Didn’t know you needed that much length. Its 2" wide and standard seatbelt weight, I have two 54" pieces. I can drop it off this afternoon.
The towstrap idea is good, too.
Ill be at the space today helping build a wall if you want to drop off a couple of bucks my plan is to make some sandwiches and snacks for tomorrow for the group. Nothing over the top but at least help people keep going. My guess is it will be a long day for them.
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V3 pouch is complete. It is towing strap - partly because we didn’t have any more seat belt webbing and partly because if v1 and v2 suffer a material failure, making another similar one isn’t a lot of help.
Here’s the design summary:
v1 Five close-together straps, seat belt webbing
v2 Three straps on 3.5" centers, seat belt webbing
v3 Five straps on 3.5" centers, tow strap
Letting one end drops shows that all three pouches release the ball easily.
You have and need to bring the v2 pouch. I have and will bring the v1 and v3 pouches. I will also bring a heavy duty hand-sewing kit if we need nominal repairs.
FWIW, I don’t recommend anyone try sewing nylon towing strap. It’s not a lot of fun. In retrospect, we might have considered leather.
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Got improved sling cables, connection to arm, new winch, and weights painted, big thanks to Allen and @ESmith for helping get things ready
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The arm snapped on full power throw, which chain reactioned into other things breaking (pivot wheels, rail track, pivot axle), to fix trebuchet and try to fire again at same weight assuming none of the frame or weight axle are bent:
Create new plywood arm upper, same design, add 1.5 inches to length
Add cable truss to front of arm with 2 1/8 steel cables running from tip of arm to middle of steel lower
Bore pivot wheel bushing out to 3/4" on bridgeport
Replace 8" pivot wheels with same or turn custom ones out of 8" aluminum round
Replace pivot wheel axle w/ 3/4" 4140 axle
Use 1/8 steel cable instead of 3/32 for sling cable (2000 lb vs 900 lb breaking strength)
Replace rail track
Could be done for ~$300
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How did we end up with the initial budget? Maybe we can scrape together a little more cash to repair and ready it for next year.
I’d like to enter the 2x4 trebuchet, Peggy jnr, next year also. It was firing with amazingly accuracy
We spent about $2,200 during the build (1500 from original allocation through PR, some from Auto, rest from donations)
We gave away Peggy jnr at the end of the competition to avoid having to haul it back
I’m up for getting her fixed. So sad I missed the event.
So is the angle track broke? Just looked up 1-1/2" angle, 3/16 is 1.50 a ft & 1/4 is about 2$ a foot. Maybe we could use split DOM as track which should be stronger than angle.
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The track deforming / flattening hopefully saved the weight axle and frame from bending, in rush to pack / unload I didn’t take any pictures of damage.
It only deformed after the arm breaking, after breaking the pivot wheels left the track and the lower arm assembly to jumped forward (rotating about the weight axle), with the weight still travelling down all that force flattened part of the rail and busted the cast wheel. If you watch the video will see that the entire 2,000+ pounds jumped up in the air some during the pivot wheel breaking / rail flattening. Making rail stronger would be possible but may not be necessary, will need to see what kind of force it takes to flatten angle iron in that orientation.
Were it not for that phenomenal Texas Twister trebuchet, Peggy Jr would have been competitive in the lightweight category in terms of both distance and accuracy.
EDIT: The “Texas Twister” has been referred to as a MURLIN, but it is a “whipper” design that uses multiple axes of rotation with the weight initially over the center of rotation for the sling arm to start it rotating then another axis for the actual drop that accelerates the arm with terrific kick. Given how this guy’s floating-arm trebuchet worked with a very short distance between the deadweight and pivot point this seems to fit in with his design themes.
I did. Let me see if I can find it…
… there we go.
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For when we do rebuild arm, anyone have any ideas on how we could test it under a static 3,500 pound of force exerted on the end of the arm? That is the theoretical centripedal force on a 7 pound object going 200 miles an hour with a 60 inch radius, the arm should see less than that during an actual fire.
The average accelerating force to accelerate 7 pounds to 200 miles / hour in 150 milliseconds is an average of 420 pounds of force, but the acceleration is very nonlinear and its moving in an arc… So testing at nearly 2 tons should be sure the arm is strong enough.
Would need to affix the weight axle somehow (over 7,000 pounds of force at weight axle due to pivot being closer to weight axle), let the pivot wheels pivot on something, then either pull or push on the end of the arm.
Or how about putting the weight axle and end of arm up on blocks then lowering 10,000 pounds onto arm pivot point?
Yes, we can drill shields. I have access to a 5,000 lb digital scale that we can then use my 2 ton chainfall to test. I have 3/4,5/8 & 1/2" eye bolts & several different sizes of shackles. I used to have a load chain but someone ganked it from one of my jobs. We could even drill 4 shields & make a plate to distribute the weight.
@John_Marlow I think we lucked into a great sling design, here is a slow motion gif of it releasing with 400 pounds of counterweight, each frame is 4.125 milliseconds, by my pixel counting it is going about 94 miles/hour at release.
You can see that when it releases the projectile actually travels between the two sides of the webbing, so it doesn’t have to push the sling out of the way as if it was made of a solid material instead of webbing
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It looks like the release point is timed well also.
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Sweet Jesus this is insightful. Some excellent engineering went in to this. Kudos to everyone involved!
I just had to chime in and say I’ve learned so much just reading through this thread. This kind of thing really makes me proud to be a DMS member.
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Well, there’s this… https://www.google.com/search?hl=en&source=hp&biw=&bih=&q=weight+of+corvette&gbv=2&oq=weight+of+corvette&gs_l=heirloom-hp.3..0l2j0i22i30l8.799.5052.0.5251.18.12.0.4.4.0.221.1469.5j6j1.12.0…0…1ac.1.34.heirloom-hp…2.16.1512.iptnit16v88
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Who ended up adopting it?
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