trep
- param system
An instance of
Systemto add the force to.- type system
System- param name
A string that uniquely identifies the force.
This is the base class for all forces in a System. It should never be created directly. Forces are created by instantiating a specific type of force..
See builtin_forces for the built-in types of forces. Additional forces can be added through either the Python or C-API.
Forces are used to include non-conservative and control forces in a mechanical system. Forces must be expressed in the generalized coordinates of the system. Conservative forces like gravity or spring-like potentials should be implemented using Potential instead.
Force.system
The System that this force belongs to.
(read-only)
Force.name
The name of this force or None.
Force.f(q)
- param q
Configuration variable
- type q
Config
Calculate the force on configuration variable q at the current state of the system.
Required for Calculations| Desired Calculation | Required |
|---|---|
| Continuous Dynamics |
|
| 1st Derivative |
|
| 2nd Derivative |
|
| Discrete Dynamics |
|
| 1st Derivative |
|
| 2nd Derivative |
|
Force.f_dq(q, q1)
- param q
Configuration variable
- type q
Config- param q1
Configuration variable
- type q1
Config
Calculate the derivative of the force on configuration variable q with respect to the value of q1.
Required for Calculations| Desired Calculation | Required |
|---|---|
| Continuous Dynamics |
|
| 1st Derivative |
|
| 2nd Derivative |
|
| Discrete Dynamics |
|
| 1st Derivative |
|
| 2nd Derivative |
|
Force.f_ddq(q, dq1)
- param q
Configuration variable
- type q
Config- param dq1
Configuration variable
- type dq1
Config
Calculate the derivative of the force on configuration variable q with respect to the velocity of dq1.
Required for Calculations| Desired Calculation | Required |
|---|---|
| Continuous Dynamics |
|
| 1st Derivative |
|
| 2nd Derivative |
|
| Discrete Dynamics |
|
| 1st Derivative |
|
| 2nd Derivative |
|
Force.f_du(q, u1)
- param q
Configuration variable
- type q
Config- param u1
Input variable
- type u1
Input
Calculate the derivative of the force on configuration variable q with respect to the value of u1.
Required for Calculations| Desired Calculation | Required |
|---|---|
| Continuous Dynamics |
|
| 1st Derivative |
|
| 2nd Derivative |
|
| Discrete Dynamics |
|
| 1st Derivative |
|
| 2nd Derivative |
|
Force.f_dqdq(q, q1, q2)
- param q
Configuration variable
- type q
Config- param q1
Configuration variable
- type q1
Config- param q2
Configuration variable
- type q2
Config
Calculate the second derivative of the force on configuration variable q with respect to the value of q1 and the value of q2.
Required for Calculations| Desired Calculation | Required |
|---|---|
| Continuous Dynamics |
|
| 1st Derivative |
|
| 2nd Derivative |
|
| Discrete Dynamics |
|
| 1st Derivative |
|
| 2nd Derivative |
|
Force.f_ddqdq(q, dq1, q2)
- param q
Configuration variable
- type q
Config- param dq1
Configuration variable
- type dq1
Config- param q2
Configuration variable
- type q2
Config
Calculate the second derivative of the force on configuration variable q with respect to the velocity of dq1 and the value of q2.
Required for Calculations| Desired Calculation | Required |
|---|---|
| Continuous Dynamics |
|
| 1st Derivative |
|
| 2nd Derivative |
|
| Discrete Dynamics |
|
| 1st Derivative |
|
| 2nd Derivative |
|
Force.f_ddqddq(q, dq1, dq2)
- param q
Configuration variable
- type q
Config- param dq1
Configuration variable
- type dq1
Config- param dq2
Configuration variable
- type dq2
Config
Calculate the second derivative of the force on configuration variable q with respect to the velocity of dq1 and the velocity of q2.
Required for Calculations| Desired Calculation | Required |
|---|---|
| Continuous Dynamics |
|
| 1st Derivative |
|
| 2nd Derivative |
|
| Discrete Dynamics |
|
| 1st Derivative |
|
| 2nd Derivative |
|
Force.f_dudq(q, u1, q2)
- param q
Configuration variable
- type q
Config- param u1
Input variable
- type u1
Input- param q2
Configuration variable
- type q2
Config
Calculate the second derivative of the force on configuration variable q with respect to the value of u1 and the value of q2.
Required for Calculations| Desired Calculation | Required |
|---|---|
| Continuous Dynamics |
|
| 1st Derivative |
|
| 2nd Derivative |
|
| Discrete Dynamics |
|
| 1st Derivative |
|
| 2nd Derivative |
|
Force.f_duddq(q, u1, dq2)
- param q
Configuration variable
- type q
Config- param u1
Input variable
- type u1
Input- param dq2
Configuration variable
- type dq2
Config
Calculate the second derivative of the force on configuration variable q with respect to the value of u1 and the velocity of q2.
Required for Calculations| Desired Calculation | Required |
|---|---|
| Continuous Dynamics |
|
| 1st Derivative |
|
| 2nd Derivative |
|
| Discrete Dynamics |
|
| 1st Derivative |
|
| 2nd Derivative |
|
Force.f_dudu(q, u1, u2)
- param q
Configuration variable
- type q
Config- param u1
Input variable
- type u1
Input- param u2
Input variable
- type u2
Input
Calculate the second derivative of the force on configuration variable q with respect to the value of u1 and the value of u2.
Required for Calculations| Desired Calculation | Required |
|---|---|
| Continuous Dynamics |
|
| 1st Derivative |
|
| 2nd Derivative |
|
| Discrete Dynamics |
|
| 1st Derivative |
|
| 2nd Derivative |
|
It is important that the derivatives of f are correct. The easiest way to check their correctness is to approximate each derivative using numeric differentiation. These methods are provided to perform this test. The derivatives are only compared at the current configuration of the system. For improved coverage, try running each test several times at different configurations.
Force.validate_h_dq(delta=1e-6, tolerance=1e-6, verbose=False) Force.validate_h_ddq(delta=1e-6, tolerance=1e-6, verbose=False) Force.validate_h_du(delta=1e-6, tolerance=1e-6, verbose=False) Force.validate_h_dqdq(delta=1e-6, tolerance=1e-6, verbose=False) Force.validate_h_ddqdq(delta=1e-6, tolerance=1e-6, verbose=False) Force.validate_h_ddqddq(delta=1e-6, tolerance=1e-6, verbose=False) Force.validate_h_dudq(delta=1e-6, tolerance=1e-6, verbose=False) Force.validate_h_duddq(delta=1e-6, tolerance=1e-6, verbose=False) Force.validate_h_dudu(delta=1e-6, tolerance=1e-6, verbose=False)
- param delta
Amount to add to each configuration, velocity, or input.
- param tolerance
Acceptable difference between the calculated and approximate derivatives
- param verbose
Boolean to print error and result messages.
- rtype
Boolean indicating if all tests passed
Check the derivatives against the approximate numeric derivative calculated from one less derivative (ie, approximate f_dq from f and f_dudq from f_du).
See System.test_derivative_dq, System.test_derivative_ddq, and System.test_derivative_du for details of the approximation and comparison.
Force.opengl_draw()
Draw a representation of this force in the current OpenGL context. The OpenGL coordinate frame will be in the System's root coordinate frame.
This function is called by the automatic visualization tools. The default implementation does nothing.