A Kinetostatic Analysis calculates the resultant forces1 at joints from a motion that is imposed on the mechanism by an 'idealised power source2. MechDesigner will do the Kinetostatic-Analysis of each kinematic-chain on a Mechanism-Plane.
A Dynamic Analysis is the opposite. It calculates the resultant motions of the mechanism from a force or torque that is imposed on the mechanism. MechDesigner does not do a 'dynamic-analysis'
1: 'Force': when we use the word 'force', it will refer to a 'generalised force', which will include 'moments'.
1: Other 'schools' call these Dynamic-Forces. See Dynamic Forces.
2: An Idealised Power Source [also Fictitious Power Source] has an infinite capacity to move the parts exactly as given by the planned motion. A simple example of an 'Idealized Power Source' would be a cam-shaft that does not deviate from constant velocity even though the torque required to drive the cam-shaft is changing rapidly.
Kinetostatic-Forces are a function of:
Kinetostatic-Forces do not include:
Kinetostatic-Forces are for 'Ideal' Kinematic-Chains:
It is important that you configure the Power Source correctly for each kinematic-chain before you analyse forces.
That is, you must tell MechDesigner at which joint [or cam or spring or gear] each kinematic-chain gets its 'power'.
* Note: The Moment Vector we show at a joint is the Torque a Servomotor needs to provide to the mechanism. When you add a Servomotor and Gearbox, you must also accelerate their inertia, and overcome their friction. To find the Servomotor and Gearbox combination for your application, see Kinetostatic Motor Torque and Speed Data.
In MechDesigner, each kinematic-chain has three different possible sources of 'Power':
The Torque and Force values at each joint are a function of the joint you select for the Power Source.
We can illustrate this with a simple mechanism
We model a four-bar kinematic-chain, arranged as a simple a parallelogram [see images below]. The angle between each part is 90º. See the images below.
The four-bar includes:
This is a Rocker. It is the vertical Part on the left.
The Rocker has a 1kg mass that is 100mm horizontally to the left of the Pin-Joint made with the Base-Part [Local Coordinates in Rocker 0,100]. Its weight is ~9.81N [1kg * 9.81m/s/s=9.81N].
There are two Parts: one horizontal, the other vertical and parallel to the Rocker, on the right.
When we configure the power source we nominate which joint, cam, spring or gear that we want to be the 'drive' for the Mechanism.
To illustrate how important it is to nominate the correct Joint, we will Configure the Power Source to be at two different joints in the 'Simple Mechanism' below.
The Mechanism is stationary. There is a Mass to the left Side, which belongs to the vertical Part to the left of the mechanism.
The position of the mass does not change when we move the Power Source from the left to the right.
However, when we move the Power-Source, the resultant Forces at each Joint are completely different.
Simple Mechanism : Power Source at Bottom-Left Joint.
Configure Power Source 1
Put the Power Source at the Pin-Joint on the left, near to the Mass.
We can imagine that the Drive Torque keeps the Rocker in its vertical position.
Simple Mechanism : Power Source at Bottom-Right Joint
Configure Power Source 2
Put the Power Source at the right Pin-Joint. The Mass does not change from Option 1.