Hi all,

Pleased to announce that the four month overhaul to vehicle movement is now stable.

Track physics has been moved off of the PhysX engine into a custom solution - opening the black box to allow your design decisions to have much greater impact on movement.

0.2.50.10 has been moved to its own branch, if you're not quite done with it.

Now entirely physics-based and behaving more like a real tank. Heavy tanks feel heavier and light tanks feel lighter. Engines simulate inertia and can stall. Tracks behave better when fully off of the ground.

As an example of the new physics-based nature: Previously, the engine generated torque and applied it directly to the tracks. Now, the engine applies torque to its crankshaft, speeding it up. The clutch then generates friction based on the speed difference between the crankshaft and the tracks and applies this torque to the tracks. This results in a torque spike when the clutch is engaged while the engine is at a higher speed than the tracks, whereas before it would have been a steady torque output.

If suspensions are bent too much, they shear or snap. To prevent this, engineers put little blocks which collide with the suspension arm to prevent it travelling past a point where the suspension will be damaged. These little blocks, bump stops, are now simulated.

Previously, there were no bad suspensions as their limits weren't enforced strongly. If suspension travel was exceeded, the wheels would momentarily detach from the suspension. Now, if suspension travels too far, the bump stop applies an impulse which suddenly bumps the vehicle up.

Suspension design now matters as hitting this bump stop gets punished with a rougher ride, reducing speed and disrupting aim.

WWI uses this same bump stop tech to simulate designs with roadwheels bolted directly onto the hull. These designs experience a lot of vibrations.

Now using a slip traction model, tracks are finally able to move at a different speed to the ground. Allows slipping, skidding and drifting.

The new physics model allows all of the artificial physics constraints to be removed, letting vehicles lean and drift more in turns. Ramming and shooting stationary vehicles will rock them more naturally.
Roadwheels no longer jump when the vehicle starts moving.

When shifting, the driver now needs to match the engine speed to the track speed in the next gear. This ties directly into transmission design with an emphasis on the steps between gears. The low gear count meta is no more. The speed limitations caused by low engine speed ranges in the earlier eras are now simulated enough to allow the excessive drag to be removed.

Track collision has been moved from the wheels to the track belt. Anywhere the belt is in contact with the ground will provide suspension and traction forces, resulting in improved climbing and much more difficulty getting stuck.

In addition, the track belt simulation now physically simulates every belt segment and its collision with wheels and the ground, resulting in some nice visuals. Belts can now detach from the wheels instead of being anchored to them.

The mass of the track belt affects how slow the track is to accelerate and how well it holds its speed when coasting.

Destroyed track belts now physically break, removing their placeholder disappearing act.
The entire powertrain, suspension and track belt simulation has been multithreaded, burst compiled and thoroughly optimized. CPU-side track belt rendering has been significantly optimized.

• The powertrain simulation is now entirely physics-based.
  
• Moved the track simulation off of PhysX into an in-house solution.
  
• Track collisions are now belt-based instead of wheel-based.
  
• Added a slip-based traction model.
  
• Clutches are now more realistic, with a maximum torque transfer and slippage.
  
• The clutch is now disengaged correctly during gear shifts.
  
• Track belts now have every joint simulated and more accurate collisions with the wheels.
  
• Destroying tracks now causes their belt to break. Instead of the placeholder vanishing.
  
• Suspensions now simulate bump-stops.
  
• Reintroduced microbumps to the ground, simulating small (<5cm) irregularities in the terrain.
  
• Torsion bars now have more realistic stiffness and travel.
  
• Torsion bars are now preloaded so that the vehicle sits at the target-angle (previously called rest angle). When the vehicle is off of the ground, suspension arms will extend down more than before.
  
• Torsion bars can no longer be longer than the track separation.
  
• Torsion bar now only offset one track if their length is above half the track separation.
  
• Volute spring constants are now much closer to real values and scale more realistically.
  
• Leaf spring stiffness is more realistic and significantly higher than before, solidifying it as a cheap, low tech, but rough ride.
  
• The bulk of the movement system is now multithreadded.
  
• Twin transmission: The driver will no longer shift down more than 2 gears to steer while holding the throttle, 4 while the throttle is released at speed.
  
• Fixed track wheels jumping when moving from a stand-still.
  
• The final drive property has been moved from the transmission to the sprocket wheel.
  
• The vehicle's powertrain speed limit is now shown next to the final drive property.
  
• Key powertrain simulation variables are now shown in the movement info screen 'V'.
  
• The driver now keeps the engine at its operating speed for 30s after a movement input.
  
• Added a 'Start in 2nd' toggle to the steering wheel.
  
• Brakes are no longer automatically applied above 5km/h, allowing you to coast.
  
• The driver only upshifts now if the next gear is capable of providing the required torque to accelerate.
  
• The driver no longer upshifts when turning.
  
• Suspension damping is now editable in WWI
  
• Raised minimum torsion bar diameter from 20 to 30mm.
  
• Raised minimum damping from 0.
  
• Improved motion blur on fast moving tracks belts.
  
• Smoothed suspension test bumps
  
• The sprocket wheel is now classed as 'powertrain', and is visible in interior view. This provides easier access to the final drive.
  
• Wheels no longer visually decouple from their suspension arms under high load.
  
• Exhaust colour and density now changes with the amount of fuel being burned.
  
• Increased exhaust speed.
  
• Added lingering exhaust fumes.
  
• Added 3 transmission mesh modes: Constant mesh, synchromesh and slide mesh.
  
• Adding new gears now copies the last ratio to the new gears, instead of attempting to smooth it from G1.
  
• Fixed vehicles jumping when exiting photomode.
  
• Fixed overly wide hitboxes for wheels.
  
• Vehicle movement is now visually smoother above 75fps.

A big thank you to everyone who helped test this update on the experimental branch!

This is a pretty foundational update which opens a lot of doors for other areas like weight dispersion, in-depth engines and more steering systems. All to come!

Up next, some quality of life features and a UI overhaul.

- Hamish