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motor for the laser

motor for the laser

Postby Monnem » Fri Jan 18, 2008 8:45 pm

Hi,
I', new here and just started with laser scanning. With interest I've read the ideas about a motordriven laser, built with a gearmotor or a stepper. This sounds quite complicate to me. I've found a motor fitting the idea "cheap and easy". The motor is called a "Spiegelkugelmotor", in english Mirrorspheremotor???. I'm speaking about this spheres you find in discos, reflecting the light with mirrors.
I've found two at Conrad-electronics:
1. 1,5V DC 6 RPM ~5 Euro
2. 220V AC 1 RPM ~20 Euro
Greetings
Monnem
 
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Postby MagWeb » Fri Jan 18, 2008 10:50 pm

Hi Monnem,

Welcome,


A motor with a 1rpm transmission means: one pass of the laser would last about 10 seconds, for you need a range of about 60° ( depends on the distance object/laser). This may be to quick for some high resoluted scans ( if you wish to detect the lasers light with every pixel you can get with one pass of the laser).

I made the best experiences with one pass only:
Lets say you do a scan at 960x 720 fps--> you get about 15 frames/s--> means you get about 150 frames / laserpass on 720 lines in vertical--> about only every fifth line of the picture does its job.
At 640x480 you will get about 30fps--> means 300 frames / pass on 480 lines--> nearly 2of3 lines do their job...... ( hope you got the principle)

----> with that speed you get a lower resoluted scanresult at a higher resoluted picture( again: preassumed: one pass only)

But using this gearmotor ( I used a similiar , a grillmotor, Landman 7.50 € 1,5v 4 rmp ) with a small "barn door" like jbeale suggestedhttp://www.david-laserscanner.com/forum/viewtopic.php?t=183 is a good idea. I used a model-railway transformator to vary the speed.

For principle handmoving or gearmotor is enough, but a pc controlled stepper has the advantage, that you can give the commands for DAVID and your setup hardware with one worksation: your PC.

Gunter



Gunter
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Postby WalterMo » Sat Jan 19, 2008 11:32 am

Hello,
At that time when jbeale opened his thread „Building a motorized scanner“ I was interested to test a simple DC-motor and bought the same motor as he suggested from www.pollin.de. Type 04885206 for 5.95 €. With a 3V DC supply it has 1 cycle per minute. But I found it was still too fast for precise scanning.
So I came back to my old stepper motor scanner and in the meantime I replaced the 3.6° motor to a 0.9° one. The attached worm gear is still in action of course.

By the way: A simple 230 V AC motor has the disadvantage that it isn't possible to change the direction of rotation nor to vary the speed.

Walter
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