How to make it: Humanoid

How to Make it: Humanoid

This is a 22 degrees of freedom humanoid robot. Before starting I should make it clear that it's not a DIY tutorial because the entire process was quite complex & tedious. Also, most of the parts I used are probably not available outside India as these are local made. I also didn't use any 3D printed parts. However, it will provide some idea regarding how to start building a humanoid robot from scratch. So let's get started!

1. Legs

First I started with the legs. My original plan was to have 6 motors per leg. To be able to do almost any motion a legged robot needs at least 6 degrees of freedom. However, the motor designs were not suitable for this. So I decided to use 5 per leg. It was a slight trade off but mostly it won't affect any motion. In fact, the only motion that's difficult to do with 5 motors per leg is the turning, but still, it's not impossible. Here are the parts I used for making the robot.

Servo motors (35 Kg-cm, metal gear, dual shaft)
Motor brackets (bought separately)
Acrylic sheets (for foot & waist)

There are two types of brackets as seen above in the images. The white coloured ones came with the servo motors. The black ones I had to buy separately. The hip & ankle joints each have 2 degrees of freedom. To make the hip & ankle joints two motors were glued using super glue. It's not the most effective way of doing but using 3D printer was not an option so I had to glue them. Finally it looked like this.

The red coloured parts are acrylic sheets used as waist & foot. As it can be seen I used double sided tapes to attach the waist & foot. It was temporary though. I was going to replace them with screw & nut for better sturdiness. Also, lots of wires! Each motor has 3 wires. I joined all positive terminals together & all grounds together. The jumper wire strip is the signal wires of each motor.

2. Body

Next up it was the body. First I thought of making the body using 3D printer but unfortunately, the machine went out of order at that time. I was anxious what to do now. The machine was not getting fixed anytime soon then. I had to complete the entire robot within a month, so I decided to use acrylic sheets & super glue to make the body. Here are the initial body design (supposed to be 3D printed) & the acrylic body design.

The left side design is the 3D printing design & right side is the acrylic design. It turned out to be OK. Finally, the body would look like this after adding the shoulder motors & waist brackets.

Here are the laser cut acrylic pieces for the body.

Here are some pictures after I attached the body to the robot.

The body contains arduino, wiring, switch, a fan & a step down converter.

3. Hands

The hands are similar to the legs. Each hand has a total of five motors including one for the gripper. Here are the parts used

Servo Motors (18 Kg-cm, metal gear, dual shaft)
Micro servo motors
Motor brackets
Acrylic sheets

hd 1.1

hd 1.2

hd 1.3

The shoulder motor is attached to the body. The arm is made by joining two motors using brackets as shown in the fig. hd 1.3. To make the forearm acrylic & one motor bracket was used. Here's the forearm part

hd 1.4

hd 1.5

Then comes the gripper. The gripper is attached to the servo horn (fig. hd 1.4, hd 1.5) on the forearm. I kept the gripper design quite simple as more complex designs were coming off as too bulky for the robot.

hd 2.1

hd 2.2

hd 2.3

In fig. hd 2.1 it can be seen how the two micro servos are joined. The blue parts are the servo motors & the red parts are the acrylic part used to join the two servos together using super glue. One of the servos serves as the wrist joint (fig. hd 2.2) & the other one is used for the gripper. The wrist joint has single degree of freedom. The gripper is made using two pieces; one stationary & one movable piece. The stationary piece can be seen in fig. hd 2.1 which is used to join the two servos. The other piece of gripper can be seen in fig. hd 2.3. The design is very basic but it works nicely. The gripping edges (acrylic parts, red coloured) are curved which helps in gripping firmly almost any object of any diameter or length. However, the wrist joint is not that strong. The servo shaft diameter is very small so the joint where the servo shaft is connected to the servo horn on forearm (fig. hd 2.2, hd 2.4) can break very easily. It works fine for light objects.

hd 2.4

4. Electrical setup

All the 22 motors are directly controlled by the microcontroller (Arduino mega). Each servo motor has three wires which act as power, ground & signal wires. All the motors are either powered directly from the battery or through a 5 V DC-DC converter with a common ground connection between battery & microcontroller. The signal wires of the servo motors are directly connected to microcontroller’s digital I/O pins. These pins can be directly addressed with desired position value to move the motors. The leg & hand motors can consume 3.5 A & 1.9 A at stall torque condition. So considering maximum torque requirement the maximum current needed was 46.4 A (3.5 A x 10 + 1.9 A x 6) excluding the wrist & gripper motors. All the motors except micro servo motors are rated to run on 7.4 V Li-Po battery. Hence a 7.4 V, 2200 mAh, 25C Li-Po battery was used to power all the electronics as it can provide a maximum of 55 A (2200 mAh x 20 C). All the motors except the wrist & gripper can run on a maximum of 8.4 V which is directly supplied by the 7.4 V battery. For wrist & gripper motors a step down DC-DC converter is used which supplies 6V at 2 A current.