Motorized Rotary Encoders

Projects General Guidance
1

Hi all,
I’ve been thinking about a project for a while after being inspired by Melbourne Instruments Nina Synthesizer that uses motorized endless encoders to mimic potentiometers with extra features like recall of a previous setting or fake detents for coarse values.

Scott Bezek’s video on the Smarknob View showed me this is also a very real thing, using a gimbal motor and a magnetic encoder chip.

However, the cost of this, when scaled to around the number of knobs in total (30), is just too much. I have a sizeable budget, but for the gimbal motor alone, that’s $900.
And if I take into account every else I’d need (a motor driver perhaps, the magnetic encoder chip), it’s even more.

Even if I find a very very cheap gimbal motor on aliexpress and pair it with possibly a custom PCB including everything else needed, it still seems too expensive. Plus, I’m not sure the quality and lifespan of a CAD $12 motor.

Is there any other options here? The requirements are a high resolution endless encoder with fine motorized control. In a video showcasing the nina synth, the author said the hardware used “drone motors”, but to my knowledge these motors are meant for very high RPM’s and not fine precise control.

Any help on this is greatly appreciated.

Thanks!

2

Why do you think that? Drone motors are three phase DC motors and they all begin rotation at zero RPM and work their way up from that. They can stop at any speed before the maximum. Just have the 3-phase controller pulses stop rotating at any speed you want.

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ALPS. 1

ALPS 2

4

Wouldn’t an AS5600 magnetic encoder (<$5 Amazon) on a small stepper (e.g. 17-19$ Pololu NEMA14) driven with low amp (e.g. $4 AS5984 Pololu) do the job for <$50 per knob?

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Would something like this work for my application then?

https://www.aliexpress.com/item/1005004019322874.html

A 3-Phase BLDC is also what’s used in the SmartKnob project, I’m just not knowledgeable in the realm of how to connect this type of motor to a microcontroller (or if that’s even done without additional hardware).

6

This might be the next best option. I’ve tried cheap 28BYJ-48 steppers, but the resistance was too much whether powered off or on and idle.

I haven’t tried NEMA steppers yet, though. Is the low-amp driver due to the scale of 30 motors at once or for a different reason?

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Maybe a lower gear ratio? I haven't tried them but here's a 5:1 DC motor with an encoder:

8

Look at the associated speed controller and see if it will do what you want. I am not familiar with such devices.

9

is a standard r/c ESC and runs BLHeli S, which supports servo style PWM input, even if no one uses it.

It would probably be better to use real PWM, which it also supports, at a higher frequency.

Arduino analogWrite() would be recognized and followed.

a7

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You might like to see the very similar thread I have recently answered.

What a coincidence two posts from different posters on the same subject:-

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I thought one would want to tune for low amps to make the knob easy to turn/override manually while powered.

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