The next step in the project will be to make the electronics not go dead when they are put into water. The idea behind what i want to build can be seen in Fig. 1. Both ends of the WTC will be closed like this.

One disadventage of 3D printed parts is, that they are not watertight. Because off how a FDM printer works the parts have small cavaties inside and under preasure the water will push through in seconds.

A 3D printed flange (yellow) is glued with resin to the WTC (grey). On top of that is a rubber seal. It covers the entire flange and the wall of the WTC. Several screws push a piece of plexi glass which acts as a bulk head down on the rubber seal and on the wall of the WTC, forming a watertight seal without relying on the 3D printed part to be watertight.

The first failed attempt can be seen in Fig. 2.

Although it worked at first, the force from the squished rubber seal tore the 3D printed part apart. ( It is totally impossible that i over tightened the screws. I am perfect! ) For the second attempt i changed the infill from 30% to 100% to have some more meat and i used heated inserts instead of loose M3 nuts. The new part can be seen in Fig. 3.

To get the tether inside and the motor leads outside of the WTC there need to be some holes in the bulk head. My best plan is "just use al lot of resin", which totally worked out. ( No really, no problems at all. No sarcasm. I mean it.)

To test the the WTC i submerged it in a ( mighty science ) bucket of water as you can see in Fig. 4. The WTC was weighted with a science grade can of paint to keep push it under water. I checked after 30min, 1h and 2h. No leak was detected. ( And yes, the salt shaker is important. )

This seams to work now, so i will add the second bulk head.