These tutorials show you how to build some of the components
we use on our rockets. While it may not always be possible to
reproduce these components exactly, many of the designs can be
customized based on the materials you have available.
The following tutorial is an updated design from our
previous version of the side
deployment mechanism. This design incorporates a couple of
improvements which we have been using in the couple of years since the
last tutorial was made.
rubber band ejection plate has been replaced with a section of
PET bottle. This is easier to construct and doesn't rely on
rubber bands that can deteriorate over time. It also increases
the ejection force.
The other improvement is the
direct release of the parachute door. The latch and pin have
been removed greatly simplifying the construction. This
arrangement also allows you to use smaller servo motors. Here
are more details.
Specific dimensions will
depend on the bottles you use and how much space you want to
allocate for your parachute. The dimensions we give here are for
this particular deployment mechanism using
90mm 1.25L bottles.
- Tape - Contact glue - Scissors - Craft knife - Long nose pliers - Drill
The assembly procedure for the side deployment
Start with 3 clean bottles with a nice aerodynamic shape
and straight sides.
Remove the labels and clean off the glue with mineral
turpentine. Wipe the bottles clean with a dry rag.
Cut off the neck and the base off the
first bottle. This will become the nosecone shell.
Cut two circles out of some Corriflute
sheet. The size of the circle will depend on the
diameter of the bottle you are using. Make sure that the
circle is a snug fit but not very tight. In this example
the circles are 90mm in diameter.
Cut out a rectangular section from the Corriflute
sheet. The size of this will vary depending on your
bottle size and the height you want to make it. Make it
taller to fit bigger parachutes. The corrugations should
be oriented vertically. Here we are using a 140mm wide x
85mm high rectangle.
Now slice only one side of the
rectangle half way along. Bend the rectangle to make a 'V'.
Cut a slot for the servo motor. The
servo motor should be positioned so that one side
(rather than the axis) of the
servo is on the centerline between the two ends of the
rectangle. It also needs to be located away from the
edge so it fits inside the V and that the
servo horn fits within the radius of the bottle.
Now drill 4 holes along both edges of the
rectangle. Space these about 15mm from the edge. Also
drill holes for the mounting holes of the flight
computer/timer. Here we are using our
Servo Timer II.
you could also use a Tomy timer in this arrangement, but
we'll leave the mounting arrangement as an excercise for the reader.
Next, cut 4 strips of thick cardboard and bend them 90 degrees along
their lengths to make four 'L' shaped brackets. They only
need to be about 10mm x 10mm.
Glue these to the edges of the V with contact glue as
Now glue the V to one of the circles.
The spine should go to the edge of the circle. Open the
V wide enough so that the sides also touch the edge of
Glue the other circle to the top.
Trim off the cardboard so that the
whole frame can slide inside the shell.
Insert the servo into the slot. We
normally cut the slot just a little smaller than the
servo and then push the servo in. This helps to hold the
servo motor tightly in place.
Secure it with one or
two small self tapping screws.
Cut a small hole in the top of the V
just big enough to pass the servo motor connector
Mount the Servo Timer II on the other
side of the V. You can use machine screws to secure it, but we
prefer to use wire ties. These place less stress on the
board during crash landings. They are also a little
lighter than screws.
Make sure that the board is
oriented the correct way round with the G-switch
Plug the servo motor connector into the
Place a strip of double sided tape on
the top circle. Stick a 9V battery to the tape and
secure it with another loop of wire. This helps keep the
battery in place. The 9V battery is located on top to
keep the center of gravity as far forward as
possible on the rocket.
NOTE: You can also use a wide variety of batteries
for the timer including much lighter LiPo batteries.
Clip on the battery clip. Note that you
may want to cut a notch in the side of the circle to let
the wires pass from the timer to the battery. This makes
it easier to slide the whole mechanism into the shell.
Slide the mechanism into the shell
so that it is about an inch from the bottom. The top
circle should still be below the curved part of the
a felt marker, mark out the hole for the parachute. The hole should be a
little wider ~3mm than the two sides of the V. This
allows space for the ejection plate to flex. Vertically
the hole should be just smaller than the inside edges of
The diagram on the right shows the two
positions of the ejection plate. Cut the hole for the
parachute so that the ejection plate (in red) can sit as
shown when deployed.
Also mark any access holes
the buttons on the timer as well as the servo motor access
hole. This hole should be a long slot to allow you to
hook the rubber band onto the servo horn, and allow the
rubber band to easily slide off. The servo horn should
be on the inside of the bottle at all times. Here are
about the required hole size.
Now cut out all the necessary
holes. We normally use a little methylated spirits to clean
off any pen marks after cutting out the holes. We've
left them here to make it easier to see the edges in the
Cut out a section of another clean
bottle. This will be the ejection plate that pushes the
parachute out. The length of this piece should be such
that it wraps around the two vertical sections of the V.
The height should be such that there is about a 5mm gap
at the top and bottom. This allows the ejection plate to
move freely without getting caught up on anything.
Now drill a set of four holes at either
end of the strip. These should match the holes on the V.
Using a couple of wire ties secure the
ejection plate at either end. Tighten the ties using a
pair of pliers and then trim off the excess.
the twisted wire.
Cut off another section of bottle. This
is the parachute door. We
normally round off the edges on one side to help prevent
the corners of the door getting caught on the parachute
lines. We make the door narrower than the opening which
allows the parachute cord to emerge from under the door.
We also usually straighten the door somewhat to make
it spring open and away from the parachute.
Next you need to make a hole in the end
of the door for the rubber band to fit through.
use a drill or a hole punch, but we find that heating up
a nail or screw of the right size and then pushing it
through the door makes a nice clean hole with rounded
edges. This stops the rubber band being cut by a sharp
edge of the door.
Tape the door to the side of the shell
about 1cm back from the hole. We normally use thick
clear packing tape for this.
White tape is shown here to make it easier to see.
Add a second piece of tape
to the inside of the door. This gives you a very good
hinge for the door.
Cut out the left half of a ping pong
ball and glue that into the nosecone. We normally just
use regular contact glue for this as it's nice and
The ball is there
purely for aerodynamic purposes. If you are using larger
bottles, you may want to use a larger plastic ball for
Now slide the whole mechanism into the
shell. You will have to push down the ejection plate to
get it into the shell. Once you have pushed it in far
enough, the ejection plate will pop out again through
the parachute hole.
The following steps describe how to
mount the deployment mechanism on top of your
rocket. Again the exact dimensions will depend on the
size and shape of the rocket you are attaching it to.
Get another clean bottle and cut off
the bottom and trim it square. This will become the
base the nosecone and deployment mechanism will sit on.
Shrink the end of the bottle at little
more than an inch by placing it for a few seconds into
hot water about 72C. This will allow the nosecone to
slide over it. See this
technique for more info.
Curl the shrunken end of the bottle on an old
frying pan on low heat.
You can use the curling technique shown in the
Now trim off the top section of the
bottle. The length of this base should
be long enough to allow the nosecone to sit clear of the
Slide the base over the top of your rocket.
Tape it in place. We like to use
electrical tape because it nicely conforms itself to the
join. It also makes it easy to remove if you want to
swap it with another rocket.
Use a couple of wraps for
Slide the nosecone over the base
so that the lower circle rests up against the curled
section. This provides the support during the boost phase of
Tape the nosecone in place. Again you
can use a couple of wraps for added strength.
If the mechanism is loose in the shell
you can place a couple of pieces of tape from the lower
circle over the edge of the shell. This will keep it
from moving side to side and forward in the nosecone.
Alternatively you can use a small self tapping screw
through the shell wall and screw into the side of one of
Note that you may need to remove the servo horn and
rotate it on the axel. See
here for the
ideal start and end positions of your servo motor.
Insert a rubber band through the hole
in the door.
The deployment mechanism is now complete. You can now
pack the parachute and push it against the ejection
plate until it is inside the deployment mechanism. Pull
the door over the parachute to hold it down and hook the
rubber band over the servo horn.
normally tie the parachute to the side of the rocket so
that when the rocket is descending it comes down
sideways adding extra drag.
The last thing to do is set the time on the timer and
you are ready for launch.