SG90 ROBOTIC ARM

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.

DEVLOG #3

I almost printed this with one pretty big problem…

Today I finished the rotating platform for the robot arm, and I also made a little servo horn fitting gauge.

I added the holes for the cross servo horn, then made the wall that will hold the shoulder servo.

The wall looked a little thin, so I added two triangular supports behind it.

They connect the wall to the platform and should stop it from bending under the weight of the arm.

Right before printing, I realized the servo bolts had nothing to tighten into inside the hollow base.

So I’m getting an M2 bolt-and-nut kit. The bolts will pass through the printed base and servo ears, then the nuts will hold everything from underneath.

Next, I’m printing the fixed base and rotating platform.

Then I’ll install both servos and check if everything fits, feels strong, and rotates without rubbing.

Do you think the wall and triangular supports look strong enough, or should I make them thicker before printing, or do you guys have any other suggestions or feedback?

D E V L O G # 2
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BUILDING THE BASE
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Alright, quick update again haha.
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The first servo fit gauge was too loose, so I measured the servo again and made a new one with a 23.4 × 12.4 mm opening. This one fit much better.
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After I finished that, I measured the mounting holes and figured out the correct position for the servo shaft.
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Then, I started designing the actual base. I made the circular housing, added the servo opening and mounting holes, built a 30 mm support wall, and added a notch for the servo wire. - (PLEASE let me know if you have any suggestions)
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The fixed part of the base is basically finished.
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NEXT: Designing the rotating platform.

I’m starting to work on my SG90 robot arm! Honestly, coming into this project, I was a bit skeptical on how I would even start. But now that I did, I found that it wasn’t so hard! For this session, I technically worked for an hour, but I guess I forgot to take a time-lapse of it. I worked on getting all the materials, getting servo measurements, setting everything up, and finally modeling and printing a fit gauge to test if the measurements for the servo fit ok to continue. On to the base!  (Next session) In the next session, I’ll continue to get into things more, and probably start modeling the base. See you next time!!