Author Topic: Questions about daily development  (Read 36161 times)

Stout Johnson

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Re: Questions about daily development
« Reply #375 on: January 05, 2018, 09:26:47 AM »
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
I read the paper of Lacoursière. From what I understand, I think it is like you say. They somehow went into a trade-off between stability and geometric correctness. This (http://lost-found-wandering.blogspot.de/2013/01/gyroscopic-forces-in-ode.html) might also be interesting for you. Looks like the paper from Lacoursière is not totally immune to criticism.

From what I understand though, the paper of Lacoursière deals with any kind of rigid body (e.g. "long thin object" like in the numerical experiment on p.11). As far as I understand, for the simulation of gyroscopic forces for wheels, there should not be much of a problem right? I quote: "the rigid body will eventually stabilize in a state of rotation about the axis with the largest inertia" (p.11 in the paper). For the simulation of gyroscopic forces of wheels there should not be any problem imho, since there is only one axis of inertia (edit: well at least the axis of rotation should be the one with the largest inertia).

So maybe the instabilities you experienced with the new library are due to other variables from your sim? The tests from h106frp might be helpful in that respect maybe? Again, from what I understand if you simulate wheels, there probably should not arise such problems. Maybe the implementation of the new gyroscopic calcualtions just made other instabilities more obvious? In other words: Can you rule out that the instabilities you experienced in your tests with Snappe are caused by anything other than the new gyroscopic code and only became obvious with the new (better?) calculations?
« Last Edit: January 05, 2018, 09:46:44 AM by Stout Johnson »
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HornetMaX

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Re: Questions about daily development
« Reply #376 on: January 06, 2018, 05:34:22 PM »
Snappe tested the MXB without gyroscopic forces extensively today, and it's worse in every area.
As expected :)

Same for GPB, so the gyroscopic forces have been re-enabled, but using the previous, stable, code.
Question: did GPB even suffer of instabilities tied to gyro forces at all ? I haven't seen much outside the occasional "normalization error" (for which I have no clue indicating it may come from gyro forces instability) ... so maybe the new ODE code was not even needed in the first place.

Checking the gyro forces computation should be relatively easy for a spinning wheel (if you have access to the current wheel state and external forces).




PiBoSo

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Re: Questions about daily development
« Reply #377 on: January 06, 2018, 09:09:54 PM »
Same for GPB, so the gyroscopic forces have been re-enabled, but using the previous, stable, code.
Question: did GPB even suffer of instabilities tied to gyro forces at all ? I haven't seen much outside the occasional "normalization error" (for which I have no clue indicating it may come from gyro forces instability) ... so maybe the new ODE code was not even needed in the first place.

No, it didn't suffer any instability. This is why I wrongly assumed that the new code was more accurate, as I couldn't see any other problem to solve.
Maybe GPB doesn't have stability problems because the wheels' inertia is closer to a box than a long stick, and because GPB uses small integration steps.
From what I can understand, most dynamics simulators ( that are not racing, of course ) run under 100hz and can use very odd-shaped objects.
Obviously your ambition outweighs your talent

HornetMaX

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Re: Questions about daily development
« Reply #378 on: January 08, 2018, 01:05:02 PM »
No, it didn't suffer any instability. This is why I wrongly assumed that the new code was more accurate, as I couldn't see any other problem to solve.
Maybe GPB doesn't have stability problems because the wheels' inertia is closer to a box than a long stick, and because GPB uses small integration steps.
Or maybe we just never reach the conditions for the instability to appear (due to the presence of the virtual rider + user inputs + road contact etc) so in practice we don't really care, especially if the "solution" to that "problem" is actually worse.

HornetMaX

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Re: Questions about daily development
« Reply #379 on: January 09, 2018, 03:35:38 PM »
OK, I had a better look at the paper and just looking at how the trajectories of the proposed solution differ from the true ones (in the test case, single body with no applied torque), it is clear this will not work for us.
We're surely better off with a method that stays closer to true trajectories with a risk of being unstable in specific situations than with a method that is globally stable but is fairly far from true trajectories.

Just wondering: ever thought about replacing the ode library with a different one ? Not really to solve any specific problem coming from the ode library itself, but maybe re-coding that part to a different library could help spot bugs/wrong stuff. It's probably quite an effort (especially if the other ode lib has a fairly different api), but ...

Did you know this ? https://simtk.org/projects/simbody

KG_03

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Re: Questions about daily development
« Reply #380 on: January 10, 2018, 01:02:09 PM »
As I see you talking about physics model I wonder what causes that on some tracks and curves the bike suspension starts to vibrate like there were many smal bumps. It is visible in the first and last turn in Victoria track not only on modded bikes but also in Murasama bike. In general the more powerfull the bike the effect is bigger.

BOBR6 84

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Re: Questions about daily development
« Reply #381 on: January 10, 2018, 04:36:41 PM »
As I see you talking about physics model I wonder what causes that on some tracks and curves the bike suspension starts to vibrate like there were many smal bumps. It is visible in the first and last turn in Victoria track not only on modded bikes but also in Murasama bike. In general the more powerfull the bike the effect is bigger.

I like to think its chatter.. but who knows lol

Warlock

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Re: Questions about daily development
« Reply #382 on: January 10, 2018, 04:53:08 PM »
Sounds to me like the track 3d mesh

KG_03

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Re: Questions about daily development
« Reply #383 on: January 20, 2018, 05:48:19 PM »
What? There wont be daily development logs?

matty0l215

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Re: Questions about daily development
« Reply #384 on: January 20, 2018, 07:44:24 PM »
What? There wont be daily development logs?

+1 on this

Also, Gone Shootin'?
« Last Edit: January 20, 2018, 09:11:20 PM by matty0l215 »

Reactive

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Re: Questions about daily development
« Reply #385 on: March 21, 2018, 09:09:51 PM »
Excuse my English, its not my native.
Ryzen7 1800x / Aorus GA-AX370 Gaming K7 / Hynix 16Gb x2 2993MHz / Samsung 960PRO 512 M.2 / nVidia GTX1060 6Gb / Windows 10 pro x64

Mace-x

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Re: Questions about daily development
« Reply #386 on: March 21, 2018, 10:04:30 PM »
interesting format, never heard of it.
might be a good thing to implement.