Trebuchet SIG 2016 Build (season over)

Immidiate thoughts:
how about spin lock nuts?
https://www.fastenal.com/products/details/11120398
It seems like the “serrated” locking mechanism might help ensure the release stays put.

Idea #2:
Use some castellated nuts (not sure if you can find any in that size) and a rollpin through the release to slot into the turrets, preventing spin.

No matter what other choices are made, I would think jam nuts would be mandatory.

Found a cheap turnbuckle on amazon, this approach will be much better since it will be possible for fine adjustment:

The design with the end of the arm being only 2.25" x 2" will be interesting, will find out how strong plywood is at ~200 mph

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buy at least 2.
And make some spare plywood… :slight_smile:

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Plano Magazine article about SlingFest: http://planomagazine.com/6th-annual-slingfest-october-30/

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Proceeds from SlingFest go to TheLab.ms, a Plano makerspace.

Regardless of the outcome, The Lab wins.

We’ve cut 3 arms and can make at least 2 more from the materials we have on-hand.

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I’m sure this is way too early to be thinking about logistics … but when you start to think about how to get the thing onto a truck, off of a truck, to Oak Point Park, etc., there is one little thing you need to know.

Oak Point Park (the Slingfest location) is in a flood zone (next to Rowlett Creek). The creek frequently overflows covering several hundred acres. The Slingfest location is the area shown in the video starting at approx. 0:13. It routinely has a foot or more of standing water after heavy rains, and that water sometimes sits for a week or more depending on the rain. Right now there are still large areas standing in water three days after Sunday afternoon’s rain. While I’m not suggesting that you will be firing in standing water, if it has rained during the month of October that big field could very well be marshy / boggy / swampy.

Might want to give a little thought about how you would wheel it across and or set it up on very soft, waterlogged ground. I’m seeing plywood …

:umbrella:

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Got some work on the arm done, but ran out of mig wire before starting on welding main axle in.

Carbide hole saws are great

Also went ahead and bought our 1000 pounds of concrete and 70 feet of rebar

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Hey everyone,

This looks awesome and I can’t wait to see this at SlingFest this year! I wanted to invite you all to our next Builder’s Meeting on Oct 5th from 7-10PM at The Plano Makerspace. We’ll be reviewing all of the rules and setup for the event and making sure that everyone competing is in compliance and ready to chunk and roll!

https://www.facebook.com/events/1129920557067475/

If you have any questions, please let me know.

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A good suggestion from @frank_lima was to reduce the static load on the arm in the rest position and to reduce the shock load as the wheels jump the gap in the rails (when arm is vertical) by supporting the weight axle when it is at it’s lowest point.

To make it as easy to use as possible / setup, instead of having to carefully setup something like sand / dirt under the weights I’m thinking of welding in a bar across the gap the weights fall in and mounting these rubber bumpers at the bottom. They will be carefully aligned so that they don’t decrease the fall height of the weights, but just help partially support the weight axle when it’s at it’s lowest point.

This will have the added benefit to hopefully decrease damage to rest of machine in the case that the arm pivot wheels fail catastrophically and the weight falls unconstrained

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We finally have a use for discarded automotive springs on the Freebie Shelf…

probably too late in the game for this round, but a curved track seems most sensible to me. This allows the weight to always be on the arm axle/wheels instead of having to transfer onto it shockingly once the height is right. Then, with the curved backswing, less jouncing/rebounding, or at least, what DOES happen, will be less shock load on the whole shebang because it’ll be smooth.

http://www.supertrebs.com/Merlin.html

But as always, I may just be looking at it wrong…:head_bandage:

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Thanks to @lukeiamyourfather we are all set with batteries for the 2,000 pound winch (batteries have 3x amp capacity winch will require, should get at least a few lifts out of each battery)

For winch placement I was thinking of this:

The huge concrete weights make it unsafe to be near it, so I am thinking of using a long pole to lift the pulley off the top of the machine after the trigger is engaged and the winch line is slack

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Good thing Luke has those awesome LiPo’s, because I just returned a well used car battery that might have been capable of running said winch a few times. Guess I’ll have to wait until the next one dies to find out how badly you can beat on one until it really does.

I got an air belt sander (to grind weight drop slot back into tolerance), more mig wire, replacement horizontal bandsaw blade, and more grade 8 fasteners for todays (October 2nd) build day, goal is getting the arm moving on the rails and starting fabricating the weights. Anyone interested in helping out is welcome to come lend a hand.

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From the reading I’ve been doing, it appears that “tuning” the sling length and the angle of the sling release hook are critical to achieving the proper trajectory.

@Brandon_Green - Might I suggest that when we start testing the sling design, that we start with it a little long and use rope as the long pieces on the prototype? This way we could just keep adding knots in the long pieces to progressively shorten it until it launches at about the 45 degree point.

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Got some expert welding help today

I made the mistake of not bracing the tops of the uprights while welding, which resulted in the 4"x4" 11 gauge steel columns to bend in at the middle, making the top 1.5" closer than the bottom, some bottle jacks and welding on the opposite side of the column should help.

Getting closer, arm halves are complete except for release pin assembly

Also picked up some drill alignment guides after some recommendations, makes it much more likely to drill perpendicular holes

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We also have a backup plan if the arm pivot wheels fail / split, milling replacements out of solid 6061 aluminum 8" diameter round (would just have to cut v groove and bore it out for some bearings)

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Will be working on trebuchet all day tuesday if anyone would like to assist, next steps include:

  • Welding release pin onto 22 gauge sheet metal cap on end of arm
  • Milling 2.5" dom tubing to have perpendicular ends (either lathe or bridgeport)
  • Welding together concrete forms
  • Renting concrete mixer and pouring concrete
  • Welding relief beads on outside of uprights to get them to straighten out some
  • Weld supports into inside of rail beams to box in end
  • Weld supports on end of arm beam to box in end
  • Align and final welding on rail tracks
  • Final welding on track on back of arm
  • Assemble triggers
  • Mock up trigger mounting location
  • Weld triggers into place
  • Mock up winch mount
  • Purchase winch pulley
  • Grind ends of rail tracks to be flush with weight gap
  • Test motion of arm after removing temporary braces
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Sounds like a lot of welding. Wish I could help. I actually enjoy welding.