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Author Topic: Driving 300 linear actuators  (Read 1348 times)
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the Netherland
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Can anyone tell me if it's possible to drive 300 linear actuators with Arduino? Or how many arduino's I'd need for this? Can I for instance combine it with servo drivers?

The actuators are 12v , >1A. We need to be able to drive them all individually or ogether. We can use external power supply.
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Leighton Buzzard, UK
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crikey what ARE you building???

anyway
a) external power is a must!
b) some sort of multiplexer is needed (look how people drive lots of LEDs same problem, you just need more power)
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the Netherland
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Thanks for the reaction!


We are building an interactive art installation.
to answer some questions:

a) external power will be no problem, I know we would need many Amps..

b) do you know what kind of multiplexer I would need if I need to be able to drive all 300 of them? And is it at all possible to multiplex with motors?
We need to be able to drive the motors for up and down (cycle is 3sec) in intervals of 0.1s at least.


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Leighton Buzzard, UK
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have a browse in the LEDs and Multiplexing forum smiley
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Left Coast, CA (USA)
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On your linear actuators, are you using them as on/off actuators. That is only two commanded positions, fully in and fully out. Or are you expecting to be able to command them to go to a specific position within their travel range and stop?

This is critical to know before anyone can think about how you will interface and control them with an Arduino.


Lefty
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the Netherland
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Thanks Guys,

we want o be able at least to go to a certain position, by saying for instance: stay on for 2.1sec, then turn on for 0.4 sec, then turn back (to zero) in 2.5 sec.
To complicate things, we also want to incorporate a switch in the zero-position, because if the motors incidently turn faster/slower, they will stop turning when they reach zero-point. Otherwise we might overload the motors.

Does this answer your question Lefty?
Grtz!
Tim
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Does this answer your question Lefty?

Yes it does. That makes interfacing and controlling the actuator a much bigger endeavor. What you want to end up with is a 'linear' servo, but if what you have is a just a 'dumb' on/off actuator, then you first need to have some kind of feedback sensor on the actuator to know what it's position is at all times, within it's total travel range, so the controlling device knows if the motor should be moved and in which direction. Do you have a link to the actuator you are planning to use?

 If it is indeed just a 'dumb' actuator then I suspect this would be a challenging project unless one has lots of both software and electronics experience, even if just using one of the actuators, let alone 300.

You know a normal rotating servo can be converted to a linear servo with just mechanical linkages, right?

Lefty
« Last Edit: February 16, 2011, 11:18:06 am by retrolefty » Logged

nr Bundaberg, Australia
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What it the travel of these actuators and the force required? What retrolefty suggests might be the idea if the travel and/or force isn't too great.

Otherwise I think you're looking at building in your own positional feedback. At the very least 2-3 hall effect sensors or similar, as long as "certain position" is always the same. If the position varies then I can think of no simple way to get the feedback, certainly nothing that one would want to do 300 times.

With all this going on x 300 I'd be inclined to have multiple processors (maybe even one per actuator) in a simple network.

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Rob
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Rob Gray aka the GRAYnomad www.robgray.com

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It sounds like you want open-loop control for the actuators, i.e. it's ok if they don't go to a spot-on position as long as it's mostly ok. That makes life easier. I'd use a whole pile of L293 chips to provide the drive and another pile of 74*595 shift registers to control them. Each L293 can drive two motors and requires four binary inputs, so you can drive 2 L293s (i.e. 4 motors) off every shift register. That's 150 driver chips and 75 shift registers.

You can daisy chain the shift registers using the shiftOut() function, but you need to be careful, since I don't believe the Arduino has enough current capability to properly drive the clock and latch lines out to 75 shift registers; you will need to use a non-inverting high current buffer in order to drive those two lines; I'd just use a dual op amps wired as a pair of voltage followers.

You can wire the stop switches into the power legs of the circuit and not worry about dealing with the logic. Use normally-closed type limit switches are wire them in parallel with a diode. Align the diode such that the motor will drive off the stop but not on to the stop with the switch pressed.
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I'm curious if you've priced out a 12 VDC, 300+ amp power supply; your budget already sounds like it going to be fairly large (it would have to be, for the number of linear actuators you want won't be cheap), but have you planned out how the power will be distributed or supplied?

I don't think you're going to drive the whole thing off of one power supply; multiple smaller supplies will likely be needed - but once again, it won't come cheap...
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Smart drive control can reduce the peak current demand way below the sum of all the peak currents. Don't start or stop them all at once, interleave motor on-states, etc. Probably won't cost that much compared to 300 linear actuators, which has got to be north of $10k.
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Smart drive control can reduce the peak current demand way below the sum of all the peak currents. Don't start or stop them all at once, interleave motor on-states, etc. Probably won't cost that much compared to 300 linear actuators, which has got to be north of $10k.

Yeah - I was thinking that too, but according to his statement, he wants to be able to drive them all at the same time - so worst-case scenario and all that...
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I think everybody is just peeing in the wind until the poster better describes how the actuators will be used and what type they are. The actuators can be small or large, and they they can be lightly or heavily loaded.
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a) external power will be no problem, I know we would need many Amps..
Yes it will be a problem, not your biggest one but a very big one. It is difficult to simply scale things up, the rules change when you do. Look at the difference between home baking and shop bought stuff.

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we want o be able at least to go to a certain position, by saying for instance: stay on for 2.1sec,
Turning on an actuator for a fixed length of time from a fixed starting position is not going to get you to the same place every time, you need to know that.

There are so many factors that are missing in the description but actually it doesn't matter because the OP is incapable of doing even a tiny fraction of this project. It is time to call in proper professional quality advice and to adapt your installation to what is possible and affordable.


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I think the only sensible approach is to break the problem down into smaller lumps - perhaps design a 16 or 32-channel driver using an Arduino and associated drivers and sort out all the issues with that, then you can scale up to 300 by replicating and adding an over-all controller to co-ordinate things...  Something like the organization of an orchestra?

The natural hierarchy of your project should drive this - and don't commit to lots of hardware without proving the design small-scale first (one actuator is a good starting point).

And when it works can we see photos?!
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