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Originally Posted by suicideneil
What about running a dynamo in conjunction with the motor on a stock emaxx motor mount, then use that to recharge the batteries as you drive! You would need a small bicycle dynamo, and a really torquey motor, but it might extend run times by a little.
I was actually doing some more late-night research into batteries, and I saw the specs on some D-cell NIMH.... up to 9000mah. Granted, they would weigh nearly twice as much as sub-c cells, but think of the runtimes....
Going the other route, I saw some good AA-size Nimh with about 2500mah capacity @ half the weight of sub-c. Now, you could build two 14.4-16.8 packs, that wouldnt be much larger than 2 7-cell packs, and then run them in parallel to get 5000mah+ at the same weight. The only factor to consider is discharge rates, but the sites I looked at werent terribly specific. With a lightweight setup and not too insane motor/gearing its a viable idea I reckons....
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The dynamo/generator idea sounds good at first glance, but you have to remember that there are losses in the motor turning electrical energy into kinetic energy and then more losses from kinetic energy into electrical. So, whatever runtime you gain from having a dynamo/generator would be negated by the added load of that device plus the losses. Runtime would actually be less.
Last time I've read about the other batteries, the large D cell 9Ah cells have lots more mass vs surface area so they will heat up a lot more and retain the heat longer. And the 2500 AA cells cannot deliver the pulse amperage these cars require. Both of these cells are better suited for applications where long runtimes are wanted but on low current devices.