This is the prime topic IMHO. I think we collectively have enough
microcontroller/computer expertise to do all the electonics. Mechanical?
Does the word Clueless come to mind? ;-)
>
> I think I've mentioned my plans to use a "retired" child's
> battery operated car. It has pleny of load capacity; plenty
> of power and are available cheep second hand. They are also
> already wired for 6v and 12v operation (with motors, wheels,
> the works.)
I took apart my daughter's car. At the heart of it was a small DC motor and
reduction gearing system that spins a gear with a tube through the middle.
The axel of the back wheel goes though the tube.
It's quite powerful. However a couple of open issues:
1) The gearing is set up to spin only forward. A "jiggle" gear slips if
the motor is spun backward.
2) Since only one motor is driving the back wheels, steering much be
accomplished some other way.
>
> > Or suggest a low-tech way to build one? I envisage a solid square of
> > chipboard,
>
> Skip the chipboard. It decomposes rapidly in the presence of moisture;
> If you use wood as a base I'd suggest Marine grade plywood.
>
> Grass, Dew, Rain, Sprinkers etc. don't make for a arid environment.
Agreed. What about plastic? Metal seems a bad idea due to weight and rusting...
>
>
> >say 0.5x0.5m (20"x20"), with two motors bolted to it and crude
> > wheels made from something suitably round (like the ends of a large tin
> > can perhaps). We would probably need to buy motors as they have to be
> > quite chunky, and I think it's worth getting a small lead-acid motorcycle
> > battery too as it is sure to come in handy. Any thoughts?
>
> (Just semantics....)
> The "motor cycle" batteries are typically 6V.
> I bought a small "garden tractor" battery that was 12V.
Well I found a place here in Atlanta that sells the biggest PowerSonic
sealed gel cell I've ever seen (get this): 12V 30 AHr! Wow!
The last interesting and inexpensive motor I've seen is from BG Micro
(http://www.bgmicro.com catalog is in PDF format). 12V 8A stall, 3.5A
continous unloaded. No torque specs available. 1/2 inch long 1/8 diameter
shaft. $4.95 each.
I'm figuring that I can get the battery, base and motors for under $100.
Any clue to guage the run time say for 3 motors (two for drive, one for
cutting?) May be easier simply to get the setup and do empirical tests.
Later,
BAJ