Adding blocks

The first step is to create a Simulation object instance

import bdsim

bd = bdsim.BDSim()

which loads blocks from a number of modules in the bdsim/blocks folder.

We create blocks using this object's factory methods. For example

gain = bd.GAIN(4)

is a gain block represented by an instance of the class Gain

>>> type(gain)
<class 'bdsim.blocks.functions.Gain'>

which has the class hierarchy Gain → FunctionBlock → Block.

Blocks belong to one of four main subclasses:

Standard blocks

Sources

Source blocks (subclass of SourceBlock → Block) have an output, but no inputs.

Name	Description
CONSTANT	A constant of any type
PIECEWISE	a piecewise constant function of time
RAMP	a linear ramp with a start time
STEP	a step (Heaviside) function of time
TIME	time since start of simulation
WAVEFORM	sine, square or triangle function of time

Sinks

Sink blocks (subclass of SinkBlock → Block) have inputs, but no outputs.

Name	Description
NULL	discards all data
PRINT	Print value to console
STOP	Stop simulation when condition is true
WATCH	Add input to the watch list
SCOPE	Plot signals as function of time
SCOPEXY	Plot one signal against another
VEHICLE	2D animation of ground vehicle motion
MULTIROTORPLOT	3D animation of multi-rotor motion

Functions

Function blocks (subclass of FunctionBlock → Block) have inputs and outputs and perform some linear or non-linear operation.

Name	Description
CLIP	limit signal values
FUNCTION	apply Python function to inputs
GAIN	multiply input by constant, any of input or constant can be numpy arrays
INTERPOLATE	1D interpolation of data
PROD	multiplication and division of signals
SUM	addition and subtraction of signals

Linear algebra

Linear algebra blocks (subclass of FunctionBlock → Block) have inputs and outputs.

Name	Description
COND	matrix condition number
DET	matrix determinant
FLATTEN	flatten matrix to 1D array
INVERSE	matrix inverse
NORM	vector norm
SLICE1	slice of 1D array
SLICE2	slice of 2D array
TRANSPOSE	matrix transpose

Transfers

Transfer blocks (subclass of TransferBlock → Block) have inputs and outputs and state and represent differential equations.

Name	Description
INTEGRATOR	integration of input signals
LTI_SISO	dynamic system described in transfer-function form
LTI_SS	dynamic system described in state-space form
POSEINTEGRATOR	integrate spatial velocity to pose

Discrete-time transfers

Transfer blocks (subclass of TransferBlock → Block) have inputs and outputs and state and represent continuous-time differential equations.

Name	Description
DINTEGRATOR	integration of input signals
DPOSEINTEGRATOR	integrate spatial velocity to pose
ZOH	zero-order hold

Connections

Connection blocks (subclass of FunctionBlock → Block) manipulate vector and dict signals.

Name	Description
MUX	concatenate signals into a vector signal
DEMUX	split a vector signal to individual signals
DICT	convert input signals to a dict of signals
ITEM	select specific item from a dict signal

Subsystem blocks (subclass of SubsystemBlock → Block) connect a block diagram subsystem to a parent block diagram.

Name	Description
INPORT	Inputs to the subsystem, like a SourceBlock
OUTPORT	Outputs from the subsystem, like a SinkBlock
SUBSYSTEM	Represents the subsystem in the parent block diagram, like a FunctionBlock

The inputs to a SUBSYSTEM block are the outputs of that subsystem's INPORT, and the inputs to the subsystem's OUTPORT are the outputs of the SUBSYSTEM block.

Unlike Simulink, there is only one input or output block per subsystem, but they can have multiple inputs each.

External block sets

Robotics

Robot models

Robot blocks.

Name	Description
ARMPLOT	Animate robot arm using Matplotlib
CTRAJ	Cartesian trajectory
CIRCLEPATH	circular trajectory
DELTA2TR	spatial displacement to SE(3)
FDYN	manipulator forward dynamics
FDYN_X	manipulator forward dynamics in task space
FKINE	manipulator forward kinematics trajectory
GRAVLOAD	manipulator forward kinematics trajectory
BICYCLE	Bicycle kinematics as for a car-like vehicle
UNICYCLE	Unicycle kinematics
DIFFSTEER	Differential-steer kinematics with wheel speed inputs
MULTIROTOR	Dynamics of a multi-rotor drone

Machine Vision