I have been working on a motion simulator for a while. During the whole process I used LFS Outsim acceleration data to test the simulator.

Only recently I started using other sims...and what a surprise, acceleration from other sims is a lot sharper than what LFS sends. For example I can perfectly feel every bump on the kerbs in other sims, but in LFS these bumps are smoothed....like if some filter was applied (and I need to tweak a lot the signal to feel them).

It is easy in LFS to guess what acceleration the driver receives, because the head moves accordingly...and when I compare this head movement with the acceleration from Outsim data....it looks like there is a smoothing filter applied somewhere.

Is there something to do to remove this smoothing? Or at least I would like to know what is the filter applied, so I can compensate for it. It may be a moving average.

I found this while doing some applications with outsim too!

I couldn't find any answers either, but I presumed that it was tweaked within the way LFS creates this dynamic data so that it works well on a G25, and other popular wheels.

You mean Outsim and FFB outputs are smoothed?

If it is the case, this is a real problem. FFB wheels and motion simulators use motors which already have a tendency to smooth the output.

Instead of a smooth signal, FFB wheels and motion simulators usually need a signal which was sharpened using filters to give better sensation. So if LFS smoothes outputs like that... I can bet without this smoothing FFB would be a lot more detailed. I can see LFS tracks like South City are very detailed (there are many bumps, every single sewer plate is modeled)...this is present in the signal but very smoothed.

The only filter LFS should apply is a "brickwall" filter to cut everything above Nyquist frequency. Let's say LFS updates FFB 100 times per second, it should apply a filter which cuts everything above 50Hz (100/2) to avoid interferences inside the FFB wheel...but even that filtering is not really necessary, because these interferences only build up when FFB signal is periodical....which never happens.

I just recorded vertical acceleration output from GTR EVO and LFS, using F3000 on Anderstorp in GTR EVO and FO8 on south city sprint 2 in LFS.

Both tracks are bumpy, both cars are very similar, I drive like a pig...accelerations spectrum should be similar.
Very high frequency should be rare because car is not shaking on kerbs all the time. Very low frequencies should be rare because car is moving all the time. Movement should be spread over a large frequency range between low and high frequency, because car is not jumping periodically but moving very differently every second. And LFS signal should spread over a larger frequency range because LFS track is more detailed than in GTR EVO.

This is what I get from both sims (x axis is frequency from 0 to 30hz):


As you can see, GTR EVO output looks as expected....rich signal, broad of frequencies represented. And LFS output is heavily filtered. Everything above 4 Hz is smashed. This is really annoying for motion simulators. The frequency humans feel best (resonating frequency when seated) is about 5Hz.

Finally I checked with directinput capture and this does not concern FFB. Only Outsim acceleration data is filtered. From the FFT it is a first order low pass filter.

Cool comparison. You're best of sending a mail to the devs for Scawen to give you a reply on the matter. If you could get him to post here for all to read, so much the better.

I sent something few days ago. Waiting...

This smoothing may come from the tyre model, but I hope there is somewhere a filter one can disable to release the power!!

OK still nothing. I was thinking about outsim acceleration data.
Maybe someone can help about that. I remember I asked for it one or two years ago and did not find the answer.
http://www.lfsforum.net/showthread.php?t=33581

Where does this acceleration come from?

1) Is it acceleration of the COG of the car body?
2) Is it acceleration of the car body at driver level?

Acceleration 1) is always smoother than acceleration 2) because it does not take into account car body rotations. For example when car is on tiny bumps like kerb, the car will tilt front and back very quickly on every bump. Car body COG will roughly move along a straight line (acceleration 1 very small) while the driver will feel every little bump because he moves up and down with the front of the car (acceleration 2 strong).

If the driver is not positioned above the CoG, you are quite correct.

Although I can't say for certain, I would expect the accelerations to be for the CoG. I would have thought you could work out the acceleration felt by the driver from this, the other data given by outsim, and the seat locations as specified in the .bin files.

Maybe you could compare the data from OutSim with data from RAF for the same lap and find out that way?

Quote from Bob Smith :

If the driver is not positioned above the CoG, you are quite correct.

Although I can't say for certain, I would expect the accelerations to be for the CoG. I would have thought you could work out the acceleration felt by the driver from this, the other data given by outsim, and the seat locations as specified in the .bin files.

Thank you for your answers!
Yes I can to do that. From COG->Driver vector, angular speed and angular acceleration I get two additional accelerations I can sum. For the moment I use some arbitrary seat position. Even above the CoG, it gives strong additional accelerations (but horizontal in that case).

But derivating the angular speed vector (no angular acceleration in outsim) raises some little issues when you start or stop a session, as angular speed jumps to or from zero. I have to detect discontinuities, put thresholds, filter the derivative (derivating discrete time series introduces unwanted high frequencies, and filtering them adds some lag).

If there was a more straightforward way to do, it would be more convenient. I suppose LFS somehow calculates acceleration at driver level for head movements...so this data is directly available inside.

OK so I will never know.

Filtered or not?
Where is the vector from car COG to driver's COG?

Long File of Secrets.

Quote from Juls :

Where is the vector from car COG to driver's COG?

You can compare the CoG position with and without a driver in the .bin outputs, and deduce the vector from there.