Ball Shooter Arm

Note that if you press and hold the touch sensor down, the ball shooter will keep firing over and over like a machine gun in "automatic" mode.  This is because a Wait for Sensor block will complete immediately if the sensor test is already true.

Ball Shooter Arm

Bumped means "pressed and then released", but more specifically, a button is Bumped if it has been pressed and released since the last time you asked whether or not it was bumped.  The touch sensor maintains an internal press count, which is tested and then zeroed whenever you test for Bumped.

An advantage of testing Bumped instead of Pressed is that the button does not need to be pressed right at the time of the test, it only needs to have been pressed and released at some time before the test.  This is handy if the touch sensor test is inside of a loop which contains other lengthy operations, such as waiting for motors to complete.

The Bumped behavior in this program means that if you press and release the button quickly twice in a row, the shooter will fire two balls, because although the second "bump" (press and release) probably occurred during the motor rotation, the bump is remembered and thus Bumped will be true right away when tested the second time after the motor finishes.  However, if you are fast enough to press and release the button three times during the first loop iteration, only two balls will be fired.  If you understand why, then I think you finally understand how Bumped works!

Ball Shooter Arm

This behavior is done by using two separate Wait for Touch Sensor blocks, one that waits for Pressed, and one that waits for Released after the ball is fired.  Note that if you release the button during the firing of the ball, then Released will already be true when the second Wait for Touch Sensor block tests it, so it won't wait for anything and will continue right away.

Now try to predict what will happen before trying this:  What will happen if you press and release the button quickly twice in a row?

Ball Shooter Arm

By inserting temporary Wait for Touch Sensor Bumped blocks into a program, you can make the robot step through the program one step (or one section) at a time and wait for you to bump (press and release) the touch sensor button before going on to the next step.  This can make it easier to determine which part of the program has the problem.

The F5-PathBug program is supposed to make Multi-Bot drive in an "N"-shaped path.  However, it has a simple bug in it, so the resulting path will not be shaped like an "N".  The F6-PathDebug program is a modified version of the program that inserts a Wait for Touch Sensor Bumped between each block.  By holding the wired touch sensor remote in your hand (or just a single touch sensor on a wire) while the robot is running the program, can you step through the program and find where the problem is?  Try it now before reading on if you want to try to find the problem yourself.

Once you find the problem and understand how the debug stepping works, can you explain why it is important that the Wait for Touch Sensor blocks test for Bumped instead of Pressed?

The Bug:  In the configuration panel of the LeftPivotAngle My Block, the programmer accidentally typed the desired angle of 135 in the Power parameter instead of in the Angle parameter and left the Angle parameter zero.  This will cause this turn to have no effect.  Because the steps before and after the turn are both Move blocks going forward, it may make it appear that the problem is that the Move before the left turn goes for too long.  But in fact, there is an invisible turn of zero degrees in the middle of the movement.  By stepping through with the touch sensor, you can see that it is actually two separate Move actions but the step where the LeftPivotAngle does nothing.

1. Pivot turn left 
2. Go straight
3. Pivot turn right
4. Stop and shoot a ball

In-between each step of the sequence is a Wait for Touch Sensor Bumped, and the movement blocks use Unlimited for the Duration.  This will cause each movement to continue until the touch sensor is bumped.  So, by holding the wired touch sensor remote in your hand, you can control the driving with touch sensor 1 (touch sensor 2 is not used).

With this technique, you can only control the duration of the movements, but not the sequence.  This can make it tricky to drive, but give it a try.  Put a target on the floor and try to drive to it and shoot it.

Ball Shooter Arm

This form of remote control is usually more natural and easier to control (although after practicing the
F7-SeqControl1 program, you may need to spend some time to unlearn that method).  Give it a try and see if it is easier (or at least less nerve-wracking) to drive.

Ball Shooter Arm

A careful combination of testing for Pressed and Released is used for this, since neither Pressed by itself nor Bumped will work easily.

Because two sensors are being tested, Switches and Motor Unlimited blocks are used, so that the Loop keeps repeating fast enough (more than 100 times per second) to see changes in either sensor when they occur.

This kind of motor control results in the following actions:

• Press and hold the left button to turn left
• Press and hold the right button to turn right
• Press and hold both buttons to back up
• Release both buttons to go forward

Note that there are four different actions, corresponding to the four different states that the two buttons can be in.  A noteable problem with this control is that there is no way to stop.

With this method, different actions for the four different button states can be assigned however you want.  In this program, the actions assigned are:

• Press and hold the left button to turn left
• Press and hold the right button to turn right
• Press and hold both buttons to go forward
• Release both buttons to stop

Compared to the F10-Remote1 program, this approach adds a way to stop, but loses the ability to back up.

• Press and hold the left button to turn left
• Press and hold the right button to turn right
• Press/hold both buttons to shoot a ball
• Release both buttons to stop

So this program adds the ability to shoot, but can no longer go forward or backwards (only turn).  This would be OK to control a gun on a turret, but is not great for a driving robot.

Ball Shooter Arm

The F13-DriveShoot program shows a complex method to surpass the four-state limit of two touch sensors by using a Timer to distinguish the difference between a button being briefly pressed and released and the button being pushed and held down.  This allows different actions to be assigned to these two cases.  This same technique is often used by desktop computers to distinguish a mouse click, a drag, and a double-click, for example.

This program uses the two touch sensors to control the following actions:

• Press and hold the left button to turn left
• Press and hold the right button to turn right
• Press and hold both button to go forward
• Tap the left button to back up until the left button is tapped again
• Tap the right button to shoot one ball
• Release both buttons to stop

Note that there are four different actions, corresponding to the four different states that the two buttons can be in.  A problem with this control is that there is no way to stop.

Ball Shooter Arm

You can use this program to make a remote controlled golfing robot.  Start with the Golfing Arm straight down and place a ball somewhere on the carpet.  See if you can drive up to the ball and hit it in the direction you want.  Make a course and see how many shots it takes to get the ball into the hole or other target that you make.

Golfing Arm

Use Multi-Bot with Treads for best traction on carpet or uneven surfaces.  Wheels will also work on smooth floors.

Because two sensors are being tested, Switches are used, so that the Loop keeps repeating fast enough (more than 100 times per second) to see changes in either sensor when they occur.  The LeftPivotAngle and RightPivotAngle My Blocks are used to achieve strong pivot turns for turning on carpet (where turning with the Move block is not as good).

The F16-Bumper2 program also adds a single Sound block that will apply to both collision directions, and note that if added to F15-Bumper, the Sound block would need to be repeated twice.  Although F16-Bumper2 is more complex than F15-Bumper, as programs get more complex it often becomes more desirable to eliminate duplicated parts.

The robot will drive straight towards the wall until one side touches the wall, then it will pivot until the other side also touches, then it will back up when both sides are touching.

Compared to the "stalling" techniques for aligning with a wall that are shown in the Driving Straight - Advanced section (B7-SquareWall and B8-StallWall), using two touch sensors may be faster, less forceful, and better able to handle a variety of different angles.