Elevator Actuation Sprocket is Slipping

[JesseK]

When we first put our lift together, the motor ran, the sprocket turned, and the chain/wires all went in unison to achieve the marvelous feat putting out 94lbs of force to move the lift up 84 inches in 3 seconds. "Sweet!" we thought, and took it apart to be powder coated.

Now, when we put it all back together with the same wires & everything, we can't keep the sprocket from slipping on the chain unless we hold our fingers down on the chain to keep it on the sprocket.

We've tried several new approaches over the last day and a half but nothing seems to be working except our age-old nylon rope + wench setup. To be honest, I want to keep at this the new way until the very last second (basically that means the programmers need it). I probably have about 3 more hours to work on it before I'm completely overruled due to other teams needing the bot. I know teams have succeeded in the past in using a chain + cable wire setup, or even a pulley + belt setup, to lift an elevator.

Any tips or suggestions?

The best photo of the full bot is at
http://www.battlefieldrobotics.org/t.../the_robot.htm

[Alex Cormier]

Originally Posted by JesseK

When we first put our lift together, the motor ran, the sprocket turned, and the chain/wires all went in unison to achieve the marvelous feat putting out 94lbs of force to move the lift up 84 inches in 3 seconds. "Sweet!" we thought, and took it apart to be powder coated.

Now, when we put it all back together with the same wires & everything, we can't keep the sprocket from slipping on the chain unless we hold our fingers down on the chain to keep it on the sprocket.

We've tried several new approaches over the last day and a half but nothing seems to be working except our age-old nylon rope + wench setup. To be honest, I want to keep at this the new way until the very last second (basically that means the programmers need it). I probably have about 3 more hours to work on it before I'm completely overruled due to other teams needing the bot. I know teams have succeeded in the past in using a chain + cable wire setup, or even a pulley + belt setup, to lift an elevator.

Any tips or suggestions?

The best photo of the full bot is at
http://www.battlefieldrobotics.org/t.../the_robot.htm

if you say you can do fine with your finger on the chain, why not add a few zipties to tighten the chain? or possibly some tensioners?

[Tom Bishop]

Chain tensioners are needed to adjust the chain as it stretches. Sounds like your chain is too long. Or it might be that you do not have enough wrap around your sprockets. You could use some Delrin guides to make sure the chain wraps around at least 50% of the teeth. Post a picture.

[MrForbes]

If you could post a picture of the chain system, it might help us think of things to do.

Older design garage door openers use a chain and cable loop, that has a spring tensioner in it. If you think that might help you, I can take some pictures of one. But it sounds like you don't have a fixed length loop, you just have too much friction causing the chain to jump over the sprocket.

Powder coating changes the dimensions of everything...

[JesseK]

Just got done with a 15 hour robot day...man we got so much done today...

We inlined the sprocket so the chain coming off both sides is exactly vertical. We then made a hardware store run and bought varying full-threaded eyebolts, made a new mount, and tensioned the crap outta both sides of the chain. It's still holding and hasn't slipped since we first did it. We DO have an interesting video with pretty cool real-life sound effects of what happens when the chain pops off the sprocket when the lift is at full height though...that was fun...

Thank God, that one part alone wasted us 36 build session hours! It's our first real elevator and man I'm glad it's over. After that every other piece only took an hour or two to integrate onto the lift and bot and it looks like we'll make Monday night.

edit: When at full height, the chain was bowing the elevator backwards, if you can picture that. Then, on the way down, the chain would pop off. To fix it, we had to fine tune our mounts and move the sprocket, pulley at the top, and all tensioners to about 1/8" or less from the gearbox on the output shaft or corresponding mounting surfaces. Wish this was in an elevator FAQ somewhere.

[R.C.]

all you gotta do is go to mcmaster carr and buy a chain tensioner. Then click floating roller chain tensioner

[JesseK]

Originally Posted by rc_cola1323

all you gotta do is go to mcmaster carr and buy a chain tensioner. Then click floating roller chain tensioner

Too heavy and expensive for what it offers when compared to alternatives.