Drone Recovery Parachute

Failure is a concern that is always present in the operation of a drone. Given the continued increase in acquisition and use of these devices by the general public, safety is of paramount importance. Even the smaller devices of about 2 kg of total weight, in case of total failure at altitude, will fall like a brick and cause damage to whatever is below.

Most configurations such as quadcopters, don't offer any intrinsic redundancy (in spite of having 4 motors). The failure of a single motor will prevent the quadcopter of maintaining level and yaw-locked flight. Some enhanced control algorithms are being developed to provide level and controlled descent in case of single motor failure. Naturally, yaw control is lost, but the on-board inertial sensors and magnetometer are capable of keeping track of the orientation, therefore knowing how to distribute throttle by the surviving motors.

Reflashing a quad ESC to BLHELI firmware in an attempt to solve pancake motor cogging issues

Ever since I've switched motors and ESC's on my "primary" quadcopter, I have been running on problems keeping it reliable. Every now and then it would crash, once because of a motor connection that got broken, and other times in a unpredictable manner without  a cause that I could identify.

Custom made BEC

BEC's, which is short for Battery Eliminator Circuit is a fancy RC hobby term for a DC-DC converter that steps down the voltage to a given value used for example by servos and control electronics such as radio gear and flight controllers.

In the market there are two main types, most of which convert from a higher voltage to 5-6 Volts DC. These can either be of the linear type, or switching mode. The first is the simplest, where a simple linear regulator is used to drop the voltage to a constant value at the output. These tend to be very low noise steady sources of voltage, but have the disadvantage of being quite inefficient, getting worse the higher the input-output voltage differential. A considerable amount of energy is wasted in the form of heat.

2nd quadcopter practically RTF...

Other than having the recently ordered flight control board (Multiwii SE) mounted and configured, everything else was completed today with the addition of the custom made landing gear:

Improved quadcopter - more "avionics" and increased run time

In the several weeks that followed a crash caused by an ESC failure, plenty of work have taken place (some of which documented here). Several things have been done since:

• Replacement of the ESCs with a 30 Amp quad ESC;
• Upgrade of the flight controller firmware;
• Building and programming the PPM Sum encoder;
• Building a BEC/filter with 12 V and 5 V outputs;
• Adding landing gear;
• Adding voltage and current sensor;
• OSD firmware upgrade;
• Change of LiPO battery from 11.1 V (3S) to 14.8 V (4S);

Smoke test after a lot of changes

It's always a stressful moment when after many changes something is put to the test. This was the case, taking into account that since the last flight there was a replacement of all ESCs, upgrade to Arducopter MPNG 3.0.1 R4, installation of PPM Sum module, addition of voltage and current measurement, and use of a higher system voltage (4S instead of 3S LiPo).

Busy quadcopter setup weekend

With the arrival of some of the parts I have been waiting for, more work accumulated with the finishing of my 2nd quadcopter. The parts were the landing gear and the quadruple ESC: The landing gear arrived with all the necessary parts as expected, including the lower crossing bar and the foam rods. The bar and other rods are all made of carbon fiber. The 4 support rings (for attaching to the frame) all had a rubber ring which helps to further dampen the vibration to additional items such as a camera:

Reflash the ESCs

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.

One step closer...

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:

New quadcopter taking shape

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).

New drone, old parts

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.

Ground Control Station

With the model aircraft hobby scaling beyond line of sight, control equipment also grows more complex and sophisticated these days. To the point where we no longer designate it of transmitter, but refer to it as "Ground Control Station".

Gathering with fellow pilots and Multicopter improvements

Most of the time I have been a lone rider in this hobby, having started from scratch on my own, since the traditional helicopters back in 2009. I would occasionally go to local air fields and try to mix in with seasoned RC airplane and helicopter pilots. But the environment would not always be too friendly, with the fixed wing guys not enjoying much the flying grass cutters.

Going higher with the flyer

After very conservative steps with this model aviation hobby, I decided to get closer to the trends, and do some updates/improvements on my quadcopter while still being careful with the budget.

Letting it hover...

While the building phase can be an enjoyable experience, grabbing the sticks, putting the chopper on the ground, and gently increasing the thrust until that custom build apparatus starts to appear light on its stands is where the real fun begins. Would we ignore the noise of the struggling motors, and this styrofoam-shielded quadcopter would seem like a magical object for which gravity would be opening an exception everytime we wanted to. There is no magic, just technology, but still there is a sense of victory in tricking gravity in a brute force manner. Not in a magnificent scale as Howard Hughes H-4 Hercules, or lighter than air as Bartolomeu de Gusmão's flying bird, but still admirable for mimicking birds in the size and ability to fly (in a cumbersome way however), and for hovering like few of these animals can.

Multicopter Madness

R/C airplane modelling exists for several decades, but with late improvements and reduced cost in microelectronics, energy storage, and RF communications, products in this domain have suffered a significant improvement in quality and innovation.