Hello Arduholics,
I am just VERY VERY new to Arduino, awaiting my nano board package to get done my first steps into Arduino sketching.
The root cause i choosed to start with Ardu was my idea of an RC Multicopter or each other flight model modular rescue system, which works independent to its power source and is very light weight of cause.
The Idea:
The Nano Board is meassuring the air pressure in pascal. This is done in intervals of 10-20milliseconds.
The Sketch tells to store the past 10 results in an array which is been compared all the time. If the pressure rises whilst the copte falls, the nano should deploy a parachute due releasing a cord via 3,3volts Servo.
Basically this sounds easy, but I need a hint, if I will need an extention shield for the Nano to trigger a 3,3Volts servo, as I´ve seen 3,3V is provided by the nano. does it deliver enought ampere for a servo to trigger?
Has anyone experience with servo controlling with the Nano 3.0 (without shield). I would try avoid a shield due more weight and parts the copter would need to carry.
To keep size/weight/power consumption down, you could use an ATtiny45/85. Use your Nano to develop and test your sketch, then use the Nano to upload the sketch to the ATtiny using ArduinoISP sketch.
No, when upload the ArduinoISP sketch to your Nano, the Nano becomes the programmer for the ATtiny. There are several tutorials about this. You must use a capacitor attatched to the Nano's reset pin to prevent it from resetting itself when you upload to the ATtiny.
In this post you can see my Nano being used to program an ATtiny85.
Before going further with this idea, you should check that you can get working libraries for the ATtiny for i2c communication with the bmp085 and for servo control. I'm pretty sure both can be done.
how are you going to tell the difference between change in Baro induced by wind, prop wash, or normal aerobatic flight and loss of altitude due to catastrophic failure of the copter?
(hint: putting a foam buffer over the hole in the baro will take care of the first two, most of the time)
how are you going to throw the chute clear of the aircraft when deployed (are you familliar with the term 'cannon-balling')?
might want to look into an accelerometer and think about a solenoid?
1.) The barometer is inside a thin 3d printed plastic case together with the 1s lipo and cabling the case has a hole 2-3mm offset the baro sensor on the pcb. holds off the wind and reacts fast enough to alt changes. This way real life my barigo altimeter for skydiving works (for instance).
2.) The idea came while packing my chute on the last jumps... have a look to a packjob of a skydive rig... You will have a loop with pack-pressure. On the copter this loop is been triggered by the servo pulling a needle off it. This releases a spring feather mounted to a push-plate which shoots out the packjob/parachute out of a RedBull/CokaCola thin, where the top is cut off. Now the pressure of the spring will be enough force to shoot the chute out until the lines are fully retracted. The other end is attached to the center of gravity on top of the copter, or any other stable enough element on the body/frame.
Now while the lines are retracted the copter pendles 90° underneath the chute... God save the gravity
While the copter releases the parachute the rotors are stopped by a function called "throttle cut" which each RC sender has. This basically is an emergency cut off.
The copter sinks with 2-4m/s depends on the parachute diameter and the wingload by the copter weight. There is a formular which can be adopted for this project.
Now the difficult part is to find the air pressure values from falling 2-3m and have a comparable curve for the 10 meassurements. This will be achieved by dropping the arduino once off and store all the values into log. OR calculating from physics formular and meteo sheets from FAA for civilian aviation.
Basically i am copying the light version of my cypres from a company called airtech. It´s Real life automated opening device for emergency situation on real life skydiving.
I am not intended in arcobatic flying rescue. That is like base jumping, it is only a question of time BUT you could override the barometer and deploy the servo manually by throttle cut and a second channel switch to trigger the servo for shooting the chute.
My goal is fpv flying, where you carrying mostly high value cameras and fly more or less due that "heavy" copters which may harm on impact others people gear or even people. I really want to avoid that and this COULD be a kind of new way... having plan B which is automonous return to home and land und shut the engines off, and plan c is cut all off and deploy.
I have my reservations on your plan, but certainly a worthy project. I would still advise incorporation of an accelerometer to detect free-fall. using throttle cut, throttle-up, or any other signal combination (far better to use a seperate channel than a combo signal, like throttle-up) assumes that the electronics are all functioning well. How come that doesn't sound viable in a catastrophic failure condition. or is it just me?
All chiding aside, go for it and let us know how it works out. Good Luck and happy landings to you.
BUT you could override the barometer and deploy the servo manually by throttle cut and a second channel switch to trigger the servo for shooting the chute.