LASERS! && Freemont Street LED array (was Re: Cray J932SE (was Re: Straight 8 up on Ebay just now))

Noel Chiappa jnc at
Tue Jul 19 17:53:36 CDT 2016

    > From: Mouse

    > my impression is that they're only for pre-prepared displays, and only
    > some displays (notably those that don't involve the beam turning any
    > sharp corners

My vague recollection is that they could do pretty sharp corners, but it's
been decades. IIRC, they were multi-coloured.

    > Turning sharp corners is the hard part with mechanical deflectors like
    > mirrors, as it means very high acceleration of the mechanical parts. 

Probably the trick is to do what old voice-coil actuator drives did for
multi-track seeks, which was to evenly accelerate up to maximum velocity,
coast at that until you got close to the target track, and then evenly ramp
down, so that the head assembly's radial velocity goes to 0 as you get to the
target track. (If you're not moving enough tracks to do the whole thing, you
only ramp up part-way, then ramp back down.) The RK05 drive did this with
fancy analog circuits, but these days one would do it in software.

I would assume one would do something similar with the mirror; evenly
accelerate up to maximum slew rate, then back down at the end of the move, so
that when one gets to the corner, the mirror is mostly stationary, and so not
so much force is needed to sharply change directions. Of course, this might
make the parts of the line where the mirror is moving slower brighter, but
perhaps one could tweak the brightness to compensate.


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