[sci.electronics] TV systems for mobile vehicles

w_smith@wookie.dec.com (Willie Smith, LTN Components Eng.) (05/14/88)

John Nagle (in a cross_posted_to_the_universe message) writes:
 
>     I'd like to hear about experience with various cameras and radio links
> used with mobile robots.  I'm interested in units suitable for a small,
> high-speed vehicle in which the vision processing is offboard.
 
I've been working on a teleoperated vehicle project since the beginning
of the year, and while Phase I is somewhat low budget, I have made a
little progress.  It's based on an R/C model "Clod Buster" chassis (a
1/10 scale car crusher pickup truck) and uses a 7 channel proportional
radio control, a Sony Watchcam, a TV Genii TV transmitter, and quite a few
other bits and pieces and mods.
 
>      The Sony Watchcam is a low-cost alternative.  Any experience here?
 
While the CCD cameras may give better pictures, the Watchcam isn't bad.
The resolution isn't the greatest, but I can navigate the vehicle without
too much trouble, the size is just right, it's not too picky about power
(5.1 to 15 volts at 6 watts max), and the price [$300] makes it affordable.
It's small and light enough that I was able to make a pan/tilt mount for it
from a couple of R/C servos.  I found that the wide angle lens accessory
really improved the view, so that's definately reccomended.
 
>      What about TV transmitters and receivers?  I've seen a few TV Genie
> units around, but not only are they weak, they're illegal.  But they do
> sbow that such a transmitter need not be large, and there are bands in 
> which one can obtain appropriate licences.  I do need something
> about that size, though, say 4x2x2 or smaller.   Is there such a thing
> as FM TV gear, to improve the noise immunity?
 
Even with tuning [I know, tuning transmitters without a liscence is A Bad
Thing, but the transmitter itself is illegal, so "in for a penny..." and
all that], the TV Genii will only give a couple hundred feet range, and
that's with a quarter wave antenna on a one-square-foot ground plane and
the low-end Radio Shack UHF antenna on the receiver.  A higher gain antenna
would probably give more range, but then I'd need a rotor to keep it pointed
at the vehicle.
 
>       Has anyone dealt with the problem of camera stabilization and vibration
> isolation in a moving vehicle?  The Steadicam gyro approach seems overkill.
> Sorbothane shock mounting is easy enough to do, but is it enough to get
> clear single frames?  Has anyone tried using data from accelerometers
> and rate gyros to stabilize an image electronically?
 
I've slowed the vehicle way down with different motors and the smallest
available pinion gears, so I can't speak of high-speed travel, but I wouldn't
think you would have to worry about it.  Leave room for extra camera suspension
and try it without.  Any kind of active suspension is going to be seriously
non-trivial.
 
>       Has anyone tried sending data back from a robot in the audio carrier
> of a TV signal or in the vertical retrace interval?  If so, with what 
> hardware?
 
I'm considering a couple of different ways for sending telemetry back from the
vehicle.  The easiest is to use the audio carrier of the TV Genii, but the
sound seems to cut out a lot, so that might result in 'holes' in the data.
The other option is another set of R/C transmitter and receiver to send the
data back in the normal (pulse position encoded, sort of) R/C fashion.
 
>      Yes, I know it's a hard, ugly problem. 
 
No, the hard ugly problem is the computer interface and operator's console
and HUD-analog (Amiga with genlock) and then learning to 'drive' this beast
with a 3 second delay.
 
For a low-cost vehicle (it's all lunch money so far with the exception of
a donated Amiga) it works pretty well, though I'm already planning the
Phase II vehicle, which will be muchly improved.  I'm not too thrilled
with the R/C industry in general, but it sure beats building my own or
buying commercial subsystems.  Phase II will probably use lawn-tractor
tires, commercial gearmotors, a 'real' camera (pan/tilt/zoom/focus), a
legal transmitter [I'd really appreciate any ideas on how to get liscenced
for legal transmitters!], and possibly an on-board computer.
 
Willie Smith
w_smith@wookie.dec.com
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