Robots are machines that sense, think, and act, so a small problem in any one part can make the whole robot fail. In a classroom robot, common trouble spots include the battery, power switch, motors, wheels, sensors, wires, and code. Learning how to debug helps you find the real cause instead of guessing.
A good repair plan starts with simple checks before changing parts or rewriting the program.
Most robot failures follow a chain: power must reach the controller, the controller must run the program, sensors must send useful data, and motors must turn motion parts correctly. If a motor whines but the robot does not move, the motor may be powered but the wheel or coupling may be stuck or loose. If a sensor gives strange values, the problem may be dirt, light interference, or a loose wire.
Careful testing, one change at a time, makes robot repair faster and safer.
Understanding Common Robot Failures and Fixes
A useful way to debug is to separate symptoms from causes. A robot that does nothing has a broad symptom. A robot whose left wheel stops only during turns has a narrower symptom.
Start by making the failure repeatable. Put the robot in the same place, use the same program, and note exactly when the problem begins. Watch indicator lights, listen for motor sounds, and feel carefully for parts that become hot.
Heat can mean too much current is flowing through a stalled motor or damaged wire. Do not keep power connected to a hot circuit. Disconnect the battery before moving wires or changing connections.
Power problems are not always complete power loss. A battery can show enough voltage with no load, then drop when motors start. Motors need more current when they first turn, when they climb, or when a wheel is jammed.
If the controller restarts when the robot moves, the supply may be sagging under load. A weak battery, thin wire, loose connector, or motor drawing too much current can cause this. Voltage equals current times resistance.
This relationship explains why resistance in a poor connection can waste voltage and make a motor seem weak. Test the robot with its wheels off the ground, then on the floor. A difference between those tests points toward a mechanical load or power capacity problem.
Motion faults need both electrical and mechanical checks. A motor can rotate while the robot stays still if a wheel hub is loose, a gear slips, or an axle binds. Unequal travel can come from different wheel diameters, rubbing parts, uneven weight, or one motor receiving less effective power.
Measure how far each side travels during the same timed command. Then inspect the drivetrain by turning the wheels gently with power disconnected. They should move smoothly without catching.
Wheel speed matters because robot speed equals wheel radius times rotational speed. A larger wheel travels farther per turn, so replacing only one wheel can make a robot curve even when the code sends matching motor commands.
Sensors need controlled tests rather than guesses. Print or display raw readings while changing one condition at a time. For a distance sensor, place a flat object at known distances.
For a line sensor, compare a dark surface with a light one. For a light sensor, block room light and then expose it to the lighting used on the course. This reveals whether the sensor works but has a poor threshold.
Calibration values collected in a dim classroom may fail near a sunny window. Sensor readings may jump because the robot vibrates, the target surface is reflective, or the program reads faster than the physical situation changes. Averaging several readings can reduce random noise, though it can make reactions slower.
Program faults often look like hardware faults. Confirm that the computer selected the correct board and communication port before uploading. Check that the new program actually starts after upload.
A simple test program is valuable. Make one motor run slowly, show one sensor value, or flash one light. Small tests prove each part separately before a full robot routine is used.
Pay close attention to units, motor port names, sensor modes, and threshold values. Keep a short log of each test, the change made, and the result. This record prevents repeated mistakes and helps classmates reproduce a fault when they assist with the repair.
Key Facts
- Power check: a robot that will not turn on usually needs the battery, switch, and power wires checked first.
- Ohm's law helps explain circuits: V = IR, where V is voltage, I is current, and R is resistance.
- Motor speed and wheel size affect robot speed: v = rω, where v is speed, r is wheel radius, and ω is angular speed.
- If a robot drives backward or turns the wrong way, the motor wires or motor direction settings may be reversed.
- Sensor readings can change because of loose plugs, dust, bright light, or poor calibration.
- Debugging rule: change one thing, test it, and record what happened before trying the next fix.
Vocabulary
- Debugging
- Debugging is the process of finding, testing, and fixing problems in a robot or program.
- Sensor
- A sensor is a device that detects information from the environment, such as light, distance, touch, or color.
- Actuator
- An actuator is a part that makes motion, such as a motor, servo, or gripper.
- Controller
- A controller is the robot's small computer that reads sensors and sends commands to motors.
- Calibration
- Calibration is adjusting a sensor or system so its readings match real conditions.
Common Mistakes to Avoid
- Replacing parts before checking the battery is a mistake because many robot problems are caused by low power or a switch left off.
- Uploading code without checking the cable or port is a mistake because the program may never reach the robot even if the code looks correct.
- Ignoring loose wires is a mistake because a connector can touch sometimes and fail other times, causing confusing behavior.
- Changing many things at once is a mistake because you will not know which change fixed the robot or caused a new problem.
Practice Questions
- 1 A robot battery should supply 6 V, but a meter shows 4.2 V. The robot will not turn on. How many volts lower than expected is the battery, and what should you check or do first?
- 2 A robot has wheels with radius 3 cm. If each wheel turns at 10 radians per second, estimate the forward speed using v = rω. Give your answer in cm/s.
- 3 A line-following robot keeps drifting to the right even though the program is unchanged. Explain two possible mechanical or electrical causes and one test you could do to find the cause.