WRLS (Water Rocket Launch System) - EU edition

Water Rocket Launch System for standard PET bottles (as found in the EU, and probably elsewhere).

Inspired by Superbeasti's WRLS, with following major changes:

1. Different bottle adapter thread to match PCO-1881 thread
2. Different seal mechanism

Additional material:

• O-ring (16mm outer diameter, 11mm inner diameter). This is actually the same ring as used on Gardena garden hose couplers (or one of the clone brands).
• Piece of rope for the release pin.
• Block of wood (or something) and three 3x16mm screws to screw base down.

Printing notes

No supports are needed for any of the parts.

The Adapter Ring needs to be printed with TPU, all other parts with PLA.
If you don't have TPU, it's probably possible to just squirt some hotglue into the Bottle Adapter and quickly screw the bottle in place.

Print the Inlet and Bottle Adapter with 100% infill, the others can be printed at 20% infill.

It's important to use Random Z-seam alignment for the Inlet, Bottle Adapter and Adapter Ring, as the Z-seam can be a source of leakage. The Launch Pad also looks better with random alignment.

Although the STL's are already oriented correctly for printing:

• Inlet and Launch Pad need to be printed upside-down (i.e. hose attachment side pointing upwards).
• Release pin needs to be printed with its flat side (with the two holes in it) on the build plate.

Tip: Inlet and Bottle Adapter can be printed with the same settings in one go (inlet centered in adapter).

Build instructions

• Slide 16mm O-ring around the Inlet.
  • I put some silicone grease on it too, just in case, not sure if it's really necessary.
• Insert Inlet into Launch Pad.
  • This has a pretty tight fit, so you may need to widen the hole a little, e.g. by scraping the Z-seam dots off with a drill.
• Attach bike pump to Inlet.
• Attach rope through holes of Release Pin.
  • Use a knot that tightens the loop, such that there won't be any rope stuck between the discs.
• Screw Base onto a block of wood, beefy plank, etc. Use three 3x16mm screws.
• Insert Adapter Ring into Bottle Adapter.
  • Make sure to carefully 'seat' it with e.g. a screw driver, it needs to go 1mm below the inner edge. Otherwise, it may twist while screwing on the bottle, and may leak.
• Screw Bottle Adapter onto PET bottle.

Launch instructions

• Fill PET bottle about 1/3 to 1/2 full with water.
• Put Launch Pad (upside down) onto Bottle Adapter.
• Slide Launch Pin over them.
• Slide the whole assembly into the Base.
  • Make sure the Launch Pin is at the curved side of the base, to prevent pulling the launch pad out of its base.
• Pump it! (I tested until 7 bar without issue, but probably start with 2 :)).
• Pull rope with a fast, firm pull.

How I Designed This

Redesigned from scratch in FreeCAD (included) to allow easy customization if necessary.

I initially tried to keep the 'locking disc' sizes the same as the original WRLS, but experiments showed that the bottle adapter was now too fragile (breaking when screwing onto a bottle a little too tight, or when it hit pavement when landing).

So, I changed the adapter to have thicker walls, but this means that it's no longer compatible to the original WRLS...

Originally published at https://www.thingiverse.com/thing:4951002

Inspired by Superbeasti's WRLS, with following major changes:

1. Different bottle adapter thread to match PCO-1881 thread
2. Different seal mechanism