Where to start on a pedal powered boat?

Discussion in 'Boat Design' started by ryan808, Aug 4, 2008.

  1. alan white
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    alan white Senior Member

    Regarding angle drives for drills: I don't know the cost, but Milwaukee makes a heavy duty one with, I think, ball bearings.
    I assume the chuck itself is threaded onto the output shaft (and the drive must in turn thread onto the input shaft).
    Milwaukees are heavy duty drills, probably up to 8 amps at 120 volt, or about 1 kw. They run 500 rpm, so the drives will handle a lot of torque (like instant braking loads).
    Cost I don't know. More than the plastic toy from Sears.
    Maybe less than the off-the-shelf ones mentioned.

    Alan
     
  2. Guest625101138

    Guest625101138 Previous Member

    Alan
    You need to examine these things quite closely to see if they will last.

    Typically they are straight cut bevel gears and not as efficient for size as the spiral bevel you get in precision boxes.

    The input shaft needs to be able to take quite high radial loads. Think about a 200lb man pushing with full effort on a crank with a 2:1 mechanical advantage over the chain. Translates to huge radial force on the input shaft. With the plastic ones you just distort the box so the gears come out of mesh. You need to look at the bearing centre spacing on the input shaft because you will not get the radial load data on the drill drive. They are intended for on-line torque, not radial load.

    So a heavy duty drill drive might work but why take the risk. You can get a precision right angle drive with stainless steel shafts that weighs very little and has numerous mounting arrangements designed in. The most important aspect is you get full design rating data so you know what loads it can accept.

    If you are just playing around then use the drill drive. If you want something that will last then take the plunge and get a precision unit. I regard the Mitrpak stuff as extremely good value. You can go down to the 3/8" shaft if it is geared properly with an oversize chainring and not intended for regular sprints. The 1/2" box is the preferred for long-term durability for most riders.

    Rick W
     
  3. clmanges
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    clmanges Senior Member

    Here's a thought -- maybe you could pick up a junk riding mower that would have a right-angle drive for the rear wheels and try that, just to play with. It would certainly be strong enough. Might be free for the asking.
     
  4. alexlebrit
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    alexlebrit Senior Member

    Rick, and any others who may have designed a push-push drive (as mentioned above) as opposed to a rotating drive. What kind of loads do you think the cables running to the rolling bearings are talking? Do you think for instance we could use bicycle style brake cables to get the drive from the cranks to the drive unit?

    Obviously they'd be some losses due to cable outer compression, but I'm thinking this would be a great way to route the cables easily without having to design in loads of hard points and pulleys.
     
  5. Guest625101138

    Guest625101138 Previous Member

    Alex
    It is not a matter of "thinking" about the loads. They can be easily calculated. The wire loads is why I chose to run a 1:1.5 mechanical advantage between my feet and and the wire. I use very flexible 1/16" stainless wire. The wire strain typically peaks at 100N for a steady cruise pace. Each wire travels in and out 0.6m in a complete stroke every second so wire speed is 1.2m/s. With wire load of 100N the power is 120W. This produced 10kph in V12:
    http://www.youtube.com/watch?v=PYoW3XjHRbw

    If you route the wire in a tube where it is rubbing on the wall then the friction on the wire will rob a large portion of the power and accelerate the wear on the wire. Better to lead it through rollers with low friction bearings. It can run inside tubes but give them clearance to avoid dragging.

    Rick W
     
  6. clmanges
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    clmanges Senior Member

    That should be easy to calculate with a little trig.
    Sheathed cables waste a lot of energy, I'm sure; there's friction along the entire length of them, and the tighter the bend radius, the worse it gets. They also waste energy by flexing. To see this happen, find a bicycle and watch the brake cable move while you squeeze the brake lever -- some of the lever excursion is being used up as the cable tries to straighten its jacket. You'll see also on bicycles that the sheathed cables are only used where it's necessary to carry a curve, and straight runs are unsheathed. I think they'd wear out quickly under constant use, as well.
     
  7. Village_Idiot
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    Village_Idiot Senior Member

    I guess I was thinking more in terms of eliminating problems with maintenance of other drive systems. Chains bring issues with lubrication, corrosion, stretching and maintenance, as well as sprocket wear. Continuous belts have the issues of slippage and maintaining tension. The one-way clutch or ratchet can be designed with low-maintenance materials, yet remain lightweight and strong. Granted, ropes would have stretch (depending on the rope), but this may not be a bad thing with this type of slingshot drive and probably easier on the joints as well. Anyway, I'm just rambling - I have no ambition to build such a thing...
     
  8. clmanges
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    clmanges Senior Member

    Okay, I'm with you now, and that's also a way of simplifying design when you look at the big picture.

    Personally, I'd need some particular reason to choose rope over cable, and I can't think of one just now.

    Your phrase "slingshot drive" got me thinking . . . at first I couldn't figure out what you meant, but it got my brain turning over. I think that a pull-cable transmission must need a return spring or tension spring somewhere in it . . . maybe that could be set up so as to provide some extra energy for the system . . . and I see another round of the complexity fight coming up. Oh well; like you say, just rambling.
    Curtis
     
  9. Village_Idiot
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    Village_Idiot Senior Member

    ...think 'flywheel'...
     
  10. clmanges
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    clmanges Senior Member

    Hmm, you say 'flywheel,' I think 'weight.' Flywheels, as a potential energy storage device, are like fuel tanks or batteries -- heavy. I'd stick with kinetic energy as much as possible. Yeah, a spring stores potential energy too, but not very much, so it's lighter.

    What I was thinking was, you push the pedal, and while it's transmitting force to the drive, it's also stretching a spring. When you take the pressure off, the spring pushes the pedal back, but also pulls a different cable, which then also transmits force to the drive. Maybe with some clever thought, you could use the same cable for both the pedal and spring.

    That might have to be a pretty stiff spring, though . . . leg cramps, anyone?

    Also, since the spring needs time to push the drive, the pedal return will be slowed down. Call it 'relaxed cadence.' ;-)
     
    Last edited: Aug 15, 2008
  11. johnnyld_3
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    johnnyld_3 New Member

    I'm new to HPB and am learning quite a bit from these posts, but, if I may....

    The system you are proposing with springs and pullies sounds like a can of worms you might want to keep closed. It could get very complicated. It might look like it could work if you draw it out, but I beleive it's functionality would be impractical since any energy stored by the spring on one pedal, would be counteracted by the spring on the other pedal, if you are using 2 springs. (I am not understanding your concept if you only have one spring) Also, the energy stored by a spring is, as you mentioned, just more energy exerted by you. (one of those laws of physics...energy can not be created or destroyed). If you want to store your kinetic energy, the flywheel is your best option as far as "return" on your energy output, practicality and simplicity. Instead of using a weight, use something with a large diameter that doesn't weigh as much, but has most of it's weight around the outside edge.... like a bicycle tire. The larger the tire diameter, the lighter it can be while allowing it to store the same ammount of energy. But then you run into problems with where to put it.
    Also, that is extra energy you are putting out and not all of it will be transferred back into kinetic energy. I'm not sure you would benefit at all with any energy-storage device.
    I would try to keep it as simple as possible....less chance of something failing.
     
  12. Guest625101138

    Guest625101138 Previous Member

    This is possibly the best engineered system of what is being discussed here (4Mb clip):
    http://forwardface.com/includes/movies/Radius_360steering_01.AVI

    You can see the operating details here:
    http://forwardface.com/includes/zrower/lu_00.htm
    http://forwardface.com/includes/zrower/st_00.htm

    Basically this is modelled on a rowing ergometer at the local gym. You do not need a flywheel because the boat carries a lot of momentum. Think about a return stroke on a rowing scull. The prop just keeps spinning freely during the return.

    Rick W.
     
  13. johnnyld_3
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    johnnyld_3 New Member

    Thanks Rick. I undertand the sytem now and I agree that a flywheel is not a good idea nor is it needed.
    I am refering to Curtis's question about using mechanical devices such as springs and flywheels to
    Oh...I just re-read what I typed...I said using springs and pullies...not springs and flywheels. I am sorry for the confusion.
    - Johnny
     
  14. clmanges
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    clmanges Senior Member

    johnnyld_3, I'm just musing with these ideas. Look at my post #29 and you'll see that I agree with you about simplicity. You've already seen how easily things get complicated.

    As to flywheels, I can't see any sense in using them in a muscle-powered boat; it just seems silly to try and store up some of your work when you're moving yourself across flat water. Same with springs. What I was getting at was, that if you had to have a spring for some other part of the mechanism, then you might as well investigate the possibility of getting some extra propulsion out of it.

    I'm just brainstorming.

    Curtis
     

  15. Petros
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    Petros Senior Member

    I think the KISS principle is important. I would not expect a Rube Goldberg device like that (flywheels and spring energy storage devices) to ever operate reliably, Murphy's law is just a valid on a boat as on anything else.

    The cable idea got to me think about another drive system that would likely have less drag than the angle drive and can be made from common bike parts. Get two ratchet drive hubs that go on multi-speed bicycles rear axles (salvage these from junk bikes and you would not have to spend anything on them). They get mounted on a propeller shaft in tandem so they ratchet in the same direction. Then you can set-up some simple lever pedals with a cable running back from of each one, that are run over pulleys and each end will have a length of bike chain attached and wrapped around the sprocket ratchets. On the other end of the bike chain after it is wrapped 180 deg around each sprocket you attach another short piece of cable to connect the ends of the two chains together. This short length of cable is run over another pulley. This way the pedal would return to the start position after each stroke from the action of the other pedel and you would not need a return spring. You can even use the bicycle's sprocket cluster to change "gear" ratios.

    I hope I am being clear: Tracing the cable path, first a cable runs back horizontally from one pedal, runs over a pulley and goes downward, changes to a bike chain and then to the first ratchet sprocket hub on the shaft, warps around it, changes back to cable and comes up over another pulley, changes back to a chain and wraps around the second sprocket, goes up vertically and changes back to cable and runs over the last pulley and goes forward to the other lever pedal.

    When you pump the lever pedals back and fourth each of the lengths of chains in turn drives the shaft while the other length is ratcheting backward on the hub.

    The most difficult detail perhaps would to come up with a simple way to mount the two drive hubs to the same propeller shaft. I am sure something could be worked out.

    I might try building one sometime.

    Good luck
     
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