I am trying to lift a mobile goal using a sprocket and chain, as shown in the image. However, the chain keeps skipping over the sprocket teeth because of the weight of the goal. How do I fix this? I have tried tightening the chain but it’s not possible, and there isn’t any space for another sprocket.
There are two main possibilities that come to my mind with your problem, the first one I would try is simply switching it out for gears rather than a chain. It might still skip but hopefully not as much. Secondly, if you want to stay with the chain, It might be a good idea to change the spacing between your sprockets, so you can get a real tight chain linkage.
6 Likes
Thanks so much. Unfortunately, gears make the skipping worse which is why we switched to sprockets. I will try changing the spacing as well.
The skipping is caused by the axles flexing away from each other. This will happen weather you use chain or gears. Two solutions are to switch to high strength axles, or to make the sides of the gearbox as close together as possible as they sandwich the gears or sprockets. The pieces I’m talking about being sandwiched can also be cross braced for added support.
Although chain is doable, high torque applications (aka your lift) will be much easier with gears. Inversely, chain is perfect for low torque applications such as a drive or intake belt.
Why? Gears and Sprockets are a trade off between friction and accuracy. Gears are more accurate and have more friction. Sprockets give up accuracy in return for lower friction.
When a subsystem regularly completes full cycles (meaning the end piece such as a wheel or intake roller spins past 360 degrees more than once) sprockets are usually better. When a subsystem never completes a full cycle (such as your lift) gears are better.
11 Likes
If you can get a different angle of your gearbox I might be able to help more. I’m not positive but it seems like you might be missing bearing blocks.
They look like this, and help keep the axles centered in a square hole. They also prevent metal to metal contact, and keep the axles from pulling apart which is what’s happening when you hear skipping. You’ll want them anywhere an axle runs through a c-channel.
And if you do have these already I apologize, just can’t see them in the picture. If you don’t, add them throughout the entire robot! And do so before trying the solutions I suggested in my first post, because they may solve the problem completely on their own.
6 Likes
We currently do use high-strength axles for both gears, but not bearing flats as I assumed they weren’t needed for those axles. When I next get hold of the robot I will add those and see if the issue still remains (and take a better picture if it does). Thanks so much for your help! 
2 Likes
Np, theres a bearings with a larger size hole just for the hs’s.
5 Likes
We had a similar problem during tower takeover with our two bar. As said previously, using gears would be most optimal, but there are some other factors. I’m not sure if you have rubber banding, but if not, it helps assist the motor with lifting larger loads. Another factor could be the orientation of the c channel. If you attach it to a gear/sprocket flat on, you will need more torque as compared as side on, some one correct me if I’m wrong.
2 Likes
Since the large sprocket doesn’t have to make more than one revolution you can zip-tie chain to the sprocket and then add a rubber band around a couple of links on non-power transferring side - this should keep chain tight even if distance between axles changes under load.
Also, you may put a spacer on a nut (as a roller) next to small sprocket to prevent the loose end of the chain from jumping or use a rubber band to keep the loose end of the chain on the sprocket, whichever works best for you.
3 Likes
Perhaps substitute an attachment link to hold elastic bands? Asking for trouble with asymmetry I guess.
1 Like
Add a chain tensioner. You could use a sprocket, or just a bolt with spacers on it acting as rollers. Bend a 1-by (flat steel) into a “U” shape to act as the ‘carrier’, then attach to a rubber band.
3 Likes
Not true. Rotating the bars will not change their weight or center of mass relative to the axis of rotation. The force of gravity acting on the bar is the same. Therefore, the work done by the motor to overcome the force of gravity is the same.
There is no magic source of torque.
Rotating the bar is a good suggestion tho. The gear box can be slimmer which helps with skipping.
6 Likes
This topic was automatically closed 365 days after the last reply. New replies are no longer allowed.