N motor rocket

construction

Components

Basic design(PDF file)

Construction Details
 Items with links are done.

1) Makeing fins
2) Apply CF to BT's
3) Assemble fincan
4) Electronics
5) Nosecone

Additional mods...

Statistics:

Weights:
Part Bare With Glass/CF Total
NC -  1lb 5oz -
Assembled nosecone E-bay  -  2lb 10oz  2lb 10oz
Upper tube -  2lb 3oz  4lb 13oz
Fins(3) 1lb 1lb 7oz -
Assembled fincan  -  4lb 4oz  9lb 1oz
Main parachute/harness   2lb 7oz  11lb 8oz
Shear pin block   1lb 6oz  12lb 14oz
GPS telemetry  6.5oz -  
Motor hardware  12lb 6oz  -  
Propellant  15lb -  

Making fins:

As with many of my projects I decided to try something new with this one.

I wanted to try nomex honeycomb for fins.
I came up with the idea to use thin honeycomb and thin G10 in a sandwich.
The G10 would create a strong edge and the honey comb would strengthen the thin G10.

I selected 1/16in thick G10 and 1/8in thick nomex honeycomb.
There would be two pieces of the honeycomb on either side of the G10.
The honeycomb would be cut smaller than the G10 so I can make a taper with expanding foam.


Fin pieces

 


Fin test fit

I glued the pieces of the fin together with normal west systems epoxy.


Fin pieces glued

I poured two part expanding foam onto the G10 so it would expand to fill the gap between the G10 edge and honeycomb edge.


Fin foamed

I trimmed the foam with a hotwire and finish sanded it with 60grit paper.


Fin carved

There were some larger voids in the foam.
I masked off the fin with tape then I mixed up some epoxy and added microballoons to make it easy to sand.
I squeegied this onto the edge and let dry.
Once dry it was easy to sand to shape.
This is the only application for microballoons in rocketry.


Fin showing holes

I layed up the fins with two layers of CF on each side with the weive of the inner layer at 45deg to the outer layer.
I used a 500deg stable epoxy to layup the fins. My concern was because the fins were going to be attached so close to the nozzle in the 4in motor.
500deg stable is way more than needed but is much better than the 120deg value of the west systems epoxy I normally use.


Laying up CF

Once the layup was complete I vacuum bagged the fins.


Fin bagged

Here is a complete fin after removal from the vacuum bag.
Looks great!


Fin removed from bag

I trimmed the excess with my dremel. Very nice.


Fin trimmed

 

Carbon fibering body tubes:

Because the fins were going to be attached to the outside of the lower BT and the fins used 500deg stable epoxy I decided I had to use the same epoxy for at least the lower BT.

Here is a photo of the lower BT with two layers of CF applied.
I used heatshrink tape and my curring oven to process this tube.


BT with CF applied

 

Assemble Fincan:

The first step in assembling the fincan was to surface glue the fins to the body tube.
I created a paper wrap to go around the body tube so I could align the fins.
Each fin was tacked in place with CA glue.

Once they were all attached I put a generous fillet.
This was again the 500deg stable epoxy with Kevlar pulp added.

If you have ever worked with Kevlar pulp you know it generally does not make a nice smooth fillet as other fillers do.
I came up with the idea of cutting strips of release cloth and laying them over the fillet so I could smooth it with my gloved hand. Then once cured I peeled back the cloth to expose a prefectly shaped fillet.


Kevlar fillets

Next I applied two layers of 6oz s-glass from fin tip to fin tip across the BT.
But first I put down a piece of Kevlar for added strength.
This was a light cloth I aquired so not bringing it to the edge did not cause a bump.
I did not bring it to the edge, and cut it square, to avoid the hassles involved with trimming the Kevlar.
This image is the day after layup with the edges trimmed. You can see the Kevlar through the glass.


Fins glassed

I drilled and tapped two 1/4in holes in the airframe for rail buttons.
I bolted them on, then ground down the excess from the inside with my dremel.
After paint I will epoxy them in place when threaded through the airframe.

I then proceeded to sand , fill and prime it.
My wife picked out a nice Flourescent Red/Orange paint for it.


Fincan Painted

Electronics:

Recovery:
I built a special acceleration based altimeter for this rocket because of the speeds it will go.
I just didn't feel comfortable using a pressure only based altimeter.

To make programming easier I simply used a 16bit value for the velocity calculation.
This does limit the max velocity the altimeter can experience to 50G for 12sec.
I don't see this as much of an issue.
It records at 200Hz.
There is a built in delay of 15sec after apogee is detected. This delay prevents the Main altitude from being detected during the apogee seperation event due to the altimeter bay venting throught he bulkhead into the parachute compartment.


Recovery Accelerometer

Location:
I was going to use a tracking transmitter in the rocket to help in location.
I decided instead to use GPS telemetry to simply tell me where the rocket is.
This was made easy by using a Tiny Trak 3 from http://www.byonics.com.
The TT3 connects between your GPS receiver and transmitter.
It decodes the GPS data and encodes it as tones that can be sent over a normal radio.
This does require a HAM license to operate but as luck would have it, I have one.

The complete setup with 9V battery is 6.5oz and quite small. The 9V runs the TT3 and GPS.
Since the GPS is a battery hog I might switch to a larger battery pack.


GPS telemetry setup

Nosecone:

The only place I could put the electronics was in the nose cone.
I placed the NC tip in a bucket of ice water then placed a 1/4-20 threaded rod down into the tip and poured in epoxy mixed with chopped glass.
The water was to help prevent the epoxy from melting the NC. I only put in half of what I mixed. The next day I did another half.
I then cut a 1 3/4in bulk plate. I covered the inside of the NC where this would rest with filled epoxy and pushed the bulkhead down then flipped the NC so all the epoxy would pool on top of this plate.
The next day I flipped the NC over and added more filled epoxy to this end.


Inside NC

This gives two forward attachment points for the threaded rod.
This rod will help to support the electronics inside the NC.

I built a sled to hold the electronics.
I started by cutting a bulkhead out of 1/2in ply that would just fit inside the sholder of the NC.
I then cut a piece of G10 and glued it to this plate so the threaded rod could pass through.
I also wanted some support at the top of the G10 so it wouldn't rattle around inside so I cut a circle out of 1/8in plywood.
I cut this circle in half and glued half to each side of the G10.
I then slid this into the NC and sanded on the 1/8in ply till it just fit nicely.
This photo shows the sled, with recovery electronics installed and batteries in position.


Electronics sled

You can see the 1/8in ply at the end before reinforcement.
To reinforce the 1/8in ply I placed a wrap of tape around it then mixed up some epoxy with chopped glass.
I poured this into the well I made with the tape and let cure.
This photo also has a good view of the Tether that will be used to release the parachute at 1000'.


Reinforcing plate

After it cured I removed the tape and cleaned it up a bit.


Forward plate

I mounted the GPS equipment to one side of the sled.


GPS telemetry

On the other side of the sled I mounted two 9V batteries one to power the GPS and the other for the Accelerometer.
I also mounted the two accelerometers. The larger one is a PICO-AA2 and it handles dual deployment.
The smaller one(1x2in) is a PICO-AA1 and it is just along for the ride. It is sampling accleration at 1kHz.


Recovery Electronics

Because the transmitter is so close to the electronics I put a faraday cage around the recovery controller and connected it to ground.


Recovery Electronics

And the complete NC after I sprayed on the BBQ paint.


NC

Recovery Harness:

Because all the electronics were in the NC I used a pyro release to prevent the parachute from opening till it reached 1000'.
I simply attached a teather to the bulkhead and hooked a piece of thin tubular kevlar to the top of the parachute so it could not open.
You can also see the vent hole in the bulkhead for the pressure sensor in the following photo.


NC bulkplate

I did not take a photo of the other end.
I put a 1/2in forged eyebolt into the front of the motor bulkhead.
This went through an Al block securing the block to the front of the motor.
This block has 3 tapped #4 holes in it for shearpins.
Once the airframe is in place the shearpins hold it on till apogee.
Thanks to Tracy 'Woody' Wood for making the block.

 

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