Astro Motors on Electric Bikes; Terrifying Speed

May 10, 2012

Some of the fastest and sexiest electric bikes on the planet are powered by Astro motors.  An Astro powered E-bike represents the pinnacle of  E-bike engineering for the ultimate in light weight performance. Only because of recent developments in battery and controller technology is an Astro powered E-bike even possible.

“Astro Flight” has been an innovator in quality small electric brushless motors for 40 years.  Recently they have become a source for motors that can be used for high-performance electric bikes, and even have a section on their website called “electric bike stuff”. There is only one E-bike on the market that you can buy currently with an Astro Flight motor, the FFR trike which is capable of speeds up to 50-MPH. All the other Astro powered E-bikes so far have been home built. There are a few people selling kits and mounting systems to aid the DIY builder to build an Astro powered ebike.

Astro 3220 Powered ebike


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:

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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).

One method of a gear-down is a planetary gear system. One example of this is the Neugart gear box, which is very small and lightweight, and easily adaptable to an E-bike. The Neugart  uses a set of planetary gears inside its housing, which reduces the input RPMs from the motor, and increases the output torque.

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A great example of a Neugart Pl-60 married to a  small Astro Flight 3205 is the Ron Rocha drive system. The smaller Astro 3205 is a safe and sane  motor which will fit in the palm of your hand and keep you under the street-legal limit of 750 watts of power for your E-bike, while still having a reasonable speed of 25-mph without pedaling. The Rocha system is designed to fit most bikes, and sells for $1500 for the drive system including the motor… The Neugart  planetary gear box reduces the Astro 3205 RPMs by 32:1, so that the drive output has the proper RPMs to allow it to be used to power the Bottom-Bracket (BB).

BB-drives allow the motor to use the bikes stock gears. This allows the motor to pull steep hills in low gear, and then still provide good top-speed on flatter terrain. This is a great design option, which lowers amp-draw across the entire speed range compared to the motor having only a single speed to drive the rear wheel. Drawing lower amps will lower motor/controller heat, and will also give you more miles per battery volume.

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The weight of the motor is 1.5 pounds, the weight of this entire drive system is 7lbs (as seen above including the motor). With a 36V / 20Ah LiPo battery, this system will add less than 20 pounds to a conversion bike. To read more about this sytem go here.  This is an easy bolt-on system that will fit almost any  mountain bike or even a cruiser. The Rocha Mountain Drive  system,  finished a 20 mile climb up pikes peak 8000 feet climb in 2011, a big achievement for an electric bike:

The Astro 3210 motor is roughly twice as large as the 3205. It weighs in at 2lbs and puts out roughly 3-HP (2200-Watts) at peak efficency of 93%.  A great example of 3210 build would be the Dogati E-bike. The Dogatis 3210 is coupled with planetary gear-set like this:

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This compact gear-set gives the Dogati drive a 16:1 ratio, geared just far enough down so that this E-bike could be powered through the pedal gear system.  Read the complete story about the Dogati  here:

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The result is as breathtaking and beautiful as it is effective.

45-MPH is easily achieved with the 3210 running through the bikes stock gear system.

For racers and hotrodders, the 3220 is the motor of choice. It is twice the motor the 3210 is, weighing in at 5lbs and capable of 9-HP (6700-Watts) with a peak efficiency of 95%. In the last few years,  Astro has made many upgrades to this motor. They have improved the epoxies and internal windings to make it less susceptible to overheating, and they have recently added the option of active cooling to the motor to make it even more reliable.

Matt Schumacher is known for making E-bike hot rods utilizing the 3220. He is currently producing his DaVinci gear reduction system, which reduces the 3220 RPMs with a 6:1 ratio. Unfortunately this is not enough reduction to go to the pedal drive line, but Matt sells his drives mostly as left hand drive units that run a separate chain to the back wheel. The primary reduction uses a belt instead of a chain, so it will run much quieter. The DaVinci, true to is name, is a work of art:

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The DaVinci drive unit is available from Matt for $575, which does not include motor or controller.  One of my favorite Astro-3220 vehicles which uses one of Matts DaVinci drives is the FFR trike, which is available from their website for around $6000, and is capable of speeds up to 50-MPH. Check out Matt’s 50-MPH trike here.

A typical controller that’s used with the Astro systems (and on all of the above bikes) is the Castle-Creations line of Electronic-Speed-Controllers (ESC)…the Castle HV110-amp controller (for a BB-drive), and the Castle HV160 controller (for driving the wheel at the axle). These are sexy looking pieces of technology and extremely powerful. They are actually very programmable using your PC, and they have datalogging…but like many RC technologies adapted to E-bikes they have serious drawbacks to the E-biker as well.  Castle controllers are not sensored, so they prefer full throttle which makes E-bike applications tricky. Also they cannot be run at any voltage over 48V, and even at 48V, you can smoke one with a voltage spike. Castle has a great replacement policy, that if you damage one of their controllers, they will replace no questions asked for half price.

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Astro Flight Factory tour-

In April of 2012, I visited the Astro Factory in Irvine,  in southern California.

Astro is under new ownership as of 2 years ago and the new owners seem determined to improve the product. They have several highly skilled mechanical and electrical engineers working in unison to not only design new and exciting motors but also to upgrade the old ones, to solve problems that the Astro motor had with cooling and reliability when used in an electric bike application.

As of now all the motors mentioned above are closed systems, completely sealed so that they are protected from the elements.  The new engineers at Astro have improved the materials used inside the motor, so even with this closed design the motor is capable of handling a lot more heat than the Astro motors of the past.  Also, Astro is working on some can designs which are open and provide ventilation to the motor components, and in addition they are adding active cooling systems that blow air through the motor ensuring that the motor runs cooler, even when running hard on an electric bike (such as when climbing mountains).

Recently Astro built a sophisticated engine dyno so that they can easily test their motors at different wattages and different loads and better understand temperature thresholds and cooling of their motors. Astro motors are made from extremely high grade components and  made 100%  here in the United States in their Orange County factory. I was impressed with their facility, manufacturing, and testing equipment they had there.

Astro Motors and Heat

Astro motors are 80%  motor and 20% toaster oven.  As already mentioned they tend to get hot when run hard.  It is highly recommended that if you are running an Astro motor, you have some kind of temperature probe attached to the motor, and you monitor the motor temperature when climbing steep trails to make sure the motor does not fry.  New products such as the Cycle Analyst V3 (read story here) will monitor temperatures and automatically limit power, or shut down the motor if it gets too hot.

Videos of Astro Motor E-bike Builds: 

Nothing will do an Astro Motor justice without a video showing them doing crazy fast speeds on small electric bikes. Here are some great examples:

Motomoto’s Astro 3210 screamer from the riders persective going through the gears. He gets to 45-MPH with this motor:


Later he would fit the same bike with a 3220 and achieve 65-MPH top speed!


The Dogati in action blasting through the streets of Taiwan with an Astro Flight 3220 powering it to speeds of over 50-MPH:


Matt Schumacher’s 3220 trikes doing donuts, showing the massive torque of a 3220 Astro Flight:


Eric has been involved in the electric bike industry since 2002 when he started a 6000 square foot brick and mortar Electric Bike store in downtown San Francisco. He is a true believer that small electric vehicles can change the way we operate and the way we think.


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