Force Needed to Push a Manual Treadmill

[Cire Venn]

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.

 

[sophiecentaur]

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.

 

[Cire Venn]

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.

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.

 

[sophiecentaur]

These kinds of manual treadmills do exist for dogs,

And hamsters have wheels, too. In both those cases, the animals have four legs and would not fall on their faces. 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.

I think you're overestimating the lack of friction a bit too much.

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,

 

[A.T.]

A hamster on a wheel is alarming to watch.

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.

 

[sophiecentaur]

watch kids in those inflatable floating balls,

... 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.

 

[Asymptotic]

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.

 

[sophiecentaur]

but rises considerably each time a tread approaches vertical at either side of the mechanism

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.

 

[Asymptotic]

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.

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.

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.

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.

 

[sophiecentaur]

I imagine it would be too touchy to be successful

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.

 

[Cire Venn]

And hamsters have wheels, too. In both those cases, the animals have four legs and would not fall on their faces. 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,

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:

 

[Cire Venn]

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.

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.

 

[sophiecentaur]

The reaction force is having to move the 100 lbs that the treads weighs.

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.

 

[Asymptotic]

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:

The photograph appears to show a 'Force' model. From the Woodway website (my underline),

The Force is a manual, stationary, sport loading platform designed specifically for speed, acceleration, and athletic performance training. With an electro-magnetic braking system built in, this performance treadmill is designed to increase resistance and push athletes to their limits. Equipped with an adjustable harness and varying levels of resistance, the Force is a dynamic training tool for all athletes looking to improve quickness, power, and anaerobic endurance.

 

[sophiecentaur]

The photograph appears to show a 'Force' model. From the Woodway website (my underline),

The braking is done electromagnetically (dynamo and resistor - as I suggested).

 

[Cire Venn]

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.

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.

 

[Cire Venn]

The photograph appears to show a 'Force' model. From the Woodway website (my underline),

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.

 

[Cire Venn]

The braking is done electromagnetically (dynamo and resistor - as I suggested).

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.

 

[Cire Venn]

The braking is done electromagnetically (dynamo and resistor - as I suggested).

No break needed on these manual treadmills:

 

[A.T.]

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.

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

 

[Asymptotic]

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.

Paraphrasing @A.T., obtaining an accurate estimate of the amount of force required depends on a lot of factors. The problem doesn't lend itself to practical calculation, but rather to an empirical approach, that is, build it, and find out. I didn't find an explanation on how the Trueform Runner operates "under the hood", but based on user reviews my guess is it was designed to dissipate a bit more power than a human runner can provide. Another guess, by placing treads on bearings in the manner you've prescribed it will be the other way around, and while a four-legged animal won't much care, a bipedal human will.

 

[sophiecentaur]

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

The OP seems to think that just keeping a mass moving will require a force. If the systems he refers to really are relying just on the bearing friction then how are variations between users catered for?
There is no Physics based answer to many non Physics based questions.

 

[jbriggs444]

how are variations between users catered for

I suspect the answer would be "tempo". You can choose how much energy you dissipate by how fast you move your legs. You choose how fast you move your legs by how fast you make the treads move. You choose how fast to make the treads move (or accelerate) by choosing where to place your feet on the concave surface and on whether you lean forward onto the hand rails.

 

[sophiecentaur]

I suspect the answer would be "tempo". You can choose how much energy you dissipate by how fast you move your legs. You choose how fast you move your legs by how fast you make the treads move. You choose how fast to make the treads move (or accelerate) by choosing where to place your feet on the concave surface and on whether you lean forward onto the hand rails.

I agree that, for a system with given inherent friction, it could be possible to choose a tempo where you would be able to stay upright and keep going.
Still, some friction / energy loss has to be involved and it doesn't have to be set by the mass of the belt.
Just how useful such a passive system is, would be open to question. As with cheap versions of a lot of exercise equipment, their effectiveness may not be as much as the makers claim. Users would not necessarily be aware and this may not matter in the absence of good performance data.

 

[jbriggs444]

I agree that, for a system with given inherent friction, it could be possible to choose a tempo where you would be able to stay upright and keep going.

Indeed. We do it every day when we walk or run down a sidewalk. And can continue to do it fairly well on sidewalks with varying slopes.

It helps that sidewalks have a great deal of inertia.

 

[Cire Venn]

Paraphrasing @A.T., obtaining an accurate estimate of the amount of force required depends on a lot of factors. The problem doesn't lend itself to practical calculation, but rather to an empirical approach, that is, build it, and find out. I didn't find an explanation on how the Trueform Runner operates "under the hood", but based on user reviews my guess is it was designed to dissipate a bit more power than a human runner can provide. Another guess, by placing treads on bearings in the manner you've prescribed it will be the other way around, and while a four-legged animal won't much care, a bipedal human will.

I shall build it then over Winter break, after this semester of college and post pictures to this thread and let you know if it works!

 

[sophiecentaur]

Indeed. We do it every day when we walk or run down a sidewalk. And can continue to do it fairly well on sidewalks with varying slopes.

It helps that sidewalks have a great deal of inertia.

Being able to find a pace that allows you to use the treadmill is only one issue. The thing about a powered treadmill is that it can be adjusted to give a range of conditions. (A variety of sidewalk conditions.) Powered is a quite expensive solution and a cheaper passive system is attractive BUT you need some degree of load adjustment for it to be an attractive proposition.

having seen many human powered manual treadmills that are commercially produced without the need for breaks.

I have searched google for passive treadmills and I have to say, they mostly seem to use a flexible belt which runs over a flat surface, which provides drag. Some appear to have a small flywheel arrangement and there is not clue as to whether the flywheel is totally free to rotate. In fact I have seen none that are explicitly described as having no resistance. Can you give me a reference to any free running version that has no friction?
Are you really determined to ignore Newton's First Law of Motion? It tells you, once the belt is moving, unless there is some resistance, you need no force to keep it going at a constant speed.

 

[A.T.]

Are you really determined to ignore Newton's First Law of Motion? It tells you, once the belt is moving, unless there is some resistance, you need no force to keep it going at a constant speed.

There will always be some resistance, and adding more resistance is not as difficult as reducing it.

 

[Asymptotic]

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.

Thought I'd attack this question with a flanking maneuver, and learn what adjustments could be made on a Trueform Runner. One of the hits was a legal document from a count case involving Woodway versus two companies (Chapco, Inc., and Samsara Fitness, Inc.) on the Trueform side. The Woodway patents and design patents cited were 8,986,169, 9,039,580, D736,866, and D763,776.

I only looked at 8,986,169 (and didn't search for any that may be specifically for the Trueform Runner), but Woodway's drawings look very much like the Trueform Runner in previous photos. Quoted from the 'background' section.

Similar to a treadmill powered by a motor, a manual treadmill must also incorporate some system or means to absorb or counteract the forward velocity generated by a user so that the user may generally maintain a substantially static position on the running surface of the treadmill. The counteracting force driving the belt of a manual treadmill is desirably sufficient to move the belt at substantially the same speed as the user so that the user stays in roughly the same static position on the running surface. Unlike motor-driven treadmills, however, this force is not generated by a motor.

It uses a set of bearing rails, too, although only along the upper side of the belt, and from what I've gathered (my eyes went woozy; patents are the very definition of tl;dr) several measures are employed to provide regulatory counterforce, including the "non-planar shape" of the belt contour itself, a one-way bearing assembly, a front drum slightly larger in radius than the rear drum, and a synchronizing belt system between them.

Google Patents
USPO (click on 'Images' then the 'Full Pages' button to get the full patent document including images)

 

[sophiecentaur]

There will always be some resistance, and adding more resistance is not as difficult as reducing it.

Yes. That's often true but it would be disastrous to remove friction and I still say adjustment is essential and that mass is only relevant at startup.
The friction forces will be all you can tinker with once the prototype is made.
I don't have too much confidence in patents. There is no guarantee that a patented device will even work. It's only done to protect an idea. Amazon reviews could be a good credibility check of a design that's made it to the market.