Brushless DC Motor Position Control

Using Arduino Motors, Mechanics, Power and CNC
1

Hi, Im looking into switching out some servos in place of Brushless Motors.
From what I understand there are 2 methods of position feedback to allow for positional control.
1 is with Hall effect sensors
2 is with feedback from the motors EMI

I have a couple questions about this

  1. What is the resolution of these two? how do they compare to one another in this respect

  2. Am I searching the wrong thing or is it really not possible to get sensored Hall effect Motors for under $100 and in a small form factor?

  3. How are gimbal motors controlled? Such as the ronin-s, they are extremely accurate, strong, and small

Any help would be greatly appreciated

2
  1. Am I searching the wrong thing or is it really not possible to get sensored Hall effect Motors for under $100 and in a small form factor?

https://www.robotshop.com/en/2-axis-stabilized-brushless-gimbal-w--motor--controller-for-gopro-hero-mount.html?gclid=EAIaIQobChMIyMDt2JeM4AIVih-tBh01-w_KEAQYCyABEgJB_PD_BwE

3

justone:
https://www.robotshop.com/en/2-axis-stabilized-brushless-gimbal-w--motor--controller-for-gopro-hero-mount.html?gclid=EAIaIQobChMIyMDt2JeM4AIVih-tBh01-w_KEAQYCyABEgJB_PD_BwE

I don't want anything in this form factor is the thing. I would like to be able to just provide step and direction to a single motor or single motor controller

4

Antwan2000arp:
3. How are gimbal motors controlled? Such as the ronin-s, they are extremely accurate, strong, and small

There's a gimbal teardown that might give you some good insight here:

5
  1. There are usually three hall effect sensors. One per phase. Depending on the number of poles, this might give you 12 pulses per revolution.

If you're talking gimbal type positioning then you go sensorless. Then you get almost infinite resolution, equivalent to thousands of pulses per revolution.

  1. What do you call "small"? Gopro gimbal? SLR gimbal? Or some other payload?

  2. They don't care what position the motor is in. They measure the angle of the camera platform relative to gravity and try to make that zero. (Or make it meet a desired tilt angle.)

Imagine you are driving your car but there is something that stops you seeing or feeling where your hands are on the steering wheel. You start by grabbing the wheel just anywhere. Drive down the road and move the wheel until the car is going straight. Do you care where your hands are? No, because the car is going the direction you want.

6

Antwan2000arp:
Hi, Im looking into switching out some servos in place of Brushless Motors.
From what I understand there are 2 methods of position feedback to allow for positional control.
1 is with Hall effect sensors
2 is with feedback from the motors EMI

I have a couple questions about this

  1. What is the resolution of these two? how do they compare to one another in this respect

Both are crude and only good enough for commutation (ie timing the drive to the windings).

  1. Am I searching the wrong thing or is it really not possible to get sensored Hall effect Motors for under $100 and in a small form factor?

Its frustrating, but this does seem to be hard to find - I sometimes see small good-value brushless motors with built-in controller on eBay, which basically allow simple speed control with a voltage or potentiometer. These
typically have hall sensors but not accessible from outside, they are mounted direct on a little circular controller pcb inside the motor.

  1. How are gimbal motors controlled? Such as the ronin-s, they are extremely accurate, strong, and small

feedback loop from an encoder or IMU - the position error drives a PID loop that sets the output phase of the motor driver.

Any help would be greatly appreciated

7

MarkT:
basically allow simple speed control with a voltage or potentiometer.

Sounds unsuitable for this application. The OP specifically asked for position control, not speed control.

I'm still unclear on what the real purpose is. There is a mention of a gimbal but maybe this idea is only "like" a gimbal.

8

"Simple" position control could be achieved using selsym transmitters but that requires an AC supply
See https://www.allaboutcircuits.com/textbook/alternating-current/chpt-13/selsyn-synchro-motors/