Zebro robots are ready to 'swarm'


The Zebro project of the TU Delft Robotics Institute recently achieved an important milestone regarding the introduction of modular design. Now, the six-legged robots can be produced as a series. The next step is the development of swarm behavior.

Article from Mechatronica & Machinebouw #8, December 2017

The tables in the robotics lab on the 19th floor of the TUD Faculty of Electrical Engineering, Mathematics and Computer Science are covered with semi-assembled robots, circuit boards and other parts. A group of students is working frantically under the supervision of their inspirator Chris Verhoeven on the assembly of a dozen of Zebro robots. These robots need to be working when they are presented at the Dutch Design Week, which starts the following day, in Eindhoven. Thanks to the new modular design, assembly is largely standardized. However, each Zebro still consists of about 200 parts that need to be connected in the correct manner. Only two robots have been finished.

The Zebro is a very compact robot. Thanks to the six rotating legs, it can move across rough terrain without getting stuck. All Zebro robots are fitted with proximity sensors. The sensor is mounted on top of the robot, shaped like a head that can move back and forth with two eyes. The sensor provides the Zebro with information concerning the vicinity of objects. In addition, the robots will soon be equipped with a localization sensor which the Zebro can use to determine its position in reference to its brothers and sisters. This is essential information for the robot which has been designed to function as part of a group.

Big bang

Edwin Hakkennes, electronics architect at technology integrator Technolution in Gouda, supports the team as technical expert and project manager. He elaborates: ‘By itself, a Zebro is not particularly useful. This changes when it is part of a swarm of Zebro robots. Such a swarm can be used during rescue missions after an earthquake or collapse. The robots search the debris and when one of them finds the victim, for example by using an audio sensor, this is shared with the other Zebro robots. A number of the Zebro robots will now activate their lights, so the rescue workers can follow the trail of lights to locate the victium. Hence the friendly appearance of these Zebro robots: people must not be startled upon seeing them."
The Zebro team is not lacking ambition. There are even substantial plans to send Zebro robots to the moon. Space researchers would like to measure the radio emission from the big bang. This is virtually impossible on earth. The interesting information is in the 100 MHz band, but this is being dampened by the atmosphere. What remains of the emission is being crowded by radio stations. Reception is much better on the back of the moon, so that is where the robot manufacturers of Delft want to send their swarm of Zebro robots. They will be equipped with antennas in order to receive radio signals. After arriving on the moon, the robots will walk to the correct location, whereupon the swarm will spread out to cover a large surface area. The result is a large radio telescope due to the fact that the Zebro robots work together during the reception of signals. The measured data will be transferred to a satellite orbiting the moon or to a transmitter that is located at the edge of the front and back of the moon. From there, the information will be sent to Earth.


Birds and fish

Before Zebro robots will behave like a swarm, a lot work needs to be done. There are various ways of creating swarm-like behavior. The use of artificial intelligence (AI) is one of the topics of this field of expertise that is getting a lot of interest. With machine learning it is possible to provide the robots with the required intelligence. This, however, is not the preferred method of the researchers at the Delft Robotics Institute. AI requires a long training period of neural software and this is very demanding on the central processor and batteries of the robot.

Swarm-like behavior can often be created quite effectively with a compact set of simple instructions. For example: in order to make a swarm of robots move into a certain direction without colliding, you only require three instructions: 1) move into the same direction as your neighbors, 2) stay close to your neighbors and 3) prevent collisions with your neighbors. These instruction are directly derived from nature. They form the basis of the complex and sometimes impressive maneuvers of swarms of birds or a school of fish.

Although the instructions are simple and compact, the implementation is not. A robot that is part of a swarm needs to monitor multiple neighbors and make decisions all the time. What is the collective direction when all neighbors are moving in a different direction? When is a neighbor too far away? When is it too close and when does it need to adjust in order to avoid a collision? What does the Zebro do when the desired direction is blocked?

Technolution has been involved in the Zebro project for quite some time now. The collaboration with the Robotics Institute is a valuable one for both parties. Hakkennes: ‘We have a lot of experience in developing electronics. We offer substantial and practical support to the team. For us, this environment is ideal to obtain new ideas and knowledge. It is very inspiring to work with these young talents on the development of usable swarm algorithms.’

Sheep vortex

The power of a swarm is especially evident in the behavior of ants. When an ant finds a dead lizard, it will try to drag it back to the nest. A hopeless undertaking for one single ant. But it never stops trying. Other ants will pass and do the same. They do not notice each other, but they all try to move the lizard. After a period of time, there are enough ants to get the lizard moving and drag the price to the nest. This type of self-organization is the result of one simple impulse of the individual ants: 'food must be taken to the nest'. The swarm makes sure the job gets done, even if some ants are pulling into the wrong direction or get tired.

Simple instructions can also backfire. A startled sheep will automatically run to follow other sheep. There are various clips on the Internet of sheep getting startled by a car and proceed to run after each other circling the car. This type of 'sheep vortex' is actually caused by a swarm algorithm ('follow other sheep') that locks up.

Coming up with the right swarming instructions and predicting and preventing undesirable swarm behavior requires a lot of thinking. Now that serial production of the Zebro robots is possible, the development and implementation of swarm behavior will be the next big challenge for the Zebro team to tackle. Eventually the swarm of Zebro robots will have to execute tasks autonomously. The first steps have been taken. One of the robotics students recently graduated on a swarm simulation which demonstrated the feasibility of a Zebro swarm. Shortly after, a different student graduated on the development of a communication and localization sensor for Zebro robots. Robots can use this to determine their position, speed and communicate their direction of movement to each other. Hakkennes: ‘Soon we will equip ten Zebro robots with such a sensor and program the swarm instructions. That will be the first swarm of Zebro robots.’

Special thanks to the students of the Zebro team, Ir.Dr. Chris Verhoeven of the Electronics Research Laboratory from the TU Delft and Dr.Ir. Edwin Hakkennes, architect for Technolution BV in Gouda.
Anton Hoexum is a corporate writer for Technolution.



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