Setup for 60mm haptic input knob?

Hello Friends

I am building a control panel for my custom cnc machine.

The main controller will be a 60mm rotary knob with feedback function. The feedback will depend on the mode we select.

Please tell me from your experience:

1 - Which motor should I take to have enough torque on 60mm knob, I will turn the knob sometimes with gloves, so the torque should be quite powerful.

2 - Which encoder to use - capacitive or magnetic?

The control panel will be outside, some moisture will be in the air. The knob has a central position ‘‘line’’, by turning on the system the knob should always go to center position, so the line on the knob is aligned with the central line on the panel.

3 - Good motor driver for this setup?

Thanks!

Hi Mastino, and very welcome to SimpleFOC!

Personally I like the magnetic encoders, but of course incremental encoders also have some advantages. The big advantage of the magnetic encoders is that they are absolute. So this would be mean that directly after power-on you know the absolute position of the knob, and don’t have to do an index-search to find where you are. Of course this may not be important for a CNC control application.

Have you seen the “SmartKnob” in our forums?

Perhaps you can ask @Karl_Makes_Music about his experiences regarding torque…

In any case 60mm will fit a fairly large motor, so you should be able to get decent force feedback from a motor that size…

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Hi All,

First let me share some details on Knob i’m working on.




Uploading: image.png(1)…

In my case the outter diameter of the knob (without the platform) is 53mm.
I use 34mm 7PP bldc motor from Ali.
I power my motor with 3.5V at 350mA current limit.
The IC Driver for motor is TMC6300.

In principle any motor with relatively low cogging would work for this application if you want to power it with low voltage, i had major success with many motors, however i realized that the cheaper motor the better.

Motors with noticable cogging like GB36-1 would work quite well too as long as you dont want to run it in “unpowered” mode.

I had success running 34mm BLDC motor with 4V and 420mA limit in Ratchet and Viscose Friction mode with no problems at all - turning is the tidious but fun part for me.

In regards to Encoder, any encoder would work even as5600 (which is considered nosiy) if you enable filtering and hysterisis bit.

My perference in terms of sensors are MagAlpha sensors MAQ430 or MA710/730 which are comically easy to implement to in SimpleFOC without external libraries.

To summarize i’d say any motor between 28-34mm 7PP would do just fine, specs are not all that important from my personal experience.

IC Driver my recommendation is TMC6300 (BOB is about 13 euro on Mouser.eu) but you can use even L6234 (SimpleFoc Driver shield) with huge success.
You do want to run these smart knobs on relatively low voltage and with current limit, so i’d say go for any driver of your choice that can run off 5V. L6234 is just waste of potential for these knobs.

In my tests running knob with 6-8V with 500-1A limit has just unreasonable amoutnt of torque for this kind of application.

Encoder like i mentioned before pick magnetic encoder with SPI bus (much more stable) but if you dont want to mess too much with 6 wires for SPI just go for I2C they work fine too.
My preference is MAQ430/MA710/730, any other AS (for slow rotation) would work very well too.

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Wow that is a great project! Thank you for the information! Now I know where should I start!
What you think about this one?
It has this noisy encoder yes?
I like that this motor comes together with encoder metal holder, looks nice.

Where I can buy MAQ430 or MA710 encoders? No results in my google.

Hi Mastino,

In terms of the motor i would choose something cheaper even, no need to spend 40 bucks on motor unless this is what you want, the benefit of this is that you have complete solution with encoder (AS5048 is good enough) and you dont need to fiddle too much with 3D printing custom adapters.

This
or
That

Should do just fine, for 2nd one you need a diametric magnet (ring) - not axial one.

In regards to MAQ430 or MAQ 710:
Mouser EUROPE/USA sell these EVAL boards:

I highly recommend them.

Feel free to ping me on DM or here if you need further help with choosing the right stuff for the job.

If you live in europe i’d be happy to send you motor i use for my project along couple of sensors (either loose or with PCB adapters).

In fact if anyone is interested in building this or similar project i’d be happy to share my Driver IC’s, Sensors, Motors etc. i have few dozens of each.

Wow that’s great! I wrote you message in Instagram are you active there?

Typically I’m most available here on DM or our Discord channel:)