Force to stop a person on a treadmill

[canucks]

We are doing a study & our calculated force is MUCH higher than our data. I'm wondering if our calculation is right.
how much force it would take to stop a person in a wheelchair (83kg) going 6km/hr and stopping in 10 cm or within 2 sec. as an example?

This is my calculation..Am I on the right track? F= ma We can find a using v=at+v0 so a=v/t so (1.67)/(2) = .835 ( v0=0 which treadmill initial speed) So f= 83*.835= 69.35 N

If you want to find it at 10cm (.1m ) you can use conservation energy formula as well Fd = 1/2 mv 2 so mad=1/2mv2so a= v2/2d so in this case a=1.672/.1= 13.94 m/s so F = 8313.94=1157.39 N

 

[russ_watters]

We are doing a study & our calculated force is MUCH higher than our data. I'm wondering if our calculation is right.
how much force it would take to stop a person in a wheelchair (83kg) going 6km/hr and stopping in 10 cm or within 2 sec. as an example?

The problem is that those are two very different requirements. Which one do you want?

 

[Dr.D]

Why would you expect to have constant acceleration during the stopping event?

 

[canucks]

the one with the stopping distance.

 

[russ_watters]

the one with the stopping distance.

The answer you calculated looks correct to me.

 

[russ_watters]

...by the way, the title of the thread is a bit confusing and implies an answer of zero. Could you clarify the setup?

 

[berkeman]

And are they on a treadmill or in a wheelchair? Or both?

 

[canucks]

They are on a wheelchair on a treadmill. The weight is weight of the participant + wheelchair

 

[berkeman]

They are on a wheelchair on a treadmill. The weight is weight of the participant + wheelchair

What stops? The wheelchair with respect to the moving treadmill surface? The treadmill surface and the wheelchair keeps rolling? Or some combination? These are kind of important details if we are to give you good help.

Do you have a sketch of the setup?

 

[berkeman]

Or (after re-reading your OP), is the person in the wheelchair moving with the treadmill initially with their wheelchair wheels not rotating?

 

[canucks]

the participant in wheelchair is moving with the same speed as treadmill. Then they told him to stop ( and as a result participant went back with a wheelchair a certain distance)

 

[berkeman]

the participant in wheelchair is moving with the same speed as treadmill. Then they told him to stop ( and as a result participant went back with a wheelchair a certain distance)

Sorry if I'm being dense here, but the volunteer in the wheelchair shoots off the back of the treadmill when they stop rolling themselves forward? Could you give a full explanation of the experiment, and say what it is that you want to learn from the experiment?

 

[canucks]

Sorry for being confusing. No I meant like brake line ( you try to stop the car by pushing the brake but you go a little distance before the car stops). Once we told the participant to stop, he went back a little trying to stop the chair before the chair fully stopped

 

[berkeman]

Sorry for being confusing. No I meant like brake line ( you try to stop the car by pushing the brake but you go a little distance before the car stops). Once we told the participant to stop, he went back a little trying to stop the chair before the chair fully stopped

So you turned off the treadmill motor at the same time the volunteer was told to stop? Do you have a video?

 

[canucks]

No. But here is the paper that our student wrote regarding this study

 

[sophiecentaur]

If this is a real, practical problem then why does the wheelchair user ever need to be traveling backwards on the belt? You can use a strap to prevent that happening and then you don't need to brake him her. But a treadmill is not a very suitable exercise machine for an arm propelled vehicle. It's specifically for leg exercise. When the runner is in the air, there is no force from the track but the chair wheels are being turned by the belt when the hands aren't pushing. I don't think it's an equivalent exercise to 'road work'. If you used a safety strap on a runner, it would topple her over but it's fail safe for a wheel chair. Hands off and wheels just go round on their own.

Or (after re-reading your OP), is the person in the wheelchair moving with the treadmill initially with their wheelchair wheels not rotating?

My brain hurt, reading this and I am trying to picture what it's like to actually do this thing. If the wheels are not rotating, the chair is moving backwards on the belt (no?). I'm assuming that the chair is being propelled by the arms to stop it going backwards but, when the hands aren't on the wheels, they will be turning 'forward' but any bearing or rolling friction will be pulling the chair backwards. This is much harder than running on the mill.
Edit: I just discovered the post with the paper. Lots of it! Great invention to have a servo assist, rather than a simple motor with a lever control. The treadmill tests are really difficult to grasp and I'll need to read them through and post again.

 

[berkeman]

I only skimmed the paper so far, but id does indeed say that the treadmill is turned off when the volunteer is told to stop their chair. Without a video, and without a clear/short explanation of what the study was trying to figure out, it's hard to be of much help.

how much force it would take to stop a person in a wheelchair (83kg) going 6km/hr and stopping in 10 cm or within 2 sec. as an example?

IMO, the treadmill experiment does not help you answer this simple question. It introduces so many other effects. Work is distance * Force, and the Work done to stop is equivalent to the Kinetic Energy in the motion of the person & wheelchair right before they begin to stop. That is a pretty simple calculation (assuming constant stopping force, which was mentioned early on as a question).

 

[sophiecentaur]

IMO, the treadmill experiment does not help you answer this simple question. It introduces so many other effects.

Absolutely. Doing it that way introduces more questions than it answers. What you could do is what they do in the UK MOT test for cars on a rolling road, But if you want to find the braking efficiency then why not use an accelerometer (included in most spare phones and Apps are available) with the chair being operated on a horizontal surface? You can measure the effect of extra drag from the drive roller this way too.

 

[canucks]

Sorry guys by my job is just comparing the data with calculation not to change the study protocol. Can you please guide me how to calculate the force in this condition? Yes , 100% horizontal and no slope.

 

[A.T.]

Sorry guys by my job is just comparing the data with calculation not to change the study protocol.

But the methodology seems flawed. A treadmill is only equivalent to movement over ground, when it runs at constant speed (equivalence of inertial frames). You cannot simulate over ground accelerations by changing the treadmill speed, because that doesn't require acceleration of the entire mass, just changing the rotation speed of the wheels.

Can you please guide me how to calculate the force in this condition?

Seems like a waste of time. The forces you get form this are meaningless for actual over ground use.

 

[canucks]

I attached the paper ! You can read for more details!

 

[A.T.]

I attached the paper ! You can read for more details!

I read the methods. The stopping distance test on the treadmill sounds bogus, as explained in post #20.

 

[berkeman]

Sorry guys by my job is just comparing the data with calculation not to change the study protocol. Can you please guide me how to calculate the force in this condition? Yes , 100% horizontal and no slope.

In order to do that, you would need much more real-time data from the experiment. You would need the velocity of the treadmill surface versus time, you would need the position data from the wheelchair versus time, and you would need other information like the moment of inertia of the wheels and the position of the volunteer's CG in the chair versus time. Do you have all of that? (You can start to see how a video with markers and associated sensor data acquisition would be of help).

Barring that information, it's probably not worthwhile to try to do the calculations to any accuracy. Why were you tasked with this? Does the person assigning you this task understand the physics of what is going on, and why a "simple calculation" is not so simple given the problem statement?

 

[sophiecentaur]

It strikes me as very possible that the work on this project was based on a treadmill because they actually had one available. Stopping time and distance are so easy to measure these days (with a smartphone, even). One afternoon of lab work would give those results.
It is hard luck for the OP to have been presented with the results of what is really a flawed bit of work but it does demonstrate how important it is to plan a viable experiment in the first place and not start with "We are going to use this equipment ". I wouldn't mind betting that that list of references in the paper were not all read very thoroughly. I'd bet this problem has already been discussed and measurements described in some of those references. In fact they are not 'references'. because they are not 'referenced' in the text It's a Bibliography.

 

[canucks]

I got the real time data for both when V= 3.5 KM/h and 6 Km/h . But we are trying to verifying the resluts..Since the force we calculate is significantly higher.. how can I attach excel sheet here?

 

[berkeman]

I got the real time data for both when V= 3.5 KM/h and 6 Km/h . But we are trying to verifying the resluts..Since the force we calculate is significantly higher.. how can I attach excel sheet here?

Try the Upload button in the lower right of the Reply window...

 

[canucks]

I did but it says it only allows pdf and a few other format not excel..how odd

 

[berkeman]

I did but it says it only allows pdf and a few other format not excel..how odd

Maybe you don't have enough posts yet. I've been helping in another thread with a user who has posted Excel spreadsheets.

I'll PM you my e-mail address, and you can send me the file to post if you like.

 

[sophiecentaur]

I did but it says it only allows pdf and a few other format not excel..how odd

It's not odd, really. Not everyone actually owns Excel but everyone can read pdf (portable data format?). Why not export as pdf? We don't need a working spreadsheet - just some numbers.

 

[sophiecentaur]

I got the real time data for both when V= 3.5 KM/h and 6 Km/h .

But what does the data consist of? If the measurements were done on a treadmill then how are they representative of what happens on the ground. It is not 'obvious' that the results mean anything.

 

[canucks]

Here is the link to data..Stopping distance for both 3 KM/h & 6 Km/h
https://www.dropbox.com/s/tstbfod8y...ky's conflicted copy 2015-01-12) (1).xls?dl=0

 

[sophiecentaur]

Here is the link to data..Stopping distance for both 3 KM/h & 6 Km/h
https://www.dropbox.com/s/tstbfod8y0b5zj7/Data Analysis List Old BWSD (Bonita Sawatzky's conflicted copy 2015-01-12) (1).xls?dl=0

You certainly have some measurements there! Can you describe the setup and what was actually measured, particularly with regard to the treadmill?

 

[canucks]

The participants were randomized to begin the study either with or without the 106 drive attached to the wheelchair operating in the indoor mode. Stopping distance data were 107 collected at two different speeds (3.5 km/hour or 2.2 mph and 6.0 km/h or 3.7 mph) with two 108 trials at each speed using a wheelchair treadmill (MaxMobility) at 0.5 degree incline to 109 standardize velocities. Participants were instructed to propel on the treadmill until each speed 110 was reached and maintained for a minimum of three seconds. The researcher then asked the 111 participant to stop the wheelchair while simultaneously turning off the treadmill. In a separate 112 test, tTo measure starting peak total forces and peak speed, participants were asked to propel the 113 chair with “one light push, in order to get the wheelchair going” from stationary on a level tile 114 floor with and without the drive. Participants were asked to repeat the light push task until they 115 were able to accelerate the chair to engage the drive

Here is a picture of smart drive: http://www.max-mobility.com/smartdrive/#mx2pluspushtracker
Weight of participant between : 60-80 kg
weight wheelchair + smart drive : 23.1 Kg

 

[sophiecentaur]

The researcher then asked the 111 participant to stop the wheelchair while simultaneously turning off the treadmill.

I am concerned about this statement because the user has zero velocity relative to the ground. If the treadmill and the chair are turned off simultaneously then there would be no acceleration and no force and the chair would still have zero velocity relative to the ground. The only forces that would occur would be due to angular momentum in the drives of the chair and the treadmill.
If there were also measurements on the floor then why not test the braking that way too? I am not surprised your calculations do not agree with what the treadmill measurements imply. When motor car brakes are tested on a rolling road, there is a force meter on the road itself and the car is held stationary. That gives the correct result without a road test. That is a totally different methodology.

 

[canucks]

Is there a way that I can verify the data?