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Large Solenoid Actuator driven Display

Hello, I am new to this site so I hope you won’t mind if I ask a few questions that I am sure are going to sound quite amateurish to most of you. 

I am an American living in Berlin working on a collaboration between two art research institutes here.  I have been given the task of putting together a proposal for a dynamic moving display. That will be featured next year as part of a conference on kinesthesia. 

My back ground is not in computing or robotics, I am simply putting together a list of materials (and their cost) that would be necessary to make this project work.  And I am responsible for finding collaborators that can help put it together. 

I found this website when I was researching solenoids.  If you have any experience with solenoids I would greatly appreciate any advice or knowledge that you would care to pass on.

So let me try to explain what we would like to do and what I think I might have figured out so far – please be patient and bear with me.

The dynamic display I spoke of can be thought of as a much larger version of this pin-art-clock

http://gadgets.boingboing.net/2008/11/25/1980sstyle-pin-clock.html 

However the display would not be used for numbers but instead for larger art-related images.  Instead of metal pins the display would use much larger plastic knobs (for lack of a better word).  The idea was to use individual actuators to individually lift up each of these knobs so that you could create a series of unique images , symbols, impression, etc.  I hope this makes sense the way I am describing it.  In theory it should be able to handle quick successive displays resulting in a seamless image concept.  To get a better idea of what I mean take a look at the following youtube vid. 

 http://www.youtube.com/watch?v=KRCeKkcTjWw&feature=related

Each knob would have to be able to be raised and lowered independently of the others and in quick succession because the images would in effect be streaming across the display.  The display would be quite large (2 to 3 meters in length and width) with several hundred knobs and corresponding actuators in order to achieve higher resolution.   The knobs would be constructed out of light weight plastic.

I located these companies for solenoids:

http://www.dormeyersolenoids.com/solenoids.html

http://www.ledex.com/

http://www.solenoids.com.tw/about.htm

I thought a small, electric - AC, linear, pull-type solenoid should suit the purpose.  The only problem is that the shaft extension length on most of them is quite short.  I was thinking that for best resolution it would be good to have a difference between the raised and lowered knobs/pixels of at least 2 to 4 cm.  However, most of the solenoids that are capable of achieving that are far too powerful (and thus expensive) for our needs.  I realize that it would be possible to devise a lever of sorts to amplify the small movement but that would result in more moving parts and thus a greater chance of breakdown and higher maintenance.  I also looked at the possibility that I saw recommended of a camshaft with suspension spring but I think this would be too bulky to place side by side and would not possess sufficient speed.

And  I thought that this microcontroller, or something like it, that I found on this forum might be what  would be needed to independently control the solenoid actuators.

http://www.societyofrobots.com/axon/

So what I would like to know is what kind of solenoid would you recommend for something like this (does not require large force, does require large shaft movement of 2 to 4cm)?  How do I determine how long it can remain on (in a contracted position) and how long it has to rest (heat dissipate) before it can be activated again.  Is is possible to get an electric solenoid that is able to be activated in quick succession (1 to several times per second) for several hours without damage?  What would be the best means of control several hundred solenoid actuators independently?  Would the microcontroller I posted above work, and if so would I need several of them to control a large number of solenoids or is one scalable – if I do need several is there a way to link them to create a seamless image? What should I take into account when deciding on an operation voltage?  Finally what would you expect to pay for the type of solenoid that I described above?  Also any suggestions on the best way to hook up a power supply would be appreciated.

I will definitely have more questions, but I thought this would be a good place to start.   I hope you will be able to help – and patient enough to make it to the end of this long posting J

Cheers,

Ryan

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I was considering something like this too. The problem with solenoids is, as you say, they're either expensive or big, and you have to have a way to choose an "interim" position too -which is not so easy.

My other thought was to use a huge array of pager motors that rotated a thread, with a mounting nut attached. If the pitch on the thread is steep enough, you can get a range of interim levels - but then you have to calibrate the pager rotations, which might be tedious.

 As for controlling a big array of solenoids/pagers, perhaps multiplexing is the way to go? -maybe this link is a fun intro into multiplexing - but I've never tried to make this thing!.

http://blog.makezine.com/archive/2007/09/make_a_pocket_led_cube_we.html


 

Thanks for the suggestion, but I think a roating head would create its own problems.  First you have this problem of calibration you spoke of, second more moving parts tends to lead to a better chance of malfunction, and finally the response time would be severely limited compated to an actuator - which would limit the speed and dynamics of the screen.  

I don't think calibration would be too much of a problem. At some point, you're going to have to feedback the current position of the actuator, and you can accomplish this with small motors by using it to simultaneously drive a small pot. 

I am sure small motors fail from time to time, but I am unclear what the failure rate actually is - versus, say, solenoids or pneumatic valves.

As for speed of response, for a pager motor that spins 21000 or 30000 rpm, putting even a modest pitch angle would give you a very fast response. Furthermore it would be relatively easy to mount a stack of motors, and simply wire them up.  I might have thought that using valves would require lots of wire, lots of tubing, and lots of potential failure points - rubber hosing might degrade too...

 

Talking about the first picture you posted: You wouldn't have to use a solenoid/actuator for every pin you see. You could use instead one per segment and divide each digit into 7 segments (just like the digits you see on alarm clock), thus connecting all those pins that belong to the same segment to just one actuator, that, i believe, could make things much easier.

I understand what you mean and maybe the clock was a bad example.  It is probably better to refer to the you tube vid. The idea would be to be able to have each actuator/pixel move independently of the others so that you could for new and novel images with the screen.  If you divide the screen into segments then you are limited to the initial shape of the segments with what you want to show.  With the clock example you can only show a series of numbers and those numbers have to be in 1 of 4 positions.  If each actuator moved independently it would be much more possible to get the waveform motion that would be of interest. 

Thanks for you intput, and I hope i explained this clearly.

 

I'm wondering if it might be easier to use electrically controlled pneumatics? If you had lots of small electically controlled valves, and each one would allow air to blow into a "pixel". Each pixel would be a light weight ball contained in a glass or plastic tube that allows some air to pass. So if air is flowing, the pixel ball floats up. if not, the ball drops.

Then you wire your microcontrollers to the valves, and you can make the pixels go up and down at your command.

No matter what approach you take, you are going to need to address a lot of outputs. How many pixels are we talking about here?

Nice idea, but the problem is that it should be wall mounted. If you use balls you require gravity to pull them back down which would limit the configuration to a horizontal mount. 

Around 100 to 200 "pixels"  This is where price (and to some degree weight) begins to play a role.  If possible more would be added to enhance the resoltion capactiy of the piece but right now I am using this as a starting point.   

Tricky. I was thinking of a horizontal display.

You could still probably do it, if you have valves that either directed air out to the "pixel" or sucked air in. Availability, cost and size of the valves would be your limitation, but it would work in theory.

Good luck with this project. Please be sure to post a link when it gets started and even better when it gets finished!

Thanks for your interest ignoble.  If this project gets the go-ahead I will definitely post the results.  Right now I am still trying to put together a price proposal and then that has to be submitted to the committee along with collaboration partners and estimated time of construction.  I am optimistic but I will take a while.

 

Thanks for you suggestions.   

In order to get a larger "throw" from a small solenoid, have it actuate the end of a lever. If you have a solenoid that moves 1 cm when powered, have it press the end of a 6 cm lever, say 2 cm away from a fulcrum, turning point. The other end of the lever, 4 cm away, will move 2 cm. It will be half as strong, but perhaps the "knobs" are light weight.

Rinse and repeat for tightly fitting many solenoid actuated levers together.