Gamepad Controlled Robot

Video games often use W, A, S and D to move: W forward, S back, A left and D right. In this project those keys drive a Mieo Pro rover, with your computer keyboard as the controller. Hold W and the rover drives straight. Hold W and A together and it sweeps round a curve to the left, the way a game character turns while running. Hold A on its own and it spins on the spot. Mixing two keys is what makes driving feel smooth.

• Checking two keys at once, one if block inside another
• Curving by running one wheel slower than the other
• Spinning by running the wheels in opposite directions
• Why the order of your checks decides which key wins

• Mieo board
• Two N20 motors and their wheels
• Battery
• 3D-printed mountings
• Screws and screwdriver
• Rover body and wheel parts, from the Mieo Pro kit
• A computer with Bluetooth
• The Robolab app (free)

1. Build the rover from your Mieo Pro kit, with both N20 motors, their wheels and the battery, as the Mieo Pro build guide shows.
2. Clear a driving area on the floor, away from stairs and table edges. A few cups make a good slalom course.
3. Switch the rover on and turn on Bluetooth on your computer.

1. Open Robolab, choose Mieo, click the connection button and pick your MIEO from the Bluetooth list. Set the switch at the top right to Arena.
2. Start with “when green flag clicked” and “show happy”, then add a “forever” loop with an “if … else” for “key w pressed?”.
3. Inside the W part, check the steering keys: “if key a pressed?” runs “run motor 1 20 % motor 2 70 %” for a left curve; otherwise “if key d pressed?” runs 70 and 20 for a right curve; otherwise 70 and 70 drives straight.
4. In the else part of the W check, add the other keys in turn: S runs both motors at -50 to reverse, A runs -50 and 50 to spin left, and D runs 50 and -50 to spin right.
5. The very last else part is “stop robot”, so the rover stops when you let go.
6. Click the green flag, click once on the stage, and drive.

Arena mode: the program runs on your computer and talks to MIEO live over USB or Bluetooth, so keep MIEO switched on and connected.

when green flag clicked
show [happy v]
forever
  if <key [w v] pressed?> then
    if <key [a v] pressed?> then
      run motor 1 (20) % motor 2 (70) %
    else
      if <key [d v] pressed?> then
        run motor 1 (70) % motor 2 (20) %
      else
        run motor 1 (70) % motor 2 (70) %
      end
    end
  else
    if <key [s v] pressed?> then
      run motor 1 (-50) % motor 2 (-50) %
    else
      if <key [a v] pressed?> then
        run motor 1 (-50) % motor 2 (50) %
      else
        if <key [d v] pressed?> then
          run motor 1 (50) % motor 2 (-50) %
        else
          stop robot
        end
      end
    end
  end
end

Click the green flag and the rover smiles. Hold W and it drives straight. Hold W with A and it curves smoothly to the left; W with D curves right. S reverses. A or D on its own spins it on the spot. Let go of every key and it stops straight away.

If it doesn't work

• Curves turn the wrong way? Motor 1 is the left wheel and motor 2 the right. The slower wheel is on the inside of the curve.
• The keys do nothing? Click once on the stage first, and check the keys are lower-case w, a, s and d in the menus.
• It spins when you want it to curve? The A and D checks for curving must be inside the W part, not after it.

1. Easy: make the curves tighter or wider by changing 20 and 70.
2. Medium: let S curve backwards too, with S and A, or S and D, held together.
3. Hard: time yourself round a slalom of cups: reset the timer when you press g to go, and say the time when you press f to finish.