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UPDATED: Bionic kangaroo hops into view at Hannover Fair

25 March, 2014

The latest creature to join Festo’s mechatronic menagerie is a hopping kangaroo that will make its public debut at the Hannover Fair in April. The company has a tradition of unveiling a new mechatronic version of a living animal at the exhibition every year and the BionicKangaroo is the latest in a long line that has included swimming penguins, flying gulls and floating jellyfish.

The 7kg kangaroo is about 1m tall and can jump to a height of 40cm and over distances of up to 80cm.

The BionicKangaroo can be controlled by gestures using an armband (supplied by Thalmic Labs) that detects the operator’s muscle movements. A position sensor in the armband also records their arm movements and this information is sent via Bluetooth to the kangaroo’s control system.

A team from Festo’s Bionic Learning Network spent almost two years trying to emulate the jumping behaviour of a kangaroo and learning from it. “With the BionicKangaroo, we have precisely reproduced the most characteristic features of natural kangaroos ­– recuperating and storing energy, and then releasing it once more in the next bound,” explains Dr-Ing Heinrich Frontzek, Festo’s head of corporate communication and future concepts.

To ensure that the mechatronic creature remains stable when jumping and landing, Festo has combined pneumatic and electric drive technologies in a highly dynamic system with precision controls and a condition monitoring system.

Like the real animal, the BionicKangaroo can recover and store energy and use it for the next jump. Festo developed two alternative forms of on-board energy storage: a small compressor; and a high-pressure storage device. Either can be used to supply the compressed air needed for jumping, which is dosed out precisely by two Festo MHE2 solenoid valves. Rechargeable lithium polymer batteries store the electrical energy needed to power the valves and the electric drives, as well as a Festo CECC control system.

When the kangaroo is standing still, it touches the floor with both feet and its tail, to give it a stable three-point contact. Its tail also provides balance when jumping with a servomotor controlling its angle of attack.

The tail compensates for the movement of the legs, which have to be brought forward for landing. The legs are also controlled by two servomotors, which sit between the hip and thigh and can be moved forward and backwards.

Each leg is actuated using a lightweight Festo DSNUP 20 pneumatic cylinder. The knee and ankle joint are connected via a “positive kinematic” device, resulting in an interlinked sequence of movements.

The role of the natural Achilles tendon is mimicked by an elastic spring element made of rubber. It is fastened at the back of the foot and parallel to the pneumatic cylinder on the knee joint. This artificial tendon cushions the jump, absorbing the kinetic energy, and releasing it for the next jump.

Festo's BionicKangaroo uses a combination of pneumatic and electric drives, and clever controls

The control system processes values from multiple sensors to ensure stability when the kangaroo is jumping and landing. The values are fed into complex control algorithms, and used to trigger the cylinders and motors at the appropriate times.

A kinematic system made of laser-sintered parts reinforced with carbon, keeps the kangaroo’s weight down to 7kg.

Before its first jump, the elastic tendon is pretensioned pneumatically. The BionicKangaroo then shifts its centre of gravity forwards and starts to tilt. When a preset angle and angular velocity are reached, the pneumatic cylinders are activated, the energy from the tendon is released, and the kangaroo takes off.

To jump as far as possible, the kangaroo pulls its legs forward during the flight phase. This creates torque at the hip and this is compensated for by a movement of the tail. The top of the body stays almost horizontal.

When the kangaroo lands, the tendon is tensioned again, converting the kinetic energy of the previous jump to potential energy which can be used for the next jump. The landing phase is critical for recovering the energy and is responsible for the kangaroo’s efficient jumping behaviour. During this phase, the tail moves towards the ground and thus back to its starting position.

If the kangaroo continues to jump, the stored energy is used for the next jump. The potential energy from the elastic tendon is used again at this point. The valves switch at the right moment and the next jump begins. In this way, the kangaroo can make several consecutive jumps.

For the BionicKangaroo to stop, it must absorb as much energy as possible. The pneumatic actuators are switched accordingly, and the tendon is actively tensioned again.

Festo says that the artificial kangaroo demonstrates how pneumatic and electric drive technologies can be combined in a highly dynamic system. The kangaroo achieves its high jumping ability with the aid of powerful, dynamic pneumatic actuators. These devices are relatively light and pliable, which means they also act as shock absorbers when landing. For functions where the highest positioning accuracy is needed – for example, to control the tail and hip – three Harmonic Drive electric servomotors are used.

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