Project - Meeting 6

Date: 31-05-2012
Duration of activity: 5 hours
Group members participating: Jeppe, Thomas and Stefan.

Goal

• Complete building the track.
• Make a sketch of the sub tasks that the robots must solve.
• Start programming the robots
• Revise the project plan.

Plan

Thomas and Stefan will go to the Chomsky lab and look for materials to build the tower and the bridge for the track. We have changed the layout of the track slightly and will provide a new sketch of this.

Jeppe will stay behind and update some of the project meeting notes.

As for the programming part, we wil have to revisit how to make the NXT's communicate using Bluetooth. The first task is to make the robots stack on top of each other without using the "hardcoding" approach, but rather make the robots communicate with each other.
We also need to add some kind of sensor to properly detect when one robot is placed properly on top of the other.

Results

In this section we will present the solutions to the tasks specified in the Goal section.

The Track

The tower and the bridge will be combined in one piece. The bowl will be the standard 9797 lego box.
The layout of the track now looks as follows:

The combined bridge and tower is depicted below:

The idea is to have the object of interest placed on the board on top. Then after fetching it, the robots must all go under the bridge.

Adjusting The Robots

Stefan mounted some touch sensors on the stacking robots. The ides is to have the stacking robots send a feedback signal to the robot currently climbing on top of it that is is now properly placed on the top and thus should stop.

Programming The Robots

Thomas started programming the Bluetooth communication software. To start with we just want the robots to send and receive some numbers. Thomas got the idea to get a fourth NXT to use for Bluetooth communication with the other NXT devices, since we had some problems getting the computer communicate directly with them.
As for the programming part we need to specify which commands a robot should be able to send to another robot. In order to get an overview of this, we decided to make a sketch of all the steps of the track to be completed.

Sketch of Subtasks To Complete

Below is an overview of all the subtasks that are to be handled.

From this overview, we derived the basic commands to be:

• Stop, send by the lower robot to the robot on top of it, to indicate that the top robot must stop moving forward.
• Move down, send by the lower robot to the robot on top of it, when the lower robot is at a position where the top robot can safely crawl down.
• Grabbing complete, send by the grabbing robot to the middle robot below, when the grabbing robot has obtained the object on top of the tower. Makes the middle robot start moving down from the bottom robot.

This yelds the following commands:

• STOP_STACKING, tells the Stacking robot to stop moving when it climbs on top of the other stacking robot.
• STOP_GRABBER, tells the Grabbing robot to stop moving when it climbs on top of the stacking robot.
• MOVE_DOWN_STACKING, tells the middle robot to climb down from the bottom robot. 
• MOVE_DOWN_GRABBER, tells the Grabber robot to start moving down when the middle robot is back down.

Revised project plan

Date	Task
31-05	Get materials for the bridge and tower cut off in the correct proportions. Sketch a overview of the sub tasks to be completed. Start programming the bluetooth communication for the robots. Buy black tape on the way home.
04-06	Mounting black line on track. Make the robots stack on top of each other using Bluetooth and a feedback sensor. Start making all the robots follow the black line on the track to the basket. The track should now be complete.
07-06	Today we want to be able to see the following thins work: Make them climb down from the stack. Make the grabbing robot drive off the two stacking robots below and grab the object on top of the tower. Make all the robots follow the black line on the track to the basket. Make all the robots climb each other again and make the grabber robot drop the ball in the basket. All this should happen using feedback sensors and bluetooth.
11-06	Putting together all the subtasks of lastweek and make the three robots complete the whole track. Getting ready for the presentation on the 14th.
13-06	Testing that everything works for the presentation.
14-06	Presentation of project at 09.00

Follow Black Line Strategy

We had a discussion on how the black line should be like in order for the robots to follow it with out the robots ending up in a non-aligned position when they are supposed to climb on top of each other.
That is, how do we make sure that the robots are completely aligned when they are to start climbing on top of each other. We will work with this next time we meet.

Conclusion

We now have a track that is more or less complete. We got the basic bluetooth code working and from the sketch of sub tasks, we got a outline of the challenges related to the programming.
Finally we also discussed how the robots will navigate on the black line and how to make sure that they are aligned for crawling on top of each other after following the black line.