The Modular Robotic Vehicle, or MRV, was developed at NASA’s Johnson Space Center in order to advance technologies that have applications for future vehicles both in space and on Earth. With seating for two people, MRV is a fully electric vehicle well-suited for busy urban environments.
One of NASA’s key purposes for the project was to have access to a technology development platform. “This work allowed us to develop some technologies we felt were needed for our future rovers,” said Justin Ridley, Johnson Space Flight Center. “These include redundant by-wire systems, liquid cooling, motor technology, advanced vehicle control algorithms. We were able to learn a lot about these and other technologies by building this vehicle.”
Just as NASA helped pioneer fly-by-wire technology in aircraft in the 1970s, MRV is an attempt to bring that technology to the ground in modern automobiles. With no mechanical linkages to the propulsion, steering, or brake actuators, the driver of an MRV relies completely on control inputs being converted to electrical signals and then transmitted by wires to the vehicle’s motors. A turn of the steering wheel, for instance, is recorded by sensors and sent to computers at the rear of the vehicle. These computers interpret that signal and instruct motors at one or all four of the wheels to move at the appropriate rate, causing the vehicle to turn as commanded. Due to a force feedback system in the steering wheel, the driver feels the same resistance and sensations as a typical automobile.
Not having a mechanical linkage between the driver and the steering wheel introduces new risks not seen on conventional automobiles. A failed computer, or cut wire, could cause a loss of steering and the driver to lose control. Because of this, a fully redundant, fail-operational architecture was developed for the MRV. Should the steer-ing motor fail, the computer system responds immediately by sending signals to a second, redundant motor. Should that computer fail, a second computer is ready to take over vehicle control. This redundancy is paramount to safe operations of a by-wire system.
MRV’s redundant drive-by-wire architecture allows for advanced safety and dynamic control schemes. These can be implemented with a driver operating either within the vehicle or by remote interface. In the future this system can be expanded to allow for autonomous driving
MRV is driven by four independent wheel modules called e-corners. Each e-corner consists of a redundant steering actuator, a passive trailing arm suspension, an in-wheel pro-pulsion motor, and a motor-driven friction braking system.
Each e-corner can be controlled independently and rotated ±180 degrees about its axis. This allows for a suite of driving modes allowing MRV to maneuver unlike any traditional vehicle on the road. In addition to conventional front two wheel steering, the back wheels can also articulate allowing for turning radiuses as tight as zero. The driving mode can be switched so that all four wheels point and move in the same direction achieving an omni-directional, crab-like motion. This makes a maneuver such as parallel parking as easy as driving next to an available spot, stopping, and then operating sideways to slip directly in between two cars.
“This two-seater vehicle was designed to meet the growing challenges and demands of urban transportation,” said Mason Markee, also with Johnson. “The MRV would be ideal for daily transportation in an urban environment with a designed top speed of 70 km/hr and range of 100 km of city driving on a single charge of the battery. The size and maneuverability of MRV gives it an advantage in navigating and parking in tight quarters.”
The driver controls MRV with a conventional looking steering wheel and accelerator/brake pedal assembly. Both of these interfaces were specially designed to mimic the feel of the mechanical/hydraulic systems that people are used to feeling when driving their own cars. Each device includes its own redundancy to protect for electrical failures within the systems. A multi-axis joystick is available to allow additional control in some of the more advanced drive modes. A configurable display allows for changing of drive modes and gives the user critical vehicle information and health and status indicators.
Each propulsion motor is located inside the wheel and capable of producing 190 ft-lbs of torque. An active thermal control loop maintains temperatures of these high powered motors. A separate thermal loop cools the avionics, includ-ing custom lithium-ion battery packs.
“While the vehicle as a whole is designed around oper-ating in an urban environment, the core technologies are advancements used in many of our robotic systems and rovers,” explained Mason. “Actuators, motor controllers, sensors, batteries, BMS, component cooling, sealing, and software are all examples of technologies that are being devel oped and tested in MRV that will be used in next generation rover systems.”
The technologies developed in MRV have direct appli-cation in future manned vehicles undertaking missions on the surface of Earth’s moon, on Mars, or even an asteroid. Additionally, MRV provides a platform to learn lessons that could drive the next generation of automobiles.
