This might end up be quite bit more than double the clutch (at bottom right of the page you get idea):
Depends on the vehicle. Lets talk realworld numbers. This is the document I'm pulling numbers from: LINK! If one were to break it down from engine to disc the total rotating inertia is comprised of: Engine&Flywheel, Clutch, Transmission, Axle/hub/hat (x2) Disc, braking surface (x2) If that measurement was made, and ended up with 0.16 kg m^2, shouldn't we be able to start subtracting things, and get a reasonably accurate estimation for the engine/flywheel combo itself? That was my current approach, but I've hit a snag. If that measurement includes the rotors, I'm already into the negative (each rear rotor has a inertia about the axis of rotation of 0.151 kg m^2.
I'm thinking about frictional losses, which could reduce measured inertia? For their purposes, frictional losses that reduce estimated inertia have no meaning as for their calculation lower inertia will result correct number when they add it to their calculations, but for us that makes a difference, however I don't know how measured frictional losses could be added to inertia.
I think of inertia as a resisting force, and thus as additional loss. I believe that the 0.16 kgm^2 measurement would contain a component of friction because you can't separate it from the system to measure it directly.
It does resists acceleration, but also it resists deceleration, however at steady state it does not do anything. Frictional loss however resists acceleration, accelerates deceleration and at steady state constantly resists motion. For some purposes you can have frictional losses and inertia as same, but when you need inertia for rF engine and drivetrain, frictional losses can't be part of that, clutch friction is there for that as well as each wheel has own friction, engine has backtorque, you need those too to get perfectly realistic behavior in all situations. Well, that is at least how I currently understand it, but it is not rare that I would be in error.
Indeed! Those tests to measure inertia were done at a constant acceleration, thus I'm stating the number 0.16 should be reduced to compensate for friction inherent in the measurement. The test is concerned with finding a measurement before the wheels come into play, and grouped everything into a lump sum. That is all I was saying in the quoted statement, but now I'm not so sure. If constant acceleration measurement = (I+ fr) losses and constant speed measurement= (fr) losses It would appear that maybe you can separate out the Inertial component?
That sounds plausible to me, as inertia should have very minimal effect at steady state, so comparing the two you would get how much it would require to overcome inertia. With rolling road dyno, drivetrain losses are usually measured after the pull, when they let speed to decrease freely, but this of course does not include engine's inertia and it can be complete different with rototest. But how you workout resistance and Inertia as units are not the same? You would need speed to have inertia as force as frictional losses are probably force? However I'm not quite sure of those, I might be wrong too.
Yeah that document glosses over how they actually get the number they got. I was thinking about this more lately, and until I solid model up more components, I won't have an answer. Perhaps the spin inertia is all things that spin (sans brake face, about the axle rotation axis), whereas the inertia defined at the corner in the pm is about the C.G vertical axis? Hmmm
No. SpinInertia overrides inertia from PM. The "around CG" part is calculated by rFactor, based on coordinates in PM and where CG is located (from HDV).
That would explain how it could be out of range. I come bearing gifts! So that is the solid model I've been working on, built as close as I can get it without purchasing the parts myself. The only things that spin that are currently missing from the model are the safety pin that holds the wheel nut on, and some of the parts of the bearing. The things are light, and everything is pretty close to the axis of rotation, so I don't expect them to change my current number much. Ixx (about the wheel axle axis) is 4216.787 kg mm^2 for the assembly. In rf HDV units that is 0.004216787. MINISCULE! The brake disc hat adds inertia to the mix: 21174.532 kg mm^2 (.021174532). Even totaled this is is nowhere near the values found in the HDV for SpinInertia= for any mod. To me this is rather telling, the number in the HDV for SpinInertia is a total of everything spinning on a corner (excludes the inertia from the brake surface ring)? I'm not sure what that means for the inertia listed in the pm file. If it would only be for tire/rim then the pm inertia would always be lower than the spin. This is not the case with the Clio Rear, and also the FR35 Front (looking at non-driven wheels, ATM).
The Clio, FR35, and the 370z all deviate from larger pm inertia for non-driven wheels. The GTR-GT1 does not. Just trying to understand how and, more importantly, why things are split in the way they are. The PM mass is from (GTR, front) The Disc Inertia when thickness is applied equates to 0.0393. If the SpinInertia does not include Disc, shouldn't it be less than the PM? In fact it is more; 0.350 vs 0.425 The Clio, rear, PM vs HDF: 0.350, 0.480 brake: 0.011 370z, front, PM vs HDF: 0.50, 0.40 brake:0.07054 Doesn't seem to be a definite relation.
But the HDV overrides the PM. To me, it seems only logical that it is included since the disc's mass is also, and thus the reason why the pm has a larger value than the HDV (HDV is split). Just a theory, if the numbers checked out then it would be easier to say for certain, the GTR breaks the pattern anyway.
I know I ask a lot of questions, hopefully I am not wearing patience thin. Can you explain more of how you've come to those conclusions? Looking back at this, the 2/5ths of a bearing mass strikes me as peculiar. The entire bearing is unsprung. It's a non-driven corner. It isn't like there is an axle where half the mass is split to sprung mass. The only thing I can think of that makes sense of that comment is if the mass is directly tied to things that actually spin. If PM Inertia is different than HDV inertia even after considering disc inertia, then they are different. Do you have any theories on how they are different?
Came across a few things. In rf2, the TGM contains data for the inertia of the tire. And I got this reply back from RRI, Sounds like friction is the same but cannot be compensated for because of other differences.
There are two inertias in TGM, one idea is that other would be wheel and other tire, but ring mass and ring inertia, are those for tread and not to be confused to wheel? Michelin S9C rear from ISI's clio: TotalMass=7.4211540233335125 TotalInertiaStandard=(0.6010835398811567,0.33886077771325035,0.3388607777132502) RingMass=6.39301881493281 RingInertiaStandard=(0.5447855575547635,0.2997520911993927,0.29975209119939156) My idea is that Ring is tread and rest of the mass + inertia is sidewall, nothing to do with wheel or anything else, but I can be incorrect too. It can then be many ways how it is implemented to hdv and pm, it can be that we input all and TGM is substracted or it can be that tgm is added, but if going by this, then tire is not in .pm at least. From GTR pm: // Rim + Disc + Brake Bell + 2/5 Bearing + Other // 7.7 + 4 + 3 + 0.3 + 1 Is 3/5 bearing then in HDV? There are bearing friction at least, but why not to have whole bearing in hdv rotational masses. Of course we want to get car made perfect, but still, how one can find out those inertias and masses being in wrong place, in hdv instead of pm or opposite when driving a car, or can it be even measured in motec? I would imagine those being something that are good to be right but their effect being rather small, leading them to be at lower priority to most then?
With the tire, I also see the two "I" values as simplifying the tire into basic geometric shapes for easier calculation. The Rim I value is already defined elsewhere (PM). Because all of the bearing is unsprung mass, it needs to be added in the PM. The note applies directly to the mass. If you look at a bearing only the parts that spin seem to be added to the wheel mass, I would think the other 3/5ths is added to the spindle. The question that remains is what difference would that make if the bearing is split to spindle and wheel or just in one or the other? Still peculiar to me. The only way I was even able to measure the Inertia is through solid modeling. I suspect that an ISI Dev will need to be contacted to see exactly how Inertia is being split/used. I kinda was hoping one would just pop in here. Might be lower priority, but was still important enough to call out and factor in separately. I find that interesting.
