What is the Mechanical Team?
The MAVRIC Mechanical Team is responsible for the design, manufacture, and testing of all mechanical and electromechanical systems on the rover. This includes major subsystems such as the rover’s chassis, suspension, and robotic arm, as well as other considerations like camera and radio mounting. The Mechanical Team also ensures the rover remains under the 50-kilogram mass limit imposed by URC. The main goal of the Mechanical Team is to create a competition-suitable rover which will remain mechanically sound through all of the competition tasks.
The 2019 Rover
All designs are first developed in-house using SolidWorks, a Computer Aided Design software (Figure 1). This is a multistage process involving several gate reviews and design revisions. Once the design is finalized, manufacturing plans and other necessary files for production are developed. The rover (Figure 2) was largely manufactured using equipment on the Iowa State University campus. Manual mills, a 4-axis CNC mill, a waterjet, metal band saws, and various other machines were employed. Various 3D printers located in the M:2:I Lab were used to create small, complex, durable, and lightweight parts around the rover. The manufacturing of the chassis was generously donated by Quality Manufacturing out of Urbandale, Iowa.
The chassis was designed with numerous mounting holes on all sides for subsystem modularity. This provides for a greater amount of iterative improvement and minimizes operational downtime. It allows the team to experiment with new subsystems without compromising rover functionality and permits backward compatibility, so new subsystems can be replaced with older ones if they fail or do not meet expectations. For example, if the rover suspension were entirely reworked, the current suspension could be removed and a new one attached within an hour without having to modify anything on the rover. The mast (Figure 3) and soil science system are also attached to the chassis by the side mounting holes. Mounting brackets inside of the chassis hold the electrical box in place and allow it to be easily removed for testing. A top plate over the front half of the chassis improves structural integrity and provides a mounting location for the robotic arm, light spectrometer, suspension differential bar, and power distribution box.
The rover makes use of a rocker-bogie suspension, which enables it to traverse large obstacles and helps keep the chassis stable over uneven terrain. The rocker has its range of motion partially limited to prevent failure in extreme terrain. The rover’s six wheels are individually driven by high-power in-hub motors, which provide enough torque to tackle steep inclines and maintain high ground clearance. High-traction 10.5″ wheels enable the rover to climb over large objects without issue. The rover utilizes skid-steering to maneuver on the desert sand; this results in significant weight savings by not requiring separate steering motors on the front and rear wheels. During outdoor drive testing in September 2018, the suspension performed very well on uneven and steep terrain (Figure 4).
The rover’s robotic arm has five degrees of freedom. The base of the arm mounts to the top plate of the chassis and contains a motor to control the left-right swing of the arm. A second motor mounted on top of the arm base utilizes a worm drive to lift the arm at its shoulder. A linear actuator at the elbow provides more precise forearm movement. A dual-motor wrist joint offers both pitch and yaw at the end effector. The end effector is controlled by a single mini linear actuator and has the ability to manipulate a wide variety of objects up to five centimeters wide. The proposed controller mapping configuration (Figure 5) will allow the arm operator to intuitively control the entire arm from the base station.
Progress Made in the Spring 2019 Semester
Changes to the robotic arm were successfully implemented throughout the semester. A new end effector was designed and implemented. Components for the new shoulder and upgraded base rotation were produced and will be assembled on the rover shortly. Feedback systems were implemented at each joint of the arm to ensure precision remote control. A manipulation board and off-rover arm test stand were produced to improve the team’s arm testing capabilities. The arm was able to lift the 5 kg requirement and perform fine manipulation tasks. Cameras were placed around the rover to improve vision from the base station. The total mass of the rover was reduced to 50.95 kg, which is above the 50 kg mass limit imposed by URC, but not enough to significantly impact the scoring during competition.
Lessons Learned in 2018/2019
The Mechanical Team learned quite a lot this academic year. The team has a much better understanding of the design process and how to set a good pace for revisions and design reviews. The team learned the importance of designing parts for manufacture, meaning the rover components are easy and cheap to make and replace. Electrical systems integration and wire management were found to be very important considerations for the design process. The team also learned how to better manage manufacturing lead times for components and plan manufacturing times to avoid peak hours in on-campus machine labs. The team learned the importance of documenting design choices and any design changes for future review and full CAD model updates.
The 2020 Rover
Design work has begun for the 2020 rover. There will be some significant differences in this new design. Instead of a rocker-bogie suspension, the new rover will use a 3-bogie suspension system. This will keep the rover more stable, yet be less complex to design and manufacture. A smaller sheet metal chassis will be used to hold the rover’s components in a more compact arrangement that makes better use of mounting locations. The goal is to better incorporate the electronics and wiring of the rover, which will allow for more secure connections and a cleaner look. A similar robotic arm system will be employed on the front of this new rover.
The team will apply the lessons learned on the previous rovers to streamline the design and manufacturing process. The majority of design work will occur over the summer of 2019, with final revisions and design reviews occurring in August and September. The design will be simpler to manufacture and easier to perform maintenance on. Manufacturing and assembly should be completed much earlier than it was for the current rover, allowing for more testing and training time. The Mechanical Team looks forward to a successful year of engineering!
MAVRIC’s Mechanical Team had the following objectives for Spring 2019:
- Work with the Science Team to ensure the soil science system is mechanically sound, robust, and ready in time for the URC competition. (Complete for Checkpoint 1)
- Improve the robotic arm by modifying the shoulder and end effector. (Complete for Checkpoint 2)
- Add feedback systems to each joint of the robotic arm to allow for precision control. (Complete for Checkpoint 2)
- Test the robotic arm’s weight lifting capacity and ability to complete fine manipulation tasks. (Complete for Checkpoint 2)
- Improve the suspension system by reducing its weight and improving its reliability. (Complete for Checkpoint 3)
- Design and manufacture camera and sensor mounts as requested by the Systems Team. (Complete for Checkpoint 3)
- Ensure the total mass of the rover is under 50 kilograms and enact a weight reduction plan as necessary. (Complete for Checkpoint 3)
- Work with all the other teams to complete tests of the rover under mock competition conditions. (Dropped for Checkpoint 3)
- Completed robotic arm with feedback, capable of lifting five kilograms and manipulating objects. (Delivered for Checkpoint 2)
- Upgraded suspension system that is lighter and more reliable. (Delivered for Checkpoint 3)
- Competition-ready rover. (Delivered for Checkpoint 3)