Petoi Bittle Lego cover

Petoi Bittle is a programmable robot dog that can be controlled with a remote, smartphone, or computer. It is relatively affordable and often used in STEM education. When I learned that it is possible to 3D-print Lego, another product with STEM applications, combining these two was the first thing that came to mind.

Bittle normally has a removable black cover on its back that encases its circuit board. You can easily swap it out with this Lego compatible clip-on cover, allowing you to expand on the robot with your own Lego decorations, structures and technical mechanisms, opening a whole new world of possibilities.
 

Update: Sideways pegs have been revised for better overhang. Front & back pegs are now 3 x 2 rows. Clips have been adjusted to fit better.

Recommended print settings
1.75mm PETG or PLA
200 Celcius for PLA
Nozzle 0.40
Line width 0.45
Layer height 0.2 (not more)
3 walls
Infill 20%
Walls before infill
Outer walls before inner walls
Top surface skin pattern concentric
No ironing necessary
Support density 10% or more, lines, everywhere
No support interface (makes support at the sides hard to separate from the pegs)
No Z-hop
enable retraction
brim 3-4 mm

top/bottom speed 3 (necessary to avoid drooping of sideways pegs, this saves a lot of post-processing time)
outer wall speed 10 (to counter ringing)
inner wall speed 30
travel speed 120 for PLA

Seam at sharpest corner. Double-check that the bottom layer of the sideways pegs is two lines wide, otherwise change initial layer height by a fraction, or the seam orientation. A single bottom line would create seams in the pegs that obstruct Lego attachment.



Before printing
I recommend printing the 2x2 Lego test piece first, to see how well the print connects to official Lego bricks. The diameter of official Lego pegs is 4.8 mm, but I've made them 4.9 mm to account for some shrinking, which worked best for the PLA I used. Adjust your horizontal expansion setting if necessary, and anything else that helps reduce stringing between the pegs. 

After printing
Use an exacto knife to remove supports at the sides of the cover. If the pegs have too much stringing or oozing, you can use a hollow steel punch tool of 5 mm to cut off the excess by manually pressing and rotating it over each peg, carefully. Again, you can practise on the test piece first. You may also cut or file the two clips at the bottom of the cover for the best fit.