Heads up: this kit is AI-designed and hasn't been test-built. Parts may not fit together or match your hardware as-is — expect to adjust holes, clearances or dimensions. Print one part and dry-fit it before printing the rest or buying hardware.*
Printed parts
SG90 Four-Axis Desktop Robot Arm
A 4-axis desktop robot arm that runs on four SG90 servos. It has a turning base, a shoulder carried on a 625 bearing, an elbow and a geared parallel gripper. There are eight printed parts.
6 of 8 planned parts designed so far.
This is a small 4-axis robot arm for the bench. Four SG90 micro servos drive base yaw, shoulder pitch, elbow pitch and a two-jaw geared gripper. The reach is about 200 mm, and it can pick up and move light objects such as dice, foam blocks or chess pieces from an Arduino, ESP32 or PCA9685 board. It is a cheaper starter alternative to MG996R arms. The shoulder, which carries the most load, is supported on both sides: the servo horn drives one side and a 625 bearing on an M5 bolt holds the other. That takes bending load off the servo's own bearing.
Every servo mounts the same way (interface I1): the body drops through a 28 mm window, and the ears are fixed with M2 screws through slots. The window is 5.8 mm longer than the SG90 body, so the servo can slide to line its shaft up with the joint axis before you tighten it. The distance from the ear face to the horn face is not published for the SG90, so that is also adjustable: the shoulder idler cheek slides ±5 mm on slotted feet, and the idler jaw pivot slides ±2.5 mm to set the gear mesh. Every horn sits in a printed pocket (I2) and is fixed with the self-tapping screws that come with the servo, using the horn itself as a drilling template.
Assembly order:
- Centre all four servos at 90° with your controller before fitting any horn.
- Base: drop the yaw servo into the deck window, shaft up, and slide it so the shaft is on the base centre. Fix the ears with M2x10 screws and nuts. Screw or clamp the base to the bench.
- Turntable: press the double-arm horn into the underside pocket, pilot-drill 1.5 mm through two horn holes, and fix it with the horn screws. Press the turntable onto the yaw spline and fit the centre screw through the top access hole.
- Melt two M3 heat-set inserts into the turntable. Mount the shoulder servo in the upright window with the shaft pointing inward.
- Upper arm: fix a horn in the shoulder hub pocket, fit its centre screw, then press the 625 bearing into the top of the hub. Push the arm onto the shoulder spline.
- Put an M5 nut in the cheek pocket and loosely bolt the cheek to the inserts. Run the M5x12 bolt in until its tip sits in the 625 bore. Slide the cheek against the arm with one M5 washer and tighten the M3 screws.
- Mount the elbow servo in the upper-arm window. Fix the forearm hub to its horn.
- Gripper: bolt the palm to the forearm with two M3x12 screws, with nuts in the forearm pockets. Mount the gripper servo, fix the drive jaw to its horn, and fit the idler jaw on an M3x20 bolt through the palm slot. Slide the pivot until the gears mesh with no backlash, then lock the nylock nut.
Tuning: run the servos from a separate 5 V 3 A supply, not from the Arduino's 5 V pin. Limit the shoulder to about ±70° from vertical in software. Close the gripper only until it stalls on the object and then back off 5°, because SG90s overheat if held at stall.
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