Saturday, December 15, 2018

Fusion360 cad beg...

I'm tryingto convert from Rhino to fusion 360.

The following was done in rhino, I'm trying to learn how to do the same in fusion...

I can easily draw this in fusion a Extruded cylinder with a hole in it.

I Can also draw my o-ring groove in fusion....



In Rhino I next draw two spheres.....(Blue and green)



Then I generate the line where the spheres intersect the cylinder.
(Inner intersection lines have been removed for clarity)
(I did this twice and the blue/green colors swapped  sorry for the confusion)


I then use the sweep2 command in Rhino to make a solid from o-ring profile and the two "Rails"
This is correctly tangent to the cylinder surface and has the correct o-ring breaks, radis etc...


Then subtract the solid and I have my o-ring grove.

So my fundamental fusion 360 issues....
I can't draw the spheres based on points, only dimensions. The lower dimension is easy to derive its the hole radius +the oring offset. The outer sphere is a lot harder as the oring groove sides are not straight and while I can place a point in the appropriate place fusion won't let me draw a sphere to the point. That problem I could work around with some triganometry, but the 2nd problem I can't seem to solve. I need to create a pair of lines to sweep the pattern, these lines need to be the intersection of a sphere and the cylinder. I can't seem to create this geometry no matter how I try.

Advice welcome.





Monday, November 19, 2018

0.018" matters...

I had a batch of end caps machined for the Carbon tube tank.
This was 4" outer, 0.035 metal liner 0.009  poly bag, and 0.004 gap.
This was all carefully measured and tested, it works well...

I thought I could reuse these end caps in the 4" 035 wall tube, alas I neglected to account for the bag.
The 0.009 on both sides or 0.0018 in diameter is enough that the caps don't seal correctly.....
Grumble Grumble....
I could line the aluminum tube with the bag and continue....


Not a huge deal, but I thought I had enough for 3 sets of flight hardware, now I have zero...
I need to machine new ones...

So even with the loose fit, I thought I'd assemble the tank and  hydro test one.
The end cap retention failed at 420PSI. The cap retaining screws failed in shear.
In hind sight I did not use enough screws, according to the screw stress calculations they should have failed at 390 psi.


So all in all its nice to actually be building and assembling hardware again.

So Mariellen's garden got its first dose of hydro test water, in about 4 years.

Wednesday morning update...
Rebuilt the test tank, used more screws, hydro ed
to 600 PSI without failure.






Thursday, November 15, 2018

Fill Drain how to make safe...

One way to fill a tank... (and how I've filled every rocket tank to date)
Is just put a removable fitting on the top of the tank and pour in the propellant.
Its real hard to make a system lighter than just a single AN cap.

This has several problems...
  • It does not scale, in a Otrag vehilce you might have 128+ tanks to fill.
  • On a biprop vehicle, once one of the propellants is loaded loading the other propellant becomes a hazard.
  • Its very difficult to precisely fill to exact levels.
  • It does not help you drain after an abort scenario.

    So I'd like to do remote fill and drain on the vehicle without adding a bunch of weight...
    Here is one possible scheme that can be done with a single tank penetration.










At the expense of wasign some propellant it ensures the system is filled to a precise level (the level of the bottom of the dip tube, and only requires one tank penetration.

It has the added advaltage that if you use the valve RV1 to vent the tank in an in flight abort, it does nto vent the all the propellant, only the pressurization gas.... With Lox its not an issue to dump propellant while in the air, with H2O2 dumping in the air can start a large area brush fire.








Tuesday, November 13, 2018

Random misc stuff...

Lots of little things....

It looks like the Fuel in 20Kg lots is about 50% lower cost.
If one eventually gets to ton quantities then its down to 18% of the present cost.
So all of that is good news....

I've been thinking that I was going to have to manufacturer my own quick disconnects.
Everything I'd found was either too big, to heavy or to expensive.. (often all three)

After a help me beg on Arocket a friend pointed me at some things on E-bay that eventually led me to these...

They are Aluminum, with viton and stainless internals. Off the shelf and not too expensive. The Really cool part is the rocket side is only 49gm!

They are available from multiple places look for FBM3314 and FBM1153. The only way they could possible be better is if they were AN fittings rather than pipe, and availible in multiple sizes. (For all of you that don't do high pressure plumbing, please realize pipe threads are horrible.)

In Pauls  pantheon of pliumbing....
  • Last choice is pipe thread.
  • AN flare fittings are ok to pretty good. Probably not good enough for directly hazardous materials near people. 
  • Swageloc are good, but both pricey and heavy.
  • The Big boys use stainless and all orbital welded connections...
That's it for Today....

Saturday, November 10, 2018

Two chemists walk into a bar, the first one says I'll have H20, the second one says I'll have H2O too... he dies....

Anyone that has followed my rocketry stuff for awhile knows I like H2O2.
(See comments on H2O2 at the very end of this post)
Both  Beal and the British Black Arrow group did some really cool stuff with H2O2.

So I've been thinking about engine cycles....



A:Regen Cat Pack 

 is what I have been running for the past few years. H2O2 comes in cools the engine, goes through a CAT pack and then ignites the fuel injected below the cat pack.
This works reasonably well, it has the following drawbacks...
1)CAT pack limits the H2O2 concentration to about 85%.
2)The CAT pack has a lot of pressure drop.
3)Cat Packs wear out or get contaminated.
4)They are some what expensive (Pure or plated silver screens)

B normal chamber with hypergol (or not)fuel.

I've been given some evidence of an available decent performance hypergol for H2O2.
I've not tested it or fired it personally. (Hypergol means fuel and oxidizer light on contact)
Its basically a traditional regen rocket motor. It needs a traditional injector, so not sure if I'll build a pintile(My fireing) , or a shower head (my fireing)` I've build and fired both with Lox Alcohol before I switched to H2O2.

This allows one to run to 100% H2O2 and to reduce the pressure drop.
The primary drawback is the fuel in small quantities from a chemical supplier is about $425 a liter.
The O:F is 4.9 so  the fuel for a full Class 2 burn is about $1300  For a full Class 3 burn that is 27K, its starting to hurt.... The H2O2 for the same class 3 burn is  $4500 so not totally out of the ballpark..

There has been an experiment that I've wanted to run for a very long time. I've wanted to try and run a wet, no catpack H2O2 engine. I've always wondered how to get it lit.  I think that at some point In testing I'll set up to use the Expensive Hypergol to light the motor, much like TEA/TEB is used in Lox RP engines and see if it continues to run well once the hypergol slug is gone.

C Odd choices....

There is some literature in the world talking about H2O2 gas generators with partial pre-decomposition and thermal decomposition of the full flow. This is the schematic of what I Imagine this might look like....  The H2O2 combines with a small amount of the hypergol to get warm, but not enough to "Burn" all the oxidizer....(This could also be part of the H2O2 flow goes through a cat pack to get hot)  This then enters into a stack of inconel screens, sort of like a cat pack, but not chemically active, its just a place to warm up and cause thermal decomposition...
Before thinking about the hypergol I'd planned to run this test with a silver cat pack and 100% peroxide, the silver cat pack would quickly melt and die, but probably not before getting the inconel screens hot enough to do thermal decomposition.... It seems the screens to do decomposition must get to and maintain at least 600C.

The big drawback to all the thermal decomposition schemes is that hot H2O2 vapor can detonate if it does not decompose.

Why am I posting all this stuff to the blog...

  • One of the primary goals for Unreasonable Rocket , from the very beginning is to excite people to try and do cool rocketry things themselves. It does not take NASA levels of $$.
  • I'm pretty much doing this project by myself in my Garage and at FAR. Last time I did this my Son was helping me, now I'm doing it solo. So using this as a portal to interact with people and maybe inspire people to help with the project is part of the blogging. 
  • Trying to establish a habit of keeping the world up to date, I've set up a Patreon account (I've not turned it on yet) and when I do my first firing in this development cycle and have cool video to share I'm going to turn it on.  (If you think I should activate it now say so...)

    If you want notification of new posts here, I will be announcing them on twitter. I'm @unrocket

*Comments on H2O2 aka hydrogen peroxide.

The hydrogen peroxide that sits in your medicine cabinet and that you put on your cuts is 3 to 5%. Meaning its 5% H2O2 and 95% water, The H2O2 were talking about here is at least 85%.

This high strength peroxide decomposes exo-thermally to steam and hot oxygen.
Any concentration above 72% has enough energy to full vaporize the water content and is thus a hazard as it can make lots of hot gas quickly.

This decomposition needs some thing to induce it, heat, or a catalyst chemical.
  • Thermal decomposition.
  • Metal reusable catalysts (silver, platinum)
  • Consumable Catalysts like the permanganates, etc...
With 85% you can run it through a silver catalyst (CAT Pack) for a very long time.
At 90% long term use will melt /degrade silver. Above 90% Silver does not last very long at all as the decomposing H2O2 melts it away, 98,99 or 100% has a more energy and higher performance as a rocket oxidizer.




Friday, November 09, 2018

Starting with the basics...
What is the tank layout?
For control authority you really want the center of gravity (CG) as far forward as possible.

So I sketched up the 5 tank layouts shown above...
I fully accounted for the weights and moments for all the fittings down tubes, up tubes etc...
for the full rocket...I estimated engine and gimbal weights base don stuff I've already fired...

I wrote a C++ program where I could instantiate parts, add them to the rocket, then run the tank to depletion and  calculate the CG....

I modeled #1, #4 and #5  #1 has the farthest forward CG, but was heaviest. If I ballast #4 by adding nose weight until it matches #1 then the CG is farther forward with #4 at the same weight at the extremes of  the flight. 

#1 goes from  152 to 255 cm from the front.
#4 ballasted to the same weight goes from  233 to 251 cm.
Its much simpler to build and the nose ballast can become more recovery gear bigger batteries, better telemetry etc...

As an added benefit #4 is much simpler to build and cleaner aerodynamically with no external feed tubes. I could do #4 with internal feed tubes, but then all the bulkheads become 5 axis machining projects, where for #4 they are all basic lathe parts.


I've simulated this rocket 3 ways...
My own written from scratch  simulator in C/C++.
Using RAS Aero II
Using OpenRocket...


All of the results agree and all say I have enough margin to cross the von-carmen line with a class 2 rocket... It will be interesting to see if  I can build it as light as I think I can.

That's all for now...

Friday, November 02, 2018

All the things.....
A stream of thoughts on the task at hand...

Starting at the front of the vehicle....


In front of the vehicle, aka airspace...

To start with FAR has a standing waiver for all class 2 rockets to at least 50Kft.

Once its time to exceed that altitude I strongly suspect that waivers requested from the FAA
with only the required class 2 information will be rejected as this vehicle will have performance capabilities that exceed what was envisioned for class 2. The next launch location after FAR will depend heavily on what the FAA is going to want for a waiver.
Possible locations: Black Rock, Space port in NM, offshore either in the pacific or in the gulf.


The nose cone
Before I shut down this effort last time, I made some 4" nose cone patterns and John Newman made some molds. So he has all the tooling to make a nice light mixed glass/carbon  nose cone for this.
The nose cone has dual requirements, it needs to handle the peak impact temperature and also be radio transparent for GPS and telemetry.

The primary electronics GNC board.
NetBurner is about to release a new module based on the Microchip arm Cortex M7. I will repackage the core electronics from our new module into a GNC/autopilot.   Basic features will be:
  • Cortex M7 cpu with hardware floating point.
  • GPS, will use Ublox until we exceed the ITAR limits.After the ITAR limits become a problem I may switch to the SDR GPS I've test flown, or one of several other GPS solutions I've got working beyond ITAR on the GPS simulator.(I have a LabSat GNSS simulator)
  • Integrated IMU 
  • Barometer
  • Pyro drive electronics.
  • Telemetry Radio (Probably an xbee socket)
  • LIN communications channel.
  • CAN communications channel.
  • I2C communications channel to talk to :Digikey 223-1507-5-ND pressure sensor.
  • SDIO/SPI interface to SD card interface.
Black Box
A package containing a micro SD card in foam inside some kind of crush resistant vault.
I expect the Telemetry data to be limited and this will be the primary "Product" from the flights.

Recovery Tracking:
The simplistic solution is to add a simple beeper transmitter....
The more complex solution is to use telemetry...(Probably means putting a 2nd tiny GPS on back side of nose cone so it can receive positions on the way down).


Camera
For flights with recovery I'll use a gopro session.
For flights where recovery is not expected I'll use  a 70 cm ATV TX and a atenna with gain on the ground. To simplify things, telemetry may be on the ATV audio channel.


Recovery:This vehicle is lighter when depleted that the HPR I tested all the GPS modules on.
For FAR area flights where I'm altitude limited and well withing the atmosphere I'll include the HPR recovery system I've used reliably.  This system weighs as much as the rest of the vehicle, so its not a choice for high altitude flights.

For high altitude flights I'll probably just eject  the nose cone at altitude  with a simple kevlar strap/streamer to orient the nose cone. Basically no recovery.

TanksThe notional OTRAG vehicle uses the carbon tanks that John Newman and I developed three years ago. That tanks uses a carbon sleeve with a poly bag liner and machined aluminum oring sealed end caps.   This vehicle will use 0.035 wall 6061 T6 4" tube.
I've ordered 24 ft of this tube (arrives on 11/6)
The only thing remaining to decide here is tanks closure. I have two competing concepts....
This will be the very firts hardware I build and hydro test...
In the next month I'm going to make a few 12" long tank sections to evaluate weight and closure...

Machined domes with oring groves retained by a collar screwed or flush riveted in behind the dome.

Hydro formed domes welded into the tank ends. This will probably not work as it weakens the underlying material too much, and its very hard to heat treat thin wall tanks.

Hydro formed domes welded into a collar that slips into the tank end and is itself welded to the tank.
This would involve building a heat sink that clamps on the aluminum tube trying to minimize the heat effected zone. The length of the collar would be whatever is necessary to move the weld beyond the HAZ. On a pressurized tubular tank the lengthwise stress is half the maximum stress in the other direction.   So if you can move the HAZ to the point it only effects lengthwise stress its a win.

Mid Tank Coupler.
The mid tank coupler is going to be a some what complicated piece, it will have the roll control nozzles and solenoids built in. It will also structurally join the propellant tanks to the blow down tank on the bottom of the vehicle.   The module will have its own local electronics with rate sensor and solenoid drivers. It will communicate with the primary controller on  the single LIN backbone.
Its possible that it might also be the fill and drain interface for everything.


Main propellant Valves.
Three choices here:
OTS aluminum ball valves with external drop off actuators.
This has the possible benefit that one could mount a monprop engine and do hovering stability tests under the fork lift.

Some version of my Spectra melted string actuators.

Some version of  a pyro valve.

Pyro or spectra shut off valve.


Gimbals and TVC actuators.I have a design for a gimbal with built in fluid channels. This is an intricate little piece 3D printed and post machined. All in all its probably 40 hours of fabrication, each....
Its light, compact and easy to gimbal.

The alternative is a simple rod end bearing assembly like the LLC vehicle used with flexible hoses.  This is easy to fab, but I'm concerned about its impact on the size/wt of the gimbal actuators
and actuator batteries. Pressurized flexible hoses are stiff and require strong actuators.

For actuators I'm going to use OTS brushless servos.


Rear End electronics:
Another custom electronics board.
CPU
Two axis rate sensors.
Actuator driver logic. (Probably servo or RS-485)
Pyro drive channels (at least 2)
LIN communication channel.
System simulation will determine if LIN is fast enough to communicate from main GNC to the TVC actuators, it the TVC actuators have local rate sensing. It this is too slow then inter module comm will be upgraded to CAN.

Thrust Chamber
The final thrust chamber here will be smaller and lighter than the 3D printed aluminum chambers I was testing when I stopped rockets 3 years ago.  The will otherwise be very similar to the previous efforts.  I may build a cat packed   based mono prop chamber to allow tethered hover testing of the GNC without risking the vehcile


Rear Fill and Drain
The  full OTRAG would require rear access fill and drain.
For the single tube test article mid point or top side fill and drain might be advantagous from a getting the weight forward stability stand point.


Batteries
The current plan is to have multiple batteries local to each of the the electronics bay, forward/nose cone(GNC And telemetry), mid bay (Roll control) , rear (Main Valves and TVC).
It may prove to be lighter to have a single battery and power distribution, but getting power from the front to the back in an aerodynamically clean way may be more weight than individual batteries.

Ground support equipment:The necessary transfer tanks, pumps, valves, regulators etc,,,,, to fill drain and pressurize remotely.

Tracking telemetry antenna.

Spar buoy to support offshore launches.

Simulation System...
I'd planned on using JSB sim when I had other people helping me with things...
I'm currently trying to get that environment running in a way that is useful to me...
BTW Did I ever tell you I hate XML.

That's enough for one day...


A list of random TLA's I might have used...

CAN -Controller area network,  initially developed for automotive communications
GNC - Guidance and navigation control, aka where are we pointing.
HAZ - Heat affected zone, ie a welding term
IMU - Inertial measurement unit
ITAR-International Trade in Arms Regulations aka don't sell ballistic missiles to bad guys.
LIN - Local interconnect Network. A single wire asynchronous communications protocol.
LLC- Lunar lander challenge aka the contest that started Unreasonable Rocket.
OTS- Off the Shelf,ie purchased and unmodified.
SDR- Software defined Radio
TVC- Thrust vector control.
TLA Three letter acronym.