finally we got to program the explorer robot and the box, and record some videos. As we do not have a rescue robot, we have done a test with a mBot operated with remote control and another with a simple program where it approaches the door, stops, and backs up.
We have been working a lot on the robot and it works well, but we had to calculate different distances and times to set the right outcome on the way back. We have also been working on the design of the box that the robot will leave the dangerous substance.
After have seen the second object with ultrasonic sensor, the robot makes a half turn and return back. When he detects the black mark with his line follower sensor he turns right to return to his starting point (the same with edge of the table).