Should have made a small scale of trigger before going for full scale, it didn’t work on first try (too much slop, wouldn’t release cleanly, will have to weld in material then grind it to remove extra clearance)
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What was the test drop like besides noisy?
Much smarter, now I can work on trigger without being on top of ladder, also CG is higher than where I hoisted it from, which was not wise
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I’m headed down there right now to sew D rings onto the test sling.
SlingFest tweeted pictures from last year: http://slingfest.com/photos/
There appears to be one floating arm trebuchet: http://slingfest.com/wp-content/uploads/2016/09/IMG_5597.jpg
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Still lots to do but an initial test fire of an 8.4 pound projectile worked great (1/5 of max counterweight), it released early resulting in a very steep angle (>70 degrees) and not much horizontal distance (~160 feet), it had 5.4 seconds of hang time, meaning it got to an altitude of ~115 feet with an initial velocity more than ~80 miles / hour. Needless to say that is the last test fire we will be doing in the back parking lot. Will need to adjust release pin and or increase sling length alter release angle.
Going to work on sunday next, need to complete trigger assembly (to add remote release), improve trigger latching (currently very sensitive to location of lift pulley on if they auto latch), pull arm out to inspect axle, build actual trough, and figure out solution to the rigidity problem when supported by legs. My initial leg idea was to have it suspended by the legs with the base not touching, but that generates a large amount of force squeezing / compressing the uprights in the middle towards each other. It deflects enough to close up the very small tolerance in the drop channel (initial goal was 125 thousandths of clearance, but after welding and then trying to bend it back it ended up more like 15 thousandths clearance) and bind up the weight axle while winching the arm up.
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Will be welding 24 feet of either angle or rectangular tube to increase rigidity in the dimension that was flexing causing the weight gap to close up. The question is if should add only 50 or 100 pounds of steel to the base.
The red line is where supports will be added (x4)
In addition to stiffening the structure, will also not load up the legs as much as I was so the base will support the majority of the vertical force instead of it all going through the legs.
Having to get more steel and do more welding on base means will probably have to wait until next tuesday (25th) to do more test firing.
From what I read, I think both of those need to be adjusted.
However … for the ballistic accuracy shots, the shorter sling is probably preferable. Most of the variability is generated in the Z-axis (vs. X- or Y-) so the accuracy should be better.
How did the pouch perform? Or is it too early to tell?
I think the pouch was good (I didn’t inspect it very closely after the firing, I think it held up), would be good to go ahead and start on a better constructed one of the same basic dimensions so that we can use the better one on the 25th. Will need to disconnect it by unbolting the steel cable looped through the D rings after measuring the current cable length (it can be taken off arm by unscrewing eyebolt that is threaded into arm)
Some other pics from yesterday, here is the trigger mechanism, @SewingStuff was able to source some 1/8" cable clamps on short notice.
it has about an inch of clearance fitting through the door:
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Will do. @Bitta is going to get us some more D-rings from Tandy so that we can have at least two pouches. She thinks we will have the additional D-rings this weekend, so I will make the pilgrimage to The Space, get the stuff, and make at least one pouch in time for the 25th. I’m going to shoot for Saturday.
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Yep…bringing them Saturday am!
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I made a new sling pouch. It replicates the dimensions of the prototype sling onto the “seatbelt” webbing, along with the new D-rings that @bitta picked up at Tandy. I did not have to destroy the prototype sling (and I have a couple more D-rings) so I suggest we keep the prototype sling as an emergency spare.
I was uber careful with the construction and it seems to be very sturdy. I put the new pouch and the prototype (which is still connected to the cabling) in the box atop the small treb.
Because the selt belt webbing is a little stiffer than the prototype webbing, it looks a little “poochy” even though it replicates the dimensions of the prototype. If it were me, I would reduce the length of that one center strap just a little bit.
After you test fire on the 25th, I can make another pouch if you’d like. I have detailed dimensions from the prototype. I took the seat belt webbing home with me so I don’t have to drive across town to pick up the webbing to make another pouch.
Let me know how the pouch performs on the 25th and what you need me to do as the next step.
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An interesting point I forgot to calculate about first test throw, it was roughly about 65-75% efficient at converting potential energy of counterweight into projectile kinetic energy. My previous range calculations assumed 50% efficiency. So it could potentially fire farther than previous max estimate of 900 feet.
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Found a problem caused during test fire, I didn’t align the Frank supports well enough and the pivot wheel axle struck the uprights as it was jumping the gap
@AlexRhodes offered to CNC cut some wood guides before Tuesday 9pm that will locate arm left and right as it jumps gap to be sure this doesn’t happen again. I will also straighten the bent axle and machine a spare
When it hit it broke off the hitch pin holding the pivot wheel onto the axle
Used a small amount of heat and press to straighten the 4140 axle
Raw materials for trigger assembly
Trigger assembly
Also started primering more parts
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I just wanted to chime in and tell you guys how impressed I am with this sucker! It’s fantastic and everyone is dumping so much energy into it. Good work guys! Can’t wait to see it live.
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A potential follow-up to the Trebuchet project
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I’m game!
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