Project - Meeting 8

Date: 07-06-2012
Duration of activity: 6 hours
Attendants: Jeppe, Thomas & Stefan

Goal:

• Make one robot climb and stopping when reaching the push sensors.
• Make three robots climb each other.

Plan:

• We will have to implement some software for detecting when a robot is on top of the other.
• Alter the robot design so the climbing becomes as easy as possible.

Results:

Software

For the stacking robots, we are using a behavior class, to make sure that only a single piece of our program is accessing the motors and sending messages to the network at a time.

Behavior.java

To this end we have copied the behavior class from lab-session 7.  A CommunicationController object has then been added to this class and a method for sending messages assuming the particular class is not suppressed, has also been added.

   //Access to communication

    public void sendMessage(Message msg){

                             if(!isSuppressed()) comcon.sendMessage(msg);

    }

To test our behavior class to see if the communication works as intended, we have implemented a stacking and a pushsensor class. The pushsensor class is uploaded to the bottom robot, and what it does is wait for the touch sensors mounted on top to be pressed. When this happens, a stop-signal (Message.STOP_STACKING) is sent to the network.

PushSensor.java

The stacking class makes the middle robot drive forward. When it receives a signal to stop, it sends a stop command to its motors. This way, when the middle-robot is on top of the bottom-car it will press down the sensors, which in turn will make it stop driving forward. Both of these classes extend our behavior class, and all access to the motors and sending of signals goes through the behavior class.
StackingMain.java

Robot design:

We have three robots: GRABBER, STACK2 and STACK1
The Grabber robot climbs on top of Stack2, which in turn climbs on top of Stack1.


As the push sensors where placed at the very rear end of the STACK1 robot the climbing robot continued driving a bit too far and almost went over the top. Therefore we decided to place some levers that are connected to the push buttons, as shown below:

To make the ramp easier to climb we have also added rails of each side of the robot like the following:

After these alterations it was quite easy for the robot to climb the other as the video below shows:

Alignment Issue

The alignment of the robots when climbing on top of each other is essential. If the two robots are not correctly aligned, the robot climbing on top might risk driving off the bottom robot. The rails would not be useful here, since they would actually prevent a robot from climbing up if the lower robot was out of alignment. Thus we decided to get rid of the rails again.

To meet the challenge we decided to mount a black line on top of the Stacking robot.

With this solution all the alignment between the two robots can be reduced to just follow the black line.

The follow line algorithm has been extended to have the following methods:

void calibrate();
void startFollowLine();
void stopFollowLine();

The complete algorithm can be found here GFollowLine.java and here FollowLine.java.

It runs in its own thread. When a stop command is send, the stopFollowLine() method is invoked.

This makes the main control algorithm pretty simple, since the only two main actions are startFollowLine and stopFollowLine which are controlled by the incoming messages.

We added a three ready signals for the three robots to send out when they are connected to the main controller and ready. None of the robots should start before the others have send out their ready signal.

The result of the line follow controlled by Bluetooth communication is show below in the videos.

The Grabber robot climbing the Stacking2 robot.

The Stacking2 robot climbing the Stacking1 robot.

The Grabber climbing the Stacking2 robot, the Stacking2 robot climbing the Stacking1 robot.

Conclusion

We came up with a fine solution for the alignment problem of the robots. We saw the robots climb each other for the first time and it works. The line follow algorithm was changed to have a "start follow line" mode and a "stop follow line" mode. The communication between the robots seems to be working very good, when the lower robot is to send a message to the upper robot. As is seen from the last video where all the robots climb each other, we need to adjust the push sensors on the stacking robots since it is clear that the Grabber robot is driving a bit too far and almost drives off the stacking robot.

References

[1], PID Control, Chapter 5, pp. 179-190 of Fred G. Martin, Robotic Explorations: A Hands-on Introduction to Engineering, Prentice Hall, 2001.