[ODE] why wheel as sphere ?

[Bob Dowland]

> (Well, maybe that was the general hint in your message Bob but just 
> asking for clarity on the matter :) )

No worries - that was exactly what I was saying. If you want to explore this, and don't know how to derive an inertia tensor n stuff.. get a book on engineering maths look in the table at the back for the inertia tensors of various shells and solids - if there is no table - get another book and repeat while(table not found) ;), then..

> If anyone has done some good testing on this it would be interseting to hear about the results.

You could have some fun spending a couple of days (making your own results) - by experimenting with different mass distributions or combinations of distributions where each represents a component of your wheel, eg a solid cylinder (axle bearing) surrounded by the shell of a torus (tire), something for the break assembly, etc.. whatever you like.

:)

Bob.



> -----Original Message-----
> From: Hannes Norda [mailto:norda at customred.com]
> Sent: 13 October 2004 11:58
> To: Bob Dowland
> Cc: Michael Rauh; Nicola Lugato; ode at q12.org
> Subject: Re: [ODE] why wheel as sphere ?
> 
> 
> I haven't got much experience programming vehicles in ODE, 
> but how about 
> using a sphere-geom and then setting a cylinder-mass on the body?
> 
> (Well, maybe that was the general hint in your message Bob but just 
> asking for clarity on the matter :) )
> 
> Wouldn't that behave better than a sphere-mass?
> 
> If anyone has done some good testing on this it would be 
> interseting to 
> hear about the results.
> 
> Cheers
> 
> /Hannes
> 
> 
> 
> Bob Dowland wrote:
> >>Just try driving around on a TriMesh with cylinders. If you 
> get happy
> > 
> > 
> > Ay there's the rub...
> > 
> > 
> >>>why not cylinders, that is the right shape?
> > 
> > 	
> > cyl<>trimesh: cylinder rims against tri edges - lots of 
> hard edgy contacts to snag on.
> > 
> > But true "inner-wheel-nature" is not in the shell used for 
> contact detection, it's mostly about mass distribution. ie. 
> the values you put in the inertia matrix. This is where most 
> of the obvious dynamics props like tendency to remain 
> vertical while spinning etc.. come from.
> > 
> > So when people claim they are using spheres for wheels, 
> this may just be short-hand for we are using a spherical 
> contact sensor/probe, others use rays of course which again 
> aren't very wheel shaped - the devil is in the (mass) distribution.
> > 
> > :)
> > 
> > Bob.
> > 
> > 
> > 
> >>-----Original Message-----
> >>From: Michael Rauh [mailto:michael.rauh at gmail.com]
> >>Sent: 12 October 2004 08:48
> >>To: Nicola Lugato
> >>Cc: ode at q12.org
> >>Subject: Re: [ODE] why wheel as sphere ?
> >>
> >>
> >>Just try driving around on a TriMesh with cylinders. If you 
> get happy
> >>with the behaviour, you can of course use them :-)
> >>
> >>Greets
> >>Michael
> >>
> >>
> >>On Mon, 11 Oct 2004 20:18:11 +0200, Nicola Lugato
> >><nicola.lugato at gmail.com> wrote:
> >>
> >>>Hi! I'm new to this list :)
> >>>I'm trying ODE and it seems a great library!
> >>>I've a question: why car simulation always uses sphere as 
> wheel? why
> >>>not cylinders, that is the right shape?
> >>>Are there other cases where it is better to use a geom that is
> >>>different from the real shape ?
> >>>
> >>>Thanks!
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