String on robots

For teams that use string on an elevator or anything, how to you secure the string? Do you knot it?

We just tie it down to a kind of hook shaped screw and hope it doesn’t come out.

Depending on the type of rope you use, you can splice it into a loop. I believe knots tend to make rope weaker.

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For both our 2018 and 2019 robots we used Dyneema rope on our elevators. We used bowline knots.

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In the 2019 season and 2018 season I just tied the strip in a loop around a strong bolt with a washer on the end to act as a flange. I also used a lighter to burn the end to prevent fraying since it was a nylon rope. This worked well for us.

This is true. Some knots (bowline, figure 8) only lose about 20-25% but others (square) can lose up to 50%. Last year we just used bowlines on all our string attachment points. We also superglued the knot on our main elevator spool, just as a little extra insurance from the knot working itself loose over time.

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Knots do become the weak point in a line (once rope is cut for a purpose, it’s technically called a line) but if you’re using the right rope it will still break after bending your mounting system, so instead of prioritizing knot breaking strength I prioritize making sure that the line is fastened in a way that won’t come undone.

We typically use 1/8in Amsteel Blue, which is a dyneem rope. It has a breaking strength of ~2500lbs. We’ve bent the ■■■■ out of 2.5in*3in aluminum tubing before breaking the line. I like to use an Overhand Knot On a Bight to anchor it, as the knot tightens down on itself and is very easy to tie. It’s pretty similar to a figure eight on a bight, just a tad simpler. Any student can easily pick it up. Haven’t had any knot failures yet

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We used 1/8" Dyneema for our cascading elevator; we started with loops/knots around a bolt with a washer flange, but ended up 3d-printing some toothed clamping blocks. Worked well and needed little maintenance.

Was this for your anchor point to the 2nd stage? Or how it attached to your carriage?

Both, actually. Everywhere the Dyneema needed to have a fixed attachment point, we used a clamping block.

It depends on the function. For light-moderately heavy duty, paracord is the go-to, though it can be rather sensitive to abrasion. As noted before, bowline doesn’t lose much strength in the knot; fisherman’s knots or braids/splices can do even better if that’s an issue. Whatever cord/line you use, be sure to keep the ends from fraying. Most plastic cord can be melted; an overhand knot will work on others; some other cords will require an aglet or swage or whipping. Clothesline, flat webbing, and regular twine will fill heavier and lighter duties and unusual geometries better.

String** not strip

Unless your line had no texture at all (e.g. monofilament), the superglue was wasted. Once pulled tight, bowlines don’t work loose unless the tension is released and something pulls on the loop around the load line.

Yeah, we weren’t particularly worried but we figured it wouldn’t hurt anyhow

Can you share some more details about your 3d printed clamping blocks? We had maintenance issues with our knots and are looking for any and all solutions.

1678 also used 3D printed clamp blocks for single end termination.

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Just in case anyone wants to try this, my experience with onyx clamps was that small teeth (<.125") were insufficient if the cable was under significant tension, and the wall strength couldn’t handle the pressure of the cable. The larger, ~.25" wide interlocking teeth we had on our competition robot slipped less than 1/8" the whole season.

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I found this, is this the clamping element?
citrus%20circuits%20cord%20attachment%20block

We just tie it down.

Yes it is.