To make sure that the Otto robot makes the right movements to walk, you need to calibrate the servo motors. Below you can read more information about this, you can get started online.
Jan van Heck
Calibrating the Otto Robot servomotors means that we determine a correction value for each servomotor separately with the help of a calibration program, which corrects the deviation from the 90-degree angle. This correction value can be a positive or negative number, because the corrections are simply determined with respect to those 90 degrees. In English this correction value is also called offset (for setting). Otto DiY, the producer of our robot, ensures that in almost every demonstration sketch they have made, this offset is used to make the movements (walking) of the robot run smoothly. A servo motor often used in this hobby is the SG10. When purchasing, make sure that it is a servo motor with a limitation. He can only do one back and forth-make movement between 0 and 180 degrees. In practice, the arc he can make is even less than 180 degrees. Pages 3, 4 and 6 of the Otto mounting instructions version_10 show where and how to attach the white two- or four-armed mounting parts together with the 3d-printed legs, feet and body to the servomotor.
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On both pages 4 and 6 of the manual it is suggested to determine the center of the extreme positions in advance. This can sometimes be done by hand, but it doesn’t always work. It is safer for the servo motor to use a tool. This can be a self-written sketch, the calibration program or – what I use for this – a Servotester. Those servo motor mounting parts have a circle with serrations on the inside that fit on the shaft of the servo motor, which also has serrations on the outside, but on the outside. And not always that multi-armed part is exactly at 90 degrees. Don’t force it, because it isn’t necessary. By performing the calibration, this will be all right.
ARDUINO SKETCHES
To perform the calibration I used the Otto_Calibrationeasy_V9.ino and Otto_Calibration_V9.ino sketches. Both are Arduino sketches from an earlier Otto DiY issue. The ‘easy’ version is only easily (read simple) programmed, but not in use. You have to recompile the sketch and upload it to the robot with every new calibration operation. The Otto_Calibration_V9.ino sketch includes a menu. Both sketches have been adapted by me for use. In my opinion unnecessary program rules have been removed and other rules have been modified in such a way that they function better. By using the menu it is now really easy to determine the correction values ​​for the servomotor.
Just don’t forget to write these correction values ​​to the Arduino Nano EEPROM as a last action. There is also a menu option for that – only in my sketch. In this way you can determine its own correction values ​​for every robot you have. So, this was the bit of theory beforehand. If you want to calibrate, see the link next to this article.