Improved chain tensioning for top beam configuration

The last couple weeks have been dominated by getting this batch of machines put together and it’s become clear that one hardware area that we need to improve is the system which tensions the slack side of the chain.

The bungee cords that we have been using which worked well in the vertical configuration are simply not strong enough.

How should we handle this? Should we go with a thicker bungee cord? Should we switch to a counterweight system? What are the solutions that folks are using, what works, and what doesn’t?

Let’s redesign that part of the machine.


I think the ‘workout band’ is great. I was looking at the surgical tubing to purchase but found that band in an old WII workout software. Same type of rubber will work.


Do you have a picture of how it’s set up?


anything based on springs/elastic is going to provide the least force when there
is more slack chain, which is when the most force is needed.

a weight based system provides a constant amount of force, which can be changed

I would suggest using 2L soda bottles or similar for the weights so that we can
adjust the weight by changing how much water is in them (and they, or milk
cartons, or similar containers should be essentially free for everyone.

The lines between the chain and the weight need to be guided around the top

Can this be done with eyelets? or do we actually need the lower friction of a


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A consideration with the weight scheme is how much vertical travel the weight must be free to travel. Without a multiple purchase attachment, the weight will need to travel about 4.5 feet between the extremes. Adding the height of the weight itself, it will be a close thing to keep tension throughout the range of travel.

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The top beam is a little over 6’ from the ground, so 4.5’ of travel should not
be a problem.

I’ve found that by mounting my motors facing outward, and positioning the chain guide roller screws loose enough to allow the nylon spacer to spin, I have NO need for the bungees or counterweights, never had a skipped chain, plenty of adhesion, all good.

My current design actually places the motor below the unistrut, unlike the photo above. This lets the back of the motor mount bracket hold flush and true against the strut body and makes for an exceptionally stiff connection.

hope this helps,


But the workarea interferes with the line of travel, so the measurement from the top of the workarea is the one of interest.

Wow, I really like this. It gets that roller guide right up close. I only recently read that the motor was threaded on both sides.

I picked up a set of bungees from homedepot for $5. This is the 30in one installed, seems to work wonders. Its a rad sketchy on the bottom corners when its stretched to the max though. Ill probably invest in a high quality one at some point.


Take a pic of the rest of the chain?

Pre roller is hanging free, post motor is suspending the sled.

Sorry, that pict looks like it was when I still had the traditional frame (v1) bungee setup, i’ve removed that and it’s not been an issue so far at all. The chain guide/roller keeps the chain fully engaged and so far (2-3 weeks) I’ve seen no i’ll effects letting the end hang free.

that depends what direction you run the lines :slight_smile: but it’s still over 5’

David Lang

having the roller in front is good, but I think the motor should be behind the
bracket, not in front of it, ans it transfers the load more directly to the top

well, one issue you will have if you just have all the slack chain hanging free
is that it will hit the ground and have a chance to tangle.

if you still have it doubled, but just hanging, that can work, but is putting
pressure on the chain and sprocket.

So far as a guide I’ve just got some blocks of wood I had as scraps pushing the chain out from the beam on the slack side. It moves so slowly when actually cutting the slight bump on the “slack” side doesn’t seem to be as problem so far.

Even running in a slot as seen in the picture I’m including (wrong way to go by the way), the chain wasn’t skipping but there was a visible catch to it…no longer the case with the wooden block to keep the chain parallel at least in the last few inches before the gear. I’m in bed or I’d take a current photo. Tomorrow.

I think the weights are the way to go for the people that have the space. I can just fit this in my shed.


I used thicker bands and it seems to have solved the issue. I also used those white plastic peices to block the the chain from sagging down too far and causing chain binding (which was happening every time before these two modifications). Ill get a picture of this in a moment.

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My builds still in the sled stage. Any idea how much force is needed? I’ve used these constant force springs wrapped around a bearing in the past as a counter balance. they are used in window and tape measures to.