Joint Calibration

Joint calibration is vital for the robot to work properly.

The pre-assembled robot should have the legs installed, but you can further improve its performance by fine-tuning the joints' calibration.

Make sure you have uploaded the OpenCat Main function firmware before calibrating.

This is a cool tutorial video made by one of our users, which briefs the process and explains its logic.

* The logic behind calibration is:

1. You don't know where the servos are pointing before they are powered and calibrated. So if you attach the legs, the legs will rotate to random angles and may collide with the robot's body or other legs and get stuck. If a servo is stuck for a long time, it may break.

2. The robot has a "calib" posture with all joints set at zero degrees. You can put the robot to the calib posture so that you know all the joints should be rotated to their zero points (though you cannot see because the legs are not attached to the servos yet). Then, you can attach the legs to the servos one joint by one joint, perpendicular to their nearby references on the body frame.

   

   Calib Posture
3. Because the servo's gear teeth are discrete, aligning the legs to the right angles perfectly is impossible. So, you will need to fine-tune the offsets within the software.

   

   Servo gear

The principles are the same for Nybble and Bittle.

Prepare to Enter the Calibration State

Entering calibration mode requires the following preparations: ‌

1. All servo circuits are connected to the motherboard

2. The battery is plugged into the controller board and is turned on (long-press the button on the battery to turn on/off the power)

3. The USB adapter or Bluetooth dongle is used to connect the robot to a computer or mobile phone

If you build the robot from an unassembled kit, do not install the head and leg components before entering the calibration state.

Enter the Calibration State

The robot's legs may point to unknown angles when booting up. When entering the calibration state, the joints will be moved to their zero positions. You can see the output gears of the servos rotate and then stop. Then, you can attach the legs and fine-tune the joint offsets in the software interface. There are 3 software interfaces to enter the calibration state and fine-tune the joints.

• Use the Mobile App Petoi

• Use Petoi Desktop App

• Use Arduino IDE

You can also enter the calibration state by booting up the robot with one side up. This method doesn't require any computer, remote, or smartphone app, so it's convenient when you are focused on assembling the robot from the kit.

Install the screws

After completing the joint calibration, install the center screws to fix all the joint parts and servo gears.