Glossary

A0

Initial angle property. Applies to torsional springs.

acceleration

Change in velocity in a unit time. In Mekanimo unit time is a second.

active

Element property. When active property of an element is set to be False, solver ignores the element.

alias

Each element can have a name and an alias. Aliases are used for ease of typing at the interpreter.

amplitude

Harmonic motion’s (oscilating motion) magnitude of change.

Where t is time, A is the amplitude, f is the frequency, and phi is the phase angle.

angular velocity

Change in orientation in a unit time. In Mekanimo, unit time is seconds and orientation is defined in radians.

API

Stands for Application Programming Interface.

application directory

The directory Mekanimo is installed in. To find out you can print the system.appDir from the Python interpreter as shown below.

>>> system.appDir
'C:\\Program Files\\Mekanimo\\'

assembly

In Mekanimo, a group of elements (rigid bodies and connectors) fit together to form a unit.

b1x

x component in body1’s local coordinate system.

b1y

y commonent in body1’s local coordinate system.

b2x

x component in body2’s local coordinate system.

b2y

y commonent in body2’s local coordinate system.

beam

A type of connector used to attach non-overlapping rigid bodies to each other or a rigid body to the ground so that they behave like one single rigid body.

behavior

In Mekanimo, behavior is defined as an condition, action, and parameters. When the specified condition is satisfied then the action is triggered.

behavior dialog

A GUI dialog used to assign behaviors to elements. Double clicking on an element or Object Assign Behavior menu brings up the behavior dialog.

belt

In Mekanimo, belts are used to transmit rotational motion between two circles.

boolean operator

and, or, not

bound element

tbd

bounding box

Smallest rectangle a rigid body can be fit into.

Box2D

Mekanimo uses Box2D as a solver. http://www.box2d.org

break force

In Mekanimo, connectors can be destroyed when the reaction forces of the connector in question exceeds the specified break force (breakForce). If the breakForce property is set to None then the connector is not breakable.

break torque

In Mekanimo, motors can be destroyed when the reaction torque of the motor in question exceeds the specified break torque (breakTorque). If the breakTorque property is set to None then the motor is not breakable.

brush

See texture.

C

Damping coefficient.

canvas

One of the main components of Mekanimo. Depending on the context, it may mean the part of the GUI that graphics are displayed or the canvas object in the API.

cartesian coordinates

(x, y) pairs commonly used in rectangulare coordinate systems.

CG

Short for center of gravity. Rigid bodies can be simulated by a lumped mass (all mass concentrated at a point) located at their center of gravity.

CG indicators

In Mekanimo, CG location is indicated by these “L” shaped indicators for rectangles and polygons, and lines for circles.

code editor

One of the main components of Mekanimo that lets the users edit Python code.. Located behind the canvas. Every action taken by using the GUI is reflected in the code panel as Python code. When the code in the code panel is modified, these modifications are reflected in the canvas.

code panel

See code editor.

code snippet

A short code example to demonstrate a topic.

coefficient of friction

When two bodies pressed together

center of gravity

Rigid bodies can be simulated by a lumped mass (all mass concentrated at a point) located at their center of gravity.

coefficient of restitution

The ratio of a rigid body’s velocity before and after a collision.

color box

A dialog box used to let the users assign colors to the objects in the canvas.

component

In Mekanimo, component is defined as an element that belongs to an assembly.

compression

tbd

connector

An object that connects two rigid bodies to each other or a rigid body to the ground. See

connector types

PIN, WELD, MOTOR, SPRING, TORSPRING, GAP, BEAM. LINK, CHAIN, BELT, HSLIDER, VSLIDER, HRAIL, VRAIL

construction tools

tbd

Ctor

Angular damping coefficient.

damping coefficient

tbd

degree of freedom

A displacement quantity which defines the position and orientation of a rigid body.

density

Amount of mass per unit volume. Since Mekanimo handles only planar objects, density can be defined as the amount of mass per unit area.

DOF

See degree of freedom.

element

In Mekanimo, an element is a rigid body, connector, force, torque, or trace that is included in the model.

flag

Flag is a term used in programming to define a value which can usually be either True or False.

force

An external influence on a rigid body resulting in change of its velocity.

frame rate

Number of changes per second in an animated sprite.

frequency

Number of cycles per second.

GIF

Short for Graphics Interchange Format. A commonly used computer image format.

global coordinates

World coordinates

grid

Regularly spaced (both verticaly and horizontaly) rigid bodies.

ground

tbd

GUI

Stands for Graphical User Interface. In this manual it is used to indicated that an action is performed by using the menus (via GUI).

GUI editor

tbd

handle

tbd

hit test

tbd

impulse

tbd

integer

tbd

interpreter

tbd

JPEG

tbd

K

Spring stiffnes [F/L].

Ktor

Torsional stiffness [T/rad]

L0

Initial spring length.

local coordinates

Body coordinates

mass

An object’s resistance to changing its state of motion due to external forces.

Where F is force, m is mass and a is acceleration.

matrix

tbd

mekanimo_startup.py

This is a python file located in the application directory. It is used to customize Mekanimo. Mekanimo executes this file while starting up.

millisecond

One thousandth of a second or 0.001 seconds.

moment of inertia

The resistance that a body exhibits to rotational acceleration (change in angular rotation velocity).

MPEG

Audio and video compression format develeoped by Moving Picture Experts Group.

namespace

A container holding key value pairs. In Python (and many other languages) variables can take different values depending on the context they are used in.

object tree

tbd

orientation angle

Used to define the angular position of a rigid body. The angle between a rigid body’s local x axis and global x axis in radians.

phase angle

In harmonic motion, phase angle is the initial displacement at T=0.

Where t is time, A is the amplitude, f is the frequency, and phi is the phase angle.

PNG

An image format with lossless data compression. Short for Portable Network Graphics.

projectile

In Mekanimo, projectile is a rigid body (usually a circle) thrown with an initial velocity.

PyBox2D

A library providing Python bindings for Box2D. http://code.google.com/p/pybox2d/ Mekanimo uses PyBox2D to manipulate Box2D objects.

Pygame

Pygame is a Python based game library. Mekanimo uses Pygame’s mixer module to play sound files.

Python

Python is the programming language Mekanimo is written in. http://www.python.org/

Python interpreter

Used interchangibly with Python shell. This is where the Python commands can be typed and executed.

rigid body

An idealized solid that cannot be deformed due to external forces acting on it. Hence the distance between any two points in a rigid body is constant. Although rigid bodies do not exist in nature, they are very useful for approximating dynamic behavior of solid objects.

rigid body types

CIRCLE, RECTANGLE, and POLYGON

snap to grid

Used for aligning and positioning objects with ease. When snap to grid option is turned on, Mekanimo aligns rigid bodies and connectors to the closest intersection of the grid.

solver

The physics engine that computes the positions, orienations, and velocities of the defined rigid bodies subject to the prescibed constraints. Although Mekanimo can use different solvers, in this release only Box2D is used.

sprite

In Mekanimo a sprite is a 2D animation (or a static image) attached to a rigid body. See Sprites

stiffness

The required force to deflect a spring by one unit length.

system box

tbd

tag

An element’s name shown visually at the CG location. They can be turned on or off from the Show/hide Tag submenu located under the Object menu.

target

tbd

tension

Force due to stretching a spring element.

texture

Also known as brush is a bitmap image applied to a rigid body shape.

time increment

Amount of time advancement that the solver uses to compute the updated positions and velocities of the rigid bodies in the model.

time step

Mekanimo’s solver computes the positions and velocities of the rigid bodies in the model by advancing time by small amounts and updates the objects in the canvas. If the time advancements are small enough and graphics are updated fast enough we perceive the changes as a continuous animation. A time step can be defined as a batch of computations the solver performs to compute the positions and velocities of the rigid bodies in the model for the given time advancement (time increment).

torque

Measure of the tendency of a force to rotate an object.

tuple

In Python a tuple is an immutable sequence.

untoggle

Act of changing the state of a toggle button. A toggle button can be either on or off.

vector

A quantity defined with a magnitude and direction.

velocity

In Mekanimo, velocity is a vector quantity, defining the rate of change of position of rigid bodies.

wall

system.box is made out of four walls. system.bottomWall, system.leftWall, system.topWall, and system.rightWall.

weight

Magnitude of the gravitational force acting on the rigid body.

Where W is weight, m is mass, and g is the acceleration of gravity.

weld

A type of connector used to attach overlapping rigid bodies to each other or a rigid body to the ground so that they behave like one single rigid body.

wxPython

A cross platform GUI toolkit for the Python programming language based on wxWidgets GUI library. http://www.wxpython.org

XY plot

In Mekanimo, xy plots display the displacement, velocity, and acceleration values vs. time.

Z order

In Mekanimo Z order is the order rigid bodies and connectors are drawn in the canvas. By default the last object is drawn on top of all other objects. This order can be changed by using the popup menu.

zero gravity

tbd