Gear Reduction for Electric Bike

Weight, cost and durability. When chain reduction will do. You will already using a gear and a chain.

Also the RPM of that motor is typical 6000 to 10000.

Misapplication of the technology leads to problems such as this. The model airplane motor is not designed to produce torque at low rpm because a spinning prop doesn't start using power until it's turning in the upper rpm range.

Not much help, I know.

For same power the combination high RPM motor + reduction gear weights less than a high torque low RPM motor.

This is the reason for the choice.

OK, Thanks. I hadn't actually considered the weight factor.

I agree that motor is not going to last (Heating) and the loading if you have a side load is going to kill the bearings. Why not go on ebay and find a better choice as the gear box that your thinking about is way expensive, for I assume you want rpm in the hundred range as an output. Woody

For simplicity and robustness perhaps you should be looking at a wheelchair motor: http://www.emd.co.uk/productrange.php These incorporate a wormdrive rightangle gearbox, quite simple but robust.

These days people seem to be going more for brushless, gearboxless dc motors (even for wheelchairs) for lower weight, longer life and better efficiency: http://www.goldenmotor.com/ I haven't looked at these in detail, but assume (for low-speed torque) that they are more akin to stepper motors or dc servomotors than the usual BLDC.

A simple option is to use a right angle gearbox that uses a worm gear type of reduction system. They are considerably more forgiving than most other gear reduction systems to having their inputs ran at high speed while still providing a reliable high speed reduction ratio in a small package.

I have seen a number of them re purposed to unusually high input speeds with little more than a change out from the original thick heavy gear lube to a thinner lightweight synthetic lube.

The rest is just a matter of staying inside the design torque specs.

From simplicity point of view your suggestion is the best but for a bike also transmission efficiency is important and from this point of view worm reductions are by far not the best. I think that a combination of chain/belt + gear would be the most efficient and as well will offer the lowest weight. Of course it is not the cheapest.

Thanks for the responses, it's a very informative forum.

What spured me to investigate gearboxes was that I saw someone offering to build a chain reduction drive within a case on one of the e-bike forums. It was fully enclosed and was basically just a sprocket & chain reduction inside.

It seemed strange to me because it's kind of simulating a gearbox. Apparently the efficiency with a chain is around 95% too whereas some of those worm gearboxes are much lower. But if that is the case you'd think people would be using chain-drive gearboxes in other applications? I haven't tried searching for them although I have heard they exist. But are they very popular?

The efficiency of the chain reduction drive is very good, but they can be extremely heavy compared with other methods, maybe not so good for a bike.

In earth drilling units (stationary) such transmissions with heavy quadruplex chains were used and with good results. For low power the solution is not optimal.

here's a planatary type gear box

http://www.anaheimautomation.com/products/gearbox/planetary-gearbox-type.php?tID=109&pt=t&cID=30&cdID=273

a hybred of planatary & roller chain http://www.gearingsolutions.com/technology.htm

Why not try and find a small, low voltage 3 phase motor and drive it via a VFD?

My favorite is still the Cyclo drive for a lot of reduction in a simple compact unit.

hi if dc a simple use of a ballast cappacitor and transistors can be used but will only give prefferd rpm when under desired load but benefitting from high tourqe as if running at full speed.