The Watermelon is the club's third 3D printer. Affectionately called "the Watermelon" due to its colored frame, this printer was built from scratch over Winter Term 2014. It is the first of the club printers to be entirely student built, and was the first to feature remote (and wireless) printing and timelapse videos for every print.


The Watermelon is a Prusa i3 design with some added capabilities, including wireless printing and live camera footage.

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The Watermelon

On top is the filament spool.

On the left side of the printer are simple Generation 7 electronics.

The power supply, mounted on the back of the pirnter, is a hacked server supply. The light on the right side indicates whether the supply is powering the motors and heaters, and is controlled by the switch near the Gen 7 board. It should usually be left on to allow for remote printing.

On the right is a mounted Raspberry Pi. This is a small computer which hosts the wireless print server and stores Gcode files.

Above is a powered USB hub to facilitate extra features of the printer. This hub powers the Pi itself, connects the Pi to the printer electronics, gives the Pi wifi, and powers the light strip for night monitoring.

At the lower right is a camerate system to monitor prints remotely and capture time-lapse footage.


Changing the FilamentEdit

  1. Log on to Octoprint and heat the extruder (Temperature > Extruder > Set PLA)
  2. Raise the extruder off the bed (Control > [Up arrow on Z axis])
  3. On the printer, find the green piece by the extruder, held in place by two screws with springs. Pull upward to release the part holding the filament
  4. Pul the filament out. It should come cleanly. If not, wait a few minutes for the filament to heat.
  5. Remove the old filament spool from the filament holder. Install the new filament, sliding the white spacer into the spool axle if it fits.
  6. Slide the new filament into the hole. NOTE: The filament will often "catch" on the lip before it slides into the black part of the extruder. You will feel a sudden "click" of resistance. To fix this, make sure the filament entering the extruder is straight. Bend the filament against its curve to get it as straight as possible. Eventually it will slide past this firm resistance, enter the extruder, and you will feel a more gentle resistance as the filament hits the hot metal.
  7. Once the filament is entirely inserted, fold up the filament holder and re-push the green piece to lock in place.
  8. Under "Control" on Octoprint, click "Extrude." The filament should be pulled in to the extruder, melted, and expelled. After clicking a few times, the old color filament should emerge from the extruder. Keep extruding until the color changes entirely (This may take especially long for dark to light color transitions - just be patient!)

Leveling the BedEdit

The Watermelon's bed is fixed by four M3 screws. This isn't ideal, since it only takes three points in space to define a plane - a fourth point out of line with the other three will torque and warp the bed. Feel free to implement a 3-point solution.

When playing with the bed, first heat the extruder and bed, and extrude some plastic. The extrude has some play and extruding plastic ensures it's in the position it will be in when it prints. Heating the bed chages its shap slightly, again representing its state during a print.

First get the center properly leveled. Home the Z-axis and adjust the screw on the Z endstop, homing after each adjustment, until the extruder tip just touches the bed.

It's likely that this was all you needed - the bed might now be level everywhere! Check by clicking "motors off" in Octoprint, moving the extruder and bed, and Z-homing at different points. If all is well, great! If not, grap an M3 allen wrench.

Put the extruder in a corner, home the Z-axis, and adjust the height of the washer sandwich holding the ben in place at that corner. Once things are loose you can probably adjust the nuts by hand. Level each corner in this way. Do them again in the same order (you should be much closer the second time around.) Once everything is level, wrench-tighten the four corners and again check that everything is level.

If things don't seem to be getting level, try dramatically loosening one corner and level the other three, allowing the fourth corner to fall where it will (though you may need to jostle it to its prefered position.)