Dynamic/Kinematic Motion Simulation explanation?

[AmateurNX]

Hello,

When making a motion simulation, there is a point where the user is asked to choose the environment: Dynamic of Kinematic. I've been having some trouble understanding the Kinematics part. When i try to use the kinematics environment I always get the error message that there are degrees of freedom left. But doesn't it mean that having no degrees of freedom left, there can be no movement? But to my knowledge, kinematics is the study of movement.

I usually always use the dynamics option but i was curious as to when i should actually use the kinematics option instead. The NX documentation only confuses me more.

Could anyone clarify this for me?

 

[ChrisAbbott]

Dynamics uses additional inputs to the motion beyond motor drivers, and driven joints. Primarily, that's gravity and momentum, which acts on any links that have degrees of freedom. That's why all links must have a mass, centre of mass, and moments of inertia.

Kinematics does not use gravity or anything other than the joints and driving inputs you define to drive the mechanism. As a result, it requires zero degrees of freedom to operate. The issue you have is that where there are any degrees of freedom, because gravity and momentum etc. are not taken into consideration, the solver doesn't know what should happen.

Chris Abbott
TEAM Engineering

http://www.team-eng.com

 

[ChrisAbbott]

In answer to your question, Kinematics is a very quick-to-solve mechanism type. It also allows an element of flexibility in what you want to drive and when, even after the solve. It is good for fully-defined mechanisms with no response to the weight of the bodies involved.

Dynamics is much more rigid in terms of the outputs you get, but is a much more realistic representation of the problem.

Chris Abbott
TEAM Engineering

http://www.team-eng.com

 

[AmateurNX]

I think i get it. I'll try to experiment a little bit.

Thanks for the quick reply!