Hello, the other day I saw a radio control boat that has a sound module in it that mimicks a small diesel engine. When the boat accelerated so did the engine sounds. How is this done please?

 

One method, Uses one channel of the RC TX to operate a servo controlling volume of the sound effect.
Max.

 

Hello,

Here are some schematics:
http://www.talkingelectronics.com/projects/DieselSound/DieselSound-1.html

Bertus