Hey, so much to talk about. Been busy. We've decided to tie the kevlar with a slip knot. John from 3Dogs sent a diagram of the knot. The airframe material along with some more removable rivets arrived. I don't have a reliable way to cut fiberglass tube so I ended up using a dremel tool with a grinding wheel. I had a friend pour water over the cut as I did it to reduce the airborn dust. The SPDT switches from Public Missiles came in and the only thing I needed to do was bend the leads over that I soldered the switch wires to because I'm starting to get pretty low on room in the altimeter bay. Drilling and sawing the switch hole took some time. I read in the Perfect Flight MiniALT/WD+ manual on a method for testing the rocket on the ground. It involves putting a suction cup over the end of a long piece of 1/8" dia. tubing and then sucking on the altimeter bay breather hole. I attached Christmas tree light bulbs to the Main and Drogue connections on the altimeter and then ran them out their respective ends of the altimeter. When it came time to test I was having a hard time "tricking" the altimeter into triggering its' launch events. When the whole rocket is assembled it is next to impossible to provide enough suction to get to apogee and then maintain that suction so that a distinct Main event is visible. What finally worked was using a vacuum pump. The pump can maintain a constant suction rate which allows for a distinct apogee event and then one can wait as long as you want to remove the suction cup and you will witness the fore light bulb flash which is indicating that the Main chute would have been deployed. At this point I'm going to try and use a power inverter in a vehicle to do some live ground tests with BP and the vacuum pump. That will help me determine how much BP is necessary to deploy the drogue and to shear the pins in the nose cone. It should be noted that I went with #1-64 screws instead of the #2-54 screws. I'm hoping this will still be plenty while not requiring as much force to separate. I used three of them equally spaced around the nose cone. Pictures to follow shortly.
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Hey, it's 10-10-10. Nifty! So much to talk about. The altimeter bays are coming along nicely, we are just waiting for the brass caps that were out of stock at Lowes. Got the idea for the ejection canisters from Vern Knowles rocketry website. The piston is modeled after the way that I made them when I built a Public Missiles AMRAAM 4 a couple of years ago. I did go to the trouble of having one of the students weld our "D" rings in order to provide an extra layer of protection with the piston. We've decided to attach the Kevlar at the attachment points using a bowline knot and then just electrical or masking taping off the ends to discourage fraying. The shear pins were confusing but after much searching around the net I found that 3 #2-54 nylon screws is most likely what we will use. The thought is to place them near the top of the rocket where the nose cone inserts. They will be evenly spaced. I found an online calculator for black powder and shear pin recommendations as well as some info and Vern Knowles site. In the end, I'm thinking that approx. 1.2 grams of black powder will be enough to shear those pins. Of course we will perform some ground testing so that we can have a successful flight. I did manage to find some smaller #1-68 nylon screws just in case the #2-54's are too thick but I don't think that it will be necessary. We're waiting for the airframe piece from 3Dogsrocketry so that we can begin building our switch bands on the altimeter bays. The switches(Single-Pole Double-Throw slide switch, use for altimeter on/off. 6 amp rating, 3 eyelet terminals for easy soldering; Fits in 1/4" x 1/2" hole in airframe) we found on the public missiles site. Also thinking about swivels for the parachutes. Oh yeah, we got some removable rivets from 3Dogs but I lost them but I was able to find them at Public Missiles site. We are going to use those for attaching the altimeter bay "permanently" to the forward airframe for flight.
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Spent most of the day Saturday figuring out how to setup the altimeter bays. The instructions are here. It was quite a chore to figure out the ejection canisters but in the end we found some pieces of plumbing hardware at Lowes. The initial bay is done and the instructions that are linked to here will guide the students through making their own. Let's keep our fingers crossed. ;)
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Just been working cutting the brass tubing for the altimeter sleds. Drilled the holes for the MAWD Perfect Flight Altimeters and epoxied the brass tubing to the back of the altimeter sleds. I spent some time tonight figuring out the best way to put the ejection charges in the rocket. Soon I should have a picture of what I figured out.
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So it took a while for us to figure out how we were going to hold onto the aft section of the rocket while doing dual deploy. It seems that one of the biggest hurdles to doing minimum diameter is attaching shock cord to the fin can assembly. After a little digging I found that Aerotech and also Cessaroni do sell a forward bulkhead that has a threaded hole in it. The hole can be used to attach eyebolts. So we obtained the casing from Balsa Machining as well as our motors. We decided to go with 5 H124 White Lightnings and 2 I motors, which I do not remember their impulse or propellent type.
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As per the instructions phase 1 from 3 dogs we epoxied on the centering rings to the motor mount. Then we epoxied in the motor mount with the top centering ring and only friction fit the bottom motor mount centering ring so that we may have access to the fin attachment point if need be. Then 3 Dogs sent us a fin jig for the Little Dog Dual Deploy (LDDD) with which we tacked on our fins with epoxy.
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The first step in this project was to give the kids their first milestone. This milestone on the project consisted of two parts. The first part the students were to mockup the little dog dual deploy in Rocksim or equivalent software (i.e. Open Rocket or SpaceCAD). The next part of the project was to sand and complete the steps found here. As this was to be our first minimum diameter rocket there was some confusion as to how the aft section of the rocket was going to be connected when we separated the rocket at apogee. Though there are many techniques we finally decided to use an Aerotech motor casing with a threaded forward end closure for attaching an anchor which was available from Balsa Machining. It seems that Cessaroni has not addressed this issue with their casings at this point but we have heard that there are work arounds.
We decided that the project this year was going to be for our 2nd year IB physics class to construct and fly dual deploy rockets. The goal is to introduce the students to more sophisticated rocketry techniques than they have been exposed to in their earlier courses.
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