Wally - The 3D Printer

Mechanical Design

So for this week is concerned, its all about Group Asssignment to develop a machine that makes (the machine). It was quite a new experience for all of us to work together in a group to develop something. Initially we planned some meetings to come up with an idea of a machine that we can make. Finally after some due delibration we decided to make a special type of 3D Printer generally called "Wally".

Wally is a wall bot where everything is mounted on the wall. Wally is a variant of reprap 3D printers which belong to Selective Compliance Assembly Robot Arm (SCARA) family. The idea was to make Wally as simple and low cost as possible, and use much less plastic and bearing than other does, but has faster speed and better resolution.

The printed parts take almost 1kg of PLA and 40-45 hours to print a complete set. Nicholas Seward recommends PLA printed at a 0.3mm layer height and 15% infill with 3 perimeters.

RepRap Community is working for the portable and replicable 3D printers. RepRap is humanity's first general-purpose self-replicating manufacturing machine. Since many parts of RepRap are made from plastic and RepRap prints those parts, RepRap self-replicates by making a kit of itself - a kit that anyone can assemble given time and materials.

Details about the concept:

• Built off a rigid back board. The board can have ribs attached to make it more rigid. The material is TBD based on prototype needs.
• Wally could be designed to fold fairly flat for storage or portability. Think suitcase with a handle on the side. Legs could fold out to make it free standing, or it could be attached to a wall.
• The design can be scaled. Perhaps a 12" backboard width at the small end. That might give more than a 6" cube build volume. A 15" backboard width might give something on the order of 10" Diameter, or an 8" square, or a 10" x 7" Rectangle -- all with a 10" height. I think this would be a good design center.
• All axis are driven from stepper motors through a Spectra fishing line drive on preferably smooth pulleys.
• The two X,Y arms are driven by rotating the elbows. This gives a build area that is limited by an arc from the shoulder with a straight elbow to the hot end.
• The ratio of the stepper drive to large elbow pulley determines the resolution and torque. 0.025mm or better with a reasonable ratio with a 16-32x microstep.
• The Z axis is a 4 bar linkage that keeps the bed flat as it is rotated up and down through an arc. Gravity lowers and a stepper winding a string raises it.
• The build platform moves through an arc as the Z is changed. The X,Y arms have to compensate for the displacement in the Y axis (perpendicular to the back board).
• A convenient place for a spool is on the lower back. Filament would be fed up through a Bowden extruder and over the top and down to the hot end.

Features

• No linear rails
• 28 cheap 608 bearings
• 12 unique plastic pieces (none require support)
• Printable on a 150x150mm machine
• Theoretical speeds in excess of 500mm/s
• Theoretical resolution is less than 25 microns

Wally works on inverse kinematics, In robotics, inverse kinematics makes use of the kinematics equations to determine the joint parameters that provide a desired position for each of the robot's end-effectors. Specification of the movement of a robot so that its end-effectors achieve the desired tasks is known as motion planning.

Once the idea was ready, now its time to divide the task and get started.

1. Develop the Wooden Frame, Electrnoics and Programming - Fida Hussain
2. XY axis Mechanical Assembling, Wireless Communication - Muhammad Asim
3. XY axis Mechanical Assembling, Preprocessor Programming - Nisar Ahmed
4. Z Axis Mechanical Assembling, Electronics and Programming - Sohail Ahmed Soomro
5. Hot End Extruder Management, Electrnoics, Electrical and Mechanics- Tomas

Link to the Group Page is here : Wally 3D Printer

Well there is quite a bit of help available for this designing this printer, first of all we made a list of the components and materials we will need during the process of making the printer.

Frame Desgning

We started our work, first one was Fida, his task was to cut and assemble frame so that we can further proceed.

All the 3D files related to Wally are available to download from here :

• Back DXF
• Bed DXF

XY Axis Working

Once the frame was ready now it was the time of print the XY and Z axis components their assembly.

Wally places the stepper motors on the walls of the frame to reduce the wieght and allow the arm to move at faster speeds. The position of the arms is adjustable through fishing line drive belt as illustrated below

Design of Wally is a sizeable task. For the mechanical design assignment I and Nisar are jointly responsible for working on the XY- axis movement framework.

The mechanical assembly of XYh movement axis required the following components

Working of the XY Arm

Z Axis Working

It was the process of controlling the Z-Axis and its movement, as in Wally Z-Axis depends on the movement of the bed not the extruder like in the most of other printers. In wally the extruder only moves in XY-Axis.

All the important parts for the Z-Axis 3D printed are here.

Once the Frame part was done, it was now the time to 3D print all the parts, it was the combined and huge task to print all those parts. We printed them after taking a huge time and the materials.

Now it was the time to assemble all the parts