Robotic Rocket

[Salik Syed]

Hi , just for fun me and some others honors physics students decided to enter a Rocket building contest.. the challenge is to build a rocket that carries an egg to 800 feet high and back in 45 seconds (the closer to these numbers you are the higher your score)


We are thinking about having 2 ejection charges, one that blows up the rocket at 800 feet (to stop its climb), and another that deploys a parachute at an optimal time. We're gonna use a pic controller hooked up to an altimeter.
what approach would you guys take?

[Nuttyman54]

Interesting concept, but I have a few questions:
1. Does the egg have to stay intact?
2. What are you using for your charges?
3. What kind of altimeter are you using?

Just a small note:
I've done a competition like this, and only relying on a parachute is not very safe. Have some back up insulation around the egg, as it will get hit pretty hard. Another small thing: try and test out your ejection charge before the test, because the judges will most likely want a whole egg back, not just some black ash.

And, on a closing note, I'm gonna quote an old teacher of mine. "When in doubt, copy NASA." Go for 3 parachutes, just for added stability. However, make sure you don't use too large parachutes, or you might have the egg drift too far when coming down.

[Cory]

I'm not sure what you're refering to about "blowing up" the rocket.

Are you talking about a normal ejection charge that just shoots out the top of the rocket body?

Because that will halt most of it's upward movement, if not push it downwards, and it will eject your payload.

I'm not entirely sure how you'd go about keeping the parachutes attached to the egg from deploying at this point though.

Ideally you'd probably want to be able to use an engine that would put the apex of the rocket's trajectory at just over 800 feet, and then you could time the ejection charge to go off once it's fallen as low as you can comfortably open the parachutes.

[Gdeaver]

If it's the contest I'm thinking of, additional electronics are not allowed for the ejection charge. You may want to get a copy of a program called Roc Sim. It's a combination of a cad program and a simulation program. With it you should be able to design a rocket-engine combo that gets very close to the altitude by design. One parachute for model rockets is more reliable than more. If you can use additional electronics then a pic sampling a pressure sensor like a Freescale MPX4115 is the way to go. 10 bit sampling would be best. As for the time it takes the rocket to come down under chute, there are some web sites with descent rate calculators.