Some background on GPS.... this post is chronologically challenged as it flips back and forth)
I have three approaches to getting the GPS to work.
They are somewhat related.....
1)Use a Swift navigation PIKSI with custom firmware.
I've flown this unit with stock firmware twice, and with custom firmware once.
Flight 1 Stock firmware, lost lock at ~5 gee, marginal GPS in all cases.
Flight 2 Custom firmware with wide open GPS tracking loops... over did it as the units were tracking sats that were not there.....
Flight 3a) (12/19/15)
Newer version of Stock firmware GPS performance much improved, still lost lock at 6 gee, but recovered at burnout...
flight 3b)Same flight different piksi hooked up to intel compute stick to log RAW signals from the front end.
2)Use a RTL SDR dongle with GNSS-SDR and write custom firmware..
Thanks to some help from a follower/friend I have this runnign on the ground with my survey grade 35DB trimble antenna, but not with the flight weight antennas, I'm waingin for some low nosie amps to make this work wiht the flight weight antennas.
3)Build my own GPS with full IMU tight integration.
This will use the same Maxim GPS front end as Piksi, but with the Zynq CPU.
I have all the prototype pieces in work....
Thursday, Friday and Saturday I had a bad sore throat and cold.
On Thursday I determined that the RTL-SDR was not going to work without the LNA I did not have.
So I switched to trying to record the raw signals from the piksi...
After napping much of the day Friday to get better I finished the Piksi raw record about midnight Friday.
Saturday I got up at 4:45 rechecked that everything was working, packed all the stuff into the car and drove to the airport. I took off about 7am in the 182 Headed to FAR , I landed on the private dirt road next to FAR at about 8:15.
Started prepping the HPR for the flight using one of John Newmans ~M experimental motors.
one of the Altimeters failed the deployment charge conductivity test, took me about 2 hours to find the broken wire down inside the avionics module. Launched the rocket at 11:07:26 It went to ~12K ft. The GPS experiments and batteries added a lot of weight to the nose cone and I did not upgrade the main chute retention nylon bolts. So when the drouge deployed at appogee the main also deployed. After driving around in the desert on the quad for an hour gave up looking for the rocket and switched to the airplane.... it took us about 5 min in the 182 to find the rocket. It was 4 miles from launch and withing 25 ft of a paved road. So we landed back at FAR and Ted took me to get the rocket in his jeep. Kind of fun to ride in a really capable off road vehicle... The rocket barely fit in the jeep and on the way back to far we jumped over a rock pile the rocket came loose and broke Ted's window ;-( When people try to budget projects like this and understand costs no one puts things like Jeep windows in the budget.....
Once back at FAR I took the GPS modules out of the nose cone, I packed up and flew to Oceanside...(OKB) The flying club I'm part of had its Christmas party Saturday afternoon and I had promised I'd give breezy rides, so I left the 182 at OKB and took the Breezy to CRQ... it was too cold and I had no breezy ride takers.... so I took the breezy back to
OKB put it away and flew the 182 back to CRQ unpacked and drove home. I got home about 6 pm and went to bed early. It was a long day...
Saturday I downloaded the data from the GPS modules. The SBP format file from the first Piksi is here: SBP format Datafile The SBP format is defined here https://github.com/swift-nav/libsbp/blob/master/docs/sbp.pdf
Decoding that the Piksi with the current stock firmware lost lock at about 6 gee and regained lock at burn out.
The second piksi was recording raw RF from the front end via the intel compute stick... from time to time it had a FPGA fifo error and the sampler would restart.... inside this zip file are a bunch of raw data files. The file ending in 110731 has the first 4 seconds of flight. The File 110822 has the balance of the boost phase.
These dat files are supposed to run in the swift nav peregrine software GPS receiver, alas my linux fu is not working and I'm unable to get peregrine working as it looks like swift has moved its library python bindings from a separate module into the libswiftnav, alas that integrated version python will not build on my VM....
If anyone wants to play with this you can find info on peregrine here: Peregrine
That's all for now. I'll update when I manage to get some info from the raw data.