Unicycle
- class roboticstoolbox.mobile.Unicycle(W=1, steer_max=inf, **kwargs)[source]
Bases:
VehicleBase
- __init__(W=1, steer_max=inf, **kwargs)[source]
Create unicycle kinematic model
- Parameters:
W (float, optional) – vehicle width, defaults to 1
steer_max (float) – maximum turn rate
kwargs – additional arguments passed to
VehicleBase
constructor
Model the motion of a unicycle model with equations of motion given by:
\[\begin{split}\dot{x} &= v \cos \theta \\ \dot{y} &= v \sin \theta \\ \dot{\theta} &= \omega\end{split}\]where \(v\) is the velocity in body frame x-direction, and \(\omega\) is the turn rate.
- deriv(x, u, limits=True)[source]
Time derivative of state
- Parameters:
x (array_like(3)) – vehicle state \((x, y, \theta)\)
u (array_like(2)) – control input \((v, \omega)\)
limits (bool) – limits are applied to input, default True
- Returns:
state derivative \((\dot{x}, \dot{y}, \dot{\theta})\)
- Return type:
ndarray(3)
Returns the time derivative of state (3x1) at the state
x
with velocity \(v\) and turn rate \(\omega\)\[\begin{split}\dot{x} &= v \cos \theta \\ \dot{y} &= v \sin \theta \\ \dot{\theta} &= \omega\end{split}\]If
limits
is True then speed, acceleration and steer-angle limits are applied tou
.- Seealso:
- u_limited(u)[source]
Apply vehicle velocity, acceleration and steering limits
- Parameters:
u (array_like(2)) – Desired vehicle inputs \((v, \omega)\)
- Returns:
Allowable vehicle inputs \((v, \omega)\)
- Return type:
ndarray(2)
Velocity and acceleration limits are applied to \(v\) and turn rate limits are applied to \(\omega\).
- Fv(x, odo)
Jacobian of state transition function df/dv
- Parameters:
x (array_like(3)) – vehicle state \((x, y, \theta)\)
odo (array_like(2)) – vehicle odometry \((\delta_d, \delta_\theta)\)
- Returns:
Jacobian matrix
- Return type:
ndarray(3,2)
Returns the Jacobian matrix \(\frac{\partial \vec{f}}{\partial \vec{v}}\) for the given state and odometry.
- Fx(x, odo)
Jacobian of state transition function df/dx
- Parameters:
x (array_like(3)) – vehicle state \((x, y, \theta)\)
odo (array_like(2)) – vehicle odometry \((\delta_d, \delta_\theta)\)
- Returns:
Jacobian matrix
- Return type:
ndarray(3,3)
Returns the Jacobian matrix \(\frac{\partial \vec{f}}{\partial \vec{x}}\) for the given state and odometry.
- property accel_max
Get maximum acceleration of vehicle (superclass)
- Returns:
maximum acceleration
- Return type:
Set by
VehicleBase()
subclass constructor.- Seealso:
speed_max()
steer_max()
u_limited()
- add_driver(driver)
Add a driver agent (superclass)
- Parameters:
driver (VehicleDriverBase subclass) – a driver agent object
Warning
Deprecated. Use
vehicle.control = driver
instead.- Seealso:
VehicleDriverBase
control()
- property control
Get/set vehicle control (superclass)
- Getter:
Returns vehicle’s control
- Setter:
Sets the vehicle’s control
- Type:
2-tuple, callable, interp1d or VehicleDriver
This is the input to the vehicle during a simulation performed by
run()
. The control input can be:a constant tuple as the control inputs to the vehicle
a function called as
f(vehicle, t, x)
that returns a tuplean interpolator called as
f(t)
that returns a tuplea driver agent, subclass of
driversVehicleDriverBase
Example:
>>> from roboticstoolbox import Bicycle, RandomPath >>> bike = Bicycle() >>> bike.control = RandomPath(10) >>> print(bike) Bicycle: x = [ 0, 0, 0 ] L=1, steer_max=1.41372, speed_max=inf, accel_max=inf
- property dt
Get sample time (superclass)
- Returns:
discrete time step for simulation
- Return type:
Set by
VehicleBase()
subclass constructor. Used bystep()
to update state.- Seealso:
- eval_control(control, x)
Evaluate vehicle control input (superclass method)
- Parameters:
control ([type]) – vehicle control
x (array_like(3)) – vehicle state \((x, y, heta)\)
- Raises:
ValueError – bad control
- Returns:
vehicle control inputs
- Return type:
ndarray(2)
Evaluates the control for this time step and state. Control is set by the
control()
property to:a constant tuple as the control inputs to the vehicle
a function called as
f(vehicle, t, x)
that returns a tuplean interpolator called as f(t) that returns a tuple
a driver agent, subclass of
VehicleDriverBase
Vehicle steering, speed and acceleration limits are applied to the result before being input to the vehicle model.
- f(x, odo, v=None)
State transition function
- Parameters:
x (array_like(3), ndarray(n,3)) – vehicle state \((x, y, \theta)\)
odo (array_like(2)) – vehicle odometry \((\delta_d, \delta_\theta)\)
v (array_like(2), optional) – additive odometry noise, defaults to (0,0)
- Returns:
predicted vehicle state
- Return type:
ndarray(3)
Predict the next state based on current state and odometry value.
v
is a random variable that represents additive odometry noise for simulation purposes.\[f: \vec{x}_k, \delta_d, \delta_\theta \mapsto \vec{x}_{k+1}\]For particle filters it is useful to apply the odometry to the states of all particles and this can be achieved if
x
is a 2D array with one state per row.v
is ignored in this case.Note
This is the state update equation used for EKF localization.
- init(x0=None, control=None, animate=True)
Initialize for simulation (superclass)
- Parameters:
x0 (array_like(3) or array_like(2)) – Initial state, defaults to value given to Vehicle constructor
Performs the following initializations:
Clears the state history
Set the private random number generator to initial value
Sets state \(x = x_0\)
Sets previous velocity to zero
If a driver is attached, initialize it
If animation is enabled, initialize that
If animation is enabled by constructor and no animation object is given, use a default
VehiclePolygon("car")
- Seealso:
- limits_va(v, v_prev)
Apply velocity and acceleration limits (superclass)
- Parameters:
v (float) – desired velocity
v_prev (list with single element) – previous velocity, reference to list
- Returns:
allowed velocity
- Return type:
Determine allowable velocity given desired velocity, speed and acceleration limits.
Note
This function requires previous velocity,
v_prev
to enable acceleration limiting. This is passed as a reference to a mutable value, a single-element list. This is reset to zero at the start of each simulation.
- plot_xy(*args, block=None, **kwargs)
Plot xy-path from history
- Parameters:
The \((x,y)\) trajectory from the simulation history is plotted as \(x\) vs :math:`y.
- Seealso:
- plot_xyt(block=None, **kwargs)
Plot configuration vs time from history
- Parameters:
The \((x,y, heta)\) trajectory from the simulation history is plotted against time.
- polygon(q)
Bounding polygon at vehicle configuration
- Parameters:
q (array_like(3)) – vehicle configuration \((x, y, heta)\)
- Returns:
bounding polygon of vehicle at configuration
q
- Return type:
The bounding polygon of the vehicle is returned for the configuration
q
. Can be used for collision checking using theintersects()
method.- Seealso:
- property q
Get vehicle state/configuration (superclass)
- Returns:
Vehicle state \((x, y, \theta)\)
- Return type:
ndarray(3)
- Seealso:
- property random
Get private random number generator
- Returns:
NumPy random number generator
- Return type:
Has methods including:
The generator is initialized with the seed provided at constructor time every time
init()
is called.- Seealso:
- run(T=10, x0=None, control=None, animate=True)
Simulate motion of vehicle (superclass)
- Parameters:
T (float, optional) – Simulation time in seconds, defaults to 10
x0 (array_like(3) or array_like(2)) – Initial state, defaults to value given to Vehicle constructor
control (array_like(2), callable, driving agent) – vehicle control inputs, defaults to None
animate (bool, optional) – Enable graphical animation of vehicle, defaults to False
- Returns:
State trajectory, each row is \((x,y,\theta)\).
- Return type:
ndarray(n,3)
Runs the vehicle simulation for
T
seconds and optionally plots an animation. The methodstep()
performs each time step.The control inputs are provided by
control
which can be:a constant tuple as the control inputs to the vehicle
a function called as
f(vehicle, t, x)
that returns a tuplean interpolator called as
f(t)
that returns a tuple, see SciPy interp1da driver agent, subclass of
VehicleDriverBase
This is evaluated by
eval_control()
which applies velocity, acceleration and steering limits.The simulation can be stopped prematurely by the control function calling
stopsim()
.Note
the simulation is fixed-time step with the step given by the
dt
attribute set by the constructor.integration uses rectangular integration.
- Seealso:
- run_animation(T=10, x0=None, control=None, format=None, file=None)
Simulate motion of vehicle (superclass)
- Parameters:
T (float, optional) – Simulation time in seconds, defaults to 10
x0 (array_like(3) or array_like(2)) – Initial state, defaults to value given to Vehicle constructor
control (array_like(2), callable, driving agent) – vehicle control inputs, defaults to None
format (str, optional) – Output format
file (str, optional) – File name
- Returns:
Matplotlib animation object
- Return type:
matplotlib.animation.FuncAnimation()
Runs the vehicle simulation for
T
seconds and returns an animation in various formats:``format`` ``file`` description ============ ========= ============================ ``"html"`` str, None return HTML5 video ``"jshtml"`` str, None return JS+HTML video ``"gif"`` str return animated GIF ``"mp4"`` str return MP4/H264 video ``None`` return a ``FuncAnimation`` object
The allowables types for
file
are given in the second column. A str value is the file name. IfNone
is an option then return the video as a string.For the last case, a reference to the animation object must be held if used for animation in a Jupyter cell:
anim = robot.run_animation(T=20)
The control inputs are provided by
control
which can be:a constant tuple as the control inputs to the vehicle
a function called as
f(vehicle, t, x)
that returns a tuplean interpolator called as
f(t)
that returns a tuple, see SciPy interp1da driver agent, subclass of
VehicleDriverBase
This is evaluated by
eval_control()
which applies velocity, acceleration and steering limits.The simulation can be stopped prematurely by the control function calling
stopsim()
.Note
the simulation is fixed-time step with the step given by the
dt
attribute set by the constructor.integration uses rectangular integration.
- Seealso:
- property speed_max
Get maximum speed of vehicle (superclass)
- Returns:
maximum speed
- Return type:
Set by
VehicleBase()
subclass constructor.- Seealso:
accel_max()
steer_max()
u_limited()
- step(u=None, animate=True, pause=True)
Step simulator by one time step (superclass)
- Returns:
odometry \((\delta_d, \delta_\theta)\)
- Return type:
ndarray(2)
Obtain the vehicle control inputs
Integrate the vehicle state forward one timestep
Updates the stored state and state history
Update animation if enabled.
Returns the odometry
veh.step((vel, steer))
for a Bicycle vehicle modelveh.step((vel, vel_diff))
for a Unicycle vehicle modelveh.step()
as above but control is taken from thecontrol
attribute which might be a function or driver agent.
Example:
>>> from roboticstoolbox import Bicycle >>> bike = Bicycle() # default bicycle model >>> bike.step((1, 0.2)) # one step: v=1, γ=0.2 array([0.1 , 0.0203]) >>> bike.x array([0.1 , 0. , 0.0203]) >>> bike.step((1, 0.2)) # another step: v=1, γ=0.2 array([0.1 , 0.0203]) >>> bike.x array([0.2 , 0.002 , 0.0405])
Note
Vehicle control input limits are applied.
- stopsim()
Stop the simulation (superclass)
A control function can stop the simulation initated by the
run
method.- Seealso:
- property verbose
Get verbosity (superclass)
- Returns:
verbosity level
- Return type:
Set by
VehicleBase
subclass constructor.
- property workspace
Size of robot workspace (superclass)
- Returns:
workspace bounds [xmin, xmax, ymin, ymax]
- Return type:
ndarray(4)
Returns the bounds of the workspace as specified by constructor option
workspace
- property x
Get vehicle state/configuration (superclass)
- Returns:
Vehicle state \((x, y, \theta)\)
- Return type:
ndarray(3)
- Seealso:
- property x0
Get vehicle initial state/configuration (superclass)
- Returns:
Vehicle state \((x, y, \theta)\)
- Return type:
ndarray(3)
Set by
VehicleBase
subclass constructor. The state is set to this value at the beginning of each simulation run.- Seealso: