RobotShop M100RAK V4 Modular Robotic Arm Kit (No Electronics)

RobotShopSKU: RB-Rbo-85
Manufacturer #: M100RAK-V4

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Sale price £659.03

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Included in this bundle


  • Four Degree of freedom (4 DoF) modular robotic arm
  • ~1Kg lifting capacity at full reach (640mm / ~29.53in)
  • All metal gears
  • General mounting plate for mounting an end-effector (no gripper)
  • Servo controller and power supply sold separately

The RobotShop M100RAK V4 Modular Robotic Arm Kit is one of the most affordable and versatile “intermediate sized” all-metal robotic arms on the market. The arm has a maximum (suggested) reach of just over 640mm without the addition of an end effector (gripper) and can lift about 1Kg at this extension. The closer the weight is to the body, the more the arm can lift. The M100RAK includes all brackets, hardware and 4x Hitec HS785HB RC servo motors. Although the functionality is similar to previous versions, the V4 uses a different design, different brackets and the mounting hole pattern is different.

The M100RAK is intentionally modular, and the design provided in the product description and the assembly guide is only one of many possible configurations. Joints and brackets can be flipped or rotated as needed, and parts from the GoBilda system easily added to make custom designs. The center of each joint and tube is hollow, so wiring can be internal. Easily customize your arm by drawing and creating 3D printed shells using the CAD files provided below.

M100RAK V4 - Side View

Most robotic arms are either too small for regular applications, or too expensive to be used as development platforms by hobbyists. The M100RAK is intended to be the perfect size for most robotic arm applications since it is roughly the length of an adult human arm, and still powerful enough to lift a decent payload. Note that each servo can potentially draw up to 1.8A under full load, so you will need a 6V power supply capable of ~5A continuous and ~10A peak. .

Warning: The arm contains open gears and is very powerful. Please take every precaution to ensure no objects (especially fingers) get caught in the gears. Should you have this fear, we suggest adding a bent cardboard or plastic cover over each joint. Keep out of reach of children.


  • Robotic arm: With the addition of a gripper, a standard robotic arm can be used for many different projects.
  • Computer-controlled camera mount: The basic arm includes a metal mounting plate which can easily be used to mount a standard camera.
  • 3D image capture: Adding a distance sensor to create a complex 3D scanner. Adding a variety of sensors to a robotic arm
  • Router-based CNC machine: Mount a handheld router and create a manual or CNC controlled router arm for experimentation
  • Scale human arm: The length of the shoulder joint to the elbow joint is almost the same length of an adult's humerus bone, while the length from the elbow to the wrist joint is almost the same as an adult's Ulna. There are two main degrees of freedom missing in the arm to make it closer to that of a human: a rotation joint within the “humerus” and a rotation joint within the “ulna”.
  • 4x - Hitec HS-785HB Winch Servo Motor
  • 4x - Servo Gearbox Frame (43mm Width, for Large Size Servos)
  • 8x - Flanged Ball Bearing (32mm ID x 39mm OD, 5mm Thickness)
  • 2x - 32mm ID Spacer (36mm OD, 4mm Length) - 2 Pack
  • 4x - Aluminum Flanged Tube (28mm ID x 32mm OD, 39mm Length)
  • 2x - goTUBE (192mm Length)
  • 1x - goTUBE (96mm Length)
  • 6x - 1-Side, 2-Post Clamping Mount (32mm Bore)
  • 4x - Thru-Hole Clamping Hub (32mm Bore)
  • 4x - U-Channel (1 Hole, 48mm Length)
  • 1x - 4mm ID Spacer (6mm OD, 16mm Length) - 4 Pack 
  • 1x - Aluminum Baseplate (6mm Thickness, 144mm Diameter)
  • 4x - Brass, MOD 0.8, Servo Gear (25 Tooth Spline, 12 Tooth)
  • 4x - Aluminum, MOD 0.8, Hub Mount Gear (32mm Bore, 108 Tooth)
  • 1x - Low-Side U-Channel (3 Hole, 96mm Length)
  • 1x - 3-Pos TJC8 Servo Extension (MH-FC to FH-MC, 600mm Length)
  • 1x - 3-Pos TJC8 Servo Extension (MH-FC to FH-MC, 900mm Length)
  • 1x - Zinc-Plated Steel Socket Head Screw (M4 x 0.7mm, 18mm Length) - 25 Pack
  • 1x - Zinc-Plated Steel Socket Head Screw (M4 x 0.7mm, 35mm Length) - 25 Pack
  • 3x - Zinc-Plated Steel Socket Head Screw (M4 x 0.7mm, 8mm Length) - 25 Pack
  • 1x - Zinc-Plated Steel Washer (4mm ID x 8mm OD) - 25 Pack
  • 1x - Zinc-Plated Steel Nylon-Insert Locknut (M4 x 0.7mm, 7mm Hex) - 25 Pack
  • 1x - 2.5mm Hex L-Key
  • 1x - 3mm Hex L-Key
  • 1x - 7mm Combination Nut Driver
  • Bottom of base to shoulder axis: 110mm (~4.33in)
  • Shoulder axis to elbow axis: 276mm (~10.87in)
  • Elbow axis to wrist axis: 276mm (~10.87in)
  • Maximum horizontal reach: 640mm (~25.20in)
  • Maximum vertical reach: 750mm (~29.53in)
  • Weight: 1.96Kg

RobotShop M100RAK Robotic Arm Kit Dimensions

  • Four degrees of freedom using Hitec 785HB servo motors
  • All aluminum frame with ball bearing support
  • Servo casing is water and dust tight and features Karbonite gears and ball bearings 
  • 9:1 gears increase torque of each servo motor by a factor of 9 
  • Operating voltage: 4.8 to 6V (6V suggested for maximum torque). 
  • Current: 1.5 to 1.8A per motor depending on voltage used. 
  • Angular range per joint: 140 degrees
  • Weight: 1.96Kg (not including electronics or gripper / end-effector)

Customer Reviews

Based on 1 review
Superior arm, lack on instructions

For $600, the arm should be superior, which for the most part it is compared to other toy/hobby robot arms. One major flaw is no instructions. The arm uses 785 Winch servos, and they are STRONG along with a large gear ratio. Have not had much time to work with it yet, but did set it up with the Phidgets servo controller and all worked ok. Just takes a little time dialing it in just so you can do basic movements. Again, RobotShop needs to provide detailed instructions. You guys have great products and I know its for hobby users, but step by step instructions is a MUST. Add this and I would give another star or two.

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