4 ms·

No, the difference is when/how you load the springs. This proposal seems to be that you load the spring with your leg in the air before it makes contact with th

No, the difference is when/how you load the springs. This proposal seems to be that you load the spring with your leg in the air before it makes contact with the ground (achieved by attaching the top of the spring up the leg), then land the loaded spring and unload. Their argument is that this allows for higher overall energy output from the human body (akin to cycling). In a jumping stilt you're loading the spring when you put your foot on the ground and unloading immediately, so the energy output only really occurs during that period of foot contact, which presumably lowers overall output.

culebron21 3y ago
You do the same in jumping stilts. You move arms and body in the air to increase jump amplitude, and land on a straight leg to compress the stilt and let it bounce back. If you try working with hips/knees while touching the ground, you'll amortize all the energy you generated, and exhaust quickly. Beginners suffer from this, and it takes some learning to run properly. Also, the energy converts from motion into spring load and back into motion, and you can keep adding it. Pro stilt jumpers can jump several times with more and more energy and increase height. When I took such classes of spring stilts, the coach showed us jumping above 2.5 m. Me and a classmate held a ribbon in our hands above our heads (we stood in stilts too), and he jumped several times towards us, each time higher, and finally flew above the ribbon. This is actually much more work than olympic jumping, where the COG of the jumper is actually a bit lower than the bar. This guy had to jump with COG much higher than the ribbon. But as I mention in the other post, if you fall down even routinely while running on stilts, it's very painful -- falling forward with your arms extended ahead, you still hit the ground with the ribs. Then they ache a month.
culebron21 3y ago
Actually, you're right, now I recall it better, you swing arms in the bottom point, to compress the spring better. Waving arms in the air does not help.
- tech_ken 3y ago
  Regardless of when you swing your arms, by doing so you're introducing additional energy into the system so is kind of beside the point. The relevant comparison (in the context of their paper) is how fast you can convert chemical energy into kinetic through your gait, not how much chemical energy you can load into the springs. Jumping stilts are a 4-step cycle: 1a. LOAD (Foot-ground contact, foot is descending) 2a. UNLOAD (Foot-ground contact, foot is ascending, optionally arms swing to boost upward force) 3a. WAIT (No foot-ground contact, foot is ascending) 4a. WAIT (No foot-ground contact, foot is descending) Their proposal is 3-step: 1b. LOAD (No foot-ground contact, foot is descending) 2b. UNLOAD (Foot-ground contact, foot is ascending, optionally arms swing to boost upward force) 3b. WAIT(No foot-ground contact, foot is ascending) Step 1b performs the same function as both Steps 1a and 4a, but is closer to Step 4a alone in terms of duration. By reducing the overall time one cycle of gait takes you're able to convert the same amount of energy from chemical to kinetic in a shorter amount of time (ie. achieve a more powerful gait cycle). This presumes that you can achieve equivalent levels of energy input with both methods, but this doesn't seem like a huge reach to me since both methods rely on springs so presumably you could fiddle with the spring constants until the overall energetics are the same. It's kind of like how an 18-wheeler can produce tons of torque (which it needs to move something heavy), but has less horsepower than a Porsche. Torque is what determines how much weight you can haul (or in the case of jumping stilts, how high you can go), but horsepower is what determines how much time it takes to go from 0-60MPH. Swinging your arms is like adding more torque, but the paper is about maximizing horsepower.
  - culebron21 3y ago
    Ok, makes sense. But I wonder: if it's so hard to run in jumping stilts (which I know personally), does it make sense to make another device that can consume your muscle energy?
    - tech_ken 3y ago
      Can't speak to that one! Just interested in the math

culebron21 3y ago

You do the same in jumping stilts. You move arms and body in the air to increase jump amplitude, and land on a straight leg to compress the stilt and let it bounce back. If you try working with hips/knees while touching the ground, you'll amortize all the energy you generated, and exhaust quickly. Beginners suffer from this, and it takes some learning to run properly. Also, the energy converts from motion into spring load and back into motion, and you can keep adding it. Pro stilt jumpers can jump several times with more and more energy and increase height. When I took such classes of spring stilts, the coach showed us jumping above 2.5 m. Me and a classmate held a ribbon in our hands above our heads (we stood in stilts too), and he jumped several times towards us, each time higher, and finally flew above the ribbon. This is actually much more work than olympic jumping, where the COG of the jumper is actually a bit lower than the bar. This guy had to jump with COG much higher than the ribbon. But as I mention in the other post, if you fall down even routinely while running on stilts, it's very painful -- falling forward with your arms extended ahead, you still hit the ground with the ribs. Then they ache a month.

culebron21 3y ago

Actually, you're right, now I recall it better, you swing arms in the bottom point, to compress the spring better. Waving arms in the air does not help.

tech_ken 3y ago
Regardless of when you swing your arms, by doing so you're introducing additional energy into the system so is kind of beside the point. The relevant comparison (in the context of their paper) is how fast you can convert chemical energy into kinetic through your gait, not how much chemical energy you can load into the springs. Jumping stilts are a 4-step cycle: 1a. LOAD (Foot-ground contact, foot is descending) 2a. UNLOAD (Foot-ground contact, foot is ascending, optionally arms swing to boost upward force) 3a. WAIT (No foot-ground contact, foot is ascending) 4a. WAIT (No foot-ground contact, foot is descending) Their proposal is 3-step: 1b. LOAD (No foot-ground contact, foot is descending) 2b. UNLOAD (Foot-ground contact, foot is ascending, optionally arms swing to boost upward force) 3b. WAIT(No foot-ground contact, foot is ascending) Step 1b performs the same function as both Steps 1a and 4a, but is closer to Step 4a alone in terms of duration. By reducing the overall time one cycle of gait takes you're able to convert the same amount of energy from chemical to kinetic in a shorter amount of time (ie. achieve a more powerful gait cycle). This presumes that you can achieve equivalent levels of energy input with both methods, but this doesn't seem like a huge reach to me since both methods rely on springs so presumably you could fiddle with the spring constants until the overall energetics are the same. It's kind of like how an 18-wheeler can produce tons of torque (which it needs to move something heavy), but has less horsepower than a Porsche. Torque is what determines how much weight you can haul (or in the case of jumping stilts, how high you can go), but horsepower is what determines how much time it takes to go from 0-60MPH. Swinging your arms is like adding more torque, but the paper is about maximizing horsepower.
- culebron21 3y ago
  Ok, makes sense. But I wonder: if it's so hard to run in jumping stilts (which I know personally), does it make sense to make another device that can consume your muscle energy?
  - tech_ken 3y ago
    Can't speak to that one! Just interested in the math