Work has been started on Medium Trebuchet 3, at least that's what we are calling it. We are rebuilding it since we pushed it beyond its limits at LOPL 08. It's going to be the same basic size and design. The size has worked well for demonstration purposes and portability. The purpose of this build is for our Oakland Ballistics jr. team which will be headed by one of my eighth graders, Geoff Becker. Since they are a jr. team they only need to launch a 5 lb. pumpkin so we optimized the design using A-treb. I hope to finish work on it next week while my school is on spring break. A-treb says a distance of about 200 ft. with 250 or 300 lbs. I am partially using this as a determinant of A-treb since it was about 40% too high on the tennis ball treb and right on the mini treb.
Speaking of the mini's, they are still selling well. We average about 2 a week. That might not sound like much, but it's good enough for now. That should allow us to completely fund Telos.
Speaking of Telos, it's moving along well. I am still figuring out the engineering numbers. It's tough,there just aren't as many siege weapon engineers around as there used to be. One thing that has helped is reading the posts from Yankee Siege. They did a great job of describing their thought process as they figured out their new arm. Start with march or so of 08'.
I have increased the size of the plates on the throwing arm, and I am almost finished with a working design for the long end of the throwing arm, though the final design could change in favor of being more efficient. Right now, though, I aiming at funtional. Once we can launch we can be more creative with our time. Once I have those two things figured out that's it for design. Then it's just a matter of building. We are looking to get help with ordering and fabrication of the few remaining steel parts that would be needed. Hopefully I will know something in about 2 weeks. Until then, tell your friends, LOPL 09 October 17th.
Monday, March 30, 2009
Tuesday, March 3, 2009
Spring is coming
Well, we took a month or two off after our crazy busy Christmas season. We sold the Mini's very well. We were averaging 1 1/2 mini's per day online and a bunch for the stores. Even with all of those sales, we are still woefully short on funds. I have done the numbers though and we are looking good over time.
Now on to the hard stuff. We purchased the A-treb simulator. It's really fantastic. It's a must buy for anyone who wants to build a big trebuchet, over 6 ft. It gives you all the numbers that you could possibly need. It also forces you learn about your trebuchet and the materials. Totally worth the $19.95.
After looking through it for a while we realized that the forces involved in Telos got really big, really fast. We tried increasing the CW by 50% and it increased the forces on the axles and frame by over 100%! We are settling into a comfortable CW zone for our trebuchet. It's a lot of weight and should be sufficient for us to do a good showing. In order to come to these realizations, I had to learn how to be an engineer. It's not that hard if you are willing to partner with your browsers Google toolbar and ask it lots of questions. Eventually I was able to understand what was going on and how to adjust it. It's very exciting to understand these things. I am now working on designing a cable-stay for the throwing arm. I beleive that the cable-stay combined with the Versa Lam lumber will be sufficient. There's a website, http://www.efunda.com/formulae/solid_mechanics/beams/casestudy_display.cfm?case=cantilever_endload
that will tell you if your throwing arm is sufficient for the forces involved. You need to know several very specific numbers for your arms material (Google) and you will need to know the forces being involved.
I will start to update the blog more regularly, I got out of the habit and have been focusing on other aspects. There is a lot going on and I want to tell you about all of it, I just have to take the time to slow down and do it.
Now on to the hard stuff. We purchased the A-treb simulator. It's really fantastic. It's a must buy for anyone who wants to build a big trebuchet, over 6 ft. It gives you all the numbers that you could possibly need. It also forces you learn about your trebuchet and the materials. Totally worth the $19.95.
After looking through it for a while we realized that the forces involved in Telos got really big, really fast. We tried increasing the CW by 50% and it increased the forces on the axles and frame by over 100%! We are settling into a comfortable CW zone for our trebuchet. It's a lot of weight and should be sufficient for us to do a good showing. In order to come to these realizations, I had to learn how to be an engineer. It's not that hard if you are willing to partner with your browsers Google toolbar and ask it lots of questions. Eventually I was able to understand what was going on and how to adjust it. It's very exciting to understand these things. I am now working on designing a cable-stay for the throwing arm. I beleive that the cable-stay combined with the Versa Lam lumber will be sufficient. There's a website, http://www.efunda.com/formulae/solid_mechanics/beams/casestudy_display.cfm?case=cantilever_endload
that will tell you if your throwing arm is sufficient for the forces involved. You need to know several very specific numbers for your arms material (Google) and you will need to know the forces being involved.
I will start to update the blog more regularly, I got out of the habit and have been focusing on other aspects. There is a lot going on and I want to tell you about all of it, I just have to take the time to slow down and do it.
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