As some of you may remember, I'm building a small robot (autonomous long range rover or ALR2) that is supposed to have a minimum automony of 10 miles. Well, I just finished the mechanical phase of the first ALR2, Koli (ALR2 is the project name, and Koli is the name of the first robot out of this project), and it is already evident that with all the weight it's going to carry, electrical energy won't be sufficient. Koli is currently based on a off the shelf RC monster truck.
Before trying electrical RC cars, I've tried nitro-methane, but those things are so temperamental, I guess because of their high performance tuned 2 stroke engines. So I gave up nitro-methane.
The help I need from you is to give some ideas on what alternative power sources do I have.
Here's what I came up with so far:
-LiPo batteries and brushless DC motors
-Gasoline (not nitro-methane) RC buggy motor
-Gasoline motor from a small ATV (50cc to 100cc)
Or even buy a used ATV and transform it. The maximum size I can go is the ATV size.
The motor must have the following characteristics:
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.
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.
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.
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?
"Padu" wrote in news: snipped-for-privacy@iswest.net:
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).
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.
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.
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.
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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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.
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