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Centrifuge System
The center stack will be powered by the Vex Robotics CIM Motor (geared 50:1) and the arm will be attached to this motor through the motor housing assembly. The majority of machined parts will be made out of aluminum 6061-T6 alloy and the counterweight assembly will be machined from AISI 1020 steel alloy. The counterweight assembly is removable, therefore the weight can be changed accordingly with the CubeLab. The brake is incorporated into the system in order to stop the system from rotating suddenly when replicating acceleration profiles, as well as for safety purposes. The centrifuge will be encased in a hexagonal frame with ABS Polycarbonate Protective material to ensure efficient environmental conditions.
Figure 1. The complete design of the centrifuge (excluding the control panel).
Figure 2. A detailed configuration for the arm of the centrifuge. The arm length is 1.5m long and carrying SpaceTango's CubeLab, which is expected to be 12 kg.
Design Fixes and Improvements
The motor housing assembly is one of the main areas of analysis since the designed control system will be in coordination with the motor. The initial driving assembly (Figure 3a) designed by the previous MAE 156B team (Spring 2020, Team 18) did not allow the CIM Motor to attach to the VersaPlanetary Gearbox (via CIM Motor Adapter), which means that the motor shaft must be shortened in order to attach to the gearbox. As a result, axial interferences were caused between the shaft and the gearbox. The team has designed a new motor housing assembly, which avoids interferences and provides better support for the motor. The new assembly includes a motor face-mounted support place, right-angle plates, and hole cutouts on the centrifuge base-plate. These design fixes provides more torsional and axial stability, as well as a better fit for the motor.
Figure 3a. Old driving assembly
Figure 3b. New driving assembly
Figure 3c. Exploded view of the new driving assembly and labels for each of the parts
Control Panel
The control panel will encase the whole design control system, which will be implemented into the centrifuge system (close to the motor). Multiple receptacles, such as the signal and power receptacles, are shown on the outside of the control panel. The receptacles are implemented in order to manage the cables and wires.
Figure 4. At the top of the control panel, starting from left to the right, the Raspberry Pi (Green) is connected to the Talon SRX (Black). The Raspberry Pi will communicate with the Talon through code. On the right of the Talon SRX, it is connected to its brake and fuses for safety purposes. Next, the electrical system continues to the Relay Circuit Printed Circuit Board (PCB). On the bottom left, there are power distributions at the top and ground connections on the bottom. On the bottom right, there are the 12VDC and 5VDC power supplies, along with the battery (connected to the 12VDC only).
Electrical Circuit Diagram
The electrical circuit diagram will be incorporated onto the control panel by sticking it onto its side (or covering). The purpose of the diagram is to provide future users a reference of the electrical connections between the major components. The diagram will come in 3 sheets total. The first sheet will display the receptacle connections and power supply connections (12VDC and 5VDC). The second sheet will display the electrical components with their respective power supply. In the second sheet, the 12VDC power supply connection is with the Talon (connected to its encoder) and the battery. Additionally on the second sheet, the 5VDC power supply connection is with the Raspberry Pi (RPi) and the Relay Circuit Printed Circuit Board (PCB). The third sheet is a more detailed connection between the Talon, PiCAN, and RPi.
A wire gauge table can be found here.
An electrical Bill of Materials can be found here.
Figure 5a. The first sheet of the electrical circuit diagram, which includes the receptacle connections and power supply connections (12VDC and 5VDC).
Figure 5b. The second sheet of the electrical circuit diagram, which includes major electrical components in connection with their respective power supplies. The 12V ladder contains the Talon connection with its encoder and a battery. The 5V ladder contains the RPi and Relay Circuit PCB connections.
Figure 5c. The third sheet of the electrical circuit diagram, which displays a detailed connection between the Talon, PiCAN, and RPi
Summary of Performance
The performance of the whole centrifuge system was conducted theoretically using ANSYS and Simulink due to delays in manufacturing. Fortunately, the team is continuously working on optimizing the electrical system and the software system (programming and coding) in order to prepare for immediate testing when the centrifuge system is completely built. Below are figures of analysis and results of theoretical testing. Click here for the programming.
Figure 6. Angular displacement profile for simulation of centrifuge.
Figure 7. Torque at the motor against time.
Figure 8. Simplified CAD assembly shown in ANSYS finite element analysis (FEA) simulation software. Red circles display where the assembly will be bolted to the ground.
Figure 9. Output predicted by the transfer function on the right. Prediction has an accuracy of 69%.
Equation 1. The continuous time transfer function used to determine the theoretical acceleration of the system.
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