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…
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
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.
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.
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
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)
Will be working on trebuchet all day tuesday if anyone would like to assist, next steps include:
Sounds like a lot of welding. Wish I could help. I actually enjoy welding.
Will the Bridgeport be available after 6PM for any length of time?
I don’t expect to use bridgeport for more than 30 minutes early tomorrow, mainly assembling parts now. Have 10 ~3" tall 2.5" diameter dom pipe pieces that I need to square the ends up on, was thinking it would be faster to put it vertically in v block in bridgeport and run shell mill across face vs chucking each one up in lathe.
I will not be able to get there till 6:30 PM. But I am ready to fuse some metal. Keep me posted, boss.
Oh, I will also be there Wednesday.
EDIT: We might be able to get around putting relief beads on the center bit. I have a portable oxy-fuel rig and I just need a rosebud tip and we can heat it up. I used to take the warp out of I beams this way.
Alternate casters arrived and they are much better than the existing ones, should be drop in replacements. It only cost us $44 to learn that you want to order your ebay 8" v groove wheels from charleskbjj and not servicecaster
(Groove not shown in this picture, but new ones look perfect vs the voids in existing ones)
You are denying your readers the money shot they desire.
Got the weights poured today, first milled the ends of pipe to be perfectly perpendicular and a consistent height
Welded on the rebar (paper template guide was not the best idea)
Turns out to be harder than expected to make the outer sheet metal a circle
Rented a mixer to mix the 13 80 pound bags
Just a reminder that the last Trebuchet Builder’s meeting will be 7PM Wednesday at TheLab in Plano: http://www.meetup.com/TheLab-ms/events/233968782/
Can anyone from our group make it? Would be good to go over logistics of the event and get some tips on projectiles and sling design.
I am planning to attend. I’ll take notes and summarize.
Any questions I should ask?
I’m assuming there is no registration for competitors, we just show up with a device?
What are slings/pouch typically made out of? Any lessons learned on what doesn’t work for sling design?
Will a 4 2.5 foot long 1/2" diameter stakes to anchor trebuchet to ground be adequate in the likely soggy soil?
If there are any other floating arms there, what arm pivot ratio, arm to sling length, and counterweight to projectile weight ratio do they use?
