Waveshare 20 kg-cm bus servo: specs and pinout
A serial bus servo (Waveshare ST3215-HS per the maker's wiki) with a 360 degree magnetic position sensor. Servos share one TTL serial bus, each with its own ID, and report position, load, speed and input voltage; it runs in servo (angle) mode or in motor (continuous rotation) mode.
Specs
| Spec | Value | Source |
|---|---|---|
| Input voltage | 6 V to 12.6 V (can be powered from a 2S or 3S lithium battery) | source Overview > Specification and Features |
| Torque | Up to 20 kg.cm at 12 V | source Overview > Features |
| Idle speed | 0.094 s/60 degrees (106 RPM) at 12 V | source Overview > Specification |
| Position sensor resolution | 360 degrees / 4096 (magnetic encoder) | source Overview > Specification |
| Serial interface | TTL serial bus, baud rate 1 Mbps, ID range 0-253 (up to 253 servos on one bus, power permitting) | source Overview > Introduction and Specification |
| Current | Wiki 'Load Current' 240 mA (printed '240mAA'; not stated whether no-load); locked-rotor current 2.4 A | source Overview > Specification |
| Feedback | Position, load, speed, input voltage | source Overview > Specification |
| Dimensions | 45.22 mm x 35 mm x 24.72 mm | source Overview > Specification |
Power
| Value | Source | |
|---|---|---|
| Supply | 6 V to 12.6 V DC | source Overview > Specification |
| Current | 240 mA 'load current' (wiki wording); 2.4 A locked-rotor. Size the supply for every servo stalling at 2.4 A. | source Overview > Specification |
Pinout
The 3-pin table is the bus servo control interface (connector CN5) on Waveshare's bus servo circuit schematic, i.e. the driver side the servo cable plugs into; the servo's own connector drawing is not covered. The wiki states each servo has two interfaces so servos can be chained.
| Pin | Function | Voltage | Notes | Source |
|---|---|---|---|---|
| 1 | DATA | Driver-side connector CN5 on the bus servo control circuit schematic; Bus data line | source Bus servo control interface schematic, connector CN5 (5264-3A), driver side | |
| 2 | VCC | Driver-side connector CN5 on the bus servo control circuit schematic; Positive supply; the schematic notes it needs high current | source Same schematic, CN5 | |
| 3 | GND | Driver-side connector CN5 on the bus servo control circuit schematic; Ground | source Same schematic, CN5 |
Build with it
Project ideas for the Waveshare 20 kg-cm bus servo. Each link opens Soldr with the prompt filled in; Soldr assigns the pins, checks power and shows how to wire every part.
- Servo status page: The servo reports position, load, speed and voltage; the maker's wiki points to its servo driver board as the controller. A 12 V supply is inside the 6-12.6 V servo range and the driver board's 9-12.6 V range. The driver board's own current rating is not sourced here.
- Two-joint desk arm: Both servos share one bus with different IDs. Each can reach 2.4 A when stalled, so a 5 A supply covers two stalling together (4.8 A) with little margin; a learning project, not a lifting arm. The driver board's own current rating is not sourced here.
- Turntable in motor mode: Motor mode gives continuous rotation with speed control. The 3S pack (XT60) reaches the driver board's DC port through the stocked XT60-to-barrel lead; check the barrel is the 5.5 x 2.1 mm size the wiki gives. A 3S pack is 11.1 V nominal and 12.6 V fully charged, the top of the 6-12.6 V servo range (the driver board's title says 9-12.6 V; use the narrower). The driver board's own current rating is not sourced here. LiPo handling: charge only with a balance charger, in a LiPo bag, never unattended; put an inline fuse near the pack (a fuse holder for the blade fuse is needed in line); stop at 3.0 V per cell (9 V for 3S) with a low-voltage alarm on the balance lead.
- Two-wheel base with feedback: Each servo reports speed and load back over the bus. Plan for 2.4 A per servo if a wheel stalls; the battery, the XT60-to-barrel lead (check the barrel is 5.5 x 2.1 mm) and the driver board must handle that current; a 3S pack is 12.6 V fully charged, the top of the 6-12.6 V servo range (the driver board's title says 9-12.6 V; use the narrower). The driver board's own current rating is not sourced here. LiPo handling: charge only with a balance charger, in a LiPo bag, never unattended; put an inline fuse near the pack (a fuse holder for the blade fuse is needed in line); stop at 3.0 V per cell (9 V for 3S) with a low-voltage alarm on the balance lead.
Common mistakes
- Supplying more than 12.6 V or less than 6 V: the input range is 6-12.6 V, and a 3S lithium pack is at the top of it when fully charged. The stocked driver board's title gives 9-12.6 V while the wiki gives 6-12.6 V for the servo: use the narrower 9 V lower limit for the board, so stop a 3S pack at 9 V (3.0 V per cell, derived) and read the driver board's own label (source: link, Specification).
- Sizing the supply for the 240 mA figure: locked-rotor current is 2.4 A per servo, and the wiki warns that many high-power servos on one bus need a power supply that can cope (source: link, Specification and Introduction).
- Connecting two servos with the factory ID: servos ship with ID 1, duplicates conflict on the bus, and EPROM must be unlocked before an ID change is saved (source: link, FAQ).
Not covered by the official source
- No PDF datasheet found; specs are from the maker's wiki page. The wiki prints the 'Load Current' value as '240mAA'; whether it is the no-load current is not stated.
- The model name ST3215-HS comes from the wiki title; the product name gives no model number.
- Servo-side connector drawing and memory table are not given; the 3-pin rows are the driver-side interface from the schematic.
- Torque is given only at 12 V.