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#181 - Acoustic Apogee 2

#180 - Light Shadow

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#178 - Acoustic Apogee 1

#177 - Reefing Chutes

#176 - 10 Years

#175 - NSWRA Events

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#168 - Casual Flights 2

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#163 - Channel 7 News

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#160 - Chasing Rockets

#159 - Measurement

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#156 - Foam Flights

#155 - Down The Barrel

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#153 - ClearCam

#152 - Mullaley, Axion G2

#151 - Competition Day

#150 - Rocket Salvos

#149 - Glide Fins

#148 - Too Windy

#147 - Descent Rates

#146 - G2 Launcher

#145 - Harness

#144 - Water vs Foam

#143 - Whalan Reserve

#142 - Doonside

#141 - Windy

#1 to #140 (Updates)



Each flight log entry usually represents a launch or test day, and describes the events that took place.
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Day 86 - In-line Parachute Deployment Mechanism
Components of the in-line deployment mechanism. Nosecone, base and PET ring.
Bottom view of the base. Skewer stick provides attach points for nosecone.
The parachute is placed on top of the base.
The nosecone and PET ring are pressed down over the parachute and secured by rubber bands to the servo.
Side view. The PET ring prevents the parachute from moving around.
An early nosecone prototype using rubber bands and ejection plate.
Top view of the same prototype.
In-line deployment mechanism ready for its first flight.
Launched at 130psi
The nosecone is attached to the main parachute line to prevent it being lost.
A Tomy timer version of the same mechanism.
The rubber bands simply wind up around the Tomy timer spindle
Polaron VIIIx on the pad for the first launch of the day.
The recovery crew is quickly on the scene.
Launch #2. DV camera decides to munch the DV tape.
Prepping the igniter for Paul's 2-stage pyro rocket.
Connecting it to the launch controller.
Launch paperwork is always important.
Booster is flying on a C6-0

(Photo:Andrew Eltobaji)

Just after staging.

(Photo:Andrew Eltobaji)

Date:  10th January 2010
Doonside, NSW, Australia
 Hot (35C) with clear skies and light breeze. 5km/h early increasing to ~20km/h later.
Team Members at Event:
PK, GK, Paul K, John K and Jordan K.

This update is a continuation from day 85.

In-line Deployment Mechanism

The last couple of weeks we have been working on a new lighter and smaller in-line parachute deployment mechanism. It is partly based on Daan and Pleun's design here.

The main design criteria were: simple construction, minimal components and lightweight. The side deployment mechanism we use on our 90mm diameter rockets weighs about 135 grams including flight computer, servo and 9V battery.

The new parachute deployment mechanism will use the smaller V1.7 flight computer, with a 3.7g servo and a small 6V battery. All up it should be around 60 grams.


The nosecone is made from the tapered section of a bottle with the neck cut off. Half a ping-pong ball is glued inside the hole left by the neck. The bottom edge of the nosecone is curled on a hot frying pan to strengthen it.

The first nosecone we made had 2 rubber bands and a corriflute pusher plate. It was a little more complicated than we liked though. There are a couple of problems with using rubber bands for this application. a) They eventually perish if they remain stretched. b) They exert a greater force the more you stretch them. This means it is harder to keep the nosecone attached as they press against the parachute.

So we replaced the rubber bands and pusher plate with a simple PET ring. It is trivial to make, does not perish and the way it is folded works a little like a compound bow, in that it needs little force to hold it in place, but once released it provides enough force to eject the nosecone and parachute.


The base is made out of a straight section of bottle with one end curled. On top of the curled section is a piece of cardboard (it could be corriflute) that helps hold the base's shape and provide support for the nosecone. To stop the nosecone moving around laterally a smaller circle of corriflute is glued on top of the cardboard. This is made to fit exactly into the rounded edge of the nosecone. This design prevents the nosecone from moving sideways but once released it provides an unobstructed platform for the parachute to slide off. There is nothing for the parachute to catch on.

A bamboo skewer stick is pushed horizontally through the base and is used as the attachment pins for holding down the nosecone. Two rubber bands are attached on opposing sides of the nosecone. These rubber bands are only stretched when the nosecone is attached to the rocket. When not in use they remain un-stretched and so don't perish.


You simply place the parachute on the base and press it down with the PET ring in the nosecone. The PET ring keeps it held down so it does not move. It is possible to use a wider ring or two rings arranged in a cross form for more force, or smaller rings from narrower bottles for less force. This might be useful when using a larger parachute. The PET ring is simply taped inside the pointy end of the nosecone to prevent it falling out.

The rubber bands are then wound once around the end of the skewer stick which makes sure the nose cone is securely held down and the end of the rubber band is hooked on to the servo horn arm.

Depending on the design the parachute can either be connected to the side of the rocket, or to the top of the rocket.

If the parachute is attached to the side of the rocket then a small channel needs to be filed in the base to let the parachute cord go through. This allows the nosecone to sit flat on the base.

Alternatively if the rocket body has a neck at the top you can make a hole in the middle of the base and thread the parachute cord through and attach it around the neck. You would most likely want to use a shock cord to prevent damage to the base when the parachute opens. The nosecone itself is attached on the main parachute line to prevent it being lost during separation.

Tomy Timer version

We have also made a Tomy timer version of this deployment mechanism. Without the parachute the entire nosecone section that includes the deployment mechanism weighs only 35 grams! (See pictures at left) we have not flown the Tomy timer version yet, but will do on the next opportunity.

Test Setup

For these first flight tests we placed all the electronics in the gap between the bottles to increase the chances of survival in case of a crash. We used the 3.7g servo as will be used in the final implementation of the mechanism. The one nice thing about setting up the servo this way means that the servo isn't really under any load as all it has to do is rotate in the direction of the pull of the rubber bands. This means the servo will not need to draw a lot of current and a small battery can be used.

Eventually all the electronics and battery will be placed in the base.

The mechanism was tested on the Tachyon VII rocket. At 3.35L capacity it was launched with 1L of water, 9mm nozzle and 130psi launch pressure.

Flight Day Report

This flight day report covers both the Day85 and Day86 updates.

  • We arrived at 8 am at the launch site as usual and set up the 15mm launch pad. We knew it was going to be a hot day and so we wanted to get the mercury experiments off the ground early.
  • We launched the Polaron VIIIx rocket  at 110psi 2 times within 30 minutes. Because the rocket is made up of the spliced pairs from the exploded Acceleron V rocket, we did not want to push them to their limits. 110psi was enough for the experiment.

    Both flights went well with good landings and without damage. (see Day 85 for experiment details)
  • While I was filming launch number 2 the DV camera stopped and said that I needed to take the tape out because it was jammed. Great, at 130psi you just don't put everything on hold. I quickly switched the high-speed camera to HD video as I needed to get the flight in real time for the experiment. It all turned out well, but I don't have high-speed of the second flight. I took the tape out and wound it back into the cassette and replaced it with a spare. No more troubles after that.
  • We put the rocket aside and prepped Paul's Pod 2 pyro rocket for it's first flight of the day. We flew it first as a single stage on a C6-5 motor to get one good flight in before attempting the two-stage flight again. The flight went well again with good landing.
  • Next was the test flight of the new in-line deployment mechanism. The rocket flew well although the parachute deployed later than was expected at 6.7 seconds after launch. The deploy delay was set to 4.6 seconds. I am not sure why the chute opened that late as the rocket flew close to the sun it is hard to see from the video. Whether the air pressure on the nose was keeping it pinned down or it just took longer to open, but the parachute opened in plenty of time for a safe landing. We launched the rocket with a 9mm nozzle and at 130psi.
  • Next we set up the Pod-2 rocket for a 2 stage flight. Since the crash last launch day we made a couple of changes to increase the chances of the second stage igniting. We reduced the motor gap to about 5mm from the previous 2cm and put some tape on the inter-stage coupler to make it tighter. The flight went well and this time the second stage ignited. This was our first successful 2 stage pyro flight. The only damage was a fin snapped on the booster on landing, but a bit of epoxy will fix that up. The booster used a C6-0 motor.
  • For the second test flight of the in-line deployment mechanism I shortened the deploy delay to 4.2 seconds to make it deploy sooner. This time the parachute opened sooner at 5.76s but still later than what I would have wanted. .

    Otherwise the results of the deployment tests were successful. Next we'll need to test it on larger rockets with bigger parachutes and at higher altitudes to see how well it works. 

Highlights video from the day.

Here are Paul's "Pod-2" flights

Flight Details

Launch Details
Rocket   Polaron VIIIx
Pressure   110 psi
Nozzle   15mm, with 1200mm long launch tube
Water   2.6 L
Flight Computer   V1.6 - 5.2 second delay
Payload   Mini DV cam MD80, Zlog altimeter, Microlab mercury switch experiment
Altitude / Time   ' (m) /  seconds
Notes   Good vertical flight. Good parachute deploy past apogee as designed and the rocket landed well. Good video and altimeter data.
Rocket   Polaron VIIIx
Pressure   110 psi
Nozzle   15mm, with 1200mm long launch tube
Water   2.6 L
Flight Computer   V1.6 - 5.2 second delay
Payload   Mini DV cam MD80, Zlog altimeter, Microlab mercury switch experiment
Altitude / Time   377' ( 115 m ) / 30.28 seconds
Notes   Good vertical flight. Good parachute deploy past apogee as designed and the rocket landed well. Good video and altimeter data.
Rocket   Pod 2 (Paul's Praetor)
Motor   C6-5
Altitude / Time   ? / ?
Notes   Good flight. Parachute ejection just after apogee.
Rocket   Tachyon VII
Pressure   130 psi
Nozzle   9mm
Water   1L
Flight Computer   V1.6 - 4.6 second delay
Payload   None - Testing new deployment mechanism
Altitude / Time   ? / ? seconds
Notes   Good flight, pitched over slightly. Late parachute deployment. Good landing without damage.
Rocket   Pod 2 (Paul's Praetor)
Motor   C6-0, first stage C6-5 second stage
Altitude / Time   ? / ?
Notes   Good burn on both stages. Rocket went mostly vertically. Parachute deployed near apogee. Drifted long way down range in the wind.
Rocket   Tachyon VII
Pressure   130 psi
Nozzle   9mm
Water   1L.
Flight Computer   V1.6 - 4.2 second delay
Payload   None - Testing new deployment mechanism
Altitude / Time   ? / ? seconds
Notes   Good flight, late parachute deployment again although not as late as first flight. Good landing without damage.


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