and Mail-Collecting Robot
Students project at the Institute of Robotics of the Swiss Federal Institute of Technology, Zurich, Switzerland
Students: Peter Luethi, Thomas Moser, Christoph Schaer, Gabriel Dondi, Michael Wuethrich
Assistants: Dr. S. Vestli, P. Buehler
Project duration: April 1999 - July 1999
During the summer semester 1999, I participated with our team
consisting of 3 electronic engineers and 2 mechanic engineers in
a robot contest at the Swiss Federal Institute of Technology,
called SmartROB Contest. The task was to collect (magnetic)
envelopes in a square area (7.9 x 7.9 meters) with some walls and
gates. The map of the labyrinth was already exactly given before
the day of the contest, only the positions of the letters were
In total 8 teams, one from the EPFL in Lausanne and 7 from the ETH Zurich participated in the contest.
After having collected the letters, the mail had to be placed autonomously in a specific box in a corner of the labyrinth. The overall time budget was 4 minutes for collecting letters and disposing them in the box.
The hardware consisted of a 300 MHz PowerPC CPU and a VME SmartCard Interface (switches, analog-to-digital converters, PWM engines, servos,...) built on a chassis. Our development software equipment was XOberon, a hard real-time operating system. That's where our team name 'Interclick' originated from: The XOberon development environment had a special mouse click feature using simultaneously two (or more?) mouse buttons, the so-called interclick. Well, I'm not really convinced about this feature...
With respect to our robot, we installed about 10 parallel software tasks, all managed by a real-time scheduler by specifying parameters such as period/priority, duration and/or deadline. The software was completely object-oriented Oberon (being also a strongly typed programming language), so it was quite confusing in the beginning. Some basic navigation and driving procedures were already available, but we had to adapt and modify them for our specific needs. So guess where we spent our weekends during that time, and at the end whole nights - assisted by dark coffee...
Here's our work place with Windows95 and XOberon. "Tonky", the
Orang-Utan mascot of team 'Interclick', kept an eye on us,
wondering why we were spending such efforts for just a
mail-collecting robot. On the shelf resides also the digital
storage oscilloscope (DSO) to tackle the issues in the dot-matrix
That's our robot with some large batteries inside. On the left
side resides the large cantilever arm incorporating an
electro-magnetic pick-up device and an inductive sensor at its
end. The cantilever arm is driven by a huge radio-control servo.
Not the best solution, but reliable enough for our purposes.
Behind the cantilever arm is the embedded PowerPC rack with the
dot-matrix LCD mounted on the top.
The pick-up of the letters, which had a magnetic metal plate inside, was realized through our very strong electro-magnet: It was so strong, that it was able to pick up twice two letters at the same time during the competition. The letters were located very close by each other. Our strategy in that case was to pick up only the first one. But, when anything must go right, it will - scarcely known as Murphy's second law ;-). Although this was never tested before, we were lucky enough by having exactly the right speed and timing, so that the cantilever arm was at an adequate position above the second letter to have sufficient electro-magnetic field force through the first letter to pick up the second one as well. You can't see the magnet, he's behind the inductive sensor for detecting the letters. Attached to the side of the aluminium cover is one of the infrared distance sensors.
Solving technical issues in limited time...
In front, our Matlab hacker Gabriel (map of waypoints and way simulation), behind the two XOberon hackers; with red T-Shirt Thomas, and finally me.
Our robot in action, already having collected some
Here you can see the two infrared distance sensors measuring the distance to the right wall. We applied plausibility checks for any delivered sensor data. If the deviation of the actual sensor distance compared to historic data was too large, the data was treated as invalid, for instance by traversing an edge.
If all data was valid, we took the arithmetic average of both sensor distances and calculated the distance of the center of the robot to the wall. This value was finally used for correcting the current position and updating the position of the robot's odometry.
To get rid of massive erroneous reflections picked up by the sensors, we used sand paper in front of the sensors to absorb and scatter all unwanted infrared light.
Note that everything can happen to data transmitted through
Check this possibility of errors always first, it can help you to save a lot of time...
During the contest, in the main hall of the Swiss Federal
Institute of Technology in Zurich, Switzerland.
The blue box in the top right square represents one of the boxes to dispose all mail at the end of run.
Again, at bottom right, there is one of the blue boxes, in
which the letters had to be discarded at the end of the run.
You can see our team watching our robot's contingency feature in action, after the robot encountered a 'spatial disorientation'.
The winning robot - great work, Pele!
They employed some very expensive laser distance sensors and a colour sensor resulting in the most expensive robot of the contest - worth around 20'000 SFr.!
We made 3rd place, not that good we expected, but there is to say, that each of the three top classified teams could have been the winner. From the technical perspective, all of them had solved the problems of picking up the letters and navigating through the labyrinth excellent. It was finally only a lucky question of selecting the right strategy against the opponent, so that the opposing robot was driving just behind the other robot getting only empty letter boxes...
Special thanks to:
|Our team: Thomas Moser, Christoph Schaer,
Michael Wuethrich, Gabriel Dondi and me.
Was great fun beside a lot of work. Thanks, guys!
|S. Vestli, R. Hueppi, Roberto, B. Peyer, P. Buehler and R. Siegwart for technical support and organization.|
|Baumer Electric, Frauenfeld, Switzerland for providing the inductive sensor.|
|Ray Weber for providing the pictures.|
And finally congratulations to Pele and his team for making first place!
Last updated: 2010/08/31