Oakland Ballistics Trebuchet Blog

Video replay idea

oaklandballistics — Thu, 13 Oct 2011 22:55:24 +0000

I’ve been working on our whipper design for about a week now and we are much closer to a forward launch but still a bit off, straight up actually. But in reviewing the slow motion video we came to a realization, to make the release pin easier to see in the video, attach a fluorescent ribbon, the kind used on construction sites. I the very next shot after putting the ribbon on I was instantly able to see that it was indeed releasing the ball. This is a really fun development since I love reviewing slow motion video. I’ll be putting some of the whipper videos online soon but first I have to do the Lake Orion Pumpkin Launch this Saturday.

Telemetry ball here we come!

oaklandballistics — Thu, 22 Sep 2011 01:53:36 +0000

I think I finally solved my problems with building a telemetry ball. In case you didn’t know, I have been trying to build a ball that we could launch then get data from it that would tell us stuff like how much force was put into the ball or acceleration, things like that. I tried building one from parts from Sparkfun but I didn’t choose a high enough G force and the thing just couldn’t take it. This time around I knew I needed a higher rating on the meter but where to get one and how to build it.

I think I have found what I am looking for. http://gcdataconcepts.com/x250-2.html

This is the device. A simple self-contained unit that I launch, retrieve, plug-in and launch again.

This should do the trick. If you are interested in exactly what it does then follow the link. Basically it has a triple axis gyro in it that is capable of up to 250G’s. That should be sufficient.

Next came the ball that I needed to launch it in. It had to be similar in size to a pumpkin but it also had to be indestructible and I had to be able to open it up. I found this online after searching for sometime, http://www.amazon.com/Hueter-Toledo-Inc-Best-Ball/dp/B0002DI32C

I plan on sawing it in half then using the spray foam like what you would find at Home Depot to fill the void. Using draw latches I should be able to latch it closed and it should stay closed. I might run a small USB extension cord to the outside so I don’t have to open it up but I think I will have to open it just to turn it on and off so I don’t get a long running graph.

Another item I decided to add is a small beeper like device. The idea is that, once launched, the ball would be difficult to find. By placing one of those key locators inside and pushing the locator button when out in the field I should be able to find the ball pretty quickly. I found this one online. http://www.improvementscatalog.com/electronic-key-finder/12301 It says it has a range of 120 ft. That should be good enough. The only problem is whether the sound will be loud enough. I didn’t find just a beeping device. That probably would have been cheaper but this adds a little bit of flair to the whole project.

Trust me, I’ll have the results up as soon as I get them.

Catapult kit revelation

oaklandballistics — Fri, 26 Aug 2011 14:29:18 +0000

Here at Oakland Ballistics, we have been working on a catapult kit to compliment our trebuchet kit. I spend some time designing it and I was unhappy with the distance. Comparing it to other kits the distance was roughly equal but I still wasn’t happy. Then I saw a design that had a very simple “cup” but it launched much farther. Many other elements were different but I surmised that the cup design might be the key.

In these pictures you can see the more traditional, cup design then the other, simpler, cut-out design. The simpler design, changing nothing else, almost doubled the distance. I found this to be very interesting and I love it.

In my opinion, the difference is in the release. The more complicated cup holds the projectile in longer and thus has a lower trajectory where the simpler design allows for the projectile to leave the arm earlier.

Sure there is the weight issue but I don’t think that accounts for much of the difference in distance.

Pumpkin Parachute works

oaklandballistics — Mon, 22 Aug 2011 18:53:45 +0000

I’ve been working on saving pumpkins and not just launching them ever since I was contacted by the ACLU. They felt that our inhumane treatment of pumpkins was grounds for a lawsuit. So, to appease them I said I would create a safety device that would allow the pumpkins to be launched safely.The pumpkin parachute is the fruits of those labors.

The chute opens when a bag is pulled off by a string attached to the trebuchet. The chute is nylon fabric and the straps and harness are nylon strapping with two clasps to strap it in.

Halving the arm

oaklandballistics — Mon, 04 Apr 2011 01:20:01 +0000

So the largest change that we are making to the design of the trebuchet is that we are going to halve the width of the arm. This of course halves the strength. We are going to beef up the cable-stay at the top and add a second line that attaches closer to the middle of the arm. This should relieve much of the stress on the arm.
The new question is how to attach the haul down line. Climbing to the top of the arm seems less easy since it won’t be as easy to slot in the ladder system. The idea is to use the haul down system that utilizes a long cable attached to the arm. You put a pulley on the end of the haul down line and this walks along the cable on the arm. I’m not really sure if there is a mechanical advantage to this or not. I plan to look into this more, but it would help with climbing to the top.

Telemetry

oaklandballistics — Mon, 28 Mar 2011 01:30:49 +0000

Last year I spent a decent amount of money trying to get telemetry to help us tune the trebuchet. I finally gave up and felt that my time was better spent elsewhere. Recently, as the weather has changed, I have started getting more and more done and started to feel more confident about what we could accomplish this year.
As a result, I have started to look back at the idea of telemetry and figure out how I can get the information that I need. I’m now at a point where I think I know what information I need and how I can get it. The hard part remains how to build something that gets me that information.
The way I see it, if I can get a device implanted into a testing ball that will read g forces, and will be able to the roll of the ball and at what point the in the swing the roll happens, I should be able to tell two important things. The first would be if my sling length is correct, that is the G forces. The nest would be what my release point is, that is the other two components. If I can put those two things together I should be all set to fine tune the machine to an optimum sling length and a 45 degree release.
I’m hoping to learn Arduino on my families spring vacation which I think will open up this area for me a lot.

Staying committed-solving problems

oaklandballistics — Sat, 12 Mar 2011 10:49:26 +0000

Since last years Pumpkin Launch, I have been re-energized about trebuchets. I made a list and I have been sticking to it. So far, I have solved some of the more difficult problems. I lined up a crane to help assemble and disassemble Telos, our team found some earth anchors to help the machine not rock violently, things like that. We have been on task. Normally we don’t even look at a to-do list until the snow starts to melt. I am very excited about this summer.
The earth anchors we found look very promising. They are 48″ long and once you screw them into the ground, they are supposed to withstand 4,000 lbs each. Two on each side of the trebuchet should keep it from rocking.
Finding this crane to help with the construction should save us almost a full day of construction. Also, seeing how 50% of the time the lift and lowering fails, this will be a huge improvement.
We are going to stiffen the base with some construction grade braces.
I am committed to learning how to weld this summer. It’s always something that I have wanted to do. With this new skill, I should be able to build a pretty cool arm wagon. With a custom built arm wagon, we should be able to move the arm on and off the trailer just like we have wanted to do for some time now.
New business cards, and lots more. Things are really picking up around here and the snow is just starting to melt.

Help wanted: eccentricity valued

oaklandballistics — Fri, 11 Feb 2011 20:17:13 +0000

Things have been slow around here. I know it’s the middle of winter but this is my best time, I have the most time. The problem is that my one teammate, Ryan, is swamped with work. He has great ideas but no time. I decided to reach out a while back to people who might be interested in joining our team. The main requirement, or two, is to want to do this stuff. That’s really the main requirement. The next one would be some skills at woodworking or metal work.
Time seems to be the problem, I want to learn how to weld, but I don’t have time. I want to start converting the medium trebuchet to a whipper but I don’t have time. If you are in the Detroit or Oakland County area and want to get involved with an established team let me know. Oh well, I’m sure things will get better if Ryan gets laid off. Here’s hoping.

Whipper notes

oaklandballistics — Thu, 30 Dec 2010 12:30:57 +0000

A few thoughts about the whipper. First, based on the YouTube comments, I will try a new arm with a ratio more in line with 4:1 or 6:1. Second, a problem that I found that will manifest itself with a larger machine is the cocking of the machine. Now I don’t think this is a difficult one to overcome, but it is something that will need addressing. Finally, next time I’m in front of this machine I will come up with a way to hold the projectile and the pouch in place. I trimmed it off of the video, but using the CW box to sit on top of the projectile just didn’t work very easily.

Here’s a link to the YouTube video

Tennis ball whipper

oaklandballistics — Wed, 29 Dec 2010 04:32:10 +0000

I had a great day. It’s amazing what two days without kids or a wife can do for you. Anyway, I was able to work on the tennis ball whipper. I started and finished in just over two hours. I did the design on the computer so I just had to measure and cut.
Okay, so it worked. I did one shot, guessing on the sling length and the pin angle. It worked great! The design itself is a simple idea, to get the arm to travel farther around. Instead of the current 60 degrees or so that a hinged trebuchet arm travels this arm travels around 300 degrees. This allows the arm to gain more speed.
I’ll have the video up in a little while but the previous best shot with the tennis ball trebuchet was 135 ft. For the one shot that I did I used about 70% of the weight, I guessed on the sling length and the pin angle and I got 225 ft.
It’s amazing. I am very excited about working with this design some more and then modifying a larger design and making it go even farther. I love this design. It’s so efficient.