Joint Calibrator
Robots can be precisely calibrated using the Petoi Desktop App.
** Download the latest version of the Petoi Desktop APP. **
For detailed installation tutorials and usage instructions, please refer to Desktop APP Introduction.
Prepare for calibration
Please follow the instructions in the subpages to prepare according to the robot's mainboard.
Only software version 2.0 can calibrate the joints via this App.
For Bittle X+Arm, you must install the short wire servo in the servo slot on the robotic arm. For more information, please refer to the instructions on the subpage.
The rationale for calibration
Understand the zero state and the coordinate system
After the robot enters 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.
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.
However, from the right side of the robot's body, the rotation directions' positive and negative are just opposite.
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.
Calibration process
Enter the calibration state
Connect the battery to the mainboard, then long-press the battery button for more than 3 seconds to power on the robot.
After a battery powers on the robot, there are two methods to enter the calibration mode:
It will automatically enter calibration mode when you click the Joint Calibrator button.
Click the Calibrate button in the Joint Calibrator interface.
Take Bittle for example:
If you are building the robot from a kit, install the servo-related components according to the picture (calibration state) and try to ensure that they are perpendicular to each other (the upper leg is perpendicular to the torso, and the lower leg is perpendicular to the upper leg). Please refer to the related chapter in the user manual for the details:
Nybble
Note: Insert the servo-related components directly into the servo output shaft; do not turn the output shaft during this process.
Installing and Fine-tuning
The joint calibration interface of different products is shown in the following subpages.
There are two kinds of kit: the construction kit and the pre-assembled kit.
For the construction kit, you must install the components (such as the head, legs, and tail) after the robot enters the calibration state. For more details, please follow the suppage instructions.
The pre-assembled kit already has the components adequately installed. You can do the joint calibration for fine-tuning.
The included L-shaped tool can be used as a reference during calibration. For more details, please follow the instructions on the subpages.
Validation and Save data
You can switch between "Rest", "Stand up" and "Walk" to test the calibration effect.
If you want to continue calibrating, please click the Calibration button, and the robot will be in the calibration state again (all servos will move to the calibration position immediately).
Take Bittle for example:
Note: You may need a second round of calibrations to achieve optimal results.
After calibration, remember to click the "Save" button to save the calibration offset. Otherwise, click the "Abort" button to abandon the calibration data. You can save the calibration in the middle in case your connection is interrupted.
When you close this window, there is a message box shown below:
To save the calibration data, please click the "Yes" button; otherwise, click the "No" button. Click the "Cancel" button to cancel or quit.
Install the screws for the construction kit
After completing the joint calibration, install the center screws to fix the components and servo gears.
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