motor speed question with base electrical frequency

I take it you are using InstaSPIN-BLDC?

Babak Kianmajd said:

pole count, and base electrical frequency (hz) affect the max rotational speed, assuming a constant PU of 1.

Inside the algorithm everything is done in terms of electrical frequency, Hz

to display RPM we need to know the # of poles.  RPM = Hz * 120 / poles

Babak Kianmajd said:

I was under the assumption that the voltage corresponded to the rotor speed. Hence, because my input voltage is 24 volts, I was assuming the maximum rotational speed I could get would be 40,000 RPM

yes, that is true. if you can source enough current for the load you should get about half the speed at 24V as you do at 48V. 

Babak Kianmajd said:

guess this thought is wrong however, and is it the combination of pole count, and base electrical frequency determines the maximum rotational speed?

The maximum electrical speed of the motor will be based on the motor design and dependent on Rs, Ls, and Flux or Bemf of the machine.

Thanks for the swift reply, yes I am using instaspin BLDC.

ChrisClearman said:

to display RPM we need to know the # of poles.  RPM = Hz * 120 / poles

So this only affects the display speed? Even if we change control from PWM control to velocity control?

poles only effects the RPM conversion from Hz

you should increase your base electrical frequency to something that fits your motor max

BTW - I highly recommend the InstaSPIN-FOC or -MOTION solution over -BLDC.  It gives you much better control with much less work.

Is InstaSPIN-FOC or motion compatible with the tms320 - f28035 microcontroller?

So far I am only able to get the display to read a factor of my actual speed: I added tape to the shaft of the motor and measured the sound frequency to grab the actual motor speed. However, the display speed on the instaspin -BLDC is only 1/2, 1/3, 1/4... of the measured speed after changing the #poles, and base electrical frequency option.

Babak Kianmajd said:

Is InstaSPIN-FOC or motion compatible with the tms320 - f28035 microcontroller?

No, you need to use an InstaSPIN enabled version of F2802x, 05x, or 06x.:

http://www.ti.com/ww/en/mcu/instaspin/instaspin-foc_MCUs.shtml

Babak Kianmajd said:

So far I am only able to get the display to read a factor of my actual speed: I added tape to the shaft of the motor and measured the sound frequency to grab the actual motor speed. However, the display speed on the instaspin -BLDC is only 1/2, 1/3, 1/4... of the measured speed after changing the #poles, and base electrical frequency option.

that doesn't make any sense at all...but I'm not sure how to help you debug either. We haven't noted something like this before.

I'll test out more pole, frequency combinations later. I also have an encoder I can attach to my motor to double check my motor's actual speed.