Landships II

You haven't specified if you mean interior/technical, or whether you mean a rivet counter's delight exterior plan. My peruse of the web has turned up some nice MkV* plans, if that's any use

V*

No doubt you've seen this

AH! I'm not an expert, but I can hopefully help a little. Firstly with this link, which shows a diagram not of a Mk V, but of a Wilson epicyclic transmission. It's figure 26.27, about 3/4 down:

here

I've wondered myself whether the descriptions of the MkV as having a four speed transmission referred to the epicyclic housings or not, because apparently it's difficult to design an epicyclic with more than three speeds, but the figure and blurb above show a four speed gearbox, so I'm presuming that any 'primary' transmission behind the engine is just a gear reduction with no ratios to change.

Locking a differential means preventing the half-axles on either side from rotating independently, effectively creating a solid axle to stop one side spinning when the other still has traction. If you don't know, this spinning happens because the gears inside a diff are located within the radius of the crownwheel, and the left/right half-shafts are geared to each other such that if left rotates forwards, then right rotates in reverse ( and vice versa); this means that in a turn, when the inside track (or wheel) needs to turn more slowly, it effectively rotates in reverse when compared with the outside track/wheel.

If you jack up a car and turn one of the driven wheels, the crownwheel in the diff, which is what the engine and gearbox drive, will stay still whilst the driven wheels will turn - but in opposite directions; this is because both jacked up wheels are free to turn, not resisted.

When drive is applied to the crownwheel, it turns, turning the entire gear assembly within it in a static state, neither side rotating relative to the other unless the vehicle turns. It's a little tricky to explain, but easy in principle for anyone who ever built a Tamiya RC car.

When the crownwheel turns, the gear teeth of the diff take the load; if both sides have traction, relative movement between left and right is limited by the torque reaction from the surface travelled on. If one wheel/track loses traction, this torque load drops away, causingthe spinning wheel/track to be even freer to spin, so the other side will tend to stop driving and all power will be lost to the side without traction. Clear? Probably not!

Performance cars often have limited slip diffs which either use friction plates to oppose the free spinning, or else the Torsen type, which I can't remember the workings of.

Getting back on topic, the epicyclic gears of the MkV were used to control the speeds of each track. Changing speed with an epicyclic box is simple, as anyone who's ridden a bike with a Sturmey-Archer 3-speed hub should realise. I'd imagine it makes a good way of steering a tank by allowing the driver to easily speed up or slow down one track, using brakes to assist the slowing down if necessary (see the link I posted yesterday for that, it mentions it in there).

As far as I can see, the question is not why the MkV needed the epicyclic gears, but why the earlier Marks needed secondary gears. The Mk V does not appear in photos or these plans to have a differential, therefore you cannot steer it by brakes alone, as both tracks would be firmly connected to each other. Instead you allow the tracks to turn at different speeds by having a gearbox for each track - an epicyclic one, so that there's no need to mess around with a clutch when shifting. Agreed?

With the earlier Marks the situation is different, because they seem to have a large diff housing in the middle of the tank, unless it actually contains no diff and is just a solid axle with a huge crownwheel. If this is the case, the secondary gears are necessary to allow the tracks to turn at different speeds, or be disengaged completely for a pivot turn; the presence of a zero position, presumably meaning no gear engaged, suggests to me that the "diff" in the early Marks is just a solid axle, making secondary gears vital.

AFAIK, the Mks I-IV had a primary two-speed box controlled by the driver. I think the use of the epicyclic four-speed boxes in the MkV may have allowed the elimination of the primary gearbox (leaving, at most, a reduction between engine and axles/epicyclics), so that first gear on the epicyclic boxes was low enough to get the tank moving and gear changes when accelerating to full speed would involve shifting up through both sets of gears simultaneously - something similar to the Whippet in a sense, but made easier by the lack of need to use a clutch for shifting.

As for methods of steering the Mk I, let me see:

1 - gradual turn using tail wheels (controlled by hand wheel at drivers side)

2 - stop tank, select neutral secondary gear for inside track and apply brake, then driver engages clutch to drive outside track.

3 - stop tank, select gear 2 for outer track and gear 1 for inner track, driver moves off.

4 - guesswork now needed. If the tank has a diff in the big housing, not just a solid axle leading out to the secondary gears, then use of the individual track brakes by the commander should allow changes of course. If the axle is solid however, that isn't possible and I'm stumped.

If there's a diff in the early Marks, I can only imagine secondary gears were fitted to reduce wear on the steering brakes, or else because experience with Little Willie night have found that excessive muscle power was required to apply the steering brakes on the move? Not sure if that's quite right historically, as I think Mother is said to have been designed/built alongside the modded version of LW, but the principle likely holds regarding muscle power.

Hope there's something comprehensible in this lot, and that it's of help.

 

TCT

 

Tanks.net says the secondary gearboxes were fitted to Mother and her offspring because they weighed twice as much as Willie, so the idea was to relieve the transmission of the load. Presumably that would only work when in gear 1 of the secondary box, as gear 2 would likely be similar to the drive ratio in Willie. This might tally with what I've read elsewhere (in a generic book on tanks from WW1 to date) that the second gear shaft was weak and prone to twisting, needing to be be strengthened for the MkIV.

-- Edited by TinCanTadpole on Tuesday 6th of March 2012 03:26:55 AM

James H wrote:

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An Idiot's Guide is what is required.

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I may be qualified to write that, as long as you didn't mean a guide for idiots.

TCT - just trying to grasp why the secondary gears were necessary in the first place,

I believe that the secondary gears were used with first gear to provide much lower gearing to allow the tank to crawl out of obstacles, or climb steep inclines, the primary gears would have been ok on the flat. I think 4x4s have a similar arrangement.

 

and how WW's invention made it easier. Have watched a few vids without becoming any wiser. Gears not my strong suit.

The gears would not have synchromesh so changing gear to get out of shellholes etc would have been a nightmare. 

The epicyclic gearbox had an arrangement of bands that locked part of the mechanism and gave drive so in effect acted like a cluch that didn't rely on a deal of skill to operate.

I don't even know what "locking a differential" means.

Differentials allow wheels on the same axle to rotate at different speeds while driving both, saves scuffing tyres and keeps traction. The downside is that if one wheel looses traction, ie is on ice or is not in contact with the ground, that wheel spins and leaves the other wheel motionless. If it is possible to lock the differential then the drive is as if the back axle was solid so drive would be equally to both wheels.

In fact, I sort of skip through passages about how the Tanks were driven/steered. Acc to W.M. Rossiter (in The Tanks at Flers) there were four possible methods of steering a Mk I.

To steer the Mark1 to IVs the official way was to stop the tank and by using only one track shift the tank on to the correct bearing.

To do this the left track could be moved forwards or reversed and so could the right track, so is that the 4 methods M.W. Rossiter means?

This is based upon some knowledge and some supposition so if anyone has more correct knowledge please share.

 

-- Edited by LincolnTanker on Tuesday 6th of March 2012 11:37:52 AM

-- Edited by LincolnTanker on Tuesday 6th of March 2012 11:39:11 AM

James H wrote:

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The mistake I've already made is to think that the gearbox itself was the innovation, but I gather it wasn't. It was an ordinary, 4-forward 1-reverse box (as on the Foster-Daimler, I think). Wilson did remarkable things with that later.

The epicyclics introduced in the Mk V were where the drive from the gearbox met the secondary gears - in the track frames, just behind the sponsons. (See picture. You'll notice that the port and starboard arrangements are mirror-images) In the Mk I to IV, the gearsmen had to change those gears manually; Wilson's apparatus somehow caused that to happen automatically when the driver operated the appropriate brake lever.

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 James, I think you still have things confuddled here: as I understand, the Daimler drove through a two speed primary gearbox, not four speed; the four speed bit comes from the drive then entering a pair of two-speed secondary gearboxes, i.e. first gear primary plus first gear secondary, second gear primary plus first gear secondary, first gear primary plus second gear secondary, and second gear primary plus second gear secondary as the four possible gear combinations.

The impression I get from your last post is that you think the MkV used a four speed primary gearbox, with drive going out to secondary gearboxes wherein some magic was worked to make the gear-shifts easy.

Not so. I can only guess at present about my thoughts that the primary gearbox of the MkV is nothing more than a gear reduction with no speeds to change, but I can say confidently that the epicyclic gearboxes of the V replaced the secondary gearboxes of the earlier Mks.

Before MkV there were only two speeds in the secondary gearboxes, so you could drive each track at either of two gear ratios. With the MkV, it seems that Wilson came up with a four speed epicyclic box; since the Wilson gearbox replaced the earlier secondary gear type, this means that instead of a two speed box in the trackframe, there was a four speed box. Okay so far?

Epicyclic gearboxes have a different type of gear from the old secondary gearbox. Instead of ordinary spur gears, they have planetary gears - refer to Wikipedia's page on epicyclic gearboxes for more info; with epicyclic gears, you swap ratios by locking different segments of the gear-train in or out, to change the path by which drive is routed through the gears. This does not, AFAIK, require the use of the clutch, so the driver has a change-speed lever to control which gear the epicyclic gearbox is in - one lever for each gearbox. By pulling or pushing on these two levers, he should be able to select gear 1,2,3 or 4 for the left track, and likewise for the right one. All the gear changing occurs within the epicyclic gearboxes in the trackframes, there is no need to have an obstinate primary gearbox to handle, as planetary gears (in epicyclic gearboxes) apparently allow for large reduction in little space.

My conclusion, more from some knowledge of mechanical things than the exact details of the MkV, is that the driver would never have to use the clutch to change gear; he would use it to pull away, but after that gearchanges should have been a simple matter of pulling/pushing on both gear levers (whichever direction it was for 'up') to move from first into second, second to third, then into top. 

So whilst the epicyclic gear housings are located where the old secondary gearboxes were, it's a completely different transmission inside. As I've said, I even think the old primary gearbox behind the engine has bitten the dust, with a more compact setup which probably has a fixed gear ratio if any.

TinCanTadpole wrote:

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That make things clearer?

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Oh, my God. I think I was out of my depth as soon as I started this. Bear with me while I try to grasp it.

I may be some time.

TinCanTadpole wrote:

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Roger - yep, that sounds like what I was trying to say, but rather more succinct! 

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Thank you, but what I've written there wouldn't make sense without your explanation!

I understand your point about the Mark V Primary gearbox, that you (and we) aren't entirely sure that it is simply a stepdown gearbox, so more research needs doing there. I like your thinking about it possibly incorporating the gear-reversal mechanism.

Now, I've just checked the diagrams at the back of John Glanfield's The Devil's Chariots (they're the old diagrams in David Fletcher's Landships) and he notes:

Marks I to IV Transmission

Primary gears: 2 forward and 1 reverse

Secondary gears: 2-speed to each track

Mark V Transmission

4-speed forward and 4-speed reverse

Epicyclic gear in final drive to each track, in permanent mesh

Further, regarding the Mark I to Mark IV, he writes:

The engine and transmission as far as the differential's half-shafts came straight out of Foster's howitzer tractor, its gearbox giving two forward and one reverse speeds. At the end of each half-shaft a two-speed secondary gearbox in the track frame transmitted drive to the respective tracks via a heavy roller chain and pinions meshing with the track driving sprockets. The original tractor gearbox could not have moved 28 tons on its own without disintegrating, hence the secondary gears, each operated by a gearsman on the driver's instruction, giving him four forward and two reverse speeds in all. A track brake on each of the secondary gears was operated by the commander seated next to the driver.

Don't know if that's any help.

One thing I'm not entirely sure about, because the diagrams don't make it clear, is how this ties in with the massive worm-gear reduction box in the Marks I to IV? Was the Primary gearbox between the engine and the worm-reduction casing?

EDIT: John Batchelor's cutaway drawing of a Mark IV in Kenneth Macksey's Tank indicates that the Primary gearbox is built into the bottom of the big worm-gear reduction casing.

-- Edited by Roger Todd on Friday 9th of March 2012 12:46:40 AM

I was never exactly a fan of Donald Rumsfeld, but I always thought it was a shame that he got such a lot of stick for that statement, because it's a superb distillation of problems concerning the limitations of knowledge. I think it was the Plain English Group or whatever they call themselves who had a go at him for using tortuous language, but it actually makes complete sense.

Roger - yep, that sounds like what I was trying to say, but rather more succinct!
There is some degree of deduction in what I wrote, rather than 100% certain knowledge, but to the best of my understanding at present, that is the difference between MkV and earlier rhomboids.
I hasten to add (again) that it is conjecture on my part that the 'primary gearbox' of the MkV is just a step-down gearbox; I do not know this for a fact, but it seems likely given the modest physical bulk of the casing, plus the fact that I think it's been said or implied that the epicyclic gearboxes had four speeds, rather than being simpler two-speed units following a two speed primary 'box. I'll need to take another look at the four-speed epicyclic gearbox link I posted earlier to see how the number of stages compares with the MkV tank plans posted by LT, but as far as I remember it looks like the tank plan shows a similar arrangement, suggesting that four speeds in the epicyclic 'box(es) is correct.
As for the primary gearbox, I noticed last night when posting about the photos inside the V* that there are two pivoted linkages on top of the primary gearcase, so there might be something going on in there after all. I'll take a look at the photos again, as the thought has occurred that the primary 'box may have had forwards/reverse gears to change, rather than incorporating reverse into the epicyclic transmission. This, again, is guesswork.
Certainly I suspect the primary gearbox of the MkV is not the same as in the Mks I-IV, as that gearbox had to contend with 105hp (or 125 for some MkIVs), whereas the Ricardo was, AFAIK, a larger displacement engine (about 18 litres instead of 13?) generating 150hp and likely to have extra torque to match. I've read that the second gear shaft in the Mk I was weak and liable to twist under load, but I don't know if this referred to the primary or secondary gearboxes. In any case, it suggests to me that the primary gearbox of the earlier tanks would not have been strong enough for the larger, more powerful Ricardo.

James H wrote:

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I feel terrible about this. 

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 No need, James! I for one have been enjoying this thread, it's been educational for me as much as anyone. That plan you've just posted is really handy too, as it shows the gears and their levers nicely.

I must confess that I have made a mistake with my deductions/suppositions about how the epicyclic gearboxes were worked. 

Looking at the V* plans I linked to earlier, I see that they have labels (in English!) for the levers used by the driver. There are four: on the right, a forwards/reverse/something-illegible-which-may-be-'neutral' selector; forwards and to the left of that, a change speed lever; than, either side of the driver's legs, a pair of control levers.

My thoughts that the MkV used independent control for each epicyclic 'box is therefore wrong; both gearboxes were controlled in unison from one lever, for acceleration/deceleration/gradients only, not for steering.

The forwards/reverse selector seems to confirm that the primary gearbox of the MkV served this purpose, but I'm now a bit confused about what exactly the control levers did in the epicyclic gearboxes to steer the tank. After all my confident waffling, I think we've come round in a circle, almost to the point where James was in his fourth post!

Panzerfaust.ca (the site with the V* plans I linked to) says that pulling on one of the control levers caused a pinion in the epicyclic gearbox to disengage, thus causing the drive to slow on that side, aided by use of the brakes (footbrake, I presume) if desired. I don't fully comprehend this description, what is the pinion's purpose and is drive still transmitted, or is the tank effectively coasting on it's inside track, with only the outer one driven? 

 

Roger - that makes sense, it looks like what Little Willie has inside, but back-to-front.

-- Edited by TinCanTadpole on Friday 9th of March 2012 03:39:07 PM

I've not given up on this one yet. Might understand things a little better now that I've looked again at what panzerfaust.ca says; the fact that part 2 of that article is inaccessible doesn't help, but I get the impression that pulling a steering lever in the MkV did indeed cause drive to disengage from that track, so that only the outer track was driven. Mind you, if the inside track wasn't driven, what use would it be applying a touch of footbrake to help slow the track? AFAIK the footbrake operated somewhere in the middle of the tank, before the drive reached the epicyclic gearboxes - so you'd be slowing a part of the transmission that was disconnected from the track. The only way it would work would be to have a secondary brake acting on each epicyclic gearbox - feasible, I think, given that they use/can use brake bands to select ratios - and connect it to the steering lever so that pulling it would first disconnect the drive and then apply the brake to slow the gearbox and thus the track. Must watch more footage of various Mks being steered!

Do I understand things now? Sadly, not by a long chalk, but I am very grateful for your and everyone else's gallant efforts to explain matters. I'm afraid my total lack of mechanical aptitude has not made your task any easier. The merest glimmer of an understanding of the principles, or even the vocabulary, would be a tremendous advantage, but it is something which in my case I have not got.

I shall persevere, and if I come across something that explains things in a nutshell I shall forward the information immediately.