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

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

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?

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

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.

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

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?

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

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.


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

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

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.

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

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.

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

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.

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

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

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

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

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

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

Give me some love.

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

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

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

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.

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

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

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

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.

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

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

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

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

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

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

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

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

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

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.

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

Paul, would it be useful to ask the folks at WPILib to change their 884 (and future 888) driver to use a period of 5ms instead of 10ms? I realize it probably makes little difference in the vast majority of cases, but there may be teams who want to close a loop at 10ms.

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

The current PWM setup in WPIlib (at least in LabVIEW) is a PWM output with a 5s period and a 'period multiplier' of 1,2 or 4. It's enumerated, so 1x, 2x, and 4x correspond to 0,1,2 respectively (I don't think you can add more multipliers if you want).

The Jaguars use a period multiplier of 1, for a 5ms period. The Victors use 2, for a 10ms period. Servos use 4, for a 20ms period, and raw PWM channels can use whatever they want (of the three choices).

All it takes to add a new motor controller (in LabVIEW) is to duplicate one of the Open blocks and change the scaling and period multiplier parameters. The Write and Read blocks will adhere to the scaling set in the Open block, and the drivers will use the period multiplier set as well.

However, the fact that the driver (in LabVIEW) uses uint8's to store full-range pulse position, so the uint8 stores the widest pulse that the library can generate and devices using a narrower range perform the scaling before converting to uint8 essentially makes the uint8 sent to the fpga the bottleneck for resolution on the entire pwm output system. So, added input resolution on any new devices (e.g. 10bit internal vs 12bit internal) makes no difference due to the 8bit limit of the library.

Looking at the library (specifically WPI_PWMConvertDeadbandMillisecondTimeTo8Bit) it looks like the u8 is a number of DIO loop ticks to hold the pulse high, and the DIO loop runs every 261 ticks of the main clock (40mhz). That would make 40mhz/261ticks the smallest interval of a pulse change possible in the fpga.

I could be wrong, but that's what I get from reading the LV code.

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

The Victor 884 class runs at 10ms. It's hard to tell from the comment if it was tested at 5ms.

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

Thanks for the correction. I will edit my previous post.

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

And it's as easy to change as calling setPeriodMultiplier in C++ and Java.

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

So the 884 could be run at 5ms. Do you know of any teams that have done this?

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

ether, can you share any info about the 888 such as operating voltage and amp rating?

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

Victor 888:

Nominal Voltage: 12V
Min/Max Voltage: 6-15V
PWM Input Pulse: 1-2 ms
PWM Input Rate: 2.1-500 ms
PWM Output Chop Rate: 1 KHz
Fan Voltage Range: 6V - 16V

No max current listing yet.

We'll be testing one to determine max current (failure current) over the next week along with a Talon.

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

Post video, or it didn't happen!

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

Links should be fixed now.

Here's an interesting visual. I wrote an awk script to read and convert the RPM vs Nm @ fixed IPW¹ raw data into a family of closely-spaced RPM vs IPW @ fixed Nm curves and plotted it with gnuplot. You can really see the change in linearity of the 884 as the load on the CIM increases.

Also, FWIW, here's a graphic of the 884 driving a 1500 ohm resistive load. You can see how linear it is. The non-linearity (when connected to a motor) comes from the interaction of the (slow) frequency the 884's output with the motor's inductance.


¹ input pulse width

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

Thanks Ether! I am going to steal that first chart for when I teach Class-D amplifier design.

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

Has anyone tested a TalonSR to see how close it is to the original Talon?

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

Our team used talons last year. 8 Total on our swerve module. No failures no problems. We have always put 20mm height EBM- Pabst fans on them. We have a big box of them from previous years. My one most important observation. Our RS-540 steering motors have never run as cool as with the Talons. Original talons not SR's. In a hot warehouse this summer (95 F) our drivers went crazy and drove non-stop for over an hour with only quick battery change for rest. Our steering motors never went over 140F. Our drive cims hit 160F for a short period. The steering motors are in a positional application- go this way no go back this way no go this ways continuously. A Nasty life for a motor and controller. I submit after this observation that the original talons locked anti-phase modulation as opposed to the sign magnitude modulation of the other controllers is superior in a position application that is always hunting and requiring motor reversal. And now they are gone. Do we use last years talons on our 2014 robot or the new SR's ?? I can not prove this with instrumentation we don't have but the observed difference is huge.

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

I am a rookie mentor, so this reply is coming long after your work, but I still wanted to thanks. When I fist read the User Manual on the Talon, I thought that when it stated a 100amp inrush/60amp maintained w/ a fan for constant loads > 30amps that there was all kinds of headroom. After looking at your charts, I see that my initial thought was wrong.

Thanks for the effort and details.