Wired follow focus for 30 bucks!

[Batutta]

Inspired by this video

, I decided to try and make a wired follow focus for my gimbal. Ended up costing me only 30 bucks in parts and surprisingly easy to pull off. The main parts are listed here. Some links aren't the exact ones I bought but comparable--

Servo tester

Battery holder

Micro Servo

.8 pitch 54 tooth gear

Extension wire


The one mistake I made was getting a servo without enough degree of movement (60). The video link below shows that version. I ordered a different motor with a wider range (180). Will report back when upgraded. But as you can see, it works. The control it allows is very fine and there is little delay. The motor makes a noise, so if you are very close to the camera you might hear it. This is the on camera mic and is mere inches from the motor. I doubt a boom any distance away would pick it up much, especially outdoors. I scavenged some parts I had lying around in order to mount it, so I won't list that here, you'll have to figure that out on your own. All the electronic parts were just plug and play. I'll be getting a small enclosure to make it all tidy, so I can mount it, and a bigger knob probably.

 

[Greg_E]

Servo City has continuous rotation servos in many different sizes. They of course won't work for A to B set ups. But you can get a "sail winch" servo anywhere from 120 degrees to 3.5 turns (maybe more) that might do a lot of work for you.
http://hitecrcd.com/products/servos/boat-servos/hs-765hb-sail-control-servo/product

http://hitecrcd.com/products/servos/boat-servos/hs-785hb-3.5-turn-winch-servo/product

 

[Batutta]

Got a sail winch servo that does 1.5 turns, which was enough range, maybe too much as I lost some precision. 1 turn would probably be perfect. As is it works fine, better on some lenses than others. Only issue I'm trying to resolve is motor buzz. It buzzes a little after moving, creeping subtly if not stopped precisely. Read something about capacitors smoothing out the power input so I might add a capacitor to the power line and see if that helps.

 

[Greg_E]

Digital or analog servo? The digitals all buzz a lot and can creep if the input signal isn't perfect.

What about changing the gear on the servo? A smaller gear might give you the precision you need, not sure if they are available though.

You may need to build an Arduino based control to keep the servo from creeping, the servo testers aren't really designed for high accuracy. A filter on the power input is almost never a bad choice, a choke on the lines might not be a bad idea either, especially on longer wires. This place looks like they have some toroids pretty cheap and it might help http://www.getfpv.com/catalogsearch/result/?cat=0&q=toroid wrap about five times around the toroid and heatshink or glue to keep it neat. Not sure if you want the 13mm or 16mm, both should let the connector through if you are using standard servo connectors.

 

[Batutta]

Digital or analog servo? The digitals all buzz a lot and can creep if the input signal isn't perfect.

What about changing the gear on the servo? A smaller gear might give you the precision you need, not sure if they are available though.

You may need to build an Arduino based control to keep the servo from creeping, the servo testers aren't really designed for high accuracy. A filter on the power input is almost never a bad choice, a choke on the lines might not be a bad idea either, especially on longer wires. This place looks like they have some toroids pretty cheap and it might help http://www.getfpv.com/catalogsearch/result/?cat=0&q=toroid wrap about five times around the toroid and heatshink or glue to keep it neat. Not sure if you want the 13mm or 16mm, both should let the connector through if you are using standard servo connectors.

It's analog. The creep only happens on lenses that require more torque to turn. The motor gets most of the way to its position, then creeps the rest of the way for a few seconds then stops. I think I'm just going to avoid those lenses and stick with my lumix zoom, which works the best. I don't want to be constantly changing lenses and re-balancing the gimbal anyway. This works well enough for my purposes, mostly on the street walk and talks. I wish I could just use my autofocus, but on the GH4 at 4k it's not reliable and too slow. I read about using ferrite toroids, I'll try it out.

 

[Greg_E]

Strange that the winch won't handle the torque, that's their whole purpose in life. You can try to power it with 6 volts, or if you want to live on the wild side try 7.2 volts. Most servos will handle that much but they put out a lot of torque then and start breaking gears. 6 volts is a standard supply for them, down to about 4.5 volts before they get really weak.