Steering a tracked vehicle

[radiomike7]

Many years ago I drove a Drott tracked loading shovel which had no diff but a clutch pedal and brake lever for each track. Left to itself it would drive in a perfectly straight line over undulating terrain until a clutch was disengaged which would initiate a gentle turn. Pulling on the brake lever would slow or stop the undriven track for tighter turns.

 

Last year I spent the morning driving a turreted 432 and got the impression that it had just a diff and a pair of brakes to slow the tracks?? The slightest change in ground conditions or camber resulted in an unplanned turn and a quick tug on a brake lever giving a feeling of instability. I appreciate that having the turret didn't do the C of G any favours but it still seemed very nervous.

 

The question is, what steering systems do other tracked MVs use?

[Adrian Barrell]

There are three basic systems in use.

 

1. Clutch/brake. Much as you described, common in plant and some tanks, particularly Russian but also Valentine.

 

2. Controlled differential. Like it says, a differential controlled by brakes, one each side. Quite common, though wasteful of power. Used by Stuart, Sherman, FV430 series etc.

 

3. Regenerative. This is a more complex system often known as triple differential. This uses a train of gears, often epicyclics and controlled by brakes. Little power is wasted because each track is driven but at a different speed, the ratio varying with the selected gear. Most common is the Merritt Brown as used in Churchill, Cromwell, Centurion etc.

 

There are and have been other systems in use, track warping, Wilson epicyclic steering units etc etc but they are all variations on a theme.

Edited February 3, 2010 by Adrian Barrell

[radiomike7]

Thanks Adrian, I might have known you would be the one to respond. I will look up the Merritt Brown system. :readbook:

[snowtracdave]

The Snow Trac uses a system called the Variator......another take on the controlled differential . Confuses a few people when they find a steering wheel in the cabin rather than sticks .

[The Bedford Boys]

Universal carriers use quite and interesting system whereby a steering wheel and "two stage" system is employed to steer the vehicle. Small steering adjustments are made by "warping" the tracks, but when more "lock" is applied to the steering wheel, the brakes on that side are pulled on, slewing the vehicle around. Great fun.

[radiomike7]

Universal carriers use quite and interesting system whereby a steering wheel and "two stage" system is employed to steer the vehicle. Small steering adjustments are made by "warping" the tracks, but when more "lock" is applied to the steering wheel, the brakes on that side are pulled on, slewing the vehicle around. Great fun.

 

A good friend of mine drove a Universal Carrier + trailer in WW2 and told me about the track warping system. He called the steering device a 'swiggle tree' if I remember correctly.

[Adrian Barrell]

A good friend of mine drove a Universal Carrier + trailer in WW2 and told me about the track warping system. He called the steering device a 'swiggle tree' if I remember correctly.

 

More likely swingle tree which is a term from horse and carriage use. It is the bar that links two horses together to the cart (or something like that!).

 

In the carrier, the steering rods work on a plate that loosely resembles a swingle tree in shape.

[Stone]

In 2S1s and other MTLB/MTLBu derivatives they have a two-stage system - first stage is switching from high to low ratio in the final drives (gentle turn) and second stage is with a track brake (harder turn). As the gentle turns are effectively digital it can be a bumpy ride!

 

Stone

[Adrian Barrell]

That's very similar in principal to the Wilson steering units as used in Covenanter, Crusader and Cavalier, though being British, it's a very complicated system controlled by air pressure.

 

Stick forward = high range through an epicyclic

First stage back = neutral

Second stage back = low range through an epicyclic

Third stage back = brake on and locked track

 

All accomplished to much hissing of air!

[AlienFTM]

Thanks Adrian, I might have known you would be the one to respond. I will look up the Merritt Brown system. :readbook:

 

You may enjoy this:

 

http://www.royaltankregiment.com/9_RTR/appendices/Appx%205%20The%20Churchill%20Tank.htm

 

About halfway down it discusses the Churchill's Merritt-Brown gearbox and how it drove the designer crazy. In the 1970s, we were still being told that people still did know why, with neutral gear selected, pulling a stck would cause the tracks to go in opposite directions and turn the tank within its own length. (It required high revs.)

 

The link suggests that the neutral turn was to be avoided. By my time, it was taught and there was even a hand signal for it.

[Adrian Barrell]

They were having fun with you or perhaps it had gone into folklore! It was designed to have such a function and is described in detail in all the wartime manuals.

 

A full description of the gearbox and all its functions is a part of most relevant Service Instruction Books of the time.

 

The advice to avoid the neutral steer function only relates to when driving on roads. In other words, not to attempt a neutral turn whilst rolling forwards.

Edited February 4, 2010 by Adrian Barrell

[AlienFTM]

They were having fun with you or perhaps it had gone into folklore! It was designed to have such a function and is described in detail in all the wartime manuals.

 

A full description of the gearbox and all its functions is a part of most relevant Service Instruction Books of the time.

 

The advice to avoid the neutral steer function only relates to when driving on roads. In other words, not to attempt a neutral turn whilst rolling forwards.

 

Evidently folklore. It seems that everybody in the RAC has heard the story. As to your last paragraph, I agree: I was commenting on the comment in the 9RTR link. Like I said, it was certainly on the books in my day and doing the turn with any way on makes no sense.

[Adrian Barrell]

I was commenting on the comment in the 9RTR link. Like I said, it was certainly on the books in my day and doing the turn with any way on makes no sense.

 

 

Understood. I bet it would be interesting though! I have never felt the urge to try it....

[harry7134]

One situation when the neutral turn ability comes into its own is when connecting the "A" frame from a casualty on to the Cent ARV. The pins used are a tight fit in the holes at the ends of the arms , and have a "twist to lock" function.

The two arms are put on the casualty (easy), and then the other ends of the arms fitted to the butterfly. which swivels, (not so easy).

Then this triangle has to be lifted to the correct height and held up, generally by a wooden block, again not easy.

Then comes the fun part, trying to get the towing eye on the ARV to mate up with the butterfly. One method is to stand on the ARV spade and use a long extension microphone lead to guide the driver. The machined pin always refuses to go all the way home and generally sticks about half way in. Now comes the neutral turn, or more correctly the driver is told to "wiggle", ie engage neutral and handbrake, and gently pull steering tillers one at a time , making the tank do a wiggle. The pin will then eventually drop in, but often still need persuading with hammer and anchor pin to turn. Some experience is needed knowing just how hard to engage the handbrake to allow the tank to move enough without it rolling away.

One trick I learn`t off an old Reccy Mech was to put a "Torch Right Angled Head" on each of the casualty`s mudguards, facing forwards, and , if your ARV had mirrors fitted, these would give the driver aiming points for lining the vehicles before connecting.

[abn deuce]

One trick I learn`t off an old Reccy Mech was to put a "Torch Right Angled Head" on each of the casualty`s mudguards, facing forwards, and , if your ARV had mirrors fitted, these would give the driver aiming points for lining the vehicles before connecting.

Sounds like a good idea , one of those unwritten easy to try things that only seem to be passed by those that have been there to those that ask and keep their minds open .

[ArtistsRifles]

Not sure how you describe the system in the BMP-1/PT-90. I guess it's probably the first in Adrian's list although it is nothing like as described by RadioMike in the first post. Neither is it like driving a 432!.

Steering is done by a tiller bar, not levers. There is a separate brake pedal to stop the vehicle rather than having to pull back on both sides of the tiller mechanism. With high ratio selected you get progressive steering - i.e. the harder you press down one side of the tiller bar the tighter the vehicle turns until at full pressure it pivots on the centre point of the inside track. In Low ratio you only get the option of the hard turn, progressive is disabled.

Driving in high ration is like driving a conventional vehicle. You have the normal clutch, brake and accelerator and pressing on the tiller results in the same action as turning a steering wheel.

I was used to driving 432's and it took a while to get used to the system. :-)