The first version of Micro Marlin's buoyancy engine will contain a single syringe with an embedded motor. This is based on a number of previous designs such as the rumblefishrobotics design.

The embedded motor with the long screw thread will pull the plunger/seal back and forth  when 5V are applied (5V works fine). This will allow the intake and expulsion of water which will change the density and therefore the buoyancy of the glider; pull water into the syringe, the buoyancy decreases and the glider will start to sink, push water out and it will instead start to float up.

Components

• 30ml Syringe (Plastipak BD)
• DC 6V Gear Motor with Long Screw Thread Output Shaft (30RPM) - amazon
• 3d printed parts
  • plunger
  • seal lip
  • motor housing

3D Parts

• All designed in OpenSCAD and printed on a Prusa i3 MK3 using Prusament PETG
• The seal lip and plunger were printed separately as reduced the need for printing round an overhang, they are secured with a bolt and nut. The rubber seal then slips easily over the lip.

• There are 2 M3 nuts which are glued into the plunger to allow plunger to be moved with the screw thread.

• By holding the motor it is possible to move the plunger within the syringe and therefore would be possible to draw in and push out water as planned.

Issues /Jobs

• The plunger needs to be longer to fully move along the screw thread
• Haven't yet printed the housing for the motor
• The thread is only long enough to move the plunger about 15mls, this will be a limiting factor in changing the buoyancy to move, it will mean that getting the right balance of buoyancy will be hard. It maybe necessary to add multiple engines or upgrade the syringe size.