Would This E-Bike Work?

Hi. I know nothing about electricity or electrical equipment, but I have this idea which I’ve shown in this rough sketch. My idea is that as you peddle and turn the rear wheel, which turns the generator, the electricity generated would run the electric motor which would assist in powering the bike as you peddle.

If this idea is feasible, can anyone tell me what types, models, watts, volts, HP, etc. of generator and motor I would need?

Well, I just looked to see if I can post an image, but I don’t see anything. Can you post an image here?

What you are proposing is an exercise bike. :slight_smile:
To answer your question, No! Sorry.

Thank you for your reply, I now see a button for posting a pic, so here is my rough sketch, and let me begin by changing my previous “peddling” to “pedaling” (it was late last night).

As you pedal the bike, the rear wheel turns a generator which powers an electric motor mounted in the front of the bike which drives the front wheel. In order for this to work you have to pedal, but it’s my feeling that the driven front wheel could make pedaling easier, especially going up hills. This wouldn’t work?

There is no free lunch. Generators and Electric motors each give up 10 to 20 loss in heat in operation. Therefore you lose at least 20+ percent of pedal input in the process. Sorry


ok. Supposing that, instead of a generator being turned by the rear wheel, it is turned directly from pedaling, i.e., you don’t pedal the rear wheel, you pedal the generator. I would imagine that the generator would have to turn very fast, in which case a series of gears might turn it fast enough?

As somebody else said - there is no free lunch. No matter how you gear it, you can not get more power out of a system than you put in.(Basic law of Physics)

In general the more complex the system ie gears or motor/generators etc the more inefficient the drive system becomes. A lot of the pedal energy input will be wasted as heat…

You can gain leverage or torque - letting you climb hils more easily with less effort but it willl take mofre time - but 1 KWH input — cannot produce more than 1 kwh output !!

Thank you. I’m not an engineer, so I can only accept what you all tell me. But, one last shot, here…

Well … Ok Bruce let’s see if we can make this work?

First - nice drawing, you might make a pretty good Engineer one day if you are interested. Persistence and curiosity are two very important traits of a good engineer. You certainly have shown those in these few post! Attention to detail (your drawing) and a love for mathematics are also required.

Secondly, I AM an engineer - degrees (EE & ME) from one of the top ten schools in the nation - 40 years ago. I’ve had a great career in engineering, designing and building major projects all over the world. I’m retired now but I’m still designing, building, and learning - just on my schedule. Actually it was a question almost identical to your’s that launched me into engineering - years ago.

Never stop asking questions. But you have to be willing to dig for the answers.

In theory - this set up could work - but you will be very tired after peddling the first quarter mile! Not sure WHY you would want to do this - the original chain drive is going to be pretty efficient - compared to all the friction and electrical losses in your design above.

Modern Rail Road Locomotives work something like your ebike design - a very large diesel engine turns a large generator which in turn drives large electric motors which are actually part of the wheels. Modern Locomotives after many years of optimizing the designs - have an efficiency somewhere in the mid 30% to lower 40%.

The efficiency of your original chain driven bicycle is probably closer to 65 -75 % most of the loses coming in the rolling friction of the tires and the chain/sprockets… I suspect your 256:1 gear box and motor/generator set up will have an efficiency factor of less than 1%.

So lets stop here an let me ask - why do want to do this?


Thank you, Larry…

Why do I want to do this? Because it’s there!

No, seriously. I’ve looked at a number of e-bikes on the Internet and they do wonderful things and they are very expensive. But then comes the clincher - 30-50 mile range with a 4-6 hour recharge time. That’s great if you you’ll never want to hit the open road and actually go somewhere.

Anyone who has ever extensively ridden a bike knows what it’s like to get on a flat, level straightaway. You get a goodly pace going and you feel as though you could keep it up forever. It would be great if you could leisurely pedal like that on any incline, uphill or downhill.

If you were to raise the back end of your bike and get on it and start pedaling, it would be very easy to pedal. Would it really be that much harder pedaling to simply turn a generator? The one thing I do know about generators is that the faster they spin, the greater the electrical output. I have no idea how much output would be needed to power a bicycle motor. I don’t know if 10,000 RPM is insufficient or if it would burn up the motor. For all I know, maybe 2,000 RPM is all that is required, in which case we could eliminate one of the sprocket sets.

I also have no idea what the effort would be in pedaling four sprockets lined up. I’m guessing it wouldn’t be that difficult, certainly not as difficult as pedaling a bike up a steep hill - maybe. I suppose I’d have to actually put together such a setup and find out.

I have seen youtube videos where people have converted their bikes into generator drivers. The back ends of the bikes are up and the rear wheel is connected to a generator with a belt. The pedaling required is fairly easy. I’m thinking, “Why not connect that generator to a motor on a bike?”
And if the generator needs to turn faster than one can pedal, then throw in a couple more sprockets so that the speed increases exponentially.

So, anyway, in my ideal world, such a set up as I’ve shown would enable me to pedal at a comfortable, consistent rate whether I’m on a level surface or climbing a hill because all I’d be doing is turning a generator and the effort would be the same. Granted, I’d go a bit slower up a hill because of gravity, but, again, the effort put into pedaling wouldn’t change. I’d also be able to go as far as I want to without “range anxiety”, and I’d be doing so under my own steam with some assist.

Welcome to my ideal world.

BTW, I sketched that first drawing by hand. The second one I did on a free program called “DraftSight”, which is essentially AutoCAD without all the bells and whistles.


Nothing like hands on experience to help understand things! Grab some tools.

Unfortunately your ideal world is pretty much limited to your imagination, You will however be cycling in the real world - and that world is not as you imagine.

The load on the electric motor will be reflected back to the generator, then back to the pedals as you try to climb the hill. Effectively there will be no difference … with the exception of all the power losses due to friction and electrical losses.

If you want to play with generators and motors You can use the starter motors off old lawn mowers or outboard motors - use one as a motor, the other as a generator - hook’em up and see what happens.

PS I have an ebike - actually a recumbent tri cycle. The motor is in the front wheel - pedals drive the rear axle. 36 volt 20ah battery. On level ground I pedal, I use the motor to help climb hills. The motor acts as a generator going down hill and charges the battery any time I apply the brakes. I also have a small solar panel on it to charge the battery. Normally I can ride about 20 miles on average terrain before the battery becomes depleted - of course the more I pedal the longer it last. If I know I’m in hilly country - I just drop her down a gear or two and pedal harder and keep the speed down with the brake going down hill. :slight_smile: But eventually the battery will discharge. In your ideal world the downhill should offset the uphills - but they don’t - those pesky inefficiencies!!
PS its an old bike - small lead acid batteries - I working on some new lithium ion batteries - but your are right they are expensive.

Oh, darn.

Well, thank you for educating me on what would actually happen in the real world. Your recumbent sounds great! Are you familiar with the Raht Racer? I think it’s somewhat along the same lines as my concept - pedaling a generator.

Bruce, happy to help you with understanding the real world laws of physics and engineering, but I don’t do financials. (Against SEC rules)

Never heard of the RAHT Racer.

Suggest you talk to Rich Kornfield (that’s rich)!!

You don’t do financials? Where’d that come from??

Oh, I see…the video. There are a few RAHT videos and I picked the one that best showed the RAHT in use. I tend to gloss over the verbage. At any rate I think it is amazing that this thing can do 70 MPH by pedaling, and like I said, I think it employs turning a generator.

Well, again, I appreciate your having taken the time to explain things to me.

Now it’s off onto the next project that won’t work.