# DMX controllable Linear Actuator



## Erwin Redl (Apr 28, 2015)

Hello-
I am looking for a linear actuator that is DMX controllable. I am hoping to simply plug it into my 12V DMX driver V+ and V-. I am imagining that I can program it to go back and forth on one ID. (For example set at 0 the actuator is at the left and 255 it is all the way on the right. The speed at which it travels is based on how slow I fade from 0-255. At 128 the actuator stops in the middle.) Is this realistic? Does something like this exist? Thank you in advance!
-Erwin


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## BillConnerFASTC (Apr 28, 2015)

you may be able to find it or a way to do it but dmx is an open system and control of most things we call rigging - where someone could get in the way or be harmed - requires closed loop systems. in other words, dmx just keeps yelling do this, do this, do this...and doesn't care or know what is happening. Rigging controls have telemetry that is always being checked to see if the piece has done what it was told.


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## DMXFactory (Apr 28, 2015)

I agree with Bill, please be very careful when using DMX512 for moving parts. A closed loop system would be much safer. If you choose to do this, it is at your own risk.

That said, I did not find what you are looking for exactly, but I did find this!
A 0-5V controllable linear actuator: http://store.firgelli.com/Firgelli_L12_I_p/l12-i.htm
A dmx512 to 0-5v analog output converter: http://northlightdmx.com/dmx512decoder.htm
Put these two together and I expect it will do the job nicely.

You can also find a number of dmx512 to servo motor controllers that you could use with a linear actuator designed to act like a servo. I have not used any of the above products myself but the theory is sound. Again, please be careful. My comments are only suggestions and may only be used at your own risk.

Good Luck!
Adam


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## n1ist (Apr 29, 2015)

The main reason not to use DMX for automation, pyro, or anything else where reliability and freedom from false triggers is important is that DMX does not have a checksum or other form of error-detection. There is no guarantee that the value received by the device is the value sent by the controller. If a light flickers for 44ms, it's not too serious. If the pyro or motion triggers at the wrong time, it could be fatal.

The only way I would do it is to have a deadman switch with an operator as the main control, and use DMX only for the timing (some systems require two or more specific channel values to trigger - ie. channel 1 = 0x55 and channel 200 = 0xAA). The effect may still glitch, but the operator would prevent a chance of injury.

/mike


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## robartsd (Apr 29, 2015)

Warnings about safety are always good; however, the OP has not given any indication that the effect he is trying to control has any impact on safety. There are plenty of things that one might use an linear actuator for that would not be cause for concern.


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## Erwin Redl (Apr 29, 2015)

The overall vision is to have two 25 foot long (7.5m) pendulums that naturally swing from the ceiling of the theater. At the end of each pendulums there will be an RGBW LED rigged within a focusing mini flashlight.
Building these pendulums as well as all of the wiring for the LED is easy and already complete. The LED will be controllable with a DMX controller. Now comes the tricky part for us. We would like to be able to control the swaying movements with the same DMX controller.
As of now we have 2 ideas for the swaying mechanism. 

Idea 1: Linear actuator. If we use a liner actuator we will mount a hinge onto its carriage. By controlling the actuator back and forth at a rate just ahead of the frequency of the pendulum we will be able to naturally swing it back and forth gradually building up momentum or slowing it down. We want it to be in sync with the lighting, so it would have to be able to accept DMX signal.

Idea 2: Stepper motor. With the stepper motor only we would mount a 3' (1m) arm onto the motor shaft. On the end of the arm we would attach a hinge. By controlling the stepper motor back and forth at a rate just ahead of the frequency of the pendulum we will be able to naturally swing it back and forth gradually building up momentum or slowing it down. We want it to be in sync with the lighting, so it would have to be able to accept DMX signal. The stepper motor in this instance would need more torque than the linear actuator motor because it will have more leverage against its position. However, we are not sure how to go about identifying how much power our motor needs.

The pendulum will probably weigh no more than 10 lbs. If we go with a linear actuator it does not need much strength. We have calculated that the frequency at 25 ft. (7.5m) of the pendulum will take approximately 5 seconds to complete its journey from starting point back to starting point, therefore we will need a linear actuator to be fast enough to travel its stroke length in 2.5 seconds. We assume that we will need 6-12 inches of stroke length to provide the pendulum sway we are looking for. So we are looking at an approximate speed of 5in./sec. (127mm/sec.)

With both options we will want to be able to control the speed and frequency with our choreographed DMX program. This is a one time use so at this point we are looking for a system that is very affordable. We found individual DMX relay boards that communicate between DMX controller and motor, but they are like $300 each and we need one for each pendulum, and that doesn't even include hardware cost. We are looking for a complete solution for the mechanism and relay that costs hopefully less than $750 maybe more like $500 for both pendulums.


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## n1ist (Apr 29, 2015)

It all depends on the power or control signals your motor or actuators need; without that, it's hard to spec the interface. There are readily available boards for DMX -> relay, DMX -> 0..10V, and DMX -> RC servo. Depending on the actuator, I'd look into an Arduino with the appropriate motor driver shield, if you are OK rolling your own, or look at Blue Point Engineering or Northlight Systems.
/mike


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## BillConnerFASTC (Apr 29, 2015)

robartsd said:


> Warnings about safety are always good; however, the OP has not given any indication that the effect he is trying to control has any impact on safety. There are plenty of things that one might use an linear actuator for that would not be cause for concern.


Which is why I qualified my comment with " - where someone could get in the way or be harmed - " No indication either way. Even the pendulum description is not clear whether these could injure someone or not.


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## Erwin Redl (Apr 29, 2015)

There is absolutely no way someone could be harmed by these pendulums. They are all suspended overhead and can not make contact with anything no matter how hard they swing.


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