Bumper-Switch Rover

The finish line

What you will build

The rover detects left and right bumper presses and escapes a three-sided test area without motor stalls in four of five trials.

Before you build

Materials, tools, and safety

Reuse-material cost: Usually under $5 with an existing kit. Supervision: Adult guidance recommended for wiring and cutting.

Build it

Step-by-step instructions

1. Step 1

   Build and roll the chassis

   Assemble the rover and turn each wheel by hand.

   Correct rubbing before wiring.

2. Step 2

   Mount the bumpers

   Hinge broad left and right paddles so each presses one switch.

   Add stops to protect switch levers.

3. Step 3

   Wire the driver

   Connect motors to H-bridge outputs and the rated battery to motor supply.

   Join all grounds.

   Builder checkpoint: After wire the driver, the first subassembly should stay aligned when handled gently.

4. Step 4

   Connect control pins

   Wire four direction inputs and two switches using internal pull-ups.

   Label every lead.

   Watch for: If this stage binds or drifts, inspect timing variation before adding more parts.

5. Step 5

   Test wheels raised

   Run forward, reverse, left turn, and right turn for one second each.

   Correct polarity in code rather than crossing random wires.

6. Step 6

   Test bumper states

   Press left and right switches while watching serial output or indicator LED.

   Confirm each input is distinct.

   Builder checkpoint: After test bumper states, operate the build slowly and confirm that motor reverse and turn sequence begins without binding.

7. Step 7

   Tune escape timing

   On the floor, begin with 300 ms reverse and 350 ms turn.

   Use soft box walls in a clear area.

8. Step 8

   Run five enclosure trials

   Start from the same center mark and record successful escapes.

   Stop after any stall or warm component.

   Builder checkpoint: At the final checkpoint, The rover detects left and right bumper presses and escapes a three-sided test area without motor stalls in four of five trials.

See the engineering

Why it works

Input

left or right bumper switch closure

Output

motor reverse and turn sequence

Motion

electrical state-to-differential wheel motion

Energy losses

wheel slip, gearbox friction, bumper flex, timing variation

const int leftBumper=2, rightBumper=3;
const int leftA=5, leftB=6, rightA=7, rightB=8;
void motors(int l, int r){
  digitalWrite(leftA,l>0); digitalWrite(leftB,l<0);
  digitalWrite(rightA,r>0); digitalWrite(rightB,r<0);
}
void setup(){
  pinMode(leftBumper,INPUT_PULLUP); pinMode(rightBumper,INPUT_PULLUP);
  pinMode(leftA,OUTPUT); pinMode(leftB,OUTPUT); pinMode(rightA,OUTPUT); pinMode(rightB,OUTPUT);
}
void loop(){
  bool leftHit=!digitalRead(leftBumper), rightHit=!digitalRead(rightBumper);
  if(leftHit || rightHit){
    motors(-1,-1); delay(300); motors(0,0); delay(80);
    if(leftHit){ motors(-1,1); } else { motors(1,-1); }
    delay(350); motors(0,0); delay(80);
  } else { motors(1,1); }
}

Make it behave

Test, troubleshoot, and tune

Keep experimenting

Try another version

Build together

Classroom and access options

Reflect on the design

1. How did turn duration change the measured result?
2. Where did wheel slip affect the build most strongly?
3. What evidence shows that reactive control explains the motion?
4. Which change would improve motor reverse and turn sequence without creating a new problem?