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Hey guys, just thought I'd throw in some bits of info since a few people asked how commercial lasershow galvos work - basically they do not have a spring or anything to return the galvo to the center position when powered off.

When my ScanPro 20 set is turned off the galvo mirros rotate freely. They have a position tracking sensor and when power is applied the chip on the driver board detects the current position of the mirrors and the position where they should be, and sends power to the coils until the mirror reaches the correct position

as i understand there are cheap open loop galvos, that use springs, and better closed loop ones.

what ive read, converting openloop to closedloop increases speed and precision dramatically

i tought about building a simple closed loop circuit for my HDDs, but i think i will sack that and just buld "real" galvos myself

something like these fellas do: http://74.58.33.200:81/FriendGalvos.htm

i plan on using a soundcard dac, i already ordered a cheap usb-soundcard. im gonna modify an audio-amp to suit my needs. so i guess its time for me to build some coils this weekend.. lets see how this works out

here are some pics of the "final" setup, i just mounted it so some scrap metal. as for now, i can do about 0.8-1Kpps at estimated 8°

on the pictures you can see the springs i mounted.

I've got a link to a diy laser show, where you can build the galvos from scratch...

http://elm-chan.org/works/vlp/report_e.html

so here's the pics, just decode it (_=/), since i'm not allowed to post links...

profile.imageshack.us_user_kendon

i am going to make some more right now, so if there are only four pictures you need to wait a few minutes.

@wummi: how did you stick the cuts to the arm of the hdd? i'm still looking for the best way to mount mirrors to anything, since hotglue is obviously not the real deal...

i use j/b weld work's real good as long as the surface is good and clean

i added a few more pics, where you can see the amp. as soon as i get a pointer which you can actually see in the video i wil upload one.

little explanation: the coils are centered by springs from a pen, since the spring on the x-coil is around half the length of the one on the y-coil the x has a little less deflection, but that is no problem. i soldered the wires directly to pins where the wires that form the coils end, and shortened the arms to lower the inertia.
as soon as i get some more hdds i will take them to my parents house, where i have access to cool stuff like a vice, an angelgrinder and other basic tools, aswell as my brothers lathe and diy-cnc...
i'm thinking about mounting the whole thing in the case of an old cdrom drive, the actual metal case of the drive itself, not an external case. i like the size of the case, i hope i can fit everything in there.

the small motor in the pics is the motor that moves the sled of cdrom, it seems to work fine for the tunnel effect or similar. need some round mirrors now...

edit: i don't think i can find j/b weld in germany, is it something like epoxy?

here's the link to j/b weld . there's a dealer in germany hope you can find them . it's good stuff
http://jbweld.net/dealer/index.php

here's the link for kendons images (for easy access ) http://profile.imageshack.us/user/kendon/images

@kendon:
to mount the mirrors i used some sticky gum-like stuff i had around. i think its for fixing pipes or something.. i have no idea where it came from.

my tip: use stronger springs. the stronger they are, the more precision you get. see my springs, the black wire you see in the picture, is additional spring steel.

of course, you will need more power to make them move, but i'm driving them at 1.5 Watts now, without them getting really hot in continous operation (tested an hour). they just get a bit warm. before mounting the harder springs, the output was just rubbish.

now the predicted output of yoghurt mixer almost matches my laser output. too bad this software has no option of an offset, as in my current configuration, the coils dont need the same power to move in both directions, so my image still gets disorted

heres a graph of the uneven spring problem.

im gonna try magnetic centereing, as i have found some neodym magnets. that should fix it.

thanks for the linking, wummi 8-)

i could have figured that out, i think i will salvage some more pens later today
i hope everday that there is a big server cleanup here at work, but nothing like that. need more hdds...

shouldn't you be able to compensate the distortion by changing the balance between r/l channels on your soundcard? i will try to draw some figures tonight, since it's finally weekend i have all night to tweak the scanner.

nope, by adjusting the balance, you can just make the whole shape longer/thinner

ah now i get it, the spring is stronger to the right then to the left (or vice-versa). sure, balancing won't help, it could with my uneven springs between channels...

well, i had it running for about an hour now, the only thing thats getting warm is the heat sink of the amplifier.

actually i think i am going to try to use a spring that's not so strong for the x-axis too, the projection is nicer when it's bigger. i'll just build another one with stronger springs for graphics as soon as i find some drives.

Like mario said, real galvo's use amplifiers specifically designed for them. If you look at the plug coming from the galvo itself, you will see that theres ALOT more than 2 wires there, maybe 4-10.

When you turn it on, the amps get feedback from the optical positioning system in the back end of the galvo (Basically a IR LED and a mirror), and sends that back to the amp, and the amp adjusts the voltage accordingly.

Tha galvo's run on I believe +/-5V signals, so if you send a signal into the galvo telling it to move, it will decrease the voltage on one of those power sources (+ or -), and it will move in that direction, but when you apply the +/-5V to it again equally, it springs back to where it is equalized.

And yes, the galvo's movements are soo tiny you cant even see them moving unless you put your finger on the side of the mirror and feel the vibrations. Thats why they also have scan angle ratings, for example, the scanpro 20's can only do 20K at a 8 degree scan angle, if you do more than 8 degree's, you have to slow them down to about 18Kpps to avoid ruining them.

ok some news here, got my lds from drew yesterday, now it is actually fun to power up the scanner, smoke a cigarette (don't like it, but need smoke ) and watch the show. i will take some more pics this evening, and it will be even possible to take videos *;D

does anybody know a good software synthesizer (don't even know if thats the correct name for what i am looking for), where i can change tones with a slider? i found something where you can enter numeric values, but i'd like to try something where i just move some sliders around my screen and change the frequency by doing so.
tried it with heathcliff, but the only way to recognize a shape is to know what it should be, everything is more or less the shape of an egg...

//edit: sinewave is already on my list, will try that as soon as i'm home.

use this generator: http://www.laserpointerforums.com/fo...1231684938/6#6

for heathcliff, you can adjust the scanning speed. as hdds are way slower, you should change the speed settings down by factor 10 or so, for recognizable shapes!

little help with that? i looked, but couldn't find it...

no problem! see:

@wummi: thx a lot, no idea how that slipped through my fingers
gonna try that now, i will use your settings at first, hope they are the correct parameters for hdds? :

@abadcaffeinetrip: laserline looks interesting, too bad i don't have access to a mac...
prophase is dumb, b/c i want to see the output on my scanner... just kidding, would be nice to have for planing and testing, but still no mac... thanks though.

i tried a few settings, the first one actually ripped my scanner to pieces because i had the amp set to maximum volume lol. i tried to get something that looks at least a little bit like the rectangular with the rotating corner, no way. got some wired spyrograph-like patterns, thats all. i guess it will stay a simple audio effect. i am thinking about building a real scanner from scratch... :

lower scanning rate equals more movement ^^ happend to me too. you have to tweak the settings. to high scanrates, and you will only get circles. too low scanrate, and you will get circles again, because of the DC filtering.

if an audiochannel stays too long on a high position, the DC coupling kicks in and moves the mirros back to zero.

try tweaking it a bit and use stronger springs. i managed to write my homepage adress letter by letter with my setup: http://ussr.at/laser/hcp.MOV (15MB) (spells www.hcpcrew.at)

i guess this all isnt too shabby at all with a real DAC (soundcard dac i say, i'm a cheap MoFo )
DC coupling ruins any shape instantly!

holy maccaroni! thanks for that link!

this laserdisc player has some amazing hardware:



have to get one ^^

maybe i'll try again, but not tonight, too tired now, and i overslept today because i played with lasers for too long yesterday... :

and also i just scrapped the diy-scanner-from-scratch idea, i think i will save some money for some galvos since i am lacking the knowledge to build some. googled for hours, found close to nothing...

I think it would be a good project to do that but if you just want a cheap scanner you can find a 10K galvo set for under $100 that will better than any harddrive or laserdisc thing.