Motor-Porn: Honda GX25 moved into new APU rig

What started out as a simple thread on a mobile-home board, ended up in more than 50 pages of discussion about a neat and small generator project based on a Honda GX25 and a Torcman 430-30 brushless outrunner motor. Some people always seem to ask, why anyone would build something like that, if they could get more output power for less money from a ready made product? Because available products don't really match the requirements and why would anyone pay money for something one actually doesn't really want or need?

Apollo-NG needs multiple independent energy sources to be able to function autonomously and independently from grid infrastructure. Although the basic requirements are supposed to be covered by alternative power technologies like solar and wind power, it never hurts to have a fallback for a rainy day. That's where the apu comes into play:

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However, it first started with this test setup to test the engine and the generator as a general prove-of-concept and to make sure that all parts were running satisfyingly, before taking them apart and reduce the whole thing to the max:

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Last week, the extruded aluminum profiles for the rig arrived and were assembled by iggy, who seemed to like to play with LEGO for adult engineers. It seemed pretty easy, but maybe it's better if he'd care to comment on the ease and quality of the build. After stripping down the engine and removing all parts that were deemed unwanted, a big pile of spare parts piled up:

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When the engine is in the rig it's pretty easy to get a good imagination how things are going to look, when it's finished:

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The next task is to reduce sound emissions by creating a new muffler system. Research showed, that a simple 4:2:3 three chamber ratio in a body 20 times the volume of the engine (displacement) should provide good results and should have no effect on the output power of the engine. The preliminary draft design on the right basically shows the setup with the three chambers and the input (upper) and output (lower) pipes in a 90° angle.

Luckily, Harald Zimmermann, who is somewhat of an expert on the topic, since he is designing and building mufflers for a long time, agreed to help out, by designing a muffler with good sound suppression and hopefully no noticeable engine power losses. Hopefully the APU will purr more quietly once the new muffler is ready and operational.