Motorized follow-focus project

Old 06-11-15, 07:57 AM
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Motorized follow-focus project


I'm thinking of building my own motorised follow-focus system for my camera rig.

I want to do this with a stepper motor, mainly because of the relatively silent operation and the ability to manually turn the follow focus wheel if necessary.

I'm a bit new in this, but I'm intending to buy the following items:

- NEMA 14 steppermotor
- TMC2100 stepper driver (for silent operation and micro stepping)
- digital wirewound potentiometer
- AA battery holder for two batteries or Lipo battery
- wormwheel

My question is: is this enough? From what I read on the internet, I might also need a microcontroller to program the speed, or is this built in the TMC2100 driver? If so, how do I program it?

I was also wondering if I can buy a normal, one shaft stepper motor and extend the shaft on the rear to make it a dual shaft motor. It looks like I can but I want to be sure.

I've (hastily) drawn a little design of what it should look like.

Name:  design.jpg
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Let me know what you think, suggestions are welcome!


Last edited by Homerus; 06-11-15 at 08:28 AM.
Old 06-11-15, 09:26 PM
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Welcome to the forums.

You are correct. You will need some type of processor to send step/direction information to the TMC2100.

Can't answer the dual shaft question. Either the motor comes with dual shafts or it doesn't. Why would you need dual shafts ?

Not sure what a digital wirewound potentiometer is. You technically need a pot that has two outputs..... one is direction and the other is pulse.

trinamic/download/integrated-circuits tmc2100 datasheet.pdf
Old 06-12-15, 03:28 AM
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Thanks for the reply PJmax,

I need it to be compact, would a processor like the Arduino Nano do the trick?

The dual shaft is needed so I can attach a wheel for manual operation (when there's no power to the motor).

Wirewound potentiometer is just a potmeter with a return spring, so when you release it it goes back to the middle.
Old 06-12-15, 10:38 AM
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I don't know this stepper controller specifically, but most need a pulsed input to control the step speed, then it handles the multi-wire motor control. The pulsed input could be a 555 timer circuit with a pot to determine the speed. Direction could be just a simple switch.

Of course a microcontroller would give you a lot more control and more options, but the 555 is a simpler solution.

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