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  • stubbornfinger

    The main component of our stubborn finger is a servo motor.
    A servo motor is a special kind of motor. It has a turning element – output shaft – that can be moved to specific positions by sending the servo a coded signal. The servo will maintain this angular position until the coded signal changes.

    Concepts and techniques in this recipe:

    Controlling a servo motor from Wiring

    BEFORE YOU START, make sure to have all the parts and tools you need for this example

    Parts and Tools

    Wiring Board

    Connector Pin
    Servo Motor
    Plastic connector

    This is what you are about to build:

    Stubborn Finger

    In this task there are 5 main steps

    1.a Examine the servo motor

    S Finger 01

    Let’s examine the servo motor before we start.
    The Servo motor is a black box with a rotating element that is the white unit of plastic on the top of the motor.
    Servo motors usually come with several plastic units that you can change according to your needs, they are usually small arm holders or round plates.

    If you want to know more about these motors visit our Servo-Motor Guide.

    1.b Servo motor wires

    S Finger 01

    The servo motor has three wires coming out of it, ending together in a plastic connector. The red and black wires are for power and ground (red is the ‘plus’ and black is the ‘minus’ or ground). To learn more about this kind of convention and what power and ground are, look at our Electronic Basics guide.

    The yellow wire is the data wire. It receives commands (in the form of electric pluses) that tell the servo motor to turn to a specific position.

    2.a Disconnect the yellow wire

    S Finger 03

    Our first goal will be to extract the yellow wire from the connector. Inside the connector are little plastic teeth that hold the wire tips in place.
    To extract the wire you need to slide a metal pin under the plastic tooth that holds the yellow wire.

    2.b Pull the wire out

    S Finger 03

    With the metal pin, push the plastic tooth upwards and gently pull out the yellow wire. it will be easier to pull up the plastic pin (2.a) and pull at the same time.

    2.c The yellow wire tip

    S Finger 03

    On the tip of the yellow wire you can see a small metal element.

    It is really useful to have this kind of metal element on the tips of wires, because they fit inside many kinds of connectors. This is a great when you are conducting fast tests with different electronics parts.
    The metal elements can be attached to the Wiring board pins as they are. However it is always better to insert them into a plastic connector. Then we can be confident that we won’t have short circuits (wires touching each other not according to the circuit plan).

    3. Insert the yellow wire into a new connector

    S Finger 03

    Take the yellow wire with the metal tip and insert it to an empty plastic connecter. Slide the wire into the connector slot until you will hear a tiny “click” sound. That means that the pin is being held by the plastic tooth inside.

    In this picture we can see a two-slot wire connector, however the most common ones have four slots.

    4. Connect the yellow wire to the Wiring board

    S Finger 03

    Connect the yellow wire connector to Pin number 0 (zero) on the Wiring board. Make sure the slot with the yellow wire is on pin 0.

    5. Connect the red and black wires to the Wiring board

    S Finger 03

    Connect the red and black connector from the servo motor to the wiring board. The red wire (plus) should be in line with the VCC pin and the black wire should be in line with the GND pin.

    Important! Please re-check the red and black pin locations.

    Stubborn Finger

    Considerations on object building

    At this point you shall have all the electronics ready to use.
    An important aspect of prototyping is making holding structures.
    Servo motors are strong and while operating they need something to hold them firm. There are many ways to hold a servo motor by attaching it to a larger object. Probably the simplest method, though impractical for long times, is to hold it in your hand.
    In the InstantSOUP example we built a small base made of Plexiglass. Then we made a little ‘finger’ using the same material and attached it to the shaft of the motor.

    There are many ways to make physical structures, starting from basic materials such as cardboard or paper.
    InstantSOUP believes that a prototype should be created in more then one level. First use simple and easy-to-find materials in order to get a fast prototype to work with. Later, if you want to improve your work and make it more robust, it’s a good idea to move from the basic materials to more sturdy ones like as wood or Plexiglas as we did.
    InstantSOUP has a special section regarding this and we highly recommend that you read it (click here).

    Construction details

    S Finger 03

    In order to give the motor a stable base and to prevent it from moving, we cut out 2 pieces of plexiglass and attached the servo motor to them with screws.
    The holders can also be made out of wood (it is very easy to use screws with wood).

    Construction details

    S Finger 03

    We then glued the side pieces to the plexiglass base.

    Construction details

    S Finger 03

    We attached the finger unit to the shaft of the servo motor.
    The shape and size of the ‘finger’ determines the best way to attach it to the motor. You can glue a straight stick of wood or plastic directly to the rotating plastic unit that came with the servo motor.