#Robotics Line Rescue Completing the rescue


David Meego - Click for blog homepageThe previous article in this series covered how to find the victim in the rescue zone for the Robocup Junior Australia Line Rescue challenge:

This article covers the steps needed to complete the rescue depending on the division you are competing in; Primary, Secondary or Open.

The sections below explain what is needed for the different types of rescue with suggestions on how they can be implemented. They assume that your robot has already entered the rescue zone and located the victim and moved up to the victim as covered in the previous article.

Completing Primary Rescue

To complete the primary rescue, the robot needs to push the victim out of the rescue area (chemical spill zone). There are two common approaches:

  1. Knowing the size of the rescue zone and the fact the robot started in the middle and moved a known distance to locate the victim. It can now move the remaining distance and push the victim out of the green area. Make sure the distance is enough to push the victim out on a corner, but not too far that the robot could fall off the rescue zone tile on the nearest edge. The formula is: Distance Remaining = Distance from Centre to Edge – Distance already moved to victim.
  2. If the robot has is designed with the ultrasonic at the front and has its colour sensors right at the front of the robot. It would be safe to push the victim forward until the sensors see the change from green to white. You would want to reset the motor counter used for the ultrasonic scan, so you can track the distance moved forward so you can go backwards the same distance.

After pushing the victim out, your robot can reverse the “push” distance and also the “locate” distance to return to the centre of the rescue zone. Points are awarded for rescuing the victim.

Finally, look at the Exiting the Spill Zone section below.

Completing Secondary Rescue

To complete the secondary rescue, the robot needs to grab the robot with some sort of claw mechanism and show it has control of the victim (ie. robot and victim move as one, however, the robot does not need to lift or carry the victim). Points are awarded for controlling the victim.

It must then take the victim out of the rescue area (chemical spill zone). There are the same two common approaches:

  1. Knowing the size of the rescue zone and the fact the robot started in the middle and moved a known distance to locate the victim. It can now move the remaining distance and push the victim out of the green area. Make sure the distance is enough to push the victim out on a corner, but not too far that the robot could fall off the rescue zone tile on the nearest edge. The formula is: Distance Remaining = Distance from Centre to Edge – Distance already moved to victim.
  2. If the robot has is designed with the ultrasonic at the front and has its colour sensors right at the front of the robot. It would be safe to push the victim forward until the sensors see the change from green to white. You would want to reset the motor counter used for the ultrasonic scan, so you can track the distance moved forward so you can go backwards the same distance.

After taking the victim out and releasing the claw mechanism, your robot can reverse the “rescue” distance and also the “locate” distance to return to the centre of the rescue zone. Points are awarded for rescuing the victim, only after the victim has been controlled.

Finally, look at the Exiting the Spill Zone section below.

Completing Open Rescue

To complete the open rescue, the robot needs to use a claw mechanism to pick up the victim and return to the centre of the rescue zone. Then it can scan for the raised platform (orange block) and move forward to the block and place the victim on the block. It can use the same method as discussed in the previous article to scan for and locate the platform.

After placing the victim on the platform and releasing the claw mechanism, your robot can reverse the “platform” distance and also the “locate” distance to return to the centre of the rescue zone. Points are awarded for rescuing the victim, only after the victim has been controlled.

Note that for open rescue, there might be additional empty victim cans and it is recommended to scan again for these additional cans. You can identify an empty victim can as it will be matt black rather than shiny silver. Some robots just rescue all victim cans whether or not they are black or silver and some robots have an extra colour sensor to decide whether to rescue or not. There is no score awarded for rescuing a black can, but there is no penalty either. If your robot only rescues one can and you find an empty black can first, you will miss out on the points for rescuing a victim.

Once it is decided that there are no more victims, the rescue is completed.

Finally, look at the Exiting the Spill Zone section below.

Exiting the Spill Zone

All three divisions offer extra points if your robot can exit the spill zone via the entrance (where the silver strip is) and start line following back down the course (as per 2019 rules).

Some suggestions to how this can be achieved are to use the rotation counter of the other motor (not the one being used in the previous article to find the object with the ultrasonic sensor) and reset it after you enter the rescue zone and have moved to the centre. Then if you always “unwind” your movements (move back the same number of degrees you move forward) you can rotate the robot back the same position and orientation as it started.

Then you can back out until the sensors see the silver strip. Then rotate around until the outside sensor sees the line, then return to your line following code to exit the spill and get the additional points.

Notes:

  • You can also use a gyroscope sensor instead of the motor rotations to ensure which way the robot is pointing and so make the exit more accurate.
  • I have seen robots go to the edge and follow the edge of the green/white boundary until they find silver. This works, but can be risky if the rescue zone is elevated as the robot can fall off.

More Information

For more information on robotics and the EV3 Basic extensions to Microsoft Small Basic, check out the following links:

Hope you find this information useful.

David

This article was originally posted on http://www.winthropdc.com/blog.

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