Thursday, February 27, 2014
Multicopters require a tight control loop for all the motors as part of their ability to perform stable flight. A basic requirement for an efficient closed loop PID system is that it has a high enough sample rate and fast response to error input when the knowledge about the system is minimal. Until recently most ESCs were designed for airplane and helicopter applications, where gradual response to input is desirable for saving the gears against abrupt torque variations. In quadcopters, direct driving of the propeller is normally the case (and as such mechanical wear is not much of an issue), and as explained, quick response to throttle input is required for good PID response. As ESC behaviour is mostly defined by firmware code running in a microcontroller (in the vast majority of cases a ATMega 8L), replacing the stock firmware with a custom one normally is enough to solve this problem. This is the case for SimonK (https://github.com/sim-/tgy), which is one such firmware. Besides eliminating the gradual throttle response, instead of accepting input at the standard 50 Hz, it responds at a maximum frequency of 400 Hz, which is the rate at which flight controllers normally output the PWM control signal. Also, the LiPo protection feature is normally disabled, which in a multicopter could have nasty effects such as causing throttle assymetry, which ultimately leads to a flip and a crash.
Wednesday, February 26, 2014
A tray for the battery was added. Keeping simplicity and light weight in mind, I have built this tray based on an aluminium foil and four threaded rods. Four plastic straws (from kids balloons) served as spacers between the tray and the quadcopter chassis. The height of the tray was set based on the Turnigy 5000 mAh 3S battery I will be using:
Tuesday, February 25, 2014
One evening at a time and this new drone begins to get closer to completion. Motors installed and thread locked. Power distribution board and flight controller also installed. The next step will be to install the reprogrammed ESCs (I will check for SimonK updates), wire things together, and make a support for the battery (I'm thinking about using some folded threaded rods as a kind of cage for holding it, or something similar).
Sunday, February 23, 2014
With all the changes and upgrades I performed on my current quadcopter, I realized I had about enough spare parts to build another one. The only missing thing was the frame, but this is where the fun part goes. With this I had the opportunity to build a frame from scratch after buying 1m of aluminum rod, and a 1.5 mm sheet of the same material. This resulted in a 177 gr frame, which is not too bad.