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I want to create an array of linear actuators for an art installation.

The easiest thing for me would be to send a PWM for each actuator. I think of using chips like TM1809 or WS2811 those chips are found in LED strips, you program one with the desired PWM outputs (9 outputs for the TM1809, 3 for the WS2811) and the chip hold these values until next change. These chips are serializable so you can generate thousands of PWM with one SPI output and refresh 50 times per seconds (this is how big LED screens works).

I thought of using motorized faders found on mix control surface (like these). They are fast enough, small and quite reliable. They have one servo track to read current position and a motor but they come without microcontroller so I have to add controller on them.

My question is what chip could I use to control the motor and correct position according to input PWM and current sensor position? It's exactly the role of the controller in a servo. Filter PWM input, read it, then control motor position with PID. Does anyone know which cheap component I could use for this ?

Is there any PID chip supporting on the fly parameter change for Kp, Ki, Kd ?

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    \$\begingroup\$ Just wondering: If you need to position-and-hold, and load is not high, why not use a stepper motor driven lead screw? They are found in old floppy drives, and possibly some CD-ROM drives as well. No power needed once position is achieved. \$\endgroup\$ – Anindo Ghosh Jul 12 '13 at 7:59
  • \$\begingroup\$ There is no load on the actuator once they stop in their position. But they will be moving most of the time. Stepper motor with lead screw are slow, I need fast reaction time <0.1s and at least 100mm stroke length (200mm would be better). I thought of using voice coil actuator like in hard drive head mechanism, but their stroke is too short. \$\endgroup\$ – bokan Jul 12 '13 at 8:13
  • \$\begingroup\$ A small micro-controller plus an H bridge should get you flexibility to tinker with the design. It won't be quite as small as a fully integrated error-amp/bridge type of IC, but it won't be that much bigger. I believe there are projects out there to make servo circuitry using things like ATTINYs, which you might examine or start from. \$\endgroup\$ – Chris Stratton Aug 11 '13 at 14:08
  • \$\begingroup\$ I think the search keyword is "servo driver": this does almost what you want except doesn't take PWM input onsemi.com/pub_link/Collateral/MC33030-D.PDF \$\endgroup\$ – pjc50 Aug 17 '16 at 10:15
  • \$\begingroup\$ You might be able to do it with a continuous rotation servo driving a belt or fishing-line with a pulley at the other end. Rather like analogue radio dial indicators, but machine-driven. No problem with stroke length and light enough to move quickly. \$\endgroup\$ – pjc50 Aug 17 '16 at 10:18
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What sort of throw do you need. There are, in fact, linear servos for model aircraft (e.g., http://www.spektrumrc.com/Products/Default.aspx?ProdId=SPMSA2030L) that might serve off the shelf. You just send these guys a PWM signal-- 50% duty would be center, and changing the duty cycle would move in either direction.

My experience is that the servos are pretty well tuned off the shelf, as they tend to be geared down enough that the servo barely sees the load, so they work just fine for a whole range of loads simply by tweaking duty cycle. You don't need to build a whole PID around them.

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  • \$\begingroup\$ Thank you verymuch for this information but it is too small for what I need. I wich I found 200mm stroke. But even the largest motorized faders are 100mm, so I'll have to start with this. \$\endgroup\$ – bokan Jul 12 '13 at 12:22

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