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I Force Needed to Push a Manual Treadmill

  1. Sep 9, 2017 #1
    I apologize if this is in the wrong thread, I'm new.
    I need to figure out how hard it would be for Jim to move the treadmill treads along its track of bearings. This isn't for homework, it's just something I want to know.
    Jim weighs 160 lbs.
    The rope isn't holding him up, it's there for him to lean forward against so he moves the treadmill with his legs instead of moving himself.
    The entire treadmill track weighs 100 lbs, not each individual piece.

    The reason I know this is a reasonable question to ask is because the weight on each bearing while it needs to turn is much less than the weight on skateboard bearings which normal people move all the time with one leg while standing on the skateboard. The bearings should only need to spin under 10 lbs of weight (assuming the weight of the entire thing was on one section, which is a vast over exaggeration) when normal skateboard bearings spin under /40 lbs each/.

    A skateboard has four wheels and people on skateboards can push themselves along with one leg while standing on the skateboard. Their body weight divided by the number of wheels (160 divided by 4 = 40 pounds per wheel) and since we know moving a skateboard works in this manner with that kind of weight on each of the bearings. So for the treadmill if we divide 260 (weight of treadmill track plus weight of person) by 24 (the number of bearings supporting just /one/ of the treadmill tracks, assuming the worst that the weight of everything is on just one area) we get 10 pounds of weight per bearing, which is still 30 pounds less than the weight on the bearings of a normal skateboard so this seems to show to me that it can't be /that/ hard to move this kind of treadmill manually.

    The bearings are the same type used in regular skateboards type-608 bearings.
    Let me know if you need more information than is printed in the picture.




    21457311_1515987755137452_2226095201924570548_o.jpg
     
    Last edited: Sep 10, 2017
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  3. Sep 10, 2017 #2

    sophiecentaur

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    Presumably your idea is to make a treadmill that doesn't use a motor(?).
    If the track bearings are good, then won't the runner just fall on his face (hanging from the rope), once he has accelerated the track to his maximum running speed. You need a brake on the track. I am not sure what you are saying about the individual bearings in your model but is it normal to use bearings as brakes at the same time. How would you vary the resistance of the track to suit individual users if each bearing needed to be adjusted? A simple drum brake on the roller at the front would make the system usable.
    You keep referring to the use of a skateboard but the only time that a skateboard requires constant input effort (ideal bearings) is when you are scooting up a hill. Your exercise machine needs a way of dissipating the Power you are using on it.
    The treadmill could be sloped upwards to save having to be tied onto it with your length of rope. That would achieve the required backwards force.
     
  4. Sep 24, 2017 #3

    These kinds of manual treadmills do exist for dogs, they're called slatmills and either dog nor human slip quite /that/ dramatically so I think you're overestimating the lack of friction a bit too much. The reason I need to knwo how hard it would be to push the slats along is because my version is about 100 pounds for the weight of all the slats, considerably more than normal tiny little slatmills.
     
  5. Sep 25, 2017 #4

    sophiecentaur

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    And hamsters have wheels, too. In both those cases, the animals have four legs and would not fall on their faces. :smile: A hamster on a wheel is alarming to watch. The wheel is a similar mass to a hamster and their movement on the wheel is very unstable. They climb up the front and then it comes down and they are carried backwards. There's a pendulum motion and I cannot see a human getting on with that when they want a simulated road.
    We both will agree that we want more than 'running on the spot' can achieve. Easy balance is essential and your legs have to be pumping in a fore and aft direction.
    You will admit that it couldn't be done using ice on the surface of your treadmill. When you walk or run forwards, you need a reaction force to counteract falling over forwards. On the ground, the reaction force is supplied by the ground on your 'pushing' foot as you move it back and, if you are not accelerating, there is a reaction force on your front foot as it lands on the ground, to keep from accelerating forwards . Between the two (and with your walking skills) you balance the two, over the period of your paces. Unless you provide enough fore and aft force with the mill surface, you cannot stay upright. You can provide a reaction force by using a high mass for your road, in excess of your human mass and an expensive and inconvenient machine. Friction could provide the necessary force. A motorised treadmill provides the balance force by its contact between the runner and the floor (using the mass of the Earth).
    As an aside, we all have seen films of astronauts walking on the Moon and it is clear just how hard it was for them to cope with the different walking conditions. Also, we have all experienced problems walking on ice or using skates, skateboards and surfboards. Your prospective customers need to be provided with conditions that are much more familiar than those. Somehow, you need to be provide reaction forces that they can automatically make use of - just like a path.
    You want this to be an unpowered system and it may be much harder than you think. The reaction forces are actually related to their (individual) body mass and leg angle. Quite hard to achieve from a single friction setting even. I guess a servo system would defeat the purpose of your idea which is a fully passive arrangement.
    PS would an Inertia Wheel system be acceptable? Added weight, of course,
     
  6. Sep 25, 2017 #5

    A.T.

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    Yes. And if you want to see how humans perform on such passive free rolling surfaces, watch kids in those inflatable floating balls, or the TV show Takeshis Castle where they run on large free rotating cylinders. It's not easy to stay on two limbs and control the speed of such a surface.
     
  7. Sep 25, 2017 #6

    sophiecentaur

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    ..... and men on stag do's too. I remember them now. (Not that I ever went in one; a stag do was different in my day)

    Perhaps a rotary damper would do the trick - propellor in thick oil with an adjustable bypass. I would say it is pretty critical if it is going to feel right.
     
  8. Sep 25, 2017 #7
    Wouldn't a wide, continuous belt be more practical than treads?

    Looking at the drawing I get an impression the force required to move the track is relatively low in the configuration shown, but rises considerably each time a tread approaches vertical at either side of the mechanism. Another option would be to use narrower treads.
     
  9. Sep 25, 2017 #8

    sophiecentaur

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    I also prefer the idea of a continuous belt but this argument is not right. For every tread that has to be lifted up there is one falling down at the back.
    I wish the OP would discuss the need to provide fore and aft forces for the runner. It's a vital aspect of a successful design.
    I just remembered. Some cycle trainers use a generator and load as a variable brake. That would give you some 'free' power to get the control right with a servo, once the runner has built up a bit of speed.
     
  10. Sep 25, 2017 #9
    Good point about the treads, but my concern is regarding tread width versus end radius, and how the treads are strung together, rather than their mass. Mentally putting the mechanism in motion, it seems to me there would be considerable force at the 9 o'clock and 3 o'clock positions against the bearings semi-circles at either end, and also in the (cables?) connecting the plates to one another. I'm thinking narrower treads would address this.

    Seconded. Running in place on this would be like running on a series of rectangular plates traversing a section of unpowered roller conveyor; the trick would be in not falling down a lot. I like your generator/brake (and rotary damper) ideas. Another approach might be a centrifugal governor controlling force against a mechanical brake, but I imagine it would be too touchy to be successful.
     
  11. Sep 25, 2017 #10

    sophiecentaur

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    Agreed. A sophisticated servo algorithm would be called for unless it was acknowledged that a user would need to 'learn' to use the machine. No problem for people who can learn to skate and have other high co-ordination skills but would enough people be prepared to learn this? I suspect the idea would sell much better is they could just step on and go.
     
  12. Sep 27, 2017 #11
    The reaction force is having to move the 100 lbs that the treads weighs. When I said manual treadmills exist I wasn't talking about animals - manual treadmills for humans exist is what I meant. And one very similar to mine in design: upload_2017-9-27_22-57-4.png
     
  13. Sep 27, 2017 #12
    I do agree that tread width should be smaller and I have halved the width of the treads in my design document, they are now half of the width than in the picture in my post.
    I disagree that walking on this treadmill would make it hard not to fall down a lot - each step is moving 100 lbs after all, and when a person runs against the ground it is mostly controlled falling combined with momentum - that's why its harder to begin running than stay running because at the beginning you're actually moving your entire mas whereas keeping yourself going is easier because you have momentum - its the same thing with this treadmill idea.
     
  14. Sep 28, 2017 #13

    sophiecentaur

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    You are missing the point. The reaction force from the tread, if there is no / low friction will be there, initially, as you start to accelerate it. Once it has reached the fasted speed that your legs can give it, you cannot get any force backwards. This is Newton's First Law and can't be ignored. Your legs will constantly need to be going backwards as fast as they can and you will need to hand onto the support to prevent you from falling on your face. You could achieve that (final) situation by trying to run on a block of ice. If you want to simulate the normal running experience, you need something for your legs to 'bear on', which can either be the ground (normal running, as I have already described) or a powered / braked tread.
    Your picture of an unpowered human treadmill doesn't show the mechanism used for the tread so it proves nothing about the basics involved in this.
    I detect a reluctance on your part to take seriously what you are being told by Physicists and Engineers. Why did you approach PF for an answer if you ignore what you are being told? Ask yourself why the market is not flooded with treadmills, based on your idea. You can hardly be the only person to have thought of it. The reason is PHYSICS.
     
  15. Sep 28, 2017 #14
    The photograph appears to show a 'Force' model. From the Woodway website (my underline),
     
  16. Sep 28, 2017 #15

    sophiecentaur

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    The braking is done electromagnetically (dynamo and resistor - as I suggested).
     
  17. Sep 28, 2017 #16
    The market /does/ have many treadmills based on my idea (its not my idea just a re-imagining of the concept) - I came here because in my plans to build one by myself based on the ones I saw out in the market I needed to know how much force moving 100lbs along many small bearings would take because I /already know/ the concept works having seen many human powered manual treadmills that are commercially produced without the need for breaks.
    For this reason, I think you are misunderstanding Newton's First Law because of the fact that manual treadmills similar to mine exist /without/ the need for a breaking system on the treads. Similar treadmills also exist for dogs as well as humans (I'll post a picture of one designed for dogs and notice it has no breaks needed because the weight of the wood being moved by the animal is enough) The picture of the manual treadmill I posted earlier has a magnetic breaking system to make it more difficult for the athletes because it is designed for speed work not because a break is inherently necessary. You cannot see the wheels because of those black steel rectangles, but they're there just line in my re-imagining of the concept.

    maxresdefault.jpg
     
  18. Sep 28, 2017 #17

    The picture of the manual treadmill I posted earlier has a magnetic breaking system to make it more difficult for the athletes because it is designed for speed work not because a break is inherently necessary as evidenced by these manual treadmills which do not have breaking systems. Which brings me back to my original question if I can convince you the concept actually exists without the need for a break - building one myself, if the wooden boards altogether weigh 100lbs and are on bearings, how much force would it take to move them for someone walking on them and pushing them with their legs being on a treadmill.

    trueform-runner-custom-color.jpg
     
  19. Sep 28, 2017 #18
    The breaking is needed on that particular treadmill because it is designed to be more difficult for athletes not because a breaking system is inherently needed.
     
  20. Sep 28, 2017 #19

    No break needed on these manual treadmills:

    athlete_area4.jpg
     
  21. Sep 28, 2017 #20

    A.T.

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    The force needed to move them at constant speed will be due to internal friction, which is not trivial to estimate.
     
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