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This Robot Power Plant project by Ken Gracey over at Parallax shows how we can get away from using huge batteries for power hungry mobile projects. There are pictures of his second build style after the jump. "Project Purpose: To develop an outdoor robot power system which can deliver many more amp-hours of energy than batteries, using a gas engine and a modified automobile alternator. The initial purpose was not to build a robot, but to prototype a Hybrid Power Plant that I could use on an over-the-snow robot. A battery would merely support surges in current demand, like a big capacitor. It wouldn’t be there to provide power for anything more than half of a minute. This could lighten my load and extend operating time, particularly for a GPS autonomous robotic project.
After building the Hybrid Power Plant and running some tests on it with real loads I decided to put some motors on it and test it out on an R/C robot requiring much more current. This additional step turned out to be a big eye-opener, and gave me another purpose to the project - to test the system on a robot.
Mechanical Design:
Coupling an alternator to a small gas engine requires that the shafts be perfectly aligned. Small "spider couplings" provide for up to 1 degree of angular misalignment, and 0.01" of horizontal offset. To align the engine and alternator I decided to make this a machining project (I had tried other ways before, and failed!). Using belts and pulleys would be out of the question due to the introduction of more moving parts, increased system slop and noise, and danger of moving parts.
The Hybrid Power Plant would was built by mounting the engine and alternator on their own plates, using a 3/4" aluminum rod as an additional alignment (and to double as handles). Although the alternator had two mounting holes, I opted not to use these since they were offset at different z-axis places. Instead, I machined the front of the alternator flat and drilled/tapped four holes in known locations. These holes allowed me to attach it to its mounting plate and perfectly identify the center shaft. The Honda mini 4-stroke engine (GX35) really needed a clutch - the power curve is way up in the RPMs and it generates little torque until 3,500 RPM. Staton-Inc makes a $60 clutch that has perfect mounting holes, enabling it to be mounted to a plate. I also attached the back and bottom of the engine to four more mounting locations on the base plate. The thought was that by mounting the engine to some sizeable chunks of aluminum I would smooth out vibration by closely coupling it to a mass. "
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