## Collision object disappear

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KKW
Posts: 8
Joined: 03 Feb 2021, 13:04

### Collision object disappear

Hi,

I found an object disappear problem when running simulation, it is as the video shows

if not reachable, here is the link

i have tested several times, the disappearing often occurs a period of time after they first collide.
According to a previous topic, i checked
• mass varies from 1e-3 to 1 kg
• principle moment of inertia/mass from 1e-6 to 1e-3,
• force of the joint from 4 to 10 Nm
• usingsim.getContactInfo to show force, maximum around 5-7N
have no clue why they disappear, is the stick to thin? the disappearing one in the video has mass 0.02kg, principle moment of inertia/mass 7e-4, 7e-4 and 7e-6.
Or should i reduce the simulation timestep? now is 3ms under ode engine.

the scene file is here
Thanks for any suggestion
Best Regards,
KKW

coppelia
Site Admin
Posts: 8450
Joined: 14 Dec 2012, 00:25

### Re: Collision object disappear

Hello,

objects disappearing are usually the result of the physics engine writing/computing bad values for object positions/orientations. In your case the objects that have disappeared have an illegal position (e.g. NaN, not a number). You can also provoke this by writing Nan-type values to object positions, inside of a script.

Try to monitor specific values to see if you get something funny just before an objects disappears (the object will however still be visible in the scene hierarchy).

Cheers