Compound Machine
For this activity, we created a compound machine out of several smaller simple machines. In the end, I learned a lot, but I learned the most about the math and calculations involved. In the end, this was a very informative activity.
Timmy Pollard-Grayson
Dylan Ionnotti and Ashmal Irfan
POE Block 2
9/25/15
1.1.6 Compound Machine Design
Design Problem
The task for this project is to create a compound machine that can lift a weight of 8 ounces up 6 inches. However, the criteria for this problem are:
Brainstorm Ideas
Dylan Ionnotti and Ashmal Irfan
POE Block 2
9/25/15
1.1.6 Compound Machine Design
Design Problem
The task for this project is to create a compound machine that can lift a weight of 8 ounces up 6 inches. However, the criteria for this problem are:
- It must use at least 2 simple machines, and at least one gear system, chain and sprocket system, or pulley and belt system.
- Also, each mechanism must have a mechanical advantage greater than 1, and the overall system must also have a mechanical advantage greater than 1.
Brainstorm Ideas
This is the final brainstorm that I created. The text says:
“When a human manually turns the crank, Sprocket A turns smaller sprocket B, which turns sprocket C on the same axle, which turns sprocket D, which is the wheel for a wheel and axle system. When the axle spins, it winds up a string from a block and tackle system, which lifts the weight.”
Final Design Proposal
Before we made the final selection, we made a decision matrix. We rated each idea on a scale of 1-4 from the following criteria:
Durability: How structurally secure would it be?
Simplicity: Is it easy to follow/understand?
Time needed/parts needed: How long will it take to build and how many parts will it take?
Testability: How easy would it be to gather information?
Function: Does it meet the established requirements?
Final Design Proposal
We ended up choosing my proposed idea and modified it slightly.
We ended up choosing my proposed idea and modified it slightly.
We changed the position of the sprockets, and we added more clarification (such as input/output) and arrows to show movement.
Design Modifications
We made in total about 5 modifications to the machine that weren’t in the final sketch.
Final Design Presentation
In the final presentation, our machine functioned just as we expected. Previously, we had some slight issues with the balance, but it went without a hitch. It was well under the 3 minute time limit and lifted around 3 inches.
Design Modifications
We made in total about 5 modifications to the machine that weren’t in the final sketch.
- We switched from a pegboard to using the metal sheets provided in the kits. We found that the pegboard holes were too big, which led to two problems. One, the sprockets were not rotating right, since the hole was too big. Secondly, the fact that the holes were too big meant that the shafts the sprockets were on kept leaning, so the chain kept coming off the sprockets. Our original fix was to add weight on the end of the shaft, but in the end, it didn’t solve the problem, so we switched to the metal.
- After we had switched to a metal sheet, the metal sheet didn’t have enough room for the block and tackle system to lift the weight the full six inches. We rectified this problem by simply adding a smaller sheet of metal to the top of the sheet, allowing for the block and tackle to work correctly.
- We originally had a layout that looked like a “L’’ or, in some of the other drawings, “---”, but in the end we changed it to a more “|___” type of shape, so we could fit everything on the back support.
- Originally, our block and tackle system had a twine thread, but it kept tangling and getting wound up. We solved this by using a larger, nylon string.
- Finally, our last design modification was just really an oversight on our part when we were drawing the final sketch. Since Sprocket A went to Sprocket B, which was on top of Sprocket C, we needed to add a spacer between Sprocket A and the metal sheet.
Final Design Presentation
In the final presentation, our machine functioned just as we expected. Previously, we had some slight issues with the balance, but it went without a hitch. It was well under the 3 minute time limit and lifted around 3 inches.
Sprocket A is the one at the top left, with the crank on it, which leads to sprocket B, the small one, on the same shaft as C, which leads to D, which is the wheel and axle for the spool with the thread for the block and tackle.
Finding the IMA, we had to do seven separate calculations. The first six were to find the ratio of the individual parts. To find the IMA of the entire thing, we multiplied it all together. So we get
0.5625*0.4*2*0.75*1.66667*4=2.250
So the entire IMA of the machine is 2.250 (The zero is significant), which means that turning the crank to lift the weight is 2.25 times easier than just lifting it up.
We calculated the AMA, and we got 0.51, which gives an efficiency of 22.6%. Oops.
Team Evaluations
Dylan
Dylan definitely followed all the group norms. He didn’t have a working phone, so he made sure he could reach us a different way. Dylan also contributed good work during the entire project, and did a lot of the disassembling and assembling, especially when we decided to scrap the pegboard and re-do it.
Ashmal
Ashmal also followed the group norms, and kept in touch very well through text. Ashmal did a lot of the background stuff when Dylan and I were building, such as finding measurements for calculating the IMA and also gathering materials. He also helped build a lot of the gear parts, like the shafts.
Me
I think I managed to follow the expectations well, I texted and emailed various pictures and calculations to Dylan and Ashmal when they needed them. I feel like I did a lot (definitely not majority) of the building, and also contributed a good amount, since my final design was eventually the one chosen, and I had several modifications in mind.
Post-Mortem
- Finding the block and tackle system’s MA was the easiest, since all we had to do was add up the number of supporting strands.
- In my opinion, wheel and axle, just because it takes a little thinking to figure out which one would be the wheel and which one would be the axle, as opposed to block and tackle systems or simple Gear Ratios.
- I would have changed the layout and size of the sprockets, since they greatly reduced our MA.
- The only thing I would have done differently was calculate the AMA earlier. None of us realized it was supposed to be done, and had not calculated it until after our presentation. Oops.