Water Rocket Construction - Side Deployment 2

WATER ROCKET CONSTRUCTION - ADVANCED TUTORIALS

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.

For a full list of all construction tutorials go to the Construction Index.

Parachute Side Deployment Mechanism #2

Introduction

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.

The 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.

Materials

- Corriflute corrugated plastic sheet
- 3 PET bottles
- Cardboard
- Wire
- Ping pong ball
- Timer (flight computer, Tomy Timer etc.)
- Servo motor, Battery

Tools

- Tape
- Contact glue
- Scissors
- Craft knife
- Long nose pliers
- Drill

The assembly procedure for the side deployment mechanism

Procedure

	1.	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.
	2.	Cut off the neck and the base off the first bottle. This will become the nosecone shell.
	3.	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.
	4.	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.
	5.	Now slice only one side of the rectangle half way along. Bend the rectangle to make a 'V'.
	6.	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.
	7.	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. NOTE: you could also use a Tomy timer in this arrangement, but we'll leave the mounting arrangement as an excercise for the reader.
	8.	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.
	9.	Glue these to the edges of the V with contact glue as shown..
	10.	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 the circle.
	11.	Glue the other circle to the top.
	12.	Trim off the cardboard so that the whole frame can slide inside the shell.
	13.	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.
	14.	Cut a small hole in the top of the V just big enough to pass the servo motor connector through.
	15.	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 pointing up.
	16.	Plug the servo motor connector into the timer.
	17.	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.
	18.	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.
	19.	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 bottle.
	20.	Using 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 circles. 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 for 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 some details about the required hole size.
	21.	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 photos.
	22.	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.
	23.	Now drill a set of four holes at either end of the strip. These should match the holes on the V.
	24.	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. Bend down the twisted wire.
	25.	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.
	26.	Next you need to make a hole in the end of the door for the rubber band to fit through. You can 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.
	27.	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.
	28.	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 quick. The ball is there purely for aerodynamic purposes. If you are using larger bottles, you may want to use a larger plastic ball for this.
	29.	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.
	30.	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.
	31.	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.
	32.	Curl the shrunken end of the bottle on an old frying pan on low heat. You can use the curling technique shown in the example above.
	33.	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 pressure chamber. Slide the base over the top of your rocket.
	34.	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 added strength.
	35.	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 the flight.
	36.	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 the circles.
	37.	You need to configure the start and end servo positions. Do this according to the manual. 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.
	38.	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. We 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.

30/8/2011