Were the Lunar Rovers faked?

[cjameshuff]

The English unit of mass is the slug.  1 slug is 14.6 kg.  You can take it from there.

This is often claimed to be so, but is not correct. The pound is a unit of mass...exactly 0.45359237 kg. When force and mass need to be distinguished, pound-force and pound-mass are used, the former being equal to a 1 lb mass and an acceleration of 9.80665 m/s^2.

[anywho]

Think of a Railway Locomotive.

I was hoping someone would mention railroading, locomotives, and tractive effort. 

Why?

What relevance does a locomotive, on tracks in 1g, have to a 4WD on a loose surface in 1/6g ?

In quoting the army test I am not using something abstract to show the rovers could not operate in 1/6g, it is the test of an actual rover wheel in a simulated lunar soil, so when it fails it fails, it not then okay to suggest it should still work well above and beyond the fail point because a train can pull x amount.

They conducted those traction tests at 2.5 ft/s which is approx 2.7kph, or a very leisurely stroll. They then gradually added a pull load and the wheel lost practical traction when it had a drawbar pull of 0.5, nowhere near the approximate 5.0 needed to operate on the moon.

What a train can pull, or a tractor at an airport, is irrelevant to the failure point in the test.

[Nowhere Man]

Fine.  Let's stick with SI, then.

But I suppose it doesn't matter, because anywho isn't making any sense or headway.

Fred

[smartcooky]

Why?

What relevance does a locomotive, on tracks in 1g, have to a 4WD on a loose surface in 1/6g ?

And therin lies one of your greatest problems; your inability to extrapolate across variations of the same problem, and it IS the same problem...the relationships between force, mass, inertia, gravity and traction  are the same everywhere throughout the universe.

[JayUtah]

Why?

Because if you understood the first thing about tractive effort you'd realize just how woefully ignorant your "analysis" is.  But you don't.

[Jason Thompson]

Why?

What relevance does a locomotive, on tracks in 1g, have to a 4WD on a loose surface in 1/6g ?

Because it shows you the same thing we've been trying to tell you: drawbar pull is simply not the value you think it is.

In quoting the army test I am not using something abstract to show the rovers could not operate in 1/6g, it is the test of an actual rover wheel in a simulated lunar soil, so when it fails it fails, it not then okay to suggest it should still work well above and beyond the fail point because a train can pull x amount.

It is not saying it should work above the fail point, it is illustrating that the 'fail point' is not what you think it is.

They conducted those traction tests at 2.5 ft/s which is approx 2.7kph, or a very leisurely stroll. They then gradually added a pull load and the wheel lost practical traction when it had a drawbar pull of 0.5, nowhere near the approximate 5.0 needed to operate on the moon.

Your continuing failure to understand what value drawbar pull actually has is the problem here. You don't need a drawbar pull of, say, 600 lb to move a 600 lb load. The examples given here illustrate that, and the same thing applies on Earth as the Moon. If a tractor with a drawbar pull of 75,000 lb can move an airliner with a weight of 200,000, why can't a rover move itself on the Moon?

We still await your explanation for what you think is actually going on in the rover film footage, by the way. Is it the real lunar surface (in which case the rover clearly works) or not (in which case you can't argue properties of the lunar surface from it). Clearly there is a vehicle that can be operated on that surface.

What a train can pull, or a tractor at an airport, is irrelevant to the failure point in the test.
[/quote]

[Sus_pilot]

I'm just catching up on this thread and I was hoping someone would mention railroading, locomotives, and tractive effort. 

Probably should have been me, given the nature of one of my vocations.

Anywho - it really is the same problem.  Do you really think we put 13,000 tons of tractive effort on a coal train?  We'd probably tear the drawbars out of the cars if we did.  But that's what you're implying with your calculations for the LRV.

[anywho]

Why?

What relevance does a locomotive, on tracks in 1g, have to a 4WD on a loose surface in 1/6g ?

And therin lies one of your greatest problems; your inability to extrapolate across variations of the same problem, and it IS the same problem..

So we should take the test results, that are specific to the lunar rover and lunar soil, then extrapolate those results to a locomotive, then extrapolate back to the lunar rover and declare that the rover can therefore far exceed what the tests show the limits are?

If you do a simulated test you do not have to extrapolate the results away from the rover and then back to it, you only have to look at the results directly.

Your continuing failure to understand what value drawbar pull actually has is the problem here. You don't need a drawbar pull of, say, 600 lb to move a 600 lb load. The examples given here illustrate that, and the same thing applies on Earth as the Moon. If a tractor with a drawbar pull of 75,000 lb can move an airliner with a weight of 200,000, why can't a rover move itself on the Moon?

That tractor has a rated drawbar pull, it is not a maximum, it is based on a set standard (I believe it is what the tractor can pull over 1 meter in 1 second). The 'test' on the tarmac proves it can pull more, if they tried continuously loading it until it could not function satisfactorily due to traction loss then that would be it's physical functional limit.

The test of continuously loading the rover found its functonal drawbar limit, and it is way off what is needed for it to operate on the moon. It is not a rating or a limit set by the manufacturer that can be exceeded, it is a test designed to find the operational limits of the rover wheel and they kept increasing load until they found those physical limits.

[anywho]

I'm just catching up on this thread and I was hoping someone would mention railroading, locomotives, and tractive effort. 

Probably should have been me, given the nature of one of my vocations.

Anywho - it really is the same problem.  Do you really think we put 13,000 tons of tractive effort on a coal train?  We'd probably tear the drawbars out of the cars if we did.  But that's what you're implying with your calculations for the LRV.

No, and they are not my calculations, drawbar pull is not the amount of force being applied, it is the additional mass the vehicle can pull above and beyond it's own weight, and the army tests show a drawbar pull of about 0.5 or 0.6 before the rover reaches it's functional limit.

The weight on the wheel in the test is 57lbs, but on the moon the mass it has to pull is 228lbs (total), so a drawbar pull of only 0.5 or 0.6 based on a 57lb wheel weight, means it can only pull 90lbs (total) before traction becomes too problematic.

Extrapolate all you want, that is a huge deficit.

[Jason Thompson]

The test of continuously loading the rover found its functonal drawbar limit, and it is way off what is needed for it to operate on the moon. It is not a rating or a limit set by the manufacturer that can be exceeded, it is a test designed to find the operational limits of the rover wheel and they kept increasing load until they found those physical limits.

Now please reconcile that with your earlier statement that you knew the rover did not have to exert a force equal to or greater than its mass to move it.

How many different sources do you need to be shown that the value for drawbar pull is NOT the maximum mass it can pull but the amount of force it can exert. Any force can accelerate any mass. Do you even understand that principle? That is why a tractor exerting 75,000 lb of pull can shift an airliner weighing many times that. That is why I, a human male with a mass of about 180-200 lb can push a car weighing over 3,000 lb. Do you think I am exerting a force of 3,000 lb to do that? I am not working against the vehicle's weight but its inertia.

As I have said at least three times now, the testing of the rover wheel applies to a situation where its weight is acting directly to oppose the forward motion of the wheel. On a horizontal surface the rover could move with a drawbar pull rating of 0.5 lb, it just couldn't accelerate very quickly. Driving up a slope it has to counteract the acceleration due to gravity that is trying to pull it back down the slope before it can even move the rover forward. Only on an upward slope does the rover actually have to pull against its own weight.

Basic principle: F=ma.

[Jason Thompson]

No, and they are not my calculations, drawbar pull is not the amount of force being applied, it is the additional mass the vehicle can pull above and beyond it's own weight,

No

It

Is

Not.

If that were true the locomotive and tractor and human examples you have been given would not be possible. Drawbar pull IS a force measurement. I challenge you to show us a source that defines drawbar pull in the manner you have defined it. Support your assertions. We've given you our sources. You show us yours.

[Captain Swoop]

No, and they are not my calculations, drawbar pull is not the amount of force being applied, it is the additional mass the vehicle can pull above and beyond it's own weight,

So how does my 150 ton loco pull 1000 tons? Shouldn't it's wheels just spin? they only have a weight of 15 tons over each of them?

[Allan F]

Then how can a 300 lb man pull a 200.000 lb jet airliner? Strong man contest?

[anywho]

No, and they are not my calculations, drawbar pull is not the amount of force being applied, it is the additional mass the vehicle can pull above and beyond it's own weight,

No

It

Is

Not.

If that were true the locomotive and tractor and human examples you have been given would not be possible. Drawbar pull IS a force measurement. I challenge you to show us a source that defines drawbar pull in the manner you have defined it. Support your assertions. We've given you our sources. You show us yours.

Okay, a quick look around shows it is generally a force, so  I apologise for the obstinance and confusion. I don't know if the method I was adamant about is archaic, or if there was different criteria among different sectors.

However, the way in which I am describing drawbar pull is correct for the subject at hand which is the army test for the rover wheels.

The pull coefficient of 0.5 or 0.6 is certainly related to the mass the vehicle can pull and the weight on the wheel, the formula they use to get the coefficient is P/W or drawbar pull/wheel load, this proves that the coefficient is based on the mass the wheel can pull and not the force needed to pull it.

If the drawbar pull was a measure of force they would have to divide it by the force needed to drive the weighted wheel, not the weight on the wheel, to get the coefficient.

[Jason Thompson]

The pull coefficient of 0.5 or 0.6 is certainly related to the mass the vehicle can pull and the weight on the wheel, the formula they use to get the coefficient is P/W or drawbar pull/wheel load, this proves that the coefficient is based on the mass the wheel can pull and not the force needed to pull it.

And the reasons for that have been explained. I'll try one more time.

The testing regime is operating on steady state propulsion. The wheel is not pulling the mass of the vehicle. The mass of the vehicle is not offering any resistance. On a flat, level surface once it is moving it will stay moving unless additional force is applied. That's basic physics, yes? All the wheel has to do is overcome the rolling resistance of the surface.

So why are they applying a load? Because once it starts climbing a slope (which is what they are applying their conclusions on the rover's behaviour to), the weight of the vehicle is resisting the forward motion. The lunar gravity is providing an acceleration opposing the motion of the vehicle. As the incline increases, the portion of the rover's weight it now does have to pull as a resisting load increases. That's what those ratios are. The portion of its weight now acting to resist its motion is determined by cosine (90 - incline in degrees). So at 25 degrees, the rover has to effectively exert a force of cos(90-25) = 0.42 x its weight all the time just to keep moving forward at a constant speed. Not its mass, its weight.

It is only when dealing with a motor trying to pull a load up an incline that drawbar pull becomes a limiting force that has to exceed the portion of the weight of the vehicle acting to resist the forward motion in order to allow the vehicle to pull the load. That's why I can shove a 3,000 lb car along a flat road but can't push it up an incline without assistance.