Module: robotics.mobile

The utilities contains functionality for mobile robots based on the EXUDYN example MecanumWheel RollingDiscPenality specific friction angle of rolling disc is used to model rolls of mecanum wheels

  • Author: Martin Sereinig, Peter Manzl and Johannes Gerstmayr

  • Date: 2021-10-01 Updated: 2023-09-15

  • Notes: formulation is still under development

Function: MobileRobot2MBS

MobileRobot2MBS(mbs, mobileRobot, markerGround, flagGraphicsRollers = True, *args, **kwargs)

  • function description: add items to existing mbs to build up a mobile robot platform, there are options that can be passed as args / kwargs, which can contains options as described below. The robot platform is built out of rigid bodies where the wheels can be modeled as rolling discs (mecanum wheel x/o configuration) or with a detailed mecanum wheel simulation approach

  • input:

    • mbs: the multibody system which will be extended

    • markerGround: a rigid body marker, at which the robot will be placed (usually ground)

    • mobileRobot: a dictionary including all information about the mobile robot platform

  • output: the function returns a dictionary containing nodes, body, object and marker numbers of individual mobile robot parts nPlatformList, bPlatformList, oPlatformList, mPlatformList; nodes, bodies, objects and marker of the platform [nPlattform] [bPlattform] [oPlattform] [] oAxisList, mAxlesList; objects and marker of the axles [a1, a2, a3, a4] nWheelsList, bWheelsList, oRollingDiscsList, mWheelsList; nodes, bodys, objects and markers of the four wheels [w1, w2, w3, w4]

  • notes: for coordinate system, see Python function definition

Relevant Examples (Ex) and TestModels (TM) with weblink to github: ROSMobileManipulator.py (Ex)

Function: Generatrix2Polynomial

Generatrix2Polynomial(param, GeneratrixFunction, tol = 1e-14, nFit = 101, nTest = 1001)

  • function description: create a polynomial describing a generatrix function

  • input:

    • param: list containing data (lRoll, aPoly, …)

  • author: Peter Manzl

  • notes: create and fit a polynomial of an order high enough to approximate the given GeneratrixFunction with a given tolerance. The error is measured as the Chebyshev distance.

Function: GeneratrixRoll

GeneratrixRoll(u, param)

  • function description: generatrix function for a roll of a Mecanum wheel

  • input:

    • u: parameter, max. +- pi/2 param[‘r’]: radius of the associated Mecanum wheel param[‘delta’]: angle of the rolls rotation axis to the wheels rotation axis param[‘dRoll’]: smallest distance of roll axis to the wheel axis

  • output: x and y values for the function in the local frame. The rotation around the local x-yxis creates the surface of the roll.

  • author: Peter Manzl

  • notes: parametric equation, x,y are the generatrix of the roll in its local frame with the axis of rotation x, see Gfrerrer2008.

Function: FunDiffPoly

FunDiffPoly(x, a)

  • function description: calculates the derivative of the polynomial \(a0*x^n + ... \)

  • input:

    • x: value at which the polynomial is evaluated

    • a: coefficients

  • output: f:

  • author: Peter Manzl

  • notes: helper function polynomial describing a generatrix function

Function: FunDDiffPoly

FunDDiffPoly(x, a)

  • function description: calculates the second derivative of a polynomial

  • input:

    • x: value at which the polynomial is evaluated

    • a: coefficients

  • output: f:

  • author: Peter Manzl

  • notes: helper function polynomial describing a generatrix function

Function: MecanumXYphi2WheelVelocities

MecanumXYphi2WheelVelocities(xVel, yVel, angVel, R, Lx, Ly, wheeltype)

  • function description: DEPRECATED: the wheel velocities of a mecanum platform for the velocities [xVel, yVel, angVel]; use MobileKinematics

Relevant Examples (Ex) and TestModels (TM) with weblink to github: mobileMecanumWheelRobotWithLidar.py (Ex), laserScannerTest.py (TM), mecanumWheelRollingDiscTest.py (TM)

Function: MecanumWheelVelocity2XYphi

MecanumWheelVelocity2XYphi(w, R, Lx, Ly, wheeltype)

  • function description: DEPRECATED: the platform velocities [xVel, yVel, angVel] of a mecanum platform for the wheel velocities w; use MobileKinematics

CLASS MobileKinematics (in module robotics.mobile)

class description: calculate 4 wheel velocities for a mecanum wheel driven platform with given platform velocities

  • author: Peter Manzl, Johannes Gerstmayr

  • notes: still under development; wheel axis is mounted at y-axis; positive angVel rotates CCW in x/y plane viewed from top; for coordinate system, see Python class definition

Class function: init

__init__(self, R, lx, ly, flagAdjusted = False, lcx = 0, lcy = 0, wheeltype = 0)

  • class function description: initialize mobileKinematics class

  • input:

    • R: wheel radius

    • lx: wheel track width

    • ly: wheel base

    • wheeltype: 1=x-config (bad), 0=o-config (good)

  • author: Peter Manzl

Class function: GetWheelVelocities

GetWheelVelocities(self, vDes)

  • class function description: calculate wheel velocities from Cartesian velocities

  • input:

    • vDes: desired velocity [vx, vy, omega] in the robot’s local frame

    • vx: platform translational velocity in local x direction

    • vy: platform translational velocity in local y direction

    • omega: platform rotational velocity around local z axis

  • output: w: wheel velocities w=[w0,w1,w2,w3]

  • author: Peter Manzl

Class function: GetCartesianVelocities

GetCartesianVelocities(self, w)

  • class function description: calculate Cartesian velocities from wheel velocities

  • input:

    • w: wheel velocities w=[w0,w1,w2,w3]

  • output: v: Cartesian velocity [vx, vy, omega] in the robot’s local frame vx: platform translational velocity in local x direction vy: platform translational velocity in local y direction omega: platform rotational velocity around local z axis

  • author: Peter Manzl

Relevant Examples (Ex) and TestModels (TM) with weblink to github: ROSMobileManipulator.py (Ex)