# Calibrator

## Prepare for calibration

Please take a look at the section [Connect to the robot](/mobile-app/introduction.md#connect-to-the-robot).

## The rationale for calibration

### Understand the zero state and the coordinate system

After the robot [enters the calibration state](#enter-the-calibration-state), with all servos rotated to their zero angles, attach the head, tail, and legs prepared in the previous section to the body. They are generally perpendicular to their linked body frames. 

Please refer to the subpage for the calibration pose (Calibration State) according to the product type.

Rotating the limbs counterclockwise from their zero states will be positive (the same as in polar coordinates). Viewed from the left side of the robot's body, the counter-clockwise rotation of the joint is defined as the positive direction.

{% hint style="info" %}
The only exception is the head tilt angle for Nybble. It’s more natural to say head up, while it’s the result of rotating clockwise. 
{% endhint %}

{% hint style="info" %}
However, from the right side of the robot's body, the rotation directions' positive and negative are just opposite.
{% endhint %}

### Discrete angular intervals

If we look closer at the servo shaft, we can see it has a certain number of teeth. That’s for attaching the servo arms and avoiding sliding in the rotational direction. In our servo sample, the gears divide 360 degrees into 25 sectors, each taking **14.4** degrees(offset of -7.2\~7.2 degrees). That means we cannot always get a perfect perpendicular installation. 

![](/files/v400iIvlmpXjiobnloRS)

## Calibration Interfaces

According to different products, please take a look at the related subpages.

## Enter the calibration state

After the battery powers on the robot, follow the next steps to enter the calibration mode. 

* Click the **Start Calibration** button.<br>

  <figure><img src="/files/GwH4B1KbYFIOhQPudrrF" alt=""><figcaption></figcaption></figure>
* Click the **Calibration** button in the calibration interface.<br>

  <figure><img src="/files/FCRxFXfNFSFOIpN7HZWo" alt=""><figcaption></figcaption></figure>

For the construction kit, you can install the body parts to the robot torso according to the instructions in the following sub-pages, based on the products you choose.

{% hint style="info" %}
For the construction kit, after installing the body parts, you do not need to use screws to fix the body parts to the robot trunk for the time being.
{% endhint %}

{% hint style="info" %}
The pre-assembled robot should already have the legs properly installed. You can do the joint calibration for fine-tuning.&#x20;
{% endhint %}

When calibrating, depending on the product you are using, select the corresponding calibration ruler in the sub-page as an aid.&#x20;

<figure><img src="/files/W3TQV4Eo3i9GcMU38nc0" alt=""><figcaption></figcaption></figure>

## Test the calibration effect

Use **Bittle** for example:

![Bittle](/files/vQv5sjbxiNJmcbZd4v2X)

You can click the skill buttons to switch between **Rest**, **Stand**, and **Walk** to test the calibration effect.&#x20;

If you want to continue calibrating, please click the **Calibration** button, and the robot will return to the calibration mode, with all servos immediately moving to their calibration positions.&#x20;

{% hint style="info" %}
Note:&#x20;

You may need a second round of calibrations to achieve optimal results.
{% endhint %}

After calibration, remember to click the **Save** button to save the calibration offset. Otherwise, click "**<**" in the upper left corner to abandon the calibration.

## Install the screws for construction kit

For the construction kit, after completing the joint calibration, install the center screws to fix the leg parts and neck servo gears.


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