In the industrial robotics world, the term "robot arm" covers two very different purchases. One is a new, unassembled arm kit that you build yourself with servos and a controller. The other is a used industrial robot arm sold arm only, with no controller or pendant included. Your choice depends on whether you want a hands-on project or a machine for serious automation.
Quick verdict
Pick the ARM-21N4 if you want a build-it-yourself arm and you're comfortable assembling mechanics and electronics. Pick the FANUC M-16IB/20 if you need a used industrial arm and can supply the missing controller, teach pendant, and cables.
At a glance
| Feature | ARM-21N4 5-DOF Robot Arm Kit | FANUC M-16IB/20 Industrial Robot Arm |
| Listed price | USD 119.23 | USD 1,800.00 |
| Condition | New | Used |
| Axis count | 5 DOF | 6 axes |
| Included items | Kit, digital servos, digital controller | Arm only |
| Output transmission | Metal gears plus double bearings | - |
| Size reference | Upper arm 121 mm, middle arm 111 mm, forearm 61 mm | 44 x 29 x 48 |
Where each product wins
The ARM-21N4 wins as a complete project package. It arrives unassembled, includes the servos and a digital controller, and gives you a mechanical arm with bearings on the moveable joints and a metal-gear output transmission. That makes it an approachable starting point for learning how a robot arm goes together.
The FANUC wins as an industrial arm. The unit is identified clearly as a FANUC M-16IB/20 (type A05B-1216-B202) with a serial number and build date, and it's sold as the arm only. If you already have or can source the control components, you're starting with an industrial FANUC arm rather than a kit.
Product notes
ARM-21N4 5-DOF Robot Arm Kit
The ARM-21N4 is a build-from-scratch robot arm. It arrives unassembled, so the first task is mechanical assembly and connecting the digital controller and servos. The construction details are solid for a project arm: all movable joints use bearings, and the output transmission uses metal gears plus double bearings. The gripper holder fits suction cups, electromagnets, forks, craws, grippers, and similar end-effectors, so you can swap tools as your experiments grow. The arm's segment lengths keep it compact: upper arm 121 mm, middle arm 111 mm, and forearm 61 mm. The limitation is that this is a 5-DOF kit, not a full industrial robot arm replacement. If your goal is production automation, you will outgrow it quickly.
FANUC M-16IB/20 Industrial Robot Arm
The FANUC M-16IB/20 is the opposite kind of purchase: a used industrial arm with a clear identity. The unit is identified as a FANUC M-16IB/20 (type A05B-1216-B202) with serial number R05476983 and a build date of 2005/04, so you know exactly which arm you are looking at. It is sold as arm only, meaning no controller, teach pendant, or cables are included. The unit shows cosmetic wear, paint loss, and signs of prior industrial use - part of buying used industrial equipment. The reason to choose it is the industrial capability in a FANUC arm. The limitation is the missing control components and the physical weight: 220 kg without the controller, or 486 lb. Make sure you have the support and lifting equipment before it arrives.
Final choice by use case
For a workbench, classroom, or prototyping project where assembly is part of the experience, choose the ARM-21N4 5-DOF Robot Arm Kit. It lists for USD 119.23 and puts the entire build in your hands.
For an industrial setting where you need a real robot arm and can source the controller, teach pendant, and cables, choose the FANUC M-16IB/20. It lists at the higher end of the range, about $1,680.77 above the ARM-21N4, and brings a 20 kg payload to the job.
