DC motors

A DC motor is designed to run on, what do you know, DC electric power! There are by far two common kinds of DC motors, the brushed and brushless types. However, these two types use certain forms of commutation, internal and external respectively, which create an oscillating AC current from the DC source.

Two pole DC motor:

A simple DC electric motor. When the coil is powered, it generates a magnetic field around the armature, which is the bit in the centre that is rotating. The left side of the armature is pushed away from the left magnet and the right side is pushed away from the right magnet.

Armature continues to rotate.

The commutator reverses the direction of the current through the coil, reversing the magnetic fields. The process repeats itself.

However, DC motors are designed with more than two poles and can start at any position. Current flowing through the coil will also definitely start the motor moving.

So as we see from above, the DC motor can operate in quite a simple manner. Connect voltage to the terminals of the motor, and the motor shaft spins. Since the motor is non-polarized unlike the solenoid that was mentioned in the previous post, it can spin in the opposite direction. Just reverse the wires connected to the motor. Now to spin the motor at a slower speed? Just lower the voltage connected to the terminals. Spinning faster would require more voltage. But what if I want to know exactly what voltage a motor should get? What’s the difference between 48V and 12V?

Voltage

Typical motors used in hobby robotics are rated at about 6V to 12V. Larger ones used in heavier hobby robotics are usually rated at about 24V or more.

So why do motors operate at different voltages? We know that voltage that a motor runs at affects the motors torque, so more voltage, more torque. However, you definitely should not be running your motor at voltages way above the recommended ratings like running a 12V motor at about 120V. This is dangerous and could melt the coils in the motor. A DC motor’s rated voltage is the voltage at which it runs the most efficiently. Keep it safe, and try to apply voltage as close to the recommended voltage as possible.

Do keep in mind that if you want to use a 24V or more motor on your robot, your robot must also be able to carry a battery that can supply that amount of voltage (which are heavier, bulkier and bigger). So unless you really need the torque to power your robot, stick to the 12V motors.

Will have more information on DC motors coming up in this post as soon as I find the time to write :)

Solenoid

My ultimate favourite when it comes to electrical actuator, the (not-so) humble solenoid.

So, the solenoid is an electrical actuator, like the DC motor or the valves that are used in modern day industries. What it basically does is convert electrical energy into mechanical energy.

The solenoids that I will be talking about in this post is basically the ones referred to in engineering, referring to a kind of transducer which convert energy to linear motion.

So what is a solenoid? Below are some pictures of solenoids:









So solenoids, be it electromechanical (AC/DC), hydraulic or pneumatic driven, when given energy will produce a linear force.

Let's take a closer look into the insides of a electromechanical solenoid:




















Inside the solenoid is motor wire coiled around in a special way. This special coil of motor wire, when energized (current flowing through the wire), creates a magnetic field.

In the picture above, we see that the motor wire has been coiled around a metal rod. This is known as the plunger. The magnetic field attracts or repels this rod that is usually made of iron or steel, applying a force on it. When the field is turned off (no more current flowing through the motor wire and therefore the coil no longer is energized), the spring that is connected to the plunger will return it to its original state.

PUSH AND PULL!
So we see that the plunger can either be pulled into the shaft where the motor wire is coiled, or pushed out of the shaft, limited only by the spring attached at the back.

This leads me on to the two kinds of solenoids that one can have: a push solenoid, or a pull solenoid.

In a push solenoid, the plunger is normally kept inside the shaft. When the magnetic field is turned on, it applies a force on the plunger, forcing it out of the shaft. This gives us a pushing force at the end of the plunger. When the magnetic force is turned off, the spring will bring the plunger back into the shaft.

Unlike the spring of the push solenoid, the spring of the pull solenoid keeps the plunger out of the shaft of the solenoid. When the magnetic force of the pull solenoid is turned on, it 'pulls' the plunger back into the shaft.

POWER!!!
So after so much talk about how a solenoid works, how can we control one?

Well, we see that the solenoid is polarized, meaning that it can only work in one direction: push or pull. We cannot make a push solenoid pull, or a pull solenoid push.

So all we need is a MOSFET and/or a relay that will trigger the current flow to the solenoid.

Do take caution when powering the solenoid as powering the solenoid at high currents for extended periods of time could lead to overheating and melting. The power rating should not be less than the voltage times the current draw of your solenoid. However, it is fine to go over this rating for intermittent periods of time.

Video Time!!!
Now time for a video as to what a solenoid can do. These are videos of a soccer robot from a Australian robot soccer team (a very good one by the way), that are using the solenoid as the 'kicker' that is propelling the ball forward:



That's all for this post. I will add in more stuff on the other points later :)

Tech: Robotics

Hi all :)

this blog will have information on the different parts of a robot.

What I have planned now would include:

1. Sensors
2. Actuators (electric, direct current)
3. Materials
4. Microcontrollers

When I become better in other areas, I will start posting up information too.

I will also have some pictures of some of my previous robots placed up on this blog.

Enjoy.