The Free Body Diagram (FBD) Solver biomechanics tool has been developed from a concept by Geoff Strauss. The html5 and Javascript code enabling its delivery on for the web has been written by James Strauss.
The Free Body Diagram Solver (FBD) has been developed from the Vector Summator biomechanics tool. As such, the Free Body Diagram Solver it has a number of features in common with the Vector Summator biomechanics tool. It utilises:
In addition since moments of force must be calculated in the solution of free body diagrams, boxes for the input of additional variables and output of data into the table has been enabled. The additional input boxes allow data for the following variables: Segment Orientation - the segment orientation is the direction of the segment defined by the distal endpoint and the angle of the segment from the right hand horizontal. Segment Length - the segment length (in metres), the distance from the distal to proximal to landmarks can be can be input. The proximal landmark is defined as the axis of rotation for the joint of interest. End to Axis of Rotation - this specification of length (in metres) enables segments of length longer than the distance from the distal to proximal landmarks to be input. For example the forearm segment has an attachment for the triceps muscle that is behind the elbow joint at a position that is an extension of the segment length (the distance from the proximal to distal landmarks).
The first addition to the table is a column that allows the force type to be defined as an internal or external force (a force acting from the segment vs. acting onto the segment, respectively). To calculate the magnitude and direction of a moment of force distance both force (magnitude and direction) and perpendicular distance values are required. If the distance along the segment from the axis of rotation (joint centre) to the point of application of a force is known, and the direction of the force is known relative to the segment orientation, then the perpendicular distance can be calculated.
It is more difficult to work in reverse in these problems. That is, when a perpendicular distance is provided, additional information about the direction of the rotation is required.
The input cells in the table currently require a distance along the segment from the axis of rotation (joint centre) to the point of application of a force, and calculate a perpendicular distance.
Finally the moment of force the magnitude and direction are calculated and displayed in the last column.
The three graphical displays are:
The moment display varies in arc length and in line thickness - the longer the arc length and the thicker the arc width the greater the moment of force. Moments of force are limited to being displayed through a 180 degree arc.
By checking the Calculate Resultant box, the resultant moment magnitude and direction are displayed in the table.
By checking the Show Resultant box the resultant moment magnitude and direction are displayed in the graphs.
By checking the Calculate Equilibrium box, the equilibrium moment magnitude and direction are displayed in the table.
By checking the Show Equilibrium box the equilibrium moment magnitude and direction are displayed in the graphs.
Geoff and James Strauss July 2011.