Two wheels differential drive with dynamic constraints

module:

navground.core.kinematics

class DynamicTwoWheelsDifferentialDriveKinematics

Bases: TwoWheelsDifferentialDriveKinematics, WheeledKinematics

Two differential drive wheels (left, right) (e.g., a wheelchair) with acceleration limits due to limited motor torque.

The two motors have the same maximal torque.

Registered properties:

• wheel_axis (float, TwoWheelsDifferentialDriveKinematics.wheel_axis)

• max_forward_speed (float, TwoWheelsDifferentialDriveKinematics.max_forward_speed)

• max_backward_speed (float, TwoWheelsDifferentialDriveKinematics.max_backward_speed)

• max_acceleration (float, max_acceleration)

• moi (float, moi, 1.0 by default)

__init__(max_speed: float = float('inf'), wheel_axis: float = 1, max_angular_speed: float = float('inf'), max_forward_speed: float = float('inf'), max_backward_speed: float = 0, max_acceleration: float = float('inf'), moi: float = 1) → None

Constructs a new instance.

Parameters:

• max_speed – The maximal wheel speed

• wheel_axis – The wheel axis (i.e., the distance between the wheels)

• max_angular_speed – The maximal angular speed, that is also limited by the 2 * max_speed / axis, if the axis is positive.

• max_forward_speed – The maximal linear speed when moving forwards (set to negative or infinite to leave unconstrained)

• max_backward_speed – The maximal linear speed when moving backwards (set to negative or infinite to leave unconstrained)

• max_acceleration – The maximal linear body acceleration

• moi – The scaled moment of inertial (moi = I / (mass * axis^2 / 8)) Equal to 1 for an homogeneous disc of diameter wheel_axis.

twist_from_wheel_torques(values: list[float], current: navground.core.Twist2, time_step: float) → navground.core.Twist2

Applies wheel torques to accelerate a twist over a time step

Does not check the motor torques are feasible.

Parameters:

• values – The motor torques

• current – The current twist

• time_step – The time step

Returns:

The accelerated twist.

wheel_torques(value: navground.core.Twist2, current: navground.core.Twist2, time_step: float) → list[float]

Computes the wheel torques required to accelerate over a time step

Parameters:

• value – The target value

• current – The current value

• time_step – The time step

Returns:

{left, right} wheel torques. May not be feasible

property max_acceleration

Type:

float

The maximal (body) acceleration.

property max_angular_acceleration

Type:

float

The maximal (body) angular acceleration.

property max_wheel_torque

Type:

float

The maximal [scaled] wheel torque.

property moi

Type:

float

The scaled moment of inertial

it is equal to 1 for an homogeneous of disc of diameter twowheelsdifferentialdrivekinematics.wheel_axis. lower for when weight is shifted towards the center.