Designing A Machine: Knowing The Difference

Design ⯀  

If you've always wanted to design your own machine that works exactly the way you want it to - this is a very exciting time. Not many people are able to say, 'this is my robot, I made it myself', so you should be proud of the drive that you have to do something so interesting. It will by no means be easy, as there are a lot of things to know before you start fiddling with wires and data, but it will definitely be worth it.

One of the first things you should figure out when starting your project, is what kind of motor do you need? There are quite a few to choose from, but don't be lazy and go with whatever one people claim to be the best, because there is always a deeper meaning to the outcome. You can be the only one to decide what you think will work best, because you're the only one who knows exactly how you plan on it being used and what its purpose is.

The conversation usually boils down to two - the servo motor, and the stepper motor.

Here's all the information you need to work out which one's best for you.

Servo Motors

The typical servo motor is built up of four things: a control circuit, a gearing set, a position sensor, and a DC motor. This can vary at times, but only on very rare occasions.

They tend to be a lot easier to control as they are a lot more precise than just the standard DC motor on its own. There is always constant power that is applied to the motor, while the control circuit regulates the draw in order to drive the servo motor, consisting of three wires being the power, ground, and control. They have been designed to carry out specific tasks rather than cover a whole area of things. They are refined to where the position needs to be absolutely accurate like it would be when controlling the rudder on a ship, or moving a robot’s fingers to be able to pick up an item off the table.

They move by rotating up to 180 degrees back and forth; they can not go any further than this as they don't have the freedom of rotating freely. They are able to move due to a control signal that is then turned into an output position for the machine to identify, and which way it moves is all down to the position sensor. The duration of the pulse is used for the control signal, rather than it basing itself on speed. So for example, if the pulse is increased, it will make the servo turn clockwise, whereas if the pulse is a lot shorter, it will turn anticlockwise.

When commanded to move, the servo will go to whatever position it was told to, and hold that position, regardless of whether an external force attempts to push against it.

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Stepper Motors

A stepper motor is very much similar to a servo motor, but uses a completely different method of motorisation. The stepper uses multiple toothed electromagnets that have been arranged around one main gear to define position, making it's system a lot simpler to function.

They must have an external control circuit (or a microcontroller) that individually engages with each of the electromagnets that make the motor shaft turn. So for example, when electromagnet #1 is put into action, it will attract the gears teeth and straightened them so that they are very close - but just offset - to electromagnet #2. This then happens to each electromagnet so that they continue to energize, and then de-energize in turn, so that a rotation starts to happen. When this process happens, each rotation is known as a ''step'', and from that, the motor turns to every angle so it can rotate to a whole 360 degrees.

The motors can come in two different forms: unipolar, or bipolar. Bipolar motors tend to be the most popular though as they are the strongest of the two, and normally have four or eight leads. There are also two sets of electromagnetic coils that are situated internally, and the stepping process is reached by them changing the direction of the current that is flowing within these coils.

The overall design of the stepper motor gives a constant holding torque without any need to power up the motor, and these can be found with companies like MOONS' motors. As long as it is used properly within its limits, then no kind of positioning errors can occur because it can move freely thanks to the motors predefined stations.

So have a think now you see the different comparisons as to what will better suit your project.

By  33rd Square