Quadcopter altitude hold

A system using sonar (and other sensors) to automatically maintain altitude on a quadcopter without affecting other functions

Quantity		Component name
1	×	HC-SR04 sonar module
1	×	PIC16F1824 Microprocessors, Microcontrollers, DSPs / ARM, RISC-Based Microcontrollers
1	×	Naze32 flight controller
4	×	Multistar Elite 2204 brushless motor
1	×	HK 260 upswept quad frame
4	×	Afro 15A ESC motor speed controller
1	×	1500mAh 3S Lipo battery
1	×	HB100 doppler radar module (not yet implemented)