BEPUphysics

Hi,

the case: I've made a basic rocket by using thruster from the demo with enough impulse to get kind of a thrust to weight ratio > 1.
The "rocket" is just a tall box, mass is 5000, thruster have (0,55000,0) as force/direction.

Rocket start a bit above the ground, thruster works well (space key activate them), speed increase, altitude increase, box's mass decrease (faking use of fuel is this very basic "simulator").

When going up, acceleration increase is obvious (not measured, yet).
After stopping using thrust (for example when mass left is ~ 100), Y linear velocity decrease then become negative, after going over 2000 units (m/s if 1 unit = 1 meter), BUT, this velocity decrease in a logarithmic way, very fast at the beginning then slower and slower until is doesn't go over -321.98 (m/s), only 2 digits as precision, and it stays at this value for about more than 50000 units (m) of free fall (linear momentum Y component doesn't change too).

It may be an issue or not, I just wish to understand what's going on there.
As there is no drag (yet), there's can't be such terminal velocity, and it should increase faster and faster going closer to the "ground" (Y =0), shouldn't it ?
Does the gravity actually change with "altitude" ? (I guess it should be a linear decreasing from Y=0 to ... very low/insignificant gravity at a very high Y value)

(links removed)


Thanks for the help.

Default LinearDamping is nonzero, which will have the effect of kinda-sorta drag. To get rid of it, set LinearDamping and AngularDamping to 0.

Damping and gravity do not vary with height or anything else. Damping is just the portion of momentum removed per second.

Norbo wrote:Default LinearDamping is nonzero, which will have the effect of kinda-sorta drag. To get rid of it, set LinearDamping and AngularDamping to 0.

Damping and gravity do not vary with height or anything else. Damping is just the portion of momentum removed per second.

ok thanks.

Any chance to get a gravity related to altitude of an entity (+ which could be enabled/disabled by a bool in the space settings) ?

I guess it could be made in the ForceUpdater method, at some cost, I may give it a shot, it would allow me to dig into BEPU internals and get a better knowledge of it.

Any chance to get a gravity related to altitude of an entity (+ which could be enabled/disabled by a bool in the space settings) ?

That's very application specific, so I wouldn't put it into the engine. You could add it to the ForceUpdater if you wanted, or set the Entity.Gravity, or any other approach which results in the velocity changing by desiredGravity * dt each time step.