Just a casual (ish) get together tomorrow (Sunday 4th) at 3pm to discuss a plan of action for collecting the materials needed for building the DMS Trebuchet and possible transportation and storage options.
Please feel free to drop by and voice your support.
Lets meet in the Lecture Hall as it appears unbooked currently (possibly too late to try and book the room?)
Hope to see you there!
(reminders for @themitch22, @AlexRhodes, @MellissaRhodes, @bgangwere (who is on vacation))
Is this going to be a regular Sunday afternoon thing?
It is doubtful I can make this one.
Yeah I believe it will be Bill.
Change of venue to Creative Arts for today
We decided to build a scale model (4’) of a floating arm trebuchet, a quick trip to home depot and ace later:
Here is an 8x slow mo video of it dropping with 50 pounds of weight, we were able to launch a small projectile ~40 feet once, but need an actual sling and wheels that are much larger than the slot the weight drops in (could have used a much narrower axle for this scale)
I think we should build the full scale (8’-10’ tall body, 11’-14’ arm) completely out of steel to make it look similar to this one:
We have a remaining budget of $1,430, for around $300 we could order enough steel to build the body, 4x 20’ 1.5"x1.5" 1/8 steel angle for the track, 5x 20’ 2"x3" 14ga rectangle tube for uprights and arm (based on quote from Metals4u that I got last month for building tables out of similar material). Then some 1" thick steel round stock for the weight axle and some rubber/plastic wheels.
Lol wow, y’all had way too much fun late last night!!
Glad you got it to firing stage, those weights look good on it.
I’ll build a sling for it and then on to trigger ideas next!
Got a basic assembly working in OnShape (you can click and drag arm through its motion, just have to manually toggle between suppressing arm and back pivot mates as the arm travels past horizontal). Makes it easy to see how different arm lengths would look, we could probably get by with a 6 or 7 foot tall body and a shorter arm just to make it easier to load and work on without requiring ladders.
Sticking a small winch across the top to pull the arm straight up would make it easy to setup for a fire. Would winch it up, attach a safety mechanism, attach trigger, release tension on winch, then remove winch entirely from the top so that the arm can swing through space where winch was. Then remotely pull out safety mechanism, then release trigger to fire. That would avoid having to have some kind of pulley system.
Ladders? >760 lbs? you crazy dawg. my unsolicited opinion - it’s gonna be worth discussing, planning, designing and building a machine that loads and reloads your weights quickly and efficiently. must travel, must be battlefield mobile
The next builder’s meeting at TheLab is Thursday, October 6 at 7P: http://www.meetup.com/TheLab-ms/events/233968782/
Using advanced wheel technology we will be able to make it mobile without too much effort. Since the energy available is mass * gravity * height, we can either double the height or double the mass of the counterweight to get roughly the same increase. Stacking lots of weights on a 2" steel bar seems easier than making something 20 feet tall.
The approximate goal is launching a 5-10 pound projectile 100+ yards
Anyone have any guesses on how to estimate the load the bar holding the weight will have to withstand?
When the weight reaches the bottom it’s going to be decelerating very quickly, and transferring all that kinetic energy into accelerating the arm. A36 hot rolled steel rod has a yield strength of ~36,000 psi, how large diameter of a rod is needed to ensure it won’t bend when 750 pounds is dropped from a height of 7 feet? (the rod has a stickout from arm to center of weights on each side of around 12 inches)
Probably the strongest force will be if it hits a stop to launch object. It will be a Max V and therefore with max energy. If no stop it will just decelerate. Agree with weight verses height … more weight. Easy to add bar bell weights. Plus people can loan for project and no cost involved.
Don’t use yield strength - this is what it takes to stretch the material. Bending moment and elasticity more relevant factor. Way too long since statics and dynamic to do calculation. Could barely do it 40+ years ago.
are you sure you want the info to this solution? are you sure you don’t want the number, spacing, and type of spring to catch the bar instead? if you want the former, will the weights be falling straight onto grass or some sort of cushion? will the diameter of the bar be constrained by the type of weights employed (e.g. gym weights have a set inner diameter unless they’re milled)?
i’m glimpsed through the project rules on github specifically for constraints and didn’t see a section specifically addressing build constraints. can you please give me the rundown of what we’re going for… how tall? made of what? i’m confused if we’re going for distance or if this is some sort of battlefield thing
I could be wrong, but I’m pretty sure this is in response to the challenge from thelab.ms folks:
the rules, etc. are linked in this thread, as well.
We are competing in this
The idea is to build a version of this: http://www.instructables.com/id/Floating-Arm-Trebuchet/
Looks like they are using a 2 to 2.25" diameter steel rod to hold the weights, as the drawings on that page show a 2.5" wide slot
thanks, i will take my weekend to look through everything. once i’m caught up to speed, i will begin working on the original question
It is now Wednesday, October 5. Looks like we have another moving target…
Okay Bill, are you a spy for the Plano rats dawgs or the Noble DMS imperialist?
more like a double agent…
