Newsgroups: comp.robotics
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From: nagle@netcom.com (John Nagle)
Subject: Re: Robotic movement question...
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Date: Tue, 9 May 1995 18:34:42 GMT
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longshot@finrod.mankato.msus.edu (Erik Green) writes:
>     What we need is a small, fairly low RPM internal combustion engine
>that runs on a cheap, clean, readily available fuel, and requires little
>cooling.  Can anybody think of one?

    There was an article in Popular Science about a year ago about a
company that was going to make a 4-cycle engine for leaf blowers,
chainsaws, and such.  I haven't seen a product based on it, though.

    Four-cycle engines can be converted to butane or
propane.  (With 2-cycle engines, lubrication is usually done by mixing
oil with the fuel, which adds pollution and isn't compatible with
running on compressed gases.  So a 4-cycle engine is needed.)
Butane lift trucks are routinely used indoors, so a butane
powered robot would be quite reasonable.   

    Small IC engines tend to run at high RPMs.  This may not be so bad.
Most engine-generator systems are designed to produce 60Hz power, which
means generator RPMs must be 3600 or some fraction thereof.  But
there's no reason a mobile robot needs 60Hz.  Voltage and frequency
can be dealt with downstream in the power-conversion electronics.
It's probably simplest to have the engine drive an alternator, rectify
to DC, and convert that as needed.  

     Basically, you're going to need a source of clean power for the
electronics, which probably means a switching power supply with a broad
input voltage range, and low-quality power for the bigger drive motors.
The engine throttle should be under computer control, so when you need
more power, you can get it.  When the robot is stationary, the engine
can be idled, producing just enough power to keep the electronics going.

     A nice addition would be the ability to use the generator as a motor
for self-starting.  Another good add-on would be a small Halon fire 
extingusher (you can get these in boat stores; they're just a gas cylinder
with a sprinkler head on top.)  With this, you'd have a plant suitable for
indoor operation.

     The whole thing could be packaged up as a powerplant about the size
of a car battery, producing a few hundred watts.  Plug in a butane
cartridge, and away you go.

     This would be a nice project for somebody who's into engines.
I'd be interested in talking to anybody who wants to do it.

					John Nagle
