Here's my design for a tunable, stackable, packable buoyancy system using the ubiquitous 250 mL drinks can. Requires just 60g of plastic per 4 cans, fill them with gravel to use as an anchor! Made of aluminium, the cans are corrosion-free, super lightweight and have a great tensile strength. PLA is plenty strong enough, no supports necessary, so everyone can print it.
For minimum plastic usage, a central axle fitted to the shape of a 250 mL can forms the core structural element, with lips at either end to stop cans slipping up or down. A 10 mm square shaft running right the way through the centre maximises the range of potential mountings.
The thin but tough band running around the outside of the cans to hold them in-place is printed edge-on, in one loop for strength (no separating layers here!). The band is sized to be a slightly too-tight fit so that it doesn't slip off or require glue to keep it in place.
Low-profile caps use the recess around the inside-edge of the crimped-on top of the can (you'll need a bit of glue here) to form an easy to make airtight seal. Just fill in the gap with glue, squash the cap on there and wait for it to dry! (remember to use a water insoluble glue!)
Many! here are a few:
Rafts - bolt the modules to a pallet or between two boards
Out-riggers - mount on 10mm threaded rod for rigidity
Floating planter - one module as a raft, another as anchor
Pool-party table / drinks / snack holder - use a ring of modules with a bucket or box in the middle. anchor or not!
RC craft - tunable buoyancy for boats etc. ... maybe even as water-wheels for an RC car (though maybe a 6 can hub would be better ... :) I can make this if there's interest).
Buoy - for demarking swimming / triathlon, or RC craft race routes. Just scale to the size of the flag!
Printed at 0.2mm resolution with no supports necessary and 20% infill.
On the band and the caps make sure that you have thick enough walls / to / bottom layers to make them solid.
This is the sort of thing that I would have loved as a kid, so I'm looking forward to seeing the projects!
I've included STLs for a basic platform and pin for anchoring, I'm sure that there are a huge number that you could come up with!