Dad Man Walking
Dontree Member
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- Aug 26, 2012
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Gentledudes and dudettes,
I'm interested in your thoughts/advice/warnings/random thoughts about a project I'm about to take on.
I'm helping a college student complete a rocketry/robotics challenge that he was engaged in during the school year. The challenge involved launching a rocket that would deploy a payload at >1000 feet. The payload is a robotic device--a rover--that has to detach itself from the recovery gear after landing, traverse potentially very rough terrain, stop to take a soil sample, and beam photos back to the rover operator. The rocket just has to get back down safely, separate from the rover.
The student team had a robot crew and a rocket crew. The robot got done but apparently the rocket crew didn't get too far. So the rover is home for the summer and the student wants to build a rocket and execute the mission before going back to school.
I've looked a couple of Arliss designs, but don't really want the complexity (altimeters) or need the re-usability of an Arliss rocket. My goals as the designer and flyer are to keep things simple and as cost effective as possible, while making sure that we get the payload out and get the rocket back down safely.
Some parameters and constraints:
My idea right now is to deploy the payload via a piston. My sketch of the basic layout is in the picture below.
The piston will be a 6-12" section of coupler tube with bulkheads on both ends. The piston will rest on a shelf or ledge made of a centering ring with most of the middle cut out.
The top centering ring will be about 3" beneath the piston shelf. I think this will provide enough room to hold the main and shock cord, and I want to minimize the volume that is pressurized with the deployment charge. My preliminary calculations indicate that a modest charge of just 1 to 1.5 grams will generate enough pressure to hit the piston with nearly 600 pounds of force due to the large surface area of the piston. But I have no idea what will happen as the piston moves through the body tube. The volume will expand significantly, the pressure will drop, and I don't know if that 600 pounds kick is actually enough to push the piston all the way out, or if it might just break things.
So ground testing will be done...
I am also thinking (hoping?) that the NC should be pushed out while the piston is pressurizing the upper chamber since there is no need for shear pins there. But if there's not enough energy to push the piston all the way out, maybe putting a drogue on the nose cone could create enough drag to pull the piston the rest of the way out?
I'm expecting the main parachute to be packed loosely in the lower compartment, so as long as I can get the piston all the way out I'm expecting that the shock cord and parachute will be extracted in short order. But should I be worried?
I want to make sure that the payload (the rover) can fall away from the rocket and deploy it's own parachute cleanly. I'm considering using a JL Chute Release and maybe a small drogue to slow the 4 pound payload until the main sets. Or maybe some sort of homemade deployment bag, where a drogue sets first and then pulls the main free. I've used the JLCR, but don't have experience with deployment bags.
One other thing I'm considering--not illustrated in the drawing--is to bring the NC and the booster down separately. If the deployment charge can push the NC free of the booster and the parachute is packed so that it will take a second or two to unfurl that might give time for the NC and the payload to fall away from each other before either sets a parachute. But is also means that the deployment charge has to do all the work in getting the piston completely out.
So that's what I'm thinking. Any feedback is greatly appreciated!
Rough drawing in the link
I'm interested in your thoughts/advice/warnings/random thoughts about a project I'm about to take on.
I'm helping a college student complete a rocketry/robotics challenge that he was engaged in during the school year. The challenge involved launching a rocket that would deploy a payload at >1000 feet. The payload is a robotic device--a rover--that has to detach itself from the recovery gear after landing, traverse potentially very rough terrain, stop to take a soil sample, and beam photos back to the rover operator. The rocket just has to get back down safely, separate from the rover.
The student team had a robot crew and a rocket crew. The robot got done but apparently the rocket crew didn't get too far. So the rover is home for the summer and the student wants to build a rocket and execute the mission before going back to school.
I've looked a couple of Arliss designs, but don't really want the complexity (altimeters) or need the re-usability of an Arliss rocket. My goals as the designer and flyer are to keep things simple and as cost effective as possible, while making sure that we get the payload out and get the rocket back down safely.
Some parameters and constraints:
- Rover was designed to fit into a 6" or 7.5" tube, so we're using blue tube (7.5")
- Rover weight is around 4 pounds
- Maximum motor is a K. My sims of the basic airframe are showing a 2000-2500 foot flight on a mid-level K, which is perfect for our purposes.
- I want to avoid using deployment electronics if possible. I'd like to use motor deploy to pop things open shortly after apogee, and get the rover clear of the rocket so that the recovery packages won't get fouled with each other.
My idea right now is to deploy the payload via a piston. My sketch of the basic layout is in the picture below.
The piston will be a 6-12" section of coupler tube with bulkheads on both ends. The piston will rest on a shelf or ledge made of a centering ring with most of the middle cut out.
The top centering ring will be about 3" beneath the piston shelf. I think this will provide enough room to hold the main and shock cord, and I want to minimize the volume that is pressurized with the deployment charge. My preliminary calculations indicate that a modest charge of just 1 to 1.5 grams will generate enough pressure to hit the piston with nearly 600 pounds of force due to the large surface area of the piston. But I have no idea what will happen as the piston moves through the body tube. The volume will expand significantly, the pressure will drop, and I don't know if that 600 pounds kick is actually enough to push the piston all the way out, or if it might just break things.
So ground testing will be done...
I am also thinking (hoping?) that the NC should be pushed out while the piston is pressurizing the upper chamber since there is no need for shear pins there. But if there's not enough energy to push the piston all the way out, maybe putting a drogue on the nose cone could create enough drag to pull the piston the rest of the way out?
I'm expecting the main parachute to be packed loosely in the lower compartment, so as long as I can get the piston all the way out I'm expecting that the shock cord and parachute will be extracted in short order. But should I be worried?
I want to make sure that the payload (the rover) can fall away from the rocket and deploy it's own parachute cleanly. I'm considering using a JL Chute Release and maybe a small drogue to slow the 4 pound payload until the main sets. Or maybe some sort of homemade deployment bag, where a drogue sets first and then pulls the main free. I've used the JLCR, but don't have experience with deployment bags.
One other thing I'm considering--not illustrated in the drawing--is to bring the NC and the booster down separately. If the deployment charge can push the NC free of the booster and the parachute is packed so that it will take a second or two to unfurl that might give time for the NC and the payload to fall away from each other before either sets a parachute. But is also means that the deployment charge has to do all the work in getting the piston completely out.
So that's what I'm thinking. Any feedback is greatly appreciated!
Rough drawing in the link