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Topic: a lot of actuators (Read 1 time) previous topic - next topic

j_derius

Hi guys!

a client asked me to realize an installation with a lot ( about 1000 ) of small plastic elements rotating around the center of each element. Although the concept is quite different, technically the idea is not very far from the popular wooden mirror realized by Daniel Rozin, so first thing I thought was to use a lot of cheap servos becouse of the good technical caracteristics tha we all know. But the client can't afford to pay an installation with such amount of servos, so I was wandering:

is there any other actuator that can do this kind of action? I just need to rotate those objects by multiple of 90 degrees.
Is there a supplier that can sell the servos (or any other device that can do the job) for a considerly lower price?

Thanks for your help

J.

Robin2

Are you talking about the sort of display used in some bus destination boards - with little pieces coloured black on one side and yellow on the other?

I assume they are flipped over by a small coil creating a magnetic field?

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

j_derius

thanks robin,

yes something like that, but they should rotate 4 times in the arc of 360 deg.
The idea to use small coils is interesting, but should be able to rotate it this way?

thanks

j.

JarkkoL

Maybe you could use regular DC motors with some kind of "screw axel" to limit the movement to 4 revolutions? DC motors are much cheaper than servos (and more quiet!) and if you buy them in massive quantity, I'm sure you can get them in 50c-$1/piece price range. What's your budget?

Robin2

You haven't said what size the small plastic elements are?

Do you mean by "rotate 4 times in the arc of 360 deg" that they have 4 faces (perhaps 4 colours instead of the 2 I suggested) and you wish to be able to display any face at will?

Are they arranged in a square or a rectangle or in a single row?

Does each need to be completely independent of the others?

Are you able to construct complex parts for the device? For example could you make some sort of escapement mechanism that would only allow a quarter turn each time?

If there are columns of segments could you run a rotating shaft up each column (through the centres of the segments) so that friction would rotate a segment if it's latch was released?

Sounds like a fun project.
...R
Two or three hours spent thinking and reading documentation solves most programming problems.

j_derius

JarkkoL, I thought about dc motors but I need to control perfectly the angle of the rotation, then I guess this is not the case, nor I want to use any sort of encoder. We still don't know the budget, we just hope that the client can afford €7-8k for everything, the hardware and our work.
Robin2, the objects will be plastic cylinders, the size is still in discussion but the diameters should'n be bigger than 5 cm and the height not more than 7 cm.
They are arranged in a matrix, fixed to a sort of metal grid trough very long shafts. The segments are aligned horizontally. Probably they won't have any bearings, they cost to much for the budget.

Yes I'm able to realize small mechanical parts, I can also use a 3d printer or a laser cutter or my own hands!
yes is a pretty fun project :)
 

JarkkoL

#6
Jun 26, 2013, 06:03 am Last Edit: Jun 26, 2013, 06:20 am by JarkkoL Reason: 1
Oh right, I got you. Cheapest servos I have been able to find are ~$2 at DHGate, but maybe you can find even better deal. Sounds like your client should be able to cover that based on your expected budget, since this is probably the biggest investment in parts.

AliExpress has 9g servos at $1.90/piece. Shipping costs are abysmal as it seems to be added to each servo, but buying in bulk will bring it down for sure so better contact them directly (:

Robin2

Your segments are quite big - I was thinking of things about 10mm square.

If your "long shafts" are continuously rotating then the segments should rotate unless they are restrained. They could be restrained by a pin from a small solenoid. It would mean they would have to pass through faces 3 and 4 in order to move from 2 to 1. But a ripple effect like you used to see on airport arrival boards can be attractive.

Another thing you haven't mentioned is how often the segments need to change. If they don't need to be changed often perhaps you could have some system of multiplexed servos in which one servo is used to align the actuator from another servo with one of several segments.

Agree your fee before you go further :)
Are we on a percentage?

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

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