Sunday, May 18, 2008

Paperwork and other projects....

We tried to do a full up static test on the vehicle last Sunday and again on Tuesday. We had some valve electronics problems that were traced to a screw rubbing in a bad place and a dead, possibly overvotaged, servo motor. This last weekend we worked on the logistics issues at FAR and will continue to do so for at least two days this week.

Since my 90 second vehicle and notional and 180 second vehicle are less than identical we need to submit two seperate experimental permit applications. 90% of the 2nd application will be cut and paste, but we still need to submit two. I finished the 90 second application  and e-mailed and fed-xed it to the FAA. If anyone read last years application this one will look stuningly familiar. I will make the aapplication public at some point in the future. If I released it now I’d be violating at least one NDA. 

I must give special thants to my friend Carl at Flometrics that spent part of his weekend doing CFD work to help me get a Cd number for the vehicle and the containment calculations. If you need a fluid or flow engineers please call them. They do a lot of really cool stuff. I’ll post some of the cool CFD pictures in the next few days.

We have been working at this full tilt for almost 18 months straight and I’m getting a bit tired. Spending a full day in the Mojave at over 100F really takes it out of you. 

Friday, May 09, 2008

A Glimpse of scary little details...

I have not reduced the data from last weekends first static fire, but I know that we had a main valve calibration problem. Tonight I brought up the flight computer to work on the main valve calibration and I got prodigious quantities of magic smoke. (All electronics runs on magic smoke, if you let the magic smoke out it stops working.) This is scary on a number of levels. If the main flight computer dies in flight the vehicle is lost, so I start asking did I make a design error, did I have an assembly error? What caused the system to let out the smoke?  So I remove the computer from the vehicle and take it into my office/lab in the house and hook it up to the current limited power supply…. no smoke. The magic smoke happened inside a closed case so everything in the case smells so no clues there.

One by one I test the sub systems… Main CPU, OK,Vane control OK, GPS OK, IMU interface OK, Telemetry Radio OK, Servo drivers OK Pressure sensor power error not OK. So I examine the little sealed DC to DC converter component that provides this power and it is failed shorted with smoke /char marks under it. The good news is that this failure would not have caused a crash, a loss of  pressure transducer data, but not a crash.

This little power supply adds to the head room for the two wire pressure transducers. I use 2 wire 4 to 20ma transducers because of the reduced wiring, from the three wire transducers. The transducers need 10V minimum, since I run the into a resistor that makes 0–>5V from 0 to 20ma I need a 15V supply. I’d been running 11.1V to the Big tonegowa servos so I added a 5V isolated DC to DC to bring the voltage up to 16.1V. In past setups I’d added one very small sensor battery,  but this time I though I’d remove one more service item. The sad part is that this is not really necessary anymore. This time around the Vane Actuators need ~18V  so I already have a voltage rail, 18V that could drive these. The smoking power supply has been voted off the project.

I wired a sacrificial 1/8W carbon 20 ohm resistor between the sensor circuit and the 18V supply so I’m now good to go. If any of the transducers wiring gets melted and shorts to ground the 20 Ohm carbon resistor will act as a  fuse. Protecting the flight critical power rails.

We also learned another lesson tonight. With LOX you can be 100% sure its gone two days later, not so with peroxide. We ran the vehicle until there was noting but nitrogen coming out of the motor. Apparently this is not enough. When my son  removed the main valve it dumped peroxide on his jeans.  No harm done, but it was exciting for a second when he leaps up removes his pants and runs out of the garage heading for the garden hose… on the way by saying “make sure we there's no fire”  Fortunately none of the many fire extinguishers were necessary.  a few teaspoons of peroxide  makes for some excitement but in this case not much else.

This does say that our run tank and main valve is clean and properly passivated.

Wednesday, May 07, 2008

Starting the paperwork...

We do not yet have an offical contest date for the 2008 NG-LLC. If they hold it around the end of October like they did the prior two years we are rapidly comming up to the FAA experimental permit submission deadline. So for the time being I’ve switched from aluminum to documents as my development mediium of choice. I feel this will be a lot easier this time around as I’ve already been involved with the FAA permit process.

For fun a cool picture….the business end of the vehicle taken from the flame trench of the test stand….


And one taken from inside the block house by Charles Pooley of the partial throttle test….(the wind was really blowing…)


Saturday, May 03, 2008

A tiny bit of hardware...

The vehicle is 99% complete. The only part missing is the IIP shutdown safety system. The IIP shutdown safety system calculates the instantaneous impact point (IIP) and shuts the vehicle down if the vehicle leaves the assigned flight hazard box.  The vehicle has been transported out to FAR for a static test in the near future so I don’t have a complete vehicle picture. I do have a couple of detail hardware pictures…


The electronics box lid off and lid on….


The box mounts on the side of the sphere at an angle and the GPS antenna mounts on the box so it is the highest thing on the vehicle.

Lastly a short video of the jet vanes moving.

Thursday, May 01, 2008

Quick update...

Having Dad here for two weeks has slowed progress, but not stopped it.Last weekend I managed to fabricate the cwenteral control box and it is now wired. The vehicle is now basically complete. We will do a full vehicle tied down static test some time in the next week or so. This should allow us to gather some vibration data on how the IMU and GPS react to rocket vibration. After that we should start testing within the month. Its getting perilously close to the hot season out in Mojave so time is getting short.

We also need to restart the FAA paperwork process so we can do some free flights.