Physics investigations on Stunts

[Overdrijf]

Wow ones again. You really are good at this. So the drag really has nothing to do with it, and my kart has a very special unreachable powergear...

[Overdrijf]

By the way, I'm probably sounding spoiled now, but it appears you where so exited about the second set of dimensions that you didn't mention were the car-to-car set is located.

[Duplode]

I can not imagine you did not find this out in a dream.

Not quite, it was rather like one of those situations when lots of apparently unrelated informations suddenly start to make sense together when you stumble at the missing piece 

Only one distinction missing: speed difference between ACURA power gear and Indy power gear.

This distinction was, in a way, already pointed out - by you  Many years ago you wrote, and a few years later I read, a "Tips for Newbies" article in which the powergears of Indy and Acura were called "flexible", in opposition to the GTO and Vette ones. That is the fundamental distinction: "rigid" (or boring ) powergear, the most common kind, works exactly the same for all cars that have it - to reach it you have to be at/above 225mph and the car must not have enough engine power to keep accelerating on its own by then. Flexible powergear, on the other hand, can be reached below the flat track top speed, and the minimum launch speed depends on the balance of forces acting on the car (including engine power, gear ratios, aero drag, steepness of slope, etc.). The launch speed for flexible powergear can potentially be much lower than 225mph, a fact that is evident on any Acura/Indy lap... The speed of the car when in PG is the speed of the car at maximum rpm in the (final) gear, so that's why Acura and Indy are different. If Acura had a value for mass that would give it rigid PG, however, it would never reach it, as the top speed is below 225mph (that is exactly the case for Audi, by the way). I like "rigid" and "flexible" terminology, guess I'll stick with it 

So the drag really has nothing to do with it, and my kart has a very special unreachable powergear...

Drag does not affect the kind of powergear indeed, but it if the powergear is flexible it changes the minimum speed (higher drag leads to easier-to-reach powergear). You mentioned to be using mass=15 and drag=19. 15 is a flex-PG value (same as Indy), and 19 is quite low, so the minimum speed might be well above 156mph (have you tested going through a loop, though?  )

By the way, I'm probably sounding spoiled now, but it appears you where so exited about the second set of dimensions that you didn't mention were the car-to-car set is located.

Oh my bad, maybe I shouldn't have gone so far in skimming detail on that post  The range of interest is 0EEh - 0F3h, and values are in the usual x-y-z pattern. I will (try to) start writing some of this stuff (and more) to the Wiki now, so stay tuned 

[Overdrijf]

So the drag really has nothing to do with it, and my kart has a very special unreachable powergear...

Drag does not affect the kind of powergear indeed, but it if the powergear is flexible it changes the minimum speed (higher drag leads to easier-to-reach powergear). You mentioned to be using mass=15 and drag=19. 15 is a flex-PG value (same as Indy), and 19 is quite low, so the minimum speed might be well above 156mph (have you tested going through a loop, though?  )

Not 15, 5. That's actually just a bit on the heavy side for a "realistic" superkart. So that would make it rigid. But no, I haven't tested a loop yet, I should probably still do that. (But I'm too lazy to do that before getting the new dashboard to work, and that's gonna take a few days.)

[CTG]

Duplode, may I have a question? How do you have so much energy for this Stunts research plus high level racing in the same time? This work is amazing!

[Duplode]

Duplode, may I have a question? How do you have so much energy for this Stunts research plus high level racing in the same time? This work is amazing!

Thanks - in my case, I think one thing feeds the interest for the other, and vice-versa 

[Overdrijf]

O, I forgot to mention, I tried the loop. As predicted by your formula, it does not powergear (for having a rigid/boring powergear and limited top spead).

[Duplode]

You can already read full report on how to control PG when tuning a car at http://wiki.stunts.hu/index.php/Power_gear_bug ...

[CTG]

Daaaaaamn, I just realized that I use a bad theory for air drag limited top speed calculations. It worked for all my custom cars, except Veyron: it should reach 245 mph without powergear, but somehow it accelerated only up to 237. Problem solved. Sometimes I should read the instructions carefully...

[gagarin]

OFF: just found this spare account, forgot about it completely... (guests cannot see the memberlist)

ON:
Have you ever noticed that car size ratios are far from real life values? Duplode described the height anomaly and that some cars are just way too big. But their relative size is weird, too. Audi Quattro and Countach have almost the same length in real life - while in Stunts, difference is 22 units (>1.3 m).

Stunts Wiki says 1 pt = 0.2 ft = 6.1 cm (confirmed).

Lamborghini Countach
Real life size: 420/200/107
Stunts size: 104/38/18; which means: 634/232/110
Difference in %: +51.0 (!!!) / +16.0 / +2.8

Way too long and flat.

Lancia Delta Integrale
Real life size: 390/177/136.5
Stunts size: 79/34/25; which means: 482/207/153
Difference in %: +23.6 / +16.9 /  +12.1

Ratios are more or less fine.

Lamborghini LM002
Real life size: 490/200/185
Stunts size: 88 (without spare wheel)/34/31; which means: 537/207/189
Difference in %: +9.6 / +3.5 /  +2.2

The largest car from the pack in real life - very undersized in the game, compared to other cars.

[Duplode]

There is a correction to be made, minor numerically but conceptually relevant, to the discussion about tile length in the opening post here. It's something that has been known for some time, but hadn't been written down yet. Back in the day, I had talked about the tile to feet conversion in these terms:

And now for the interesting stuff, during which I'll use imperial units so the numbers get prettier. Since one mile is exactly 5280 feet, that means one tile measures 204.95 feet, very close to an integer number... since we should expect a slightly higher speed than 245mph due to truncation, it is perfectly reasonable to admit the developers made it so that each tile has exactly 205 feet, or 62.484 meters. That, in turn, triggers a cascade of interesting implications: [...]

There are two naive assumptions in the quote above. Firstly, there is no reason to expect a speed higher than 245 mph, as that is a hard limit which the game imposes by cutting off engine power when it is hit. Secondly, though the feet might feel like a more natural unit for describing the displacement of a car, it turns out the game goes directly from mph speed to displacement in internal units, without feet as an intermediate. The practical consequence is that the conversion factors 1 graphical point = 0.2 feet and 1 mph = 11/30 graphical points per frame are exact, and therefore 1 tile = 1024/5 feet = 204.8 feet. The Car Model Physics article in the Wiki was updated accordingly.

[Cas]

Track tiles measured in feet don't feel very natural.... They should be measured in wheels instead    Anyway... good to have the precise data now documented! 

[Matei]

I just found some interesting comments.

How long a track tile actually is?

It's 32 meters.

The obvious experiment is to race a car through some distance at constant speed, measure how long does it take and calculate the length accordingly,

Which is wrong, as will be shown.

And finally: have you ever had the impression that Stunts cars are a bit too large for the tracks they race on?

When I looked at them, they actually always seemed too small. It's obvious that the speeds shown by the indicators and mentioned above are wrong. The tracks are smaller and the cars are not larger. Anyone can check the sizes in my game, where all the data is in text files (*.geo) and everything looks right.

An interesting observation is to note this way of modelling the landing on a surface is very simple and quite unphysical (no forces, no torques, just a forced change of orientation)

This is what I did in my game before making it with physics, although the cars weren't yet landing, because they weren't flying.

https://matei.one/idxscr.html#versions

The next comment is from another topic.

Of course it is an ancient game, and compared to say, Test Drive 3, it has constant timing and pretty good car handling relatively.
[...]
The oversteer seems very very fake,

As noticed by 2 people so far, Stunts has no physics, but it's a good game because most car games are junk. I played Test Drive 6 Gran Turismo 6 on Playstation 3 and the cars don't even rollover properly. Anyway, one advantage of Stunts is that it can do races, i.e. it has some opponent cars driven automatically, which is difficult to do when physics are also involved, not to mention the tracks with stunts. TORCS has good opponent cars, but last time I played it, the physics were 2D and I didn't check out the new version with 3D physics. I never saw a car upside down though.
 
 

[Duplode]

This is indeed a pretty interesting topic, @Matei . The unavoidable root issue is that the relative sizes of the objects within Stunts are inconsistent with reality. That's noticeable in things like building sizes and ramp heights (a 450/1024 = 43.9% gradient is wildly unrealistic!), and comparing the sizes of the original cars with each other gives a clear illustration:

For instance, contrast...

• Real Lancia dimensions (mm): 3895 x 1620 x 1355
• Real Corvette ZR-1 dimensions (mm): 4480 x 1800 x 1190
• Real LM002 dimensions (mm): 4790 x 2000 x 1850

... with:

• Game Lancia dimensions (Stressed units): 79 x 34 x 22
• Game Corvette ZR-1 dimensions (Stressed units): 103 x 42 x 20
• Game LM002 dimensions (Stressed units): 91 x 34 x 25

That being so, correlating dimensions as they appear within Stunts to the real world requires making a choice and accepting some trade-offs. If our main concern is the gameplay of Stunts itself, using the speeds rather than the cars as the reference has several advantages: first and foremost, it relates more closely to the playing experience within Stunts, which mostly happens from behind the wheel on the F1 camera with a speedometer facing you. Also, it means you don't have to arbitrary pick one of the 11 DSI cars to assume as being correctly sized, only for your choice to be belied once you race against Skid on a different car. As a bonus, the track width that follows from that choice is actually quite plausible for a race track:

Using the 62.5 m/tile approximation mentioned in the Wiki, the width of a Stunts road is 62.5*240/1024 ~ 14.6 m, which looks quite reasonable next to the FIA guidelines. For another data point, the USA standards for highways dictates 3.7 m wide lanes; 3.7 * 4 = 14.8 m, which again looks pretty reasonable, considering that having four traffic lanes on a Stunts road would fit visually.

The reasoning above has mainly to do with the specific quirks of Stunts and how it is played. It's not really relevant if you're making a different game with consistently sized objects, as you have been doing, and thus it's perfectly fine to take a different approach in order to solve the inconsistencies. With SimcarStunts, I'd say the road feels narrower to the driver on the "F1" camera, which is consistent with the single carriageway look of the graphics, and there's a heightened sense of speed, which is actually a wish not unheard of for Stunts:

However, I also feel like some combination of the car sizes, the view heights, the way the track looks like a two lane road, the general lack of details and some other stuff make the elements seem smaller and slower. The mph figures often feel more like kph figures, and as such the small corners often feel a bit like something you could encounter in your own neighborhood. If you're trying to fix the scale issues in Stunts, I feel like that's the angle I'd come in from, trying to make the game feel more like it models super fast cars on race tracks, like it actually has the scale it has.

As noticed by 2 people so far, Stunts has no physics, but it's a good game because most car games are junk.

Perhaps surprisingly, there's no real disagreement between us. The title I gave this thread, "Physics investigations on Stunts", is tongue-in-cheek. It's very much a fantasy model of objects that move and interact, one that does a commendable job for the time of incorporating a few select aspects of car dynamics, while being a long way from a simulation with pretensions of realism.

[Matei]

There are no trade-offs. The cars in Stunts are toy cars, not with people inside, so everything fits. The only problem is that gravity is not modelled very well. Also:

on the F1 camera with a speedometer facing you

https://autoily.com/speedometer-reading-faster-than-actual-speed/

Speedometers are also made like this (with a factor of safety) so you don't exceed the speed limits. In my game the speed is not shown by the speedometer in the car.

the width of a Stunts road is 62.5*240/1024 ~ 14.6 m, which looks quite reasonable next to the FIA guidelines. For another data point, the USA standards for highways dictates 3.7 m wide lanes; 3.7 * 4 = 14.8 m

It should be 3.7*2, because the roads are obviously with 2 lanes, considering how they are marked. If you want roads with 4 lanes, you have them in my game (the first download):

 https://matei.one/idxscr.html

There's no reason to make any connection with FIA.