Stardance Devlog #3
I thought I was ready to print, but one tiny servo screw turned into today’s whole challenge.
I finally figured out how the cross horn actually connects.
The raised circle on the horn faces down and presses onto the SG90’s splined shaft. The tiny center screw only holds the horn to the servo.
The printed platform goes on afterward. Its recess faces down to leave space for the center screw head, while the two outer screws connect the platform to the horn.
I originally had it flipped, which bent the horn slightly and caused a weird noise when it rotated. I caught it before printing the final parts.
Sorting Out the Screws
I also confirmed that my screw kit really is M2 by threading one of its nuts onto a bolt.
The M2 screws will work for mounting the servo ears with washers and nuts. They are not meant for the tiny center or side holes in the servo horn.
It took a while, but I finally understand what every screw is supposed to hold.
The Two Main Parts
My fixed base is 100 mm in diameter. It has a hollow interior, a servo opening and a cable notch.
The rotating platform is smaller at 65 mm because it needs to stay light enough for the SG90. It has the shoulder-servo wall, two support gussets and the horn mounting holes underneath.
The two circles are different sizes on purpose.
Finally Printing!
I loaded both parts into Bambu Studio with:
- 0.20 mm layers
- 4 wall loops
- 5 top layers
- 5 bottom layers
- 20% Gyroid infill
- No supports
The fixed base is printing with its hollow side facing upward. The rotating platform is flat on the plate with its wall and gussets pointing up.
They have officially been sent to the printer.
Once the print finishes, I’m testing the base-servo fit, shoulder-servo fit, screw alignment and rotation.
I still don’t know how well the SG90 will handle the completed arm’s weight, so I’ll test it in stages before adding everything.
If you’ve built an SG90 robot arm before, let me know what failed first or what you would change before I continue.