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I just have a small question that I don't know where else to post.

Is there any accurate way (or any way at all really) to calculate proper Inertia values for custom cars? I usually use 1600, 2400, 900, or 2000, 2800, 1100 on the majority of my cars because that seems to work. I'm just curious if there is a proper way to do this as all the stock cars seem to have this.

Skarma wrote:Is there any accurate way (or any way at all really) to calculate proper Inertia values for custom cars?

Not sure as I have personally not focused on that point yet, but I guess we may find a good approximation if we consider the car as a homogeneous cuboid of mass M and dimensions (X, Y, Z). Then, the inertia matrix should be something like: [source] I don't know if we can get close to the stock cars value with this formula. After a quick try with AMW the values I found were a bit larger (1340 instead of 700, 1650 instead of 1100, 510 instead of 350). Maybe it's because I used the car's bounding box and a smaller cuboid should rather be used...

Actually that sounds like it might be more right than wrong. As I have recently mentioned...I don't much like math...so Jigebren, that equation looks just like gibberish squared to me, lol...but inertia is a subject of special interest to me. That is something I strive to get balanced right off the bat. In my opinion, those values that the stock cars have are basically just an easy compromise that does in fact work relatively well for most vehicles.

Inertia can be said to express how much of a tendency a given mass has to remain in motion...or how quickly it will come to rest. Given that, this value can also be said to express...or dictate...how much apparent mass a given object has.

So essentially...giving all the stock cars a similar value dictates that they will all behave in...basically...the same manner as far as how much mass they seem to have. As I am sure you have concluded at this point, those stock values don't express very much mass.

And that brings us to the question...what exactly is a 'proper' way to calculate inertia values for custom cars. First is that you want to determine how you want your car to behave...or feel when you are driving it. And second, is a question of how you want it to perform. Do you want it to bounce and wiggle like a cheap light-weight toy, or do you want something closer to a life-size vehicle. Or it can be anything in between.

My recent testing and experimentation has led me to believe it is largely a matter of scale. As I scale a vehicle up there is a noticeable increase in the amount of dynamic interaction that you can actually detect as all the individual parts move together while the car is in motion.

So instead of you experiencing a quick -bounce- input as you do when you hit a bump or go over a jump with one of the stock vehicles, you get to actually feel the weight of the vehicle as it dips into the springs, you feel the weight once again as it is pushed back up by the restitution, and you get a sense of the weight as the car rolls all the way over to right itself instead of just flopping over onto it's back like a plastic turtle.

So I've been doing a whole lot of experimenting in this area as of late because it is the relationship between the CoM, the vehicle's weight, the spring values and the inertia matrix that determine whether or not your vehicle will run like a dream or a cheap piece of broken toy parts. And all too often, pure gold is only one or two very short steps away from utter crap. It's dialing in that last little bit though, that will make or break a tune.

A car just won't want to jump, land or even handle correctly until you find that magical mix of synergistic values. At least those are my humble thoughts on the matter.

By the way...that's great news about engine sounds. So are those going to be fully customizable...as in we can find or record our own and include them with custom cars? Or will we just be able to choose from those already included with the game?

For me, the Inertia has always been depending on car weight. The formula that I finally determined is somewhat empirical. But it works reasonably well. I’ve used it for my packs and vehicles for a long time now – for Carmageddon packs (with a ref_inertia coefficient suitable for RL feel, i.e. 2100) and for the upcoming Hot Wheels pack (with a ref_inertia coefficient suitable for HW feel, i.e. 400) and for my own RC style creations (with a ref_inertia coefficient suitable for RC feel, i.e. 700).


The actual formula for calculating inertias is this:
• Inertia=ref_inertia*weight+(weight-1)*inertia_coeff*weight,
Where:
ref_inertia is 700 (the inertia at weight 1 kg),
inertia_coeff is 350 (an empirical coefficient to get the calculated inertias to spread out evenly according to car weight),
weight is the car’s weight in kg (the parameter Mass under the section “Car Body details”).

Calculate the first Inertia value with this formula (X_Inertia).
The second Inertia value (Y_Inertia) = X_Inertia multiplied by 1.5.
The third Inertia value (Z_Inertia) = X_Inertia divided by 2.


You can play around with the ratios (1.5 and 2) for an individual handling.
And you can play around with the ref_inertia (700) for different effects. For example, 2100 (i.e. 3 x 700) gives the RL inertias and 400 (almost halved) gives Hot Wheels like inertia.


There’s also a helpful spreadsheet if you want – open it, insert your car’s weight and get fitting base Inertias (in MS Excel and OpenOffice format).
Click here.
You can use it and distribute it as you like.

Oh, and for me it seems that Acclaim used somewhat arbitrary values for Inertia. For example, Genghis feels very heavy in-game, and weighs 2 kg, but Bertha feels much lighter, although it weighs 3 kg. That comes directly from Inertia values (2830, 3270, 970 for Genghis and 3000, 8000, 2500 for Bertha). As you see, Bertha’s inertia is way higher, so it should feel more sluggish, but it doesn’t because it’s mass is higher. In Re-Volt high mass needs higher inertia values to feel the same, and even higher values to feel heavier.
Bottom line: my 62 kg Heavy Metal truck was spinning really fast in air with the usual Toyeca inertia values, until I increased them _much_.

I've moved this conversation into it's own thread. As a general note, be sure to post advanced re-volt questions in the TTT section.

So yes, the intertia is similar to mass but for angular motion (rotation). Instead of a single mass value as for linear motion, we have three values for each direction of rotation (along the X, Y, Z axes). The larger each value, the heavier and harder it is to rotate the car in that direction. As far as the re-volt engine is concerned, I doubt there is any use in calculating these values, you just set them empirically till you get the desired "heavyness" when rotating in each direction.

Thanks, Huki. I was actually worried about the 'offtopic-ness' of that convo. Good call on moving it. :nonexistentthumbsupsmilie:

from my experience, not only you must change inertia values depending on the car weight, but also depending on the separation between the wheels.
I always play with the values until i find the values i'm happier with.

Once you've finished the car model and adjusted the wheels where you want them to be, start putting ridiculously high or low values, and then fine tuning them until you find an average value which works well for your car.

Just an information for those who are still interested in Inertia values: I have assumed that the shape is a half an ellipsoid (then a full ellipsoid) and wheels are cylinders the I applied Huygens' formula and guess what... I got "similar values" but not "exact".
(same goes with parallélépipède [parallelepided?])

So Inertia values are empirical (Could be an `on the fly` programming [laziness ftw] or it was necessary to make it look revoltish).

So anybody's method above is actually "correct"