Instruction Guide: EV3 - Hand Slapper Challenge


LEGO EV3 Robotics Kit – the brain, battery, touch sensor, and motors, are essential. Sensors are optional and may be included by some groups. Ultimately each group will build their own “slapper” so it will be up to them which pieces to use.

Internet access.

EV3 software on desktop/laptop - the whole point of this lesson (besides having fun slapping hands) is to teach some advanced programming concepts to students – therefore the iPad won’t cut it.



Build the hand slapper ahead of time following the pictures in the attached .pdf

Program and test the hand slapper using the attached programs.


Day 1


Show the students the hand slapper and have some of them come up to play with it. Ask them to point out what the slapper is doing differently at each level.

Return to level 1 and examine it in detail. Emphasize the use of the touch sensor to trigger the slap as well as the repetition of the action.

Share the program with them and explain it in detail. Depending on their prior knowledge this could either be review or new material.




Have the students build their own hand slapper using photo slide show.

Have them program the hand slapper to do the actions in level 1.

They can use this video to help them with their programming:


Day 2


After the students have built the hand slapper and programmed level 1 show them the remaining three programs and have them program each one. The teacher can decide if they want to cover each program in detail ahead of time or to allow the students to figure it out themselves as they write the programs. The videos show and explain each what each program does in detail.


Level 1 uses a loop and the touch sensor.

Level 2 uses a variable to slap faster each of five successive times.

Level 3 uses a random block to vary the time it takes to slap after pushing the touch sensor. A loud sound precedes the slap to add a little excitement to the program.

Level 4 uses two variables to make the slap faster each time and to lessen the distance the paddle raises each time so it is closer for the next lap.



Day 3 -5


After each group has shown you the four programs on their slapper (formative assessment) have them come up with their own idea for a program. Encourage them to use any of the new concepts they have learned while programming their slappers or any of the following concepts: a second sensor, a switch, multiple loops, variables, random, ranges, math blocks, compare blocks. 


Some examples my students have come up with:


  1. An annoying sound that runs on repeat. To turn it off you have to push a touch sensor, but when you approach the touch sensor, an ultrasonic sensor triggers the slapper. If you manage to turn off the sound using the touch sensor, a loop will turn it back on in a few seconds.
  2. When you push the touch sensor different sounds will occur randomly. Only one will precede a slap. See an example here.
  3. Your hand is placed on a platform where you have to depress a touch sensor. Two sounds can occur: a fake and a real one. The real one precedes a slap and you need to move your hand. But if the fake sound comes on and you move your hand (releasing the touch sensor) the game will end and you lose.
  4. Other students have used random blocks in different ways to vary the time a slap occurs after a given sound or to vary the speed. There are endless variations they can do.




Some students have a lot of difficulty with the higher levels of programming. It is up to each teacher to determine what is appropriate for their class.


Some students will come up with ideas that they don’t know how to program. This is a great opportunity for a teacher to sit down with students and figure it out together.