A special circuit that can be used for brushless conversions . There are radio instalations that have brushed ESC built in and no allowance is made to take the throtle channel signal feed without messing about with the all in one board and soldering directly . 

This circuit board makes the job easier by taking the controlled brushed outbut and creating a PWM signal This is feed through any servo plug inpu of a brushless ESC and then to a brushless motor. 

Suitable applications are most small RTF Helis that come with brushed motors , the tail rotor brushless conversions , RTF 2.4ghz planes like Kyosho . Ember etc.  

The conversion is straight forwards but we would recomend this system for advanced modelers only.