All Right! So here is our MCM, the most critical module that will help us in the competition!
please click to enlarge picture
Here is the 3D view of our machine. Looks pretty simple, but that's what we are trying to achieve! Simplicity is not to be overlooked, but rather be viewed as an art :) However, although the machine might look pretty simple, it was not as simple as we thought to manufacture it.
Here is the side view of the machine.......
And a closer look to the machine.......
Overall, we are proud of our MCM and it definitely worked out!
Future Objectives:
Now that the MCM is done, we have to move on to the manufacturing of our other module.
This will not be as easy as our MCM. Lots of process will be involved just to create that arm, and here is the materials that we will be using:
Hurray! We are done building and assembling the 5 MCM parts! However, we came across certain problems that we did not foresee while planning. Thankfully, we have come out with solutions for these problems.
Brackets
Original plan: -For the assembly of the box, we decided to use screws to constrain the whole box together. The plan was to screw the sides of the box and the top of the box together.
Problem: -This method does not hold the box well. Firstly, by screwing the box together, the screws could only withstand moments from one axis, leaving it unstable if any external forces would apply on our box. Secondly, the wood is really thin for us to put some screws on, and this would cause the woods to splinter, which is not desirable.
Solution: -We decided to utilize brackets to constrain the sides and the top of the box together. This is a much better idea as the brackets are able to hold of moments from 3 axis, making our box fundamentally sound.
-We manufactured the brackets by using the aluminum 90 degree angle stock. First, we band saw the long piece of aluminum to the bracket sizes that we wanted. Then, we marked the brackets for us to drill holes. Finally, the brackets are drilled using the drilling machine to create holes for the screws to enter. We also created more holes on the sides and the top of the box for the brackets to function. Guide Rails
Original Plan: - The guide rails are to be constrained to the base of the MCM by using screws.
Problem: - Since the guide rails are only constrained at one point, they will be able to rotate about its pivot since there are no counteracting moment at the pivot.
-The guide rails are not parallel to each other, causing our guide rails rod to be misaligned.
Solution: -We decided to buy a 4" long #4-40 threaded rod that goes through both holes on the guide rails. Firstly, this will ensure that the distance between both the guide rails are kept constant. Meaning, the guide rails will be parallel to each other. Secondly, due to the square shaped holes on the acrylic, the guide rails will not rotate about the pivot's axis uncontrollably. Having said that, there is some space for the guide rails to rotate slightly to prevent overconstraining the part. Another issue that we have is how to apply a torque onto the rotating shaft using a motor. This is what we plan to do: 1. Construct a mounting platform using the plywood that we have left into slightly a bigger size than the motor. 2. Constrain the mounting platform to the side of the box by using 2 brackets. 3. Tap 4 holes on the mounting platform to constrain the motor by using screws. 4. Utilize bevel gears to translate the direction of torque which allows the rotating shaft to rotate.please click to enlarge picture
For the past week, we met to decide the engineering drawings of the MCM. Most of the details of the MCM (e.g. dimensions) were worked out. Starting this week, we can use the waterjet and laser cutting machines to manufacture our parts. We plan to complete 3 parts of our MCM, namely, the box, the base and the guide rails by Friday 20th Nov, and the last 2 parts, the rod and the motor holder will be completed next week.
Here is a summary of what we are planning to do for each of our MCM Part:
1. Box
-We decided to use 2 different materials for the sides of the box, the hardboard and the birch baltic plywood. We decided to use the acrylic for the top of the box so that we can look at the process of the machine working, making it easier to detect errors if anything goes wrong. We will laser cut the whole entire material along with hole on it to make everything as precise as possible.
2. Base
- We bought a material for our base; a thick aluminum plate with attached rubber padding on its bottom. We needed this material as the rubber on its bottom provides us with a higher coefficient of friction that will prevent the whole base to slide along the arena's carpet. For its manufacturing process, we will water jet the whole material to get the precise shape and size of it. As for the holes, we decided to drill them using the drilling machine. 3. Guide Rails
- This is really tricky to make, especially with the materials that we have. We decided to use the thin, wide piece of aluminum, 1/ 16" thick and water jet them along with the holes to their planned sizes and shape; a base and curved beams. Then, we will use screws and nuts to constrain the water jetted plates, making them into the shape of the guide rails that we wanted. 4. Guide Rails Rod
-First, we cut a 3/8" aluminum rod to its specific length that we wanted using the bandsaw. Then, we decided to lathe the ends of the rod. The ends will be lathed so that it will fit to the guide rails perfectly. This should be relatively easy.
5. Rack and Pinion Motor Holder
-The motor holder will comprise of pieces of plywood and thin steel sheet. We decided to laser cut the plywood and water jet the thin steel sheet to its planned size and shape. For its assembly, we decided to use epoxy glue to constrain the pieces of plywood and thin steel sheet. Additional Note: Also, we solved the problem of driving our rack and pinion inside the arena. The solution was to use one side of the double gear box, and attach a gear at the end of the shaft. The motor will rotate in the x-axis, the shaft will rotate in the y-axis, and the spur gear attached to the shaft will drive the rack in the z-axis.
Our most critical module consists of 5 different parts, listed as follows:- 1. The box, made of wood and acrylic, houses all the other parts. It acts as a support for the whole machine, and also functions as the part that connects the whole machine together.
2. The base, which is made of aluminum with a layer of rubber padding at the bottom, is designed to provide support on the table and ensure that the machine does not move laterally during operation. It also acts as a mounting platform for the guide rails and the motor holder. 3. The motor axle, made of a single aluminum rod, is used to hold the rotating arms in place and also acts as the axle on which the arm rotates about. 4. The motor holder. It is made of sheet steel on the sides and acrylic on the bottom. It is designed to hold a motor which drives a rack and pinion on the arm so that the arm can be extended and contracted at will. 5. The guide rails. These 2 rails serve to guide the motion of the motor holder as the arm sweeps up, restraining its degree of freedom and also providing support to the motor holder. When assembled, the MCM looks like this: The fully assembled machine looks like this: Here, you can see how the arm is made to rotate about the motor axle, and how the motor holder is interfacing with the arm. The guide rails are also supported through a cut on the top of the box so that they will not break under the weight of the motor holder and motor combined.
please click to enlarge picture
Here is the side view of the machine.......
And a closer look to the machine.......
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