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I am trying to create 8 motorised lasers that move (ideally randomly) between a 135Ë angle. I doubt with my level of knowledge i will be able to make them move randomly but if i can't just moving back and forth between the 135Ë would have to do.These motors would have to be reversable and travel between 2 points making an arc of 135Ë, I'm looking at making this in the cheapest way possible. By mounting cheap pen lasers onto mini motors and somehow getting them do this. I will need to see the beams of light so unless i can find a better way to used focused light cheaply, i'll have to use a smoke machine or something.
Having no real knowledge of this, would it be easily achievable, i would use a microcontroller to make the motor movement random within that 135 degrees but i have no idea how i'd go about it.

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You've described what you think you want to build, but you have not really described the problem you're trying to solve. Are you wanting to do a "light show", with lasers swinging around randomly?

You can probably get that effect much more easily with refraction than with reflection or repointing the lasers directly. There was a project in a recent MAKE to build different laser-show effects using mirrors and transparent CDs (the spacers they put into large packs). That may be a much cheaper way to achieve what you have in mind.

It's for an art project. The plan is to have 8 of these lasers moving back and forth ideally randomly on the corners of an octagonal room, each wall of this room is covered with a mirror at the hight of the lasers (ankle height), the idea is to bounce the light around in this way to create patterns. The randomness of the lasers will increase the complexity and make the patterns more interesting.
It is a laser-show of sorts but an interactive one using separate mirrors across a small room.

Ah! So each one is individual; that make much more sense than putting eight lasers, each on a separate motor, into a box :-)

To just wave back and forth, you don't need any complicated gubbins at all.

Just a motor actuating an arm. Put your laser on the end of the arm, and you're sorted. Because the arm doesn't rotate, just wave, you can wire the laser into the same power-supply as the motor.

Ah, an instant of why didn't i just think of that. Brilliant. Thank you so much, a simple solution that's solved my problem. I take it making anything move randomly in that arc is a whole extra level of difficulty?

you could take two motors of different speeds and offset mirrors and reflect the laser off of the two spinning mirrors

OR, if both motors are the same speed, just gear them differently :-)

More difficult, but maybe not excessively so. I think you could get pretty close to random (in terms of what people perceive) by replacing the fixed pivot point above with a second small radius motor (just make sure the slot is long enough to handle the extreme positions).

If the small motor turns at a rate which is not a simple ratio with the big wheel, then the end of the arm will wave back and forth, stop, reverse, stop again, and so on.

Think about the "epicycles" in Ptolemy's geocentric solar system, which he needed to get things like Mars moving retrograde at various times.