is it possible to put the chain outside of the frame? I have narrowed down my purchase decision to 3 locally made folding bikes...am going to experiment with a fork mounted motor with chain drive. I am concerned about the problem that might occur if a chain or belt broke and got entangled in the front wheel, causing the bike to stop immediately and throwing me over the handlebars. Any way around this? Can the gear be put outside of the frame?

You would need a way to turn the hub from the outside of the axle. Given that normally the hub rotates on the QR skewer or bolt axle (the axle itself does not move), it would mean potentially making a system where the axle and hub are one piece, held in the fork ala 20mm thru-axle style (but with bearing collars holding the axle rather than there being a huge 20mm axle bolted tight), and then a cog put on the outside of the aforementioned axle. Thats quite a bit different from how bicycles are usually done. There might be another way to do it for sure, but this is what comes to mind for me.


http://www.sheldonbrown.com/harris/surly-pugsley/index.html
Take a look at the Pugsley fork too. Its designed to hold a *rear* wheel, you might be able to work a way to keep the chain mostly outside the fork, only dipping in as it comes around the bottom of the cog. The large amount of clearance on the cog-side of the fork would also make it less likely that you could experience a total jam should the chain fall in. Downside? You would need to use those huge-ass large marge rims, which would require huge tires like those shown in the picture. That could either be undeniably cool, or undeniably annoying.

You could also build yourself a giant dork disk.

As for the chain though, chains are strong. Quite strong. Typically, they only break because of considerable lateral movement (such as shifting a front derailleur under load), and breaking them without shifting at all is quite rare. You could also use a singlespeed chain if you weren't shifting gears, which would be bomber - those chains are thick.

Bicycle wheel axles and dropouts are very poorly suited to putting any sort of gear further out than the dropout. There's some risk of bending the axle and there's the problem of mounting both sides of the axle so that the axle can spin freely but is secured to the dropouts.

Now, if you used most of a unicycle in place of your fork&front wheel, you'd be in good shape- axle spins relative to drop out (regular bicycle axle does not) and axle does not spin relative to wheel (a regular bicycle axle does).

Figure out how to mount a gear on one side instead of two cranks with pedals, and you're set.