Well, that's what control systems are all about, isn't it?
VFD AC motors are great, but for a light load - and I wouldn't want a
*heavy* prop flying around the venue, anyway, I figured DC motors with
quadrature encoders. <Insert hand-waving, "The rest is all software!", a
project manager's nightmare...>
Quite powerful DC motors are available surplus, or pull-outs from
treadmills. I have one scrapper treadmill myself, and another that hasn't
been used in a few years; I might get away with pulling the motor from it,
and the Boss never notice!
] On Behalf Of Jason Creager
Sent: Friday, August 03, 2012 6:49 PM
Subject: Re: [Technical_Insanity] RC Ghost? Another Crazy Halloween Idea
Good luck with that,
The math involved is extremely complicated. It's simple on paper, but in
real life, it's a whole other story. You would have to define the virtual
space and the position of the winches in software, define the effective
edges of the motion profiles (you can't hold the line completely taut
between two points), then combine the feedback from the encoders in
software to determine the actual position of the ghost versus the
calculated position, figure out how to correct for the difference, etc.
Then there's the whole issue of how you're going to control the drives for
the motors. You'd want AC motors driven with VFDs. How is the line going to
unspool from the drum? What kind of line? What kind of speed? (fast = $$$$)
What kind of brakes for the winches? What kind of limits so you don't
unspool all the line?
If you can do all that on your own, you would be guaranteed a job with my
If not, we could build it for you, but it would likely cost at least what
you'd pay for a house. We make the fastest, most accurate stunt winches in
the world and have flown everything from 1,008 white spheres synchronized
to lights, projections, and video to snowmobiles to cars and people at up
to 55 feet per second with 1/32" accuracy. (Google Fisher Technical
Services, if you want to see what we've done.) The Spiderman Flying Rig is
all of the above questions times about a million!
However, even without having to buy a copy of Navigator 3D, I (and most
folks) couldn't afford to build the infrastructure to run it.
On Friday, August 3, 2012, Dave Bell wrote:
> For years, I've wanted to build a ghost that could track over the entire
> front yard, suspended from three or four fast-acting winch drums. It would
> then have full 3D freedom within a large volume. An operator with a 3D
> mouse/joystick would watch from a hidden, high vantage point.
> You could even control the effect by manually dragging a bob around a
> model of the yard, with the three or four suspension strings running over
> rotary encoders that would, in turn, drive DC motors on the real winches.
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