Off-Topic: electric bicycle

I read Leitmotif's post, and decided to share a notion I've been kicking around. Maybe somebody might have heard about it before, or if it's possible.

I sometimes ride a bicycle to work. Most of the way is flat, but here in Florida, wind can be a real issue at times. Seems like whichever way I'm going, it's in my face.

So what I have been daydreaming about while pedaling myself into a heart attack is a variation on the electric assist bicycle. The goal is to make the torque produced by the rider the same in almost any circumstance by conserving energy in battery form, and expending it as needed.

Basically, the idea is a 12VDC generator in place of the pedal sprocket. I was thinking a 12VDC right-angle gearmotor with a through-shaft, pedals mounted to the shaft, maybe a 5:1 gear ratio. Pedaling charges the 12VDC battery, mounted in a bike basket in the rear. Battery powers a different 12VDC motor turning the rear wheel of the bike at a rate set by a handlebar accelerator.

On level ground, pedalling would be a net zero gain - your energy would be running the drive motor. On an uphill, you would lose power from the battery at a reduced rate, supported by the generator.

The magic is on a downhill. On a downhill on a regular bike, you build momentum but quickly lose it once you level out. With this bike, your downhill momentum means your pedaling charges the battery. You can save the power *until you need it*, instead of losing it as soon as you reach level ground.

So am I totally off base here, or could this work? For you purists out there, I couldut a 12VDC Unitronics M91 monitoring power output, charge-discharge condition, battery remaining, a spedometer and a clock.

Any thoughts?

TM

It would work. -- BUT
GOING UP Assume you spend 100 AH of battery to climb a hill and you do not pedal to drive the generator.
GOING DOWN In theory you should regain the 100 AH -- disregarding the added friction and wind resistance because you are going faster -- EXCEPT on recharge you need to add about another 30% ie 30 AH to get back to where you started so you need to replace 100 AH with 130 to break even. At least that is how the numbers break down on discharge and recharge submarine batteries - I maintained the battery records and did the calculations.

NOW from a very distant memory bank the human can generate about 375 watt of power (I think that was a maximum short term output). So we make poor prime movers of generators and bikes going up hill. I live in Seattle and we have a few hills - I rode a bike to my paper route and wished for some assist uphill.

I wonder with bearing and brush loss etc etc if you are gaining on the trade off of inefficency from the chain drive?

WHY is it the wind is always in your face on a bike - seems that way even with a 50 mph tailwind.

You may be better with one of those electric motors that drive direcly on the tire. You would still have the regen effect downhill of course.

Dan

I agree with Leitmotif on the front wheel friction drive. If you KISS it then the battery/motor would assist on demand,say 10 MPH/uphill, and any excess speed would/could regen the battery. You still supply prime power through the chain.

What we need is a cheap pancake motor that replaces the spokes and rim. Then rip apart an old CD drive and use those electronics to trigger some kick tail HexFETs.

I have access to used DC servo motors - 5 to XX HP. Or check Ebay.

Have fun

When I was in grade school, several kids had little generators on their bikes to run a poor excuse of a headlight and a tail light. I rode one of them, and figuring how small the generator was, and the two flashight bulbs, I couldn't believe the additional effort it took to pedal when you turned the switch on.

I would hate to try it on a hilly stretch of rode. I could see the gearmotor arangement on a coasted brake set up, and an additional DC motor acting as a generator, but it would need to be disengagable when "emergency" pedling, or when the drive motor was on.

Great idea, along with Dan's 4wd electric car, specially if you can get a "BIG" government grant to fund R+D.

regards.....casey

I think that gas engine that used a ribbed gear to friction drive a bike years back would do in place of the electric idea. Taking into account your body weight (NO pun intended, as you may weigh 90#'s), battery weight, etc.

Just room for thought.