Bytes to Bites: Drawing Pancakes with G-Code

G-code Commands

PancakeBot is a CNC machine which uses basic commands to move the bottle to different places on the griddle, and drop pancake batter.

The commands are written in a programming language called G-Code that tells a machine how it should make a pancake.

Here is a list of the commands that commands that PancakeBot uses.

Typical G-Code File Setup

When creating a G-Code file, you simply use a text editor and change the extension of the file from .txt to .gcode. You will neet to set up your settings on your computer to see file extensions if you cannot see them.

You can add comments after the semicolon after any command.

For Example, if you want to make a comment after the G-Code command to turn the motors off, you write the following:

M84; Turn Movement Motors Off

You can also just add a semicolon and a comment afterwards.

A newline is a new command.

Task 1:

Write the G-code command to create a line from the following points:

10,15 to 30,40

Task 2: Write the G-code command to set the speed to 5.4 meters per minute

Task 3: Write the G-code command to turn the batter pump on, and then add a the comment “Batter is flowing!”

• Open up a new text file and save it with the name BigSquare with the extension “.gcode” – BigSquare.gcode
• Add the following starter parameters to the file by either copying or pasting them into your file.

*******

;Set Up My PancakeBot

G21; Set Units to MM

G1 F7600; Set Speed to 7600 mm per minute

M107; Turn Batter Dispenser off to stop batter flow

G28; Home All Axis

;Making My Pancake

;Finish Printing

G28 X0 Y0; Home all axis

M84; Turn Movement Motors Off

*******

• Leave several spaces after the “Home All Axis” and the “Making My Pancake Comment”

Once the file is set up, we can now begin looking at how we will draw our square pancake.

Note that this setup can be used for al types of pancakes!

When you look at the griddle of the pancakebot, you will need to imagine that there is a grid made up of one by one mm squares. There are 220 squares along the short side of the PancakeBot griddle, and 485 squares on the long side of the PancakeBot griddle, this means we have an area of 220mm x 485 mm. In Figure 1, we shows squares every 10 mm (not to scale).

For your first pancake, you’ll only need to go out at least 150 mm. You can set up your graph paper to have as many mm per square as you want based on the scale of your drawing. In Figure 2, each square is 10mm X 10mm

This grid shows a square with the following coordinates

(30,30)

(130,30)

(130,130)

(30,130)

Notice that the points aren’t in any order, so you could start drawing your pancake from any point. For this example, we will start at (30,30) and move in a counterclockwise fashion. Use Figure 3 as a referance.

Next, we need to take these coordinates and write them into the G-Code so PancakBot can understand what to do.

We’ll go ahead and start off with 30,30 as our first point and work our way around.

G00 X30 Y30; Move bottle to coordinates (30,30)

G00 X130 Y30; Move bottle to coordinates (130,30)

G00 X130 Y130; Move bottle to coordinates (130,130)

G00 X30 Y130; Move bottle to coordinates (30,130)

G00 X30 Y30; Move bottle to coordinates (30,30)

Figure 4 shows how the G-Code and Coordinates relate to one another.

These are the G-Code Commands we will be using to tell the PancakeBot to move from one spot to another.

Copy the G-Code commands from the previous two steps to complete your square file.

It should look something like this.

**********

;Set Up My PancakeBot

G21; Set Units to MM

G1 F7600; Set Speed to 7600 mm per minute

M107; Turn Batter Dispenser off to stop batter flow

G28; Home All Axis

G00 X30 Y30; Move bottle to coordinates (30,30)

G00 X130 Y30; Move bottle to coordinates (130,30)

G00 X130 Y130; Move bottle to coordinates (130,130)

G00 X30 Y130; Move bottle to coordinates (30,130)

G00 X30 Y30; Move bottle to coordinates (30,30)

;Finish Printing

G28 X0 Y0; Home all axis

M84; Turn Movement Motors Off

********

Test Your Code

Take your file and save it to the SD Card. Try running the pancakebot without any batter and see if your code works.

Once you tested it, and the PancakeBot moved in a square, you need to tell the PancakeBot to turn on the Pancake Bottle Dispenser.

We use the M106 & M107 commands to start the batter pouring.

**********

;Set Up My PancakeBot

G21; Set Units to MM

G1 F7600; Set Speed to 7600 mm per minute

M107; Turn Batter Dispenser off to stop batter flow

G28; Home All Axis

M106; Turn Batter Dispenser On to start batter flow

G00 X30 Y30; Move bottle to coordinates (30,30)

G00 X130 Y30; Move bottle to coordinates (130,30)

G00 X130 Y130; Move bottle to coordinates (130,130)

G00 X30 Y130; Move bottle to coordinates (30,130)

G00 X30 Y30; Move bottle to coordinates (30,30)

M107; Turn Batter Dispenser off to stop batter flow

;Finish Printing

G28 X0 Y0; Home all axis

M84; Turn Movement Motors Off

********

Now that your batter control is started, give your file a test run with PancakeBot and test out your print.

First Consideration: Mind The Gap

After your first test print, did you notice something strange about your square pancake? It probably looked like this.

But why?

Well, let’s look at what is happening. You have a gap at the beginning of the line, and a blob on the end. When you start off your square, you turn the batter bottle on, and instantly start moving the head of the PancakeBot.

Since batter can be thick or thin, the batter may not start flowing instantly, so if the head is moving, you will get a space on the griddle between the time the head starts moving, and when the batter hits the griddle.

To avoid that, you can start the batter flow, and use the pause command to give the batter time to hit the griddle.

Look back at the first code, and look for the pause command.

The G4 command pauses the movement of the machine for a specified time.

The time you specify depends on how thick the batter is.

A good rule of thumb is that thin batter, needs about .5 seconds to get to the griddle if the bottle is in the lowest notch, and thick batter, can need about 1.35 seconds to get to the griddle if the bottle is in the lowest notch.

You can change the pause time as you see fit, but go ahead and place it in between the start of the bottle and the first movement.

**********

;Set Up My PancakeBot

G21; Set Units to MM

G1 F7600; Set Speed to 7600 mm per minute

M107; Turn Batter Dispenser off to stop batter flow

G28; Home All Axis

M106; Turn Batter Dispenser On to start batter flow

G4 P750; Pause the machine for 750 milliseconds (¾ of a second). This allows the batter to drop down to the griddle.

G00 X30 Y30; Move bottle to coordinates (30,30)

G00 X130 Y30; Move bottle to coordinates (130,30)

G00 X130 Y130; Move bottle to coordinates (130,130)

G00 X30 Y130; Move bottle to coordinates (30,130)

G00 X30 Y30; Move bottle to coordinates (30,30)

M107; Turn Batter Dispenser off to stop batter flow

G4 P750; Pause the machine for 750 milliseconds (¾ of a second).

;Finish Printing

G28 X0 Y0; Home all axis

M84; Turn Movement Motors Off

********

Last consideration: The Blob

Run your print one more time and see how it looks.

Here is an image of the anticipated results based on our last change.

Do you notice that there is still a blob at the end of the print? Why do you think this might happen?

When the head of the dispenser reaches the end, it stops the batter flow by switching to a negative pressure and retracting the batter. This of course, takes a bit of time to fully stop the flow since there is a gap between the bottle tip, and the surface of the griddle.

The way this is addressed is by stopping the batter flow before it reaches the end of the line.

Based on the viscocity of the batter, this timing will vary. Unfortunately the PancakeBot does not have the ability to adjust the timing and distance delay on the unit itself, so one has to do this with G-Code.

To do this, you will break up the last line between coordinates (30,130) and (30,30) into two shorter lines. The first line will take us from (30,130) to (30,40).

G00 X30 Y130; Move bottle to coordinates (30,130);

G00 X30 Y40; Move bottle to coordinates (30,40);

You will then stop the flow by turning of the dispenser with the M107 command.

M107; Turn Batter Dispenser off to stop batter flow;

Then, you will continue to the last coordinate

G00 X30 Y30; Move bottles to final coordinates (30,30);

Here is the final code.

**********

;Set Up My PancakeBot

G21; Set Units to MM

G1 F7600; Set Speed to 7600 mm per minute

M107; Turn Batter Dispenser off to stop batter flow

G28; Home All Axis

M106; Turn Batter Dispenser On to start batter flow

G4 P750; Pause the machine for 750 milliseconds (3/4 of a second). This allows the batter to drop down to the griddle.

G00 X30 Y30; Move bottle to coordinates (30,30)

G00 X130 Y30; Move bottle to coordinates (130,30)

G00 X130 Y130; Move bottle to coordinates (130,130)

G00 X30 Y130; Move bottle to coordinates (30,130)

G00 X30 Y40; Move bottle to coordinates (30,40), stopping the flow before reaching the end.

M107; Turn Batter Dispenser off to stop batter flow

G00 X30 Y30; Move bottle to coordinates (30,30)

G4 P750; Pause the machien for 750 milliseconds (3/4 of a second)

;Finish Printing

G28 X0 Y0; Home all axis

M84; Turn Movement Motors Off

********

 If all goes well, you should either have not blob or reduce the blob at the end of your print.

What was the most challenging aspect of writing code for PancakeBot? What was fun or exciting? How long do you think it would take to become comfortable writing in G-code?

How do you think the timing of the dispensing (The Gap and The Blob) relate to other CNC devices or 3D Printers?

Anticipated Difficulties: 

Many students will be new to computer programming. Start the lesson by appealing to students’ sense of how the world works. They will quickly see that their favorite songs, shows, art supplies, sports equipment, video games, etc. all require technology to exist. Using lots of visuals, step-by-step instructions, and strong teacher modeling to give students confidence with programming will help.

Some students will not work well in pairs. Constant circulation of the teacher and any other adults in the room will help to keep groups focused and productive.

Stamina may also be an issue. If students are struggling, provide more support by talking them through the process step by step.

What G-Code coordinates are needed for the follow shapes?