Blog 7- G10

Blog 7

Between March 9th and March 23rd, the team mainly focused on machining the casted prototype. The cast had some imperfections due to air pockets forming which ended up creating holes. These holes were mostly concentrated in a small area in the fins shown in Figure 1. The team believes that the holes would not substantially affect the functionality of the device other than a minor decrease in thermal performance. The team could redo the cast and make another prototype but a minor loss in thermal performance is not worth the time to recast the prototype.



Figure 1. Holes on one side of the cast.

After the team decided to keep the cast, the fins were machined. The fins were made slightly thicker than originally planned to reduce the chance of them breaking since the holes had already weakened the structure. Based on the heat transfer calculations from semester one, the new fin design still provides enough cooling to prevent overheating. Figure 2 shows the current machining progress on the prototype. The hole-filled side is facing down in Figure 2. 

Figure 2. Work in progress machined prototype

The inside of the prototype will be smoothed out and bolt holes have been drilled to hold the back cover shown in Figure 3. The drilled bolt holes can be seen in Figure 4. Originally the design was a unibody design with the fins being longer and the back having no opening. However, the back of the motor has a plastic cover which would not contribute to dissipating heat so instead a back cover was used to save on the amount of aluminum used. The back cover was machined from a spare aluminum round bar and is mounted using bolts to the rest of the casing. With the machining finishing this weekend the team is right on track with the project.


Figure 3. Aluminum back plate

Figure 4: Bolt Holes drilled into the Prototype

Once the machining is finished, the team will focus on validating the prototype. All of the validation is expected to be completed in the next two weeks. The casing will be measured with a ruler and calipers to make sure it is within the constraints. The casing will be mounted on the motor to compare the torque output with the casing and without the casing when the motor is hooked up to a generator. The team aims to finish the motor testing as quickly as possible to return the motor to the client. The waterproofing test will performed in a trash can with water leak strips sealed in the motor casing to determine if the casing is waterproof. Thermistors will be used to measure the internal and external casing temperatures which will be used to calculate the net heat transfer from the case.

One potential problem the team might face is a fin breaking off when handling the prototype. Suppose the prototype fails to pass the heat transfer validation. In that case, the broken fin area can be accounted for in the calculations to determine if the broken piece caused the failure in the validation vs if it was a design problem.