[ODE] Disappearing boxes.

[don]

I have a small test program with two boxes (0.5 per side) connected
with a slider joint.  The boxes are placed on the ground plane, and
for several steps, sit there fine, then suddenly they vanish.  Here
is what some debug statements show for the positions of the boxes
and the contacts (position and normal vector):


    Contact at (0.25,0.25,0)->(0,0,1)
    Contact at (0.25,-0.25,0)->(0,0,1)
    Contact at (-0.25,0.25,0)->(0,0,1)
    Contact at (1.25,0.25,0)->(0,0,1)
    Contact at (1.25,-0.25,0)->(0,0,1)
    Contact at (0.75,0.25,0)->(0,0,1)
    box[0] at 0.00, 0.00, 0.25
    box[1] at 1.00, 0.00, 0.25
    slider length = 0.00
    Contact at (-0.2499,-0.249876,-0.000537152)->(0,0,1)
    Contact at (0.2501,-0.249876,-0.000336663)->(0,0,1)
    Contact at (-0.2499,0.250124,-0.000288699)->(0,0,1)
    Contact at (0.750092,-0.249878,-0.000451106)->(0,0,1)
    Contact at (1.25009,-0.249878,-0.000267436)->(0,0,1)
    Contact at (0.750092,0.250122,-0.000207432)->(0,0,1)
    box[0] at -0.00, 0.00, 0.25
    box[1] at 1.00, 0.00, 0.25
    slider length = -0.00
    Contact at (-0.2499,-0.249876,-0.000578244)->(0,0,1)
    Contact at (-0.249896,0.250124,-0.000407131)->(0,0,1)
    Contact at (0.2501,-0.24988,-0.000336659)->(0,0,1)
    Contact at (0.750092,-0.249878,-0.000482246)->(0,0,1)
    Contact at (0.750095,0.250122,-0.000310571)->(0,0,1)
    Contact at (1.25009,-0.249882,-0.000267433)->(0,0,1)
    box[0] at -0.00, 0.00, 0.25
    box[1] at 1.00, 0.00, 0.25
    slider length = -0.00
    Contact at (-0.2499,-0.249876,-0.000555651)->(0,0,1)
    Contact at (-0.249898,0.250124,-0.000407131)->(0,0,1)
    Contact at (0.2501,-0.249878,-0.000336658)->(0,0,1)
    Contact at (0.750092,-0.249878,-0.000459326)->(0,0,1)
    Contact at (0.750093,0.250122,-0.000310571)->(0,0,1)
    Contact at (1.25009,-0.249879,-0.000267433)->(0,0,1)
    box[0] at 0.00, 0.00, 0.25
    box[1] at 1.00, 0.00, 0.25
    slider length = -0.00
    Contact at (-0.2499,-0.249876,-0.000535694)->(0,0,1)
    Contact at (-0.249898,0.250124,-0.00040713)->(0,0,1)
    Contact at (0.2501,-0.249877,-0.000336658)->(0,0,1)
    Contact at (0.750092,-0.249878,-0.000439514)->(0,0,1)
    Contact at (0.750093,0.250122,-0.00031057)->(0,0,1)
    Contact at (1.25009,-0.249879,-0.000267432)->(0,0,1)
    box[0] at -433652246062745205348723040640789462627348853706922884440403300779990644945749822588481223775572882836003225600.00, -74808686709466890340489562484868188643904491706967773687698533465468578897941594125131245161169041067285151744.00, 4088682472354953982016429309268625150041243088199935728551085795194540655534757057798347480352863846269304010964992.00
    box[1] at 433652246062745205348723040640789462627348853706922884440403300779990644945749822588481223775572882836003225600.00, 74808686709466890340489562484868188643904491706967773687698533465468578897941594125131245161169041067285151744.00, 2851064448790457136741608190450523618793438996546022139899023686123492217040914486824097747629179701130678933389312.00
    slider length = -1042450368414203386824011434795684809964944176404925549431571197216180692157059717757769163226535720872512061440.00

Don Reid