I am considering an ebike for commuting. My trek 1200 currently serves this purpose well. I would like to keep it as is. I do have a trek 520 gathering dust and rust in the basement and I believe it would be a good candidate rather than the usual mtb ebikes I see.

What I am thinking of doing is something along the cyclone type rig where you drive the crank rather than rear hub. But, rather than using a different crankset, I was thinking of using my existing triple ring with the smallest ring being used for the motor drive. I never use the damn thing anyway.

I doubt there is room behind the crank to mount it as the cyclone does. Instead I would mount it under the forward tube or whatever they call that tube.

Also, I am not looking for something I can sit back on and enjoy the 30 mph ride. Instead, I would like to be pedaling my arse off enjoying a 30 or maybe better mph ride. So, I am not looking for much power. I suspect 200 watts might be enough.

Another question. I want to keep this thing as simple and bulletproof as possible. Could I get away without a controller? I'm not looking for precise low speed control. I just want a bit of a push at higher speeds/hills.

I built one similar to that by putting a crank gear on the other side and driving it with an electric motor.

Here's the trouble with that type of logic:

1 - You must always pedal as fast as the motor

If you turn off the motor, you'll be pedaling to turn over the motor. Real hard
If the motor drives the crank, you'll be pedaling as fast

It's not a very good design.

I ended up removing the pedals entirely but that just made the eBike an illegal eBike because there were no functional pedals anymore.

If the motor used a freewheel drive gear, you wouldn't have to spin the motor all the time.

A Freewheel on the motor... this is exactly the thought I have been having after I hear people talking about how you have to pedal so much harder on an e-bike after the motor quits. Conceivably, a person should be able to modify an existing rear hub (say... from a BMX or something) to mount onto the motor... perhaps if you gave the motors axle threads (where it protrudes from the motor), one could more easily mount an old single sprocket hub onto the motor using fairly standard bicycle wheel parts. Although, I would think that the hub would need to be narrowed some depending on the length of the axle and every thing. I suppose the motor would also need an axle of the exact right size to thread... which could be ground down if someone knew what they were doing... or sized up by fitting a correct sized pipe over top...

Just some thoughts I've been meaning to throw out there.

200 watts wouldn't be worth the weight and the hassle, IMO.

If you got a decent Trek 520 why not sell it? Bikes like that are in high demand with people that want a 'serious' commuter. Or old school tourer....turning a decent utilitarian bike into an e-bike is a waste to me...there are plenty of old mtn bikes out there better suited for the purpose.

Keep a classic a classic. Big size I'll even buy it.

Just my two cents worth.

The 1200 was in the shop last week, so I rode the 520 to work after cleaning it up and adjusting the RD.

Damn that thing rides nice. I got new calouses though on my fingers from trying to shift the non existent brake lever paddles!!!! The ST shifters really are great for the rear, but, give me a friction shifter any day for the front. The guys at the LBS screwed up my front shifter on the 1200. Gotta bring it back soon.

You are right, littlefoot. I shouldn't muck it up. Think I am gonna hang on to it and try to get the wife/daughter interested in it or maybe my son in a few years when he's big enough.

Or maybe I will sell it. There is a guy at work interested. Unfortunately, it is a little too small for me as well.

The Freewheel part is pretty easy. A Shimano BMX freewheel screwed onto a bottom bracket cup (threads are compatible) bolts to the motor shaft. The rest is what's keeping me sketching.

A Freewheel on the motor... this is exactly the thought I have been having after I hear people talking about how you have to pedal so much harder on an e-bike after the motor quits. Conceivably, a person should be able to modify an existing rear hub (say... from a BMX or something) to mount onto the motor... perhaps if you gave the motors axle threads (where it protrudes from the motor), one could more easily mount an old single sprocket hub onto the motor using fairly standard bicycle wheel parts. Although, I would think that the hub would need to be narrowed some depending on the length of the axle and every thing. I suppose the motor would also need an axle of the exact right size to thread... which could be ground down if someone knew what they were doing... or sized up by fitting a correct sized pipe over top...

Just some thoughts I've been meaning to throw out there.

Been rethinking this a bit. I have decided that it might be a better idea to drive the big ring rather than the small one for a few reasons.

1. Better torque. Whatever motor I would use would have some pretty tight size restraints which means a small motor spinning faster rather than a big torque monster lugging along.

2. Ease of removal. A requirement is that I want this to remain primarily a human powered bike. If I drive the big ring, I will be able to remove this thing in a few minutes without breakng the chain.

3. Using the big ring allows the drive sprocket to be set further off center which gives me an extra inch or so for motor width which will still be kind of small.

The only downside is that I will loose some top speed on downhill runs, but, I can still manage a little better than 30 mph on my middle ring, so it's not that big a deal.

If anyone has any ideas for motors, I would like to hear about them.

I am also guessing that a higher voltage might be helpful as it should allow for a smaller motor.

I started out along the lines you are considering. I bought a Kollmorgen 400w brushless 24v motor for the job. One nice thing is it has a built-in controller so you just need 24v and a 5k throttle. They are a CCW rotation out of the box but there a number of people on the web that know how to reverse them with a little work.

Not to be crass, but there's a guy I know who has one for sale on eBay right now :innocent:

They are also available for a reasonable price from superkids.com.

The one drawback for me with the approach is that you will always have to pedal when under power, unless you freewheel the big sprocket which doesn't sound like what you're after.

I'd sure like to know what you end up doing, inspiration for my next ebike...

Yeah, not being able to coast while under electric power is a bit of a drawback. It also has me thinking back to driving my little sprocket as I wouldn't need to pedal so damn fast.

That kollmorgen sounds interesting. We use a kollmorgen on a machine at work. It is a high quality unit and pretty damn pricey.

How big is the one you are talking about?

5-1/16" Overall Diameter
3-5/8" Depth including shaft