robstride_sdk

1. Introduction

Standalone C++17 SDK for the RobStride CAN actuator protocol (RS00–RS06). No ROS dependency — this package only talks to SocketCAN. It is consumed by robstride_hardware_interface.

Designed to sustain a ≥300 Hz control loop against multiple motors on one bus:

• One non-blocking SOCK_RAW/CAN_RAW socket per interface, with 1 MiB send/receive buffers.
• A background read thread per bus, driven by epoll and draining frames with recvmmsg() in batches of up to 64 rather than one blocking recv() per frame.
• SendFrames() submits a whole batch through a single sendmmsg() call.
• Each motor's decoded state is a set of std::atomic fields written only by the read thread, so the control loop never locks or waits on CAN I/O.

2. Installation

Usually pulled in as a dependency of robstride_hardware_interface. To build it on its own:

cd ~/${WORKSPACE}/src
git clone https://github.com/kmj060703/RobstrideSDK.git

cd ~/${WORKSPACE}
colcon build --packages-select robstride_sdk
source install/setup.bash

Consume it from another ament_cmake package via the exported target list:

find_package(robstride_sdk REQUIRED)
target_link_libraries(your_target ${robstride_sdk_TARGETS})
target_include_directories(your_target PRIVATE ${robstride_sdk_INCLUDE_DIRS})

3. Layout

include/robstride_sdk/
  robstride_protocol.hpp   Wire format: comm types, run modes, per-model limits, parameter
                           index table, fault bits, float<->uint16 quantization, extended-ID
                           pack/parse.
  robstride_motor.hpp      RobstrideMotor: frame encoders (motion command, enable/disable,
                           set-zero, parameter read/write) and the HandleFrame() decoder.
                           MotorState: the lock-free telemetry snapshot.
  can_bus.hpp              CanBus: one SocketCAN interface, epoll read thread, batched I/O.
src/
  can_bus.cpp              CanBus implementation.

4. Control modes

RunModeFromString() maps a name to the motor's run_mode parameter (0x7005):

Name	Mode	Driven by
motion (or mit)	MIT-style	Type-1 frames carrying position, velocity, kp, kd and torque together
position_pp (or pp)	Profile position	loc_ref (0x7016)
velocity	Velocity	spd_ref (0x700A)
current	Current	iq_ref (0x7006)
position_csp (or csp)	Cyclic sync position	loc_ref (0x7016)

run_mode lives in the motor's RAM and is lost on a power cycle, so it has to be re-sent whenever a motor comes back.

Parameter frames carry their communication type explicitly (EncodeParamReadFloat, EncodeParamWriteFloat, EncodeParamWriteU8, EncodeParamWriteU32), so a write can never be tagged as a read.

5. Actuator models and limits

GetActuatorLimits(ActuatorType) returns the quantization ranges (position, velocity, torque, kp, kd, current) used to encode and decode Type-1 and Type-2 frames, taken from the official RobStride manuals. Position range is ±4π for every model; the rest differ per model.

ActuatorTypeFromString() accepts "00".."06", bare "0".."6" (xacro drops leading zeros), or "RS00".."RS06".

Position wraparound

Position feedback loops within ±4π rather than reporting a continuous angle. A joint crossing that boundary would otherwise appear to jump by ~8π in a single frame with no physical motion, which a position-holding controller reads as an enormous error.

UnwrapPosition() reconstructs a continuous value by watching for an implausibly large frame-to-frame delta and folding it into an accumulated offset. Two things reset that offset to a fresh baseline:

• A gap of more than 1 s since the last frame from that motor. A power cycle or downed bus may have reset the motor's own position framing with nothing linking it to the pre-gap value, so carrying the old offset across would produce exactly the phantom jump this exists to prevent. Automatic.
• ResetPositionTracking(), called after a set-zero command, since recalibrating the mechanical zero relabels the raw position the same way a physical wrap would.

Joints that stay within roughly ±π of zero never reach the boundary. This matters for continuously-rotating joints.

6. Detecting a wedged bus

SendFrames() returns how many frames reached the kernel, and last_send_errno() reports why a short send stopped. ENOBUFS means the interface is not draining its transmit queue at all — typically bus-off on a controller that cannot restart itself. Without checking this, a bus that transmits nothing looks identical to every motor having gone silent.

7. CAN interface setup

RobStride motors run at 1 Mbps CAN 2.0 with extended (29-bit) IDs. Bring the interface up with setup_can.sh, which applies the bitrate, restart-ms where supported, and a txqueuelen large enough that a batched send is not silently truncated.

8. License

Apache License 2.0. See LICENSE.