Hey Everyone

[Adrianking]

Hi, I'm Adrian and new here! Looks like you have a good forum and would like to join in.

I have a specialized stump jumper elite and want to do a DIY electric conversion. I don't have any money limit set but would not like to go crazy spending thousands lol

I was looking around and can't find a crank set where the motor drives the left side allowing front gears to be untouched as they are on the right. Is this possible?

I have found a couple of motor company's online which do custom builds. The main types I am looking at are right angle worm gear motors which will keep the width of the build nice and narrow, a bit like a water bottle bolted to the frame.

Just wondering what the ideal final drive rpm should roughly be, I have read anywhere from 80 to 400rpm. I would also need the motor to drive the gears without spinning the pedals.

Any inputs, thoughts or links much appreciated

 

[spinningmagnets]

It sounds like you want to drive the rear wheel by attaching a motor to the left side of the rear wheel?

Direct Drive (DD) hubmotors turn at the RPMs of the wheel. This is in-efficient (26-MPH in a 26-inch wheel is about 336-RPMs, very slow for an electric motor) but...it is also simple and cheap. The DD hubs have remained popular with some builders because they can be given more power than a bicycle chain can survive, and also DD hubs have the capability to run very quietly (most quietly using a sine-wave controller). 9-Continents (9C), Yescomusa, and Crystalyte HT/HS series are popular DD hubs.

The next most popular are the geared hubmotors. Internal gears allow the motor to spin 5 times faster than the wheel, so there is slightly better efficiency. They are lighter, but the biggest are only around 7-inches in diameter, plus they have a poor heat-shedding path, so...geared hubs sometimes do not survive if hot-rodded. If kept to their well-known power limits, they can last a long time. MAC, eZee, Bafang-BPM, etc are popular.

If you are using a non-hub motor, and driving the rear wheel on the left side, the pedal-drive on the right side is undisturbed. plus, you can raise the volts and change the gearing to keep the motors RPMs high enough to stay in the motors best efficiency range (which also helps it run cooler).

Here's an article with some links and pics that may help you decide on what will work best for you:

http://www.electricbike.com/diy-mid-drive/

 

[Adrianking]

Thanks for the reply, didn't think about directly driving the rear wheel, would be good for speed but would like hill climbing abilities also.

I didn't explain very well, I was thinking of BB drive (I think that's what it's called where it uses the gears). I would like to some how connect the motor through the front gears on the left side so that the motor drives a shaft on one fixed sprocket which spins the 3 gears at the front on the right side which leaves the standard gearing untouched. The gearing of the bike can then reduce or increase the load on the motor as required.

This seems easy to do apart from the fact the pedals would have to be independent from the gears so the would not spin with the motor but would also engage the gears when then motor is not running (bit like how bmx works?) also mounting a single sprocket on the opposite side which drives the other front gears on the same shaft might be tricky?

I hope that makes a bit more sense

 

[dogman dan]

The GNG kit seems to be popular now days. Typically a freewheeling front chain ring on the crank accomplishes transferring power to the existing chain on this type of non hub kit.

Cyclone is another type, not sure if they are still available anymore.

Then there is the stokemonkey, which does a similar thing, but uses a hubmotor to provide the power.

I'm not the non hub motor guy, and am quite ignorant. But the worm gear drive types I've seen come on ready to ride bikes, not kits. So you might look at whole bikes for the worm drive type.

I don't know if they still have them, but High Tek Bikes used to sell them.