# Motor math

1 year 9 months ago - 1 year 9 months ago #29534186 by glmnet
Motor math was created by glmnet
I have a brushless motor with a FBL2360, it has hall sensor and encoder.
The output shaft of the motor is connected to a 1:15 gearbox then a wheel.
When I hand rotate the wheel a full turn I get 30,000 pulses in the encoder and 450 in the hall sensor, after dividing by gear box ratio it gives me 2000 encoder pulses per revolution and 30 hall counts per revolution, I divide 30 by 6 as in the manual states for calculating number of mag poles of motor, is 5.
So I enter these value in the configuration, and then go to run tab and set the motor to rotate, now I read Encoder RPM being much less than Hall RPM, why is this so?

EDIT: If I enter 20 in the mag poles, the Hall RPM and Encoder RPM matches ok, that is, if I leave 5 the difference is by a factor of 4.

EDIT2: Now I am using 500 instead of 2000 in the encoder pulses/rev and it seems to work ok, so if I count 2000 pulses in the logger, I should instead enter the value divided by 4 there. Please correct me if I am wrong, also measuring with revolutions with chronometer it seems to be working properly. I had to recalculate PID values.

Thanks.

1 year 9 months ago - 1 year 9 months ago #29534188 by Gabriel_Isko
Replied by Gabriel_Isko on topic Motor math
Figure 3-16 from page 54 of our User Manual explains what is going on very nicely.

Our encoder counters count on the rising and falling edges of an encoder signal. On a quadrature encoder we get 4 counts per pulse.

It seems that you have a 5 pole motor with a 400 PPR quadrature encoder. These should be the correct settings. Make sure that both counters increment when you give the motor a positive command in open loop. If they go in the wrong direction, it will cause problems if you try to use a closed loop mode. You will have to change the polarity if it is going in the wrong direction.
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1 year 4 months ago #29534602
Replied by Vanlaint96 on topic Motor math
Hi you!
Do you use Robo Run+
Can you give me how to configuration gearbox ?
You config encoder is 30,000 or 2000 ?