[ODE] Bounciness on Trimesh terrain

[Shamyl Zakariya]

> Are you adding any dampening to your bodies? A rotational torque and a 
> linear velocity that's something like -0.01 or -0.02 the magnitude of 
> your actual velocity will help a lot.

No, but that sounds like a good idea -- I've already got mechanisms in 
place to do this ( to simulate aerodynamic drag... )

> Also, what is the ERP and CFM of the suspension joint? You shouldn't 
> have to tweak the contacts, but the suspension is very sensitive. Try 
> making it stiffer -- it may be that you currently have found a 
> resonance point for your suspension spring.

Also sounds like a good idea. More tweak-run-tweak cycles ahead, I 
assume ;)

> Last -- are you running those 80 Hz at a FIXED time step? If you're 
> using a variable time step, it will not ever be stable. You have to 
> make sure you always step physics the same amount of time each time 
> (that would be 0.0125 seconds for 80 Hz).

Yeah -- I learned a while back that only fixed timesteps work. I've got 
the physics running in a separate thread.

Thanks!


Shamyl Zakariya
   "this is, after all, one of those movies where people spend a great
   deal of time looking at things and pointing."
	From a review of _Fantastic Voyage_

On Jan 17, 2005, at 11:38 AM, Jon Watte wrote:

>
> Are you adding any dampening to your bodies? A rotational torque and a 
> linear velocity that's something like -0.01 or -0.02 the magnitude of 
> your actual velocity will help a lot.
>
> Also, what is the ERP and CFM of the suspension joint? You shouldn't 
> have to tweak the contacts, but the suspension is very sensitive. Try 
> making it stiffer -- it may be that you currently have found a 
> resonance point for your suspension spring.
>
> Last -- are you running those 80 Hz at a FIXED time step? If you're 
> using a variable time step, it will not ever be stable. You have to 
> make sure you always step physics the same amount of time each time 
> (that would be 0.0125 seconds for 80 Hz).
>
> Make sure you do all three for best stability!
>
> Cheers,
>
> 			/ h+
>
>
> -----Original Message-----
> From: ode-bounces at q12.org [mailto:ode-bounces at q12.org]On Behalf Of
> Shamyl Zakariya
> Sent: Monday, January 17, 2005 5:57 AM
> To: ODE mailing list
> Subject: [ODE] Bounciness on Trimesh terrain
>
>
> All
>
> I'm writing a game for fun. I have a 4 wheeled vehicle, using a
> simplistic but more or less realistic suspension system and spherical
> wheels, on a trimesh terrain.
>
> Now, the game's been working great -- but in the interest of polish and
> more realistic scale I recently "shrank" the player vehicle as I had
> realized that it was too big to be plausible. Now, the vehicle's about
> 2.5 meters long with wheel spheres about 1 meter diameter. ( it was
> huge before... something like 8 meters long )
>
> After shrinking it, the vehicle *bounces* heavily on flat surfaces of
> the terrain. It just sits there and vibrates. As soon as you drive onto
> a hill, or go to any raised surface the bouncing stops and it behaves
> quite well. But, drive back to the flat surface and bouncing starts
> again.
>
> I've tried a few things to minimize or eliminate bounciness.
>
> 	-I raised the level of low points in the terrain to be 1m higher than
> 	 the "ground plane", to eliminate any chances of coplanar conflict
>
> 	-I've tuned dContact parameters ( set bounce to zero, twiddled
> soft_cfm and
> 	 soft_erp ) until my fingers bled.
>
> But I've been unable to quelch it completely.
>
> That said, I could just go back to the full-sized vehicle I was using
> before but I'd like to have more realistic scale in my game.
>
> For reference, I'm using ODE 0.5 on Mac OS X. I'm running ODE at about
> 80 Hz, so I don't think it's an issue with too long a timestep, and as
> I said before, when I drive up a hill it becomes rock-solid and stable.
>
> The issue is clearly with terrain triangles with a normal pointing
> straight up.
>
> Any ideas?
>
> Shamyl Zakariya
>    "this is, after all, one of those movies where people spend a great
>    deal of time looking at things and pointing."
> 	From a review of _Fantastic Voyage_
>
>
>
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