Documents for this section can be found in the Subsystem Design Documents folder.
Team Vision for Subsystem-Level Design PhaseIn the Subsystem design phase our team began to explore the details associated with critical subsystems of our design. Major sections of the design which we aimed to address in this phase were the vibration, structural, and dampening subsystems. Key developments of this stage include development of a clearer test specification plan and a more comprehensive CAD Model which will be analyzed for structural failure using COMSOL and used to develop an initial bill of materials. Other major milestones include analysis and selection of a dampening methodology, development of a more accurate system architecture model, and research and selection of a piston, compressor, and solenoid for the vibration subsystem.
As per Dr. DeBartolo’s recommendation we explored the option to use the Instron machine in the mechanics lab. This would eliminate the need for a power source and would limit our project to just creating a fixture. After meeting with Dr. Gupta, the Director of the Advanced Materials Lab, he explained that this would not be a feasible plan. The Instron machine is only able to control and measure two variables of distance and force. As in if you control the distance at which you want the specimen to use the device will measure the force required and vice versa. Therefore, we can control our amplitude, but not our frequency. Another Dr. Gupta pointed out is that our system mass is far too small. With our current system design weighing around 30lbs it is nowhere the near few hundred that the machine is intended for. For these reasons we will not be pursuing this option any further, and focusing our efforts of creating our stand alone device.
Feasibility: Prototyping, Analysis, Simulation
Forces were calculated using an assumed mass of 10kg
Design of System: The piston system designed for the test rig is a pneumatic controlled piston. There will be a double acting piston controlled by a solenoid valve and powered by a compressor (shown bellow).
Requirements: This system will need to hit the test described above and most notably:
- Frequency range of 5 to 100 Hz
- Able to lift ~30 lbs
- Amplitude of 0.501 in
By using a double acting piston we hope to mitigate difficulties with reaction time of the cylinder. These cylinders will be able to lift the required 30 lbs of the base plate and p-pod so it qualifies it as use for our lift. The difference between these two specs is the cost and the diameter which effects the pressure requited. The reason we have both as options is if the design changes before purchasing and our plate the weight changes will be more ideal to use one or the other. Currently we are going with the larger diameter piston (specs on the left).
Solenoid Directional Control Valve
By using a directional control valve we are able to cycle at the desired frequency with the response time 18ms or less (figures based off 24 VDC Single Solenoid) for the solenoid on the left and 4-8 ms for AC and 10-15 ms for DC. We chose a 4 port valve because we are using a double acting piston and that is what is required to control them properly. The valve is also a solenoid valve because we need to electronically control the system. This left valve also allows for flow control which will allow us to have an air supply to be decided on (currently considering a stand alone compressor or shop air). We are leaning towards the solenoid on the right because it can definitely hit the desired frequencies as well as being a cheeper solution, but might need flow control valve.
Summery of part options:
- Compact Nonrotating Tie Rod Air Cylinder 1.5" Diameter
- Compact Nonrotating Tie Rod Air Cylinder 2.0" Diameter
- Solenoid Air Control Valves with Flow Control
- Skinner V935 Soleniod
The damper is the mechanical system which transforms energy resulting from vibration into other forms of energy. The goal for our damping subsystem is to isolate vibrations being made to our system (test rig) from its fixed, resting table.
1. Which of the two options is most ideal and why?
2. What analysis can be done to prove that our damping system is capable of isolating our system from the tabletop?
Analysis Tool: Force Transmissibility Concept
The smaller the value of the damping ratio, the smaller the value of T.R. and the better the isolation.
Shock and Spring
RubberIn order to isolate our system vibration from the tabletop, we need to use highly damped materials (i.e. rubber) to change the stiffness and damping between the source of vibration (our system) and the table. We want our force transmitted through the base to be as low as possible.
Drawings, Schematics, Flow Charts, etc.
System Inputs and Outputs
-From our last review we have changed the orientation of our P Pod to vertical with concerns for center of gravity.
-CAD model parts for the t slotted rails, and the corner frame set were obtained from McMasterCarr's website. This was to ensure the accuracy of our model.
-Bottom support for actuator is shown with suppressed parts to better display actuator.
-This CAD model is representative of our groups findings and will continue to change up until we have all secured our part choices based on specifications.
Bill of Materials (BOM)Bill of Materials for cost visualization.
This bill of materials addresses our previous concerns in that our previous design review we were looking into singular parts that cost hundreds of dollars, but now we are most certainly within a reasonable range. Also, any raw material needs for manufacture or machining can most likely be found in the scrap pile of the machine shop. We have already acquired all of the 80/20 rails needed for our build with some extra, and also have some aluminum sheet metal for the construction of CubeSat's. All prices are also subject to change based on vendor.
Some parts on the pricing BOM are not shown on the CAD drawing BOM because the CAD model is only representative of our standalone system, with some additions to come.
Feasibility: Prototyping, Analysis, Simulation
COMSOL Structural Analysis
1. Will the structure withstand the necessary forces to shake the CubeSat?
2. Are there ways to optimize the design and reduce material cost?
Before prototyping the rig and buying the bill of materials, it is good practice to ensure that the design is strong enough to withstand the necessary forces on each member. There are a few ways to do this but the best is a finite element analysis. To save time and ensure accuracy, COMSOL is being used to perform this analysis. Using the 3D CAD models from above, COMSOL is able to model the forces and loads applied to the system and perform a structural analysis. Before purchasing the bill of materials and knowing the exact specifications for each member, some assumptions need to be made to run the analysis effectively.
1. All materials are going to be made from 6063-T83 Aluminum
2. The mass of each CubeSat is at the maximum, 1.33kg
3. The P-Pod and CubeSats will act as a single rigid body and will be fixed to the baseplate
After importing the 3D model into COMSOL, loads and constraints can be applied to the model and the finite element analysis can be run. To do this, COMSOL will generate a mesh grid going over each member to form the triangles that it will analyze, these are the finite elements. When the forces are applied to each element, COMSOL can show the stress and deflection experienced for each and sum them across each member to show a real world simulation of the input model. A time dependent analysis can also be run with the frequency functions given above to see how the structure will withstand the entire test. This will be representative of a cyclical loading test to show how well a moving assembly will stand up to the forces applied over time.
The model is currently in process and is being worked to move forward with a better and more realistic analysis. Some of the issues that are currently being faced are the result of heavy resource requirements from the system. In order to continue, the following alternatives are being considered.
1. Run the finite element analysis on a larger computer with more resources
2. Divide assembly into subsystems to perform peicewise analysis
3. Reduce the file size and precision of the model
4. Perform the finite element analysis in a different program like ANSYS or through SOLIDWORKS with the ANSYS tools
- Updated Risk Assessment with ownership added
Plans for next phase
Deliverables by OwnerOur goals and tasks going forward.
1. Finite Element Analysis preliminary results
2. Safety subsystem feasibility
3. Calibration CubeSat and sensors
1. Finalize design of piston assembly
2. Consider ways to control the piston assembly
1. Determine reliability of rubber mats through the relationship between Shore A hardness (durometer) and Young's Modulus
2. Sensitivity analysis for variables that increase damping for springs
3. Benchmarking for rubber mat as damper for systems
1. Continue to update the CAD model accordingly based on teams findings and product choice
2. Design to manufacture as well as for cost sensitive parts. Specifically from the base plate upward.
3. Bill of materials management
1. Develop plan to account for inability of vibration system to meet lower displacement requirements
2. Establish inputs/connections between controls and system