Javascript On-Line Learning Interactive Environment for Simulation

See the 'Simulation Playground', Butterflies and the Billiards game below!
Also examples for a Dynamics course and a game with sliding Penguins.

With an easily-remembered domain name, Jollies.com can be a landing page for several other sites.

www.esscont.com and qld4350.com/esscont both lead to the same support site for two Routledge books,
Control Basics for Mechatronics (2023) and Essentials of Control Techniques and Theory (2009)

qld4350.com/essdyn.com supports Essentials of Dynamics and Vibrations (2018). I intend to expand it with links to the simulations that are just listed in the printed book.

qld4350.com/essmech.com/ supports Essentials of Mechatronics (2006). This has an index of chapters, with links to the simulations that relate to them.

This site was first developed decades ago by Professor John Billingsley. Over the years, JavaScript has changed and some old graphics techniques no longer work. So it is time to clean up the pages and link to many more examples.

JavaScript makes writing simulation code easy, with a variety of graphics techniques that can bring your state equations to life. Jollies are just web pages which contain panels of JavaScript code. These can be edited on-screen, simply by typing in the box, and then the code can be executed. That is the situation as I edit this page now, but I fear that security concerns might block that quite soon.

So there are two essential parts to a simulation. The first is code that will step the variables forward as time advances, the second is code that will draw graphs or move pictures to interact with the user.

Central to displaying the results is HTML5, with its "canvas" object. This goes far beyond mere display, allowing a video stream to be analysed for real-time vision control.

To start with, here are some examples written long ago.

A simulation of diffusion in a two-dimensional field is here and a very simple example of a first-order system is here.

Canvas waits for a break before updating the display, meaning that some ingenious software structure has to be used for 'show it as you go' simulations.

As an alternative to plotting graphs, shapes can be moved around the screen to represent the behaviour of the system being simulated. It extends the ability to move images by making it possible to rotate them. Here is an example of controlling the roll channel of an aircraft. After clicking "run the model", click in the image to one side, then the other, to control the roll rate. Try to keep the aircraft in the centre and you will see the difficulties of a fourth-order problem.

A lot more examples will follow. Some are in structured sets, others are oddments that have been developed along the way.

In every case, you can 'view source' to see the engine-room of the simulation. The aim has been to keep everything as simple as possible.

Remember that for the code to work, you have to permit scripts to run.

The first example is meant to show that a 'real' position controller requires a lot of feedback.
You can first see a response which does not look too bad, but on applying a disturbance in real time it becomes obvious that the control is 'soggy'.

Values of 100 and 50 for position and velocity gains give a much better response - but what do these values mean in terms of natural frequency and damping factor?!

The second example shows a simple vehicle suspension, damped only by friction. Run it. Now change the lines of code which determine the friction and run it again.

It is easy to make teaching demonstrations with Jollies -
this example illustrates the unit circle and its links with the sine and cosine functions.

With JavaScript and Canvas, you can learn a lot about your drawing devices. 'Drawpressure' is not meant for serious artwork, but as a diagnostic for checking your touch-screen, pressure-sensitive pen or mouse. You can set colours as RGB and even opacity.

Moving icons are fun, but more serious work demands a plotted graph.

The use of Jollies is not limited to control theory.
The next example illustrates some simple image processing in which the edges of a binary (black-white) object are smoothed. The shape is first smoothed and then the edges found..

Canvas allows grey-scale or full colour drawings to be made - depending on the screen driver selection.
This example shows a 'noisy' grey-scale image being smoothed by two applications of an IIR filter.

Another example of real-time moving graphics is a rotating cube

A more elaborate coloured version can be found here.

Canvas allows events to be captured and acted upon, so that mouse movements can be used to edit an image.

In this case the example is based on the 'Bilby contest' where mobile robots find their way through a maze. Dragging left or right mouse buttons across a square will set it to be white or black respectively, after you have clicked the 'Build maze' button. To see the buttons, you might have to hide one or two toolbars - the screen is rather full.

The trails of red or blue dots represent signals from the optical sensors mounted on the Bilby.

Another Bilby simulation has been added which works entirely in JavaScript - no canvas. Instead it uses the method of the first example, but a lot more of it!
The "Edit Maze" feature has not been finished.

In preparation for some tutorials, a set of pages were prepared as a simple introduction to animated simulation - a Simulation Playground.
Five progressive versions exist at present:

1 A ball moves in a circle. Modify the code to make it spiral inwards.
2 A ball falls under gravity. Make it bounce.
3 Bouncing.
4 Precursor to the billiards game
5 Adding interaction

Remember to click the 'reset' button before running each of them - it sets up variables according to the instructions you place in the 'other' text box.

A Billiards Game has been developed for use in connection with an educational programme for primary schools. It should help to teach some of the elementary principles of dynamics - while being fun to play.

A 'self playing' demonstration version is also included.

A further education project was the simulation of infestation of a crop by caterpillars(!)

The first version gives greater simulation possibilities, but is not really 'graphical enough' for the young viewers of STEPS. Over the years, many examples have built up. You can find an index to some of them here.

A more visually appealing version of Butterflies has been written - at the cost of some realism in the simulation.

Indeed a third version was probably the one which was shown to the TV audience, in which the eggs hatch simultaneously and the generations are kept separate.

More recently, the Jollies techniques have been used to illustrate some fun examples for a dynamics course. A lot of more serious examples can be found at www.essdyn.com , a support website for the book 'Essentials of Dynamics and Vibration', Published by Springer

Another book that uses them is:
Control Basics for Mechatronics, published by Routledge, with support site to be found at Control Basics for Mechatronics (esscont.com)