University Rover Competition Manipulation Sub-team

The Competition

The rover was designed to complete the tasks laid out in the 2019 Mar’s Society University Rover Challenge (URC) competition rules.

  1. Science mission- The rover must conduct an in-situ analysis to determine the presence of life, either extinct or extant, at designated sights
  2. Extreme retrieval and delivery- The rover must pick up and deliver objects in the field while traversing a wide variety of terrain no further than 1 km.
  3. Equipment servicing- The rover must perform operations on an equipment system after traveling up to 0.25 km
  4. Autonomous traversal mission- The rover must autonomously traverse between markers across moderately difficult terrain up to a total distance of 2 km

Requirements developed according to the tasks of the competition and developments during the design process. The design of the arm was based on the following requirements.

Carrying Capacity and Reach

  1. The arm shall be able to lift up to 5 kg at a 1 ft extension from the front of the rover without loss of stability or structural failure.
  2. The arm shall able to lift objects with handle features up to 5 cm in diameter and up to 40 x 40 x 40 cm in total volume.
  3. The arm shall be able to reach 3.5 ft vertically from the ground at 2 ft from center of rotation of the rover arm base. The arm shall reach the ground when mounted to the rover.

Safety

The arm shall be equipped with a stop switch (separate from the rover stop switch) to stop all motion of the arm in case of loss of control

Dexterity

  1. The rover arm shall be able to use hand tools such as a screwdriver, press buttons, type on a keyboard, pull levers, operate joysticks, open drawers, and push away small objects.
  2. The rover arm shall be equipped with a fiber optic probe to analyze samples for life.

Other

  1. The arm and any attachments or tools carried by the arm shall weigh less than 10 kg. Any tools or attachments carried by the arm shall not leave the rover during missions.
  2. The arm shall fold into a stabilized position while the rover is in motion.
Rover arm grabbing handle on structure

System Design

The rover arm is the Gearwurx Arm 3.0. This arm was chosen for its ability to lift over a 5 kg payload and reach 3.5 feet which meets the requirements set by this team. The rover arm originally purchased from Gearwurx was kept intact and not equipped with any permanent attachments or adjustments. The rover arm has six degrees of freedom and is composed of three linear actuators, three servo motors, and casing made of aluminum and carbon fiber.

Schematic for system
Arm parts labeled

The rover arm is powered by 12 DC volts at 7.5 peak amperes. An emergency button interrupts power to the arm if necessary. A slider controller purchased from Gearwurx or a Logitech F310 controller are capable of controlling the arm. When the Logitech controller interfaces with the arm motors, software designed to mimic the Robotic Operating System (ROS) MoveIt package runs to control the position of the motors

Methods and Testing

Precision, Accuracy and Tools Test

  • Test - Opening/Closing latches, typing on keyboard, pushing buttons, fastening screws and moving joysticks. Created and used a 3D printed screwdriver
  • Result - Successfully grabs, presses, and turns with high precision. The 3D printed screwdriver works, but the point is not visible from the camera location.

Reach and Range Test

  • Test - Determine maximum reach and the range within which the arm can operate.
  • Result - Arm reaches 3.5 ft and operate at all locations of interest.

Torque and Stress Test

  • Test - Confirm arm is capable of lifting 5 kg and operate with no damage.
  • Result - Able to lift 5 kg with difficulty. Able to lift up to 10 kg with noticeable difficulty.

Size Capacity Test

  • Test - Verify the arm is capable of picking up an object with a handle diameter of 5 cm.
  • Result - Able to lift objects with diameter of 5 cm while hand is tilted upwards

Control Test

  • Test - Verify ability to control arm with slider block controller or video game controller
  • Result - Able to control with slider blocks. Easier to control with gaming controller.
Arm grabbing grocery sack • Robot arm purchased from Gearwurx holding 6 kg and a 5 cm diameter handle.
Gripper holding Styrophone object
Grabber extended
Velcro part holder

Attachments were added to help the arm fulfill the requirements, including:

  • 3D printed screwdriver.
  • Mount for the fiber optic probe
  • Rubber bands to improve grip
  • Mount for a camera

Conclusion

The manipulation team met all of the system requirements, including those related to lifting 5 kg, reaching 3.5 ft, grasping 5cm in diameter objects, and performing dexterous movements such as pulling levers, pressing buttons, opening drawers, and operating hand tools

In the next iteration of the rover, we would like to implement a slip-ring at the wrist of the end manipulator to allow for a continuous rotation servo. Continuous rotation at the wrist would significantly decrease the difficulty of operating a screwdriver. We would also like to see a method for improved visibility through the rover's cameras when using the custom-made screwdriver. Future software iterations would solve forward or inverse kinematics to more precisely control the end manipulator. For electronics, a future iteration would include a remotely controlled relay switch to stop power to the arm in case of an emergency, instead of the current wired version.

Cad complet arm and grabber
Grabber closed • Robotic claw purchased from Gearwurx with Arm 3.0

The rover’s manipulation capabilities meet the requirements set by the team. This will allow the rover to properly interact with the objects that it would encounter during the competition. The science needs of the team are also met for the competition. A fiber optic probe for spectroscopy mounts to the Gearwurx Arm 3.0 allowing for detection of life, either extinct or extant, during the competition.

Throughout the project, we learned how to optimize the design process to meet requirements and constraints. Creating a decision matrix to evaluate all of our options was a key lesson in choosing the Gearwurx Arm 3.0, which met all of our functional requirements and ultimately allowed us to build a functioning rover within the time constraint of the project.

As a sub-team we have learned to communicate as part of a larger organization, to coordinate and share responsibilities, and to schedule in advance for the unexpected problems that will come along. In the future, we want to see the rover compete at URC in Hanksville, Utah. This team is dedicated to passing down the lessons we have learned to new members, and future iterations of the ARES Rover.

Merrill Hall, Kyler Hendrickson, Kaden Ledbetter, Rachael Paskett, Nicholas Wallace

Thank you to Spencer Wendel and Blair Martin