Reliability, Testing and Troubleshooting

Lesson

A robot that works once on the bench is not finished. It has to work in every match, after collisions, hours of driving and being carried around. Reliability is the difference between a robot that drives for a full event and one that loses a wheel in the second match. This lesson covers the habits that make a robot dependable.

Why robots shake themselves apart

Motors, wheels and collisions create constant vibration. Over time, vibration slowly turns screws and nuts loose, especially small set screws in hubs and shaft collars. A loose screw rarely fails all at once; first a wheel wobbles, then it slips, then it falls off. The fix is to use fasteners that resist loosening and to check them regularly.

Method	How it works	Where to use it
Medium-strength threadlocker	A liquid that hardens in the threads and holds the screw, but can still be undone with hand tools	Metal-to-metal screws that vibrate, especially set screws in hubs and collars
Nylock nuts	A nut with a nylon ring that grips the screw thread	Bolts through the frame that use a nut; replace them after many reuses
Witness marks	A paint-pen line across a screw head and the part	Any important screw, so you can see at a glance if it has turned
Regular checks	A scheduled inspection with hex keys	The whole robot, before practice and between matches

The inspection habit

Push and pull every wheel: there should be no wobble or sideways play.
Check witness marks and retighten anything that has turned.
Tug gently on every connector to make sure it is fully seated.
Look for cables rubbing on wheels or sharp edges, and for cut or crushed insulation.
Check the battery is charged, secured and undamaged, and the main switch works.
Look for bent channel, cracked plates and metal shavings that show something is rubbing.

Testing a new chassis

1
Hand test
Battery disconnected. Spin every wheel by hand and push the robot across the floor. It should roll smoothly.
2
Power-on test
Robot on a stand, wheels off the ground. Turn on the main switch and check the Control Hub lights and the Driver Station connection.
3
Single-motor test
Run the motor test OpMode. Check each wheel spins, in the right direction, with its encoder counting up.
4
Floor test at low power
On the field tiles, drive forward, backward and turn slowly. For mecanum, try strafing left and right.
5
Endurance test
Drive for several minutes, including some gentle bumps. Then switch off and repeat the inspection checklist.

Troubleshooting systematically

When something goes wrong, the worst approach is to change five things at once and hope. Instead, describe exactly what happens, list possible causes, test the easiest and most likely one first, and change one thing at a time. Write down what you tried, even when it did not help, so the team does not repeat it.

Symptom	Likely causes	What to check
Robot pulls to one side	Binding wheel, one motor reversed, uneven weight	Spin each wheel by hand; run each motor alone; check directions in code
One wheel does not move	Unplugged cable, wrong port, loose hub	Connector seating, configuration name, hub screws
Robot will not strafe (mecanum)	Wheels in a diamond, wrong motor directions	X test from above; strafe signs in code
Robot cuts out when bumped	Loose battery or power connector, switch not secure	Tug test on power connectors; battery mounting
Clicking or grinding noise	Loose set screw, missing spacer, damaged gearbox	Witness marks, wheel play, motor sound with wheel removed

Troubleshooting is a loop: test, analyse what happened, make one change, then test again.

TEXT

1Date: ____   Tester: ____   Battery: ____
2
3Test              | Result      | Problem found        | Fix
4------------------|-------------|----------------------|-------------------------
5Hand spin         | Pass / Fail |                      |
6Single motor (FL) | Pass / Fail |                      |
7Forward 2 tiles   | Pass / Fail | drifts left          | tightened BL hub screw
8Strafe right      | Pass / Fail |                      |
95 min endurance   | Pass / Fail |                      |

A simple test log format you can copy into a notebook or spreadsheet.

Key terms

Reliability: The ability of a robot to work correctly every time, through many matches, bumps and hours of use.
Threadlocker: A liquid applied to screw threads that hardens to stop the screw loosening from vibration.
Nylock nut: A nut with a nylon insert that grips the thread and resists loosening.
Witness mark: A line drawn across a screw head and the part so you can see if the screw has turned.
Systematic troubleshooting: Finding a fault by testing likely causes one at a time and recording each result.

Practical exercise

Run a full test session on your chassis

1Apply threadlocker or nylock nuts at the high-vibration joints and add witness marks to important screws.
2Do the full inspection checklist and fix anything you find before powering on.
3Run the five-step test sequence and fill in a test log as you go.
4Pick one problem found during testing and troubleshoot it by changing one thing at a time, recording each attempt.
5Repeat the inspection after the endurance test and note anything that loosened.

Deliverable: A completed test log for your chassis and a short troubleshooting record of one problem: symptom, causes considered, tests tried and the final fix.

Knowledge check

Answer every question, then check your answers.