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Questions about daily development

Started by Alby46, June 21, 2016, 09:07:24 am

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PiBoSo

Quote from: HornetMaX on January 04, 2018, 12:23:12 am
Quote* GPB / WRS / KRP / MXB: update to the latest version of the rigid body dynamics library


Interesting. Anything major ?


Major change in the gyroscopic forces calculation.
The new gyro computation makes the simulation explode with very fast spinning objects, like wheels, so it has to be disabled.
The bike is then less stable, but it's not necessarily a bad thing, as it looked a bit over-damped previously.
Testing is still in progress.
"Obviously your ambition outweighs your talent".

HornetMaX

Ugh, no gyro at all sounds pretty bad though. And doesn't cope well with the "I'm a sim not a game" tagline :)

Vini


PiBoSo

Quote from: HornetMaX on January 04, 2018, 10:58:36 am
Ugh, no gyro at all sounds pretty bad though. And doesn't cope well with the "I'm a sim not a game" tagline :)


It should be easy enough to revert to the old gyroscopic calculation.
However, that probably wasn't correct either, given the super-stable wild-running bikes after some crashes or, most important, the difficulty in doing whips with MX bikes.
The new gyroscopic code is probably more accurate but, sadly, not stable enough with very high velocity spinning objects.
"Obviously your ambition outweighs your talent".

h106frp

Would have thought a gyroscopic force was more stable with higher rim velocity?

HornetMaX

Quote from: PiBoSo on January 04, 2018, 01:21:47 pm
It should be easy enough to revert to the old gyroscopic calculation.
However, that probably wasn't correct either, given the super-stable wild-running bikes after some crashes or, most important, the difficulty in doing whips with MX bikes.
The new gyroscopic code is probably more accurate but, sadly, not stable enough with very high velocity spinning objects.

Is the "gyro code" yours or is it part of ODE ? I was under the impression gyro forces are automatically computed by ODE given the rigid body description (bodies, linkages, dofs etc).

PiBoSo

January 04, 2018, 05:17:28 pm #366 Last Edit: January 04, 2018, 05:19:57 pm by PiBoSo
Quote from: HornetMaX on January 04, 2018, 04:55:29 pm
Quote from: PiBoSo on January 04, 2018, 01:21:47 pm
It should be easy enough to revert to the old gyroscopic calculation.
However, that probably wasn't correct either, given the super-stable wild-running bikes after some crashes or, most important, the difficulty in doing whips with MX bikes.
The new gyroscopic code is probably more accurate but, sadly, not stable enough with very high velocity spinning objects.

Is the "gyro code" yours or is it part of ODE ? I was under the impression gyro forces are automatically computed by ODE given the rigid body description (bodies, linkages, dofs etc).


It's part of ODE, but the library is open source, so it's easy to change it.
"Obviously your ambition outweighs your talent".

HornetMaX

Quote from: PiBoSo on January 04, 2018, 05:17:28 pm
Quote from: HornetMaX on January 04, 2018, 04:55:29 pm
Quote from: PiBoSo on January 04, 2018, 01:21:47 pm
It should be easy enough to revert to the old gyroscopic calculation.
However, that probably wasn't correct either, given the super-stable wild-running bikes after some crashes or, most important, the difficulty in doing whips with MX bikes.
The new gyroscopic code is probably more accurate but, sadly, not stable enough with very high velocity spinning objects.

Is the "gyro code" yours or is it part of ODE ? I was under the impression gyro forces are automatically computed by ODE given the rigid body description (bodies, linkages, dofs etc).


It's part of ODE, but the library is open source, so it's easy to change it.

Clear, thx !

Stout Johnson

Quote from: PiBoSo on January 04, 2018, 10:07:00 am
The new gyro computation makes the simulation explode with very fast spinning objects, like wheels, so it has to be disabled.

Hope it is just a temporary workaround.  :-\  with the new gyroscopic code the sim would probably have the potential to be more accurate. Might mean a lot of tweaking for your sims, but in the end it will surely be for the better.
    -----------   WarStout Kawasaki Team   -----------

PiBoSo

Quote from: Stout Johnson on January 04, 2018, 08:42:41 pm
Quote from: PiBoSo on January 04, 2018, 10:07:00 am
The new gyro computation makes the simulation explode with very fast spinning objects, like wheels, so it has to be disabled.

Hope it is just a temporary workaround.  :-\  with the new gyroscopic code the sim would probably have the potential to be more accurate. Might mean a lot of tweaking for your sims, but in the end it will surely be for the better.


Snappe tested the MXB without gyroscopic forces extensively today, and it's worse in every area.
Same for GPB, so the gyroscopic forces have been re-enabled, but using the previous, stable, code.
"Obviously your ambition outweighs your talent".

matty0l215

Its odd that new code makes it unstable. Surley like everyone has said. New "better" code should give better simulation.

Do you know where the problem lies? Is it a problem of imcompatability with another part of your engine or is new code just not as good as the old one for this aplication? (As in for a motorcycle simulator)

PiBoSo

Quote from: matty0l215 on January 04, 2018, 10:26:48 pm
Its odd that new code makes it unstable. Surley like everyone has said. New "better" code should give better simulation.

Do you know where the problem lies? Is it a problem of imcompatability with another part of your engine or is new code just not as good as the old one for this aplication? (As in for a motorcycle simulator)


Yeah, it looks like the new algorithm ( or its implementation ) is not suited for a racing simulator.
"Obviously your ambition outweighs your talent".

matty0l215

Fair enough. :)

Is it a secret what you are using or could you share?

PiBoSo

January 04, 2018, 11:06:41 pm #373 Last Edit: January 04, 2018, 11:09:27 pm by PiBoSo
Quote from: matty0l215 on January 04, 2018, 10:57:57 pm
Fair enough. :)

Is it a secret what you are using or could you share?


According to the ODE code, this is the new algorithm used: https://www8.cs.umu.se/research/reports/show.cgi?year=2006&nr=005
"It is also shown that this scheme introduces physical anomalies in the system"  :o
Looks like its goal is to improve stability at the expense of accuracy. So the end result in GPB is that it is less accurate and less stable as well. Good riddance.
Meanwhile, the "old" explicit gyroscopic calculation is very stable ( probably thanks to the very high update rate of GPB ).
"Obviously your ambition outweighs your talent".

h106frp

January 05, 2018, 12:10:48 am #374 Last Edit: January 05, 2018, 01:27:55 am by h106frp
Out of curiousity I tried;
reducing brake rotor mass - you can make this very low without issues (went down to 100g) - handling appeared to improve marginally in a positive sense, not a big observed change
reduced front wheel mass -  you can reduce this quite a bit and handling improves with small instability under heavy braking with silly values of mass
reduced rear wheel mass - oddly, reducing this creates big issues, very low values crash ODE as soon as you go to track, more modest reductions create a lot of instability under heavy braking which seems odd relative to the observations with the front wheel

Bike does feel more lively (in a realistic way) with lower rotating mass, less tendency to run wide on turns and less crabbing on inclines - reminds me of beta6 for some reason.  Straight line, high speed stability does not seem to change much at all, curiously I did not get a riderless runaway bike issue despite trying  ::)

Tried changing the mass back to default and scaling the moments instead, nice easy handling but the bike seemed to lose a bit of 'character'