Hall Sensor on BLDC as Encoder

T Chap

My go to motor is Dual Shaft BLDC with 400CPR encoder on the motor. I always have some type of gearbox on the motor 12.5:1, 15:1, 30:1. I bought some 30:1 motors a few years ago for a project that never got used and I planned on putting encoders on the shaft driven at the output of the gearbox. Most of these motors didnt get used so they have been sitting and were a lot of money. I have a project I can use some of these on but the hassle is adding hardware to put the encoder on the drive shaft which is no problem just more parts and work. This project is not requiring high resolution encoder positioning and it occurred to me what if I just count 1 of the hall sensors and the count will give me a good position. Then it occurred to me to look at the BLDC truth table, and interestingly enough it gives a nice quadrature output on either A>B, B>C, A>C There are a few repeated outputs but that does not matter in this case with 30:1 and I just need basic positions. Maybe someone may find this of use.