[Laser] Stepper motor control of laser communication unit
Kerry Banke
kbanke at qualcomm.com
Fri Oct 22 11:19:50 EDT 2004
Actually we use the micrometers to move one end of a 12" bar hinged at
the other end. If I did the calculations right the StepperMike moves our
laser beam about 1" per step at 10,000 feet. There are three reasons
that come to mind for trying the stepper approach. Just placing my hands
on the manual micrometers puts tension on the mechanics no matter how
careful I am. I found that working on a target 4 miles out with a 12"
spot is a problem when you try to let go of the micrometers as things move
slightly. This maybe not a problem if one is hauling around a very heavy
base & mechanism but that's not what we do. We use the same tripods used
for our microwave hilltopping. I also have found that we end up
nearly always doing a manual raster scan to find the target as our scope
and laser are never perfectly aligned after transporting & setting up. The
cross hairs on my 24X rifle scope are wider than the laser beam at 4
miles. The final reason is that since we stumbled across these
StepperMikes, the opportunity to learn seemed to good to pass up. These
units may also be useful as we move up beyond 47 GHz.
- Kerry N6IZW -
At 07:15 PM 10/21/2004, you wrote:
>Kerry,
>
>The stepper motor approach works pretty good.
>I use a pair of "BIG" compumotor drives that were used for disk drive servo
>writing. I put a pair of mirrors (x,y) and used them for pointing the beam.
>
>The 1/10000 of a turn (0.6mR)is still a bit course.
>Typical beam divergence is about 2mR (0.1 degrees). 360 degrees = 2*PI
>radians.
>If you run thru a 10:1 beam expander, divergence will drop by 10 to 0.2mR.
>So you might want to use some mechanical leverage to reduce movement.
>
>I ran my 1/50000 steppers into a leadscrew system that stepped it down to
>10uR.
>
>Jim
>N9JIM/6
>
>-
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