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Underwater gliding

A project log for Open source underwater glider

A versatile autonomous environmental drone using a buoyancy engine

Alex Williams 08/02/2017 at 09:555 Comments

I have been able to use a pool to test the glider and although there was not a lot of video footage, it provided a lot of information about how well the glider currently works and any flaws that the current design has.

The below video only shows the descent phase as the buoyancy engine was not working reliably enough at this point to demonstrate the transition between descent and ascent. Also, the IMU has yet to be integrated into the control software, so the glider does not have a PID algorithm to adjust the position of the mass; you can see that the mass does not move from its fixed position at the front of the rail. As the mass is at the front of the rail, the glider’s angle of attack is high so the glider’s glide ratio is quite low.

The exterior printed parts would fill with water through very small imperfections, this caused the glider’s ballast trim to become incorrect over time (to the extent that the glider was unable to become positively buoyant at all). I will tackle this by reprinting the parts with a 100% infill, so water would be unable to enter the prints.

Also, when the engine motor has insufficient torque to drive the plungers, the plungers will jam with the rotor still rotating. This causes the nut to dig into the drive screw and the nut wears away the thread. This then causes the plungers to jam more frequently. A peristaltic pump would potentially address this issue. I plan to design a peristaltic pump proof of concept within a couple of weeks.

Discussions

Jarrett wrote 08/22/2017 at 18:03 point

Oh yes, I would recommend that as well. Even with 100% infill, 3D prints are super porous.

They make special-purpose coatings that will work. Check out XTC-3D, for example:

https://www.smooth-on.com/product-line/xtc-3d/

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Alex Williams wrote 08/23/2017 at 14:00 point

Thanks for the recommendation, I can get XTC-3D fairly cheaply here in the UK, so I will see if that fixes the problem.

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biolippi wrote 08/22/2017 at 15:27 point

3D prints are often not watertight. Use Epoxy coating to remedy the issue!

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Alex Williams wrote 08/23/2017 at 13:53 point

Thank you for the suggestion, I will definitely look at doing this in conjunction with the 100% infill.

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Horst Schlawutzke wrote 08/06/2017 at 15:24 point

looks good!

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