Advancers – Gravity


This week we decided to create a Lunar Lander game that demonstrated the effects of Gravity.

The Plan

As always we started with a plan:

  1. A Spaceship Sprite with 4 Costumes
    1. No power
    2. Up Rocket firing
    3. Left Rocket firing
    4. Right Rocket firing
  2. Buttons to control the Space Ship
  3. Stage which should be a picture of the moon.
  4. A landing pad to land on – just draw on the Stage
  5. Code to control the Space Ship
    1. 3 Variables, to store Gravity, Power and LeftRight information.

Space Ship Sprite

This what mine looked like:


Space Ship Sprite




The Left and Right costumes can be confusing, to move left, the flame needs to come out of the right, and to move right the flame needs to come out of the left hand side.








My Stage looked like this:



One thing to remember is to have the landing pad in a different colour.

Buttons and Code

I’ll put these 2 parts of the plan together as it makes more sense.

We decided to use 3 different buttons to control the Space Ship

  1. Up Arrow – This would fire the rocket at the bottom of the Space Ship
  2. Left Arrow – This would fire the rocket on the right side of the Space Ship
  3. Right Arrow – This would fire the rocket on the left side of the Space Ship

And now the code.

We needed code for each of the buttons, code to move the Space Ship and code to know when we have landed. This meant we had lots of small pieces of code all running together in Green Flags with forever loops.

We also decided that we would need 3 variables to store information so we could work out how far to move the Space Ship.

  1. Gravity – This would change as the Space Ship got higher, just as real gravity does.
  2. Power – This would change when the Up arrow was pressed and also when nothing was happening
  3. LeftRight – This would change when the left or right arrows were pressed

And don’t forget if we have variables, we should set them to starting values when the Green Flag is clicked.



This also has the code that puts the Space Ship in to a starting position. Note the Y value as this is used later in the code to see if we are on the ground or not.


For example, when the one of the left or right arrow keys was pressed we would change the Costume and change the LeftRight variable.



We did the same for the left arrow. Note that we just add (or subtract for the left arrow) a small amount from the LeftRight variable.

The delay is to make sure that the variable is not updated too fast if the arrow button is held down.


For the Up arrow we have to change a different variable



Note the wait is much shorter, this is to match the wait in the forever loop that moves the Sprite.

We also change the Power variable by a large amount as this helps with the calculations.


Once we had the buttons working we could move on to the Code that moved the Sprite.

The Left or Right movements were easy, that would just be the amount in the LeftRight variable.

The Up or Down movements were a little trickier as we had to account for Gravity as well. So we just used the Y position of the Sprite and added 180 (to make it a positive number). This meant that Gravity changed as the Sprite moved up or down, which is exactly how Gravity works in real life.

This is how the code ended up



We move first and then check how high we are.

If we are above the ground, we know this by checking that we are above the starting position of the Sprite, then we adjust Gravity and adjust the Power down.

Note the wait is the same as the Up Arrow code.

Also, if we are on the ground, we set Gravity and Power to 0.



There was one final piece of code that we didn’t do but I have added here, this was to check if we had landed and if we had, display a message and end.

It was just another Green Flag with a Forever loop and we kept checking to see if we were touching the colour of the landing pad.



Not much here, but might be better if there was a wait as well.




Finally, if you want to see all the code in one go, here it is



The project that we built is available on the Scratch Web Site:

User Name : cdadvancers1819
Password : advancers

Project : Class-Gravity

Remember, you can put your own projects up there as well if you want.

Platformer Engine Week 2

This week we did a little code to finish our engine and spent the rest of the time working on our own platformer games using it.  The code changes we made to last week’s game engine were:

Hit Boxes:

Fixed the platformer so that our character doesn’t get snagged on edges by its whiskers.  This we did by learning about hitboxes. The hitbox is just a costume which is rectangular in shape.  Before we do our animation, we switch to the hitbox costume and after we switch back to the costume we want.


Head Bumping:

Fixed the platformer so that we can bump our heads against the platforms without popping up.  This was by adding a couple of lines to the “stay above ground block” sprite to move down if we are touching the ground while moving upwards.

The entire code for the platformer is below:



Example Game: Mentor Dash

Finally Mark showed an example game pulling all the elements in together – “Mentor Dash”.  It has the same code as we covered, but adds a bit of animation, level changes, sound and some sillyness.



There were lots of brilliant ideas from the ninjas on their own games .. looking forward to seeing what you can do!

Scratch Advanced: General Purpose Wireframe 3D Engine

This week in Scratch advanced we took on the ambitious task of writing a general-purpose 3d wireframe engine.  The goal here was to build an engine that we could use to view any structure in 3-dimensions as though we had x-ray vision.   We didn’t really know how it might turn out but were delighted with the results!  If you just want the code, skip to the bottom!

We didn’t quite know how to start this so we Googled 3D and Wireframe, and we found this article on wikipedia that really helped us understand what it was:

wireframe examples

Continue reading

“Tick” Technique in Scratch – Illusions and 3D printing!

Today in scratch advanced, Mark covered a very useful method to organize your programs better if there are lots of moving sprites – which he calls the “tick” technique.tick_loop The idea is that a single master loop ticks time and the Sprites react to this tick in their own way.

We showed two examples of using this tick – an optical illusion that shows that things can move in circles while just doing straight lines and a technique for building 3D models by layering sprites the same way that a 3D printer layers resin.



The FULL Instructions for today’s projects are here – Enjoy!!

It would be great if you tried out some of your own Tick projects, and demonstrated them next week at Scratch Advanced!

Scratch Advanced: Week 3 Top Down Game Engine Part 1

A “Game Engine” is a piece of code you can use to build different types of games.  This week we looked at doing a top down scrolling game engine.  It’s still pretty basic at the moment but it’s enough to get started on some projects of your own.   What can you build with it?

Top Down Scrolling Game Part 1 Notes


Download the code for part 1 here.

Scratch Advanced: Twister Part 2

There was a huge group for today’s class where we took the Shape block from last week and built an amazing Twister project out of it.

We learnt:

  • more about angles and Sine and Cos
  • some basics of creating 3D illusions on a computer screen


Twister Notes Week Two.

We didn’t get it quite finished, but managed to get to some 3D. Follow the notes to get to the end and check out this sample project that has all the pieces from the doc and a few extra features in. It’s addictive playing with the twister!

Download the completed project here!

Scratch Advanced: Twister Part 1

In Scratch advanced this week we learned some cool math formulas that are really handy for doing interesting stuff in programming.


The things we went through!

  • We revised X and Y and reminded ourselves how it works
  • We drew a house using X and Y
  • We learnt about circles and radius
  • We learnt about the math formulas Sin and Cos and how they can be used to get X and Y positions on a circle
  • We learnt about Custom Blocks in Scratch
  • We wrote our own Custom Block that could draw a shape of any size and number of sides, using Sin and Cos to figure out the points!
  • We used that Custom block to make lots of neat patterns (some by accident!)

The notes are attached in PDF and if you follow them you will have a project ready to go for this Saturday – we are going to take that custom block and do some really cool things with it.    Don’t worry if you don’t have the time to do it or can’t follow the notes though – we’ll have this shared out so you can just take off where we finished!

Twister Notes Week1

Download the Scratch Code here!

CoderDojo Athenry at Coolest Projects 2015

Congratulations to everybody from CoderDojo Athenry who participated in the CoderDojo Coolest Projects event on 13 June 2015. It was a very impressive event, held in the RDS Dublin, with over 500 projects from CoderDojo ninjas from Ireland and worldwide.

Here are photos of the participants from CoderDojo Athenry.

Games Category:

James from the Minecraft Modders group with his technically impressive XyZ Mod with World Gen and Gauntlets:


Eoin from the Minecraft Modders group who entered the detailed and very well structured Global Cuisine mod:


Ruaidhrí and Luke from the Minecraft Modders group who entered the Weapons, Armour and Money mod:


Hardware Category:

Michael and Mikey from the CoderDojo Athenry PiDojo who entered their clever and topical Shower Evaluator project that times your shower and displays the amount of water used, cost of water, and cost of energy:


Alaidh from the PiDojo group who entered the very innovative Sensor Guide for the visually impaired, which was impressively backed up with scientific evaluation:


Scratch Over 10s:

Emily and Chloe from the Scratch Advanced group had a Scratch program with great environmental potential, Cúisneor, that helps to reduce food waste:


Scratch Under 10s:

Rachel from the Scratch Beginners/Intermediate Group was our youngest entrant from CoderDojo Athenry, aged 8, and had a fantastic Scratch app for helping young children to learn the letters of the alphabet:


Well done to everybody who entered!

We should also mention that three projects won prizes:

  • Ruaidhrí and Luke won a prize for best use of Microsoft technologies (Microsoft owns Minecraft, of course)
  • Alaidh won a prize for being a finalist in the Hardware category
  • Mikey and Michael also won a prize for being a finalist in the Hardware category.

Information about the 2014-15 Season at CoderDojo Athenry


From Saturday 11 Oct 2014, we are starting a new season of CoderDojo Athenry, at our usual time and place. (The Saturday before, on 4 Oct, we will be having an introduction session for new mentors and other volunteers.)

Here is a the overview presentation (PDF): 1-CoderDojoAthenry-InfoSession-2014-Sept

This season, we will have the following streams:

We look forward to seeing you there!

–  Michael and the CoderDojo Athenry mentors.

CoderDojo Athenry Belts Awarded May 2014


We awarded a record number of 87 belts at CoderDojo Athenry in May 2014:

  • 3 White belts for ongoing participation
  • 55 Yellow Scratch belts for competent  coders
  • 15 Blue Advanced Scratch belts
  • 1 Yellow Python belt
  • 3 Blue Python belts
  • 10 Green Minecraft Modding belts for creating and ublishing Java/JavaScript mods online

In keeping with the CoderDojo ethos, these belts were earned by our young people meeting agreed standards in different coding disciplines. Belts are not for winning competitions against each other, but celebrate personal achievement, and are never given away without being earned.

Congratulations to all the young people who earned their belts!