Hi guys, I'd like to make my own frameless laser harp, but I'm kinda stuck on some technical aspects.
Here's how it works:
A laser is sent over a mirror, creating a "string", then it is turned off, the mirror turns a little bit (thanks to a motor), and turned on again, to make the second string, and so on...
Not gonna explain the reception part here, because it's not related to my problem.
After some researches on internet, I found that I could use a <100mW green laser pointer to get a cool effect, but I really don't know what kind of motor I should use, in order to get at least 7 "persistent" strings. Servomotor ? Galvanometer ?
Is there anyone here who had fun with lasers, vision persistence, or anything related who can help me out ?
Easiest would be a stepper motor or a regular DC motor with an encoder.
>>965417
>Servomotor ? Galvanometer ?
consider a multifaced mirror that continuously rotates. this is how scale barcode scanners operate.
a brushless motor will be practically silent if that is important
out of your two suggestions a galvanometer would probably be better because less mass, friction and momentum than a servo.
>>965420
If it continuously rotate, getting the feels that the string is there (and not blinking to much), and beeing able to know what string is beeing "displayed" at any time (Mandatory in order to know what note is beeing played) seems pretty hard, no ?
The galvanometer is also more expensive, isn't it ?
>>965424
a galvanometer is what, a coil of wire, a magnet and a spring?
turning the laser off then moving the mirror then turning the laser on will take longer than keeping it spinning. the faster you can do it the better the persistence of vision.
a brushless or stepper driver will give you a good idea of where the mirror is. a dc motor will need some marker to tell you when its at the start of the cycle. google pov (persistence of vision) for some ideas of synchronising motors to lights
>>965425
Okay, thanks, I'll take a look at it !
>>965417
Why not just stick 7 laser diodes and a power supply in a pretty black box?
>>965440
Because :
1) It would need 7 pretty expensive lasers (in order to be bright enough)
2) They couldn't move (not very important, though, and the multifaced mirror doesn't allow it either)
3) It would need to make them blink anyway (even though it's not the hardest part), in order to know what note is beeing played.
But... It could also work. I don't really know.
>>965446
>It would need 7 pretty expensive lasers
just use cheap laser pointers and run a fog machine
lasers + fog machine = win win
>>965472
Hum, yeah, it could be this simple, for a first try !
>>965446
Have you checked actual prices against visibility? From what i can see the laser would have to have retardedly high power (and price) to be visible in daylight in regular room air.
Give it some dust or steam to work with and suddenly it's a pretty beam. Maybe that's a direction to explore?
>>965485
Yeah, anyway, the goal wasn't to be able to play it in daylight in regular room air. But, using it in a non-dusted/steamed room at night would be pretty amazing. (and, from what some people said on the internet, a <100mW green laser is kinda visible without any steam in the night)
Just shine it through a diffraction grating, no need for motors.
>>965494
Why are you using a 100 mW laser? Anything greater than 5 mW is considered dangerous and could blind people.
>>965546
He needs his harp to be louder than 5mW so he can play in public settings.
>>965546
This.
>>965417
Laser harps like this one don't even use the beams for anything other than showing the location of the detectors anyway so you don't need that much power. I use green laser pointers a lot when doing astronomy and I can assure you that 5mW is plenty visible in a dark room. 100mW is way too much: it is very dangerous to vision, will draw a ton of power, and will likely cause the whole rig to heat up. over time, limiting the duration of use and the lifetime of the product.
>>966643
Yeah, maybe 100mW was a little bit overkill
This kind of laser harps uses the laser reflexion by the hand coupled with a light sensor in order to retreived the played string, so I'm not sure a 5mW laser will be enough.
Anyway, I bought some cheap ones, so I'll try when I'll receive them.
>>967332
I have a laser scanner uses a 3 mW laser. It can scan a laser around 360 degrees a second and measure the distance at every degree. You can damn well sense a 5 mW laser dot.
https://www.youtube.com/watch?v=q0kETJwL9mY
>>967332
>This kind of laser harps uses the laser reflexion by the hand coupled with a light sensor in order to retreived the played string, so I'm not sure a 5mW laser will be enough.
It depends on your skin color and whether or not you wear gloves, honestly. If you are white or you wear white gloves you should have no problem with 5mW.
Why do you need to step the mirror? Just get a motor with a constant speed and strobe the laser at the correct frequency.
>>967738
This is not possible, because two rays must not be prompted at the exact same moment, in order to be able which string is beeing cut at any time.
>>968356
In order to get some persistance vision (not seeing the lasers blinking), they have to be turned on for a short amount of time. If the motor spins constantly, I'm not sure that it would be possible to get a non-blinking string.
