Arduino/Raspberry Pi Robotic Arm – Part 1: Unpacking and Assembling the ROT2U 6DOF Kit

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Today, we will discover the ROT2U 6DOF robotic arm kit that will allow us to start a new series of articles. In the previous series of articles, we saw how to assemble and drive WiFI a 2-axis Pan-Tilt articulated system using Blynk, Cayenne, Node-RED and the Nodejs Johnny-Five library. I propose to attack a project a little more complex this time with a robotic arm with 6 degrees of freedom (5 axes + 1 clamp). In this first article, we will discover the kit ROT2U 6DOF found on Chinese shops for about $70. This robotic arm kit – let’s say a manipulator arm – is a very good tool to start learning programming. The movements are carried out using servomotor type MG996R having a torque of between 13 kg.cm (at 4.8V) to 15 kg.cm (at 6V). Here is a small example of what we can do with this arm once assembled and controlled using an expansion card for Arduino Uno like this one.

Unpacking the ROT2U 6DOF Kit

The kit is delivered in a simple carton. The subassemblies are packaged in separate bags. The structural elements of the robotic arm are made by stamping aluminum plate. To give a better appearance and deburr the edges, the pieces are sandblasted. Black anodising (visible on the assembly instructions) has been abandoned.

To my surprise, there are no instructions or any list of spare parts. For the assembly, we will have to be satisfied with a notice in image available on Sky Drive here. For assembly, you will just need a 2.5 Phillips screwdriver.

Positive point of this kit, we find very easily spare parts. Most structural elements, servo motors MG996R, flanged base, clamp (or claw) are standard elements that are found very often in model kits or radio-controlled car.

Last update was on: 24 November 2017 4 h 04 min

Parts nomenclature

The bags are numbered on the previous picture.

Designation / reference Bag Dimension

L x l x h (mm)

Quantity
Servomotor

MG996R Tower Power

6
Long U shape 1 90 x 43 x 11 2
U shape 2 65 x 55 x 25 2
Square 2 36 x 30 1
Support plate 2

58 x 37 x 25

3
U shape 3

65 x 55 x 25

1
Support plate 3 58 x x37 x 25 2
Claw / clip 4 1
Stainless steel screws
M3x5 screew 5 31
Round head screw M4x8 + nut (fixing of servomotors) 6 21
Round head screw M3x8 + nut 7 31
Flat head screw M3x7 8 4
M3x10 Flat Head Screw + Nut (Bearing Mounted Side Mount) 8 4
Ball bearing 8 4
Fluted servomotor base 9 6

Characteristic of MG996R Servomotors

The MG996R servomotor is classic in model making. They are often found in Futaba, Hitec, Sanwa, GWS airplane, car, helicopter or radio-controlled boats. They are shock resistant. Here are some features

  • Dimensions: 40 x 19 x 43mm
  • Weight: 55g
  • Movement speed: 0.17sec / 60 ° under 4.8V without load
  • Maximum angle of rotation: 180 °
  • Operating Speed: 0.13sec / 60 ° under 6V without load
  • Torque: 13 kg.cm with a supply voltage of 4.8V
  • Torque: 15 kg.cm with a supply voltage of 6V
  • Supply voltage: 4.8 – 7.2Volts
  • Reducer: metal gears
  • Cable: orange / red / brown, 300mm (depends on the manufacturer), female connector

All technical specifications of Tower Pro

MG996R Digital Metal Gear Servo For RC Model

$4.79
Last update was in: 24 November 2017 4 h 04 min

Base assembly

The base makes it possible to turn the arm on its vertical axis (servo 1). To assemble the base, you will need

  • 2x U-shaped supports (bag 1)
  • 1x servo
  • 1x fluted base (bag 9)
  • 12x screw + nut M3x8 (bag 7)
  • 4x screw + nut M4x8 (bag 6)
  • 1x M3 flathead screw (bag 9)

Assemble the base by following these steps

  1. Assemble the 2 U-shaped brackets together opposite each other using the 8 screws and nut M3x8
  2. Then fix the plate to the base using 4 screws + M3x8 nut. The base must be perpendicular to the base
  3. Fasten the servo motor and put the pin inside the assembly
  4. Turn the servo motor shaft by hand until it stops on one side. This will be the maximum position of the servo on this side. Insert the fluted support to find the correct orientation of the support plate. Attach the splined bracket to the servo output shaft with a flat-head M3 screw.

Vertical arm assembly

The servomotor 2 makes it possible to incline the arm on its vertical axis. To assemble the vertical arm, you will need the following parts

  • 1x U-shaped support (bag 2)
  • 1x servo
  • 1x fluted base (bag 9)
  • 1x screw + nut M3x10 (bag 8)
  • 1x ball bearing (bag 8)
  • 4x screw + nut M4x8 (bag 6)
  • 4x screw + nut M3x8 (bag 7)
  • 4x M3x5 screw (bag 5)
  • 1x M3 flathead screw (bag 9)

Here are the assembly steps. Some pictures to help you just below

  1. Insert the M3x10 screw into the central hole of the joint (see photo)
  2. Fix the servomotor using the 4 screws + nut M4x8. Insert the splined bracket and rotate the servomotor shaft to find the low position of the arm.
  3. Insert the bearing on the M3x10 screw. The shoulder should be on the side of the servo bracket.
  4. Insert the U-shaped bracket starting on the bearing side. It takes a little force to insert the servo side. Secure the servo with 4x M3x5 screws to the fluted support. Fix the bearing side with an M3 nut.
  5. Secure the other U-bracket with 4 screws + M3x8 nut to finish the vertical arm

Elbow assembly

The servo 3 allows to tilt the elbow. See will need the following parts to assemble the elbow:

  • 1x U-shaped support
  • 1x Squares (bag 3)
  • 4x screw + nut M3x8 (bag 7)
  • 1x screw + nut M3x10 (bag 8)
  • 1x ball bearing (bag 8)
  • 4x M3x5 screw (bag 5)

Here are the steps of assembling the elbow. You can help the photos below as well.

  1. Fix the bracket with 4 screws + nut M3x8 on the U-bracket
  2. Fix the servomotor support plate to the bracket (use the picture below) with 4 screws + nut M3x8
  3. Insert the M3x10 screw in the central hole of the joint (see photo) and put in place of bearing (side shoulder servo)
  4. Fix the servomotor using the 4 screws + nut M4x8. Insert the splined bracket and rotate the servomotor shaft to make it stop.
  5. Put the main arm vertically
  6. Insert the elbow first side bearing then forcing slightly to insert the side servomotor
  7. Find the low position of the elbow (using the photo below)
  8. Rotate the fluted support to find the correct position adjustment
  9. Attach the elbow to the splined bracket with 4 M3x5 screws and secure the splined bracket to the servomotor output shaft with a flat head M3 screw

Wrist assembly

The wrist will allow rotation in 2 directions (servos 4 and 5). You will need the following parts to assemble the wrist:

  • 2x supports plate
  • 2x servomotors (n ° 4 and 5)
  • 8x screw + nut M3x8 (bag 7)
  • 2x fluted supports (bag 8)
  • 1x screw + nut M3x10 (bag 8)
  • 1x ball bearing (bag 8)
  • 2x M3 screws with flat head (bag 8)

The wrist mounting steps

  1. Fix the two plates with 4 screws + nut M3x8. Help the photo
  2. Fix the servo 5 (see photo) using 4 screws + nut M4x8
  3. Insert the M3x10 screw in the central hole on the right (see photo)
  4. Fix the servo 4 (see photo) with 4 screws + nut M4x8
  5. Put the two fluted supports on the shafts. Slowly turn the servo 4 shaft slowly to the end without forcing
  6. Put the arm and elbow vertically. Set up wrist on the elbow. Add the position of the fluted support.
  7. Fix the fluted support with 4 M3x5 screws and fix the fluted support on the servomotor output shaft with a M3 flat head screw

Claw assembly

Servo 6 opens and closes the clamp. Here is the list of parts needed to assemble the clamp:

  • The clamp
  • 1x servo (n ° 6)
  • 10x M3x5 screws
  • 1x M3 flat head screw (bag 8)

The assembly steps:

  1. Open the pliers and place the last fluted support. The plane face up.
  2. Close the clamp and fix it on the splined support with 2 screws M3x5
  3. Flip the pliers.
  4. Insert the servo n ° 6 into its housing. The axis is inserted into the fluted support.
  5. Secure the motor with 4 M3x5 screws. Fix the bracket with the last M3 flat head screw

Last step

And now, it remains only to screw the base of the clamp on the fluted support of the wrist with 2 M3x5 screws. These are the two most difficult screws because of the lack of accessibility.

Degrees of freedom of the manipulator arm ROT2U 6DOF

Here, the arm is assembled, here are the degrees (possible movements) of freedom of the manipulator arm ROT2U 6DOF. The MG996R servomotors can rotate up to 180°. This is enough for the joints but we can be limited at the wrist and the base for example. If this is a problem for your projects, you can replace it with a 360 ° servo motor such as a JX PDI-6221MG or JX PDI-HV5932MG. In the diagram below, you can see the rotational movements available for each joint (servomotor).

That’s it, everything is ready. in the next tutorial, we will see how to manipulate objects with Arduino code, python code … in short, what will we do next Christmas holidays that approach 🙂

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