Elements you need to build Kayra.


  • 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


  • 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)


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