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Homemade Remote Head

Published : 21st September 2003

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style="margin-top:0;">So, being the ever tireless tinkerer, I'm thinking it ought to be not overly difficult to turn my Mitchell Gear Head into a remote head, yes?

Where might I look for the.stuff.to make this. I'm assuming there's some sort of transmitting device I can adapt to my wheels that will send a signal to motors I adapt to the head itself. Any suggestions (besides, get a real one) are appreciated.

Thanks bunches.

Roderick Stevens

Az. D.P.

www.restevens.com

 


 

Roderick E. Stevens II wrote:

 

>I'm assuming there's some sort of transmitting device I can adapt to my >wheels that will send a signal to motors I adapt to the head itself. Any >suggestions (besides, get a real one) are appreciated.

  

Take a look at Hot Gears. It's exactly what you're proposing.

 

http://www.hotgears.com/

 

Mike Most

VFX Supervisor

IATSE Local 600

Los Angeles

 


 

So, being the ever tireless tinkerer, I'm thinking it ought to be not overly difficult to turn my Mitchell Gear Head into a remote head, yes?

 

I briefly looked into the same thing for my own compact geared head, and I came up with a little info, but haven't had the time or money to explore/develop the idea further.

 

What you are looking for is a proportional rotary encoder which will drive a controller for a DC servo motor or stepper motor.

 

I was shying away from stepper motors as they are generally noisier than servo motors, and not quite as smooth.

 

I've seen controller kits ($35-40) for DC servo motors down at my local electronics store which work off of variable resistance- That means that you can easily rig some type of joystick control. The controller sends short pulses of the full voltage to the DC servo motor. The less resistance, the closer together the pulses are. The inertia of the motor smooths out the pulse interval. This allows the motor to exert nearly it's full torque at even slow speeds while still being smooth.

 

The trick comes in using the hand wheels as a controller. Finding inexpensive rotary encoders online is relatively easy, as is finding DC servo motors and controllers. The thing I've had the most trouble finding is the interface to decode the pulse phase from the rotary encoder and translating it to a voltage or resistance which will drive the servo control.

 

Proportional encoders generally use a spinning wheel and two light sensing diodes. As the wheel spins it turns alternately blocks and unblocks the light from each of the light sensors. This essentially creates a square wave. By determining how out of phase the square waves from each sensor are, the controller can judge direction and speed.

 

Absolute encoders give you the exact position of the axle. While this is useful, my research seemed to indicate that Proportional encoders where better suited for this application.

 

I don't know enough about electronics to wire up my own interface. I was tempted to bust open a mouse and write a simple software application to drive a servo controller from the serial port of a computer, but that seemed like it was overcomplicating things a bit. Besides this didn't seem like it would be robust enough to survive in real world production.

 

I've seen hot gears, but I'm convinced I can do a no-frills version for far less $$ - besides their kit won't fit on my 33lb NCE geared head.

 

So if anyone knows where I can have an interface made or a manufacturer who has complete kits. Please let me know as well.

  

Thanks,

  

Rachel Dunn

http://www.racheldunn.com

Cinematographer Los Angeles

 


Rachel Dunn wrote :

 

style="margin-top:0; margin-bottom: 0;">>Proportional encoders generally use a spinning wheel and two light >sensing diodes.

 

I believe you mean "incremental" encoders. This is what you want, more than likely, as an absolute encoder would be overkill, and make electronic gear boxing more difficult.

 

There are many servo drivers out there that will accept encoder input directly.

 

Jeff "collects servo motors, though not intentionally" Kreines

 


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Hi,

 

Ideas :

 

- Modify focus motors?

 

You'd probably need to change the output gearing, though, and I imagine the miniaturised casing wouldn't let you have much flexibility.

 

- Radio-control model servos.

 

No, not nasty little ones, big sail-winch servos as used on miniature sailing boats. They rotate infinitely and could be controlled from a radio-control handset or simple PWM electronics (I have boards for this somewhere, but the rotary encoding is still a minor issue if you want to run it off wheels.)

 

- Trained hamsters running in wheels attached to head respond to pan and tilt demands by dangling food in front of them.

 

Phil Rhodes

Video camera/edit

London

 


 

Just for starters try "ahha." They make do-it-yourself CNC controls and motors for the home machine tool hobby/industry. They are friendly, relatively inexpensive and have lots of material to study.

 

But I think they are still stepper motor based.

 

style="margin-top:0;">www.ahha.com/

Jerry Cotts

style="margin-top:0;">DP/LA


 

Rachel Dunn writes :

 

>I was tempted to bust open a mouse and write a simple software >application to drive a servo controller from the serial port of a computer.

 

Combine something like this with an integrated touch screen (and/or mouse pointer) follow focus/zoom system and the world will beat a path to your door.

 

>I've seen hot gears, but I'm convinced I can do a no-frills version for far >less $$ - besides their kit won't fit on my 33lb NCE geared head.

 

Hot Gears can do neat tricks besides straight remote control. For example, stopping on a pre-programmed dime so you can, say, follow a falling egg and end up on a perfectly composed static composition when it splatters on the pavement, narrowly missing the protagonist.

 

Dan Drasin

Producer/DP

Marin County, CA

 


 

Jeff "collects servo motors, though not intentionally" Kreines wrote :

 

>I believe you mean "incremental" encoders.

 

>There are many servo drivers out there that will accept encoder input directly.

 

Yes, you are right, I did mean incremental encoders.

 

Thanks,

 

Rachel Dunn

Cinematographer Los Angeles

 


 

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