# Big Servos



## Hippie Crane (Sep 17, 2019)

Does anyone have any experience with modifying certain motors to make large servos?

I saw in several videos that people were using wiper motors to make giant servos. What I want to use is use those smaller worm gear motors with a crank and rod to move certain movements in an animatronic. I would like to know if anyone has done this and how did you do it? as of right now I know i need an h-bridge drivers to controller the larger motor and I can probably use the circuit out of a standard servo. I also need to have a potentiometer mounted to the frame with a rod attached the the movement (possibly a hybrid linear displacement potentiometer or even a linear variable differential trasnformer)


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## bfjou812 (Aug 15, 2008)

Dr Morbius did just that a few years ago. Do a search on this site for it. He used it for a wiper motor, but I'm sure you could use it for your application.


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## RoxyBlue (Oct 6, 2008)

Is this the thread you're taking about, bfjou?

https://www.hauntforum.com/showthread.php?t=6016


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## bfjou812 (Aug 15, 2008)

I think there was one where he went into some detail about the construction, parts and the application. I checked some of his past posts last night but got tired , too many to try at once.


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## halstaff (Nov 18, 2009)

I've done this with my own boards with some success but this is the one I'm trying now - 



 (not my video)


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## Hippie Crane (Sep 17, 2019)

halstaff said:


> I've done this with my own boards with some success but this is the one I'm trying now -
> 
> 
> 
> (not my video)


Hmmmm... I wonder if that would work for my pneumatic servovalves as well. I've got some big movements that only make sense to use the large bore cylinders I have with a closed loop proportional system.


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## scary rick (Dec 6, 2008)

You should check out xrobots, James has experimented with both pneumatics and servos.


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## Hippie Crane (Sep 17, 2019)

scary rick said:


> You should check out xrobots, James has experimented with both pneumatics and servos.


I've seen those video's. However I've got the real deal servovalves. I've got some from disney and other places. They have a coil inside them with an armature attached to a flexure. And A tube with a tiny slit that aims into 2 really tiny holes to control the speed and direction of the air cylinder. I've got flapper nozzle servo valve, jetpipe servovalve, rotary direct drive servovalves, and lapped spool and sleeve servovalves. They make the movements move like disney animatronics and they are really cool. What was the driver the guy was using in the video above? All of my servovalve take a 0 to +/-10v signal to control the flow and direction of the actuator.


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## Hippie Crane (Sep 17, 2019)

when I say big servos I really mean big servos:


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## Hippie Crane (Sep 17, 2019)

I made some big servos! They work great!
(the one in this video isn't tuned as well as my other ones)


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## DarkOne (Oct 16, 2012)

I'm interested to see how this came together. I know that it may be beyond the realm of the average haunter due to cost, but maybe you'd be willing to do a write up? I'd really like to know about the valves and sensors used to make this happen. Thanks for the video!



Really awesome!


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## Hippie Crane (Sep 17, 2019)

DarkOne said:


> I'm interested to see how this came together. I know that it may be beyond the realm of the average haunter due to cost, but maybe you'd be willing to do a write up? I'd really like to know about the valves and sensors used to make this happen. Thanks for the video!
> 
> Really awesome!


The method I used in that video is called "poor mans position control". It must be done with 2 poppet valves configured 3 way normally open mode. Where if both valves are off then both sides of the cylinder become pressurized. Pulse width modulation is used to exhaust a little bit of air from the side of the cylidner in the direction I want to make it move in. (a bias is applied so that if the cylinder reaches the target position the rod side become slightly more pressurized than the rear side to eliminate creep and oscillations )

They must be poppet valves with relatively high response time (clippard minimatic normally open 3 way valves may word for this).

(valves would be housed in a soundproof box because we are essentially vibrating them and since they are poppet valve they are basically frictionless.

I used 2 MAC 45a valves with the A ports (normally closed) blocked off in the video.

I controlled the cylinder position from of VSA software.


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## DarkOne (Oct 16, 2012)

So the noise in the video was the valves clicking on an off rapidly?


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## Hippie Crane (Sep 17, 2019)

DarkOne said:


> So the noise in the video was the valves clicking on an off rapidly?


yes! You can use 2 normally open 3 way valves, or a 4 way 3 position open pressure center valve, or a 4 way proportional/servovalve


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## Hippie Crane (Sep 17, 2019)

Heres is an elbow joint i made for testing out different actuators. I tested the air servo with VSA software.


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