Modular Robots for Space Applications
CAD, Stress Analysis, Electrical Design, Mechanical Design
Managed and led a team of eight in developing a modular robotic system, composed of modular units, built to be able
reconfigure into different high-strength structures such as manipulator, arms, and cranes on extraterrestrial bodies.
These modular robots would also be able to reduce payload weight for rocket transportation, as a set of modules can be reused for a variety
applications. These robots can also ideally facilitate rapid equipment repairs by hot-swapping malfunctioning modules instead of replacing entire machines.
The end goal of the project was to design and construct a tabletop modular robot prototype, capable of transforming into different geometric configurations using the
same set of modules. These modules should also be able to withstand static loads in a cantilever arrangement.
After defining our module system's requirements, through client interviews, we created a function tree, visualizing an overview of steps and functions needed for a modular system to reconfigure into different structures.
Figure 1. Modular Robotic System Function Tree
Through this function tree, we identified four critical subsystems that require design solutions to enable the modular robotic system to reconfigure effectively:
Figure 2. Latch Connection Architecture
Seen above is the latch connection scheme integrated into the modular system. The connection subsystem is designed to withstand extreme loads and bending moments, while being easy to manufacture. Each aluminum connection face consists of four aluminum static and active latches. When the connection scheme is actuated, the four active latches rotate out of the inner modular frame, allowing the connection face to hook onto the static latches of an adjacent connection face, as seen in Figure 3 below.
Figure 3: Active Latch of one connection face hooking onto the static latch of another connection face
Figure 4. Turntable Architecture
The turntable is composed of two further subassemblies. The function of the first subassembly(shown in the back left of Figure 4) is to rotate the connection face. This assembly is composed of a DC motor that generates torque to rotate the driver pulley, a second driven pulley mounted onto the connection face that recieves torque from the driver pulley actuated by the motor, and a tensioner pulley that eliminates belt slack. The function of the second subassembly(shown in the front right) is to counter the belt tension and ensure accurate positioning of the connection face with respect to the frame. This assembly is composed of a bar that serves as a mount for the linkages onto the 80-20 frame, the driven pulley that is rotated by the belt driven by the driver pulley, and the linkages whose position can be adjusted to create a force pulling the driven pulley towards the bar.
Figure 5. Frame Architecture
The frame subsystem consists of three principal components, as depicted in the figure above, each fulfilling unique functions. The first component, the 80-20 T-slot beams, acts as the system's framework and bears the majority of the loads applied to each module. Additionally, these beams serve as the primary mounting mechanism for other components during integration. The faceplates are then securely attached to the 80-20 framework using 16 screws per face. These faceplates facilitate the installation of connection modules and enable the actuation of rotational motion from the turntable subsystem. When any two modules are connected in a cantilever configuration, the faceplates allow the module ti withstand significant axial and shear loads. Lastly, the bushing is positioned between the connection module and the faceplates. Its circular design encompasses the connector disk, accurately aligning the disk within the faceplates' circular hole. Moreover, it plays a crucial role in minimizing friction during actuation by incorporating a thin Teflon layer between the sliding aluminum plates.
Figure 6. Electronics Architecture
The electronics of the system are designed to be as simple as possible to demonstrate the functionality of the mechanical components, as the focus of the project has been placed on mechanical design. The modular robots use an Arduino, as a microcontroller, powered by a 6 Volt battery pack which also powers the linear actuator. The DC motor is powered separately by a 22.2 V LiPo battery. The microcontroller sends PWM signals of two different frequencies to the linear actuator and DC motor to control their motion to trigger actuation. The duty cycle of the PWM signals can be varied to adjust the extension length and rotation speed, respectively.
Figure 7. Software Architecture
For the software, we created a virtual port on a computer which was connected to the Arduino via Bluetooth. We used this virtual port to mimic a physical serial connection. A Python script was written to communicate with the Arduino using the PySerial module. Text commands are sent by the user in a terminal on their computer. Among the options for these commands are the capability to engage and disengage the latches, turn the turntable clockwise and counterclockwise, set the speed of the turntable’s rotation, and brake the DC motor. After the command is sent, the microcontroller sends a response to the computer, indicating whether the action has been successfully completed.
Figure 8. Modular Robot CAD Architecture
Figure 9. Shear Loading Test Diagram
The maximum shear loading that was tested was 284.6N, applied to the edge of a non-fixed module. This surpassed our desired maximum specification of 163 N. Additionally, the maximum bending moment our module was able to withstand was 65.5 Nm, surpassing our desired specification of 36 Nm. We did not test to failure as the module had to be used for the final demonstration and our high-strength specifications were already met. However, the modules looked to be able to withstand higher loads as there was no visual or structural signs of potential failure or damage during the test.
Figure 10. Axial Loading Test Diagram
The maximum axial loading we tested was 309.3N applied at the center of the non-fixed module, surpassing our maximum desired specification of 249 N. Again, The team did not test to failure, as the modules needed to be used for the final demonstration. Again, the module could mostl likley withstand higher axial loads as there was no visual or structure signs of potential failure of damage during the test.
Unfortuantely, I am not able to share more about this project here, however if you would like to learn more feel free to contact me here.