LittleArm Big: a Large 3D Printed Arduino Robot Arm

The LittleArm Big is a fully 3D printed Arduino robot arm. The Big was designed at Slant Concepts to be a viable 6 DOF robot arm for upper level education, and makers.

This tutorial outlines all of the mechanical assembly of the LittleArm Big.

All code and files are available on the LittleBots Website.

You may also purchase the hardware and electronics for the Big here.

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All Parts for the LittleArm Big are included in the kit.

Feed servo wire through the tunnel out the back of the servo slot.

Start the servo into the slot angled so that the wire-side leads. Then press firmly to set the servo.

Use 2-4 long servo mounting screws to secure the servo into the base. Insert screws in a star pattern

Use a servo horn to gently rotate the servo fully clockwise. Then remove the horn. (Servos have a range of motion of only 180 degrees)

Insert a servo horn into the slot on the Shoulder Yoke. Secure with two short servo horn mount screws

1. Feed the wire through the hole on the side of the servo slot
2. Lead with the wire side of the servo and set into the servo depression. (To allow the servo to enter more easily you may file the edges of the servo slot)
3. Repeat for the partner servo.

You may use a rubber mallet to gently set the servos.
DO NOT hit the servo armature with the hammer

Note: The end of the Upperarm with the small nub is the top or elbow joint. The large nub is the shoulder joint

1. Rotate the the Shoulder Servo fully counter-clockwise
2. Rotate the Elbow Servo fully clockwise
3. While not necessary you may use 2 screws per servo to secure the servos in their slots. Stagger the screw positions.

1. Feed the servo wire through the hole in the back of the servo slot.
2. Set Servo into Servo Slot
3. Secure with 2 short servo mounting screws
4. Use a spare servo horn to GENTLY rotate the servo fully clockwise

1. Set the servo horn into the slot on the Wrist Yoke
2. Attach the Wrist Yoke to the wrist yoke servo so the horn points to the right and the arrow points to the left.

Set servo into the Wrist End. If it is difficult remove a sticker from the side of the servo. There is no need for screws.

1. Apply adhesive foam to the grooves on the gripper finger tips. Or run a bead of hotglue along the pads of the fingers.
2. Press the servo into the Gripper Palm
3. GENTLY rotate the servo fully clockwise
4. Attach the servo gripper finger. Place the armature hole onto the servo first then press the other side of the gripper onto the rotation nub. BE CAREFUL not to spread the finger gears too far or they may break.
5. Apply the Idler Finger similarly. Ensure that the finger gears mesh so that the fingers are symmetrical.
6. Close the fingers firmly and apply the servo horn.
7. You may use a short servo mounting screw to secure the horn to the finger. BUT this can result in damage to the servo if the finger is jammed. We recommend leaving the horn loose.

1. Press the Wrist into the slot on the Gripper.
2. Feed the gripper wire through the wrist organizing loop.
3. Hot glue the gripper wire into the small depression in the Gripper Palm

1. Feed the Cuff servo wire through the holes in the Cuff and the Elbow Yoke
2. Apply hot glue to the channel at the base of the Elbow Yoke and then press the Yoke to the Cuff so that the wire slots align

1. Connect the Gripper and Wrist End to the Wrist Yoke. Lead with the servo armature.
2. Position the Wrist at a 90 degree angle to the Wrist Yoke and apply the servo horn as shown. Secure with screw.

1. Remember that the small nub on the Upperarm is the elbow rotation nub
2. Connect the Elbow and Uppearm. Lead with the servo armature
3. Rotate the Forearm to the clockwise extreme and apply the circular servo hub
4. Align the holes of the servo hub with those in the elbow yoke.
5. A single short servo mounting screw is sufficient to secure the Elbow Hub at either of the two locations

2. Connect the long (50 cm) wire extensions to the Gripper, Wrist End, and Wrist Cuff servos.

• Black to Brown
• Read to Red
• Yellow to White

3. Run the servo wires through the Upperarm in the following order

• Elbow Servo
• Wrist Cuff Servo
• Wrist end Servo
• Gripper Servo

4. When complete all wires should be through the Upperarm with slack at the top for motion.

5. Thread all wires through the Shoulder Yoke and base.

Coil wires through clockwise side of base and apply the shoulder as shown to Base.

1. Connect the Shoulder to the Shoulder Yoke. Lead with Servo Armature
2. Place the Upperarm at a 90 degree angle to the Base and apply the servo horn
3. You may use a Short Servo Mounting Screw to secure the horn and improve the precision of the arm. But it is not necessary.
4. At this point the arm should be pointed down and to the right as shown.

1. Insert the Board into the electronics box so the power adapter and USB connection point toward the matching holes in the box.
2. Secure the board with the 4 Arduino Board Screws.
3. Connect the short (10 cm) servo extension wire the shoulder servo wire.
4. Thread all servo wires through the electronics box lid.

1. Connect Servo Wires according to the diagram.

2. Seal the electronics box

It is easier to identify servos based on the length of the wire.

The Arm is finished! Just upload the Arduino code and connect to one of the apps. (Note: Make sure bluetooth is not connected when uploading the Arduino Sketch. The Bluetooth and USB interfere with each other.)

You may download the arduino code and desktop software here.

Here is the Bluetooth App.