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Low cost follow focus


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#1 Jeff Cools

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Posted 14 January 2007 - 05:18 PM

:huh: I just wanted to mention to some newbie-s that might be looking for a low cost video follow focus. I made this one using a digital proportional radio transmitter. I works well, but is only good for one motor. The whole systems reciever and battery's are nested in a lite weight plastic box that slides onto the matt box rails. The receiver motor is attached to the video lense. This bracket is available at www.jimmyjib.com. The entire unit can be made for under $400. Hope this helps.

Jeff Cools
www.jeffcools.com
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#2 Matt Burton

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Posted 14 January 2007 - 05:57 PM

You should post some pictures Jeff :D
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#3 Imran Naqvi

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Posted 14 January 2007 - 06:00 PM

Hi Jeff,

Welcome to the Forum. This place is great for getting help and advice from some of top ops in the field, but it comes with one caveat, that your use your real name for your username.

It helps us all generate a sense of community by not using handles.
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#4 Jeff Cools

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Posted 14 January 2007 - 10:34 PM

You should post some pictures Jeff :D


Sorry Matt, I tried to post pics,,it didn't work..,I will try again.

Here's some pics. Attached File  ff1.JPG   36.96KB   365 downloadsAttached File  ff2.JPG   26.38KB   304 downloadsAttached File  ff3.JPG   17.57KB   309 downloadsAttached File  ffcontrol.JPG   13.76KB   261 downloads
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#5 Eric Fletcher S.O.C.

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Posted 15 January 2007 - 12:35 AM

That's one way of doing it. Kinda harkens back to the old Seitz 8700 which was a Futaba PCM Helicopter radio repackaged and running Heden Servos
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#6 JimBartell

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Posted 15 January 2007 - 01:02 PM

That's one way of doing it. Kinda harkens back to the old Seitz 8700 which was a Futaba PCM Helicopter radio repackaged and running Heden Servos


And let us not forget the late, unlamented WRC-4, which was Airtronics RC airplane electronics at the core. Or the WRC-3, whose guts were built by a now-defunct RC model company from San Diego.

Jim "still having nightmares" Bartell
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#7 Jeff Cools

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Posted 15 January 2007 - 01:09 PM

That's one way of doing it. Kinda harkens back to the old Seitz 8700 which was a Futaba PCM Helicopter radio repackaged and running Heden Servos


And let us not forget the late, unlamented WRC-4, which was Airtronics RC airplane electronics at the core. Or the WRC-3, whose guts were built by a RC model company from San Diego.

Jim "still having nightmares" Bartell


I used a regular 2 channel Futaba car controller. We broke off the return spring inside the hand unit and modified the servo to throw as fas as I could. The Futaba radio used was T2PH. The transmitter has a very long range (not sure why you'd use it 200 feet away) buy you could. The servo is being held in place with a bracket from http://www.jimmyjib.com . I bought gears for Fuji, cannon and a film gear 32 pitch.
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#8 Eric Fletcher S.O.C.

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Posted 15 January 2007 - 02:03 PM

That's one way of doing it. Kinda harkens back to the old Seitz 8700 which was a Futaba PCM Helicopter radio repackaged and running Heden Servos


And let us not forget the late, unlamented WRC-4, which was Airtronics RC airplane electronics at the core. Or the WRC-3, whose guts were built by a now-defunct RC model company from San Diego.

Jim "still having nightmares" Bartell



Jim, Jim, Jim....

I think you remember that I know what's in the WRC-4 :) $1500 receiver module my ass!

LOL

You really want to have nightmares let's talk about the LDS!
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#9 RobVanGelder

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Posted 15 January 2007 - 07:12 PM

Yep, i went that route too in the beginning of my Steadicam career. But I found the slack/lack of precision specially with lenses that need a high torque or have a large barrel (so have a large circumference) too much.

To counter that i made the mark on the handunit moving slightly with the direction of the turning of the handwheel en so compensating for the slight distance in the handwheel where the motor does not move.
That worked well, but had to be adjusted to the type of lens.

a higher resolution system would work better, but at that time only 1024 bits were available, giving 512 steps, theoretically. Nowadays you might find better?

Still i think that this kind of DIY is important for the future career, i encourage it!
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#10 kip ross

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Posted 17 January 2007 - 08:58 AM

Still i think that this kind of DIY is important for the future career, i encourage it!
[/quote]

What motor is used in this set up? Does the transmitter somehow activate the built in servo on the lense?

As a newbie, this DIY focus control is of particular interest, given the relatively high cash outlay the newbie would need to justify at the early stage of his Steadicam career.
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#11 RobVanGelder

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Posted 18 January 2007 - 01:32 AM

As i can see from the pictures, it is a RC-servo from Futaba, with a rod attached to mount it on the support bars of the camera/lens.

The main problem with these servos is their lack of movement, they can rotate most likely 120 degrees either side of 0. many even less then that. That's why he has the BIG gear wheel that compensates for that. However, the force that the servo can deliver at the teeth of the gear goes down with the size of the gear disc.
Also the precision goes down with the bigger size.
This may be useful with video lenses with a limited range of focus movement, but for many film style lenses it is not enough to reach both ends.

I opted to use a Heden motor that i already had, which has 5-7 turn capability, is smaller and more powerful.
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#12 chuck colburn

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Posted 18 January 2007 - 02:07 PM

Yep, i went that route too in the beginning of my Steadicam career. But I found the slack/lack of precision specially with lenses that need a high torque or have a large barrel (so have a large circumference) too much.

To counter that i made the mark on the handunit moving slightly with the direction of the turning of the handwheel en so compensating for the slight distance in the handwheel where the motor does not move.
That worked well, but had to be adjusted to the type of lens.

a higher resolution system would work better, but at that time only 1024 bits were available, giving 512 steps, theoretically. Nowadays you might find better?

Still i think that this kind of DIY is important for the future career, i encourage it!


Hello Rob,

There have been improvements to the hobby radios, this one might help those who want to DIY.

http://www.towerhobb...a/futl8926.html
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#13 RobVanGelder

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Posted 18 January 2007 - 09:05 PM

I am sure there are improvements after 12 years that I worked with them, however, the basic limit: the amount of revolutions of these servos are limited. The biggest rotation I found is a winch-type servo for sailing purposes that offers 360 degrees, one full turn.
I could not find the resolution they work with but if it is still 1024 bits, then it has not increased in 12 years so the resolution is the same. meaning you have a low resolution /accuracy with this 360 degrees servo and a higher resolution with a 120 degrees (2x60) servo. For the purpose, reeling in rope, a very accurate movement is not really needed.

I am not saying it cannot work with certain lenses, but for sure you will find the limits to it soon.

The main limiting factor is the potentiometer in the servo, which is a single turn type in the RC servos and a 10 turn high quality (and therefore very expensive) type in a motor like Heden.

And if one of you ever opened a Heden motor to see what's inside, you would appreciate the technical genius behind it!
Not to play down the technical aspects of these miniature RC-servos, they are little wonders too, but made for their purpose only.
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#14 Ivan Casalgrandi

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Posted 19 January 2007 - 01:37 PM

Hi people,
The robotic's boys use modified RC servos.They Convert a 90/180/360 degrees Servo to Continuous Operation. Digital hitec servos are programmable, they can have a 15kg kg*cm torque and metal gear.Inside heden there is a Faulhaber motor (Germany) and is a close loop servo system, RC servo is a open system.
Is a good idea to have a backup system with a RC servo and a Futaba radio, I'll try.

by
Ivan
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#15 AndreasKielb

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Posted 19 January 2007 - 03:04 PM

Funny enough I use a very similar setup for the same reason (...lack of money). It's an older picture and in the meantime I upgraded to a stronger servo (HITEC HS-5745-MG). It is strong enough to be precise with stiff 35mm lensens as it has a torque of 190 Ncm but it also has the 120 degrees turing radius originelly. I modified both servos to make a 180 degree turn by adding two resistors to the pot (http://mypage.yhti.n...s148retract.htm). Had no luck to modify the servo to a proportional turning radius over 180 degrees. When I tried to add higher resistors the servo began to move continously.

This setup together with the big gears can move a standard video lens through it's hole range. It's also OK for 35mm lenses up to 25mm but with a 50mm lens the problem comes again...
So all draw backs Rob mentioned are my all day reality but he forgot to add the slide noise RC servos make. I use the DIY setup sometimes on low budget student movies but I always recommend to rent a real remote focus for the day. For paid jobs I always rent the remote focus but I carry the DIY as backup :P .

However, would you mind sharing the model number of that 360 degrees winch-type servo, Rob? It wouldn't hurt to add this one if it's fully proportional and strong enough to be precise with stiff lenses.

"I opted to use a Heden motor that i already had, which has 5-7 turn capability, is smaller and more powerful."
Do you mean that a 3pin RC receiver is actually signal compatible and can be modified to drive a professional 5pin Servo like a Heden? That would bring me a big step further...
I know it's all about impulses between 1 and 2 milliseconds but not enough to dry such a modification...

"Still i think that this kind of DIY is important for the future career, i encourage it!"
I'm still in my beginners shoes but without DIY nothing would have happened at all. Please check out my new 12V/24V sled if you like :): www.andreaskielb.de/new_sled.htm

cheers,
Andreas Kielb

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