Mechanical Design, Machine Design

Group assignment: Part 1
  • Design a machine that includes mechanism + actuation + automation + application
  • Build the mechanical parts and operate it manually.
  • Document to group page.
Group assignment: Part 2
  • Actuate and automate your machine.
  • Document to group page.
Individual:
  • Document you individual contribution.

Group Assignment

Idea: Polargraph

Polargraph controller Copyright Sandy Noble 2018. http://www.polargraph.co.uk/

Our team member Dorian had the idea for a wall drawing machine. This wall drawing machine, sometimes also known as a polargraph , is a type of robot that uses two stepper motors to move a pen or marker along a vertical surface, such as a wall or a large sheet of paper. The motors are controlled by a computer program that sends commands to adjust the length of two strings, which are attached to the pen and run through pulleys. By varying the length of the strings, the motors can move the pen in any direction on the surface. The computer program can be controlled by a user, who can draw images or text using the machine.
The special feature about our wall drawing machine is that it can be put onto windows/glass via two vacuum lifting tools on each side. Making it useful for reating any glass art and especially for writing text or art on the display windows of shops.

Work distribution

Since we're all living very far apart (France, Australia, Germany) we can't work on the machine together in person. Therefore, we're building multiple versions of it at our own Labs with our own small twists to it. Throughout the process we did several meetings and collaborated on a Fusion project. We shared our progress and ideas for the project and it's outcome. That's why we don't have clearly divided tasks, but we are all helping each other throughout the whole process.

Design & Assembly

Note: Dorian and Uwe created a 3D design of the plastic part of the vacuum lifters which already has an integrated stepper motor bracket. I have slightly different sized vacuum lifters plus I also wanted to produce the prototype as fast as possible, so I used existing 3D models for the brackets and the gondola from the web and mounted them using screws.

Component How Often Needed
Arduino UNO 1x
L293D Motor Drive Shield 1x
L293D Motor Drive IC 2x
Nema 17 Stepper Motor 2x
MG90S Servo Motor 1x
GT2 Pulley 20 Teeth Set 1x
GT2 Rubber Belt 5mm 20T (3-5M) 1x
9V Power Supply 1x

This was the general idea behind the machine.
I started with printing the stepper motor brackets and the gondola.
Then I designed the wooden part to connect and hold all of the components. It includes mounting holes for the Arduino UNO, the stepper motor brackets, the vacuum lifters, the battery and multiple holes to wind up the cables in a clean way.
Fusion file
I made a test cut with the lasercutter using cardboard to see if the mounting holes would fit the actual components. The holes for the Arduino UNO were off by a few millimeters. So I adjusted the design in Fusion.
Now that everything was fitting, I continued to lasercut the piece out of 5mm MDF.
Here you can see that the Arduino aligns with the holes -> I used screws to fix the Arduino to the holder.
The next thing to do is mounting the motors onto the brackets and the brackets onto the wooden holder.
I am using the L293D Motor Drive Shield which plugs directly onto the Arduino. I've read that the L293D Motor Drive IC's that are on this shield tend to overheat in this application.
So I got two extra IC's to solder them ontop of the original ones.
This is supposed to help with overheating since it "splits the work".
With everything prepared it's time to plug it onto the Arduino and connect the motors and servo etc.
I weaved the long cables of the motor through the holes of the wooden holder...
M...and connected them to the Motor Driver.
See all of the connections here. Left and right the motor connections, at the top the servo and at the bottom the power supply.
Moving to the gondola: The pen is fixed with a screw.
The servo is a press fit for the holder and doesn't need any screws.
This is my makeshift construction to elongate the rotating piece of the servo.
The gondola needs some weight to it. I used a pack of AA batteries.
The rubber belt is fixed to the gondola with cable ties (like everything in this project)
On the other end another pack of batteries is attached as weight.
For the next steps it's easier to have the polargraph on the window.
This small add-on helped tremendously. The spirit level is very handy for putting the machine up horizontally. Btw, the loose cable ties underneath are for holding tha battery later on.
Let's get back to the important stuff: It's time to put the belt on the pulleys.
Now the gondola will look like this. The weights help in making it steady.
With everything set up, the machine looks like this.
This is the circuit for comparison.

Programming

Please note that this section was carried out on Windows. Peculiarities of other operating systems will not be addressed.

External sources used for this section: YouTube: Make Arduino XY Plotter Drawing Robot | Instructables: XY Plotter Drawing Robot | Arduino | Polargraph

Polargraph with Processing and Arduino UNO

Whats Polargraph?
Polargraph is originally a particular brand of CNC plotter machines. It is often used in a generic way to describe any of these kinds of machine, but it's not the official name for machines like this.
Currently, the Polargraph brand/project is on hiatus, but it's source code is still available. The latest bundle (2017) is available on Github. It includes the polargraph-controller, which is a desktop application for controlling a polargraph machine, communicating using ASCII command language over a serial link. But we'll see what that means later.
To run the polargraph-controller, we need a certain version of Processing . Processing is a flexible software sketchbook and a language for learning how to code. (links and explanation down below)

Links to the stuff you have to download: (The listed versions are important, polargraph-controller is likely to not work if you are using the wrong Processing version) Let's get started: - Arduino
Install Arduino IDE 1.8.16
Copy the library folders out of \Polargraph 2017-11-01\arduino-source\libraries into your C:\Users\xxxx\Documents\Arduino\libraries
Copy \Polargraph 2017-11-01\arduino-source/polargraph_server_a1 into your Arduino/ folder
Start Arduino IDE. Open the polargraph_server_a1.ino source code in Arduino: File->Sketchbook->polargraph_server_a1. Fourteen files will open up and be displayed as tabs in the IDE. This is the source code of the firmware.
Let it compile.
If it compiles, connect your Arduino UNO and press the "upload" button in the toolbar to upload it to the Arduino.
Once you do that, you should confirm that it is working properly - use the serial monitor on the board, set to 57600 baud to make sure that it is issuing "READY" every couple of seconds.
Processing
Install Processing 2.2.1. Run Processing and find where your sketchbook folder is: (File->Preferences, sketchbook location).
Visit the Polargraph link above and download the ZIP file and unzip the code bundle.
Copy the three code library folders out of Polargraph.2017-11-01\Polargraph 2017-11-01\processing-source\Processing libraries into your C:\Users\xxxx\Documents\Processing\libraries
Copy the whole polargraphcontroller folder from Polargraph.2017-11-01\Polargraph 2017-11-01\processing-source\ into your Processing sketchbook folder: C:\Users\xxxx\Documents\Processing
Restart Processing and go file->sketchbook->polargraphcontroller to open the app source code. Press the run button in the toolbar to run the sketch.
This should open.
Polargraph Controller


Machine dimensions

Supply power to your board.
Connect your polargraph controller.
Enter the Setup section from the tool bar.
Adjust the size between two pulleys on the Machine Width
Adjust the Machine Height (height between the pulley and the end of lowest your machine can go with the length of it's belt)
After machine dimensions, adjust the size the area you will draw. E.g. the area of the window you will draw on.
Then, first click the Center Page button and then set the Page Pos Y value 120.
Secondly click Center Home Point and set Home Pos Y value 120.


Stepper motor and pulley settings

Set the MM Per Rev value according to the pulley and belt you are using. For example, if the belt is GT2 the lue is 2mm. If the pulley has 20 teeth, 2x20 = 40mm. So, the belt will advance 40mm each full turn.
Adjust Steps Per Rev according to the stepper motor type. For example, if te step angle of the used stepper motor is 1.8 degrees the value is 200 steps. This value is adjust to 400 because dual motor is used.


Servo settings

Pen Up Position and Pen Down Position values are the operating angle of the servo motor.
Click Serial Port and select Arduino's port from the list of connected devices.
When the correct port is selected, the 'No Serial Connection' display will turn GREEN.
Click on 'Command Queue' and command transmission is activated.
Click Upload Lift Range, then click Test Lift Range and test the servo motor angle.


Save settings and home polargraph

Save your setting. Load your setting every time you turn on the program.
Click the Input tab and switch to the main screen of the program.
Then we will manually set the gondola for 'Set Home' manually. Move the gondola by manually and move it to the previously defined home point (12cm down from the center between the 2 pulleys). The gondola must be adjusted this way before each drawing before clicking 'Set Home'.
After this adjustment is done, Set Home and Set Pen Position are clicked.
Click Set Area to specify your drawing are. Then click Set Frame to Area to make all necessary settings for drawing.
Click on Move pen to point and click anywhere on inside the frame. The gondola should move to this point. This is helpful in testing your settings and the connections of the motors.
Here you can see it working.


Upload an image

Find any vector drawing image. Convert image to the SVG format from any converter platform.
After select Load Vector from program. Adjust image size with Resize Vector. Move the image to the desired area with Move Vector.
Finally, click the Draw Vector command to start the machine.
In action! You can see the G-Code being sent to the machine. Slow but steady.
While its drawing! :D
One thing to note though is, that the machine still has a problem with overheating. Especially in hot weather. Therefore I mounted some heatsinks, which made it a bit better. But this is definitely a part for further improvement in the future! :D

End of group assignment