Landships II

James H · Legend

Sueter, Caterpillar Tracks, and Captain Scott.

Richard Peskett · Private

With reference to the Wolseley sleighs of Captain Scott herewith is some information from Commercial Motor, April 1910.
Richard Peskett.
Wolseley sleighs.jpg

kieffer · Commander in Chief

Great pictures James, Richard!

the last alinea of the magazine article, I do not understand completely:
'the bottom of the chain stands still, while the sleigh is underway, and that the top half travels forward at twice the speed of the whole machine'.
Has that something to do with the sprocket based 'on the floor'?

regards Kieffer

James H · Legend

It's something to do with the physics of caterpillar tracks. I've read it before somewhere in relation to Tanks, and can't claim to grasp it entirely. It goes something like this: A fixed point on the track is obviously stationary in relation to the ground while it's in contact and the Tank is passing over it. When the rear of the Tank reaches it, it then travels up-and-over and makes its way to the front, but while it's doing so the Tank moves forward by its own length. The fixed point therefore has to travel up the rear face of the rhombus, along the top, and down the front face in order to return to its position relative to the Tank - about twice the length of the vehicle. The upshot seems to be that the top of the track does, indeed, travel at twice the speed of the bottom.

Erm . . . imagine the two points at the front and rear of the vehicle, at the extremes of the part of the track in contact with the ground. By the time the point at the front has made its way to the rear (travelling along one side of the rhombus) the point that was at the rear has had to travel along the other 3 sides in order to reach the place where the front point was previously. So it must have travelled at twice the speed.

It does, as young people say nowadays, my head in but must be true. Something to do with loci, I expect. I'm sure someone with a proper knowledge of physics will explain the phenomenon far better. In fact, the whole matter of the physics of the caterpillar has intrigued me for some time. I get the bit about low ground pressure, but there are other aspects that I should like to understand, such as why the application of the force by the sprocket gives it so many advantages over the wheel. There is a work on the subject on t'Internet, but it's not downloadable for free: http://www.123helpme.com/preview.asp?id=153414 Perhaps we have an expert amongst our number.

-- Edited by James H on Friday 1st of October 2010 11:14:46 AM

kieffer · Commander in Chief

James, thank you! Clear and readible, wished my old physics teacher had explained me things this way.
Some other thing came to my mind: the idler sprocket. May be it prevented clogging the tracks? Some ww2 German half track vehicles had a kind of snow cutting device, some extra disks on the hub. (see picture)

regards, Kieffer

-- Edited by kieffer on Friday 1st of October 2010 03:49:32 PM

-- Edited by kieffer on Friday 1st of October 2010 03:54:12 PM

James H · Legend

I could be wrong.

kieffer · Commander in Chief

If, I am not prosecuting you. But it is a bit remarkable that it's mentioned in that article as if it was something particular, concerning only this contraption, don't you think?

Regards, Kieffer

Rectalgia · Legend

Kieffer, I think you have the explanation when you refer to "something particular" - that "contraption" was probably the first tracked vehicle those people had seen in action.� Amother contemporary account puts it this way:Those who have seen the sleigh on the Norwegian ice-fields were struck by the illusion that the chain, where it touched the ground appeared to stand still while the sleigh glided over it. The chain from the top of the forward wheel to the top of the after wheel was traveling forward at twice the speed of the sleigh, which accounted for the illusion. - these were people more accustomed to seeing wheeled vehicles in motion and even motor vehicles were a novelty.

That quote is from material in the forum http://www.practicalmachinist.com/vb/antique-machinery-history/ot-crawler-tractors-196276/ by the way - much discussion (and pictures) of assorted eldrich contraptions in there! Including the Wolsely sleighs.� And that quad "bike" with the machine-gun that I think has been posted on these pages already, in times gone by.

James H · Legend

It has now occurred to me that my explanation above cannot possibly be true. What on earth am I talking about?

The position of the track relative to the ground is a red herring. It just gives the illusion that the top is moving faster than the bottom.

Imagine that the ground isn't there, or that the Tank is suspended from a crane. Now start the engine and put it in gear. All that happens is that the track moves round the frame, at a perfectly uniform rate. Take any two points, and their position relative to each other remains constant.

I do apologise for the attack of idiocy above. Please disregard it.

I was more on the Arts side, you see.

LincolnTanker · Commander in Chief

I think that chap called�Einstein explained such things. It's realivity.

If you was to lay down in front MarkIV, or any other track layer,�and it ran over you the track plates that crush you would not move horizontally relative to you. But the rest of the Tank, except the track, would be traveling at 3mph, the track on top of the track units don't travel at the same speed as the tank as they need to travel from the rear to the front so they move at 3mph relative to the hull. Therefore the track at the top is moving at 3+3 = 6mph.
At this point you wouldn't be bothered about the relative speed of the tracks.

-- Edited by LincolnTanker on Sunday 3rd of October 2010 01:59:24 PM

-- Edited by LincolnTanker on Sunday 3rd of October 2010 02:00:33 PM

kieffer · Commander in Chief

Hi Chris,
now we're talking business, Einstein yes! It is like this: if a fast moving tracked vehicle that you want to photograph is passing, time is short. If the same panzer is crushing you the whole proces feels like it takes an hour. Do I fantasise? No, dr Einstein gave a similar explanation, the time you sit on a burning stove and the same time, same place you're sitting there with your fiance next to you ( she probably not on the stove).

Regards, Kieffer

James H · Legend

Ah. It seems I am simultaneously right and wrong. Einstein would have approved of that.

Rectalgia · Legend

James H wrote:
... simultaneously right and wrong. Einstein would have approved of that.

No (IIRC) he hated quantum superposition, tried his level best to resolve the uncertainty principle differently, indignantly wrote "God does not throw dice," or words to that effect.� But yes, modern physicists would approve.� We don't know what Schr�dinger's cat might think though biggrin

�

James H · Legend

Surely "Schr�dinger's Caterpillar"?

I am completely out of my depth now.

Rectalgia · Legend

James H wrote:
Surely "Schr�dinger's Caterpillar"?

LOL! Nicely served Sir!

Nobody sane understands superposition, I'm sure of it.

�

LincolnTanker · Commander in Chief

kieffer wrote:

Hi Chris,
now we're talking business, Einstein yes! It is like this: if a fast moving tracked vehicle that you want to photograph is passing, time is short. If the same panzer is crushing you the whole process feels like it takes an hour. Do I fantasise? No, dr Einstein gave a similar explanation, the time you sit on a burning stove and the same time, same place you're sitting there with your fiance next to you ( she probably not on the stove).

Regards, Kieffer

Hi Kieffer,� you don't have to sit on burning stove to prove relativity, I remember as a child going to Skeggy (Skegness to those who don't know) in the family Morris 12,� it seemed to take 3 hours to get there but only 30 minutes to get back.

Just one thing, boringly going back to topic, isn't the Wolseley elegantly simple?

Another link to info.

http://query.nytimes.com/mem/archive-free/pdf?_r=1&res=9C03EFD81539E632A25755C1A9649C946296D6CF

One may be in existance in NZ or is still laying on the bottom of an Antartic sea after falling through the bottom of a ship.

I remember reading a welcome post to a new poster that said something like "you'll not find a better group of friends."� �The welcome post left out that we are also as mad as a box of frogs.

�

CharlieC · Legend

Shackleton's motorised sledge in New Zealand was taken to the Antarctic on� 1907 expedition. It proved to be almost useless and was abandoned. It was retrieved by NZ Antarctic Research some (35?) years ago and is displayed in the Canterbury Museum in Christchurch.

My comment on the apparent motion of tracks - think about the motion vectors of the top and bottom run of the track and the vector of the vehicle hull. The resultant vectors of the top and bottom track runs w.r.t an external observer pretty much explain the observation in the original article.

Regards,

Charlie

kieffer · Commander in Chief

LincolnTanker wrote:

�

in the family Morris 12,� it seemed to take 3 hours to get there but only 30 minutes to get back.

Just one thing, boringly going back to topic, isn't the Wolseley elegantly simple?

a Ford Anglia did the same trick, but some geo-psychological aspects were involved too, the map reading skills of ma and the patience of dad.
I agree, the Wolseley is elegant simple. Great lead you gave, and what an illustration!

regards, Kieffer

�

kieffer · Commander in Chief

James H wrote:

Imagine that the ground isn't there, or that the Tank is suspended from a crane. Now start the engine and put it in gear. All that happens is that the track moves round the frame, at a perfectly uniform rate. Take any two points, and their position relative to each other remains constant.
James, that idea came to my mind too but as you call it: it's track-laying, the vehicle dragged over it's own track, when on the ground of course. I think there's the 'Pudels Kern'. The explanation you gave is about the same as on Wikipedia, I don't think you're wrong.
I was more on the Arts side, you see.
I still am...visiual minded, show me and I believe it, like the working of a differential axle on a motor car. Don't try to explain...

�

James H · Legend

Back to the original topic:

-- Edited by James H on Tuesday 12th of October 2010 05:34:36 PM

Rob · Legend

I saw 'The Great White Silence' in the cinema today, the official record of Scott's journey to the south pole by Hubert Ponting, digitally restored with a new soundtrack, and there's a scene a few minutes long showing the Wolseley motor sledges in action, great to see

TinCanTadpole · Legend

I think I can explain the track phenomenon: if the vehicle is moving at 5mph, then the speed of any horizontal section of track is 5mph.

The top run of the track does 5mph forwards, and the lower run - on the ground - does 5mph backwards (in effect - it would be backwards if you lifted the vehicle off the ground so that the tracks were spinning).

This means that the speed of a particular track link (or fixed point on the track) relative to one going the other way is 10mph - it's like the closing speed of two cars approaching each other at 60mph (each) being 120mph.

If the vehicle is stationary with the tracks spinning, the top section of track will move forwards at 5mph, whilst the bottom section which is slipping on the ground is doing 5mph backwards. Mathematically you would use 'plus' and 'minus' to denote direction, so forwards equals +5mph and backwards equals
-5mph.

If the track then finds some grip, instead of the vehicle staying put whilst the track moves at 5mph relative to it, the lower track stays put and the vehicle moves above it. The direction of relative motion stays the same, but since the lower track is not moving, the vehicle moves in the opposite direction - forwards.

All this time the upper track has been doing 5mph relative to the vehicle body; it still does 5mph relative to the vehicle body when the vehicle starts moving, but relative to that fixed point on the lower track it moves at double speed - 10mph whilst the vehicle itself does 5mph.

Confused? Probably! Think of it like two cars heading in the same direction: if car A is going 5mph faster than car B, you can say it is doing 5mph relative to A, just like the upper track does 5mph relative to the vehicle body.

If car B is travelling at 5mph, then car A must be going 5mph faster than 5mph - which means 10mph.

Therfore if the bottom of the track stays put on the ground and the vehicle does 5mph above it, then the top of the track which is doing 5mph relative to the vehicle (overtaking it, in car terms) will have a ground speed of 5+5=10mph.