I have been working on human powered watercraft

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

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  1. upchurchmr
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    upchurchmr Senior Member

    Elliptical gears were the rage 10 years ago.
    For all the theory, they didn't seem to get used.
    Does anyone know if they are used in the Tour d'France?

    That would prove to me that they actually provide benefit.

    Of course if it was a significant benefit, then all the amature competitive riders would be using them.

    How about the Gossomer Condor? Did they use them?
     
  2. Deering
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    Deering Senior Member

    I don’t think that accomplishes what you’re aiming for. Any leverage/velocity advantage gained by the oval gear attached to the crank is immediately counteracted (lost) at the other gear. In the past some bicycle chain rings (the sprocket connected to the cranks) utilized an oval shape for that purpose, but the rear sprocket was round, not oval. The differing distance between the two could be addressed by the pivoting chain tensioner in the derailleur. I don’t know if that arrangement is used any longer, but racers at the time rejected it because it resulted in an uneven pedaling cadence.
     
  3. Deering
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    Deering Senior Member

    Ah, now I see what you’re getting at. I don’t think the oval gear business at the flywheel buys you much, if anything. Attach the prop shaft to the flywheel shaft, and the flywheel gear (round) to the crankshaft gear (round or oval) and angular momentum will take care of the rest.
     
  4. Yellowjacket
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    Yellowjacket Senior Member

    The OP missing the point. He's thinking in terms of torque efficiency and not power. All of this talk about efficiency is just trying to justify a position based on theory. In order to break a speed record you need power. Power is force time the distance per unit TIME. In order to set a record you're going to need peek speed for just over 2 minutes to cover a measured mile. The acceleration time is relatively short. Efficiency is nice, but power at the output shaft is what you need and peak efficiency is less important. You need a drive system that produces the greatest power and that is not necessarily the one that best converts pedal force to output shaft force because things are different at higher crank speeds. Remember that power created is torque multiplied by shaft speed. The OP is thinking about force and how efficiently it gets to the drive shaft to produce power, but he's ignoring the effect of the speed at which that force is put into the system. That is, since you generate more power by pedaling faster, your force applied times the speed of the crank is what equals the power output. In order to create high power you don't want to stop and then accelerate your legs on each cycle. If you do you're expending energy to accelerate your lower leg and that is work expended for acceleration that isn't recovered with long arm pedaling arrangements. With a conventional crank system that inertia is used to drive through the top and bottom of the stroke and to some extent that evens out the forces. While long crank arrangements are likely more efficient for low speed cruising, you don't see them on racing bikes because they don't provide more power. The guys doing human powered flight knew that power was more important too. If you're trying to fly the amount of power is key. They looked at all kinds of systems including combined arm and pedal cranking systems and in they ended up with a conventional bicycle arrangement where the pilot was standing up pedaling, even though that created more drag than other positions. What they realized was that power output was key and that is what the present conversation is missing. What the OP needs to do is get his rig on a dyno and compare it with the power output generated by a conventional crank system. I'm pretty sure he'll soon learn that if there was a better way to get more power from a human being than a pedal and crank system it would have been found a long time ago.
     
  5. Ad Hoc
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    Ad Hoc Naval Architect

    Exactly!

    And that's all you need to know :)
     
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  6. kerosene
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    kerosene Senior Member

    Forget force for a second.
    95% of energy from muscles becomes energy at wheels.

    And in given unit of time that is power becomes power.

    Power is what matters.
     
  7. Deering
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    Deering Senior Member

    Not quite. 95% of the energy imparted to the pedals does get imparted to the road. But the human muscle part is nowhere near 95% efficient, as evidenced by all of the heat we produce. There are fairly narrow constraints to harnessing that muscle energy optimally, hence gear ratios and crank shaft lengths and body position and all of that other happy kinesiology stuff.

    My point being that the mechanics associated with the human body interface has an enormous impact on the available power ‘input’ at the pedals. The discussions related to leverage and force, etc. are relevant.
     
    Last edited: Aug 16, 2019
  8. W9GFO
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    W9GFO Senior Member

    Power (at the wheels) does matter, but the amount of power that makes it to the wheels will depend upon efficiency - and in a human powered vehicle there is so little power to begin with. If it's just for recreation then losing some power due to inefficiency is no big deal, especially if it increases reliability/safety. But if you are record setting then you either need a power plant with a good surplus of power (athlete) or you need to not waste power - preferably both.

    It is worth emphasizing I think that in a bicycle, >95% of the muscle energy put into the driveline via the crank makes it to the wheels. This is not a measurement of force. If you want greater force at the wheel then you put more energy in, you pedal harder. You still get 95% of that greater energy input at the wheel. Another way to get more force at the wheel is to use mechanical advantage; longer cranks, or change the gearing to be lower. Through gearing we can make the force at the wheel be whatever we want, but the power will not increase because as the force goes up, the distance traveled goes down.

    Regardless of what kind of mechanical advantage this secret solution is using, the power output will always be less than the input power. How much less depends upon the efficiency of the system. A good bicycle (using the "flawed" crank) loses less than 5%.
     
    Last edited: Aug 16, 2019
  9. W9GFO
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    W9GFO Senior Member

    This is similar to discussing a propeller's efficiency, taking into account the power input via the engine and the propeller interacting with the water. We do not need to consider the fact that the engine itself is converting only about 25% of the chemical energy in the fuel to rotational energy - the rest being wasted as heat, mostly going out the tailpipe.

    How well muscles convert energy into motion does not enter into this, unless the device uses muscle movement in such a way as to become more efficient. I don't doubt that improving muscle efficiency is possible, but I do doubt that the gains to be made are significant to what we are discussing. For example an athlete will train to improve their technique, a fraction of a percent of improvement is meaningful when competing, but that same improvement gained through a clever bit of hardware would not be very meaningful, unless it was also simpler and more reliable than the crank, and of course did not introduce its own set of efficiency losses.

    If DHaggsway is claiming that his "solution" improves muscle efficiency by a significant amount (a few percent at least) over using a crank then I would not believe that claim without some real evidence to back it up.
     
  10. Deering
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    Deering Senior Member

    Actually it’s all about improving muscle efficiency. Or at least ‘human’ efficiency.

    Consider the bicycle example. There’s not much that can be done between the crankshaft and the wheel to make it any more efficient. But at the human side of it there’s a tremendous amount. I’m not talking about the Olympic athlete who works hard to shave off a fraction of a second.

    Think back to the first bicycles, those tall ones with the giant front wheels. Actually they’re the most efficient bike possible. There are no losses in the crank bearings, chain, gears... Those things were direct drive, one shaft. With modern materials they’d probably be 99% efficient. So why aren’t they being used in the Tour d’France? Because they don’t align well with our muscle needs. As soon as it hit a hill it became too hard to pedal - power output from the human didn’t remain constant, it declined, rapidly.

    Geometry, leverage, force...they all affect power (from the human) in a big way. We’re not ‘ideal motors’.

    Now I’m not trying to defend DHaggsway’s claims of some mysterious, magical improvement that will increase the power to be harnessed from a human. I have no idea what he’s talking about.
     
  11. W9GFO
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    W9GFO Senior Member

    Derogatory, perhaps, but the claim that there was "not a stitch of discussion" is as empty as the claim that you "have improved on the method of propelling a watercraft with human power".
    It is unfortunate that you are offended. Claims require evidence. Extraordinary claims require extraordinary evidence. Without evidence claims can be, and should be, dismissed. You have provided zero evidence. In fact you have provided negative evidence by showing that you don't understand some basic physics concepts. You have provided no reasons whatsoever to support your claim, but you have provided reasons to doubt it.
    First, you don't know that. Many people like to share their ideas so that they can be of benefit to others, and so that others may improve upon their ideas. Second, the people that I know that I consider to be reasonable, sane people, would never publicly announce that they have a new idea of substantial value on a forum then chastise the members for asking for details about the idea. That's just weird.

    I must have missed that part. The bulk of the discussion has been about the efficiency of bicycle cranks, the claim that the crank is 67% efficient is what has been strongly rebutted.
     
  12. W9GFO
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    W9GFO Senior Member

    You are still confusing force, power and mechanical advantage. Without understanding how these are different it is no wonder that you are convinced that you have "solved" something.

    You should take this idea to someone you trust with an engineering background. They should be able to tell you what you have overlooked. Or, maybe they will think it is brilliant and you will get rich off the idea.
     
  13. upchurchmr
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    upchurchmr Senior Member

    Good luck making your fortune.
    You're not going to convince anyone with words.

    Ideas are a dime a dozen, without engineering or appropriate tests, there is nothing to talk about.

    Sorry you can't understand the need for proof.

    A "designer" without engineering is just a sketch artist.
    If that was all it took we would be already to nearer stars.
    I forgot, we didn't even get a sketch.
     
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  14. kerosene
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    kerosene Senior Member

    Its efficient not “efficient”.

    Lungs are the limiting factor not the mechanism. There was a “bike” that combined weird rowing motion. Basically more of a whole body movement. Ine could ride much faster than a traditional bicycle but only for a moment. Bicycle is 95% efficient and there is no magic free lunch around it.
    Creating a system where you could utilize longer range of effective work is unlikely to be novel but more importantly it doesn’t answer to a need. Existing pedal systems can already very efficiently turn any kind of sustained human effort into mechanical power.

    “At 1m85 and 92kg, the now-retired Sir Chris Hoy would blast out 2500 watts as he raced round the velodrome at 80km/h. One of history’s most decorated cyclists, the 11-time UCI World Champion and six-time Olympic Champion had thighs measuring 68.5cm.”

    So the system can put 3 horsepowers through at apparently 95% efficiency. What exactly can you offer that would improve this fine tuned, robust, well known and cheap system?
     

  15. Tiny Turnip
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    Tiny Turnip Senior Member

    Some thoughts.



    Stages of energy transfer:



    1. From chemical energy in blood sugar to kinetic energy in muscle contraction. (derived from digested food, stored fat, glycogen)
    Part of this process is 'whole body' - the lungs, available blood sugar, transport in the cardiovascular system to the cells (1a);

    and part is cell respiration in the muscle fibres, converting the blood sugar and oxygen to kinetic energy in the muscle contraction (1b)

    2) The biomechanical transfer of that muscle contraction to useable (external) movement through the bodies system of muscles, bones, joints, ligaments etc.

    3) The drive, converting the body movement into propulsion, e.g. pedal driven cranks to propeller.

    4) Forward movement of the vessel/vehicle, taking into account the various resistances.


    3 and 4 are, I believe, fairly well understood, certainly on this forum with respect to boats. Rick W did a great deal of work here with respect to pedal powered boats. As I recall, a well designed propeller for human power can, in fact, also achieve high levels of efficiency for that part of the system. There seems to be consensus that a bicycle crank based system can achieve efficiencies in excess of 95% fairly readily.



    The overall rates of power which a human can achieve for stages 1 - end of 2 are also well established, varying from 100w for an hour for an average adult, perhaps 75 w all day, double that for a fit, trained club level athlete, and perhaps 400w an hour for an elite international level athlete, hitting momentary (seconds long) peaks of perhaps up to 2kw in an all out sprint or similar.

    It is unclear to me to what extend these overall figures for human power output are limited by the 1a, or 1b part of the process. If they are limited by the 1b part of the process, it is feasible that a drive system which allowed a person to engage more muscle cells, i.e. use more muscles in the body, might allow that person to increase the maximum power available. If it is 1a, however, then only aerobic, cardio-respitory training will improve the power available.



    The combined stages 1 to end of 2 are rather inefficient; experimental estimates vary from between 15% and 30%, the waste energy going to heat. (I have not found any information on what the relative efficiencies of stages 1a, 1b, 2 are.) There has been some experimentation in capturing the waste heat and converting to electrical energy; however this only achieved efficiencies around 2% for that process. Further work was also done on identifying where the bodies complex biomechanical process is in a 'braking' action, and attempting to apply a 'regenerative braking' technology to these phases of movement, to generate energy.



    It is worth bearing in mind that, considering all four phases of energy transfer, from 1 to 4, it is estimated that cycling is not only much faster than walking, but is up to 5 times more efficient than walking, and perhaps 10 times more efficient than running; despite adding some mechanical complexity to the system, the bicycle allows the available power to be delivered in a more efficient manner.
     
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