# COUPLER

Returns force component due to Constraint_Coupler element in reference frame of marker RM.

## Format

COUPLER(id, jflag, comp, RM)

## Description

jflag indicates whether force acting on I or J marker is desired. The Constraint_Coupler element can involve either four markers for 2-joint couplers (I, J on the first joint and I, J on the second joint) or six markers for 3-joint couplers (I, J on the first joint, I, J on the second joint, and I, J on third joint).

## Arguments

id
The ID of the Constraint_Coupler element.
jflag
jflag = 0: forces/torques on the I marker of the first joint associated with the 2- or 3-joint coupler.
jflag = 1: forces/torques on the J marker of the first joint associated with the 2- or 3-joint coupler.
jflag = 2: forces/torques on the I marker of the second joint associated with the 2- or 3-joint coupler.
jflag = 3: forces/torques on the J marker of the second joint associated with the 2- or 3-joint coupler.
jflag = 4: forces/torques on the I marker of the third joint associated with the 3-joint coupler.
jflag = 5: forces/torques on the J marker of the third joint associated with the 3-joint coupler.
component
1
returns the force magnitude.
2
returns the force x component.
3
returns the force y component.
4
returns the force z component.
5
returns the torque magnitude.
6
returns the torque x component.
7
returns the torque y component.
8
returns the torque z component.

## Example

<Post_Request
comment   = "frc-expr"
id        = "70000044"
type      = "EXPRESSION"
expr1     = "COUPLER(10,0,1, 20)"
expr2     = "COUPLER(10,0,2, 20)"
expr3     = "COUPLER(10,0,3, 20)"
expr4     = "COUPLER(10,0,4, 20)"
expr5     = "COUPLER(10,0,5, 20)"
expr6     = "COUPLER(10,0,6, 20)"
expr7     = "COUPLER(10,0,7, 20)"
expr8     = "COUPLER(10,0,8, 20)"
/>

This request element stores the COUPLER element forces into column vectors F1 through F8 of the request frc-expr.