Preliminary Detailed Design
Table of Contents
Team Vision for Preliminary Detailed Design PhaseOur team plans to:
- Test old prototype
- Complete a redesign of the prior CAD model of our system, including a ratchet system, arms, and structural base
- Design schematic and PCB for lab test system
- Start programming microcontroller for lab test system
- Update risk assessment
Our team actually did:
- Sourced all parts currently on BOM
- Created test plans and implemented early testing
- Designed 90% of schematic and PCB for lab test system
- Working on Lakeshore interfacing with lab test board
SolenoidA Ledex 3E 45 degree clockwise rotary solenoid in being used to actuate the system.
The solenoid housing is very similar to the previous design. It allows the solenoid to be mounted slightly above the cryostat base plate and the torque from the solenoid is reacted into the mounting on the housing. Cross-drilled hole allows for ease of assembly with lower ratchet mechanism.
Arm Support Plate
The arm support plate has two functions. It allows for the mounting of the flex pivots to be located relative to the centerline of the solenoid, and it compresses the compression spring which resides in the ratchet assembly.
Ratchet & Cam
Upper and Lower Ratchets
The teeth geometry of the ratchets allow only for clockwise rotation of the peanut cam. Counter-clockwise rotation of the solenoid will result in the teeth skipping and the peanut cam remaining in its current position. This will make it so the solenoid only has to be pulsed to open and close the system.
7075 Aluminum was selected for both ratchets for its increased strength, wear-resistance and availability compared to the more common 6061 Aluminum. The teeth geometry promotes design maximum engagement area during actuation and better surface finish over alternative designs. The Lower Ratchet connects to the solenoid by a M2-0.4 set screw.
The bearings by default rest in the recesses of the peanut cam, holding the system open. When the peanut cam is rotated, it pushes the bearings apart, causing the arms to close on the salt pill. The force exerted on the peanut cam by the bearings should hold the arms in this state until the solenoid actuates again.
The peanut cam is connected to the upper ratchet by a M2-0.4 set screw. 7075 Aluminum will be used for its increased wear-resistance compared to 6061.
The ratchet housing contains the top of the return spring and assists in keeping the upper and lower ratchet in alignment. Since the load it sees is negligible and it shall not see much wear, it will be made out of 6061 Aluminum.
A return spring acts upon the upper ratchet keeping it in contact with the lower ratchet. The spring allows for the the upper ratchet to move vertically as the lower ratchet is rotated by the rotary solenoid.
A 9.5 mm long, 5.5 mm OD, 0.5 mm wire diameter compression spring with a spring rate of 0.29 N/mm was chosen as the return spring. The spring allows for a sufficiently large diameter on the shaft of the upper ratchet, while maintaining a downward force that is not too large for the solenoid to overcome.
Arms & Bearings
The arms have the same profile as the previous design, but the bends were removed making the arms planar. It removed the upward and outward forces that were acting on the head of the arms and allows for smoother motion.
The bearing assembly is attached to the arms in order to translate the rotational motion of the cam to linear motion of the arms. The bearings are ceramic in order to limit heat transfer into the cam. The size was reduced from the previous design to allow for a more compact design.
A form of bearings that allows one side to be fixed while the other side is free to rotate, mainly used to isolate systems from vibration. Already implemented into the design, the flex pivots were moved back to the center of mass of the arms to increase the travel of the arms and reduce the moments on the flex pivots.
Bill of Material (BOM)here
Test PlansA benchmark test was already performed on the previous design. The purpose of this test was to determine if the solenoid would actuate at 77K and the electrical resistance at 77K. From this testing, a preliminary equation to calculate the resistance based off temperature but, the solenoid did not actuate at lower temperatures.
For the iterated design, we plan to perform multiple tests next semester including:
Vibration TestA vibration test stand was created by the previous team to be mounted to a pre-existing vibration tester. Both vertical and horizontal vibration tests can be performed using the tester. However, since the height of solenoid housing and arms has decreased, it is possible modifications will be made to the stand.
Heat Conduction TestA stand with a mounted power resistor was created by the previous team in order to simulate the salt pill. A 5 Ohm resistor is connected to a piece of copper that is mounted on a length of plastic. This can be tested in both the lab and inside the Cryostat.
- Spring rate validation when hardware arrives
- PCB Test
- Code Test
These tests will be performed throughout MSD II.
The link to the live document is here.
Design Review Materials
Plans for next phase
- The team will be ready to present the gate review and DDR
- The system design will be completed pending DDR changes
- All Analysis will be completed to ensure design meets Engineering and Customer Requirements
- All manufacturing and production documentation will be complete
- Test plans to be executed in MSDII are written