Adding blocks to your model

The first step is to create a Simulation object instance

import bdsim

sim = bdsim.BDSim()
bd = sim.blockdiagram()

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.

Block-catalog shows how to obtain a list of all available blocks.

Blocks belong to several 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
EVENT	trigger an event when condition becomes true
NULL	discards all data
PRINT	Print value to console
STOP	Stop simulation when condition is true
WATCH	Add input to the watch list

Displays

Display blocks (subclass of GraphicsBlock → SinkBlock → Block) are graphical sinks.

Name	Description
ANIMATION	Create an animation from user-defined setup/update functions
SCOPE	Plot signals as function of time
SCOPEXY	Plot one signal against another
SCOPEXY1	Plot one signal against another with optional clipping

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
POW	raise input signal to a power
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

Continuous-time dynamics

Continuous blocks (subclass of ContinuousBlock → Block) have inputs and outputs and state and represent differential equations. TransferBlock, seen in older code, is a deprecated alias for ContinuousBlock — it's a subclass of ContinuousBlock, not the other way round.

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
DERIV2	derivative with second-order smoothing

Two more blocks are commonly used alongside these but aren't literally ContinuousBlock subclasses — they're SubsystemBlocks composed internally from simpler blocks:

Name	Description
DERIV	derivative with first-order smoothing
PID	PID control subsystem

Sampled-data (discrete-time) dynamics

Sampled blocks (subclass of SampledBlock → Block) have inputs and outputs and state and represent sampled-data dynamics. ClockedBlock, seen in older code, is a deprecated alias for SampledBlock.

Name	Description
DERIV_S	derivative, first order difference
INTEGRATOR_S	integration of input signals
LTI_SISO_S	dynamic system described in transfer-function form
LTI_SS_S	dynamic system described in state-space form
ZOH	zero-order hold

DINTEGRATOR is a deprecated alias for INTEGRATOR_S, not a separate block.

As with DERIV/PID above, PID_S is a SubsystemBlock rather than a literal SampledBlock subclass:

Name	Description
PID_S	PID control subsystem

Connections

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

Name	Description
DICT	convert input signals to a dict of signals
DEMUX	split a vector signal to individual signals
INDEX	index/slice selection for vectors, arrays, lists, tuples, strings, or dicts
ITEM	select specific item from a dict signal
MUX	concatenate signals into a vector 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.

Hardware I/O

Hardware I/O blocks (ANALOGIN, ANALOGOUT, DIGITALIN, DIGITALOUT, PWMOUT, TELEMETRY) are source/sink blocks that bind to a runtime I/O provider. They currently live on the unmerged feat/realtime branch, not main — see Real-time overview.

Spatial

Spatial blocks mostly operate on SO2/SO3/SE2/SE3 types when spatialmath is installed (subclass of FunctionBlock → Block), except for the two pose integrators which are stateful (ContinuousBlock/SampledBlock subclasses).

Name	Description
POSE_INVERSE	inverse of pose input
POSE_POSTMUL	post-multiply input pose by a constant pose
POSE_PREMUL	pre-multiply input pose by a constant pose
TRANSFORM_VECTOR	transform Euclidean vector by pose input
POSEINTEGRATOR	integrate spatial velocity to pose (continuous-time)
DPOSEINTEGRATOR	integrate spatial velocity to pose (sampled-data)

Vision

vision.py is currently a placeholder module; there are no registered vision blocks at this time.

External block sets

When toolboxes=True (the default), bdsim also loads block sets contributed by robotics-toolbox-python (RTB) and machinevision-toolbox-python (MVTB). These packages own and document their own blocks in full; the tables below are a quick-reference index of what's currently registered (sim.blocks(), see Block path), not a substitute for their own docs.

Robotics (from RTB)

Module	Blocks
roboticstoolbox.blocks.arm	FKINE, IKINE, JACOBIAN, ARMPLOT, JTRAJ, CTRAJ, CIRCLEPATH, TRAPEZOIDAL, TRAJ, IDYN, GRAVLOAD_X, INERTIA, INERTIA_X, FDYN, FDYN_X
roboticstoolbox.blocks.mobile	BICYCLE, UNICYCLE, DIFFSTEER, VEHICLEPLOT
roboticstoolbox.blocks.spatial	TR2DELTA, DELTA2TR, POINT2TR, TR2T
roboticstoolbox.blocks.uav	MULTIROTOR, MULTIROTORMIXER, MULTIROTORPLOT

A few worth calling out directly since they appear elsewhere in this wiki:

Name	Description
ARMPLOT	Animate robot arm using Matplotlib
VEHICLEPLOT	Animate a wheeled vehicle's pose using Matplotlib
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 (from MVTB)

Module	Blocks
machinevisiontoolbox.blocks.camera	CAMERA, VISJAC_P, ESTPOSE_P, IMAGEPLANE