# Sensored BLDC Motor Question ...

Discussion in 'Sensors and Actuators' started by Fish4Fun, Mar 30, 2020.

1. ### Fish4FunSo long, and Thanks for all the Fish!

464
105
Aug 27, 2013
So I ordered one of these:

https://www.ebay.com/itm/4600W-6384-120KV-BLDC-Outrunner-Sensored-Brushless-Motor-For-Electric-Skateboard/164069170610?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

I am attempting to build a driver for it, but I expected the sensors to have outputs like this:

OR the Hall Effect elements themselves to be Bi-Polar and alternate between 1/4V - 1/2V - 3/4V depending on Field, ie: >> North - None - South << ie Like this:

What I was NOT prepared for was the following:

Assuming the sensors are bits arranged ABC and that each sensor combination should have a "fixed period" for any given rotational velocity, then the sensors should progress through 6 distinct "steps" with roughly equal periods (like the first reference diagram above) ... Like this:

Code:
```(Assuming the period per field is 3m/s (~55.5hz output)
001=> 3ms
011=> 3ms
010=> 3ms
110=> 3ms
100=> 3ms
101=> 3ms
-----------
001=> 3ms
011=> 3ms
010=> 3ms
110=> 3ms
100=> 3ms
101=> 3ms
.---------
.
etc
```
What I am seeing progresses through 6 steps, but two of the steps have a much larger period than the other 4 steps .... As Follows:

Code:
```000 => 3.0mS
010 => 2.6mS
011 => 4.4mS  *******
111 => 3.4mS
101 => 2.0mS
100 => 5.0ms  *******
----------------------
000 => 2.6ms
010 => 2.6mS
011 => 5.0ms  *******
111 => 2.8ms
101 => 3.0ms
100 => 4.6mS  *******
-----------------------
.
.
.
etc
```
What I don't know is if these "mismatched" timing cycles are by design or represent a flaw in the production of this particular motor. I have measured the sensors at various rotational rates and very consistently found every third pulse to be slightly less than twice the period of the two preceding and following pulse periods.

I have NOT disassembled the motor to take a look at the Hall Effect sensor PCB. The sensor outputs DO require pull-up resistors to function properly, but I don't know if this implies unipolar Hall Effect sensors or Bipolar Hall effect sensors with comparator outputs ...

I was honestly expecting either 3 bipolar sensor outputs OR six sensor outputs (AH AL BH BL CH CL as typically found in a brushless servo). I am not exactly sure how to use the six sensor steps to produce a an output waveform that makes sense. Perhaps I am missing something obvious, but I can't think what it might be .... so any help would be appreciated!