Monday, December 21, 2015

Flight of 12 19 15

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....

After action...

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

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.

Sunday, December 06, 2015

After Action report...

So this was  a FAR weekend.
I had intended to do three tests, only got one done.

I fired the 3D printed motor with larger diameter plumbing on the main valve and a turbine flow meter so I can measure C* and ISP.

Results are mixed....
The test stand I'm using is an amalgamation of an old test stand and a bunch of valves from the silver ball.  In short it is a mess. I worked on making it better this week. (largely why I only got one of my tests done)  We hydroed the basic structure and tested the relief valve a few weeks ago, and all of that is solid.  The new valves and arrangements form the main outlet to the motor are solid.

The valves for the fuel side and the pressurization system are 100% Silver ball leftovers.
They largely worked two weeks ago when we ran it, this weekend two of the fuel side valves were frozen and the actuators died.  I had one spare actuator with me so I replaced the fuel valve actuator and changed the fuel side vent to manual operations.

The 2nd deficiency of the system is that all the wiring is an unreliable mess. I hope to clean that up repackage the electronics and make it all a solid solution before I use the stand again.
I  left the test stand at FAR but brought all the valves and sensors home.
The actuators are all dynamixel RX-64, 18V actuators  run off a 5 cell lipo and an ac power supply to keep things topped up.  I have a nice 40V  13.8V AC powered supply, thinking about trading the RX-64 for MX-64 that would be happy running at 13.8V. This is a $1K decision, I need to sleep on that.

My old sureflow pump for loading oxidizer died this year. I bought an air powered diaphram pump from McMaster car to replace it as the model of sureflow pump is not longer made.
The problem with this pump is that is really pulses, the flow is not smooth so hoses jump around and do unpredictable things.  I mounted the pump to a 3 hp roll around aircompressor and added a remote dead man switch activated valve to turn the pump on/off.  I also changed the loading procedure form opening the top of the tank to having a separate valve and a hard connection on the bottom for fueling, no ladders involved. These changes mostly worked as designed and I'm happy with them. much less risk drama in oxidizer loading.  I need to do something similar for the fuel side and will do so.  I still have hope that I can find a good steady electric self priming oxidizer pump..... I've ordered a couple of candidates, we will see how they turn out.

The firing ran well about 78 seconds. The CAT pack worked well and I got good data. The feed pressure was up about 20 psi from last time, the chamber pressure was up about 10, not sure where the other 10psi went.... motor ran at about 180 PSI target is 200. On shutdown the fuel feed pressure stayed up witht he fuel valve closed.  So I suspect that rebuilding the fuel side of the system in the mojave dust introduced enough material to clog the fuel orfices.  I've ordered a small sintered 10 micron fuel filter to add to the system.  Well see when I examine the engine this week....

I forgot to do a final last minute tightness check on all the plumbing. Got distracted by a rocket launch that required everyone under cover and for got to tighten one pressure transducer... sprayed peroxide all over everything...this part was after the main valve so was not part of the pre-fill leak check.

Then wheil disassembling things I dumped fuel all over the open ox inlet port on the motor.
So before I run it again it needs to come apart and be properly lcleaned for oxidizer service.

Things to do before next test:
Rebuild and test all the valves and actuators.
Package the electronics in a more robust manner.
Add flow meter to the fuel side.

I'll probably run another motor test the first FAR event of January that should be Jan 2nd
For the Far event on the 19th of December I'm going to try and fly my GPS experiment and test the little TJ-20A turbine as a potential first stage motor.  

I'll try and post some of the test data when I have looked at it later this week.