[ODE] Need help with hinge and non-uniformly distributed mass

[Keith Johnston]

Saw the video - very cool!  So it looks like you actually used a similar
solution - you attached a second body to use as a counterweight.  Did
you first try redistributing the mass of the arm of the treb so that it
would swing on its own around its center point?

I should have been more clear - you can attach the fixed axis of the
hinge anywhere you want, but the other end of the hinge is always at the
center of mass for the body.  The other issue is that the center of a
body is always at its center of mass.  

So there are two possibilities:

1. Create a hinge where the anchor is at the center of the body.
Because the body's center of mass is always at its center, the body does
not rotate.

2. Create a hinge where the anchor is off-center.  The body will 'swing'
around the anchor point (not rotate).

> -----Original Message-----
> From: ode-admin@q12.org [mailto:ode-admin@q12.org] On Behalf Of Nate W
> Sent: Wednesday, June 04, 2003 2:14 PM
> To: ode@q12.org
> Subject: RE: [ODE] Need help with hinge and non-uniformly 
> distributed mass
> 
> 
> On Wed, 4 Jun 2003, Keith Johnston wrote:
> 
> > First of all, I do not think it is possible to attach a hinge joint 
> > anywhere to an object other than at its center of mass.  At least I 
> > couldn't get it to work.  This was the fundamental problem I kept 
> > bumping into.  I wanted to have a single mass swing back and forth 
> > like a pendulum.
> 
> This is definitely possible with ODE.  For example, in the 
> trebuchet video I posted a few days ago, and the trebuchet's 
> counterweight is a body with a hinge anchored well away from 
> the body's center of mass.
> 
> I'm glad to hear that you found a way to get the pendulum you 
> wanted, but I'm certain that it's not necessary to use a 
> second body to make that work.  However, I'm just as stumped 
> as you are as to what exactly was wrong with your first attempt.
> 
> -- 
> 
> Nate Waddoups
> Redmond WA USA
> http://www.natew.com
> 
> 
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