I haven't had a chance to do much work on the TR-1 motor...I'm satisfied with the design and am ready to start machining. I just need to finish machining the hardware that I mentioned in my previous post.
I modeled the nozzle in 3D. I find that this helps with the machining if I can move the part around and think how best to machine it.
MiniSShot nozzles that I machined in that it consists of two main pieces. There were a number of reasons that we chose to construct the MiniSShot nozzle in two sections, but for the TR-1 motor the decision was made simply to ease fabrication. Constructing the nozzle from two pieces allows me to use some stock that I had on hand and more importantly significantly reduces the amount of material that I'll need to remove. I have a piece of 1018 for the shoulder portion of the nozzle and some 12L14 for the convergent/divergent piece.
Wednesday, May 30, 2012
I'm currently trying to finish up a test set-up for the SStS project that will allow us to test a single grain segment with the star core that we've used for the last two motor firings. It's simply a short section of the casing material with two end closures, one made of Aluminum and the other of steel. Looks roughly like this:
I used the new center drill indexing the steel bulkhead and the difference was immediately noticeable. Don't use dull tools kids! Anyway, after realizing what a difference it made I decided that i needed to stock up on the # 1 size center drills. I managed to find a set of four # 1 center drills on Ebay. I paid about what I did for the set from Harbor Freight, so a great deal!
Here is a shot that shows the bulkhead after I indexed it. You can see the Dremel set-up in the tool holder and the indexing holes on the main gear of the lathe. You can also see the indexing pin in the casting between the back of the chuck and the gear.
Here are a couple of shots showing the machining progression on this piece. This is the first time in a while that I've done something this larger using 1018 steel and it's definitely slower that using 12L14 steel.
Saturday, May 26, 2012
I'm starting to be able to make more time for rocketry and inevitably that means more machining. In the past year or so most of the machining that I've done has consisted of indexing and drilling holes...a lot of indexing. I use a Dremel rotary tool in the lathes tool holder to mark the hole locations in whatever stock that I'm indexing. The Dremel takes a 1/8" bit which corresponds to a #1 center drill. I have a bunch of center drills but only one of them was a #1 so it borne the brunt of the abuse over the course of this last year indexing well over 300 hole locations. I've noticed the last couple of times that I used this set-up that the bit was getting dull and last weekend indexing with it I felt that the accuracy was be compromised. I figured that I would order a bunch of #1 bits from McMaster-Carr, but they were $14 a piece, fortunately Harbor Freight carried a set for $7. Don't get me wrong, McMaster-Carr is great, they have almost anything you could ever need, some things you don't know that you need yet, the site functions well and is full of useful info, customer service and shipping are great, but a similar set (theirs has 6 bits vs 5) cost over $200. I opted for Harbor Freight, but it took a few visits before I found them in stock. I've actually been spending a lot of time restocking, cleaning, and organizing... tools, batteries, bits, etc.
Thursday, May 24, 2012
Thursday, May 17, 2012
Wednesday, May 16, 2012
With my sons first visit to the desert to view a rocket launch and to help out with the static test of the Sugar Shot to Space's latest motor a few weeks behind us, we've decided to build a rocket. The last new motor that I designed, built and flew was this one:
That was about two years ago and Theo doesn't remember it at all. That was a new motor that used an existing aero shell that had to be extended a bit to fit the new motor. The whole process of designing and building a rocket is fun for me and actually getting out and flying it is the icing on the cake. Since Theo loves tinkering out in the garage as much as I do, we're going to design and build this from scratch. We don't plan on re purposing any existing pieces, other than maybe some of the electronics. While it may take a little more time with Theo's "help". Did I ever tell you about the time I thought he was cleaning up on the other side of the garage but was actually bungee cording my motorcycles together. Despite any setbacks we may encounter, I'm really looking forward to going through the whole process with him. I'll try and document the entire process here.
Theo's requirements are that the rocket be big and orange...maybe with some blue. With that in mind the motor is going to be based on this N-class motor that I designed, built, and tested a while back. You can see that motor by going here. The biggest difference is that the TR-1 motor will utilize EMT for the motor casing. As you may or may not know, EMT is one of my favorite motor casing materials. I'm not sure why, I think it's because of other peoples attitudes towards it. I discussed my feelings about EMT, or steel in general during the development of my last motor (the one pictured above), you can read that by clicking here if you're interested. The biggest advantage that I'll get from EMT for this motor is that I can use a standard four inch mailing tube for a casting tube. Four inch EMT actually has an OD of 4.5" and with a wall thickness of 0.083" the ID should be around 4.334". That should allow for a few wraps of rosin paper to be used as an insulator, like I did in the my other design. Though with EMT this isn't necessary for the casing, but will help cut down on the heat transferred to the aeroshell. My initial 4inch motor had and ID of four inches and I was rolling the casting tubes by hand, very time consuming and messy. Using Richard Nakka's "casing" spreadsheet I found that 4 inch EMT has a burst pressure of 2573psi. With a design pressure of 1050 PSI I end up with a design safety factor of 1.7 and a burst safety factor of 2.45, pretty conservative.
I did an initial SRM design, summarized here:
While my previous N-class motor was on the edge of the M/N class this new design ends up solidly in the middle of the N-class and should provide for an awesome experience.
More to come...
Monday, May 7, 2012
I was out at the FAR site helping out with a SStS static firing and took my son along. It was his first time to the site and I think he loved it. I certainly did. I had a lot of fun watching him explore the area. He scoured the facility looking for "treasure" at one point I looked in the back of the van and found a pile of this treasure consisting of a broken cinder block, a one inch iron rod, half a dozen rocks (one of which was cool enough that we actually brought it home), and various nuts, bolts, washers, and pieces of scrap metal. We saw a couple of launches and a few static test, all in all a good day.
Souvenirs found on one of the Lunar Lander Challenge pads
Guarding the SStS motor prior to testing
Running for cover