MilliMobile is a first of its kind battery-free autonomous robot capable of operating on harvested solar and radio frequency power. The MilliMobile prototype has a 1 x1 cm chassis and weighs less than 1.1 g. It can carry payloads 3 times its own weight, and only experiences a 25% reduction in speed when carrying a 1 g payload.
MilliMobile is able to move across a variety of surfaces, including concrete and packed soil. Image credit: Mark Stone / University of Washington.
Small mobile robots carrying sensors could perform tasks like catching gas leaks or tracking warehouse inventory.
But moving robots demands a lot of energy, and batteries, the typical power source, limit lifetime and raise environmental concerns.
Researchers have explored various alternatives: affixing sensors to insects, keeping charging mats nearby, or powering the robots with lasers.
Each has drawbacks. Insects roam. Chargers limit range. Lasers can burn people’s eyes.
“We challenge the conventional assumption that motion and actuation are beyond the capabilities of battery-free devices and demonstrate completely untethered autonomous operation in realistic indoor and outdoor lighting as well as radio frequency delivery scenarios,” said University of Washington doctoral student Kyle Johnson and colleagues, who developed MilliMobile, a tiny, self-driving robot powered only by surrounding light or radio waves.
Equipped with a solar panel-like energy harvester and four wheels, their robot is about the size of a penny, weighs as much as a raisin and can move about the length of a bus (10 m, or 30 feet) in an hour even on a cloudy day.
MilliMobile can drive on surfaces such as concrete or packed soil and carry three times its own weight in equipment like a camera or sensors.
It uses a light sensor to move automatically toward light sources so it can run indefinitely on harvested power.
“We took inspiration from ‘intermittent computing,’ which breaks complex programs into small steps, so a device with very limited power can work incrementally, as energy is available,” Johnson said.
“With MilliMobile, we applied this concept to motion. We reduced the robot’s size and weight so it takes only a small amount of energy to move.”
“And, similar to an animal taking steps, our robot moves in discrete increments, using small pulses of energy to turn its wheels.”
The researchers tested MilliMobile both indoors and outdoors, in environments such as parks, an indoor hydroponic farm and an office.
Even in very low light situations — for instance, powered only by the lights under a kitchen counter — the robots are still able to inch along, though much slower.
Running continuously, even at that pace, opens new abilities for a swarm of robots deployed in areas where other sensors have trouble generating nuanced data.
These robots are also able to steer themselves, navigating with onboard sensors and tiny computing chips.
To demonstrate this, the team programmed the robots to use their onboard light sensors to move towards a light source.
“Internet of Things sensors are usually fixed in specific locations,” said University of Washington doctoral student Zachary Englhardt.
“Our work crosses domains to create robotic sensors that can sample data at multiple points throughout a space to create a more detailed view of its environment, whether that’s a smart farm where the robots are tracking humidity and soil moisture, or a factory where they’re seeking out electromagnetic noise to find equipment malfunctions.”
The scientists will present their work at the ACM MobiCom 2023 Conference in Madrid, Spain.
_____
Kyle Johnson et al. MilliMobile: An Autonomous Battery-free Wireless Microrobot. ACM MobiCom 23; doi: 10.1145/3570361.3613304
