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Old 03-03-2014, 07:28 AM #1
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Default Bare Minimum (laser harp) Scanner?

Hey, guys - here's the deal:

I've read through the forums a fair bit, I understand most (if not all) of the terminology, and I'm trying to get up to speed with everything here.

My main objective is a functional laser harp - I've got the laser (~70mW 532nm, extremely visible (even in light) with fog) and I'm moving on to the scanner portion of the build.

I know that there are a lot of really high-quality, really expensive options out there. I am (unrealistic as it may be) attempting to keep the total cost of the laser harp beneath $100. I figure I don't need a ridiculously capable scanner - certainly not near the realm of the requirements for a full laser show - just to scan a single beam back and forth along a single axis. I want to get 12 beams through POV.

My first attempt was a single 12V motor, and I was trying to modulate the beam to turn on and off perfectly as the motor spun to achieve the POV - this failed. The laser could only be on for an extremely brief amount of time (sub millisecond) before it had to be turned of again, or else what was supposed to be a solid line of a beam ended up more of a narrow plane - if on that short, however, the laser was not very bright at all.

So, now I'm coming to you guys - for POV, hopefully around 60FPS, 12 beam split, what do you recommend? Have I missed something obvious? Is a stepper motor out of the realm of possibility? Remember, I'm trying to keep the costs down as much as possible - with 12 beams and 60FPS, I should (hypothetically) only need 720PPS, right? Or am I wrong there?

Thanks for the help guys! I'm really encouraged to find such a great, supportive community!


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Old 03-04-2014, 05:00 AM #2
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Default Re: Bare Minimum (laser harp) Scanner?

Well since scanners are measured in points per second, and you are only drawing 12 lines (or points) you shouldn't need too much at all!

I don't know how slow scanners get but i am sure you will have no problem getting a scanner of that speed or higher for relatively cheap. I just don't know where.

It seems like you have your facts straight. Good job! Thanks for doing research and acquiring knowledge yourself! Many junior members seem unable to do that...


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Old 03-04-2014, 05:07 AM #3
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Default Re: Bare Minimum (laser harp) Scanner?

Stepper motors aren't really fast enough to make this work correctly, and you would have to align the beams between their steps otherwise you'd have the same issue as with the motor.

As I mentioned in my PM, really the best option for this is to get the cheapest galvo's you can (you can get a set sub $100 on eBay), and if you're really needing to cut cost, sell off the 2nd.

The only other alternative that could work is a polygon scanner, however I'm not sure how you're intending to do beam detection, as a polygon scanner won't work with the typical frameless method.
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Old 03-04-2014, 01:17 PM #4
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Default Re: Bare Minimum (laser harp) Scanner?

Thank you both for the input - I am (from what I understand) using a fairly traditional method of beam break detection - a phototransistor and matching that up with timings on the stepper/galvo/whatever.

My main reservation with buying $100 galvo pair and splitting it is still the cost. I really don't need much performance - should honestly be <1K, so getting something higher powered seems like a waste of money. And, seeing as I really want to keep costs as low as possible...

Are there no other options/

Thank you guys so much! I don't mean to offend or sound like I'm ignoring your advice, I just really want to go with something less expensive if possible.
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Old 03-06-2014, 06:25 AM #5
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Default Re: Bare Minimum (laser harp) Scanner?

I'd more than welcome you to try using a small stepper motor to do the job. The issue with them is they have a relatively large rotor mass compared to a regular galvanometer, so they don't like accelerating quickly. This wouldn't be an issue on a single sweep, as the rotor would already have some inertia to it, and you could use the "step" of the motor as a time for the beam to display, but the problem is it has to make it to the other side, turn around, and come back, and at a rate that's too fast for noticeable flicker. If you can find a teeny tiny stepper motor (after all, you only have to move a small mirror), then maybe you could drive it hard enough to overcome the rotor mass.

You will need to be careful with how fast you drive them though, while the harp will still work if the motor skips steps, you might find your beams slowly drifting away to one side while you're playing. The advantage to galvo's is they're closed loop, so the beam will always be in the exact same position no matter what.
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Old 03-06-2014, 06:46 AM #6
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Default Re: Bare Minimum (laser harp) Scanner?

Thank you for the input! That's definitely one of many avenues I'll look down. Did you have any specific models of motors in mind, or..?

Additionally, are there any really low-cost, questionable-quality galvos out there? Since I don't need extreme performance - or even medium performance - frankly, fairly LOW performance - I was thinking that might be another avenue to test.

Thank again!
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Old 03-09-2014, 05:15 AM #7
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Default Re: Bare Minimum (laser harp) Scanner?

More research ahoy:

From what I've seen, it's looking a bit difficult to get a stepper motor up to the speed I'm looking for. I've started looking a little into servos - does anybody have experience using these?
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Old 03-18-2014, 09:10 PM #8
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Default Re: Bare Minimum (laser harp) Scanner?

Hi Snipeye.

I happen to sell laser harp kits.

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50mW 532nm (ripped from a cheap stage projector)
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1W RGB (500mW-660nm, 200mW-532nm, 500mW-450nm) Touch the white beam and it is: "AUCH!!"

The white laser burned the paint off from the door!
I am thinking of starting a "door-etching-business"
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Old 03-18-2014, 09:17 PM #9
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Default Re: Bare Minimum (laser harp) Scanner?

Servos are also too slow and not accurate enough.

I think if they would work, they would wear out very fast.
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50mW 532nm (ripped from a cheap stage projector)
500mW 532nm (in the laser harp)

1W RGB (500mW-660nm, 200mW-532nm, 500mW-450nm) Touch the white beam and it is: "AUCH!!"

The white laser burned the paint off from the door!
I am thinking of starting a "door-etching-business"

Last edited by camvo; 03-18-2014 at 11:29 PM.
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Old 03-18-2014, 11:47 PM #10
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Default Re: Bare Minimum (laser harp) Scanner?

Quote:
Originally Posted by Snipeye View Post
More research ahoy:

From what I've seen, it's looking a bit difficult to get a stepper motor up to the speed I'm looking for. I've started looking a little into servos - does anybody have experience using these?
Servos are waaaaayyyyyyy too slow unfortunately. If steppers aren't going to cut it, then your only other options are galvos, or possibly you could get a polygon scanner to do it (although will have the streaked line option as you've said earlier)
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