littleBits Grappler: the robotic space arm

Written by: roboguru

Picture of littleBits Grappler: the robotic space arm

A grappler is on the end of the ISS Robot Arm and is used to grab onto objects in space – like astronauts! We created a working replica using an acrylic tube, a desk lamp and modules from the littleBits Space Kit.

Use the grappler at home to pick up "space" objects with the help of a household remote control and remote trigger.

Bits used:
power + remote trigger + wire + DC motor


  • Desk lamp (IKEA)
  • Acrylic tube (D4”, D3.5”)
  • Acrylic sheet T3.15mm
  • 3d printed battery holder (
  • Double sided tape (3M VHB)
  • Teflon sheet
  • M3 screws and nuts, flat and locking washers and M2 screws and nuts
  • Fishing wire
  • Metal tape
  • Nylon bushing


  • Laser cutter
  • 3d printer
  • Screw drivers
  • Pliers
  • Acrylic glue and applicator plus instant glue
  • Utility cutter and scissors,
  • Sandpapers
  • Saw
  • Masking tape
  • Ruler
  • Hand drill
  • Dremel
  • Clamps

Step 1: Create the Circuit

Picture of Create the Circuit

Build the littleBits circuit:

power +remote trigger + wire + DC motor

Step 2: Prepare the pieces for the body and arm

Picture of Prepare the pieces for the body and arm

1. Using the template file, cut out all the acrylic part out of 3.15mm acrylic board.

2. Cut 2 acrylic tubes.

  • Big one has 101.6mm (4”) diameter and 80mm height
  • Small one is 88.9mm (3.5”) in diameter and 48mm in height

Be mindful making drum edges straight and clean since we are going to glue other parts at the edge of the drums.

3. Remove the head from a desk lamp, so you are just left with the arm. Consider how you can attach you grappler head to the end of the lamp arm

Step 3: Build the inner drum

Picture of Build the inner drum

1. Build the smaller drum that goes inside.

2. Glue the thin ring and the disk with D-shaped hole, at each end of the smaller tube. A template printed on a paper may be useful aligning all three part well.

3. Add Teflon strips on the rims of each end. It helps the disk turn more smoothly.

Step 4: Create and attach the battery assembly

Picture of Create and attach the battery assembly

1. Print out two battery holders. (

2. Put a battery in it and screw down to the bottom part of the grapper.

Step 5: Assemble drum

Picture of Assemble drum

3. Using M3 screws and nuts, stick the bottom part to the tip of the desk lamp arm. We had locking washers outside to keep the screw stay tight and flat washers inside to spread the load evenly and prevent the acrylic from break.

4. Lay all the bits at their corresponding bit holes. It’s a good idea to have some thick double sided tape like 3M VHB or gluedots under each bits, especially on the DC motor because it is a part needs to stand a lot of load.

Step 6: Attach circuit to drum

Picture of Attach circuit to drum

1. Assemble all the outer part: bottom part, two stands, a disk with a circle hole at its center, and the bigger tube part. Use acrylic glue.

2. Attach the Teflon ring on the disk that the DC motor shaft goes through. Also put a nylon bushing around the shaft. These may help your grappler move smoother and keep the DC motor in right place. We had to sand down a nylon bushing to the tickness of the acrylic board.

3. Put the smaller drum inside of the bigger drum temporarily and mark where wires to be attached. There should be 3 marks on each drums that are distributed evenly every 120º. From the outer ring (the thin ring shape part which has teflon tape around), mark it 4mm above for the bigger drum marks, 4mm below for the smaller drum marks.

4. Draw a hole at every marked point and put a M2 screw through the acrylic tubes. Make sure that any of these screws touch any other part and let the small drum turns well. We used counter-sink-head screws.

5. Tie wires on the M2 screws, connecting one on the bigger drum to one on the smaller drum. The length of the wire should be slightly longer than the diameter of the big drum (about 4”). Secure them with M2 nuts.

Step 7:

Picture of

1. Plug the DC motor shaft to the D-hole on the smaller drum, allowing the smaller drum slide inside of the outer drum.
2. Stand the desk lamp arm on the clamp.

3. Use a household remote to control your Grappler.

This is similar to the arm that grabs onto moving vehicles in space!