Line Tracking Car Kit
This kit came from AliExpress. It contained parts to build a 2 wheeled "car" that was supposed to be able to follow a track. The track provided was an oval comprising of a wide black line printed on a small sheet of white paper. Here are the parts as delivered, excluding the "track":
The kit was built carefully and checks were made with a multimeter several times during construction. Just before adding the motors, a final check revealed the power was not getting to the motor contacts and nor were some LEDs receiving power. Further investigation pointed to a possible problem with the circuit board tracks or one of the components. Replacing the battery box with a feed from my bench power supply made no difference. Although it's not 100% certain, I think it's likely that I wasn't to blame for this failure. The balance of probabilities pointed to a fault with the kit.
The two motors and the wheels were salvaged completely undamaged since they were never fitted. The battery box was also salvaged and some other components were desoldered and tested, so it wasn't a complete loss.