. It has always been 2.1ms on the 884, but we just did a bad job documenting that fact.

Paul

The Talon input is interrupt driven so it can be updated at ~2.1 ms. We published 3 ms to add conservatism for variations due to calibration points and non standard pulse widths.

If the input pulse produces a rising and falling edge the Talon will process it.