Im working on a rocket project for school, it works like this: We have a small rocket, it will fly a few hundred meters up and descend on a parachute. Inside the rocket there is a pi zero w, a barometric pressure sensor to measure the altitude and a servo to release the chute once the rocket is at its apex. The altitude data is saved in a file and can be retrieved via a usb drive once the rocket is on the ground again. Now this works really well in testing but hasn't been flown in a rocket jet, I guess it will work fine, but I'm kinda worried that the altitude measurement will be flawed and the chute therefore wont open. Because of this I thought it would be awesome to be able to release the chute remotely from the ground via some kind of radio, this comm could also be used to get the altitude data while the rocket is still flying. I really don't know how to achieve this radio comm, I read a lot about different kinds of radio that could maybe be used, but I'm really not into radio so i don't know what to do. If you have any cheap and relatively easy to implement ideas, I would be incredibly thankful.

  • Wouldn't a gyro or accelerometer be easier than a radio. – Steve Robillard Jun 3 '18 at 22:22

The Pi Zero W has WiFi capability, and that will be your best/easiest option to implement wireless control. A few hundred meters may be pushing the limit for WiFi, but since it's essentially "straight up" it might work fine. You'll need to do some testing to determine the range limit, and you should do this testing with the Pi mounted in the rocket just as it will be when it flies. And give yourself the benefit of getting the rocket above the ground as much as you can manage by mounting on a pole (if that's possible) when you do your testing. I say this because elevation makes a huge difference in rf propagation losses.

Your range can also be increased with a small investment in a directional antenna for your "ground station". This one from Amazon is fairly low cost, will extend your range to perhaps 400 meters or more. The downside of this is that the antenna gets its "gain" from being directional, and that means it will need to be pointed at the rocket. This shouldn't be too difficult though, as the beamwidth will be in the range of 30 - 40 degrees. You can work out the "pointing error" of this antenna as a trigonometry problem!

But there may be an easier alternative - easier than wireless remote control that is. You could start a timer in the RPi when the rocket takes off, and use the timer to make a decision to deploy the chute. The challenge here will be how to start the timer at "liftoff". That's something you can contemplate with your classmates.

Those are two options, broadly defined, that can provide the solution you need. My final suggestion is to give these some thought, weigh them up, make a decision, and sketch out some possible implementations. Once you've progressed to a preliminary design, post follow-up questions with more details. We'll be here for you.

  • Nice answer. I wonder if it would be feasible to also deploy the chute when the WiFi SSID is lost or drops below a certain RSSI as a fail-safe? Might not be fast enough though... – Roger Jones Jun 14 '19 at 17:59
  • @RogerJones: Offhand, I don't know. You could try posting it as another question, or at Ingo may know offhand? – Seamus Jun 14 '19 at 20:17

A radio signal would be a difficult thing to implement without weight issues, would it be possible to calculate distance/altitude and use within the program a timer circuit to initiate a release once desired lift altitude as been reached?

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