# Touchdown points for collision detection, etc.

#### Sword7

##### Member
I reviewed Orbiter source codes and learned about touchdown points for collision detection and friction, etc. I noticed that touchdown vertices use dampness, stiffness and compression. Also I see routines use them for rolling as rover, taking off and landing. What are them for? Does anyone have good sources of books explaining dampness, stiffness and compression?

I found a book on Amazon called "Road and Off-Road Vehicle System Dynamics Handbook" from CRC Press. Does anyone think about that and recommend that?

Does anyone have a good listing of books for rover simulation, taking off/landing procedures, etc?

Thanks,
Tim

#### Sword7

##### Member
I found a book called "Real-Time Collision Detection" from CRC Press but it did not mention about stiffness and damping. Physics books mentioned that. Objects are hard or soft depending on its mass. Collision detection need sitffness and damping calculation for realistic suspension, bouncing and contacting effect.

#### francisdrake

If you are interested in how Orbiter handles touchdown points, a good source is the Orbitersdk, here the API_Reference.pdf.

Stiffness is how rigid a contact point reacts to compression. Think of it as a spring. The unit is N/m.
The Deltaglider gear points have a stiffness of 1e6, while the hard contour points have 1e7 (= 10 x as stiff).

When a contact point is moving, damping wants to slow it down again. This damping factor is 1e5 for all DeltaGlider contact points.
___

For a 'wobbly' contact, e.g. when a capsule drops into water and it shall bounce around for a while, less stiffness and damping is used. For the Orion I use a stiffness of 9e4, and a damping of 1e2.

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