Brushless electric Motor for Bicycle
What is an Astro Powered E-bike? Watch this 19 second video of a 55-MPH E-bike speed run to get an idea what Astro is about:
Yes that’s right Astr0 is sex and spinning magnets!
It turns out that electric bike makers (with the advent of lightweight and powerful batteries) are also looking for highly efficient, powerful, small, lightweight sexy electric motors. Astro motors represent the top rung of RC motor technology for those seeking to build the best E-bike possible.
Astro Flight was founded back in 1969 by electric motor guru Bob Boucher, with the intention of making high quality made-in-USA motors for RC aircraft and even a few human powered aircraft:
Astro Flight specializes in small and powerful inrunner motors. An inrunner is a motor where the rotational core is contained within the motor’s can. The Astro is a completely sealed motor. The pluses to this are that you do not have to worry about debris or water getting into your motor, the bad side is Astros tend to run hot when run hard, especially when climbing. The brushless motors that Astro markets for electric bike builders are the 3205, the 3210, the 3215 and the 3220, all considered industrial sized motors offering incredible power to weight ratios at a price:
3205 1lb $400 max 2hp
3210 2 lbs $425 max 4hp
3220 4lbs $700 max 8hp
When you look at the Astro motors, these all have the same diameter of can, and the various power levels are achieved with additional length. The 3210 is twice as large as the 3205, and the 3220 is twice as large as the 3210.
One important characteristic of Astro Flight motors is that they are designed to be run with RC controllers and are most efficient (90-95%) when run at high RPMs. The most efficient RPM is somewhere around 7500. The amperage needed to obtain this RPM depends on the voltage you are running, and the wind of your motor. 7500-RPM is far too fast to be useful for an electric bike with a single-stage chain to the wheel, so the E-bike builder needs to use some kind of gear reduction system. At 7500-RPMs the motor must be reduced by at least 10:1 (750-RPM) and for some builds it is as high as 40:1 (187-RPM).