I have been working on human powered watercraft

Discussion in 'Projects & Proposals' started by DHaggsway, Aug 8, 2019.

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  1. DCockey
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    DCockey Senior Member

    Interesting claims but so far nothing to indicate how they might be achieved. Until DHaggsway presents his ideas about how to achieve thise claims I expect further discussion to have very little value.
     
  2. W9GFO
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    W9GFO Senior Member

    I expect the output would change with temperature, a lower temperature would increase the density of the air and therefore the oxygen content of each breath and it would carry away waste heat faster. Changing the step height would also have an effect (gearing). I think that standard step height is probably optimum for the average person but I am sure some people would do slightly better with shorter or taller steps. As far as footwear, you would wear whatever enables you to perform your best. Wearing something heavy might slow you down, but then the extra weight you are lifting is accounted for in the calculation.

    That would tell you how much energy the body is processing but not what the output is.

    Theoretically that is possible, but not practical. Humans put off at best - heat that is 100F, in order to extract energy from heat there must be a temperature difference. Even if you were pedaling in 0F weather, that is only a 100F difference in temperature - which is an abysmally low temperature difference for heat engines - maybe you would get a couple watts, probably less. Even under the very best circumstances a heat engine can only be up to 64% efficient. Thermoelectric generators are far less efficient, topping out at about 10%.
     
  3. W9GFO
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    W9GFO Senior Member

    Since a propeller is at peak efficiency at one single rpm, then any variation in that rpm will necessarily mean a loss of efficiency. Detrimental, yes. Very detrimental, no. For example, a sufficiently sized flywheel will all but eliminate any variations, but the addition of a few kilos to the lightweight vessel may introduce more drag to the hull (increased displacement) than the smoothing effect is worth - it is something I would like to experiment with, I only hope that the difference will be measurable.
     
  4. W9GFO
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    W9GFO Senior Member

    The Wright Brothers are credited with the first powered flight, but many others had flown in gliders before them. I am quite a fan of non powered flight, so I felt compelled to make this clarification.
     
  5. Deering
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    Deering Senior Member

    “I expect the output would change with temperature, a lower temperature would increase the density of the air and therefore the oxygen content of each breath and it would carry away waste heat faster. Changing the step height would also have an effect (gearing). I think that standard step height is probably optimum for the average person but I am sure some people would do slightly better with shorter or taller steps.”

    Agreed. Point being that even simple environmental and ergonomic factors will affect work output.

    “Wearing something heavy might slow you down, but then the extra weight you are lifting is accounted for in the calculation.”

    Not really. Wearing 10 lbs ankle weights would have a far greater effect than carrying 20 lbs in a backpack.

    “That would tell you how much energy the body is processing but not what the output is.”

    Aside from some internal cellular/metabolic functions like digestion and cell growth, it does tell you the output. Energy isn’t being destroyed, and unless you’re eating it’s not being stored, so it’s either putting coming out as mechanical energy or heat. You’d need some sort of metering system (ergometer) to determine what percentage is mechanical. Even your stairs example might provide that.

    “Theoretically that is possible, but not practical. Humans put off at best - heat that is 100F, in order to extract energy from heat there must be a temperature difference. Even if you were pedaling in 0F weather, that is only a 100F difference in temperature - which is an abysmally low temperature difference for heat engines - maybe you would get a couple watts, probably less. Even under the very best circumstances a heat engine can only be up to 64% efficient. Thermoelectric generators are far less efficient, topping out at about 10%.”

    Agreed. The laws of thermodynamics don’t offer much given current technologies. But technologies change. An athlete can produce something like 400 watts of mechanical energy for an extended period of time, more for shorter durations. If the body is operating at 25% efficiency, that means that there’s 1,200 watts of thermal energy to play with. Converting even a few percent of that into mechanical energy is a significant increase in net output.
     
  6. W9GFO
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    W9GFO Senior Member

    I can see why it would be that way, you would be accelerating an extra 10 lbs with every step not just lifting it. Since about 50% of the time your foot is stationary, when it does move it needs to travel about twice as fast as your body or it would be left behind. It would make sense to use light footwear. That explains why amputees using lightweight prosthetics can be so quick.

    Before this is cited as a reason that bicycle cranks are flawed let me point out that there is no stopping and accelerating when pedaling; similar to how a point on a tire tread does not lose momentum when it meets the pavement, then accelerate to twice the vehicle speed when that point is opposite the road. It maintains a constant angular momentum. A shoe however comes to a complete stop on a stair step, it loses all momentum. It must be accelerated with each step. The acceleration does not take place over the entire height of the step, momentum will carry it part of the way but the momentum (of the shoe, not the person) goes to zero when it lands on the step.
     
  7. W9GFO
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    W9GFO Senior Member

    I'm not sure what you mean. Force on the pedals will vary throughout the revolution. Depending on what the ratio is from pedal to prop the variation in propeller speed could be anywhere from extreme to slight. Stiffness in the driveline and rotating mass will also have an effect.
     
  8. Deering
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    Deering Senior Member

    That explanation makes total sense. I’d add that the muscle groups involved in lifting the leg aren’t as large or powerful as the ones that propel you up the stairs, so adding weight there is more likely to fatigue those muscle groups sooner than the other groups. A chain is only as strong as its weakest link...

    I mostly agree about the bicycle crank. During steep assents while pedaling out of the saddle, there’s a distinct pulse in the velocity of both the crank and wheels during the downstrokes. But for normal riding the angular momentum is quite steady. Skilled riders will work to smooth out that momentum by engaging all leg muscle groups to propel the crank through the entire rotation, lifting up on the return as well as pushing down on the stroke. Being cleated to the pedals allows that. The leg isn’t being used solely as a piston as DHaggsway is suggesting.
     
  9. W9GFO
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    W9GFO Senior Member

    The variations should be less with a high ratio. A high ratio does not mean it requires great force. The propeller is sized to absorb the power being fed into it. You determine how much power it needs to absorb based upon your knowledge of what the power plant (the human) can produce. The pitch and diameter of the prop are then chosen to match that power and the rpm at which it needs to turn. The higher the ratio, the faster the prop will turn and the smaller it will be - the power to drive it does not change.

    What you are describing - high forces on the pedals along with high ratio, would simply require a much greater power input than what the system would be designed for, the ratio is too high (lugging). In that case the (too) high ratio would be detrimental and it would increase the variation in rpm.

    If the system were massless, then the high ratio would not be a benefit to smoothing since all the energy instantaneously goes to the propeller and none to angular momentum. In that case it would not matter what the ratio was with respect to smoothing. Of course it is not massless so you get the benefit of stored energy in angular momentum which is recovered between the power pulses. Increasing the rpm increases the amount of energy a given rotating mass can store - which is why a higher rpm helps to smooth out the power pulses.
     
  10. Deering
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    Deering Senior Member

    Skilled bicycle racers endeavor to power to some extent through the entire crank rotation. Whether that’s to maintain constant angular momentum or to simply involve as many muscle groups as possible I don’t know. Likely some of both. There may be other reasons too.

    Whether that’s relevant to powering a propeller rather than a bicycle is an open question. Perhaps riders involved in other record attempts could shed light on that. I’m assuming that they were also advanced cyclists (that’s who I would choose to power my boat). Given that you have revealed nothing about your claimed revolutionary propulsion system it’s impossible to say.
     
  11. gonzo
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    gonzo Senior Member

    If it is truly a more efficient pedaling system, bicycle racing is where the market is. Breaking a boat speed record is a waste of time since the market for the boats is practically nil. As far as the claims of the mechanics of pedaling, like the force is tangent to the projected circle of the pedal, it is not true. Powercranks are used to even the force of both legs (PowerCranks - for cycling, running, and rehab success https://www.powercranks.com/). Also, when sprinting, athletes both pull and push on the pedals.
     
  12. Yellowjacket
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    Yellowjacket Senior Member

    Exactly. When you pull upwards on the aft pedal, that additional force is added to the forward pedal, increasing the crank torque as a factor of 2x the amount of pull added to the aft pedal. As I said earlier you have to multiply the force you apply by the speed that you apply that force to get power, and note that at that speed you are accelerating the legs of the person doing the pumping. If you totally stop and start that process then a substantial amount of work is expended in accelerating the mass of leg and foot AND the cranking system. If that mass is rotating then it's already up to speed and the effort expended is put into useful work as opposed to accelerating that mass and doing no useful work with that effort. In order to make power the speed of the force input is of equal importance as the force applied. If you're just standing on the pedal, you're putting in high force, but if the speed is slow, then you aren't generating any power and doing any work. The OP seems to think that efficiently putting in force will suddenly make more power and that is a fallacy unless the person putting in the force can do so at the same or greater pumping speed and not incur losses in accelerating the body parts and the crank system weight.
     
  13. Ad Hoc
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    Ad Hoc Naval Architect

    It has been that position since the opening post.
    Endless claims and no evidence. Yet retorts in a very emotive and bizarre deflective manner very unbecoming of an scientist engineer with a claim of 'something' new - but just notes he is not going to show/tell anyone - ggeessss.
    It is in essence a 'faith' based approach to an engineering issue rather than a factual/evidence based one.
    The debate is endlessly circular - like religion. As you note - it has zero value other than amusement to others reading the thread.
     
    Last edited: Aug 18, 2019
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  14. Yellowjacket
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    Yellowjacket Senior Member

    Correct. The lack of engineering is getting painfully obvious. When I was in engineering school we got a lot of press on a project we did and a lot of "inventors" with no real engineering background came out of the woodwork to have us look and evaluate these "great improvements" in technology. Many were machines that violated the first or second law of thermodynamics. After the pitch you'd ask a key question.. and then they'd get a startled look and pack up their machine and be gone... The only ones that were decent were brought in by engineers with a real technical background. Not to poo poo anyone's idea without seeing it, but this entire thread has been a trolling expedition. The OP needs to put his system onto a bike and try it and see if he can go faster using his rig as opposed to a conventional bike. In short, quit the theory and go out and prove it works. IF it does then he can go apply for a patent. If not then let it die. If I were the OP I'd do a patent search first. My bet is that something very similar has been tried and patented already. There are tons of alternative to pedal and crank systems already patented and if there wasn't one that covered what the OP was doing I'd be surprised.
     

  15. upchurchmr
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    upchurchmr Senior Member

    +1 to the above 2 comments.
    Maybe +10
     
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