Hand and Forearm Overview

There are a total of 18 printed pieces.
• 4 Finger Tips
• 5 Finger Joints
• 4 Finger Knuckles
• 1 Thumb Joint
• 1 Thumb Tip
• 1 Palm
• 1 Forearm Body
• 1 Forearm Cover


Components & Materials:

• (17) M3 nylon lock nuts
• (17) M3 x 20mm bolts
• (17) feet 50Lb test fishing line
• Crimp tubes
• (2) 10/32 x 1 inch bolts
• (2) 10/32 square nuts
• (4) standard hobby servos (with horn and hardware)



• Hex wrench
> M2.5
> 5/32
• Needle nose pliers
• Wire cutter
• Philips screwdriver
• File


Step 1:

We are first going to assemble all five fingers. Every finger except the thumb is built from a single tip, joint and knuckle. The thumb is built from a thumb tip, thumb joint, and a joint. Each finger uses three M3 x 20mm bolts with a locking nut which lock into the pieces. There are two different finger variations. One has the bolt head facing to the right of the finger the other has it facing to the left (see picture). The thumb can only be assembled one way and the thumb joint has a ridge that is facing the left of the finger.

Step 2:

Install the four servo motors into the Forearm Body matching the orientation in the pictures. Use the hardware and double horn provided to secure each servo. Route servo motor wires under the other servos and out of the notch in the back. Notice there are two servo horns on the left and two on the right. The servo horns on the left will be starting at the position shown and rotate 180 degrees counterclockwise. The servo horns on the right will start at the position shown and rotate 180 degrees clockwise.


Step 3:

Cut ten 20 inch lengths of fishing line and crimp one side by feeding the line through one way and feeding it back through the other way. Feed each length of wire in each of the slots in the fingers. Start from the tip and feed until the line exits the bottom of the Palm. Connect the hand by feeding the loose line through the Forearm Body and secure using the 10/32 nuts and bolts.


Step 4:

We are now going to crimp the fishing line from each finger to a corresponding servo motor. The picture below shows what servo corresponds to what finger. Start with the fishing line that flexes the finger and attach it to the servo horn by using a crimp tube. Makes a small loop in the fishing line before crimping as shown. The servo should be in a position so it can rotate in its correct rotation. This means that if we crimp the line that flexes the finger to the motor and rotate it in its correct position the finger will flex by the servo pulling on the line. When you crimp the flexing line make sure you have tension on the returning line. Rotate the horn 90 degrees and crimp the return line to other side of the servo horn. Make sure both lines are tensioned. You should be able to rotate the servo horn by hand and see the finger flex and return based on direction of servo.


Step 5:

Attach Forearm Cover to Forearm Base by sliding the lip into one side and using two M3 x 20mm bolts and lock nuts. Attach Hand and Forearm to the Lower Rotation Joint by using four 10/32 x 5/8 inch square nuts in the slots on the Inner Rotation part and four 10/32 x 5/8 inch bolts.



The Hand and Forearm is done!



1. Hand Assembly

2. Elbow

3. Rotation Joint

4. Shoulder