paper: Cyber Blue FRC 234 Motor Test Report 12-8-2017

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#1

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Cyber Blue FRC 234 Motor Test Report 12-8-2017
by: Chris Fultz

During the fall of 2017, Cyber Blue completed performance testing of CIM, MiniCIM and VEXPRO 775 based drives. Multiple numbers of motors and combinations were tested. This report summarizes the testing.

During the fall of 2017, Cyber Blue completed performance testing of CIM, MiniCIM and VEXPRO 775 based drives. Multiple numbers of motors and combinations were tested. This report summarizes the testing.

Tests included acceleration, top speed, turns and pushing, using low and high gear options for some of the tests.

Cyber Blue FRC 234 - Motor Test Report 12-8-2017.pdf (1.58 MB)

#2

During the fall of 2017, Cyber Blue FRC 234 completed a series of tests on FRC motors that are commonly used for drive systems.

Motors tested included CIM, MiniCIM and VEXPRO 775’s.

Multiple combinations of motor counts and combinations were used. Tests included acceleration, top speed, time to 50 feet, a turns course and a wall push.

This report summarizes the findings from the report in both table and graph forms.

The base data can be found here: https://tinyurl.com/FRC234MotorTestData

#3

Ahh, the sweet smell of data…

Thanks for the work Chris & company!

#4

Sweet data! From a quick glance, looks like 6 mini-CIM is the best?

#5

Super useful, thanks!

One thing: On page 6 you list the power from the 775 pro drives at 80% of their max power ratings. However you limited the motors to 80% of their input** voltage**, not power. According to this recent discussion, the power available at each voltage-limited motor is actually 0.8^2 or 64%.

#6

4 MiniCIMs do not beat 4 CIMs in a drag race! :ahh: Your experiment results are backwards. Please fix it. :ahh:

This is great baseline data. Great job with the experiment setup, data collection, and presentation! It is a little difficult to discern between some of the blues in the charts of the PDF, but the provided data is helpful in sorting it out. Thanks for all of the hard work!

#7

I’m not sure that conclusion can be drawn. Since the gear ratio was (roughly) the same for all tests, the drive trains weren’t optimised for different amounts of power available. That said, this is really useful data for validating acceleration simulation models.

#8

Welp. I was having a very productive afternoon. Can’t wait to dig into your results.

Thanks for doing this test and sharing. This will be hugely helpful in our decision making process next year!

#9

Awesome data. It appears the available current from the battery posted in the battery spec sheet is about right, don’t plan to get much more than 270 amps out of it. The behavior you’ve shown has confirmed a lot of the modelling I’ve done on this. Thanks for sharing!

Depends what you mean by best. The 6 mini CIM drive had a slightly higher free speed than the other CIM configurations and the voltage limited 775 pro configurations. In a 50ft sprint I would expect the slightly higher gearing to be an advantage.

#10

The results are recorded correctly. This is a summary of the raw data, with no factoring or adjustment for input speeds. That is why we also included the raw data files.

#11

This is spectacular, and ever so timely! Thanks, Cyber Blue!

I’m not convinced of that result - what makes you think so?

#12

Ah yeah, good point.

It was at the top of most of the charts, especially the on-ground speed tests. It’s definitely not conclusive, just a first-glance takeaway.

#13

I hope you took the emojis to mean that my mind is blown by the finding, rather than a challenge to the results :).

Page 22 shows that nearly all of the setups took a full 1 second or more to stop from full speed. It is significant that such a “small” action in a full cycle of 2017 could eat away at 2 or more seconds of cycle time, and isn’t an insight I would have even thought of.

In test #4, did the “stop” happen simply from brake mode on the talons, or was a reverse thrust applied before the robot motion was fully-arrested?

#14

How soon until the elite teams start fitting disc brakes to their drivetrains for extra-high deceleration :slight_smile:

#15

I call that a “wall” :slight_smile:

#16

If you have a shifter, immediately shifting to low-gear to slow down basically does this. We found it quite helpful last year.

We might run our own versions of some of these tests to verify the data here. I find the shifting results a bit surprising, but I think “shift after 2 seconds” is the likely culprit; it’d be nice to test with actual autoshifting code.

#17

I wasn’t sure on the CIM comment, but it was a good point to make that we are reporting raw data, so the different input speeds are an influence. We chose to not do a lot of data manipulation.

#18

You can see this in the data for each test. Starting with Config 2 (6 CIMs), we go from 1 to -1 over approx 300 ms

#19

Chris, this is an incredible service to the community. Thank you and your team for the dedication.

#20

A CIM drivetrain (4 or 6) geared to the same free speed as a miniCIM drivetrain would almost certainly be faster (if it weren’t, I’d be questioning the test methodology). In this test data, 6 miniCIM is faster than 6 CIM almost across the board. It’s interesting that, in most cases, the marginal difference in free speed makes a bigger sprint speed difference than the 50% torque difference.