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15. Mechanical design

This Weeks Task:

  1. Design a machine that includes mechanism + actuation + automation.
  2. Build the mechanical parts and operate it manually.
  3. Document the group project and your individual contribution.

Group Assignment

Here is a link to our group page.

Individual Assignment

To start of this project, each of us should choose a machine that we want to build and distribute its design development and manufacture among us. We started by looking at different projects that were made by previous fabacademy students and then researched online on similar projects and mechanisms to come up with different ideas. The mechanism that we decided to develop is just like the plotter machines using a slider mechanism. However, we didnot want to repeat the same idea again by developing a plotter machine and having it to draw a specific thing. Therefore, we searched for different ideas using the similar mechanism and got inspired by this video.

This is an automatic car washer by using almost the same mechanism as we want to use, but ofcourse, we are going to do it on a smaller scale. The first thing we did before developing our project was to divide the tasks among us in order to know what each of us will be doing. Since we are 5 students, we have 3 of us working on the mechanical aspects, including me, and the rest 2 working on the electronics part. The project includes: 1. Mechanism 2. Working principle 3. Structure 4. CAD model of design 5. Joints and fittings 6. Material selection 7. Fabrication 8. Electronics production

In this project, I will be responsible of the joints and fittings, material selection, fabrication and a little bit of CAD.

Joints and Fittings

This section will be about how to assemble our machine together and what are the best methods to use in our case. There are different types of fittings and joints used. Here is a guide to joints to help you understand and get started.

Here is a summary of all the joints.

For our design, I thought of having box/finger joint which is similar to pressfit kit designs, in addition to corner 90 degrees brackets with nuts and bolts. We will also be having some joints using screws to assemble our parts together.

Here are some areas of which we will be having our joints.

  1. The holes here were to assemble the main structure of the machine using 4mm bolts and nuts together with the brackets for cornered edges. This was done to increase the stability of the model.
  2. Box/finger joint were used to attach the rest of the parts together instead of using nuts and bolts in the entire model.
  3. Sharp edges were removed to reduce the stress concentration.

Material selection

Two materials were considered for our model, MDF and acrylic. I was thinking of using the cnc machine for cutting the MDF or using the laser cutter for the acrylic. However, we will be using water in this project to demonstrate how it will wash a car toy. Therefore, MDF will not be a practical material to use in this senario since it reacts with water and destroys the wood over time. As a result, I thought acrylic will be a better choice. We also have a wide range of colours to choose with a shiny finish to it, which will give a neater look for the end result.

Fabrication

My colleague Zainab was responsible of designing the CAD model with my other colleageu Abdullah which helped her with the structure modelling and mechanism. In relation to the joints, we all sat together and discussed about how we want to assemble our parts together and designed the joints and fittings according to that. After the design was ready, I thought of testing it out by laser cutting it using matboard as a prototype, to ensure that everything fits well and prevent issues that may occur with the acrylic design. You can visit our group page in order to download the CAD files.

Since we have used solidworks to design our model, we exported the files to DXF format and used inkscape to prepare it for laser cutting.

  1. I started by arranging the parts by using up the maximum space to avoid material waste. The matboard sheet dimensions were 600 mm x 300 mm and so I edited the document properties according to the sheet size.

  2. I edited the stroke colour and stroke style. The stroke style used for laser cutting is 0.001 inches.

  3. Save the file as pdf.

  4. Click on File > Print and adjust the properties before printing the file. Below are the settings used. The speed, power and frequency was set by referring to the epilog catalogue software which comes along with the laser cutter machine. After setting everything, click print.

Here is a timelapse video showing the prototype assembly.

Prototype images

Problems faced

Fortunately, there were no major problems faced while assembling the model. Some minor changes were made such as the distances of the bolt holes since they were not overlapping and therefore we were not able to screw some parts with the other. The changes that were made were very minor which only required change in distances by +/- 1 to 2 mm. Luckily, the main structure had no issues and everything fit properly together.

The other change was in the shape of the structure itself since we noticed that it lacked stability and wiggles a lot. Therefore, we thought of making the structure stronger by adding more support and attaching it with box/finger joint.

So in total, 3 more parts were added for better stability.