Automatic transmission

[rookie1]

I think following is a way to calculate optimum shiftdown threshold,

When shifting gear from X+1 to X (ignoring clutch for the moment), the wheel speed should be continuous, so we have the following relationship just before and after the gear shift.

Code:

engine speed at gear X+1 / gear ratio at gear X+1 = engine speed at gear X / gear ratio at gear X

To have optimum shift, the engine speed at gear X just after shift should be at engine peak rpm (this is just my guess). So the threshold engine speed at gear X+1 should be

Code:

engine speed threshold at gear X+1 = engine peak rpm / gear ratio at gear X * gear ration at gear X+1.

Using 3S as an example,

Code:

peak-engine-rpm = 6500rpm
gear-ratio-1 = 3.31
gear-ratio-2 = 1.84
gear-ratio-3 = 1.31
gear-ratio-4 = 0.97
gear-ratio-5 = 0.76

Using the above formula, the threhold values are

Code:

From gear 5 to 4 -> 5145rpm
From gear 4 to 3 -> 4812rpm
From gear 3 to 2 -> 4627rpm
From gear 2 to 1 -> 3613rpm

Of course, this is from someone with completely nil experience in automobile engineering. Do the above values sound reasonable?

[thelusiv]

I'm not positive on how it's really done, but I think what you're talking about is a good idea to try. I'll let you know if I think of anything that might be useful...

[reece146]

[*]Shifting is still allowed with the manual shift buttons, maybe they should be disallowed over 1st gear.

It's probably worth keeping this ability in place OR making it an option.

When in "automatic mode" you can manually select a gear with the shifter as well.

[joevenzon]

I agree with reece146... keep in mind, as implement this isn't an actual automatic transmission, which has completely different physics, it's more like an SMG where the computer is tapping the shift up/shift down levers for you (which is fine).

[reece146]

Just thinking about this a little more.

Manuals have something like:

R-N-1-2-3-4...N (in reality you can go 1-3-5 or whatever of course).

What if when you select an automatic mode you get something like:

P-R-N-D-N...-4-3-2-1

This would be more "realistic". For a car that has real auto-shift / paddle shifters you would need a way to switch modes dynamically to do +/- shifting. Park ("P") could be faked out with full brakes (hand brake?) and zero tail lights for the sake of functionality.

If it is a big headache to code up, forget I said anything.

[joevenzon]

I prefer the idea of "automatic mode" as being just automatic gear-shifting rather than automatic transmission emulation....

[rookie1]

I prefer the idea of "automatic mode" as being just automatic gear-shifting rather than automatic transmission emulation....

2nd that. To the average player, simpler control is more important than total realism. Too much realism may destroy the fun.

[thelusiv]

I agree that we don't need a perfectly realistic "consumer-grade" automatic transmission. After all, they suck...but my concern with being able to shift when using the Automatic Transmission is more that when playing, I constantly second-guess it, and try to shift anyway. I end up double-shifting, which is terrible. So I ask the question, would a lot of people like to be able to shift when using the auto option? If the auto shift points are good enough, then if you're going to turn it on, then why not use it?

[thelusiv]

Tonight I checked in a bunch of changes to automatic transmission mode. Now the clutch is used, and the down shift point is much better.

rookie1, I used your suggested downshift algorithm but changed one thing. Using the raw "optimal" shift point using that method, I found that sometimes (on some cars) it would shift up, then back down immediately, then back up and down repeatedly. Thus I made it shift slightly lower than the optimal point:

Code:

down shift point = optimal point - ( 100 / current gear )

so for instance, in gear 4, it would shift at the optimal point less 25, in gear 5 it would shift down at the optimal point less 20. The reason I didn't subtract off a constant amount was that otherwise I found caces where it would shift from 5th to 4th when really it should shift from 5th to 3rd (too much overlap).

So anyway, that's how it's done now. Please test this by driving different cars using it.

There are a few (possible) issues with this mode. Since up and down shifting relies on the peak engine RPM, there could be some cars with less than optimal peak engine RPM settings, where automatic shifting could be a little strange. Another issue is that when using a button or key control as gas, the gas must be released a little early before the shift happens or the RPM will jump immediately to the maximum (because the gas is still pressed, and the clutch and flywheel are now disengaged). I'll see if I can find a workaround for this...

[thelusiv]

Alright I figured out a way to avoid over-revving during auto shifts, for players using button controls. It now remembers the time when an auto shift occurs, and for 2 tenths of a second sets the gas value to 0.0, then for the next 2 tenths of a second only allow the gas value to get as high as 0.5. It seems to work pretty well, auto shifting is much smoother now.

All this is in SVN r1330. Please test

[thelusiv]

A few more updates to this:

• fixed a bug where the car wouldn't rev past peak engine speed in highest gear
  
• made the gas restriction time longer depending on the length of the car's shift delay
  
• made gas restriction apply to analog controls as well as button

[joevenzon]

Works great.

[cotharyus]

Since a lot of this is related to the autoshift (That's what I was really testing) I'm going to put it all here, even though some of this is not specific to the autoshift.

Testing is by car, drove each car on Lemans with autoshift on, ABS off, TCS on.

CS: Shifting from 1->2 and 2->3 is buggy.

G4: Rear end is way too loose. Downshifting also tends to be a little agressive. Even a relatively high performance auto won't downshift until the revs are pretty low.

FE: Downshifts from 4th to 2nd. In addition to destablizing the rear end of the car, if you jump on the gas at the right (wrong?) time as this happens, you can peg the RPM's in second gear, and it won't shift to third until you let the RPM's drop back below the shift point.

GT: The brakes on this car are way too weak.

RG: Completely undrivable. If you can't reproduce an undrivable condition, I'll make and post a replay.

TL: Downshifts from 5th to 1st under braking.

XM: Downshift is too aggressive. It's downshifting at way too high an RPM

T73: Completely undrivable. Just try it.

Overall, the auto is not bad so far. The unpredictability and lack of control make me hate it just as much in this game as I do in real life

[joevenzon]

Keep in mind this isn't meant to emulate an automatic transmission! It's still a manual transmission, but someone else (the game) is working the clutch and shifting the gears. That's why it's set to be so aggressive. I think it's pretty good. Sure, you lose traction often because you'll be in a turn and BAM it downshifts and your back pops loose, but that's the price you pay for letting someone else work the gears. :-)

I guess one improvement could be to inhibit downshifting until the steering wheel is pointing relatively straight.

[cotharyus]

Nah - leave it. It'll give me the advantage of the poor sap that chooses that when driving against me once we get the multiplayer stuff sorted