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 Some Focusmotors 
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Joined: Wed Nov 11, 2009 10:45 am
Posts: 1678
Location: Merritt Island, Florida, Estates Unitas
Post Some Focusmotors
I shot this picture of my museum of all the different models of focus motor I've made for a Kickstarter project we plan to launch soon. When I started pulling old models out of drawers, I was kind of surprised at how many different models I've made over the years.

https://www.flickr.com/photos/sciencelo ... 849568400/

[flickr]https://www.flickr.com/photos/sciencelookers/15849568400/[/flickr]


Tue Dec 16, 2014 9:26 am
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Joined: Thu Jun 16, 2011 7:01 pm
Posts: 38
Post Re: Some Focusmotors
Are some of those BLDC? What did you use to control the motors with encoders?

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Wed Dec 17, 2014 12:53 pm
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Joined: Wed Nov 11, 2009 10:45 am
Posts: 1678
Location: Merritt Island, Florida, Estates Unitas
Post Re: Some Focusmotors
The tiny brushless DC motors with encoders have the encoder on the back shaft and a tiny orbital gearbox on the other end. Resolution of the encoder is multiplied more by the gearbox, so output shaft position is known very accurately. I think they could be used with mantis right now if anyone wanted to. They are prototypes for a realtime focus system we plan to make. Frank did some work on a controller for them and also did parallel work on a stepper model and one with a stepper and encoder not in the picture because it was at Frank's when I shot the motors picture.

The real big focus motors used these DC motors from Servocity

https://www.servocity.com/html/3-12v_gear_motors.html

All the different gearings have the same gearbox mounting hole pattern so they are interchangeable, giving the user incredible freedom in choosing the speed range. Those were usually driven by Dynamic perception MX-2 and MX-3 dolly engine controllers. We also made some with these DC motors with encoders from Pololu.

http://www.pololu.com/product/1446

The Pololu motor also has gearbox mounts that match the Servocity line, so they interchange easily with the other motors in the same focusmotor frame. We also offered a NEMA 14 motor for the same frame, which accepted any of six right angle output gearboxes ranging from 1:1 to 30:1. ......Those are very adaptable focusmotor frames. In minutes, armed only with a screwdriver and allen key, anyone could swap out the motor and/or right angle output gearbox with any of the others, even swapping a stepper for the DC motor. We can still make them as a one-off if anyone still wants one.

Then there is a variety of stepper focus motors in the picture. These are what we mostly make now. There is even a circuit we call the stepout, which lets you drive the stepper focus motors from Dynamic Perception MX-2 and MX-3 controllers. It reads the output of the controller and generates step and direction signals which go to its internal stepper motor driver. We can also provide stepout circuits where the step and direction signals are routed to a socket, so you can use stepper motors of any size with an external motor driver.

If you don't see what you want, we do make one-offs!
Thanks for asking.


Mon Dec 22, 2014 8:40 am
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Joined: Wed Feb 15, 2012 3:36 pm
Posts: 400
Post Re: Some Focusmotors
You have a fascinating collection of focus motors!

I haven't paid much attention to my focus motor, as I use a motor direct, i.e. no gearbox, a Nema11 stepper motor 50mm long. I find that using it direct and with micro stepping, it still has enough power to move the lens. But without the micro stepping, the steps are too clunky and they would disrupt the lens focusing with minute bumps.

But I think probably it is better to use a larger size (but short length) Nema with 0.9 degrees in micro stepping mode. Being bigger, it will have a little more torque, while the 0.9 degree and micro stepping will help with the smoothness.

I find it essential to use a lens clamp when doing macro (or telephoto), as the motor will move the lens barrel a fraction, on starting or changing direction.

Edward



PS. I think I may try a Nema14 (28mm long) with 0.9 degree steps.


Tue Dec 23, 2014 3:00 am
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