pxt-calliope/docs/device/servo.md

Equipping a microservo with Crocodile clips

~ hint

If you are running a class or activity, you should consider preparing all servos before hand.

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Using a microservo with the @boardname@

The @boardname@ provides just enough current to operate the SG90 microservo. The servo requires 3 connections: GND, 3V and a logic pin. In this tutorial, we will equip the servo with crocodile clips to make it easier to use. However, you could also use a shield or female to crocodile clips to acheive the same effect.

The easy way: Alligator/Crocobile Clip to Male Jumpers #hintconnection

The easiest way to connect a servo to the @boardname@ is to use cables that have an Alligator/Crocobile clip on one end and a Male jumper (pig tail) on the other end. You can purchase bundles of such cables from various electronic resellers or easily build yours as show below.

https://youtu.be/XtzsydSTXEg

Materials

• 1 Crocodile clip cable
• 1 male (pig tail) cable
• Cutting pliers or wire cutter
• 1 shrink wrap cables and a lighter

Simple cut the cables, strip them, thread the cables together and cover with the shrink wrap.

~ hint

It is very important to ensure that there is a good connection between the 2 cables. If the connection is weak, the microservo will not receive enough current and it will not work. If you have access to a soldering iron, we strongly recommend to solder this connection.

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Direct connection

You can also connect your crocodile clips directly to the servo.

Materials

• Cutting pliers or wire cutter
• Tape (masking, duct tape, and/or packing tape)
• 3 crocodile clips, yellow, red and black.
• 1 micro servo 9g (SG90)

Step 1: cutout the connector

Using the cutting pliers, cut out the dark plastic connector.

Step 2: strip out cables

Using the plier or a wire stripper, strip the plastic from the cables.

Step 3: threading the servo cablers

Thread the servo cables.

Step 4: crocobile clip

Cut a crocodile cable in two and strip out the casing. If possible try to use the same cable colors as the servo!

Step 5: thread cables together

Place the cables next to each other

... and thread them together.

~ hint

It is very important to ensure that there is a good connection between the 2 cables. If the connection is weak, the microservo will not receive enough current and it will not work. If you have access to a soldering iron, we strongly recommend to solder this connection.

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Step 4: protect the connection

Protect the connection with shrinkwrap tubes, electrical or duct tape.

Step 5: repeat for all cables

Repeat the same process until all cables are connected.

Step 6: testing!

It's time to test that your connection are all proper and that the servo will function when the @boardname@ is powered by battery.

• Connect the microservo to the @boardname@. Black cable on GND, red cable on 3V and remaining cable on P0.

~ hint

When attaching the crocodile clips to the pins, don't hesitate to grab the side of the board with the jaws.

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• Download the following code to your @boardname@

basic.forever(() => {
    pins.servoWritePin(AnalogPin.P0, pins.map(
        input.acceleration(Dimension.X),
        -512,
        512,
        0,
        180
    ))
})

• When powered by USB, make sure that the servo moves when you tilt the board.
• When powered by batteries only, make sure that the servo moves when you tilt the board.

Calibrating

Using the servo calibrator program to determine the best angles to use in your make.

Troubleshooting

If your servo seems to sutter and stay stuck at a particular position, it means that it is not receiving enough power. This is probably due to a weak connection or low battery level. Check each connection and check your batteries.