pxt-calliope/docs/device/servo.md
Sam El-Husseini e3975e65e5 pxt-microbit Accessibility PR ()
* Accessibility changes
2017-09-07 13:42:08 -07:00

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# Equipping a microservo with Crocodile clips
## ~ hint
If you are running a class or activity, you should consider preparing all servos before hand.
## ~
## 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.**
## ~
## 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.
![](/static/mb/projects/inchworm/servo1.jpg)
## Step 2: strip out cables
Using the plier or a wire stripper, strip the plastic from the cables.
![](/static/mb/projects/inchworm/servotrim.jpg)
## Step 3: threading the servo cablers
Thread the servo cables.
![](/static/mb/projects/inchworm/servo3.jpg)
## 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!
![](/static/mb/projects/inchworm/servo4.jpg)
## Step 5: thread cables together
Place the cables next to each other
![](/static/mb/projects/inchworm/servo5.jpg)
... and thread them together.
![](/static/mb/projects/inchworm/servo6.jpg)
## ~ 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.**
## ~
## Step 4: protect the connection
Protect the connection with shrinkwrap tubes, electrical or duct tape.
![](/static/mb/projects/inchworm/servo7.jpg)
## Step 5: repeat for all cables
Repeat the same process until all cables are connected.
![](/static/mb/projects/inchworm/servo8.jpg)
## 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``.
![](/static/mb/projects/inchworm/circuit1.jpg)
## ~ hint
When attaching the crocodile clips to the pins, don't hesitate to grab the side of the board with the jaws.
![](/static/mb/projects/inchworm/circuit2.jpg)
## ~
* Download the following code to your @boardname@
```blocks
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](/examples/servo-calibrator) 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.