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

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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Actually I did consider that, and still am.  The only draw back I thought would be that it would at to the amount of moving parts and thus lead a larger chance of eventual failure.  If this screen was in regular use you would expect the bearings of the fulcrum to wear out rather quickly (at least compared to the life of the solenoids).  I also thought it would dramatically increase the cost and complexity to put a lever of sorts on top of ever solenoid.  Maintenance would also be tricky.   But it is definitely a possibility and might in the end result in a lower cost then a more expensive solenoid with a longer shaft.  

Oh, and I just thought of this.  the less expensive solenoid type is the pull version.  The pull version is also good because it would minimize the chances of onlookers being "poked" with an ejecting solenoid.  A simple lever would in effect reverse this pull action.  

 Interesting possibility though. 

I saw the video - interesting too, my suggestion would be more along the video..  What about of an air nozzle vs a pneumatic solenoid?  You could put a plastic ball on a small plastic air nozzle.  The air goes on the ball goes up on a jet of air.  The Bernoulli effect would keep each of the balls in place.  This probably does not match your requirements for the display, yet I would imagine that the air nozzle / ball approach is :

1. cheap (needle air nozzle)

2. and light - (all plastic and air hoses & control wires)

needle_air.jpg

I would want each nozzel to be connected to a PWM output - so you could get a range of motion vs only ON/OFF of a typical solenoid - this could add to dramatic effect as a wave turned into a static wave.. etc

 Good Luck - dang this looks fun :)

Hmm. I really like the idea of using air to move the display. Excuse us for hijacking the thread to continue down this path even if you don't follow it. ; j

Those valves look like you adjust them with a set screw that turns. So depending on if a half turn is enough, you could just hook up a servo. Or use servos attached to a gear set to get more range of motion.

There is an advantage to an electrically controlled valve. You could run flexible tubing to the back of the display, so as long as you have access to space behind the display, you aren't limited to very small valves. That would give you more flexibility on choosing parts that work and are cost effective.

For a vertically mounted display, having both a vacuum tank and pressurized tank along with a three-way valve would be a cool set up. The valve connects each pixel to either vacuum or pressure. Even if the valve is either "on" or "off", you could switch rapidly to set the balls at varying positions. More complex programming if you go that way, though.

You'd need to re-pressurize and re-vacuum the reserve tanks periodically, but you wouldn't need a full time air compressor and vacuum running all the time. That plus remoting the valves could make the display nice a quiet. You can and speakers for sound effects sych'd with the display.

Cool idea. Thanks for bringing it to LMR to kick around.

Yah,

this has potential - you don't need to use a servo - but directly connect the electrical output (plus BJ Transistor) to the needle valve.  If you pulse the the needle valve with PWM - you can get an analog pressure from the needle valve.  Air, water, or electricity - pulsed can provide a gradient of pressure if you can vary the duty cycle.

I have heard of really cool fountains regulated with air pressure, which in turn is regulated by a needle valve.  With computer control segments of water fly from one nozzle to another giving the impression of bouncing water segments....

Then there is the BMW kinetic sculpture -I have not read the details but I imagine this works on servos and wire.

I think they pulled it off very well.  Balls on air would not probably have the range - but they would be potentially quicker.

Thanks for the link GroG!  That was great.  So you guys are suggesting a sort of inverted version of that kinetic sculpture piece – instead of the balls hanging from the ceiling they would be pushed up from the floor via a controlled air current.  If this was a horizontal piece then you would not need the 3-way valve that ignoble suggested you would just let gravity do the work.

I liked GroG’s idea of creating analog air pressure pulse for controlling the balls that seems to be the easiest way instead of opening and closing the air valves with a servo – and much faster and more responsive .  But correct me if I am wrong you would need an air tank per valve/ball it you went this way.  Imagine you have a small grid (thus low resolution) of 100 balls in parallel (10x10) Each ball would have a corresponding valve.  There would be no way to direct and control the air pressure from a single tank.  Correct me if I am wrong but as some point you would have to have a mechanism (individuals servos perhaps) that would redirect/modulate the air flow from the single tank to each valve.    

If you have a tank per valve or if go with ignoble’s idea of a three valve system with servos and a single tank wouldn’t you create a piece that would almost or more expensive then something that uses a solenoids?  Also the amount of space that would be required for the valves, airtank(s) and tubbing (three types in ignoble example plus a plastic casing for the balls) would make the whole structure quite large.

What do you think about this? Let me know.

I just thought of this too.  If you had a horizontal piece you would need a much larger range of movements in order to create an "image" because in effect you would not be creating an image or silhouette but instead an outline (much as they created an outline of a BMW in the Kinetic piece.  

Each ball would have a corresponding needle valve -

" There would be no way to direct and control the air pressure from a single tank." <-- um, you can - that was the point.

Picture is worth a lot of typing ... so here

 ballsculpture.jpg

microcontroller, wires, needle valves, hoses, a single tank and a single compressor  would be the list of parts.

The limitation would be on the microcontrollers ability to provide enough PWM signals - it could be multiplexed but you begin losing individual control (resolution) of the ball movement.  But that would be an issue depending on what images you want to make

I realized that my previous picture of needle valves are not electric - here is a more appropriate picture

 

PSV_Valve.jpg

I have only seen the bernoulli effect in action with something like a reverse vacum cleaner that was supplying a large and constant flux of air.  I assume that the design above would allow for a quick flux of air and then the ball would settle back quickly on the nozzle.  

 

Just a thaught why not use Micro servos with a linkage to produce linear motion, then you can control extentsion level, plus they are small, light and cheap :)

 

Just my two cents.

So instead of using a solenoid you would suggest using a servo like they suggest here ( http://letsmakerobots.com/node/5581#comment-18056 See: OddBot -To imitate a pneumatic ram)

This would allow you to create a range of motion as well, correct?  Do you know how fast the servo's are?  I ask because the whole idea would be to have a fluid image moving across the "screen".  This is why I was staying away from the thread mounted motor with because of the time it would take to adjust them up and down.  If they are fast, and able to handle a moderate load (the load being the ball or knob that is used as the "pixel), and cheap this might be a nice solution.  

 

Are there any other problems that might arise from this?