Tanks - tracked vehicles driving and handling

[lex__1 422]

The problem with CVR-6e is Bobcat and IFV-6с Panther.
Rollers and caterpillar tracks do not rotate, after some collisions.
With other heavy equipment, I could not reproduce this problem.

 

It is not recommended to watch a video, for people with a weak nervous system and bad vestibular apparatus :)

 

 

Bug report

[scotg 204]

@lex__1 That is insane! I was furious on your behalf until the launch, when I started laughing my butt off. Looks like it's headed to... Argentina?

[R3vo 2654]

9 hours ago, lex__1 said:

The problem with CVR-6e is Bobcat and IFV-6с Panther.
Rollers and caterpillar tracks do not rotate, after some collisions.
With other heavy equipment, I could not reproduce this problem.

 

It is not recommended to watch a video, for people with a weak nervous system and bad vestibular apparatus :)

 

 

Bug report

 

Oh man. I can't stop laughing. BIS is launching tanks into space again :D

[Tankbuster 1746]

10 hours ago, lex__1 said:

The problem with CVR-6e is Bobcat and IFV-6с Panther.
Rollers and caterpillar tracks do not rotate, after some collisions.
With other heavy equipment, I could not reproduce this problem.

 

It is not recommended to watch a video, for people with a weak nervous system and bad vestibular apparatus :)

 

 

Bug report

 

Did you try with the (apparently named by a toddler) Slammer? It has the same chassis as the Bobcat and Panther.

[Strike_NOR 898]

12 hours ago, lex__1 said:

It is not recommended to watch a video, for people with a weak nervous system and bad vestibular apparatus :)

 

Haters will say it is unrealistic.

 

Just like Jetfuel can't melt steel beams, I think we need a new phrase....

 

Poles can't fling steel beasts! (Must be the government finding new ways to ship vehicles overseas).

[lex__1 422]

1 hour ago, Tankbuster said:

Did you try with the (apparently named by a toddler) Slammer? It has the same chassis as the Bobcat and Panther.

 

12 hours ago, lex__1 said:

With other heavy equipment, I could not reproduce this problem.

[oukej 2911]

Nice vid ;) We're aware of this one (abrupt acceleration, tracks doing weird stuff, loss of control).

[Beagle 684]

19 hours ago, Strike_NOR said:

 

Hmmm. This could actually be a feature. If there is absolutely no recoil then I think it's a bug. But HE ammunition generally has lower muzzle velocity because it's more sensitive to the heavy acceleration in the barrel. Less acceleration = less recoil. (not factoring in weight here.)

Recoil is defined by muzzle velocity and projectile weight, not bei muzzle velocity alone. Multi Purpose Warheads have a weight of 11,4 - 13,5 kg at 1200-1400m/s while tungsten or DU penetrators have a weight of 8-10 Kg at 1600-1700 m/s. The result is a comparable amount of recoil.

[Strike_NOR 898]

54 minutes ago, Beagle said:

Recoil is defined by muzzle velocity and projectile weight, not bei muzzle velocity alone. Multi Purpose Warheads have a weight of 11,4 - 13,5 kg at 1200-1400m/s while tungsten or DU penetrators have a weight of 8-10 Kg at 1600-1700 m/s. The result is a comparable amount of recoil.

 

Whoa whoa, stop right there :) It would be better to just hear from the Devs how the recoil is calculated and transferred into a force acting on the vehicle. If it is related to projectile mass and velocity, then all is fine. If it is only related to velocity, well that may be why we are seeing different amounts of recoil. It may just be that they forgot to tweak the HE magazine values.

 

Either way, before debunking my statement and settling on "fact" you should find a more credible source. Like a specific gun's actual ammunition types and their respective muzzle velocities and projectile (not shell/cartridge) weight. Just claiming that MP ammunition weighs 11,4 to 13,5 kg is very general. Putting some quick maths into your examples we get Ke=1/2*m*v^2 = about 8Megajoules for the HE shell and 10Megajoules for the APFSDS. That's a considerable difference.. Using your examples :)

 

Technically we would need the correct mass and muzzle velocity for say.... a popular 120mm tank gun.

 

So to prove how far I'm willing to go to support my point (and possible also keep realism in ArmA3 :) )... I dug up some info online.

 

Take the Rheinmetall M256 120mm Smoothbore.

 

The M829 APFSDS Penetrating Rod (with sabot) weighs 9kg. It's muzzle velocity is 1575m/s. This amounts to ~11,2 Megajoules.

 

The M830 HEAT-MP-T Projectile weighs 11.4 kg. It's muzzle velocity is 1140m/s. This amounts to ~7,4 Megajoules.

 

So we have a difference of about 3,8 Megajoules, or easier to understand 40% difference in Kinetic energy.

 

 

I hope this clears things up. But this only goes for the real life 120mm Rheinmetall Smoothbore with exactly the M829 APFSDS and M830 HEAT-MP-T as an example. It does not portray recoil for any of the tanks ingame.

 

Therefore I want the devs to comment on it :) Please feel free to use my calculations, they are not copyrighted :p

[Beagle 684]

Hello Strike_NOR, what I can tell from personal experience is, that you won't notice a difference between a practice round, a HEAT or a KE when fired as an observer of a tank Shooting regarding the vehicles physical reaction. In a real tank the recoil is to a large part absorbed by the backwards gun travel. It would also make a big difference if the gun is in 0/180 degree or 90/270degree position.

 

By the way it would be very nice if it was possible to add the barrel going up after the shot for reloading.

 

 

This charts here correlates with the data we were given in my active service times, but we did not have a free choice of ammunition, only DM 33 and DM 12: http://www.kotsch88.de/m_120_mm.htm

[Strike_NOR 898]

Hello @Beagle! The stuff you are talking about such as the recoil dampener, turret bushings, chassis, suspension and finally tracks are all contributing to reducing the "felt recoil". You are absolutely right, but I can't for the life of me see how this results in the exact same appearance of tank recoil. I mean, please correct me if I got this wrong, but the whole point of recoil is to spread the force over a greater period of time, namely the "impulse". The mass of the tank is so huge, that if the entire recoil was absorbed in an instant (i.e if the tank does not have a recoil dampener) it would be an extreme load on the gun mounts, turret, chassis and crew. Why? Because the tank wouldn't really move that far back due to the mass and ground friction, so all the force would be distributed instantly.

 

It's essentially the same reason that modern cars have "crumple zones" to absorb high-energy crashes better. Old cars were almost like solid steel. Crashing at 70km/h meant that the entire momentum of the vehicle was experienced in an instant. The following G forces applied to the people in the car would kill them, contrary to modern cars where the car would systematically collapse over time so that the net force of the crash is distributed, which means a lower G-force.

 

So why am I still bothering you guys with this? Well.. If the tank is exposed to let's say 10 Megajoules of recoil, I will make a rough estimation of what happens:

 

First the barrel slides backwards (this is already happening a tiny bit while the projectile is still leaving the barrel), compressing the gas/hydro in the dampener. This is the major feature of the weapon that reduces the impulse, newton said the recoil is still 10 Megajoules, the energy has to convert into something. Some energy is converted to heat followed by the rise of pressure in the hydropneumatic dampener, but not enough to significantly matter for this thought experiment. During the dampening, the force has now been evenly transferred to the gun mounts, turret, turret ring, chassis, which are all pretty rigid. The next part of dampening happens in the suspension, energy is stored in springs and shocks which finally transfer some final force to the tracks. The tracks pose some serious friction due to the weight of the tank, and normally the final energy is spent here. The stored energy in the suspension now lifts the tank back to its resting state, and the gun dampening system returns the barrel back to firing position. 

 

This is what I assume goes on, you know,  kurzgesagt! 

 

So how on earth is say 30-40% less force applied to this system, going to impact the tank just as much?! The only reasoning I can think of is that the recoil dampener system knows what ammo type you are using and adjusts the dampener pressure accordingly to achieve the same impulse. 

 

It would be just like saying that crashing the modern car from my example above in 100 km/h and 60 km/h will damage it just as much!?!?

 

As a final point here's a video from the glory days where people had more imagination than respect for safety :P This (Ironically named) "High Impulse Weapon System" (Should be named low impulse because of recoil reduction :P) Is shoulder fired 76mm projectile.

Now imagine firing that with a shell that had less kinetic energy. You would simply NOT bounce back as hard. Or else I give up entirely on this Endeavour, or quest for the truth behind Tank Recoil simulation in ArmA3 :p

 

Now I am only talking from a physical-theoretical standpoint, but I must be onto something right? 

 

Still, the devs remain silent. Maybe I've scared them off... :p No wonder.... *cries in physics*

[danny96 80]

One question straight for the developers - as a reaction to your newly made smooth driving from commanding position.. wouldn't be possible to also make it for gunner? Like if you set manual fire on and you switch to cannon you would be able to also aim with it ?

[R3vo 2654]

4 minutes ago, danny96 said:

One question straight for the developers - as a reaction to your newly made smooth driving from commanding position.. wouldn't be possible to also make it for gunner? Like if you set manual fire on and you switch to cannon you would be able to also aim with it ?

You can already do that as long as you start as commander of the tank. Switch to the gunner position then and you'll be able to drive and shoot.

[danny96 80]

1 minute ago, R3vo said:

You can already do that as long as you start as commander of the tank. Switch to the gunner position then and you'll be able to drive and shoot.

Didn't realise that. That is pretty neat!  

[lionhawk123 20]

10 hours ago, Strike_NOR said:

 

Whoa whoa, stop right there :) It would be better to just hear from the Devs how the recoil is calculated and transferred into a force acting on the vehicle. If it is related to projectile mass and velocity, then all is fine. If it is only related to velocity, well that may be why we are seeing different amounts of recoil. It may just be that they forgot to tweak the HE magazine values.

 

Either way, before debunking my statement and settling on "fact" you should find a more credible source. Like a specific gun's actual ammunition types and their respective muzzle velocities and projectile (not shell/cartridge) weight. Just claiming that MP ammunition weighs 11,4 to 13,5 kg is very general. Putting some quick maths into your examples we get Ke=1/2*m*v^2 = about 8Megajoules for the HE shell and 10Megajoules for the APFSDS. That's a considerable difference.. Using your examples :)

 

Technically we would need the correct mass and muzzle velocity for say.... a popular 120mm tank gun.

 

So to prove how far I'm willing to go to support my point (and possible also keep realism in ArmA3 :) )... I dug up some info online.

 

Take the Rheinmetall M256 120mm Smoothbore.

 

The M829 APFSDS Penetrating Rod (with sabot) weighs 9kg. It's muzzle velocity is 1575m/s. This amounts to ~11,2 Megajoules.

 

The M830 HEAT-MP-T Projectile weighs 11.4 kg. It's muzzle velocity is 1140m/s. This amounts to ~7,4 Megajoules.

 

So we have a difference of about 3,8 Megajoules, or easier to understand 40% difference in Kinetic energy.

 

 

I hope this clears things up. But this only goes for the real life 120mm Rheinmetall Smoothbore with exactly the M829 APFSDS and M830 HEAT-MP-T as an example. It does not portray recoil for any of the tanks ingame.

 

Therefore I want the devs to comment on it :) Please feel free to use my calculations, they are not copyrighted :p

 

This is not the calculation that should be used to determine the amount of force exerted on the tank. An object's momentum is NOT equal to its kinetic energy. And kinetic energy is not inherently related to force (as we see in your example. Ke=1/2mv^2 does not take into consideration the acceleration of the object, so F=ma does not apply.) What you want to calculate is the change in momentum of the shell corresponding to whichever ammo type you are considering, P=mv where P is momentum, m is mass, and v is velocity. Velocity should be the value immediately after firing (or as close to immediate as you can get) and m should be total mass of the projectile immediately after firing. If the round is a sabot, this calculation should INCLUDE the mass of the sabot AND the penetrator (I can see somebody mixing that up int he near future.)

 

The change in the momentum of the shell (which, assuming the tank is not moving as it fires, should just be Pf - Pi= Pf) will be the same as the change in momentum of the tank. So, you can then apply P=mv to the tank, except in this case you must consider the CHANGE in momentum of the tank. So instead of P=mv you will have deltaP=m deltav. (In other words, the Pf of the shell equals the mass of the tank times the change in the tank's velocity.) Of course, the force exerted by the round being fired is not applied to the entire tank at once but just the recoil assembly, so keep that in mind if your calculation says your tank should jump a few meters.

 

That is all. c:

[Beagle 684]

7 hours ago, Strike_NOR said:

Hello @Beagle! The stuff you are talking about such as the recoil dampener, turret bushings, chassis, suspension and finally tracks are all contributing to reducing the "felt recoil". You are absolutely right, but I can't for the life of me see how this results in the exact same appearance of tank recoil. I mean, please correct me if I got this wrong, but the whole point of recoil is to spread the force over a greater period of time, namely the "impulse". The mass of the tank is so huge, that if the entire recoil was absorbed in an instant (i.e if the tank does not have a recoil dampener) it would be an extreme load on the gun mounts, turret, chassis and crew. Why? Because the tank wouldn't really move that far back due to the mass and ground friction, so all the force would be distributed instantly.

 

It's essentially the same reason that modern cars have "crumple zones" to absorb high-energy crashes better. Old cars were almost like solid steel. Crashing at 70km/h meant that the entire momentum of the vehicle was experienced in an instant. The following G forces applied to the people in the car would kill them, contrary to modern cars where the car would systematically collapse over time so that the net force of the crash is distributed, which means a lower G-force.

 

So why am I still bothering you guys with this? Well.. If the tank is exposed to let's say 10 Megajoules of recoil, I will make a rough estimation of what happens:

 

First the barrel slides backwards (this is already happening a tiny bit while the projectile is still leaving the barrel), compressing the gas/hydro in the dampener. This is the major feature of the weapon that reduces the impulse, newton said the recoil is still 10 Megajoules, the energy has to convert into something. Some energy is converted to heat followed by the rise of pressure in the hydropneumatic dampener, but not enough to significantly matter for this thought experiment. During the dampening, the force has now been evenly transferred to the gun mounts, turret, turret ring, chassis, which are all pretty rigid. The next part of dampening happens in the suspension, energy is stored in springs and shocks which finally transfer some final force to the tracks. The tracks pose some serious friction due to the weight of the tank, and normally the final energy is spent here. The stored energy in the suspension now lifts the tank back to its resting state, and the gun dampening system returns the barrel back to firing position. 

 

This is what I assume goes on, you know,  kurzgesagt! 

 

So how on earth is say 30-40% less force applied to this system, going to impact the tank just as much?! The only reasoning I can think of is that the recoil dampener system knows what ammo type you are using and adjusts the dampener pressure accordingly to achieve the same impulse. 

 

It would be just like saying that crashing the modern car from my example above in 100 km/h and 60 km/h will damage it just as much!?!?

 

As a final point here's a video from the glory days where people had more imagination than respect for safety :P This (Ironically named) "High Impulse Weapon System" (Should be named low impulse because of recoil reduction :P) Is shoulder fired 76mm projectile.

Now imagine firing that with a shell that had less kinetic energy. You would simply NOT bounce back as hard. Or else I give up entirely on this Endeavour, or quest for the truth behind Tank Recoil simulation in ArmA3 :p

 

Now I am only talking from a physical-theoretical standpoint, but I must be onto something right? 

 

Still, the devs remain silent. Maybe I've scared them off... :p No wonder.... *cries in physics*

No need to get all academic about that Issue. All I sad was: as an Observer you won't be able to tell what kind of ammunition is shot. In short words: no recoil action for the 120mm HE-T is a bug, not a feature.

[Strike_NOR 898]

On 10/20/2017 at 5:51 AM, Beagle said:

no recoil action for the 120mm HE-T is a bug, not a feature.

 

Well. If you look ingame on devbranch there is recoil so your point is invalid. The question you should be asking is essentially, is there enough recoil? There is just slightly less recoil for the HE-T than the APFSDS, which by all means seem perfectly coherent with my calculations. Others have also claimed that the "HE does not have recoil, it must be a bug". No recoil literally means the tank does not move at all when firing HE.

 

It absolutely does ingame. That's why I wanted to get into the depth of this problem and see if it actually needs to be changed in order to reflect real life, or it should remain as is because the physics adds up.

 

On 10/20/2017 at 2:01 AM, lionhawk123 said:

This is not the calculation that should be used to determine the amount of force exerted on the tank.

Thanks, you are right it's been a decade since I did this stuff in school. Clearly I have forgotten some things. What you say about momentum is true, so whatever momentum is gained by the shell should in turn also be applied to the tank in an equal and opposite reaction. Given the tank's mass it won't be as dramatic as if the cannon was "hanging" in free space, In which case the mass of the cannon is only a fraction of the tanks total mass.

 

But my point still stands doesn't it? That if you have slightly more mass accelerated to a lot less velocity, the momentum becomes lower, and as such the force exerted on the tank also becomes smaller.

 

 

 

Edit:

 

I did some tests with Kuma in devbranch now. Set up a simple measurement system with two striped poles. 

 

FYI the tank is placed on perfectly flat surface, so I have not included a "reference picture from stationary tank". See link below. The recoil difference remarkably resembles my rough estimation of difference in energy. But still, we know nothing about how it is actually calculated and applied ingame. But it seems to match real life performance of the shells of an equivalent weapon. The screenshot is taken during slowmotion at the maximum compression of the shocks.

 

https://imgur.com/a/iro1Y

 

 

Edit 2:

 

As @lionhawk123 pointed out, I have used the wrong formula to calculate recoil. Recoil velocity comes from conservation of momentum.

 

In the previous example of a 9kg sabot+rod travelling at 1,575m/s at the muzzle, versus a 11,4kg HEAT-MP shell travelling at 1,140m/s at the barrel, with the barrel alone being the "countermass" to the projectile, I get the following results.

 

M256 weight (only cannon, not mount) = 1190 kg

Sabot recoil velocity = 11,9m/s (seems plausible)

HEAT-MP recoil velocity      = 10,9m/s (quite similar)

 

In terms of percentage increase in recoil velocity, we get a 9,17% increase in recoil velocity. This means that in the 1st second after firing a sabot round, the cannon would move 1 meter further back than if HEAT-MP was used.

 

However, I found that if the entire mass of the tank is included (62 tons), the tank would have a recoil velocity difference of about 0.01 m/s, which still amounts to a roughly 9% increase in velocity when using sabot.

 

If we were to stop right here, I'd say that @Beagle's observations from firing experience would be quite accurate. The average human looking at a firing tank, taking into the account of the pressure shock, vibrations and all interfering with the visual observation at the time of firing, would have serious difficulty in telling the difference between recoil from a Sabot or HEAT-MP shell. 10% is not very much, and a lot less than my incorrect 30-40% difference in Kinetic Energy calculations.

 

A major missing part of the equation is "second recoil" that comes from gases exiting the barrel, like a rocket engine, pushing the gun backwards. This recoil tends to be greater than the one of the projectile (in some cases 30% higher - which is why muzzle brakes are so popular).

 

To shed some light on this the charge weight of the sabot is 7,9 kg, against the much lighter 5,4 kg charge of the HEAT-MP a 47,5% difference in charge mass.

 

To be honest, I am giving up right here. I don't have time to get into computed fluid dynamics, or bernoulli's laws or any of that. The momentum change of pressurized gas leaving the barrel between the two types of ammunition is bordering rocket science. We're talking about the area of a 120mm cannon barrel acting as a rocket nozzle accelerating gas at god knows what speed, density and mass out of a barrel with varying charge.

 

Either way, what @x3kj says is a good point, and from a realistic point of view wrong. However, ArmA is a game that needs to be moddable, and adding realistic calculations to recoil, may pose problems for unrealistic mods. Say I were to make a walking Mech with a 250mm Gauss gun that fires shots at 3000m/s, well... the mech is probably gonna do multiple backflips and make the mod impossible. So you would have to "cheat" the other way and make the player think the weapon is a 250mm gun, but rather put a much smaller shell/speed in the config to attain usable recoil for your addon.

 

A recoil modifier may be exactly the thing that makes it EASY to make/tweak mods with no understanding/respect for physics. While a better recoil calculation make it easier to recreate realistic properties of real world weapons.

[x3kj 1247]

Recoil force onto vehicles thus far was proportional to their hit value (=damage). They never gave us any formula to calculate it. Recently they introduced the muzzleimpulse modifier, with which the automatically calculated hit-value dependant. It's still a completely backwards method, as i've described a few posts earlier.

[scotg 204]

On 10/19/2017 at 4:52 AM, oukej said:

Nice vid ;) We're aware of this one (abrupt acceleration, tracks doing weird stuff, loss of control).

Not to throw shade, but nothing in this statement implies exploring solutions. :-\

Offhand, is there a thread covering other aspects of tanking besides driving/handling, like crew animations, turning in/out, or firing modes? Should we just post discussions or questions about these issues here?

[lionhawk123 20]

14 hours ago, Strike_NOR said:

But my point still stands doesn't it? That if you have slightly more mass accelerated to a lot less velocity, the momentum becomes lower, and as such the force exerted on the tank also becomes smaller.

 

I don't want to say you are right or wrong, because I haven't done any of these tests myself. I would assume that the HE-T shell has a lower velocity because it has a higher mass, although this doesn't really include any consideration of the propellant used, how much of it was used, how efficient it is, etc. So, it's best to say we don't really know how much recoil SHOULD be there without more information on how much the chemical reaction of the propellant (and subsequent explosion) changes the momentum of the shell being fired.

 

I can only assume that there would be a marginal difference between the APFSDS-T and the HE-T, but I really can't say for sure without much more information to work with.

[lex__1 422]

The jet stream of the gases of the burnt gunpowder creates a rollback of the barrel. For APFSDS it is important to get a high speed - at least 1600 km / h. Perhaps APFSDS uses more powder charge, more gases burnt gunpowder, more jet stream of gases, more inertia on the barrel.
HE does not need high speed, uses less charge of gunpowder, less gases of burnt gunpowder, less reactive gas jet, less inertia on the barrel.

 

 

 

[R3vo 2654]

Marid and Marshal handle much better now. But I noticed and issue with turning out/in.

 

The units turn out quicker now than the hatches open, both on the Marid and Marshal, maybe even other vehicles.

[scotg 204]

2 hours ago, R3vo said:

The units turn out quicker now than the hatches open, both on the Marid and Marshal, maybe even other vehicles.

I noticed this in some BI tanks a few months ago. I wanted to bring up issues like this, but I hesitate because it's not exactly within the scope of this thread: tracked vehicle driving and handling. However, I think this could better serve as a general tank improvement thread, if they broaden the topic. 

[R3vo 2654]

4 minutes ago, scotg said:

I noticed this in some BI tanks a few months ago. I wanted to bring up issues like this, but I hesitate because it's not exactly within the scope of this thread: tracked vehicle driving and handling. However, I think this could better serve as a general tank improvement thread, if they broaden the topic. 

It's funny you say that. I actually wanted to ask a dev whether they could open a "General Tank Feedback" thread. Because there are quite a few things which could be fixed but do no fit into this thread nor the Tank DLC Feedback one.

[M. Glade 524]

Make ramps have the ability to be opened on APCs. Happy with the sound overhaul!

 

That is all.