Ideas on power sources

You could try a turbine engine for hobby helo's driving a small
generator.  No, they're not the most fuel efficient, but they're out
there, and you can make a relatively big honkin gas tank.  Or try
constructing your own turbine engine (efficiency will probably be crap
though, no offense to your skills or anyhting).

You can drive the wheels through the turbine and the electronics through
the generator, or all throuhg the generator.  It'll be really quiet
relative to other combustible fuel engines, the sound it will make will
be really cool, and they generate tremendous power for the size.

--Andy P

I am working on a bot with similar goals to yours. I set 5 miles of open
desert as my target. My approach is to use a pair of electric wheelchair
motors and a pair of deep cycle marine batteries. My target weight is
about 200 pounds. I have not done any modeling, but my reasoning is that
an electric wheelchair carrying a large adult will run several hours on
a paved surface. I will be carryng less weight and larger batteries, so
this should offset the added friction of the off road environment. Until
I finish the motor controller, this will remain unverified and may be wrong.

I looked seriously at using a 4 cycle engine (about 5 hp was my guess)
driven hydraulic system for power, but it looked like it would push the
size, weight and cost up substantially. Hydraulic oil stinks and gets
everywhere, especially in an experimental vehicle. Hydraulic drive has
advantages in controllability, and good torque, but my lack of
experience with it along with the other issues I mentioned eventually
pushed me away.

Model engines are messy, the two cycle and four cycle ones both use
similar fuel with oil mixed in. The high RPM that they operate at makes
the power train a complex and expensive thing. Turbines are horribly
expensive, very hungry for fuel and run at insane RPM's. Both turbines
and reciprocating engines are precision machinery and sand coupled with
high ambient temperatures are hard on them. Weed whacker type engines
are not quite so high RPM or so precise, but still have high enough
operating RPM that I did not want to mess with a drive train. I briefly
considered a weed whacker engine driving a generator. This approach
seemed too fragile.

Your idea of an ATC has merit if you want to build something in that
size range. The manufacturer will have taken care of the drive train,
cooling, fuel capacity and many other issues. You could probably
multiply your distance goal by 5 with an ATC platform. The ATC or small
motorcyle engine could be quiet as well. The 50-100cc motorcycle or ATC
engine would also make a good power source if you want to make your own
chasis. I looked at this idea as well.

The quietness, easy control, easy storage, and low maintenance aspect of
electric drive were too attractive to pass up for me. This bot is a
multi year project for me and the ability to leave it to sit in the
garage for months at a time while work eats my lunch are important. This
is a hobby/personal learning project for me not a PHD or work project.

Good Luck,
Bob

"MetalHead"

I thought about that too, but my main goal is on building the AI and
tackling the problems of dealing with the environment. That's why I'm
leaning towards platforms that are "almost ready". The RC seemed very
attractive at first, but it's hard to provide enough energy. The limited
size may also be a problem.


Interesting, I was looking at different 4-stroke gas engines from Honda.
Their entry level is a 1HP 2Kg that measures about 25x25cm, it costs about
$300, but again the problem would be to build the drivetrain around it. It
surely would be very interesting and educational, but it's not really my
main goal in robotics.


Besides that, 2 stroke engines don't idle very well. I did some experiments
with a 1/8th scale nitro-methane RC car and it is not really appropriate for
robotics. It's really hard to adjust the carburator, and if you need to get
it stopped for a minute or so, it will probably stall.

<snipped>


Take a look of the Yamaha Grizzly 125. It seems a very good option for rough
terrain and a price that is not absurdely prohibitive.


I couldn't agree more, but if you need something to run 170 miles, it starts
to get really tough to use electric. In my case, my robot will probably take
one or two years to build. I hope so, because it is my thesis project, and I
want to graduate soon.

Cheers

Padu

I have a Honda 'walk behind' mower, which has a hydrostatic drive. Seems to
me that this is probably the best bet - you already have the drivetrain
stuff to turn ~ 8" wheels, and you can vary the speed from nothing to lots.
There is no clutch to worry about. The power (5HP 4 stroke) is more than
adequate. You would basically need to add steering instead of the fixed
front wheels (and perhaps remove the grass cutting blades ...)

Dave




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Why not buy a used snapper rear engined riding mower and use it
for your platform? You can probably get one for $500 if you look
around. You could replace the blade with a hydraulic pump or auto
alternator depending on how you want to control the mower. Rugged
and simple. I've got one I've had for ~10 years and it is still
going, and will carry at least 200 lb of rider in and out of
ditches and such with out problems. Add some extra fuel capacity
and it would probabaly travel your distance easily.

http://www.snapper.com/rear_engine_riders.html

"Si Ballenger"

Thanks for the suggestion. I looked at small honda motors for weed wackers
and mowers. Although it seems very attractive, I would spend a lot of time
building the chassis. If I have no other options, then I think that's the
way, but I'm still going to spend a few more time searching for other
alternatives.


Cheers

Padu

If your platform is going to go on dirt or gravel roads, you will
need something pretty heavy duty just to get traction and not get
bounced around or tipped over. Visit your snapper or riding mower
dealers and look at how they work. Super simple and they may have
a "fixer-upper" they took in on trade cheap, or may even donate a
junker to the cause if you explain what you are doing (also check
the for sale ads in the paper). I'm not sure about other brands,
but they may work in a similar way. I've seen junkers at the
recycling center that probably need just a little TLC to get
going again.

Have you considered making the chassis a little bigger
and using motorized bicycle wheels?   One advantage
is that everything is pretty much off the shelf and
10 miles would be easy even with fairly light batteries.
You'd still need to steer it, so maybe a tricycle with
two powered hubs in the back to drive and a servo in
the front to steer?

See http://www.electric-bikes.com/others.htm  for some
ideas and links to follow.

Good luck!

Bob Smith

What is the maximum range you want to accomplish?

I've thought about lightweight frames coupled with lighter than air bags or
"pods". Just enough
Helium to counter some of the gravitational pull, not so much to lift the robot
off the ground. This
may also allow some "out of the box" steering mechanisms. IF you have an "almost
lighter than air"
robot, you could utilize some aerodynamic steering mechanism(s).


Joe



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