Mechanics Frame

Here is where we list the mechanical parts of the robot from the metal or plastic arms or moving mechanism to the nuts and bolts and wiring involved.

We will try to cover some of the important concepts involved in what is called mechanical engineering as it relates to robots such as simple machines, inverse kinematics, pneumatics and hydraulics and how robot arms involve the study of gears and linkages and more.

We will talk a little bit about some of the advanced math involved in movement in a different section like the matrixes of inverse kinematics and the Jacobian method for calculating IK.

Now, in the next section we will explore gears as it relates to robots and cuckoo clocks while in another section we will talk more about the importance of the joint for movement and a discussion of linkages and belts and pulleys and screws as they all relate to making your robot move.

The study of movement and mechanics has a long history.

In fact this topic goes back to medeival times with people like Davinci who described the 6 basic simple machines including the lever, the screw, wheel/axis, the inclined plane the pulley and the wedge.

From here they combined simple machines together to create compound or complex machines.

They decided that the main ingredient to movement was the joint and there were 4 types of joints called the revolute joint, sliding joint, cam joint and the gear joint which could work along with cables and belts and pulleys.

In mechanical engineering they talk about movement with the word kinematics and then talk about forward and inverse kinematics as it relates to moving an arm on a robot.

There is talk about the hinged joint and linkages and various kinds of gears and gear trains. We also can deal with belts and chain driven arms or leg mechanisms on a human or vehicular robot.

Eventually as you build robots, you will come across more mechanical engineering concepts like dealing with DOF of each joint and discussions about the x, y and z axis and the cartesian coordinate system.

Check out this amazing Youtube video of the Festo robotics company demonstrating the technology they use in creating very realistic moving arms and also insect robots.

The cartesian coordinate system is simply put, a way to represent the x, y, z plane using numbers. Just like how you play the game submarine by calling out the coordinates of where your ship is located (x, y) etc.

This area gets very complicated very fast when you or if you decide to get into inverse kinematics to determine the motion of an arm in relation to its end effectors. But few people will really need to know any of this to make very useful robots.

You can buy some of the mechanical parts and of course the electronics from a store like Servocity

Now lets in this section talk about some of the first simpler questions when building a robot like what kind will you build and from what material and how you make those choices.

A vehicular outdoor robot will require different parts and types of materials than perhaps an indoor humanoid robot.

So the initial questions would be like the following

– what is the purpose of the robot? Will it do work like welding or carrying something outdoors or simply greeting customers indoors

– where will it operate? indoor or outdoor would dictate the use of plastics versus metals and if all the electrical parts would have to be protected from wet or cold weather

– how will it move? will it be a 2 legged humanoid or wheeled or stationary or will it be an animal type robot with legs or wheels or will it be a working stationary indoor robot with 1 or 2 arms

– how realistic will the humanoid or animal looking robot be? Will it require expensive eyeballs, latex skin, moveable legs or wheels, hair

A trivia fact is that the human body has 206 bones with a few extra in special case of an extra rib and with half of the 206 being in your hands and feet…we have 580 muscles in the body and half of them are below the waistline.

So once you pick the main category or purpose of the robot you can begin the design process on paper or with a 3d design program like Blender or Autodesk or any of over a dozen free or paid programs.

Full size humanoid robots mean one should choose lighter weight materials like plastics because heavy robots cost more.

There would be a need for more expensive and higher torque servos, stronger batteries or perhaps it would have to be plugged into AC house power.

If a 100 pound plastic robot falls over it will probably break some of its parts.

Metal like light weight aluminum must be cut and assembled with nuts and bolts or with welding which requires additional skills.

An older steel industrial smaller one arm assembly robot in a factory can weigh nearly 4,000 pounds and require specialized equipment to move.

Heavier robots might that need to lift heavy loads may have to be designed with hydraulic lifting arms or legs.

Most hobbyists will design small dog like roaming robots or 1 foot tall humanoid robot looking robots.

The inmoov project has been around for over 10 years and they encourage people to download their free 3d design to print out their own full size humanoid robot and then add the wiring and servos and download the moving software and of course make modifications as required.

So every movable joint (DOF degrees of freedom) requires some ball joint or a collection of nuts and bolts to allow for movement.

NoMetal will make noise when it moves and cheaper servos make a whirring sound so you may want to look at sound proofing materials and ensure that there is proper ventilation and sound electrical practices followed to not overheat the materials and cause a fire.

– heavier, more expensive servos,

If you were building a humanoid robot you would need brackets to hold the servos for the arm at the elbow at the shoulder, the wrist. Servo brackets for the legs and knees and the hips and the neck and on and on. In the head you may have brackets to hold the servos to control the eye and the eye lid and then the raising of the eyebrow and then the mouth and perhaps more.

Screws and bolts and all with a consideration to the weight and the access to repair and safety.

You may need to protect it from the elements with rust proofing unless it is a form of plastics but then you must protect the servo motors and other electric components