Digital Motor for Follow Focus ??

[ChristianNicco]

Hey Everyone,

I'm currently in the process of creating a follow focus but I'm having some difficulty selecting the correct motor to drive the mechanism.

So far i attempted to use a Nema 17 bipolar stepper as well as a 360 servo which i later on was informed that i could not give that 360 servo precise coordinates  to move to with a Pot( not sure if that info was correct )
Could anyone assist me with locating the type of motor use in this Red Rock Focus Rig  its the one on the left. All they say is that its  a digital motor, but i cant seem to locate a motor so silent like these.


Just to clarify i'm looking for a servo/stepper thats capable of making incremental movements with a Pot, or from what i read possibly an optical encoder  with low noise and vibration
All impute is a appreciated  XD
THANKS!

[Robin2]

If you explain how the stepper motor wasn't suitable it may help us to understand what you are trying to do.

...R

[ChristianNicco]

If you explain how the stepper motor wasn't suitable it may help us to understand what you are trying to do.

...R

The issue i had with the stepper was the 12v power source needed, i would ultimately like this follow focus unit to be wireless and run on a smaller power source something similar to a DSLR battery if possible.  The other slight issue is vibration and sound, on these professional follow focus systems the motor makes very little noise

[Robin2]

I don't have any specific advice about parts that might be suitable, and you haven't said how much torque you need or how fast you want to change position. Perhaps a small DC motor with suitable gearing and an optical encoder would be suitable? But I suspect you already have that in mind. I suspect silence comes with soft motor mounts and plastic gears - and trial and error.

If you describe the mechanical arrangement that you have in mind it might lead to some suggestions.

...R

[ChristianNicco]

My apology for lack of knowledge on this  but i'm not quite sure how much torque i need. I would like the movement speed to match the speed that i move the Pot/optical encoder. 


here's a clip of a professional grade follow focus
http://vimeo.com/43330022

much thanks for your assistance !

[Robin2]

From your photo it looks like you are trying to make an external device that turns the focus ring on a camera in response to something that you control. (I presume as a cheaper alternative to the parts in the photo?)

I'm being deliberately vague about the control as it may not be necessary for it to be a rotary device - why not a potentiometer? Or just a pair of push buttons - which is what a lot of the small still cameras use. Maybe you could have 4 buttons for fast and slow in both directions. All this is just to put other ideas in your head.

There shouldn't be a lot of torque needed. How many revolutions can the focus ring make from end to end?

How do you know when the view is in focus? If it's just by looking in the viewfinder I suspect a continuous rotation servo would do the job with suitable control from an Arduino - your human computer can compensate subconsciously for a lot of variability in the machinery.

...R

[ChristianNicco]

Yes, i'm looking for a less expansive set up. What kind of motor do you think they are using ?
Unfortunately buttons wont work i'm going to need to Pot so i can make incremental movements, and ultimately i would want the motor to turn simultaneously with the pot. A lens focus movement is within about 270º never reaching a full rotation so i need to be able to adjust within that distance.  To vaguely break it down when the focus ring is a 0º the lens in focusing on something thats lets say 1 foot away then as i move the focus ring to 270º the focus adjust to object further away then finally reaching infinity which focuses on everything beyond 8-10ft .  I will have an external monitor that i will be viewing a live feed from the camera to focus as well as a distance sensor to assist.

I think i'm going to give it a go with the Stepper motor , hopefully i can figure think up solution for the noise

[Robin2]

Commercial stuff could use any sort of motor because it's worth their while spending money on system design and software to save a few pennies in the cost of the hardware.

I'm still not clear from your comments whether you determine "in-focus" manually (by eye - eyeally?) or whether you want the system to "know" that it must turn to (say) 175deg for a focus of 6ft.

If you are doing it by eye then I don't see the need for much precision in the system as long as you can be sure it can turn the focus ring through it's full range. I'm sure some sort of servo setup would be adeqate.

If you want it to be fully automatic - so you can rely on it being in focus without looking at the viewfinder, that's a different matter - how will the Arduino know what the desired range is? But I suspect a servo should be adequate unless you want very high precision of the focus ring position.

If, by "motor to turn simultaneously with the pot" you mean that there is virtually instant correlation between the focus ring and the pot position I think that will be a challenge as higher power and speed will be needed, and probably a precision pot.

...R

[ChristianNicco]

I assumed the same about the motor but i wanted to get some impute from another party just incase they had any info leading to something similar. For best results on my end i need to have a knob style device to adjust the motor. I actually came across a post that i'm going to attempt.

http://adisoffer.tumblr.com/

Thanks so much for your impute Robin it's much appreciated

[Robin2]

I don't know why I'm the only person that made any input.

Perhaps it would be worthwhile either changing the title of your thread or starting another thread with a "better" title - though I don't have any suggestions for the change.

...R

[JuceBachs]

Greetings Christian,

If your still around, i'm in the process to building out my BMCPC rig with a arduino minded pot (maybe a different hand control... i'm found a few comfy alts) controlled duel servo system. One servo for Focus, the other for zoom (depending of the glass obviously). I have several answers to many of your questions, but i'm not going to burn the time typing it all out unless your have yet to achieve your goal, and if you have perhaps we could compare notes.

[Tofer]

Hello! Did you find a proper motor?

For me stepper doesn't work because of the reaction it has on changing the parameters. Also it's not accurate in steps. I've used NEMA 17 with a4988 driver.