## Simple bar rotating

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hamzaali
Posts: 2
Joined: 18 Jan 2018, 13:41

### Simple bar rotating

Hi Guys,
I am beginner to V-rep and this forum. So sorry in advance for etiquette.

Model:
i am rotating a simple bar, undamped and zero friction.

Problem:
After running the simulation, i found out that i leave bar at -90 degree. But the free vibration could not reach -90 degree during oscillation it was -83 degree.

https://mega.nz/#!IGBXEDYS!ETVNMkVUof0U ... KrSyypgBKo

As it is basic physics, energy is conserved, how can i reach -90 degree during oscillation?

coppelia
Posts: 6968
Joined: 14 Dec 2012, 00:25

### Re: Simple bar rotating

Hello,

this is directly dependent on the physics engine you use. You can notice that with the Newton engine, the oscillation amplitude is growing. Each physics engine will use different parameters and perform different calculations. This is sometimes difficult to influence. You will have to look at the dynamic parameters of joints, shapes, and also at the overall dynamic settings for the physics engine (such as dynamic simulation step size, constraint solving iterations, damping, kinetic loss, etc.).

Best in your situation is to reduce the dynamic simulation step size to 1ms: you can do this in the dynamics engine general properties. The reason why this has such a large influence is because physics engines have difficulties handling large rotational velocities.

Cheers

hamzaali
Posts: 2
Joined: 18 Jan 2018, 13:41

### Re: Simple bar rotating

coppelia wrote:
22 Jan 2018, 09:47
Hello,

this is directly dependent on the physics engine you use. You can notice that with the Newton engine, the oscillation amplitude is growing. Each physics engine will use different parameters and perform different calculations. This is sometimes difficult to influence. You will have to look at the dynamic parameters of joints, shapes, and also at the overall dynamic settings for the physics engine (such as dynamic simulation step size, constraint solving iterations, damping, kinetic loss, etc.).

Best in your situation is to reduce the dynamic simulation step size to 1ms: you can do this in the dynamics engine general properties. The reason why this has such a large influence is because physics engines have difficulties handling large rotational velocities.

Cheers
Hey I reduced 5e-3 to 1 e-4 and the problem was almost solved.
Can you please explain, what is the reliability and credibility of my simulation in V-rep? because from what i think it can't be used without knowing the results, because it will mess up even in basic simulation!!!

coppelia