Doug Conner attended Maker Faire in San Mateo, Calif., and was impressed by a compressed-air rocket demonstration. These are not actual rockets -- they're projectiles -- but he was sufficiently inspired to go home and make his own PVC-based rocket and launcher. He started sending rockets 200 to 300 feet high from his backyard. Then a brainstorm hit. What if you could watch the flight from the rocket's point of view?
Conner decided to strap a video camera on to the rocket. This required calculations to accommodate the additional weight of the camera. He increased the body diameter and length of the rocket and sent it up with a live camera shot of the trip.
Doug Conner calculated that he could achieve approximately the same flight with the extra weight of a camera if he increased the body diameter and length.
Doug uses a launch pressure of 45psi for the flights, which typically last 7.1-7.4 seconds.
You really need to read the article before commenting. No PVC pipes or steel ones are flying. The PVC is a launch tube and steel would be safer because it would not have a brittle fracture problem like PVC.
The "rocket" itself weights 60 grams and is mostly paper and foam shock absorbing material. Although I try to avoid being hit by it, I don't think it would do much damage to me. I fly my rockets on my property and I'm the only one that they could land on.
I suppose the absolute answer is more a question of how much acceleration your payload can withstand. These are projectiles, not rot really rockets, so the speed and eventual maximum altitude are limited by the barrel length and the acceleration.
200g acceleration over 20 inches will result in 146.5 ft/sec, 400g will get you 207 ft/sec.
For a launcher built from PVC pipe such as I'm using, I limit the maximum pressure to 50 PSI. This is well below the pressure rating for the PVC, but PVC under pressure fails with a brittle fracture that is very dangerous with compressed air. If you want to go with higher pressure you should encase the PVC in steel that can contain any potenetial explosion of the PVC. Better yet use a metalic pipe rated for the pressure that will fail gracefully if it does fail.
My analysis shows that I should be able to get a 100 gram to 120 gram total mass up to 250 to 300 feet with the PVC type technology I'm using. To do this I'll double the length of the 2 inch air cylinder and increase the rocket body diameter to something around 1.5 inches and lengthen the launch tube slightly.
To go larger and higher you'd probably want to go with a higher pressure system, or a real rocket.
October Sky - Now thats a GREAT movie, Charles! Very inspiring. I remember watching those boys in their rocket house blowing up rockets until they got it right. I need to go rent it again. We did a birthday party a few years ago and bought a 12 pack of easy to build rockets for one of our son's birthday parties. We took them to the park by our house and all the kids got to shoot off their rockets. So much fun is to be had with model rocketry!
I'm still using the original camera. it has survived quite a few flights. Even if I use a parachute for a gentle descent, the camera still has to withstand around a 200 g launch acceleration. It's a good thing the camera is inexpensive, I never would have tried this with a $100 camera.
As far as more construction details you should try the build instruction link. That will let you download what should be sufficient information to build one of these.
I've already got a 3-axis accelerometer, a 2 axis rate gyro, and a barometric pressure sensor I'm testing. All these sensors are very small and light. The weight does climb some when you start adding the microcontroller, an acutator, and a power source capable of driving the actuator. The actuator is the power problem, the rest of the electronics requires very little power.
Right now I'm working on putting a recovery system in the rocket that uses an acutator to deploy a parachute based on a set time from the launch. This is simple and doesn't require even a microcontroller. It does add more weight that I had hoped, about 20 grams. To keep the weight down I really should be implementing everything with surface mount devices but it's a lot easier to assemble through-hole prototypes (at least for me).
Once I get a reliable recovery system I'll consider adding more complex electronics.
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