Gyrostabilizers

[Marlow]

Can anyone provide any technical details on U.S. gyrostabilizers? I did a search, and only came up with why they are either overrepresented (i.e. on every Sherman), or undermodeled (not as effective as they should be), but nothing about how they worked. Also, if they were effective, why did the tankers allegedly disconnect them? If I was facing German heavies, I would want any advantage I could get. Could it have something to do with inexperienced crews and a lack of familiarity with new technology? Did the percentage of tankers using gyros increase as the war went on?

[Guest Big Time Software]

Oh boy, you sure know how to pick an easy topic to discuss

My knowledge of the mechanics is rather small, but the principle is easy to understand. Part of the device (the gyro) is designed to remain "level" with the Earth's surface, no matter what position its container (in this case a tank) is positioned. Electric sensors around the gyro then make adjustments to the gun's position in order to keep it "true" while the vehicle bumps and moves over terrain. In practical terms, the gun does not bounce around with the tank, but instead remains pointed at the target. If you have ever seen a steadycam in action, the principle is the same.

This is, of course, all theory. The devices in today's tanks are damned near perfect as far as I know, but of course the ones used in WWII were much more primative and therefore did not result in "perfect" results. In fact, there were various different gyrostabilizers used by the US, with the later ones (1944/45) being noticably better than the earlier ones (1943).

In theory all Shermans and all 37mm armed vehicles (M8 and M3/M5 Stuarts) had gyrostablizers. However, through abuse, missuess, and "sabotage" they were not always function. The earlier gyro systems were apparently rather fragile, but the later ones were pretty robust.

As for crews disconnecting them, there is considerable debate as to how many in fact did this. There are no hard numbers, but we suspect the percentage was rather low. But like many things coming out of war, the guys that complain the loudest generally got more attention. So if 1 in 10 tankers disconnected the device, and loudly said "this thing sucks!!" people tend to attribute these feelings to more than just the one guy.

Some of the guys disconnecting their gyros were probably ones that had problems with the earlier models, and therefore had an unshakable distrust of the thing. Of course, undertrained crews might also have listened to some grumbling vets, and in an attempt to increase there chances of survival, listened and disconnected the thing. These are just theories of ours, but they make sense.

As for CM, we were sorta forced to make the functional in elidgable vehicles all the time, instead of most of them most of the time. To partly compensate for this we only give US vehicles with gyros a very small accuracy bonus when on the move. When the tank is still, there is no bonus at all. And since the best method of engaging is when sitting still, the impact of gyros on the game is minimal.

Steve

[Marlow]

Thanks for the quick answer.

[Dittohead]

Don't forget that alot of the tanks that were knocked out, were able to be repaired and sent back into action. And an inoperable gyro did not render the tank non-combat ready and repairing it was not a priority. Plus as US tankers suffered excessive casualities many shermans were manned with very inexperienced crews as the war went on. Most of their experience then was probably engaging infantry with large moving tank on tank battles a rarity.

[:USERNAME:]

Its really a servo system and would of course be susceprtible to drift, rise time and overshoot.

I HIGHLY doubt it would do anything if a unit was doing a "fast move". The main reason would be that a gunner would have a hard time keeping his head on the sight alone. I have read of people here thinking it would work on a hellcat while it was "getting air" off bumps in the ground! I doubt it could be that responsive. They worked well in slow rolling ships but would reach a limit in a tank across unpaved terrain. The best application was to make the coax MG keep the enmys heads down while closing in.

CM should model the effects as being slight and only when HUNTing or perhaps MOVE.

Lewis

[109 Gustav]

Gyros were disconnected because they made the gun harder to load. If you were moving across rough terrain, the gun would be staying level. However, to the loader, it would appear to be moving and shaking around, making it that much harder to load. One of the vehicles on this site http://www.kithobbyist.com/AFVInteriors/archive.html describes the gyrostabilizer. I'm too lazy to look it up, but I think it was in the article about the M10, or maybe the Chaffee. Probably in the archived vehicle articles.

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No one but the enemy will tell you what the enemy is going to do. No one but the enemy will ever teach you where you are weak. Only the enemy tells you where he is strong. And the rules of the game are what you can do to him and what you can stop him from doing to you. -Ender's Game

[Jeff Heidman]

Another thing to realize is that WW2 era gyros only stabilized in the vertical plane. They did not "track" the target horizontally.

Like Steve said, there is considerable questions about how often they were used, and how often they were used properly, and how often they were simply disconnected.

There is definitely a lack of documentation on the subject, but I have yet to see anything that would make me doubt the conventional wisdom that they were not used more often than they were.

Jeff Heidman

[Guest tero]

If the Sherman gets partial benefit on accuracy when firing on the move because of the gyrostabilizer shouldn't it also get partial penalty on reload time when firing on the move, because of the gyrostabilizer ?

[Guest machineman]

Did some poking around on the kithobbyist link of Gustav's (fascinating reading, BTW), should be sleeping, but machinery and all.. this was all I found on stabilization so far:

Chaffee:

"A US gun stabiliser system was installed and allowed some increased gun performance in elevation only, although most crews were not happy with the bouncing breech when the system was switched on and they were traveling over uneven ground."

Pershing:

"Interestingly, the M3 gun as fitted into the Pershing had no stabilization equipment, although the 105 howitzer support version of the vehicle, the M45, did have elevation stabilization. Perhaps Sherman crew's less than enthusiastic reports about the stabilizer in that AFV convinced the designers to forgo similar equipment in the M26 turret."

German:

"German orders were clear that there could be no firing on the move in WWII, the vehicle had to stop and shoot, then move on to another position if necessary. Stabilized sights would not reach German tankers in any quantity by the end of the war, which some claim put them at a disadvantage compared to the Sherman. But stabilized sights came with their own problems."

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"Environment is everything - The Lion may be king of the jungle, but you airlift him to Antartica, and he's just some Penguins bitch" - Dennis Miller

[Olle Petersson]

From what I've read in several sources, the main task for the stabilisers was to keep the gun pointed at the general area of the target. This way it took a bit less time to adjust the aim once the tank stopped to shoot.

The way to fight was to move ("hunt", in CM) and look for targets, since moving was a way to avoid being hit. Stationary tanks were sitting ducks.

Once a target was spotted the gun was pointed at it while the loader made sure the correct type of ammo was loaded.

When the gun was loaded and pointed at the target the driver hit the brakes. The gunner adjusted the aim and pressed (or was it pulled?) the trigger.

As soon as the shot went off the driver released the clutch and off they went while reloading and the TC gave corrections to the gunner, preparing the next shot.

This was the general practise for all sides, with or without stabiliser, and was retained into the 80ies when stabilisers had developed enough to allow not only shooting, but also actually hitting targets, while moving.

Read the WW2 veteran tanker's story posted here a couple of weeks ago.

How does this translate to CM?

Not very well, since the stop-fire-go tactic isn't modeled (or at least not visualised in the movies). The real effect of a stabiliser was that the time spent stationary was shorter (about 25% less) than without the gyro, while reloadtime was increased.

One possible workaround to tweak this into CMBO is to;

- have all vehicles keep moving during Hunt command, and don't stop until they run out of orders. (They're assumed to halt when firing, but this isn't shown on the film.)

- vehicles with gyro are more difficult to hit when they're hunting than vehicles without. This is a generalisation, but not the first detail of "realism" to be dropped in CM, and I don't mind.

- vehicles with gyro have a greater increase in reload time when moving than vehicles without.

- once reloading is done, vehicles with gyro get the shot off about one second faster than vehicles without (who'll need about 4sec after reloading).

For later versions of CM it would be cool to actually see the tanks hit the brakes to shoot and the jump off to avoid the return fire.

Cheers

Olle

[:USERNAME:]

<BLOCKQUOTE>quote:</font><HR>Originally posted by 109 Gustav:

Gyros were disconnected because they made the gun harder to load. If you were moving across rough terrain, the gun would be staying level.

<HR></BLOCKQUOTE>

Well its true that a bobbing breach is hard to load. But the gun is TRYING to stay at the last elevation.

The device more than likely was an closed loop type control system. The gyro gives a command error signal. This could be, lets say, 1 volt per 1 degree of elevation error. This command signal is sent to an amplifier that drives an electric motor attached to the elevation gears. The motor is calibrated to move a certain number of degrees or has a rotary pot on it that could close the loop. Optical encoders were not around so I would bet it was a rotary encoder.

Anyway potentiometers drift, servo systems overshoot, gyros get out of whack, AND a system like this would have "lag" time that could have been worse than a human closing the loop ;ie just anticipating the terrain coming up and elevationg/depressing the gun by hand. Heres an example: You are driving over undulating bumpy terrain and the gun/gyro is responding so that by the time you have reached the top of one crest, the gun is just getting level yet goes a little too far (this is overshoot) and the system takes time (lag) to then correct this overshoot. By this time, you are descending over the crest and the process starts again..

Crews might have found that they had to drive very slow (this is all acceleration driven) and decided that the thing is more trouble than it was worth for POINT target shooting. It might have been great for shooting at houses or infantry in treelines, etc. In other words, an area fire tool. I have read that it was used for MG fire on the move to get the range on a stationary tank with tracers but the shermnas would stop before firing AP rounds. This would work best for a 76mm sherman firing the coax 30 cal tracer.

As I have said, it worked for ships in slow rolling seas. It would just be dangerous in a fast moving vehicle because the breach would be counter responding to the accelerations and impulse loads the vehicle would be seeing. I wonder if it was a switchable device that could be turned on and off at will. It most certainly would have been something that could easily get out of tune.

Interesting topic and I hope BTS sees the logic in limiting the FAST MOVE benefit. Nowadays there are microcontrollers that allow critically damped systems and keeping a gun steady in all orientations is easier because sensors are better also. But the origional M1 was only stabilized in the elevation I believe.

Lewis

[This message has been edited by :USERNAME: (edited 11-10-2000).]

[Formerly Babra]

For those wondering how gyrostabilization works:

A gyroscope is any rotating body that exhibits two fundamental properties: gyroscopic inertia, or rigidity in space, and precession, the tilting of the axis at right angles to any force tending to alter the plane of rotation. These properties are inherent in all rotating bodies, including the earth itself. The term gyroscope is commonly applied to spherical, wheel-shaped, or disk-shaped bodies that are universally mounted to be free to rotate in any direction; they are used to demonstrate these properties or to indicate movements in space. A gyroscope that is constrained from moving around one axis other than the axis of rotation is sometimes called a gyrostat. In nearly all its practical applications, the gyroscope is constrained or controlled this way, and the prefix gyro is customarily added to the name of the application, as, for instance, gyrocompass, gyrostabilizer, and gyropilot.

Gyroscopic inertia is the rigidity in space of a gyroscope. It is a consequence of Newton's first law of motion which states that a body tends to continue in its state of rest or uniform motion unless subject to outside forces. Thus, the wheel of a gyroscope, when started spinning, tends to continue to rotate in the same plane about the same axis in space. An example of this tendency is a spinning top, which has freedom about two axes in addition to the spinning axis. Another example is a rifle bullet that, because it spins or revolves in flight, exhibits gyroscopic inertia, tending to maintain a straighter line of flight than it would if not rotating. Rigidity in space can best be demonstrated, however, by a model gyroscope consisting of a flywheel supported in rings in such a way that the axle of the flywheel can assume any angle in space. When the flywheel is spinning, the model can be moved about, tipped, or turned at the will of the demonstrator, but the flywheel will maintain its original plane of rotation as long as it continues to spin with sufficient velocity to overcome the friction with its supporting bearings. Gyroscopes constitute an important part of automatic-navigation or inertial-guidance systems in aircraft, spacecraft, guided missiles, rockets, and ships and submarines.

In these systems, inertial-guidance instruments comprise gyroscopes and accelerometers that continuously calculate exact speed and direction of the craft in motion. These signals are fed into a computer, which records and compensates for course aberrations. The most advanced research craft and missiles also obtain guidance from so-called laser gyros, which are not really inertial devices but instead measure changes in counterrotating beams of laser light caused by changes in craft direction. Another advanced system, called the electrically suspended gyro, uses a hollow beryllium sphere suspended in a magnetic cradle; fiber-optic systems are also being developed.

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Sounds like 100% weapons-grade Balonium to me.