View Full Version : Saving gas money. Electric bicycle

05-24-2008, 11:06 PM
I go to town every week or two to pick up supplies. I usually drive my truck while my wife takes the PT Cruiser as usual. During the summer my wife takes Friday afternoons off and I will be going in with her on Friday mornings. I thought it would be a good idea to save some gas by riding a bike around town to do some of my shopping. The problem is that I can't depend on my muscles to keep going long enough to make it a viable option. So, I decided to do something about in view of our gasoline prices which are hitting over $5 per gallon.

My wife recently picked up a used bike for me at a yard sale, cost $15. It's in pretty good shape and everything works. I have an old mountain bike that isn't so good so I decided to scrap it. I also have a spare permanent magnet 4 pole starter motor from a lawn tractor and a collection of the usual bits and pieces in my packrat stash.

This is the prototype. It's put together just well enough to test it, especially the gear ratios.


There is much more to do but today I was able to determine that I have finally found a good gear ratio to match the motor. Total gearing is about 17 to 1 reduction and with that the bike accelerates well and will cruise at around 20 mph.

I have much more to do and will gear it down further because of the hills around here and in town. The motor needs a good sized heat sink and maybe a fan too.

I will be buying a small deep discharge battery, maybe a gel cell type to replace the utility battery I am using for testing.

There is one item that makes this drive system different than most. I have included a magnetic clutch that makes it possible to completely disconnect the motor from the rest of the drive. It also makes regenerative braking easy to implement as the motor can be back driven at the flick of a brake switch, not possible with a free wheel that is normally used. The clutch uses little power, around an amp at 12 volts.


Total incremental cost to build this so far is $15 for the bicycle. All the rest I had on hand or made including the large HTD pulley on the magnetic clutch.


05-24-2008, 11:32 PM
I like the hell out of that. I live in a small town with few hills. It would be perfect.

05-24-2008, 11:57 PM
I've had the same project in mind myself, for some time. I've nearly scrounged all the parts :)
It's not quite clear Evan. How have you mounted the sprocket to the hub. Looks like it's clamped somehow?

05-25-2008, 01:39 AM
i had a similar setup, but with a commercial electric bicycle hub motor. One of these: Here (http://www.electricrider.com/crystalyte/index.htm)

I put the battery on the rear bike rack just like you have, which makes the bike IMPOSSIBLE to lift off the ground due to the extreme weight imbalance, and I zip-tied the heck out if it to keep it on. Well, the first little pot hole i hit broke all the zipties and the battery and speed control went flying off. Luckily they didn't hit the ground, because their wires acted as a safety. Lesson learned.

looks like you have elctrical tape holding on that battery? I hope you get something better.

Also, I can understand why you would put a clutch, but I would guess that it's robbing more power than it saves.

Along that same line, in my research, i found that the regenerative braking isn't worth it unless you have super-capacitors. The efficiency to charge your battery is very low.

I see electric bikes as a viable option, at least for warm weather. Mine can go 20-50 miles on a charge, at 20mph, depending on batteries and how much you "assist" it.

I'll be interested to see your progress.

05-25-2008, 01:44 AM
The sprocket is mounted cheap and simple. Bore out the chainwheel hub to fit the wheel hub for centering and then five small bolts clamp it with fender washers to the spokes close to the hub where they cross.

By the way, have you ever tried to hold something with five spokes? It won't fit a 2, 3 4 or six jaw chuck and is too large to clamp on the outside on my lathe. It took me an hour to finally figure out a way to hold it.

looks like you have elctrical tape holding on that battery? I hope you get something better.

This is very crude at this point. The battery will be clamped on with a steel strap over the top and anti tamper bolts. The clutch is very efficient. I rewound it so that it draws an amp or so instead of 100 ma. It doesn't slip until maybe 5 ft lbs of torque. It does however slip for a turn or two when the power is applied which takes some of the shock from the drive system. As for regenerative braking, we have some very long hills here. If I decide to ride it to town I have a 11% grade nearly a mile long UP (!!!) and then about 6 miles of downhill after that. I need the regen braking just to keep the bike under control.

A.K. Boomer
05-25-2008, 01:53 AM
I like how the seat has an empty place to put your nads, I agree you need to get that motor cooled as its not designed for what your doing and I have to question its efficiency, BUT, Way cool Evan, I know its just a rough proto type but I hope you keep progressing with it as I know it will keep getting better and better and am looking forward to many of the "upgrades":)