I think Eric summed it up.. gear ratio prop pitch being the first culprits I'd think too. motors not geared to spin-n-breath.. like 80-85% of free spin RPM, are gonna cook! (I'm a simple guy that likes to tinker, and its usually much smaller projects) not taking sides but as a vendor I'd be frustrated hearing "this is junk!" and as a customer I'd be just as frustrated with "this stuff dont work!" as either one of em, yup, I'd likely get real pissy real quick. personally, I'd be breaking out the calculator, prop pitch to motor RPM etc.. trying to find the ratios that are gonna let the motor spin-n-breath instead of smokin the windings and brushes, then trying the experiment again (differently and improved). its making an assumption something IS drastically wrong mechanically. it might be a good kit initially, but the motor is being badly lugged-loaded and cookin. calculator, tachometer and thermometer time! I'm not "majorly experienced", so its just somewhat educated guessing with no intent to insult anyone who really DOES know better... but, I'd guess tied off to a dock with full power applied, if the motor is able to reach 70-75% of free spin RPM, then underway it's likely to land close to a pretty safe ballpark range that can be fine tuned after if needed. (watching the heat a pretty good indicator) to a point, the easier it's spinning the less current its gonna draw too, with an R/C car gearing to that 80-85% of free RPM is gonna run much cooler and give you all kinds of nice responsive throttle control, accelerating and decelerating without having to use the "brakes", you get around a track a whole lot better-faster. overgeared will top out faster, run hotter, more sluggish acceleration-deceleration and have you leaning on the brakes a LOT.. and the runtime goes right down the drain. kinda similar theoretically anyhow. they're using brushed and brushless PM motors, PWM speed controllers, nicads, nimhs, lipos etc.. its all just smaller. same for small fast electric R/C boats with gearboxes in em for swinging larger props to get some speed.. but with models the batteries are usually dumped before motors are gonna get cooked. -not always tho! a 7 cell outrigger hydro toy NEEDED both air and water cooling for its fast as hell ridiculously hard working 3-1/2 minute runs.. passing up glow-engines etc.. FUN, but with models you can get away with things approaching murder suicide too no doubt. other thoughts.. free spin motor RPM is one consideration, but chained up to the propshaft with its bearings seals and whatever losses are imposed by the mechanical reduction.. how does motor free RPM compare to spinning it all up without any load at all? its kinda "incidental", but it can possibly change the kind of gearing ratio you might want in place. if it means going from 3:1 to a 3.5:1 for the sake of safety and reliability, oh well.. depends on the motor too, some might be as happy-cool at 70-75% of free spin RPM under full load, for a good long time (couple hours!) it all gets more complex with prop pitch theoretical distance (88 fpm per mph) vs prop pitch with prop slip inclusive and actual speed, can sometimes get into stuff that'll keep ya awake at night swapping hands tryin to scratch head rump and eyeballs simultaneously on top of juggling the calculator pencil and notepad.. oh boy! anyhowz, enuf boring babble-rantz, hope ya get the project together successfully! (maybe the babble helped?) --- On Tue, 4/24/12, Carter Quillen <twowheelinguy@yahoo.com> wrote:
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