Non Self Locking Worm Gear

"How will it affect my desire to use the pedals- with and without the engine working?" A centrifugal clutch is the device to use here. When the engine runs at speed the clutch will engage, and it will release when the engine RPM drops off.

"I have already a 1:30 worm gear, but the deaaler who supplied me this worm gear wasn't aware that this special gear will suffer from very low efficiency!" Is the ratio of 1:30 appropriate? I believe adding more RPM reduction schemes to reduce the 1:8 further to overall 1:30 will be less efficient that the single mechanism... spinning more parts does not improve efficiency.

Where should be the centrifugal clutch placed?

There is such clutch between the engine and the gear.

The output shaft of the engine is the driver, and the clutch should be installed between the engine and gear. It sounds like you have it correct. This will effectively disconnect the engine from the pedal drive train if the engine is not running at speed.

This scheme does have an energy price: there will be some drag from the clutch when pedaled. Once again, spinning more parts does not help efficiency.

You also need a over running or one way clutch not just a centrifugal clutch.

A over running clutch is what your rear bike wheel has in its center.

With one of those you would not be turning the whole gear reduction system in reverse up to the centrifugal clutch on the engine when you peddle.

I personally see a lot of problems with a worm gear, not the least of which, is their tendency to lock up when not being driven, as you probably already know....

Surely a toothed belt/cogs might be a better idea and far quieter, though you may need two trains to get the gearing you wish......

Also have you looked at gearboxes from Mopeds? Small, lightweight with up to 4 gears and a clutch.....Cheap if bought at a junkyard.....or a small motorbike gearbox, Honda 50 comes to mind.....One of these maybe:-

You can use a "one-way clutch bearing" inside the final driven sprocket on the motor's drive train. Here is an example.

You have received many good answers but the application of many of them sounds of limited benefit.

Clutches and gear boxes are going to add weight and drag.

Applying the power to the pedals requires a higher reduction gear than if added later in the transmission.

Worm gears cease to be reversible in action above a certain ratio and their efficiency falls off rapidly as you approach that ratio.

In the 1950's I remember seeing bicycle assist applied much later - at the wheel rim itself. A little motor pack was bracketed behind the saddle and hinged down to press on the tyre. The tyre had to be more robust and thicker than standard as it was rubbed by a two inch (50mm) pinion like drive wheel and these did not prove popular for long.

My suspicion is that you may end up adding so much weight and drag that the tyres require much more effort to push them along the road and you end up running the engine more often than you expect, if not all the time. . . Going up hill may not be much easier than without all the extra gear. Going down hill your brakes might be much less effective too.

I wonder where you are going to mount the motor so that it is out the way of your gyrating feet???

Best solution is probably a moped, except that you won't get the exercise and your health will suffer if you have no other source of major exercise.

A Moped with no fuel, or just a small bottle carried for emergencies only will get the OP fit in a very short time!!!

To the OP:-

If you have never seen a motor bike with a worm drive (I haven't myself), it may be because its a poor idea........just a thought!

Well said!!!

You will also need the clutch system to disengage when braking. Perhaps throttling back and letting the centrifugal clutch open would be adequate.

Dear JT,

it was not completely clear as to which post on the forum weblink you wanted us to read...the link appears to leave the choice completely open, conclusion, a useless link!

Can you define it better for us please?

Can I leave it to the op please? i.e. it's not my link/answer, and a search

should provide what is required, maybe more. (I am a bit tied up right now*)

jt.

* I was asked "did I buy my wife anything for Valentines day?"

"Yes, I said, a belt and a bag." "That was kind, did she appreciate them?"

To soon to say, I said, but at least the vacuum will work better now."

More useless information? Like father like son?

It looks like there would be a lot of information there on designs for motorizing a bicycle. GA!