Today’s successful launch of the Mars 2020 mission not only marks the beginning of the latest efforts in humanity’s search for extraterrestrial life, but it also represents advances in robotics. The Perseverance Rover will use robot arms to collect and process soil samples. It and an aerial drone have pushed the technical specifications of precision motors, sensors, and other components.
Over the past three decades, maxon motor ag has provided more than 100 drives for robots sent to Mars. The Swiss company said its brushed and brushless DC motors are also used in demanding robotics applications in surgical equipment, humanoid robots, and industrial automation.
Perseverance requires precision for robotic sampling
The Mars 2020 mission includes the Perseverance Rover, the fifth robotic rover that the National Aeronautics and Space Administration (NASA) has sent to Mars. The nuclear battery-powered rover, which is about the size of a car, is designed to take multiple soil samples, seal them in containers, and deposit them on the surface of Mars so that a future mission can return them to Earth. The Mars 2020 mission plans to search for signs of previous life and gather data for potential human exploration of the planet.
NASA’s Jet Propulsion Laboratory (JPL) asked maxon to produce 10 drives for the rover. Several maxon motors will be used to handle the samples in an internal laboratory, called the Sample Caching Subsystem. For example, maxon DC motors are installed in the robotic arm, which will move the samples from station to station. Maxon motors will also be used for sealing and depositing the sample containers.
“The arm and end effectors have motors from us,” said Robin Phillips, head of the maxon SpaceLab, which has personnel in Switzerland and Germany. “That arm is absolutely critical to the success of this $2 billion mission.”
Editor’s note: For more of our conversation with maxon SpaceLab’s Robin Phillips, listen to the latest episode of The Robot Report Podcast.
As with previous Mars missions, these drives are based on standard products from maxon’s catalog, with modifications. For the first time, NASA is using maxon’s brushless DC motors, including nine EC 32 flats and one EC 20 flat in combination with a GP 22 UP planetary gearhead.
The modified EC 32 flat drive, nine of which are in the Perseverance Rover. Source: maxon
“When we first started developing maxon’s modern space motors about 10 years ago … we discovered that a lot of maxon’s medical applications, which had to be autoclavable or sterilizable, were a very good start for the space applications,” Phillips told The Robot Report.
Working closely with specialists at Pasadena, Calif.-based JPL, maxon engineers developed the drives over several years and tested engineering models thoroughly. “Then we built a qualification unit, where we formally track how we built it and everything that went into it,” said Phillips.
Space missions place the highest demands on drive systems. This includes vibrations during the Atlas V rocket launch, vacuum during the journey, impacts on landing, and the harsh conditions on the surface of Mars, where temperatures fluctuate between -125 and +20 degrees Celsius and dust can affect external components.
Improved controllers, materials, and shapes made it possible to use brushless motors, Phillips said. For example, nonreactive titanium proved useful for both space applications and medical implants, he said.
“Then, for your flight models, all you need to do is to is make sure you build exactly the same way as you built the qualification unit, which is easier to say than it is actually to do,” said Phillips.
Ingenuity to be controlled with maxon DC motors
Perseverance is expected to land on Mars on Feb. 18, 2021 — but the rover won’t be alone. A drone helicopter called Ingenuity will be attached to the underside of the rover. It weighs 1.8 kg (3.96 lb.), is solar-powered, and will perform several short flights, as well as take aerial images. The main goal of this experiment is to test the concept for future drones.
maxon has provided motors for the arm to deploy the drone, as well as six brushed DCX motors with a diameter of 10 mm (0.39 in.) controlling the tilt of the rotor blades and the direction of flight. The drives are very light, dynamic, and highly energy-efficient. These properties are crucial, because every gram counts on the Mars helicopter.
Flying on Mars is not easy, noted Phillips. The atmosphere is extremely thin, roughly comparable to the conditions on Earth at an altitude of 30 km (18.64 mi.). The drone helicopter has flown in a simulated test environment in the JPL laboratory. Whether it will lift off on Mars remains to be seen. First, other obstacles, such as the rocket launch, must be successful.
“Many of the people we were working with have spent years working on the rover itself, but everyone is fully aware that the helicopter, if it works properly, will completely dominate the headlines,” Phillips said. “You should view the helicopter as being the modern equivalent of the Sojourner rover — it’s just an engineering test. … That will enable future missions where you can be more ambitious and start attaching more science instruments [in addition to] a camera.”
“We hope that everything goes well and that we’ll soon see our drives in action on Mars,” said maxon CEO Eugen Elmiger. “We’re all keeping our fingers crossed.”
“We’ve learned a lot from this exciting project,” Phillips stated. “We now have very broad expertise in space applications and have established quality assurance processes that meet the expectations of the industry. Customers from other industries such as the medical sector, where requirements are often similar, can also benefit from this knowhow.”
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Why they decided to use brushless DC motors and not servo motors on the Perseverance rover?
Brushes in brushed DC motors wear out overtime but, brushless DC motors don’t have such problem and they are also slightly more efficient then brushed motors.