I love riding my bicycle and I think its a shame that the suburb of Dayton I live in is designed for car use only. That means no bike lanes, high speed limits, busy intersections, and a low density packing of places I’d want to ride to.
As a result I’m the only one I ever see pedaling across the nearby 6 lane intersection to the store. Or shopping while dripping with sweat and a backpack full of groceries for that matter.
I figured an electric bicycle could make my life a lot easier. Plus they’re freaking cool.
Unlike my electric motorcycle project, e-bikes are a very environmentally friendly and practical mode of transportation. Bicycles are the most energy efficient human powered vehicles and electric vehicles are the most efficient form of powered locomotion. Combine the two and magic happens.
But I’m not interested in dropping $4,000 on a brand new e-bike, or even $1,300 on a standard hub motor conversion kit.
All I need is an occasional boost, so over the past couple months I’ve created a low cost high value EV conversion kit: The ‘Bicycle BoosterPack’.
The BoosterPack (so named because it makes me think of a jetpack) is designed to quickly mount to the seat post of adult size road commuting bicycles to give them an electric boost at the push of a button.
It uses friction to drive the rear wheel, but it only touches the tire when the button is pushed. The drive motor is on a swing arm with a spring pulling it away from the tire. When the button is pushed the rapid spinning of the motor swings it into the tire. In this way it doesn’t add drag or rotating mass when not in use!
Another big feature of this design is that it can be completely removed in seconds. Unlike traditional E-bikes where the entire vehicle is expensive and at risk of being stolen off the bike rack, the Bicycle BoosterPack can be taken with me wherever I go.
What’s more awesome is that I don’t need a special license or registration to drive this thing. E-bike laws vary throughout the US, but this hybrid technology is considered legal as long as I abide regular bike laws. The bike is still a regular bike when it’s not boosting!
The blue brick is the battery pack and while it has an extraordinarily high energy density, expectations for this thing need to be kept grounded in reality.
As it is the entire assembly only weighs 4 lbs and the bike gets a 5 mile range of pure boost with a top speed around 25 mph. A second or third battery can be added easily if more range is desired. For me, 5 miles drawn out over intermittent 10 second boosts is more than enough to get around.
Friction drives have been around for a while of course, and I was not the first to think of building one using RC components and a swinging motor mount.
The ultimate credit for the concept goes to a couple engineers from Australia named Kepler and Adrian, who created fully functional products a few years ago. The ‘Eboost’ and the ‘Commuter Booster’, pictured below.
So why can’t I buy a ‘Commuter Booster’ or an ‘Eboost’?
Unfortunately, they were never able to successfully commercialize their designs, despite a huge demand for their products.
Their primary challenges turned out to be manufacturing costs, managing consumer support (they used a custom interface and throttle), and restrictive Australian (& European) bicycle laws.
On the other hand, my 3D printed design and supplier relationships have enabled me to produce a more universal and easier to use device at a reasonable cost. And I live in the glorious United States of Freedom.
Also I have the time to experiment until it’s perfect
My little projects need to start pulling their financial weight around the house and selling BoosterPack kits is an exciting new kind of experiment for me. But I have my own unique set of challenges to face first.
- Anyone familiar with EVs already knows this but batteries are the biggest limitation. The energy dense Li-Po batteries I used are quite safe when handled appropriately, but I wouldn’t say that they are kid proof. I do have the capability to package some ultra-safe long life LiFePO4 batteries, but at a much greater cost than the Li-Po batteries.
I plan to sell the kit minus the battery and provide a link to a 3rd party supplier and instructions for battery care & installation.
- Friction drives don’t like water. While the entire device is electrically contained and water resistant, it simply won’t drive a wet tire. My experiments with a sandpaper drive roller greatly improved wet traction but at the cost of noticeably increased tire wear. I think this can be resolved but more research is needed.
- I wanted this device to be as universal as possible. But bicycles are as varied as dogs, perhaps more so, and the number of standardized parts and dimensions is fewer than you might think. There can never be a one size fits all solution.
That said, my clamp design can hold onto round seat posts of the most common sizes (from 21mm to 39mm), and the frame is adjustable enough to function on most adult size road commuter bikes. (No knobby mountain bike tires though).
I’m working on a second configuration that can mount lower on the frame. The tricky part is preserving the portability/removability aspect that I value so much.
- The biggest challenges are non-engineering related. People want these things and I want to sell it to them, but providing adequate installation support to something that is inherently not simple and protecting myself from litigation are real hurdles to deal with.
When I figure all that out I’ll post the first batch on Ebay and make an Instructables to share the assembly directions, how to use it, and design theory. If you want to be one of the first people to own one then you can send me an email at MechEngineerMike AT gmail.com or you can keep watching this blog for a notification!
If you want to help out then you’re more than welcome to leave some feedback in this brief survey. Thanks! http://goo.gl/forms/eJ7aIb8OMi
EDIT 4-10-16: The instructables is out now, check it out here!