Actuators specifications
Servomotors
| Property | Value |
|---|---|
| Model | Feetech STS3215-C001 (7.4V version) |
| Quantity | 12 |
| Supply voltage | ≈ 6.0-8.4V |
| Gear ratio | 1:345 |
| Stall torque | 19.5 kg.cm at 7.4V |
| No-load speed | 0.22 s/60° at 7.4V |
| Weight | 55 g |
| Position sensor | 12-bit magnetic encoder (4096 steps/rev, ≈ 0.088°/step) |
| Available feedback | Position, speed, load, voltage, temperature |
Tip
Chromapi’s architecture is permissive enough to use the 12V version of the STS3215 if you need more torque, provided the power supply is adapted accordingly.
Leg layout
Each of Chromapi’s legs has three joints, named according to the convention below:
| Joint | Name | Axis | Range of motion |
|---|---|---|---|
| Hip | coxa (*_1) | Yaw | ±70° |
| Hip | femur (*_2) | Pitch | ±90° |
| Knee | tibia (*_3) | Pitch | ±90° |
Servomotor IDs on the bus are assigned leg by leg:
| Leg | Coxa | Femur | Tibia |
|---|---|---|---|
tl (front left) | 1 | 2 | 3 |
bl (back left) | 4 | 5 | 6 |
br (back right) | 7 | 8 | 9 |
tr (front right) | 10 | 11 | 12 |
Communication bus
| Property | Value |
|---|---|
| Bus type | Half-duplex serial (Feetech protocol) |
| Baud rate | 1 Mbps |
| Reading rate | 200 Hz (synchronized read of the 12 servomotors) |
The STM32 polls the 12 servomotors with a single synchronized read frame, then sends their state back to the Raspberry Pi. Commands sent by the Raspberry Pi are re-encoded into Feetech frames and relayed on the bus: see the communication protocol for more details on how communication works.
Resources
- Firmware driver:
sts3215_hal.c,sts3215_protocol.candsts3215_regs.h