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Why it's better to use glavos instead of RC servos for a projector

Kmor2004

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The idea has been floating around my head for a while, about using RC servos, since they are a little easier to DIY control vs galvos not to mention a heck of a lot cheaper.

I knew I had some micro RC servos lieing around, and thought I'd give it a whirl.....


The end result, you can't really tell in the video but the servos have too much of a "step" so when you try to make a diaganol line, it actually makes steps up/down then over.

Also despite the servos being able to travel 60 degrees in .13s its still too slow to make smooth movements.

Lastly...I apologize for the crapiness of the video, 1) I didn't set the servos to center point when I cut the slot in the gear for the mirrors so the side to side mirror over traveled the smaller vertical mirror, 2) digital camera are not the best for taking videos, and 3) I was using the controller to move the servos so it was very unlikely I could of even tried to make circles.
 

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Frequency response, servos are too slow...
the output shaft of servos is geared down,
a galvo is direct drive no gears so it can
react much faster than a servo can, that's why...
 
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Things

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Servo's probably would make OK laser scanners .. if they could move a couple thousand times faster :p

Interesting experiment anyway.
 

Benm

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They have entirely different design goals indeed.. a typical RC servo would provide a lot of torque, but due to the gearing and motor design be extremely slow.

A laser scanner galvo is the opposite: it only needs to move a mirror that weighs less that 0.1 gram, but it has to do that very quickly. Also, it doenst really need to account for variable load as the mirror is always the same and doesnt provide different amounts of resistance depending on something like terrain in a RC car.

The only common thing is that they both need to be able to position an axis as precisely as possible and use feedback to accomplish that task. This would make a galvo a servo in theory, but in practical use they are very different.
 

kiyoukan

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there is an object that worked great for me.
2 cd tray motors with 2 mirrors glued to them.
I made it back in 09 i think i threw it in the vet box.
If dave break it out and hooks one motor up to left and one up to right channel audio you can make very cool computer controlled spiro even draw shapes i was able to make a square, circle infinity and kinda a star with blanking.
Its super cheap, and was fun just to try it out.
After that i tried the same thing but using some small stepper motors.
One coil was given constant power to hold it in place. while the other was feed varying audio that would vibrate it back and fourth and always return center.
Using that setup you can make some very cool effects and even draw words.
Ive seen it done but there only stick words.
But with the price of galvos being 75$ your better off buying a cheap set of 15ks and a dac.
i spent almost a year fiddling with stepper motors and even using speakers.
Fun to experiment but no where near a galvo.
 

Kmor2004

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I just through this togther just to see the how it would actually perform, at minimum I was hoping to be able to create a solid straight line, but as I've discovered and all of you have pointed (also knew before doing this) the servos move entirely too slow.
 

kiyoukan

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if you want to throw something together use small dc motors with an audio signal. the trick is to fine a way to keep them going back to center.
 

Benm

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I just through this togther just to see the how it would actually perform, at minimum I was hoping to be able to create a solid straight line, but as I've discovered and all of you have pointed (also knew before doing this) the servos move entirely too slow.
Ah well, why not give something like that a try anyway, especially if you have the parts handy.

I guess the system with servo's could entertain a cat for the rest of its life, perhaps you can sell it to someone :D
 

Kmor2004

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Nah it was put together in a card board box, and besides the RX/TX are still used for my quad copter, and jet (if I ever get either completed),
 

bobhaha

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Have you thought about maybe making the servo's move less and expand it with a lens? Like instead of moving the servos 60 degrees only makes them move 10 or 5 degrees max. It would be pretty cool for a cheap light show/simple shape maker. Obviously resolution will diminish, but its still cool for a DIY project.

I think I'm gonna try this :D
 
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Kmor2004

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The problem is in the fact that the servos acualy have steps, at least the ones I have and I think each step was 5-10 deg any ways.
 

perfo

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This is my first post and I must confess to being a Laser nooby.
Reading this post I had an idea which may or may not be silly but would be very cheap, possibly even cheaper than RC servos.
If you made two rotors (hubs) with a number of faces on, say 20 to give a 20 degree scan.
You then set the two rotors up so that they are connected together by a gearing system so that one rotates X amount of times faster than the other.
Put mirrors on each of the faces of the rotors and arrange it so that the x axis scans are done by the fast hub and the y axis by the slow hub.
It should then be possible by switching the laser on and off at the right time to create any image (within reason) .
You would have to use an optical pick up or something similar to sync the hubs with the controller.

If you had a 100 by 100 matrix then the X axis hub would have to scan 100 times per Y axis scan and if the complete image to be displayed at 25 hz (which I would imaging may be acceptable for a small DIY type image). Then the X axis hub must do 2500 scans per second, but as it'll do 20 scans per rev then this is 125 Rps or 7,500 Rpm which is quite do able for a small DC motor.
Sorry if this has been discussed many times before it's just an off the cuff thought.
 

perfo

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A square would be relatively easy if you are at home soldering a few bits together. You need two movements on up/down the other left/right. A couple of solenoids or adapted speaker coils could give you the required motion. Use signal on for up on one coil and left on the other coil and use a purpose made stereo sound track or a micro controller to sequence it.
 

parimah

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perfo;
i used 2 two galvo for scan
but now i have problem for create square
i dont know about needed frequncy for create a square
 
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