String thing and tensile ferris wheel update
Update 9/19/07
I tried the large pulley but got no obvious benefit.
Tonight I'll work on building a stand and spring-loaded backing roller to get better contact (and hopefully better velocity transfer) between the pulley and the loop.
I also thought up a potential idea for deploying large loops by running the loop through an array of pulleys like a block and tackle, with one end movable (mounted on a truck?) to increase or decrease the length of cable contained in the pulley array. With a moving distance of two hundred meters, and ten pulleys, a total cable deployment distance of up to 2 km should be possible. Increase by adding more pulleys, more distance, or more moving trucks.
Ok, so a couple weeks ago I was musing about the shape of a loop of string pulled through a set of rollers, and possible wacky applications thereof:
http://tevarin.livejournal.com/171062.html
You guys had some good comments that fleshed out and improved the idea; I talked with Cody and Kathryne at the Towson physics dept, and they thought it might be feasible. And last night I finally got around to testing it out.
I used an electric drill to spin a ~2" diameter wooden pulley on a tinkertoy stub axle, and a bent wire hanger hook to keep the string from jumping off the pulley. I used the downward-dangling-loop configuration, figuring it would be simpler than trying to get a stable upward loop on the first try.
An actual string is no good, it got tangled up on the wooden pulley. I'm not sure whether this is due to string fibers getting stuck on the rough pulley surface, or turbulence from the braided surface of the string, or too much air resistance and too little weight, but it definitely didn't work well.
Thin flexible aquarium tubing worked much better. I was able to use a section of plastic straw to join the tubing into a loop with almost no bumpiness for a smoother flow.
But still no circularity. With my drill at full speed, the tubing hummed merrily through the pulley as a long, stable dangling oval, pretty much indistinguishable from the shape of the loop at rest. Switching from a 7-foot circumference loop to a 3-foot loop didn't seem to cause much difference, though the shorter loop had a greater tendency to jump off the pulley.
Maybe the speed wasn't high enough? I'm carving a larger pulley on the lathe this evening, and I'll give it a try.
It's also possible that the speed of the pulley isn't transferring well to the loop. To fix this I think I need a good backing roller instead of a simple wire hook to press the loop firmly against the pulley. I'll try that if the large pulley still doesn't work.
And it's possible (as Alan suggested) that a long, narrow oval is the stable shape even at high loop speeds. Worth finding out in any case.
I tried the large pulley but got no obvious benefit.
Tonight I'll work on building a stand and spring-loaded backing roller to get better contact (and hopefully better velocity transfer) between the pulley and the loop.
I also thought up a potential idea for deploying large loops by running the loop through an array of pulleys like a block and tackle, with one end movable (mounted on a truck?) to increase or decrease the length of cable contained in the pulley array. With a moving distance of two hundred meters, and ten pulleys, a total cable deployment distance of up to 2 km should be possible. Increase by adding more pulleys, more distance, or more moving trucks.
Ok, so a couple weeks ago I was musing about the shape of a loop of string pulled through a set of rollers, and possible wacky applications thereof:
http://tevarin.livejournal.com/171062.html
You guys had some good comments that fleshed out and improved the idea; I talked with Cody and Kathryne at the Towson physics dept, and they thought it might be feasible. And last night I finally got around to testing it out.
I used an electric drill to spin a ~2" diameter wooden pulley on a tinkertoy stub axle, and a bent wire hanger hook to keep the string from jumping off the pulley. I used the downward-dangling-loop configuration, figuring it would be simpler than trying to get a stable upward loop on the first try.
An actual string is no good, it got tangled up on the wooden pulley. I'm not sure whether this is due to string fibers getting stuck on the rough pulley surface, or turbulence from the braided surface of the string, or too much air resistance and too little weight, but it definitely didn't work well.
Thin flexible aquarium tubing worked much better. I was able to use a section of plastic straw to join the tubing into a loop with almost no bumpiness for a smoother flow.
But still no circularity. With my drill at full speed, the tubing hummed merrily through the pulley as a long, stable dangling oval, pretty much indistinguishable from the shape of the loop at rest. Switching from a 7-foot circumference loop to a 3-foot loop didn't seem to cause much difference, though the shorter loop had a greater tendency to jump off the pulley.
Maybe the speed wasn't high enough? I'm carving a larger pulley on the lathe this evening, and I'll give it a try.
It's also possible that the speed of the pulley isn't transferring well to the loop. To fix this I think I need a good backing roller instead of a simple wire hook to press the loop firmly against the pulley. I'll try that if the large pulley still doesn't work.
And it's possible (as Alan suggested) that a long, narrow oval is the stable shape even at high loop speeds. Worth finding out in any case.