Project Meeting 9

Date: 10-06-2012
Duration of activity: 6 hours
Attendants: Jeppe

Goal

• Make the robots drive down again after they have climbed on top of each other.
• Modify the bottom stacking robot to be able to stop when the basket is reached.
• Make the robots complete the track.
• Film the robots to identify issues.

Plan

• Last time we meet, Stefan started implementing the procedure for the robots to climb down. This procedure will be completed and tested on the robots.
• A sensor for detecting the basket at the end of the track will have to be mounted. Two ideas are to be tested: A color at the end, or a push sensor that is pressed when the basket is reached.
• In order to make the robots complete the track, all that is missing is 1) to have the robots climb down, 2) start following the black line when all the robots are back down on the track. The robots should have a "climb each other" signal when the first robot reach the basket.

Results

In this section we will present the solution to the items presented in the Plan section above.

Climb Down Procedure

The climb down procedure runs in its own thread and is sleeping until it is ordered to start crawling down. The action of climbing down has been implemented by a tacho count on the wheels. After the wheels has turned x number of degrees, the robot backs a bit the right side. This is done in order for the robot to be located on the right hand side of the black line, since the robots will automatically seek to the left in order to find the black line.

Detecting The Basket

At first the idea was to put a color on the track near the baseket. Thus when the line follower saw a certain color, it would automatically stop. However it turned out that just mounting a push sensor was a much easier approach to implement.

The push sensor is mounted in front of the STACKING1 robot, which is the robot that will reach the basket first. Once the sensor is pushed, the robot will send a message to indicate that all the robots should stop their follow line program and enter the state: "climb on top of each other".

Refinement Climbing Part

In some cases the robots would make some sudle movements when climbing on top of an other robot.

There were two reasons for this: 1) The black line on top of the Stacking robots was a bit too short and the robot on top would get a bad reading once it's light sensor was out of the paper. 2) The line follower algorithm is build to be very sensitive to the black line, this would cause the robots to make very sudden movements if they saw some thing "black".

To solve the problem two things were implemented: 1) A "follow line carefully" mode has been added. This mode is used when the robots are climbing on top of each other. It is essentially made to avoid the robots from making any sudden movements like the ones they normally would make if they reach a sharp right turn (hitting the black line straight on). 2) the black line on top of the two stacking robots was extended just a few centimeters.

First Tryout

As mentioned in a previous blog entry, we are using a third NXT unit as a broadcaster. When all the robot are placed in their starting positions and calibrated, they will enter a "wait for broadcast controller to connect" mode. Thus we can start the whole show from the broadcast controller.

The first tryout of the whole track is shown in the video below:

As seen from the video we have a few issues that must be adressed:

• Adjust the backdown algorithm, such that the robots are sured to be on the right side of the black line.

•  Make the arm of the grabber lower under the bridge.  

•  Make the space between the robots a bit bigger when they are driving toward the basket.

Conclusion

Now the three robots can almost complete the track. We only need to adjust a few issues before we can have a perfect run. This will be done the next time we meet.