Idler pulley for chain: Question

[rykoala]

Does the idler pulley have to be a pulley that holds the chain captive from side to side? Or can it be a gear? I have thoughts of using a gutted and totally freewheeling (forward and backward) coaster brake hub with a 18-20 tooth gear as the pulley. I'm worried that the chain would fall off of it constantly though.

Any thoughts?

[trikeman]

As long as you have some way to keep the chain from getting too slack, it should work. After all, that is the way a regular chain and sprocket work. I have seem some recumbents with mid-drive sprockets instead of the pulley and they often have one of those parts from the bottom of the derailer that keeps the chain tight.

http://www.rotatorrecumbent.com/trends.html

You will also have to have the chain in line with the two sprockets to keep it from jumping off. I have seen several designs where they build a set of small brackets to keep the chain from jumping off.

[AtomicZombie]

Is this is what you are considering?....

http://www.atomiczombie.com/gallery/randaljones/batmobike.htm

It does work well, and you can add a small tab made of flatbar around the chainring to stop the chain from bouncing off.

Brad

[rykoala]

Something along those lines, yes. Maybe I'll weld a bracket with a couple of 10 tooth jockey wheels from a derailer to hold the chain to the idler. But for now just picture a kids bike coaster hub with the torque arm cut off. I gutted the brake out of it and now its just a gear on bearings. I'll give it a shot and see how it goes. I am going to work on that this weekend if I get time.

[AtomicZombie]

You can also use a rear hub with the multi speed free hub removed. Ask your bike shop for a "track cog" It is a single 12 tooth ring that just threads on to the hub. It makes a nice light idler system.

Brad

[rykoala]

Thanks for the suggestion :)

[TheKid]

When I built mine, I didn't have a pulley. Since the pulley is used on the return side, I used the derailler without the springs method, like on the Streetfox. It worked fine.