2018 FRC Brushless DC (BLDC) Motor Questions & Answers

**Here’s a link to some brief tech notes I put together based on the limited information presently available.

And here’s a list of some questions about the BLDC motor and controller for which I haven’t yet found authoritative answers:

EDITS in blue:

How many stator pole pairs and rotor pole pairs does the motor have? 5 rotor pole pairs

Is the motor trapezoidally or sinusoidally wound? sinusoidal

Does the controller use 3 Hall sensors for commutation? Yes

If so, is the tach signal derived from the 3 Hall sensors, or is there a separate tach sensor? tach signal is derived from 3 Hall sensors

**

There is this note in the manual Richard linked (http://www.hurst-motors.com/documents/TDE1006.pdf):

This seems to be the controller IC:

https://www.digikey.com/product-detail/en/allegro-microsystems-llc/A3930KJPTR-T/620-1289-1-ND/2000020

Thanks Mark, I didn’t see that.

So how does controller generate 15 pulses per rev from 3 Hall sensors? (that’s why I asked about stator poles and rotor poles).

**EDIT:
See this post for possible answer:

https://www.chiefdelphi.com/forums/showpost.php?p=1707308&postcount=98**

Thanks Marshall.

I will look at that in detail when I get back home later this afternoon.

I’m guessing it’s 6-step (trapezoidal) commutation? If so, I am wondering if the motor is trapezoidally wound, and if so, do they still do trapezoidal commutation when an encoder is available for commutation?

Or do they only put an encoder on a different (sinusoidally wound) motor, and do sinusoidal commutation?

Here’s a link to some additional technical information about the motor and controller. Thank you Richard.

See this post for some discussion about the “tach” signal:

*To Beta Teams who are testing the BLDC motor+controller:

Have any of you determined:

a) if the controller in its default mode is actually doing on-board closed-loop speed control

b) if it’s possible to change the control mode to on-board closed-loop position control, as claimed in the marketing video.

c) what is the actual stall torque and stall current at 12 volts

d) what is the actual max power output at 12 volts