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Are the matlab motor efficiency calculations for the 12V motor correct?

#1

I am using the listed motor and the accompanying matlab code to calculate motor efficiency in hopes that I can find the reason for discrepancy with my simulations. I assumed the efficiency would be somewhere around 80% but this program is giving me a maximum of 30% which I feel cannot be correct. I entered the following:

Please enter the stall torque in oz-inch [17]: 240
Please enter the stall current in mA [700]: 5600
Please enter the rated voltage in Volts [6]: 12
Please enter the free run currennt in mA [40]: 300
Please enter the free run speed in RPM [290]: 130

This results in the attached image which indicates an efficiency of less than 30%. This seems incredibly strange. Please advise.

#2

Hello.

We just finished preliminary performance tests of that gearmotor, and here are the resulting performance graphs:

In general, small brushed DC gearmotors like these will have typical peak efficiencies in the range of 30% to 40%. For additional datapoints, see the performance graphs we have published for our micro metal gearmotors and 20D metal gearmotors. Out of curiosity, what is your expectation of ~80% peak efficiency based on?

-Nathan

1 Like
#3

I think I based it on some false assumptions about larger motors which show higher efficiency: https://www.energydepot.com/RPUcom/library/MISC003.asp

This has been incredibly helpful, thank you!

#4

Just wanted to do a quick update and say that you may want to put a disclaimer with the MATLAB script included in the motor description as the curves definitely do not match this. Thank you for this graphic though, this has really helped a lot of things make sense.

I also wanted to verify that I’m reading this correctly. The highest load you put on this was approx 80 kg-mm, resulting in 85 RPM, a current demand of almost 2A, and an efficiency of 30%. This efficiency is the percentage of electrical power (like what the reading of a power supply might state) that has been converted to mechanical power. Correct?

This is also at 12V. I’ve been using the encoders for speed feedback. If I tell my craft to operate at, say, 60RPM the motor controller should modulate the amount of voltage I see. This would assumedly affect the efficiency curves but I’m curious by how much. We don’t have a direct measurement of load, but for our 10 trials at 60 RPM the average pull of each motor was 0.264A. Would we use the load as a guide?