I have decided to place a parachute deployment system on my water rockets for 4 reasons:
1. The rocket is destroyed on ground impact.
2. It is impossible to place an onboard micro-camera as flight recorder because of (1).
3. I want to extend the total flight time (the descent phase will take more time).
4. It will be more fun..
So what does the parachute deployment system need to do?
1. Successfully deploy a parachute that will unfold before ground impact.
2. Deploy it on the beginning of the descent stage so it will not affect the apogee height and also give it time to fully unfold by the air drag.
3. Since the rocket is descending and points downwards, the parachute should be placed and deployed from the rear.
4. Avoid using the air drag (flap) to detect the descent phase, because it will decelerate the rocket on the accent phase or make the flight erratic.
My first attempt was to place the parachute inside the nose cone and let one side of the cone loose in order to separate and let the parachute out upon descent. It was a failure, because the loose nose cone made the flight very erratic, the apogee was dramatically lowered and the parachute never deployed on time (sometimes earlier, others too late or never). I can remember one occasion when after a crazy flight the parachute fully unfolded just about 1m before hitting the ground.
My second design was to deploy it from the rear end, however soon it became clear that the parachute had to be placed in a small box that will open on the beginning of the descent phase, otherwise it was going to unfold on ascent phase. I needed to find a mechanism to detect descent. Also since all bodies fell with the same acceleration (Newton’s law) and I don’t want to use the air drag, the parachute somehow had to be ejected from the box.
So the challenge was: First detect descent then eject the parachute.
I solved the second part by placing the folded parachute in a small box in the tail of the rocket just next to the water nozzle. Inside the box there is a spring under the folded parachute. The box cap keeps the spring squeezed and the parachute inside and it is released by removing a pin. It’s like a toy box which a clown pops up when you open the cap. This simple device (eject device) really did the job and the parachute ejected nicely!
However the problem remains. How can I detect the descent phase?
My current approach is to bypass the detection and pull the pin by a dc motor some seconds after launch. So the equipment on board will be:
1. The eject device with the parachute (already built)
2. A dc motor with gears to pull the pin (got one from my sons’ toy cars)
3. A small electronics board to count down about 4 seconds (apogee occurs around 3 seconds after launch) and then power the motor (this will be the onboard computer!)
4. A small camera battery (4LR44 @ 6V)
This approach increases the total weight of the rocket by several grams, but it’s the only viable solution that I have in mind for now and also I could decrease a bit the volume of water in the rocket.
So the flow is: 1) Launch (power up the circuit *) > 2) Countdown 4 seconds (circuit) > 3) Power up the motor > 4) Pull the release pin > 5) Eject the parachute and stop the motor (**) > 6) parachute unfolds by air drag.
(*) I will need a switch that turns on the circuit on launch.
(**) Don’t know how to yet.
The electronic circuit of time delay will be based on a 555 timer IC and will use a potentiometer to adjust the delay. The desired value is around 4 seconds. I have combined some time delay circuit layouts that I found on the internet and ended up to this.
The switch will close on launch to start counting.
Since I don’t know much about electronics I hope it will work.
After building and testing it on the ground I will post pictures and the test results.
Thanks for reading.
1. The rocket is destroyed on ground impact.
2. It is impossible to place an onboard micro-camera as flight recorder because of (1).
3. I want to extend the total flight time (the descent phase will take more time).
4. It will be more fun..
So what does the parachute deployment system need to do?
1. Successfully deploy a parachute that will unfold before ground impact.
2. Deploy it on the beginning of the descent stage so it will not affect the apogee height and also give it time to fully unfold by the air drag.
3. Since the rocket is descending and points downwards, the parachute should be placed and deployed from the rear.
4. Avoid using the air drag (flap) to detect the descent phase, because it will decelerate the rocket on the accent phase or make the flight erratic.
My first attempt was to place the parachute inside the nose cone and let one side of the cone loose in order to separate and let the parachute out upon descent. It was a failure, because the loose nose cone made the flight very erratic, the apogee was dramatically lowered and the parachute never deployed on time (sometimes earlier, others too late or never). I can remember one occasion when after a crazy flight the parachute fully unfolded just about 1m before hitting the ground.
My second design was to deploy it from the rear end, however soon it became clear that the parachute had to be placed in a small box that will open on the beginning of the descent phase, otherwise it was going to unfold on ascent phase. I needed to find a mechanism to detect descent. Also since all bodies fell with the same acceleration (Newton’s law) and I don’t want to use the air drag, the parachute somehow had to be ejected from the box.
So the challenge was: First detect descent then eject the parachute.
I solved the second part by placing the folded parachute in a small box in the tail of the rocket just next to the water nozzle. Inside the box there is a spring under the folded parachute. The box cap keeps the spring squeezed and the parachute inside and it is released by removing a pin. It’s like a toy box which a clown pops up when you open the cap. This simple device (eject device) really did the job and the parachute ejected nicely!
However the problem remains. How can I detect the descent phase?
My current approach is to bypass the detection and pull the pin by a dc motor some seconds after launch. So the equipment on board will be:
1. The eject device with the parachute (already built)
2. A dc motor with gears to pull the pin (got one from my sons’ toy cars)
3. A small electronics board to count down about 4 seconds (apogee occurs around 3 seconds after launch) and then power the motor (this will be the onboard computer!)
4. A small camera battery (4LR44 @ 6V)
This approach increases the total weight of the rocket by several grams, but it’s the only viable solution that I have in mind for now and also I could decrease a bit the volume of water in the rocket.
So the flow is: 1) Launch (power up the circuit *) > 2) Countdown 4 seconds (circuit) > 3) Power up the motor > 4) Pull the release pin > 5) Eject the parachute and stop the motor (**) > 6) parachute unfolds by air drag.
(*) I will need a switch that turns on the circuit on launch.
(**) Don’t know how to yet.
 |
| Time delay electronic circuit |
The electronic circuit of time delay will be based on a 555 timer IC and will use a potentiometer to adjust the delay. The desired value is around 4 seconds. I have combined some time delay circuit layouts that I found on the internet and ended up to this.
The switch will close on launch to start counting.
Since I don’t know much about electronics I hope it will work.
After building and testing it on the ground I will post pictures and the test results.
Thanks for reading.
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