Moderator Comment by Chris Anderson on September 3, 2009 at 7:32am

Nice! Can you add some pictures of it?

Comment by Andrus Kangro on September 3, 2009 at 7:41am

Picture is here.

Rev A board is inside plane, Rev B is right next to it.

Moderator Comment by Chris Anderson on September 3, 2009 at 8:01am

You can embed picture inline here by clicking on the camera icon.

Comment by viky on September 3, 2009 at 8:12am

great work andrus

Moderator Comment by Gary Mortimer on September 3, 2009 at 8:59am

Like that...

Moderator Comment by Gary Mortimer on September 3, 2009 at 9:00am

Good work Andrus, the next T3 round will be announced very soon!

Comment by Laurent on September 3, 2009 at 2:33pm

Thank's for this description, your autopilot is very advanced, specially on thermal.
Do you plan to share your works (code/opensource ) ?
Very good work Andrus

Comment by Andrus Kangro on September 3, 2009 at 8:29pm

Thanks. My code is not secret, who asks can get it, but I do not feel that it has enough quality to make it permanently visible. This may change, as I'm cooperating with a guy for his drone project and one of the topics is rearranging code in a way which enables both of us to focus on specific functionality and still have same product.

As far as hunting thermals, its actually very simple. Please note, even though I use pressure sensor for altitude measurement, its sensitivity is about 2 meters and its noise is around 4 bits, so I cannot trust it to find lift. So I use GPS for thermal detection in spite of its 3 sec latency! Its far from optimal or advanced, but sufficient for having flights like this:

Code is here:
(calculations loop, entered every 20 ms. At the end of it, servos will be outputted)

energyg=9.8*gps_z+((airspeed)*(airspeed))/2;//pot + kin energy wo mass
energygsum=(99*energygsum+energyg)/100;



if((ch[7] > 1750)&&((altitude-home_alt) < 350)&&((altitude-home_alt)*4>dist_home)){//hunt for thermals!

                if(state_flag&(113)){//new gps altitude received

                        if((gps_z > gps_z_old+1)&&(energyg > energygsum)){//if both altitude and energy are increasing, then enter/continue turn

                                liftcounter=10;//if lift is lost, then circle 10 sec more

                                if(gps_lat >0){//northern or southern hemisphere dictates circling direction

                                        turndir=TRIGHT;//turn right

                                        } else {

                                        turndir=TLEFT;

                                        }

                                } else {

                                if(liftcounter>0){

                                        liftcounter-=1;

                                        if(gps_lat >0){

                                                turndir=TFRIGHT;//we are out of lift; turn right faster

                                                } else {

                                                turndir=TFLEFT;

                                                }

                                        } else {

                                        turndir=dir_set;

                                        }

                                }

                        }

                

                } else {

                liftcounter=0;

                turndir=dir_set;

                }

Its the code which did fly the plane like in above pic. I've now modified the code not to only detect presence/absence of lift but also react on lift strength, but its not tested yet.
As you see, the code is very simple and sensors are very inadvanced, but it works.

Comment by fefenin on September 7, 2009 at 7:04am

hi,
yeah that's cool project ,i made one autopilot as well pic based no stabilisation at all just return to home ..
i haven't got the tools to program DSpic so i jsut gave up for ardupilot ...

i would like to now if your altimeter with the mpx4165 works now,
i would like to add an altimeter using the mpx6145 that i've got (pretty much same as 4165) to get an accurate altimeter variometer...

if you've got something running 'id be very interrested about it!!

regards
fefenin

Comment by Andrus Kangro on September 7, 2009 at 7:35am

Hi, you can use pickit2 or pickit3 to program & debug dspic, they are very good value for money.
I use ADC autoscan feature to read MPX4115 value and ADC interrupt to write it into variable altinp. Conversion to altitude happens with below procedure, called before calculations loop.
pow btw is very expensive function, it takes about 1ms

void calc_altitude(void){//calculate altitude (in m) based on pressure
        //

        //mpx2125A output voltage formula is vout=vs*(0.009*pressure(kpa)-0.095)

        //we are using 12-bit ADC, maximum ADC value is 2^12-1

        //metric altitude=(1-(pressure/groundpressure)^0.190263)*44308

        //input is altinp which contains pressure sensor ADC value

        //output is in variable altitude.

        //ground pressure is set to 101325 or to maximum measured pressure

        double p;

        unsigned int d1;

        extern unsigned int state_flag;

        extern int altinp, altitude;//, gps_z;

        extern double ground_pressure;

        extern unsigned int d;

        

#ifdef __DEBUG

        altinp=0x0cfe;

#endif

        

        d1=TMR1;//this code is used for timing below code segment       

        p=1000000.0/9.0/4096.0*altinp+95000.0/9.0;

        if((ground_pressure

15)))ground_pressure=p;        //ground pressure update ok until gps fix obtained

        

        //altitude=gps_z;//lets skip barometric stuff and use gps 

        altitude=(int)(44308.0*(1-pow(p/ground_pressure, .190263)));

        

        d=TMR1-d1;//this code is used for timing above code segment 

        state_flag &= ~(111); //bclr  _state_flag,#11

        

        asm("nop");

        return;

        }

I did search for mpx4165 and mpx6145 and nothing came up...?

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