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Vehicle Engine can't rev up if vehicle faces resistance to movement
Acknowledged, WishlistPublic

Description

The engine of the PhysX simulation cant increase rpm if your vehicle has some form of resistance to it's movement. Resistance means high vehicle mass, an incline/hill, or a physical object in it's path.
Mostly affected by this are tanks because of their high mass/movement resistance, but also wheeled APC's. It severely limits offroad capability. Cars are only affected if there is an object blocking them because of their high power/weight ratio compared to tanks.

The reason for this is, because the clutch simulated in vehicle PhysX seems to be hard-tied to the controlls for throttle. As soon as you apply any form of throttle the clutch seems to be closed. Therefore, the engine can't rev up to produce torque.
The only torque the vehicle can use for starting it's movement is therefore the torque at engine idle rpm, which is close to 0.

To solve this issue the closing of the clutch has to be delayed by some time after the inital application of throttle. A delay of 0.25 - 1.0s should be sufficient. Ideally (to simulate use of real clutch) the clutch should close lineary from 0 to 1 over a time period of x (0.5-1s might be a good start).

Edit:
I guess i was wrong to say the operation of the clutch is properly simulated with physx. I did more reasearch on this topic and started a topic on the nvidia physx forum.

It seems to me as if the characteristics of the physx clutch system are responsible for this problem. In case you stand still and give thrust the resistance produced by the clutch can be so high that any acceleration of the engine is prevented. Its current function is, that it is closed when wheel-rotationspeed = 0, and opens once wheel-rotationspeed (gearratio factored in) approaches engine-rotationspeed. Basically the inverse of what you want: Half-opened when wheel-rotationspeed is 0 and fully closed once wheel-rotationspeed is increased. Here is the topic https://devtalk.nvidia.com/default/topic/764824/physx-and-physics-modeling/clutch-strength-question/ [^]
(my posts are hidden unfortunately, here is a picture [4mb] with all the text http://abload.de/img/compiledeqsy5.jpg)

Since i have not received any further answer from Nvidia i think they just ignored it. Maybe it would help if BIS Devs contact Nvidia directly rather then some random dude complaining about unrealistic Simulation on their badly moderated forum.

Details

Legacy ID
2932316539
Severity
None
Resolution
Open
Reproducibility
Always
Category
Game Physics
Steps To Reproduce

Try to drive up a hill in a tank in reverse

Or drive on a very steep hill with a tank in forward, completely stop and try to move on.

Additional Information

For Tank forwardmovement this issue is partially reduced by fake gears but not completely removed. Fake Gears produces servere stuttering at slow speeds (see http://feedback.arma3.com/view.php?id=19182) and nasty audio problems (especially when turning).

The stuttering during turning can also cause the game to feel as if it is dropping frames very badly, but in reality it's the jerky movement of the vehicle, not the frames

Event Timeline

Fennek edited Steps To Reproduce. (Show Details)Jun 12 2014, 12:42 PM
Fennek edited Additional Information. (Show Details)
Fennek set Category to Game Physics.
Fennek set Reproducibility to Always.
Fennek set Severity to None.
Fennek set Resolution to Open.
Fennek set Legacy ID to 2932316539.May 7 2016, 6:45 PM
R3vo added a subscriber: R3vo.May 7 2016, 6:45 PM
R3vo added a comment.Jun 12 2014, 6:45 PM

Upvoted!

A proper clutch simulation is badly needed, driving tanks at low speeds is a pain and feels, in addition absolutely unrealistic.

kind regards

R3vo

Thanks for this accurate description of what feels wrong about difficult terrain mobility of vehicles.

Fennek added a subscriber: Fennek.May 7 2016, 6:45 PM
Fennek added a comment.Aug 5 2014, 4:53 PM

I guess i was wrong to say the operation of the clutch is properly simulated with physx. I did more reasearch on this topic and started a topic on the nvidia physx forum.

It seems to me as if the characteristics of the physx clutch system are responsible for this problem. In case you stand still and give thrust the resistance produced by the clutch can be so high that any acceleration of the engine is prevented.
Here is the topic https://devtalk.nvidia.com/default/topic/764824/physx-and-physics-modeling/clutch-strength-question/

Fennek added a comment.Aug 6 2014, 9:21 PM

i think i found the underlying problem in the physx implementation of the clutch.
Let's hope Nvidia will implement a solution in a timely manner so it can be fed back into Arma 3

https://devtalk.nvidia.com/default/topic/764824/physx-and-physics-modeling/clutch-strength-question/?offset=7#4277592

Edit: for some reason my posts are hidden, will try to unhide them so you can see the discussion

I compiled the whole thread in the physx forum as image (4MB) as i can't figure out how to make it viewable to public and have gotten no reply from the forum guys
http://abload.de/img/compiledeqsy5.jpg

I think adding a kickdown effect to the vehicle turbo could help. similar to shifting down a gear to rev up the engine just before an overtake irl.

so, whenever you push the vehicle turbo button while driving/accelerating, engine would be disconnected from drivetrain for a very short time to allow engine to build up more rpm and more torque when it connects back together again.

this would make the use of the vehicle turbo button more authentic/realistic while driving roads, but also help climbing terrain by being able to downshift/kickdown manually (to keep higher speed/traction) before the vehicle itself would do a gearchange itself.

Vehicle turbo does nothing but to change throttle to 1.0 (or to whatever value it is set in the config). If you do not push "turbo" you don't drive at maximum throttle. It's an illusion, the turbo is not a turbo, it's standard throttle. The regular accelerator is a retarder instead, not applying full throttle.

To have a kick down effect give you any use it requires a proper working clutch in the first place. And kickdown doesnt solve 0-speed torque. It can only improve the acceleration once you are in motion, depending how efficient the autogearbox operates. Right now all of them operate very efficient so this wouldn't have a big influence.

Bohemia added a subscriber: Bohemia.May 7 2016, 6:45 PM

BI, its still not fixed.... How many time you need to fix most important bugs? Look at older ticket instead of new ones, this is real reports, not some kids-crying ultra-laser weapons lack.

It's a shame really. I'm currently creating a mission with a BLUFOR mech. inf. attack but especially the Marshall is so slow on medium offroad terrain. It often can't reach 20 km/hour. The whole attack proceeds at a teeth-grinding slow pace.

(off-topic, because the infantry moves very slowly as well in COMBAT mode, there is no way to compensate in any way, the whole mechinf force moves very slow)

There should appear "AGRESSIVE" mode for infantry for faster attack. "COMBAT" mode is good when you have small squad with infantry only

i had a look at the physx source code in the hopes to maybe find something valuable, but the solver and all that is fine. It's, like i assumed earlier, the clutch that is the sole problem.
I would have hoped to offer a simple solution but adding new controll inputs into the physx framework is beyond my limited programming abilities.

BIS needs to implement a way to modify the clutch strength depending on drive situations, because i dont see Nvidia pulling their finger regarding this.

Especially not now since the code is accessable with permission to modify to nvidia partners.

Thanks for your detailed investigations Fennek, I hope BIS will pick up the ball on this one day and make tracked vehicles shine!