|UPDATE!! (11/10/14) Just added a support bar for the catapult which helps keep the sides together. I made these a while back just forgot to upload them:
||Also included some spacers for the top bar. Have uploaded another pic to show where they go.
I wasn't too happy with how the original Seej catapult arm worked so I made a custom arm for myself which I think works alot better and is easier to do.
Similar too this one http://www.thingiverse.com/thing:128388 by MacGyver which I tried but it snapped after a few goes. So I just made a stronger version based on that design and added a few extra things.
You can tell by the pics its alot stronger looking and has 2 cylinders on each side to stop it sliding left or right, I just used one of the original crossbars which is a bit small but doesn't matter because once the arm and the rubber-bands are on its held firmly in place.
You can use either the bottom or top slot(or both) on the arm for the rubber bands, If you use the top one it may interfere with the Atlas but still works. You can use as many rubber-bands that will fit in the slots as you want which will make it shoot further if need be. I found using one on the bottom slot pretty efficient for my game size.
I also recommend using this mod:
http://www.thingiverse.com/thing:194000 made by thoromyr for the front and back crossbar which you can see in the pics I posted.
Since I no longer needed the 2 square holes on each side I decided to make a coin holder to take advantage of them, Each holder holds 15 Pennies or 15 5c pieces if your Australian like me;) (I still had some pennies leftover from a trip to America a year ago)
There are two versions one that needs supports and one that doesn't. Not much difference between the two other then height once installed (see pics) I made the square plugs longer and slightly bigger so they fit snug and don't move.
I prefer the one that needs supports when printed as it sits flush with the sides top. You can use one on each side if you want but I just leave one of the original winding keys in so I can hold the Catapult in place easier when firing.
COIN/AMMO HOLDER LONG.
Lastly this is something I made to hold extra coins so you can just reload the Catapult coin holder without needing to go searching for the coins you have already fired. Each player could have one so they can quickly set up and reload again if they want to play a few games simultaneously each compartment holds the same amount as the Catapult holder (15 x4)
I printed all of this at 2mm with 100% infill except for the long coin holder which I did at 3mm and 10% infill. I believe It makes sense to print most of the catapult parts which take a fair amount of stress when firing at 100% infill, Used ABS.
Well that's all, Sorry for the long explanation but I wanted to cover everything properly.
A few other tips I use:
1: Place a rubber-band around all of the feet to keep the catapult a bit more firm (which you will see in one of the pics) Nothing has been glued. (except the feet)
2: If you find the Atlas not sitting in the position you want it too meaning it may just droop down. Put some blue tape or any sticky tape really on the crossbar to make it slightly bigger so the atlas stays in position properly.
EDIT: Forgot to upload the cylinder's.. Whoops.. everything should be there now.
Thats all i promise:P
Thanks, Enjoy and go Shoot some Bloxen.