Would you recommend the replacement of the stock motor and gear box with the Astroflight Firefly (they both use the same propeller)? Has anyone attempted this?

From : Don Stackhouse

We tried the Astro Firefly, both the 4:1 and 16:1 versions, back when we were developing the original RK series models. It did not perform well at all in these models. It's far more expensive than our MPS-1, about the same weight, and only puts out about half as many watts. Very nice little motor, very quiet, but pricey, and its 1/2 amp absolute limit makes it impossible to get much wattage out of it unless you use an excessive number of cells, which of course pushes the weight way up. That many cells also makes use of a BEC questionable, which means a second battery just to power the radio, which means even more weight. It did a little better with a Castle Creations Pixie 7 that would feed it up to about 3/4 amp, but it still was anemic in these models. Also, Astro tells us that the brush life of the Firefly is very short at anything more than 1/2 amp. It just doesn't fit this application at all, simply the wrong combination of parameters. I still have four of them in a box here, and I'm hoping to find an application for it someday. Like I said, it's a beautiful motor, but so far I haven't had any luck finding the right airplane for it.

We tried all sorts of different power systems including the Firefly when we developed the original RK models, and all of them either cost way too much or would not perform well or both. Much of that initial year of development work that went into the first of the series involved finding the right power system. We finally (in desperation) developed our own, our MPS-1. The models are designed around this, and the correct quantity of MPS-1's are included in each of the kits.

Don Stackhouse
DJ Aerotech