The Craftmans Shop > Backyard Ballistics
Gifts for relatives
ddmckee54:
When I printed the second gift box, I used it as a map to open the first. I haven't got the solution committed to memory yet, but I will.
I re-designed the internals for the rubber band gun and I'm getting much more reliable operation. It's still not working properly, as the hammer/wheel it tends to pinch the rubber band between the wheel and the frame. I think I just a simple fix away from my goal now. I want to get this figured out, because what started this whole mess was me deciding - a long time ago - to build a clip fed semi-automatic rubber band gun. I'm close to getting a reliable firing mechanism, now I've got to get the clip part worked out.
Don
ddmckee54:
There's still no joy in Mudville, and I still don't have pictures - but I've got cartoons.
The first attachment is the bitmap of the working bits of my test RBG. It shows the RH side of the test Frame, the Hammer/wheel, the Sear, the Trigger and the link between the trigger and the sear - Trigger2. For some reason, that I have yet to figure out, I cannot change the layer/color of trigger, the link or the sear - they're always blue. (Maybe they're sad because they don't work?)
The problem that I'm having right now is that as a single shot RBG this thing works just fine. When I load multiple "rounds" onto the hammer/wheel, it goes into MetalStorm mode discharging everything at once. While impressive, it's no exactly the result I was after. I've even tried loading just one rubber band, then rotating the wheel as if multiple rounds were loaded. This should cause the gun to dry-fire until the loaded band comes around. Nope, wheel just rotates.
Sitting here looking at it I may have had an idea, it was either that or a brain-fart - too early to tell. I'm starting to think that the problem is where I have the rubber band I am using as the sear spring attached to the sear. It is currently wrapped around the sear, so I don't think the rubber band has much leverage to move the sear back into position stopping the hammer/wheel. I know it's possible to make this work, I've watched videos of a guy building a semi-auto RBG out of plywood that uses a similar set-up - principles are the same anyway.
I'm going to try adding a lever at the bottom of the sear that will project toward the rear of the gun. I should be able to double or triple the amount of leverage that the sear spring can apply on the sear. Of course I'll have to modify the existing cavity for the sear, but that's what mills were invented for wasn't it? If it works, then I'll modify the print files, print the parts again, and see if it still works.
The second attachment is the 3D PDF, it doesn't have the rubber bands modeled, or the additional text.
Don
WeldingRod:
It looks like your trigger2 might be holding the sear open. You might want to dream something closer to an escapement, so you get one tooth per pull.
Or come up with something so the the sear can return to position without interference from the trigger bits.
A thought: a double sear. One sear cycles with the firing pull. The second sear catches the wheel after the first releases. Then the first sear has time to reset. Releasing the trigger pops the second sear, putting the wheel onto the first sear and ready to fire again.
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ddmckee54:
When the trigger is pulled back to the stop Trigger2 slides past the Sear. The Sear then has the clearance it needs to swing back into the stop position. But you may be right, Trigger2 may not be releasing the Sear soon enough. I'll have to look at the geometry of where I've got Trigger2 releasing the Sear. I've probably got too much time overlap between hammer release and sear release. Back to the proverbial drawing board to see what this looks like.
I thought about using an escapement, but I must have some type of a problem with that. I may be doing something wrong because every time I try an escapement, the design I come up with releases the rubber band on trigger release not trigger pull - and that just feels backwards to me. The escapement location may wrong maybe, but there's not a lot of interior room in this thing - it's only 120mm X 80mm X 25mm max.
My whole problem may be that I'm starting with a gun and trying to fit the guts into it. Maybe I should start with the guts and when I've got them working, fit a gun around them.
Don
ddmckee54:
I tried adding a lever to the sear, all I got for my efforts was another paperweight. I've got it re-designed - again, and I've printed both frame halves. I'll print the internal parts tonight and we'll see if I add another paperweight to the pile. Maybe I'll get really lucky and it'll work this time.
I think I figured out what my problem with the escapement was, I was trying to keep the trigger and the escapement linked together all the time. This time around I'm using the trigger to release the sear/escapement which in turn, lets the wheel cycle through only one tooth on the wheel. It takes the forward and backward movement of the sear/escapement to cycle through each tooth.
I know pictures or even cartoons would help this explanation, but I don't have any right now. If this works I'll show what it looks like. If it doesn't work I'll probably show you what is looks like, and I'll be wondering what I did wrong this time.
Don
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