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The Earth Explorer Project

The Auxiliary Power Unit

The alternator test bed.

Somewhere along the line I decided I wanted unlimited range. My reasoning was that I wanted to send the Earth Explorer on missions that may last several days. If I relied only on batteries, then my batteries would have to be huge. I could emulate NASA and use solar panels. But I don't have that much money...

It seemed more realistic to use a more conventional power plant. I thought of lawn mowers that run for hours. (At least it seems that way when you have to mow the grass.) They keep going and going. As long as you keep filling it with gas and oil. I needed some way to get the mechanical power from the engine to the wheels. Or I needed a way to generate electrical power and use electric motors to run the wheels.

I decided to use an alternator from a car and drive it from the gas engine. I have an alternator off my old police car that I junked. It happens to be a 100 amp unit. It is big! It weighs xx lbs.

Another trip to my dad's place netted me a *Toro snow blower. (He collects as much junk as I do. I wonder where I learned that habit. :-) It was one of the small ones that looks like it shouldn't even work. All of these small ones seem to use the same generic 2-cycle engine made by Tecumseh.

I tried to start the engine but the fuel line was rotted. So I immediately ripped it out. I tried to get it to run by taking the carburetor apart. That was my first mistake. Because I destroyed one of the gaskets. I could have easily made a new one. But I smashed a needle valve while I was trying to unscrew it.

So now I had the option of spending money to fix this engine or find another one. Turns out that I also have one of those small snow blowers. It convinced me a long time ago, in a snow bank far, far away, that they don't work very well. So I decided it would power my robot. I tried to start it and it fired right up. I pulled that engine out and proceeded to building the "alternator test bed".

I found a piece of 3/4" plywood in my garage that was about 16" square. It had two 2x4s nailed to it. I think it used to be a monitor stand or a printer stand. I made a mounting bracket for the engine out of an old aluminum chassis that was lying around. I made mounting brackets for the alternator from 1-1/2" angle iron. (Not the aluminum stuff I usually use.) I got a pulley and belt from Axman.

I bolted it all together and wired up the original regulator that came out of the car. I thought it generate electricity on it's own, without a battery. I figured that rotor may have enough residual magnetism to get it going, but it didn't. So I started the engine and flicked the power terminal to a 12V battery and it came up to voltage. Actually it came up to about 15V instead of the 13.8V that I expected. I seem to recall the voltage in my car was higher than I expected also. I was using an old head light bulb as a load. But I needed a bigger load since I was only drawing about 75W.

So I took it over to Alan's Robot Shop-Of-Horrors to test it. Brynn brought a bank of light bulbs. They were 12V bulbs that fit in a regular 110V light socket. We wired it together with those test clips like Radio Shack sells, but they were slightly better quality.

So we fired it up and applied power. It was running one light bulb. So Brynn started screwing in more bulbs. After about three 50W bulbs the engine slowed down and died. We were all puzzled. we tried it several times and just wasn't putting out any real power. We tried increasing the speed by playing with the governor. I was going to adjust the jets on the carburetor, but it didn't seem to have any. 150W - Now we were really puzzled.

Then I remembered that I rebuilt the muffler. I took it apart to turn it around and all the guts fell out. It apparently got hot and the steel baffle plate shattered. So I made a new one out of aluminum (because it was handy) and probably used smaller holes than the original. I also packed some fiberglass inside when I reassembled it. It was nice and quite. BUT, it cut the power way down.

So Alan, in one of his decisive moments, said "Let's run it with the muffler off!". We seem to do alot of things that annoy his neighbor at Robot Night. (Remember I cranked the governor up before this.) So we ripped the muffler off and fired it up. It was screaming like a banshee. We flicked the battery and one light came on. So Brynn started screwing in light bulbs and it kept running. It got a little more throaty and coughed up some 2-cycle smoke, but it didn't flinch. It ran for about 60 seconds with all the lights on. Which was either 450W or 500W. Then the lights all went out and the engine smoothed out, still screaming like crazy. So I shut it down.

Brynn said something like "I think you had flames coming out of here...". I thought "Oh great, there goes my expensive alternator". We looked at it a little harder and realized it was just that a test lead burned off. Those things get warm at around 10 amps. I decided we were running about 33 amps through it. So it had a right to complain.

Ron showed up later with one of his wild projects. It may have been his one bladed helicopter.

I decided the test was successful and I would have to decide how to integrate the APU (Auxiliary Power Unit) into the design. I need to build a 24V regulator since I run a 24V system. I also needed to find a smaller alternator.

* Note: For those in a milder climate. Snow is white rain that is sometimes fluffy, sometimes wet, but always cold and annoying. A snow blower is what one uses when one is fed-up with shoveling huge piles of this nasty white stuff.

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