Sounds like fun... it seems from my experience that you will have some
difficulty finding a generator for 20amps that is relatively small. I am
thinking that you may be able to use a small car alternator to generate
the DC you require. Since you have a PIC involved, perhaps you could
drive the alternator phases (A/C) and use the alternator like a 3 phase
motor for starting your gas engine.Once the engine is running, you can
switch the alternator into generation mode.  The rpm ranges for the
motor and alternator are close, I would start with a 2-1 reduction
between the motor and the alternator. You will probably have to do some
bench work to see if the aternator has enough low end torque to start
the r/c engine. Keep us informed of your project... I would love a
similar unit to keep my ham shack battery charged during power outages.
cheers

On Thu, 2001-11-15 at 14:18, Andy Meng wrote:
> Hello,
>
> I am making a generator for a large radio-controlled vehicle. The
purpose
> will be to keep the main 12V batteries (about 30Ah worth) charged. The
> engine I am using is a 4-cycle R/C aircraft engine, about 1HP (.61
in^3
> displacement). The engine will be coupled to the generator, which will
then
> be controlled by a PIC.
>
> The generator also needs to be able to start the engine by acting like
a
> motor. The engine speed will be controlled by the PIC by means of a
servo,
> with the PIC adjusting the speed for a certain voltage output from the
> generator. However, I don't know which type of motor/generator would
be best
> suited for this purpose. Since everything is DC, I assume it would be
easier
> to use a DC (permantent magnet) motor/gen. Efficiency isn't really
> important, since the project is mainly for fun. I think 20 amps from a
> generator (only about 250W, with about a 750W input) would be about
right,
> but it has to be about 14V output (to charge up the sealed lead-acid
battery
> bank), and turn with a good amount of torque (current is mostly
> insignificant on engine start-up) to start the engine (with 12-13V
input).
> If anyone has ideas on what type of motor/gen to use, I would really
> appreciate it.
>
> Thanks,
>
> Andy Meng
> N8MX
> www.qsl.net/n8mx
>

=====================================================================
Lawrence Glaister VE7IT              mailto:ve7it@shaw.ca
1462 Madrona Drive                   http://jfm.bc.ca/
Nanoose Bay, B.C.                    http://members.home.com/cncstuff
Canada          V9P 9C9              http://gspy.sourceforge.net
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