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Old 02-27-2011, 07:35 PM #1
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Default Homemade X Y Galvo System

Hey guys i was looking at some homemade laser shows and wanted to build my own..i like the galvo system the best as we all do and was looking as the cheapest way to get it done..i came accross a video on youtube where it seems to me that the guy is using regular full turning motors and still getting the galvo effect..can someone please explain how this is happening..i would like to try it..thanks everyone..

Here is the Video


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Old 02-27-2011, 10:58 PM #2
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Default Re: Homemade X Y Galvo System

Considering how those "galvos" really can't draw much of a picture anyway, you might be better of just attaching a pair of mirrors to motors and making a spirograph instead. Otherwise, you could try something like using some brushless motors from a CDROM drive and alternate between the poles. Watch out doing that though, because I've burnt out Hbridge chips trying it.
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Old 02-28-2011, 02:17 AM #3
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Default Re: Homemade X Y Galvo System

Yeah but i still dont understand how that guy got that effect using regular motors..does anyone know?
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Old 02-28-2011, 02:49 AM #4
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Default Re: Homemade X Y Galvo System

I'm going to guess on this... and I'm no physicist... REALLY this is a guess

Electrically, the audio out of each channel is balanced (spends equal time on either side of Ground)... in this guy's case he's making a test signal so it's a perfectly balanced, symmetrical signal...
So the motors at rest here are physically balanced so they want to point as they are in the video...
When you apply a voltge to a motor, there's induction and the coils attached to the motor shaft try to align themselves with the magnet in the shell of the motor, turning the mirror a bit - the amount is proportionate, sorta, to the voltage applied.
And the direction of deflection = polarity of the incoming signal
I think he's turned the x-axis side's audio out down to accomodate the smaller reflectable area

If you wanted to try this, maybe a proper Current Balance would be an easy way, they're simple and require less current than this setup I'd think : ) and they look nifty

Very cool find!
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Old 02-28-2011, 02:51 AM #5
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Default Re: Homemade X Y Galvo System

Oops I just re-read and realized I answered that poorly. Again, I'm guessing.

The short answer:
The mirrors don't go all the way around, they just vibrate a bit.

If he raises the volume I think the mirrors would actually spin (if they're not constrained) and then he would have a lightshow.
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Old 02-28-2011, 03:08 AM #6
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Default Re: Homemade X Y Galvo System

Maybe you are right but i think for that to work you would have to be very lucky..these motors were made to spin..i wish he had shown the motors themself during the demonstration..
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Old 02-28-2011, 03:34 AM #7
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Default Re: Homemade X Y Galvo System

But given distance between device and wall, size of output, and the final mirror's orientation, how can those mirrors be going all the way around?

Aha! There's a text comment under the video that alludes to a hot glue strand being the key... I stick with my earlier guess! Elastic resistance to applied force..! You could prolly do the same with a rubber band...
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Old 02-28-2011, 04:16 AM #8
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Default Re: Homemade X Y Galvo System

I guess you were close to the truth lol..greats guess man..
By the way, im VishalBaal..im the one who asked the question posted under the video..i was waiting on the reply lol..
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Old 02-28-2011, 04:25 AM #9
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Default Re: Homemade X Y Galvo System

Ok preliminary results (I got curious )
Turns out the design can be simplified and the elastic component taken out entirely... the motor i tested with has a Rest Point (magnetic closest point??) so as long as you don't exceed that it'll always go back to zero.
It's kinda late and I just wanted to test the theory, so my setup only has one axis. Two could be done if I could be bothered to find another pager motor in the chaos that is my lab :S

Actually produces more swing than this, but when the already weak audio out's split between the motor and a speaker so you can hear that it works, it's pretty weak. I need smaller pager motors!
Sorry about the background noise, it's the limitation of my camera

...now, how to upload video... EDIT: ugh, 16mb avi limit, need to dig up some kinda editing software!
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Old 02-28-2011, 04:28 AM #10
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Default Re: Homemade X Y Galvo System

Amm..upload to youtube and post up the link..i would like to see what you got..
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Old 02-28-2011, 05:31 AM #11
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Default Re: Homemade X Y Galvo System

ok not the most coherent video ever and the ending's unexpected (I have no editing software handy) but I made an account on youTube and posted the vid:
YouTube - Laser Deflection, Step 2

Hahaha I'm glad you got the answer to your post then! : )
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Old 02-28-2011, 08:57 AM #12
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Default Re: Homemade X Y Galvo System

this is way more interesting than sleep..! pardons if i babble, it's 5am here
ok so if you are thinking of building this, and you want it to do more than just simple x/y plots...
1-why have two mirrors? one mirror with 2 (maybe 4, one on each edge) pushing coils should do...
2-the big problem with this setup is that the deflection angle means the beam doesn't project linearly to the current put into the coils (1mA difference =\= constant x cm difference)... can either use a squaring lens (I hear they're expensive!) or soft/firm-ware to compensate... the second option's much cheaper, hardware-wise... especially as you have to control the coil current anyway... and it's just a really crazy lookup table software-wise...
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Old 02-28-2011, 11:09 AM #13
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Default Re: Homemade X Y Galvo System

Dude thanks for the video, really kool thank you did that so fast and at that time in the morning..and that ending was priceless lol..i know that the setup wouldnt be very precise but its cheap and would still look pretty kool..i would try it and let u know how it works out..
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Old 02-28-2011, 03:38 PM #14
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Default Re: Homemade X Y Galvo System

Quote:
Originally Posted by Lumin View Post
If he raises the volume I think the mirrors would actually spin (if they're not constrained) and then he would have a lightshow.
I doubt it - these are DC motors, and the output of a (unmodified) sound card has a DC component of zero. Only if the AC component was very low in frequency would the motor be able to spin: it'd have to complete a revolution within one audio cycle.

As far as making anything that resembles a real projector using motors like these: forget it. completely.

Real projectors rely on galvo's that have positional feedback, which their driver uses to keep them in the desired position, even if things like inertia would carry them somewhere else. Even if you would manually try to move the mirror, the servo would push it back - i wouldn't recommend trying that since you could break the mirror straight off before it gives way. Also, galvo's are designed such that the moving part is very lightweight, allowing for greater speed per watt of power spent.

The feedback system also allows for linearity. The response of the motor part in a galvo isn't liner per se, but the feedback loop allows it to respond linearly by comparing input signal and feedback.

If you want to do proper projection, DIY is hardly feasible. A set of very usable galvo's, complete with driver boards and power supply can be purchased for $100-$150, and i doubt anyone could built it themselves for less with similar performance.
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Old 02-28-2011, 06:36 PM #15
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Default Re: Homemade X Y Galvo System

I understand what you are saying but the reason for this thread is not for us to go by galvos, it is to archive a similar effect for cheap..and if you look at the video posted in the first post, the guy used the regular motors and had a pretty impressing effect, close to actual galvos..i understand that they wont work as precise to rel galvos, but at a cost of next to nothing you really cant go wrong..
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Old 02-28-2011, 07:04 PM #16
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Default Re: Homemade X Y Galvo System

Cheap effect? Check this out if you haven't:
Cool Laser Scanner Effect for Music
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