Camera lens remote follow focus system. "Direct drive" of a stepper motor. How?

[SCM_Ming]

I know very little about stepper motor. All I know is that this thing require power and a circuit board to drive it.

I'm planning to make a remote follow focus system for a camera using stepper motor. A follow focus system is simply a gear to drive the lens' focus ring. So we can control the focus accurately. And I want to use a stepper motor with a gear on it to drive the focus ring.

And there's a controller look like a knob. Turning that knob=turning the driving gear=turning the focus ring.

There are 2 technical problem.

Firstly, the motor must be smooth and precise and fast. So that the motor turns as soon as I turn the controller knob.

Secondly, I want to know if it is possible to set up a turning knob so that I can "remotely" drive the stepper motor? Ideally it should be 1:1 ratio. That means I turn a remote control knob clockwise 60 degree the motor turns CW 60 degree too at the same speed.

RC Servo is not suitable. Because RC servo's motion is limited to 180-360 degree motion. But I want more than 720 degree.

For reference I will include a picture of how a "mechanical" non-remote follow focus system should look like.

http://www.redrockmicro.com/assets/images/mff/Z1_M2_mFF.jpg

Now what I want to do is to seperate the "knob" and the driving gear. So that I could control the focus without touching(causng shake) the camera.

Thanks for help 🙂

[Wes_P]

Hi,

To set up a motion system, you will need a controller, which is usually a PCI card in your computer, a drive, which takes in logic signals and outputs the power needed to turn the motor itself.  NI has many PCI controller cards available.  NI also has many drives available which will interface easily with these cards.  NI also has many stepper motors available for sale.

Stepper motors have a fixed number of physical poles or "steps" on the motor itself.  A very common number is 200.  This essentially means that there are 200 discrete positions that the stepper motor can be in.  If you need to have finer control, you can use microstepping.  Microstepping is a capability of the motor drive that can hold the stepper motor between poles.  So you can essentially set your motor to have a higher number of steps per revolution.