sábado, 26 de enero de 2013

The motor (1)

You can take 2 ways when choosing the motor. The easy one and the not so easy.

The easy one is to use a normal servomotor configured to infinite rotation (sometimes called full rotation). A normal servomotor controls the POSITION of his axis. This means, it turns until it reach his commanded POSITION. But it is possible to modify this kind of servomotor in such a way that it turns to a certain SPEED but never reaches is command position. You can do this my "fooling" the control installed into the servo. You interrupt the position feedback. Therefore, the servo keeps turning and turning but never reaches is target position.

There are different ways on how to do this. Have a look here and here.

You can also purchase a ready made continuous servo. For example here.

Working in this way allows you to directly connect the servo to your controller. No additional electronics are needed. Less wiring and therefore less complexity. This is the way I used for my first prototype.

But there is a draw backs in this approach.

Servomotors are a combination of a DC-Motor + Electronics + Gear. The included gear has a big reduction ratio. Therefore, the original motor (high-) speed is reduced to a small one at the output. This is necessary to increase the output torque of the servo. Low speed is good at the beginning as it let's you clearly see what's happening. But very soon you will want more speed.

If you purchase a DC Gear Motor, you choose the Gear ratio. So, you can select a faster or slower motor.
Have a look here to see a selection table that shows 2 motor types with different Gear Ratios.

In motor (2) I will show you the combination DC Motor + Drive. Things will be faster there!

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