elliptical engineering

At higher resistance, the display shows higher Watt burn. How does the mechanism modulate the cam shape?

Generator and a resistive load, PWM'd for adjustment.

Pretty simple.

There have been some that have been grid tied and the power sent back to the utility.

boB

It would seem to me that the bicycle has the distance the feet move multiplied by the ratio of the driving sprocket to the diameter of the rear wheel. Similar to the way you trade power for distance in a set of gears where one is larger than the other.

when running every time you land and have to lift you body again up again some energy is lost because of the weight of you legs there is a limit to how fast you can swing them back and forth

on a bike all the energy goes into moving you forward and you can pick a gear that keeps the optimum speed of your legs for the speed you are going, as long as you can produce enough power to do so

With a bike, all* of the leg motion is converted to forward motion. With running there is up and down motion as well as forward motion.

That's the essence of it. No need to get into force vectors, mechanical losses, physiology, efficiency etc.

Ed

Maybe for a person with an otherwise sedentary lifestyle. 15min daily does not buy you any endurance. So when you are tasked to run in hilly terrain for a few hours to dodge a thunderstorm or for some emergency you'd be in trouble without having done much more substantial exercises. Same if you had to chop a cord of firewood within a reasonable time.

The Army story reminds me of my Army time. In the German forces, we were stationed next to a unit of the British Army during boot camp. One day we did a march with light gear, huffing, puffing and complaining. Suddenly we heard "clomp, clomp, clomp" behind us. British soldiers ran (!) past us, throwing us a "Good day, chaps!". They ran in full gear. In the evening I asked one of them when they were back. "Oh, shortly after lunch, this wasn't a big one". We had been back a bit later and they had run the same route.

Not the rising leg.

A good runner doesn't bounce, the center of mass remains mostly level, that's a small loss.

Not close to explaining the colossal difference in efficiency between running and biking.

This is a relatively minor effect.

Same for bicycling. Anyway, swinging the legs faster, while running, would merely burn more power, it wouldn't increase efficiency.

Again, that doesn't explain the efficiency/speed difference.

Look, in either case, the idea is to convert glucose into forward motion, against losses. Does your metabolism change, because you sit on a seat? Talk of gears and such misses the point entirely.

You might try the popular wheel diameter explanation - but I wouldn't advise it -

No, the gear ratio trades torque for distance, which is the definition of mechanical advantage. It doesn't bear on the question of energy usage.

For an engineer to trip over that, oh boy -

You have inserted quotes that were not in the post to which I replied. I'll identify the insertions with a line of equal signs. ============================================

============================================

You don't see the * where I wrote "all*"?

The runner is supporting his mass, against gravity,

100% of the time he is running. He is constantly accelerating downward by gravity, and counteracting that acceleration by accelerating upward with muscle usage. That is NOT a small loss, whether or not there is large perceptible bounce.

The biker's mass is supported, against gravity, by the bike. Yes - since you mentioned it - he does use some muscle power to raise the mass of his legs but that is small in comparison to supporting his entire mass.

The OP seems to disdain efficiency in an explanation. Quoting him again: >>> or distance? Nobody yet has answered correctly - they >>> only spew word salads containing 'efficiency' in multiple forms -

Wind resistance can certainly reduce efficiency in a moving bike, no question. To avoid those losses - and make efficiency such a small factor that it can be ignored, consider bike vs running speed at the gym - a treadmill vs a stationary bike. You can go MUCH faster on the bike than on the treadmill, and wind resistance is not a factor.

Aside from that, with a mass moving through air, wind resistance goes as the _square_ of the velocity. So a bike going twice the speed of a runner would have 4 times the wind resistance, all other conditions being equal. I can't compare drag coefficient and area between a rider hunched over on a bike and the same person running - perhaps you can. Those affect wind resistance and mean that all other conditions are not necessarily equal.

Ed

PS - to the OP. I apologize for getting into all that, but RichD raised good points, and deserves a reply with more detail. Ed

If you use toe clips, the rising leg does pull up on its pedal. That's only a small contribution, though; commuter cyclists rarely bother.

I'd claim that the inelastic foot-striking-ground was a major energy loss for the usual gaits, and the cushioning in running shoes does get quite a workout. Kangaroo locomotion uses special tissues for spring-like efficiency.

There is a kind of brake, used to test motors, that is basically a turbine rotating near another static turbine, both in a case filled with water. The water can get hot and even boil, so it is renovated constantly (when testing a motor).

Another kind, for slow motion, uses some magnetic dust with a rotor inside. There is an electromagnet around it. When powered, the dust solidifies in more or less degree, controlled with the current on the magnets.

Not the kind for this usage, though, cooling would be difficult.

Magnetic and eddy currents is easy to do and regulate, water can be flowed to cool it down. But the magnets are electromagnets for easy regulation. Can be electronically controlled to emulate different type of loading. Coupled to a motor, they can adjust for constant speed, constant torque... whatever. Emulate going up a slope for a car, overtaking, etc.

On March 2, ehsjr wrote: ========================================

Which applies to both runner and bicyclist.

A human supports his mass all day long, and hardly feels it. That isn't a factor here, in this question of athletic performance.

The legs pump up and down, as the calf muscles cushion the landings, that's a loss Still, in the larger picture, it's a minor factor.

The real energy expenditure, and loss, is in FORWARD motion, not bouncing. Think about it: at higher speeds, the runner fatigues, more than the biker, duh. Is there any difference in the bounce?

Wind resistance doesn't "reduce efficiency", it's the primary drag, to be overcome. Efficiency measures how well that's accomplished.

You're confused. Efficiency isn't a factor to be ignored, it's central!

The point is, if a runner traveled at 25 mph, like a bike, he'd face the same wind resistance. But he CAN'T run that fast, he can't overcome those losses like the biker! Which is the whole point of the question: why not?

By definition, the bike is more efficient. The runner is less efficient, he suffers greater losses, in converting ATP into forward motion. What/where are the losses? No one in my experience has yet answered correctly. Of course it's simple - after you see it -

I used to get only about 300 -400 miles out of my running shoes, and that includes the extra 50 (??) miles I got by using hot glue to restore the "nubs" on the soles after each run, once I was somewhere over about 200 total. I was doing about 30 - 40 miles per week, so it got expensive. Ed

Kangaroo locomotion uses special tissues for

Once again, you misquote. I guess you're only here to argue.

If you wish to ignore losses, good luck in understanding efficiency.

So, using the example I posted - the gym comparison - please show where efficiency _with regard to wind resistance_ is central. I get the impression once again - I hope I'm wrong - that you only want to argue.

Ed

You're quite confused. Last chance, Ed. Here's a big hint: race a runner vs. roller skater, side by side. It isn't close. What explains the skater's advantage? Or, the runner disadvantage?

Same answer for the bicyclist.

If you continue to flop around, without content, I have to conclude you're just here to argue -

Are you dense? The skater is never airborne. The runner is. I have to spoon feed you? Very well. Each time the runner's foot lands - due to up and down motion - that kinetic energy goes to zero. It has to be replaced to keep the runner from falling flat on his face, as the forward kinetic energy (while reduced) is not totally lost.

The skater or cyclist or walker does not have the loss of the same amount of kinetic energy, because he/she is never airborne. His/her mass is supported by direct contact with the ground 100% of the time. Most of the energy expended goes to creating lateral motion. A runner spends energy with every stride getting the body airborne - energy not expended by the skater/walker/cyclist.

Compare sitting and standing. All other things being equal, it is a whole bunch easier to sit than to stand. Why? Because in standing your legs must support 100% of your mass, which takes muscle and energy. In sitting, your legs support a portion of you mass, but the greater portion is supported by your butt. Think about it. A cyclist is sitting. A runner isn't. You don't see a difference?? When you understand the difference you can visualize the force vectors involved and see where energy must be spend. You can understand the obvious losses that are inescapable. If you had accurate measurements you could quantify how much of 1/2mv^2 energy was lost in each direction, how that reduced the speed, how much energy had to be replaced and so forth.

But first, you have to recognize the difference in motion between cycling and running, which you don't. In fact, you first seemed to indicated that wind resistance was the reason the cyclist went faster than the runner. It had to be pointed out to you that the cyclist faced greater wind resistance than the runner.

Now, I'm glad you mentioned "Last chance, Ed."

Thanks. Ed

if it was minor running on a thread mill would be easy ...

it explains the speed difference, if you have the power to go faster but can't move your legs any faster you need a gear