Chain jumps off sprocket

[rscott77092]

I finally got elec problems sorted out and scavenged a motor controller off a "mobility" grocery store shopper. Everything works great except...

As soon as there is any kind of "torque" on the drive train the chain jumps off the sprocket.

Even tho' my motor and jackshaft brackets are welded from 1/4" steel bar, I suspect that there's just barely enough "flex" to allow the 500W motor to bend the bracket just enough for the chain to jump off. I've already tried adjusting the slack to be as tight as possible and it still happens. I don't THINK it's an alignment problem because when the tricycle is up on a crate I can turn it on and squeeze the throttle and everything spins fine from slow to full speed. If I then put my foot on the peddle to operate the coaster brake, the chain will jump off.

Lookin for some brain-stormin here. If any of yous guys could post links to pics of your home-made brackets it might inspire me to rebuild mine. I have some material and just got a fresh bottle of MIG gas, so I just need to get motivated to stare at it long enough to imagine a better design. Maybe....

Any of you bike & scooter experts care to share chain jumping stories/ideas/engineering principals?

I was hoping to have this running for Earth Day events; turns out it doesn't matter, cuz our Earth Day is being rained out. (ironically)

 

[Miles]

Hi,

Could you post a photo of your drive?

 

[rscott77092]

Pictures - yes I just ran off to get some. Left & right side of motor & jackshaft bracket:
[Crom! The software chopped up my url and I'm trying TinyUrl]

... 0_0139.jpg
http://tinyurl.com/c55txq

.. 0_0141.jpg
http://tinyurl.com/caaxnm

I misspoke about the material. Most of it is 1-1/2"x1-1/2"x1/8 angle. the jackshaft's adjuster slots are cut off an old echopper and they are 1/4".

BTW, here's what you can do with an Amigo Mobility shopping cart's motor controller. I put it in a more water-resistant box on the sissy bar.
... 0_0140.jpg
http://tinyurl.com/d3vxff
Here's my EVAlbum page
http://www.evalbum.com/1490
I haven't gotten to ride it enough to find out if it can be burned up.

 

[etard]

Can you describe which chain falls off? I see you welded the jackshaft sprocket, is everything straight there? I also wonder if you loosened the chain up and added a idler sprocket to maybe help guide the chain.

 

[rscott77092]

I'm sorry - I should have been more specific. It's the chain between the motor & the jackshaft that jumps off.
In fact, when I tested it up on a crate, it was the 11tooth sprocket on the motor where the chain jumps off.

I do have a small idler sprocket from the echopper that I could use but I'm not sure how I would do that. Not much room to work with.
If only I had a machine shop to play around in, I could machine some very small parts.

I'll stare at it a while & think about that.

 

[mud2005]

when i had a similar problem, the solution was alignment. hold a straight edge against the larger sprocket and make sure it aligns perfectly with the motor sprockets. also make sure the motor is not slightly crooked as far as being perpendicular to the bigger sprocket. lastly I would hold the rear brakes on mine and hit the throttle with the wheel off the ground and watch for any flexing which would cause misalignment.

 

[rscott77092]

I've been working on mounting an idler sprocket. It increases the chain wrap on the 11T sprocket by about 1-1/2 sprocket tooth - haven't tested yet. It took this long to do the welding [I don't claim to be a welder]
Busy preparing for a job interview.

 

[scoot]

How are you coming along on your dilema?

If you haven't commited yourself to the welding project, have you considered a spring loaded tensioner type of device? When i was looking at your pic, it appeared that such a device might be easily mountable on the frame. I am at work right this moment, but I could post a pic later today if you are at all interested, and not comitted with the welding approach. Do you know what chain size you dealing with? It looks bigger than a N-25 to me.