feasibility of a motorized slider

Hi guys!
Sorry for my english

I'm new to the world of Arduino, but i have an idea and i would like to know the feasibility of it.

I would like to make a "fader slider" for a homemade MIDI controller.
How can i make a "motorized" version of a fader slider so it can be either moved by my software but also by hand?

Would you use a Servo motor for this ?

Thank you

I'd just buy one. Search for "motorised fader" and you'll find loads of them.

Steve

slipstick:
I’d just buy one. Search for “motorised fader” and you’ll find loads of them.

Steve

Yes, but when you buy them, can they be moved by hand + by software input ?

Here are examples at Digikey

https://www.digikey.com/products/en/potentiometers-variable-resistors/slide-potentiometers/78?k=fader&k=&pkeyword=fader&sv=0&pv2009=377085&sf=0&FV=-8%7C78&quantity=&ColumnSort=0&page=1&stock=1&pageSize=25

(delete the extra characters the forum adds to the start and end of the link)

evanp886:
Yes, but when you buy them, can they be moved by hand + by software input ?

That was routinely done when I was fiddling in sound tech - 20-something years ago. No doubt modern ones can still do this.

evanp886:
How can i make a “motorized” version of a fader slider so it can be either moved by my software but also by hand?

Would you use a Servo motor for this ?

This is not an easy thing to do and a hobby servo would not be suitable because you will damage them by pushing against the gears.

A rotary system would be easier to make - you could use a small DC motor or stepper to rotate a potentiometer. Again, you would need the motor drive to have no gear system or one with very little resistance. It would be important that the motor would only be powered when it is actually required to move the potentiometer.

The problem with a slider is how to convert the motor’s rotary motion into linear motion with a minimum of resistance for manual movement. One option may be a drive belt - it could be a toothed belt but I suspect that would not be necessary.

If you want the software to be able to set the slider (or potentiometer) to a specific position then you will need some means to detect the actual position - perhaps with a rotary encoder on the motor shaft. You can get absolute position encoders but they are a lot more expensive than relative position encoders. However the relative position encoder would need additional hardware (usually a limit switch) to establish the ZERO or HOME position when the Arduino starts. That would mean moving the slider to the HOME position and probably losing whatever position it had previously been at.

Another thought is that if the Arduino could measure the resistance setting of the potentiometer without interfering with the circuit the slider is controlling then that could provide a simple absolute position feedback mechanism.

If you can buy motorised sliders that might be the best option.

…R

evanp886:
Yes, but when you buy them, can they be moved by hand + by software input ?

Yes they can. That's the point of them. You can automate the movement. And you can record manual movements to play back with the automation.

That's one reason why they don't use servos because servos really don't like being moved manually.

Steve

It is fairly straightforward that you simply need a slipping mechanism between the motor and the actual slider. This tends to preclude a screw drive as it has end limits.

Then you absolutely need the position sensing to be the actual potentiometer itself. If you are using a digital system such as MIDI, this is no problem at all since you already have it as an analog value rather than a gain control.

I can envisage a gearmotor with a pair of spring loaded friction discs bearing on a metal strip attached to the slider. This sort of mechanism used to be used in old radios.

Note the assembly on the right.