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Unicycle-bot that can balance while not moving
TECHNOLOGY
Unicycle-robot that can balance while stationary AS ANY unicyclist knows, balancing on one wheel while staying in one spot is pretty tricky. But a robot that can do just that could be used to squeeze into tight spaces during search and rescue missions, or possibly even as a form of transport. Most wheeled robots have more than one wheel, but this means they need a chassis – something that gets in the way when trying to squeeze into gaps. Mono-wheeled robots would avoid this problem. But while the same gyroscopic effect that lets a spinning top balance as it spins also helps keep a moving wheel upright as it turns, once the wheel stops, balance and control become much harder. Previous efforts to create a mono-wheel that is stable when stationary, like the Gyrover, developed by Ben Brown at Carnegie Mellon University in Pittsburgh, Pennsylvania, have a second wheel that spins within the first to act as a gyroscope. But this uses a lot of energy.
So Patryk Cieslak, a PhD student at AGH University of Science and Technology in Cracow, Poland, and colleagues decided to take a different approach. Their robot is packaged within a single wheel: its motor, battery and controls remain stationary in the centre of the wheel while a rubber tyre
A mono-wheel’s balancing act A self-balancing robotic wheel can stabilise itself even when stationary Wheel movement
Balancing lever movement
LEVER
MOTOR
As the wheel starts to fall, sensors detect the movement and activate the lever, making it move in the opposite direction to correct the tilt
Hybrid cars are poised to give flywheels a spin THE next generation of hybrid cars could get a boost from an old technology – the humble flywheel. By replacing hefty batteries in hybrid electric vehicles with a lightweight flywheel that uses a novel form of magnetic gearing, a British engineering company claims that the same fuel-efficiency savings can be achieved at a much lower cost. The system, called Kinergy, is to be tested initially in airport buses, starting this week. It uses a carbonfibre flywheel spinning at up to 60,000 revolutions per minute to store energy recovered from the engine and braking, which it then delivers back when needed. Engineers 22 | NewScientist | 11 June 2011
rotates around the outside. To keep it upright, the team have placed a weighted lever that can tilt to either side within the body of the wheel (see diagram). If the wheel starts to fall to the right, for example, three sensors will detect the movement: an inclinometer to detect tilt, plus an accelerometer and a gyroscope to detect changes in direction. These then send a signal to a control circuit to move the lever to the left to provide counter-balance. By making
led by Andy Atkins of Ricardo, the Shoreham-on-Sea firm that developed the system, hope it will increase buses’ energy efficiency by 13 per cent in urban driving conditions. Storing vehicles’ energy in flywheels has been tried in trains and buses for decades, but the devices have typically proven too large and heavy to be practical. Ricardo’s design is just 23 centimetres in diameter and the wheel weighs only 4.5 kilograms, but can deliver 30 kilowatts of power to a vehicle’s transmission. Kinergy’s high speeds are possible because it spins in a vacuum – air resistance and heat would otherwise rip it apart. To transfer energy in and
out of an object spinning so fast in a vacuum-sealed chamber, the team had to devise a gearing system that makes no mechanical contact. The system achieves this through magnetic gearing, where an array of powerful permanent magnets is set into the flywheel’s shaft and another array of magnets mounted on an external shaft. In between, a ring of steel segments interferes with the
“The flywheel spins in a vacuum. If it didn’t, air resistance and heat would rip it apart” magnetic fields in such a way that as one shaft turns, it causes the other to spin at a different rate. With a gearing ratio of 10 to 1, the speed of rotation becomes manageable for conventional transmissions, Atkins says.
constant adjustments, the lever keeps the wheel upright (Robotics and Autonomous Systems, DOI: 10.1016/j.robot.2011.05.002). “There are many potential uses for this kind of robot because of its thin body, simple construction, good mobility and traction, and the efficiency of using only one wheel,” says Cieslak. He says that the next step is to set the robot rolling, possibly using the lever to steer the robot as it moves, before equipping it with vision and extra sensors that will let it guide itself. Eventually the concept could be used for transportation. There are already mono-wheel motorcycles in which the rider sits inside a giant rotating wheel and steers by leaning, says Cieslak, but they can be hard to control. A scaled up version of the mono-wheeled robot could be safer, as it would actively balance itself. Using a lever to balance a wheel is a valid approach, says Brown. “It simplifies things in some ways. Of course it makes the control a lot more complicated.” The robot will be harder to steer the faster it goes, Brown adds, as the lever has to overcome an increased gyroscopic effect. Kurt Kleiner n
If the bus tests are successful, they could hasten the broader adoption of flywheels to help power hybrid cars. “This is going to be very attractive in mobile applications”, says Alan Ruddell of the Energy Research Unit at Rutherford Appleton Laboratory in Oxfordshire, UK. Ricardo won’t be alone. Volvo announced last week that it is developing flywheel hybrids. And Jaguar is looking at commercialising a system based on the Formula 1 kineticenergy recovery system being used by the Hope Polevision team in Le Mans, France, this month, developed by Flybrid, in Silverstone, UK. Flywheels are coming, says Flybrid founder John Hilton. “It will make hybrid technology at between a quarter and a third of the cost of electric,” which in turn will make for much more affordable hybrid cars, he says. Duncan Graham-Rowe n
Unicycle-robot that can balance while stationary AS ANY unicyclist knows, balancing on one wheel while staying in one spot is pretty tricky. But a robot that can do just that could be used to squeeze into tight spaces during search and rescue missions, or possibly even as a form of transport. Most wheeled robots have more than one wheel, but this means they need a chassis – something that gets in the way when trying to squeeze into gaps. Mono-wheeled robots would avoid this problem. But while the same gyroscopic effect that lets a spinning top balance as it spins also helps keep a moving wheel upright as it turns, once the wheel stops, balance and control become much harder. Previous efforts to create a mono-wheel that is stable when stationary, like the Gyrover, developed by Ben Brown at Carnegie Mellon University in Pittsburgh, Pennsylvania, have a second wheel that spins within the first to act as a gyroscope. But this uses a lot of energy.
So Patryk Cieslak, a PhD student at AGH University of Science and Technology in Cracow, Poland, and colleagues decided to take a different approach. Their robot is packaged within a single wheel: its motor, battery and controls remain stationary in the centre of the wheel while a rubber tyre
A mono-wheel’s balancing act A self-balancing robotic wheel can stabilise itself even when stationary Wheel movement
Balancing lever movement
LEVER
MOTOR
As the wheel starts to fall, sensors detect the movement and activate the lever, making it move in the opposite direction to correct the tilt
Hybrid cars are poised to give flywheels a spin THE next generation of hybrid cars could get a boost from an old technology – the humble flywheel. By replacing hefty batteries in hybrid electric vehicles with a lightweight flywheel that uses a novel form of magnetic gearing, a British engineering company claims that the same fuel-efficiency savings can be achieved at a much lower cost. The system, called Kinergy, is to be tested initially in airport buses, starting this week. It uses a carbonfibre flywheel spinning at up to 60,000 revolutions per minute to store energy recovered from the engine and braking, which it then delivers back when needed. Engineers 22 | NewScientist | 11 June 2011
rotates around the outside. To keep it upright, the team have placed a weighted lever that can tilt to either side within the body of the wheel (see diagram). If the wheel starts to fall to the right, for example, three sensors will detect the movement: an inclinometer to detect tilt, plus an accelerometer and a gyroscope to detect changes in direction. These then send a signal to a control circuit to move the lever to the left to provide counter-balance. By making
led by Andy Atkins of Ricardo, the Shoreham-on-Sea firm that developed the system, hope it will increase buses’ energy efficiency by 13 per cent in urban driving conditions. Storing vehicles’ energy in flywheels has been tried in trains and buses for decades, but the devices have typically proven too large and heavy to be practical. Ricardo’s design is just 23 centimetres in diameter and the wheel weighs only 4.5 kilograms, but can deliver 30 kilowatts of power to a vehicle’s transmission. Kinergy’s high speeds are possible because it spins in a vacuum – air resistance and heat would otherwise rip it apart. To transfer energy in and
out of an object spinning so fast in a vacuum-sealed chamber, the team had to devise a gearing system that makes no mechanical contact. The system achieves this through magnetic gearing, where an array of powerful permanent magnets is set into the flywheel’s shaft and another array of magnets mounted on an external shaft. In between, a ring of steel segments interferes with the
“The flywheel spins in a vacuum. If it didn’t, air resistance and heat would rip it apart” magnetic fields in such a way that as one shaft turns, it causes the other to spin at a different rate. With a gearing ratio of 10 to 1, the speed of rotation becomes manageable for conventional transmissions, Atkins says.
constant adjustments, the lever keeps the wheel upright (Robotics and Autonomous Systems, DOI: 10.1016/j.robot.2011.05.002). “There are many potential uses for this kind of robot because of its thin body, simple construction, good mobility and traction, and the efficiency of using only one wheel,” says Cieslak. He says that the next step is to set the robot rolling, possibly using the lever to steer the robot as it moves, before equipping it with vision and extra sensors that will let it guide itself. Eventually the concept could be used for transportation. There are already mono-wheel motorcycles in which the rider sits inside a giant rotating wheel and steers by leaning, says Cieslak, but they can be hard to control. A scaled up version of the mono-wheeled robot could be safer, as it would actively balance itself. Using a lever to balance a wheel is a valid approach, says Brown. “It simplifies things in some ways. Of course it makes the control a lot more complicated.” The robot will be harder to steer the faster it goes, Brown adds, as the lever has to overcome an increased gyroscopic effect. Kurt Kleiner n
If the bus tests are successful, they could hasten the broader adoption of flywheels to help power hybrid cars. “This is going to be very attractive in mobile applications”, says Alan Ruddell of the Energy Research Unit at Rutherford Appleton Laboratory in Oxfordshire, UK. Ricardo won’t be alone. Volvo announced last week that it is developing flywheel hybrids. And Jaguar is looking at commercialising a system based on the Formula 1 kineticenergy recovery system being used by the Hope Polevision team in Le Mans, France, this month, developed by Flybrid, in Silverstone, UK. Flywheels are coming, says Flybrid founder John Hilton. “It will make hybrid technology at between a quarter and a third of the cost of electric,” which in turn will make for much more affordable hybrid cars, he says. Duncan Graham-Rowe n