Let's Make Robots!

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


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. 


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:




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.


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



Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.
I still haven't seen a definitive answer regarding the 'value' or 'shade' each pixel will need to be capable of. Both solenoids and pneumatics are notoriously difficult to control in any situation that requires more than a simple on/off, or in your case, black/white system.
To make a pneumatic or solenoid actuator loiter mid-stroke with even low accuracy typicaly requires a significant investment in feedback hardware and software.

Well before I was not actually considering giving each pixel a shade.  I thought black and white would only be necessary and not really grey(s), so to speak.  I thought the best way to go would not to have a static image but one that quickly moves across the screen.  

Imagine this: you have a vertical screen in front of you.  It has 100 of these pixels that are able to move up and down.  Each pixel is is a ball (choose your color) connected to a linear actuator.  Unless you have a very large range of movement I am not sure that the eye would be able to distinguish very well between balls that were not completely elevated or at rest.  If you have a ball at 75% maximum height and an adjacent one at 65% I am not sure the eye would be able to distinguish the difference (of course that might depend on lighting as well)  

But I did not think it would be necessary to have anything more then a simple on/off when producing waves or image silhouette that were moving across the screen.  For example in the youtube vid I posted earlier there is no shading.  You have a signal that propagates out from the center.  As one pixel is in mid stroke the next one start up, and when it is mid stroke the next one starts up.  THis works because the image moves fast enough that your eye is able to perceive the over all movement of the piece.  If you were to have a static image that remained on the screen then I think you would have to have some sort of shading.  But if you did have a static piece (even a very simple image) you would need many more pixels.  Again in the you tube video I think there is something like 2,500 pixels just for a moving wave.  In the kinetic sculpture piece you have something like 800 to 900.  I think cost wise 500 to a 1000 might be feasible (might be) but to get really good resolution where shades of grey would be required would greatly exceed what is feasible.  I think. 

Does that make any sense?  


It really comes down to the level of detail the images need to have. 2 level imaging restricts you to basic silhouettes, lettering characters, etc.

The "Box Dance" video does in fact use graded values for height; you can see this by observing the pixels near the center - many of them never reach the full height of the other pixels. If you were to attempt a smoothly propogating wave with binary pixel values you'd need to carefully match the wave speed to the rise/fall time of each pixel.
For an actual image to move across the screen without blurring the edges you'd need to ensure the movement period (seconds per pixel) was sufficiently below the rise/fall time of each pixel.

If you use micro servos, geared motors, or similar then there is virtually no overhead involved with adding shading. With other designs there will be significantly more added cost and complexity.

As far as the Bernoulli effect design goes you'd need to ensure that each ball was isolated from the surrounding ones, otherwise the venting of adjacent valves would disturb the ball's stability. For the balls to become trapped in the air stream the valves must also open and close gradually, otherwise inertial effects will shoot to ball out of the stream, or at the very least generate excessive turbulence. The only way I can see this working effectively is if the balls are either contained in transparent tubes, or if they have a small area of open space around them and they are securely tethered to the valve, preferably with an elastic cord. The second of the above options will require a significant amount of extra air pressure compared to the first option, due to various turbulence and loss effects.