pic: Telescoping Arm Warning

[daltore]

Update: The 3840 lb. Dyneema works! To weight test the system, I stood on the arm and the motor lifted me right up, no problem! Did the same for the robot, and then Richard and I hung on it. The first time we hung, something dropped down, but the Dyneema was fine, it was just under enough tension that it forced a spacer on the axle (a Delrin shroud that extended the 1/2" steel axle to 1") away from the sprocket and popped down to the next level. We fixed that problem and got all 4 feet off the ground for several seconds. It was quite impressive! We're adding in a tensioning system for the one knot we had stationary because it undid a little bit and detensioned the rope, but overall, I'm very happy with this material!

I highly recommend this stuff, just a few suggestions if you use it in the future:


1) It's a little hard to work with, but as was said before, 2 half hitches or a taut-line hitch work well when tying it, and always use a much bigger rating than you think you will need. Example: 500 pound load, didn't hold until we went to almost a 2-ton line!

2) Spectra/Dyneema (brand names of Ultra High Molecular Weight Polyethylene, UHMWPE) is very slick, and does not like any kind of friction-based system. It will not work like a belt, it has to be tied down (the knots only work because there's so much pressure between the strands of material). To drive it off of our shaft, we actually had to drill a hole through the shaft, and then tie it down with a constrictor knot to keep it from moving in the hole.

3) If there is ANY kind of rubbing or abrasion, it will VASTLY weaken the rope. Just because the breaking strength is high doesn't mean it's hard to cut. The rating is just for a tension load, not shearing. We broke our first rope with 50 pounds of weight on it alone because we sheared it when it jumped a pulley.

Thanks for all the help, and good luck in competition!