Water Rocket Parachute deployment

Hi all..

Here's what i'm trying to do : I wish to deploy my parachute in my water rocket ...

I had 2 ideas.. the first one is not the i prefer but a alternative if my second one is impossible..

Idea 1 : Would be a servo that move after a specific time .. Example.. as the rocket launch, the timer start, at 10 seconds the servo move 179 degree, what deploy the parachute.

What i dont like about this idea.. is that the flight time might change each time.. so 10 seconds could be 12 next launch.

Idea 2 : Again a servo, but this time.. no timer, but instead with the help of accelerometer ( i think ) when the rocket start to move.. it wait until apogee and than it trigger the servo witch deploy my parachute..

I have been looking around and just not to sure what i should buy.. To take in consideration .. my ID (internal diameter) of the rocket is 40mm, and i think a Arduino uno 3 is larger than that ? (somewhere around 53mm)

I dont know much about arduino product (else than the 3D printer i had) so not sure i could do it with a other arduino type board than the uno 3...

If not possible with something else.. im willing to change my rocket tube seize to fit a uno 3.

Is any one able to guide me through my experience ?

Tank you ;)

Use an arduino nano or pro mini. They are small format versions of the UNO 3, (almost). As for triggering the parachute, I assume the rocket remains almost vertically upright on climb, then tips over. If that's the case, probably a simple tilt switch could detect when parachute deployment is due.

Seems kinda like over-kill for a water rocket. I have seen devices where the acceleration/gravity holds the parachute in place while the rocket ascends. When it starts to fall, the 'chute is passively deployed - no electric parts at all.

Over-kill or not.. im looking to add electronic to my rocket. Mechanic method is not what im looking for. Most of those method require some sort of flap on the side of the rocket.. witch make less aerodynamic. But hey.. if you got a good design, im willing to look at it !

For a tilt switch, i would need to look at that idea.. i would only be scared that if my flight pattern goes wrong (let say the rocket loop right at the start) it trigger the parachute to early ??

not sure if the weight of the added electronics would be worth the effort.

consider that you need power, a controller, a motor/switch

that said, the BME280 had a pressure sensor that can tell when you go between floors of your house. so, figure 3 meters is easy to know.

in thinking about this, if your rocket height goes to say, 2,000 feet, you might want to delay opening for a bit to have it land closer to the pad.

since barometric pressure would not change much in the time between liftoff and chute deployment, you could see the ground elevation pressure, then add some value to that.

say you are sitting on the pad, taking readings, last 100 are the same, then the pressure changes drastically indicating liftoff. just add some value to the average of those 100 readings and then deploy at that new value.

I am thinking digispark as the micro and the bme280 is less than half the size of a 6 pin DIP chip.

for weight i still have about 600 grams of payload left … a lipo battery, a servo and a nano board… should be that heavy ?

I would love to be able to add a arducam to it to … a altimeter maybe will see…

I dont know much about pressure sensor… lift off would make the pressure go high i guess ?

Hey Dave … i just watch a video with a Altimeter system… it use a MSP430 LaunchPad board and a SEN-11084 pressure sensor … it seem to work well …

problem is the seize of the LaunchPad… doesnt fit my rocket…

What seem nice about the LaunchPas… is that its already program and have neat little buttons to set it up …

But you are saying i could do it with the digispark… plus the bme280 plug to it … is that digisoark able to make a servo motor work ?

Than my last challenge would than be to program that stuff right ?

ckielcave:
Hey Dave … i just watch a video with a Altimeter system… it use a MSP430 LaunchPad board and a SEN-11084 pressure sensor … it seem to work well …

problem is the seize of the LaunchPad… doesnt fit my rocket…

What seem nice about the LaunchPas… is that its already program and have neat little buttons to set it up …

But you are saying i could do it with the digispark… plus the bme280 plug to it … is that digisoark able to make a servo motor work ?

Than my last challenge would than be to program that stuff right ?

the BME280 is an I2C chip. uses 3.3 volts. that means 2 pins on any Micro.
the ATTINY, 8 pin has 2 pins that you can use with the Ic2 to get the readings.
that leaves a couple pins for whatever else you want to use.

here is a battery from an electronic cigarette and my BME280.
that is a penny it is sitting on.

since it has an absolute pressure sensor, it is measuring atmospheric pressure. the higher the altitude, the lower the pressure. so you would see it relatively stable for the couple minutes it takes you to get things set and open the flood gates. once you launch, the pressure would drop rapidly then you have plenty of time to look at the last 100 readings, pick the point of launch, then just add some value to your reading and as the unit descended, you could fire your solenoid or whatever to release your chute.

BME280.JPG

BME280 Pressure Range: 30,000Pa to 110,000Pa, relative accuracy of 12Pa, absolute accuracy of 100Pa

MPL3115A2 Pressure output can be resolved with output in fractions of a Pascal, and Altitude can be resolved in fractions of a meter. The value of altitude can be read directly from the device in increments of 0.0625 meters

either of these would work. the MPL3115A2 seems to be designed for use as an altimeter. the BME280 can be used in a gamepad and allow you to move up and down to have your player move on the screen.

since either can see fractions of a meter, and I would assume you want your chute to open at more than 30 meters above the ground, you would be safe with either.

and, as you can see, your battery will be the heaviest thing, and even that can be of gossamer design. probably more for your servo than anything else.

ckielcave: for weight i still have about 600 grams of payload left ... a lipo battery, a servo and a nano board.. should be that heavy ?

I would love to be able to add a arducam to it to ... a altimeter maybe will see...

Pressure sensors is what they use to make altimeters.

I dont know much about pressure sensor.. lift off would make the pressure go high i guess ?

No, depending on how sensor is placed on rocket, its speed will affect pressure readings , but for the purpose of sensing the peak altitude (== minimum pressure value ) it is just fine,