pager motor as galvo?

[YEAH]

this is my first post here!

could you take this:
RPM2 - Regular Pager Motor 2 « Products « Solarbotics
and add a feedback sensor and use it for a galvo?

if so you could make xy scanner alot easier then currently


i was thinking to use this:
http://www.solarbotics.com/products/qrd1114/
as the sesnsor and have a paper disc printed with a pattern or just a gradient.
for the dac:
then you could amplitude modulate a soundcard dac as in have the card output a constant 15k or so sine wave
and only change the loudness of that wave. no dc in there but you can display dc (?) lol

EDIT:
i was tanking about vector, not raster.
but it could work with raster

 

[HIMNL9]

sorry, but i think you can't use them for a x-y scanner.

Galvos used usually are proportional positioners, not simple motors, and with that type of sensor, i think you can detect presence of obstacles, but not too much precise patterns, so probably you can't use them for position feedback.

 

[magonegro]

Well I think we have here a raster scanner project. I barely remember to see something similar a time ago. If you attach a mirror to it and have some feedback for its position, and you make the same for the second you shoud have here a *possible* raster scanner using TTL/analog modulation of lasers. But, number by number at the perfect case you have 31900 RPM max, two motors, this is around 531 turns every second and you have to paint say 531 lines (one at a turn), well then you need that one of the motors turns 1 time a second (60 RPM) for one frame/second. If we want more than 1 frame/second we have to increase turns/second in the second motor. For example 25 frames second=1500 RPM. this is 25 times less the time you had before, so you have to decrease resolution to 531 lines /25=21 lines. That's 20x20 dot scanner resolution. That's bad for a TV, but you can find intermediate results for a curious lasershow I guess. Between this and the galvo's option I see *VERY MUCH* simpler the galvo's option, though not being a raster one.

 

[MISTERWILLING]

You can get a set of galvos w/ amps for $120 shipped off ebay. If you can afford this you will get much better results than trying to build your own galvos.

 

[laserist]

Pager motor - no it has brushes - brushes mean discontinuous contact – which means your feedback would have holes in it – unless you limit the angle to stay on one set of contacts – but still – a best a geeky waste of time.

On the other hand a brushless DC motor could work. It would be easiest if the coils were connected in a Y configuration. Then you just have to mechanically limit the rotation and ignore the “dead” phase. (You’d have to disconnect one phase inside the motor if its wired delta. Not impossible – you could even just burn it out – but who knows what that would do to the other two coils…)

 

[YEAH]

well the amplitude modulation part is ok.
and the encoder wheel.
i think i'll go with a diy version of an hdd voice coil,
as it would be cheaper then buying a torx set.

could you take the output of a soundcard DAC driver and feed it through this:
http://software.muzychenko.net/eng/vac.html
into some program that would modulate a 20,000hz wave as a carrier
and send that to the output?

that might be easier then modding the soundcard.
you'd just need a rectifier and a filter cap after the card.

or would windows audio mess that up?

 

[Things]

Real galvo's require a +/-5v signal input, and when people use soundcards to drive them, they use opamps to up the voltage from the sound card. You will have to modify the sound card, because you need to tap into the audio signal BEFORE the coupling capacitors, or your output will be messed up.

Windows handles outputting clean audio fine, it's the sound card. Do not use any capacitors between the galvo's and the DAC output, otherwise the capacitors will "smooth" the voltages, and your images will be distorted.

 

[LSRFAQ]

Real galvo's require a +/-5v signal input, and when people use soundcards to drive them, they use opamps to up the voltage from the sound card. You will have to modify the sound card, because you need to tap into the audio signal BEFORE the coupling capacitors, or your output will be messed up.

Gooogle laserboy forumns and sound card dacing.

There is a 24$ USB sound card that can be DC coupled for RGB and XY output with few issues and plenty of software that supports it.

As for the pager motor, a encoder is too slow and massive, you need 2 photodiodes and a led for each scanner mirror as a analog differntial feedback loop.. I would not waste my time with a stepper or pager motor, but I might consider a brushless faulhaber motor. You can geta set of real galvos with a PID loop for 200$ or less, and you will not achive the low inertia of a galvo, which you need for low flicker.

Pager motors have been done, and the results are dissapointing. Try googling ELM CHAN and LAser if you feel you must build.

Steve

 

[YEAH]

i was thinking to have a CONSTANT 20,000hz tone and modulate the VOLUME of that.
the tone has no dc in it and the information is carried by the loudness.
like AM radio.
then you fullwave rectify and smooth(we are looking for loudness, not the actual wverform)
and then amplify the rectified and smoothed signal.
if i'm going to be doing all theese hacks to make it cheap i might as well use a rubberband open loop.
the rubberband stores energy and helps with inertia i think so it probably would be better than any diy galvo
i could do without spending way too much time.
i have seen elm chan's laser. very impressive.

 

[Things]

I have one of the sound card/laserboy DAC's and it works fine, just that it can be a bit dodgy when you are doing real shows that must be perfect.

 

[ElektroFreak]

^Have you tried LFI laserplayer or HE laserscan with your sound card DAC? The only dodgy issue I've had when using spaghetti is that every once in awhile the imagery freezes for about 1 sec. Other than that things look great. I recently started using LFI laserplayer, and it's awesome! Not all ILDA files look perfect when using it since some ilda files are optimized differently than others, but most of mine work great. The motion is silky smooth, almost like a "real" DAC.. no freezes etc. By using both spaghetti and LFI together, I've been able to do some pretty neat shows. Also, I've noticed that if you use ilda files that are from a system like pangolin originally which are optimized very well, they also look great in Spaghetti. It really seems like it depends on the file. Gary's blanking optimizations make Spaghetti work with more .ild files than LFI, so it's nice in that regard. I can only imagine that as time progresses Spaghetti will become more and more refined. These "dodgy" issues aren't really the fault of the DAC as much as they are the fault of the software. The soundcard DAC is quite capable of completely smooth, fluid motion comparable to name brand DACs if given the right shows on the right software.

 

[Things]

I meant dodgy in the ways that is indeed a sound card, and windows could start outputting audio to it accidentally etc. It works fine, yes, but since I now do many shows not just in my garage I felt I needed something with a little more "power" (the DMX feature on the FB3 is one of the key features!)

Yes, I have tried HE laserscan and LFI player, great pieces of software! HE laserscan takes a bit of time to get your head around though.

 

[carmangary]

^Have you tried LFI laserplayer or HE laserscan with your sound card DAC? The only dodgy issue I've had when using spaghetti is that every once in awhile the imagery freezes for about 1 sec.

Yea, there have been some reports of this when using the sound card DAC. There are a few different reasons that this might occur and depends on the frames you are trying to display, project or show mode, system memory, other applications running, etc. But, without knowing the above I can't offer an explanation.

 

[paulkruger]

I'm not so sure about the positioning not possible. I just stripped down an HP multi function printer for parts expecting to find some stepper motors and steel guides. Guides i got but not one stepper motor.

We know that position is important when you want to print something but HP uses just DC motors, not much different than you would find in a toy. But then they place optical encoding on the movements and are able to drive them to achieve precise positioning using, on one motor, a disk and on the left/right travel for the print heads they have a linear transparent strip printed with vertical lines. It seems they just count these divisions and based on where they want the carriage to go, run the motor with pulses and count the lines, shutting the motor off when it reaches it's destination.

That said, I doubt this would work well for a laser scanner because of the nature of the electronic feedback and the circuit needed to accomplish this...but a clever designer might pull it off.

They are so tiny however ! You could put a chip of a mirror on them, mount at 90 degrees and vary the speed of each for some interesting patterns but probably not create vector graphics on the wall.

One could drive a spinning polygon mirror to use in a raster scan device probably...if you could find a really tiny polygon mirror. The ones I scraped from scanners would work but not be that tiny.

I assume you want to make a really small device or you would be looking for larger scanners?

 

[crazyspaz]

Wow. Necro posting on a 5 year old post...