paper: Cyber Blue 234 Drive System Test - Performance and Power
 

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Cyber Blue 234 Drive System Test - Performance and Power by Chris Fultz

Re: paper: Cyber Blue 234 Drive System Test - Performance and Power
 

This fall Cyber Blue completed a series of drive system tests to compare the acceleration, top speed, voltage drop and amperage for 4 different motor combinations and two robot operations.

We used a special built, kitbot chassis, 4 WD and tested with 2, 4 and 6 CIM and 4 CIM + 2 Mini-CIM motors. We tested with the robot "alone" for a 50 foot test run, and also pushing a 130 pound, unpowered, robot for a 25 foot test. The unpowered robot had a 4 CIM drive, with the Victors in "brake" mode.

Re: paper: Cyber Blue 234 Drive System Test - Performance and Power
 

Thanks a lot for performing these tests! This is extremely useful data and will definitely be a significant factor in our drivetrain design next season.

Re: paper: Cyber Blue 234 Drive System Test - Performance and Power
 

YES!
Thank you so much for releasing this data on CD. We will for certain use this to determine out drive train next year.

Re: paper: Cyber Blue 234 Drive System Test - Performance and Power
 

Your data is enlightening. Thank you!

Re: paper: Cyber Blue 234 Drive System Test - Performance and Power
 

This is great!

I find it really interesting that on paper, the 4 + 2 CIMs are comparable, and sometimes beats the 6 CIM option.

Quick question, am I correct in assuming that the "Peak Amps - 1 Motor" for the 4 + 2 CIMS was a Mini-CIM? (as "Peak Total Amps" for 4 + 2 is higher than 6, but "Peak Amps - 1 Motor" is lower)

I'm not sure hard it would be to organise, but from that data I'd be really interested in seeing how more combinations of Mini-CIMs (say 2CIMs + 4 Mini-CIMs) stack up.

It seems that even though the CIMs are higher power, by operating the Mini-CIMs closer to their MPP they perform noticeably better. This implies that in some drive trains, Mini-CIMs would actually perform better than standard CIMs. However it should be noted that (assuming the same gearing form CIMs and Mini-CIMs) the closer you get towards the CIMs MPP, the closer you get to the Mini-CIMs stall condition.

Re: paper: Cyber Blue 234 Drive System Test - Performance and Power
 

Very insightful. Thank you for putting together such a detailed paper and making it available to us all.

Re: paper: Cyber Blue 234 Drive System Test - Performance and Power
 

Yes, in all of the test runs (3 trials) the mini-CIM was the highest amperage, but they were very close (44-47 Amps for at least one of the CIMs in each test). So while slightly higher, i think i would say "almost the same" given the accuracy of our data capture.

We plan to save the test chassis, and may do more testing next summer / fall to do more comparisons. With the CIM, mini-CIMs and "CIM adapters" for other motors there might be some interesting information to be found.

Re: paper: Cyber Blue 234 Drive System Test - Performance and Power
 

This will certainly come in useful in just a few days when selecting our drivetrain. Thanks a bunch for saving us some major time.

Do you have any idea why the 4 CIM + 2 Mini-CIM configuration draws a similar current when pushing as the 6 CIM configuration? I seem to recall that Mini-CIMs are about 2/3 as powerful as a CIM, so it would seem to make sense if replacing 2 CIMs with 2 Mini-CIMs in this configuration, the total current drawn (at least in theory) would be reduced by about 11%.

Re: paper: Cyber Blue 234 Drive System Test - Performance and Power
 

Thanks for sharing this very useful data.

Knowing that the 4+2 combination is so close to the 6 CIM opens up options for motor allocation. Your report also provides good objective data for CIM speed under "real world" load conditions.

Re: paper: Cyber Blue 234 Drive System Test - Performance and Power
 

This is very interesting and useful. Now I'm really interested and seeing how this data changes as the gear reduction gets reduced and top speed rises. I know for many teams that use 6 CIM or similar drive trains it's to be able to get a higher top end speed without losing to much low end torque on a single speed gear train.

Our final ratio last year was 6:1 and I predict a 4 CIM drive struggling to handle that.

Re: paper: Cyber Blue 234 Drive System Test - Performance and Power
 

Very interesting study and thanks for sharing. I am a little surprised that the actual top speed is only about 75% of the theoretical top speed. I had assumed somewhere between 80 to 90% depending on gearbox and gear reduction.

Re: paper: Cyber Blue 234 Drive System Test - Performance and Power
 

What are you using to get the theoretical top speed? I ran the numbers quickly and it seems right to me. Theoretical top speed is around 11.65 fps (CIM at 5300 RPM and 4in wheels) and recorded for the 4 CIM is 10.76 fps which is 92%.

Re: paper: Cyber Blue 234 Drive System Test - Performance and Power
 

i agree with Allen's math -

The total reduction is 7.95:1, counting the gearbox and the belt pulleys.

Theoretical = 11.63 FPS
4 CIM = 10.76 = 93%
6 CIM = 11.06 = 97%

To be more accurate, we would need the true free speeds of the CIMs and the actual diameter of the "4 inch" wheels with tread, but these are close.

Re: paper: Cyber Blue 234 Drive System Test - Performance and Power
 

Sorry, I misunderstood what 37-42 Step Up mean. I also did not notice you published the final drive ratio which would have told me I did it the opposite way.