Materials

Elements you need to build Kayra.

Mechanics:

• M3 Screws (5-7mm and 20-23mm in length) and nuts
• Disc shaped servo-horns, same amount as servos
• 15 Servos (eight are sufficient for a biped / lower half humanoid):

• metal-gears
• high torque (ideally 35kg/cm)
• high speed (0,11 sec/60 per degree @ 7,4 V)
• up to 7.4V operation
• we are using the DS3235MG

• 3 smaller Servos for the neck and the thumbs: CS-929MG

Electronics:

• servo control board, we’re working with the pimoroni 2040 servo controller based on the Raspberry Pico 2040, easy to program via Micropython

• alternatively (currently not supported in Kayra’s software stack): a “traditional” servo controller board based on the PCA9685 chip (e.g. Ebay) Note that you need a single board computer (like a Raspberry Pi Zero) to work with it)

• If you want to do more advanced movements and analytics, we recommend an IMU, right now we’re using the BNO055
• If you want to stream video from Kayra to you host and/or control Kayra over WiFi, you can add an ESP32 Cam to Kayla’s head.

Power supply:

• A benchtop power supply (usually upto 30V, 6A, e.g. Ebay) OR
• We are using 2×18650 LiPos (that are also used in e-cigarettes) and a matching battery holder

• Alternatively: LiPos delivering 7.4V (please check whether your servos can operate on more than 7.4V as fully charged LiPos deliver higher voltage)
• LiPo charger (e.g. Ebay)