Boof, you might find this funny.
This arvo, I went about fixing a 10 year old Radio Controlled car. Gear Box wasn't engaging, or perhaps faulty electric motor... Stripped it down, took it all apart, opened up the gear box, had a play, adjusted the cogs/gears, rear axle, and "re-test". Same problem still there.
Stripped it down further, extracted the electric motor, blew it off, dusted out the "mother board", thinking this thing has f#$ked resistor (flux capacitor?) or something, that I'll never figure out... I was thinking, "bin it, in parts..."... But I re-assembled it, only took 10 minutes (max), plugged the battery into in, and BANG !! It was working again!

My 4 year old was mesmerised at the seeing the cogs in the gear box, wheels off, canopy off, suspension "spread eagle"... etc... The thing was a total mess... as far as a 4 year old thinks !