how to: prevent chain from dropping

[sockman]

having a lot of chain dropping issues...
got a chain tensioner and 2 rollers to prevent it popping off the big chainring
now its not skipping off the bigger chainring but at the smaller freewheel...even when pedalling with no input from motor...
i'm already using single speed chain and ring tooth.

any ideas?

 

[Thud]

If your throwing chains, you have potentialy 2 problems.

#1 alignment. If chains are in line then they will run very true with little maintance

#2 flex. there is no way to maintain alignmet if something is flexing under tourque.

Tensioner's & guides are only stop gap solutions. look at the points of your set up for flexing & add re-enforcments as required to maintain alignment.

good luck.

 

[BMX]

Alignment is very often the cause, but if that is good also check the chain for stiff links, if you joined the chain with a chain breaker then you may well have a stiff link somewhere and when that hits the sprocket it may climb out rather than flex. The chain breaker can be used to loosen off a stiff link by supporting the middle of the chain while pushing the pin through an extra 0.1mm or so...

George

 

[sockman]

the alignment is ok....it was thrown off when i tried to climb up a small kerb...
flex could be the issue...cos its a steel frame...

guess i'll have to look at adding more guides...

george,
checked on the stiff links...non found

just wondering how the others do it...cos i'm getting paranoid trying to listen to the chain when cycling

 

[REdiculous]

The frame shouldn't flex that much should it? It looks pretty beefy from here.

The first problem I had was alignment. I got that mostly-fixed and then it was frame flex (my bad). It stopped dropping chains when I added a good tensioner. Then I added a frame reinforcement so I could dial the tensioner down a little.

I finally just decided that the chain needs to stay just a little tighter than it would be on a normal bike. Even minor bumps can combine with it tilting side to side...no more fun.

My first tensioner/idler attempt was kinda like yours...the way the chain goes over it before going to the rear sprocket. I think it turned out that the torque was pulling the tensioner down and letting the chain slack off..

I switched it around so the chain goes under the tensioner and the problem went away. Now the torque can't over power the tensioner the way it did before. Maybe you've got a similar problem here?..I dunno..hard to say.

Best of luck..hope you get it sorted quick!

 

[etard]

How flexible are your tensioner arms? Does it pop off by just revving the motor on the bench or only when you are riding? Have you spun it slow to see if the chain is entering the freewheel head on, or is it coming from one side in? Is it possible your whole tensioner setup rotated where before it came off one sprocket now the other? Are there any signs of mounting brackets twisting?

 

[sockman]

How flexible are your tensioner arms? Does it pop off by just revving the motor on the bench or only when you are riding? Have you spun it slow to see if the chain is entering the freewheel head on, or is it coming from one side in? Is it possible your whole tensioner setup rotated where before it came off one sprocket now the other? Are there any signs of mounting brackets twisting?

i've tested it on bench with a trainer set at various tension...it was fine...
the chain is aligned and actually quite smooth with low drag when i spin the rear wheel...
it pop off when i was riding it across a traffic junction...it wasn't even on electric power...and the speed was actually quite low (just a small road kerb about 2" or less)

there were some chain bobbing (top side) when its running (due to a slight off centered big chainring)
my tensioner arms were a bit flimsy...i'll try to double the thickness or change it to a stiffer material...

do you guys get a lot of chain drag? (in a non chain throwing setup?)

 

[amberwolf]

If it pops off when pedalling, it's because the chain is being backfed from the wheel towards the motor, which puts the pulling torque on the *bottom* of the chain, and loosens the top of the chain. That's the opposite of what the motor does when it is running, and what your tensioner is there to help with.

But even with that, if it's all aligned perfectly, the chain still shouldn't come off. If it appears perfectly aligned when the bike is stationary, and stays on whether pedalling on the trainer or motoring, then it probably is aligned fine there but is flexing under some circumstances on the road.

FWIW, that is a lot of extra chain to deal with. Is there any way you can reverse the reduction setup, so that the motor is in front, and the freewheel/jackshaft in back, so that the chain can run directly from the freewheel to the rear chainring on the wheel? If you do that, and eliminate all the extra chain length, you can also get rid of all the tensioners/guides for it. Just make the mounts that hold the whole reduction drive with sliding slots for the mounting bolts, so that you can slide it forward to tighten the chain and then secure the mounting bolts.

This will also make it quieter, and perhaps a bit more efficient, powerwise (though maybe not enough to see a difference).

 

[REdiculous]

do you guys get a lot of chain drag? (in a non chain throwing setup?)

Not too much, but more than I'd want to pedal against for very long. I'd liken the drag to those old-school dynamo lights...a pita for people on long rides but a motor can overcome it easy enough.

My setup seems to take about 6w to get the wheel barely turning on the bench. I know a small fraction of that is lost in the controller and motor but the rest would be the reduction, chains and tensioner..

So maybe 3 to 4w worth of extra drag...sound right? later