Here is a small video of a demo run of the robot arm.

The Arduino UNO program can be downloaded from github.

Bill of material

• 4x Servo SG90
• 1x Hex Socket Head Cap Screw M2x10 DIN 912
• 1x Button Head Screw Flanged M2.5x25 ISO 7380-2
• 3x Hex Socket Head Cap Screw M2.5x20 DIN 912
• 1x Hex Socket Head Cap Screw M2.5x15 DIN 912
• 8x Hex Socket Head Cap Screw M2.5x8 DIN 912
• 2x Hex Socket Head Cap Screw M3x10 DIN 912
• 1x Hex Nut M2 DIN 934
• 2x Hex Nut M2.5 DIN 934
• 4x Self Locking Nut M2.5 DIN982
• 2x countersunk head tapping screw 2.2x6 DIN 7982
• 1x countersunk head tapping screw 2.2x8 DIN 7982
• 6x metal balls with 4mm diameter

This reduces the height of the original gear and changes the center hole to 1.4mm diameter to fit with the width of the nail.

This changes one fixing hole for SG90 servo from 2.5mm to 2.0mm to match the size of the other hole. And make some room for the nut in the center.

Change the holder for the potentiometer taken from the SG90 servo.

Change the holes from 2.5mm to a 2.2mm diameterto allow the 2.5mm screws to be tightend.

I could not get a clean 3D print of clamp_main. Therefore I split it into two parts for printing. To assemble glued them together.

The lowerBearing holds the nail in the right position. It fits into the larger hole in the Arm-L_base.

Start assembling the roboter arm. Please note that the gripper mounted rotated by 180 degrees compared to the original CAD drawing by FrN. I followed here FrN's photos and not the CAD drawings.

Please note that you need to remove some material to be able to fix the center screw

Place six metal balls with a diameter of 4mm

Then fix the baseTop part.

I was not able to buy a potentiometer that would fit the original design of FrN. Therefore I decided to disassemble a SG90 servo and reuse the potentiometer found in it. The potentiometer is the green block in the upper right edge

Motor and electronics taken out of the plastic housing

Potentiometer bended a bit to be able to cut the connections to the pcb

Potentiometer top

Potentiometer side

Potentiometer bottom

We have to build now the mechanics that will drive the potentiometer. i started with a metal nail with a diameter of 1.4mm and a length of 25.0mm. Then I cut it down to a length of 19mm. The round head of the nail is then rasped down to model a small "hammer".

The original nail

The round head cut down to build a "hammer"

Closer look to the "hammer"

The "hammer" fitting into the rectangular space in the center of the potentiometer

A closer look

Plug potentiometer into the Arm-L_VRmount_mod

Other side showing how the clips fix the potentiometer

Fix the modified nail into the Arm-L_gearVR_mod

Place lowerBearing into the Arm-L_base as shown

Place the nail with the gear into the lowerBearing and attach the Arm-L_VRmount_mod as shown. Then fix it with two M3x10 screws as shown.

Insert the motor and the modified pcb back into the plastic box of the SG90

Fix the remaining parts of the SG90 servo

Fix the SG90 servo into the base and solder the connections from the servo to the potentiometer.

Clean up cables.

This is a small handmade pcb that connects the +5V power from USB to the servos. It also simplifies the connection of gnd and the 5 signal inputs of the servos to the Arduino UNO.

The is the Arduino UNO connected to the pcb ready to run the demo code.