University Rover Competition Power/Drive Sub-Team

The Competition

The rover was designed to best complete the tasks laid out in the 2019 URC competition rules

  1. Science mission- The rover is required to 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 is required to pick up and deliver objects in the field while traversing a wide variety of terrain no further than 1km
  3. Equipment servicing- The rover is required to perform operations on an equipment system after traveling up to 0.25 km.
  4. Autonomous traversal mission- The rover is required to autonomously traverse between markers across moderately difficult

The rover was designed based on the following requirements. The requirements were developed according to the tasks of the competition.

Rover on Mars

Suspension

  1. The rover will be able to travel over objects with a maximum height of 12 inches and a minimum width of 24 inches
  2. The rover shall continue to operate after vertical drops of 1 m.
  3. The rover must fit on a 1.2 m x 1.2 m platform.
  4. The rover will have a center of gravity less than 15 inches from the ground.

Motors

  1. . The rover shall have a torque of 80 oz-in per motor at speed of 120 rpm and a torque of 1400 oz-in per motor at speed of 40 rpm.

Provide power to the rover

  1. The rover’s power supply will be able to continuously supply power to all electronics for a minimum duration of 2 hours
  2. The Rover cannot have an isolated, air-breathing power system, nor can it accept ambient air for any reaction that produces power.
  3. All equipment shall not be damaged by a sudden shutoff of power

Other

  1. The rover shall weigh less than 33 kg in any configuration.
  2. Must be able to operation in light rain, dust, and temperatures up to 100 F

System Design

The structure of the rover uses a rocker-bogie concept that is similar to the wheel suspension system found on NASA rovers. To insure a strong suspension system a minimum safety factor of 2 was applied throughout. Using this safety factor, and Solidwork's topology tool, cutouts were applied to the frame giving the suspension system a unique look with the smallest weight.

The power system uses 4 lithium-polymer batteries that can sustain heavy driving for over 2 hours. The system has an emergency stop button and various fuses that will kill power to the electronics in case of fire, short circuits, or a runaway rover.

Cad Frame suspension

The motors were chosen to meet the speed criteria of 120 rpm on flat ground and 40 rpm on a 45° incline. The motors have a strength of 1983 oz-in and 584 rpms. A gearbox of ratio 10:1 is attached to the motors. Beach wheels were chosen because they perform best in the competition's rocky, sandy environment

Schematics of the power system

Methods and Testing

COG testing

  • Test- Placed on platform and tiled to different angles up to 45 deg
  • Result- Rover held on platform with no issues

Battery testing

  • Test- Operated the rover for 2 hours under normal circumstances
  • Result- Rover lasted 2 hours on only 2 batteries

Traversal Testing

  • Test- Marked distance of flat and inclined ground traversed
  • Result- Cleared distance at 146 and 159 rpm

Torque Testing

  • Test- Stall torque found using a dial torque wrench
  • Result- The toque was 14.1 N-m

Drop Testing

  • Test- Dropped a distance of 1 m
  • Result- The rover continued driving after the drop testing
Plasma cutter, cutting
Rover from top view with no arm

Prototype

  • Fabricated in the metal factory
  • Plasma cutter used to cut rocker bogey suspension
  • Body was bent and welded together
  • Custom parts created for mounting and wheels

Conclusion

The power/drive team was able to meet all of the requirements, including those related to 2 hour battery life, ability to climb over 12 inch objects on, RPM , torque, mass budget, stability on an incline, and impact from a 1 meter drop.

In the next iteration of the rover, we would like to see a gearbox with a higher gear ratio, positioned inside of the wheels, and a motor placed at a right angle to prevent becoming high centered. The rocker-bogie should be made taller to allow for easier pivoting. For the electrical system, the power draw of the components can be tested more thoroughly and parts can be exchanged accordingly.

The rover’s drive capability meets the requirements set by the team. This will allow the rover to properly handle the rough terrain of the competition. The power needs of the team are also met for a two-hour span. This will allow the rover’s cameras, processors, motors, laser, and arm full power and capability throughout each day of the competition.

Rover on the hill
cad view of rover with batteries and motors

Throughout the project, we learned how to optimize the mass of a design without losing structural integrity, how to design the electrical system of the rover, and how to find the correct motors and wheels for the drive. As a sub-team, we learned how to effectively communicate with the team as a whole and the importance of sharing responsibilities. We would like to see the next year's rover go on to the competition in Southern Utah and win. This sub-team can help facilitate other teams testing more over the next year as it will be primarily optimizing the rover instead of creating one.