Linear Motion Control - Servo?

Curt Welch wrote:


... and only to one of the states - you need to address each row twice to get 1's *and* 0's :-).

I suspect it could be quite a bit quicker than this, but...

Not video, true. But is it art? Slow refresh could add intrigue... and by not scanning in consecutive order you could get some very interesting progressive-exposure effects.
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True, it could produce some very interesting effects.
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Curt Welch http://CurtWelch.Com /
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Clifford Heath wrote:

Exactly my approach, Clifford!
But there is no need in the cylindrical magnets - just use the coin-like ones! Use the PCB coils and you are set!
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pixel . If you need to just simply push or pull and have a spring return, then a simple electromagnet will do the job and will cost pennies to make. Take a nail, wrap it with wire, put a spring loaded piece of metal glued to the back of your little mirror, power the coil, zap! Unpower and it returns to neutral or off. The original ENIAC had a bunch of donut wound magnets for digital control... I think you can also find them by the thousands in some salvage yards that were used for telephone switchboards.
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Richard Greenberg wrote:

τΑΛΕ 33 square mirrors backed with plastic/wood (you could use foam plastic) with little magnet attached. Put those on the common axis with nice spacers. Take the laminated FR-4 and make 33 printed coils. Energize the coin in the needed direction to attract/repell the magnet. Assemble 33 of such rows in one column and you are done. Do not use servos - it is total overkill. Do not use linear actuators - this is absolute overkill. Making 1000 square mirrors will be your hardest problem - make those from brass foil with silver on it (do not forget use the laquer).
Arcady
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Hi all. We are most intrigued with the concept of the spinning motors. We think that by creating the "different" states by way of spin (along with interchangable faces on the disks) we open up a whole dimension of creativity (that is not a direct copy of the existing "mirrors" out there). That is, the image could look very different depending on which set of disks are used. Also, our feeling is that the cost of going this route would not be too great. Also, the construction seems simpler. Anyway, here are the questions at hand.
1. What kind of motors do you recommend? 2. How do we address motors individually from a computer (what are the main components to pull this off)? 3. Do motors have different "end types"? Such as...Are there motors with simple female threaded ends? 4. How do we control the speed of each motor independently? (We are thinking that having variable speed control will make things more interesting, but we are open to the idea of the on/off binary situation as well.)
So, we know this is asking alot, but if any of you have the time to address these questions with answers that we may understand, we would be most appeciative. We really just need some "basic" concepts/components info at this point.
Thanks, Em and DAD

pixel
controlled
computer.
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small cheap ones? I'm no expert on motors but you can search around for robotics and motors and find many sights selling small cheap DC brush motors. These have permanent magnets in them and run off of DC voltage. The direction of spin is controlled by the direction you apply the voltage. I'm not sure how these are normally mounted. I think some might come with taped screw holes but I think most are expected to be clamped into place somehow. Many someone here with more practical experience with them can provide some insight.

What type of computer are thinking of using? A normal PC or some type of embedded processor? There's a lot of different ways to go with that and it will depend a lot on the type of experience your team has.
No matter what you do, you will need some type of I/O port on the computer connected to some type of drivers to power the motor. The I/O ports on computers won't in general have the power needed to drive a motor directly. So you need some type of driver circuit to basically amplify the signals from the computer to provide the current to the motor.
One class of such devices is called an H-Bridge. These are devices that not only allow you power the motor, but to also switch the direction of current to make the motor spin in either direction. They also allow you to control the speed of the motor. They normally do that by turning the power on and off very quickly with different ratios of on time vs off time.
There are multiple options on how a computer might connect to the H-Bridge driver. The small embedded processors have digital I/O lines. These are a single wire coming from the processor can have it's binary value set to 1 or 0. At 1, it's held at something like +5 Volts. For 0, it's held at ground. The computer can turn these digital I/O ports on and off in any sequence you want to program and it can do it fairly quickly (thousands of times per second).
Some H-Bridge devices are meant to be driven straight from a I/O lines like these. You might use two of them, and depending on the combination of 1 and 0 values the computer has output to these I/O lines, the H-Bridge will make the motor spin forward, or reverse, or act as a brake to make it stop.
Other H-Bridges can be driven with the pulse width signals used to drive servos.
If you are using a standard PC, the closest there is to single I/O lines is a parallel port (which newer PCs don't even have any more).
There are devices for controlling H-Bridges with serial ports from computers, and there are probably some USB options. Though I don't know what's available that way.
Your problem however is how to control a large number of motors without costing a fortune. You could buy 1000 H-bridge devices and find some way to make your computer send signals to all 1000 H-Bridge devices - but that's going to be expensive because a H-Bridge is not all that cheap.
A quick search on the web turns up this:
http://www.robotstore.com/store/product.asp?pid1&catid86
Which is a device you can hook to a serial port on your PC. You then buy one of the their dual H-Bridge circuits to connect to the serial board. With those two boards, you could write software on a PC to send data out a serial port, which would control only 2 DC motors. And those two boards would cost you $100 total. So that's $50 per motor.
That serial board is designed so you can hook many to the same serial port and end up controlling a total 254 motors. Using that with 4 serial ports on a PC and you could control 1024 motors. But it would cost you $50 per motor.
That H-bridge however is larger and more expensive than what you will need. But there are probably multiple options like the above, that you could buy off the shelf parts and not have to do any electronics other than wire parts together. Search for things like robots and h-bridge on the Internet to find more about these things.
Now, the other option you have, is to develop a custom circuit for making this work for less money. How much of this you will be able to do depends of anyone on your team has any electronics experience (or if you can get someone that does). There might be people in this group that could even hire to do some work for you at a low rate. I know the theory, but don't have the practical experience to do anything other than give you some ideas.
What you can do is hook all your motors into a large X-Y grid where you have row and column wires where the motor is attached at the intersection of each row and column wire. You will also need a diode in series with each motor. With this configuration, you can build a circuit to apply power to one row wire, and one column wire at a time. Doing that will activate the motor located at the intersection of that row and that column wire.
A custom driver circuit would then have to be built to apply the power to the row and column wires in response to the signals from the computer. But this could be made much cheaper, than using 1000 individual motor controls.
With this circuit, you could only spin the motors in one direction. If you want to spin them in two directions the same idea could be used, but with more column wires and drivers.
The computer would have to be programmed to do a complex pattern of turning row and column power drivers on and off to make everything spin correctly. But to some extent, you could could control the speed by how often you turned motors on and how long you left them off. The programming could be rather tricky.
So that's some ideas to get you started.

Most the small cheap motors just have a small shaft sticking out with no threads or any way to attach anything. You have to either pressure fit something on to it, or weld or glue it, or use a collar with a setscrew. But if you check around, you might find other options.

As above. The H-bridge circuits allow you to control speed by turning the motor on and off quickly. But even the cheap H-bridge circuits that you can buy off the shelf will cost you a lot if you use a separate H-bridge for every motor.

That's a start for you.
If you search the Internet for robot stores that sell robot kit parts and search for H-bridge and motor speed control and start reading everything you find you will start to get an idea of what's out there and you will find a lot of sites that offer introduction information to all the technology. What you will be able to do has a lot to do with how much electronics experience and computer experience your team can put together so you can custom create a solution instead of having to try and make it work with off the shelf plug-n-play devices that will cost you a fortune.
Maybe there is some product that I've not heard about for controlling a matrix of motors - but it's such an odd application that I would doubt it. But maybe you can find info on controlling a matrix of lights that you can adapt to your project?
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Curt Welch http://CurtWelch.Com /
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I see nobody suggested this...
take small dc hobby motors
a) the torque of a dc motor like that is proportional to the amount of current being run through it
b) the position of a spring (like say a coiled one) is proportional to the amount of torque on it
this is like the meter idea, but with motors
so for each mirror, you do
motor---mirror---coil spring
pretty simple at that level, if you add some drag to each mirror shaft (maybe just the motor shaft) you can reduce the effect of the inertia, those are all servo calculations
now lets say you have 1000 hobby motors and springs, controlling them this isn't so hard actually
if you control each motors power with PWM, you can break it down to wiring all the motors into 10 rows and 10 columns, which, if the highest PWM duty you need on them is 10% becommes quite a straightforward task with a small microcontroller, say an atmega32
the great thing is that with the spring return, you only need to have control over a single direction of the motor, so you only need 20 driver transsitors to operate the array.
if you did a bunch of math, you could probably get a good responce time from the array, I'm thinking maybe 500ms update time, but I dont know if you would have to immerse the whole thing in oil to get the damping right :)
you woldn't need feedback on the system, you could use software to compensate for positioning differences between the mirrors.
cost maybe $1500 in motors, $50 in springs(?) and maybe $100 in controller parts.
dan
Richard Greenberg wrote:

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If the front of your mirror is your XY plane, about which axis are you going to be spinning the blocks? I am guessing that your blocks are going to be cubes, how big are they? If you are spinning a cube and lets say it is a 3" cube you are going to need 5/8" on each side and that would make this mirror over 11' if you had 32 rows. I just think the gaps would look weird. Just a thought. I am interested to see how they go about controlling 1000 motors separately. Keep us posted.
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Rich,
I don't know if this will help, but I remember reading about a project where an articulated mirror was controlled using piezoelectric devices (I think the application was for a solar furnace). You may be able to find some materials that could be glued to the back of the mirror segments and used to control it... such an arrangement might be a lot more amenable to mass production (and small size) than motor or solonoids. Some cleverness may be required to make the concept work.
gary
Richard Greenberg wrote:

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Have you looked into Flexinol (like NiTinol) wire ? http://www.dynalloy.com/PriceGuide.html http://www.dynalloy.com/TechnicalData.html

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Here are a few ideas;
The minature airplane hobbiest make their own actuator by gluing a rare earth magent to a wire pivot. This is then placed inside a small spool of magnet wire. The magent will rotate to a position based on the presence, direction, and strength of current applied to the coil. This is essentially the same as has been mentioned elsewhere in this thread, but you can get some real-world directions by looking up the "Indoor and Micro Models" forum at www.rcgroups.com and search for "coil" to get some of the threads.
In the airplane, the wind rushing past the air foil acts as a spring against which the coil actuator can act. But, gravity can be made to do the same thing as long as you are careful in your design. The biggest challenge for the students will be to create a manufacturing process that is pratical and accurate enough for each of the 1,000 actuators.
Rather than a moving a tile directly, perhaps it may be easier and more fun to do it indirectly. Perhaps air could be controled using similar coils. I don't have a full idea in my head, but for starters a normal peg-board could be used as the base, with a box behind it that has a fan blowing into it. Then in front of each hole, hang something which can move because of the air blowing on it.
However, I don't like the idea of mirrors or even seqence. The problem with those is that they are very sensitive to viewing position. Hmmm... thinking more, perhaps mirrors could be used if a focused light were aimed at them, and then the reflection falls on a wall for the image. Then, you've produced something like a giant DLP!
There are other alternatives, perhaps the air can disrupt the flow of water down the face of the peg board (I think a polished marble surface with tiny holes drilled into it would be better)
I don't think purchased servomotors is a good way to go. This is because they are prone to failure, and could be quite a maintenance chore when you are looking at 1,000 working for 8 hours a day.
For a completely different idea, picture a single beam with 100 actuators that simply poke out a small armature(solenoids). If this beam is moved across a surface of sand, it could draw a picture. Alternatively if the beam were stationary along the upper edge of a waterfall that had a nice smooth surface to the falling water. The armatures could disrupt the falling water so that it would form a 2-d image... but it would be a quickly moving image as the water fell.
If the above mentioned beam were just a collection of coils, without the innter pin, it might be able to flip over a collection of magents on a table to form an image. I recall a board game from my childhood which flipped magnets like this with a playing piece. Another childhood magnetic toy is the bald face behind plastic that had iron filings in it. You used a small magnet to draw hair on the face.
Joe Dunfee
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