I think it could be solved by somehow making a 3rd point to the left with a pivot that somehow connects to the chain and then with another chain going to the cog on the wheel....the distance between the pivot point and the wheel wouldn't change, only the angle...or just about anyway.

Bah, if it was full carbon you OCP guys would jump all over a 2 wheel drive bike

Same as you would with a 2x2 motorcycle.

https://www.ol-d.com/rokon/

Do us all a favour and stop thinking.........please.

too late, they have, Christini 2WD mountain bikes have been around for a while now.

Not quite dual chain drive (they are out there, mostly home-made) but close, and definitely the most refined example of an all-wheel-drive bicycle I've found is here:
https://www.christini.com/

(edit: doh! didn't read the whole thread. Oh well, at least I contributed the link)

wouldn't a 2wd bike be far less energy efficient?

if you get stuck in the mud in a bike, thats what feet are for

Yes, there is probably some mechanical loss from the (for example) shaft drives on those Christini bikes, but which is less efficient:
1) a few percent lost from switching on the front wheel drive, or
2) getting off the bike, pushing it, getting back on it, riding off?

Sounds like 2wd > feet , at least if efficiency is what you're worried about.

a.k.a. "Occam's Razor" ..... A great philosophy and so true when it comes to systems troubleshooting and many other things. I love it.

From Wikipedia, the free encyclopedia:

"Occam's Razor (also Ockham's Razor or any of several other spellings), is a principle attributed to the 14th century English logician and Franciscan friar, William of Ockham that forms the basis of methodological reductionism, also called the principle of parsimony or law of economy.

In its simplest form, Occam's Razor states that one should make no more assumptions than needed. When multiple explanations are available for a phenomenon, the simplest version is preferred. A charred tree on the ground could be caused by a landing alien ship or a lightning strike. According to Occam's Razor, the lightning strike is the preferred explanation as it requires the fewest assumptions."

Bicycling Magazine had a bike a few years ago where the front wheel was driven by a flexible shaft. There are motorcycles where the front wheel is driven by a hydraulic system.

Interesting idea but it seems it would make your pedaling a bit jerky. Since your left side would be a one gear ratio and your right side would be at a larger gear ratio. You would be pedalling harder with your right foot because of the higher ratio on that side.

But I had a similar idea a few weeks back. Chainrings on both sides but with fewer teeth and the rear gears would have fewer teeth too. This is to get the same gear ratios as you would with the chainrings on the same side.

Having a foot slip onto one ring is better than three?

The level of intelligence here is 'simply' astounding.

Reminds me of my favorite Einstein-ism:

"Make everything as simple as possible, but no simpler."

The famous French company Specialities-TA experimented with a Traction Avant (front wheel drive) before giving up and doing something much better.
https://www.specialites-ta.com/hidtorique_gb.htm

They have. One has a drive shaft going up inside a frame tube and one used a spinning drive cable like an old fashioned speedometer. They don't function better than a single wheel drive mtb in most conditions. Slightly better in sand possibly.
There is added friction and weight.

Are you getting the feeling no one read your post? Or just did not understand?