Making a radio-controlled submarine with Lego and other materials.
At the end I test it in a lake. Enjoy!

The submarine specs:
Length: 22 cm (8.7 in)
Displacement: 1880 grams (66 oz)
Speed: 0.2 knots (10 cm/s)
Operating depth: 3 m (10 ft) - ballast tank will fail after that
Hull: 1.5 liter lemonade pitcher (Orthex)
Forward: Lego m-motor runs two 9-length propellers (2952)
Turn: Lego m-motor runs a geared-up (0.67:1) small 3-blade propeller (6041)
Ballast tank: Lego m-motor runs a Lego linear actuator connected to a 60 ml syringe (Eotia marinade injector). Active range 20 ml
Radio control: 27 MHz controller dissembled from a toy submarine (Zantec Mini RC U Boot). L298 H-bridge to drive motors
Power supply: 9V Lego battery box for the motors, 3.7V battery for the radio controller

The yellow toy submarine at 6:00 is this one: https://www.amazon.de/Zantec-S....chiff-Fernbedienung-