I printed the Hallway Seej set and while the idea is absolutely fantastic the model didn't fit at all for me. It had way to loose tolerances. Furthermore even with the largest stopper it shot way to low. To reach any distance, I had to take it into my hand and point it upwards.

But since I liked the idea so much I went ahead and completely remodeled the catapult. While I took a lot of inspiration form the original model I tweaked and improved a few things. It now is a tight fit and snaps together which means you wont need any tools or glue to assemble it. I also tried to improve printability of the stopper by changing its shape and splitting it into separate files. Lastly I tweaked the projectile exit angle to be able to reach a reasonable distance. The wheels I added are more or less for aesthetic reasons only. I also remodeled the flag pole since the original one was way to thin to fit the flag and base.

Printing

• The files with "c0.5mm" in their filename have more clearance in the bearings. Use those if you cant get the bearings to move properly when printing the regular files.
• Print everything in the orientation the files are provided
• No supports or brims are needed but the arm will print nicer if you activate supports for it
• I tested Layer heights from 0.2mm to 0.1mm. Everything in that range should work well
• I made one from PLA and one from PETG. Both seem to work great - no stability issues with either so far
• Use flexible filament for the stoppers (e.g. TPU)
• You can choose between the complete wheel or a wheel that consists of the wheel an a tire. If you choose the latter, print the tire with flexible filament as well.
• You will need the tower, flag and flag base from the original thing (files "tower_round_v2-150.stl", "pennon_flag-165.stl" and "pennon_base-165.stl")

Some tips

• The wheels are slightly elevated on one side. The elevated side has to point towards the inside since it prevents the wheels from rubbing the braces when turning.
• Use some silicone spray to make the arm and wheel bearings run super smooth (and remove any squeaking)
• In the original thing the rubber bands are attached to the braces. For me it worked much better to just leave them on the top bar (as seen in my pictures). I got significantly more power that way. But I guess that has something to do with how long the rubber bands are.

Updates

2020-01-23:

• Added files with more clearance in the bearings ("c0.5mm")