Glossary
Terms used on the Strido site and in this wiki, A–Z. Each entry says what the term means and, where it matters, how it applies to this robot; follow the link for the wiki page that explains it in depth.
A
Abduction
Sideways swing of a leg away from or towards the body's centre line. On Strido it is the hip joint, driven by the servo in the body; see kinematics and gaits.
Accepted deviation
A hole that misses a verification band but is deliberately kept, recorded in accepted_deviations of hardware/verification/tolerances.yaml with an ADR and a builder action. The only one is ADR-009, the servo-mount M3 pilots; see fasteners.
ADR (architecture decision record)
A short record of a design decision: context, options, decision, consequences and when to reconsider. Strido keeps them in decisions.md.
Arachne
PrusaSlicer's variable-width perimeter generator, enabled in the kit profile, which fills thin walls instead of leaving gaps; see 3D printing.
Arming port
The XT60H jack in the back shell (arming_port_bezel): W02 from the main fuse on one contact, W03 to the UBECs on the other. It connects the servo power branch only when the loop key is inserted; see safety.
AWG (American Wire Gauge)
Wire size scale where a smaller number means a thicker wire. Strido uses 14 AWG for the battery trunk, 18 AWG for UBEC outputs, bus jumpers and the logic branch, 22 AWG for the servo leads, signals and the Pi 5 V feed; see power.
B
Balance charger
A LiPo charger that monitors and equalises each cell through the pack's balance lead. The BOM includes a B6AC-class charger; see batteries.
Bed adhesion
How firmly the first layer sticks to the print bed. Too little and the part detaches; with PETG on smooth PEI, too much can damage the sheet; see 3D printing.
Bearing seat
A printed bore into which a ball bearing or sleeve is pressed. The fit gate accepts a seat from 0.15 mm under to 0.30 mm over the bearing's outer diameter; see mechanics.
BEC / UBEC
(Universal) battery eliminator circuit: a switching regulator from RC models that turns pack voltage into servo voltage. Strido uses two Hobbywing UBEC-10A at 6.0 V, each feeding two legs; see power.
BOM (bill of materials)
The list of everything to buy, with quantities and offers. Source: hardware/bom.yaml; published as the BOM page.
Brim
Extra lines around a part's first layer that increase bed contact. In the kit: 5 mm brim on parts taller than 40 mm; see 3D printing.
Buck regulator (step-down)
A switching converter that lowers a voltage efficiently. The Pololu D36V50F5 makes the 5 V logic rail from the 2S pack; see power.
Build kit
The downloadable ZIP with everything needed to print and build a robot; see downloads.
C
C rating
A LiPo's maximum discharge current as a multiple of its capacity,
CadQuery
A Python library for parametric CAD. All new and modified Strido parts are CadQuery booleans on the upstream geometry; see CAD as code.
Catalogue
The browsable list of all 76 part types (printed, purchased and fasteners) with images, sizes and assembly steps; see the catalogue.
Clearance hole
A hole a screw passes through freely. ISO 273 sizes for M3 are 3.2 mm (fine) and 3.4 mm (medium); printed holes are chased with these drills; see fasteners.
COBS
Consistent Overhead Byte Stuffing: an encoding that removes zero bytes from a message so 0x00 can mark the end of each frame. Used on the USB link between the Pi and the XIAO; see firmware.
CRC16
A 16-bit checksum appended to every protocol frame (CRC16-CCITT-FALSE) so corrupted frames are rejected; see firmware.
CSI
Camera Serial Interface: the ribbon-cable camera connector on the Raspberry Pi 5, used by the Camera Module 3 Wide via a 22→15-pin cable; see sensors.
Cut list
The table in the wiring check that gives every wire's routed length and the length to cut: routed length + a termination allowance per end (WAGO strip 11 mm, solder 6 mm, crimp 3 mm, screw terminal 7 mm) + slack of 8 %, at least 10 mm. Builders cut every wire from it; see cable management.
D
Docker
A tool that runs software in containers with all its dependencies. The ROS 2 Jazzy image for the Pi and for Gazebo is built from docker/compose.yaml; see Docker.
Domain randomisation
Varying simulation parameters (friction, servo stiffness, mass, IMU noise) during training so a learned policy copes with the real robot; see simulation and RL.
Dupont connector
A 2.54 mm pitch crimp contact and housing that plugs onto header pins and holds by friction. Used for the Pi 5 V feed (W12), W17/W20 at the PCA9685 and the twelve servo signal wires (re-crimped into 1-pin housings); see tools and workshop.
E
E-stop (emergency stop)
A latched stop. On Strido, /strido/estop makes the firmware pull PCA9685 OE high and stop all pulses; the physical servo kill is the loop key. See safety.
Elephant foot
The flared bottom edge of a print caused by the squashed first layer; it tightens bottom-facing holes; see 3D printing.
Engagement length
The length of a screw that actually forms or engages thread. The fit gate wants at least 1.5 d in printed pilots (4.5 mm for M3); see fasteners.
ESD (electrostatic discharge)
A static spark that can damage chips. Handle the Pi, XIAO and sensor boards by their edges after touching grounded metal; see safety.
ESP32-S3
Espressif's dual-core microcontroller with USB, used on the Seeed XIAO ESP32-S3 motion controller; see microcontrollers.
F
FDM (fused deposition modelling)
3D printing by extruding molten plastic line by line and layer by layer; see 3D printing.
Femur
The thigh link of a leg, between the leg servo module and the knee; four are printed (femur).
FFC (flat flexible cable)
The flat ribbon cable that connects the camera to the Pi's CSI port (300 mm in Strido).
Firmware
The program running on the microcontroller. Strido's firmware (firmware/strido_esp32s3, PlatformIO) runs the 200 Hz control loop and the safety logic; see firmware.
Fit gate
The verification step python -m strido_verify.fits that measures every screw hole and bearing seat in the CAD against the bands in tolerances.yaml; see fasteners.
Four-bar linkage
Four links joined in a loop by four pivots. Strido's knee uses a parallelogram and a four-bar to drive the tibia from the knee crank; see mechanics.
Fuse
A wire link that melts above its rated current and so protects the wire after it. Strido uses a 25 A main and a 7.5 A logic ATO blade fuse; see safety.
G
Gait
The pattern in which legs move. Strido's default is a trot (diagonal leg pairs together) in packages/strido-core; see kinematics and gaits.
Gate
An executable check that must pass before a change is accepted (interference, ROM, fits, clearance, printability, electronics, wiring, BOM). See the verification page.
Gazebo Harmonic
A robot simulator that runs the ROS 2 stack unchanged against a simulated Strido; see simulation and RL.
Go2 convention
Joint names, signs, frames and topics copied from the Unitree Go2's ROS 2 interface, so code written for a Go2 can drive Strido; see ROS 2.
Ground star
The single point where all grounds join. On Strido it is a heat-shrunk splice beside the battery input, from which W04 runs to both UBEC inputs (14 AWG) and the switch ground (18 AWG); one point keeps the servo return currents out of the logic grounds; see power.
Gyroid
A wavy, self-supporting infill pattern that is strong in all directions; the kit uses 30 % gyroid; see 3D printing.
H
Heat shrink
Tubing that shrinks when heated to insulate and strain-relieve a soldered joint; see tools and workshop.
High-side shunt
A current-measuring resistor placed in the positive supply line. The INA260 measures the logic branch this way (VIN+ in, VIN− out); see sensors.
Hole compensation
A slicer setting that shrinks or grows printed holes. The print list asks for X-Y hole compensation −0.15 mm on the servo mounts (ADR-009); see 3D printing.
Horn
The arm or disc that fits on a servo's splined output shaft and transmits its torque. Strido uses 25-tooth (25T) aluminium disc and clamping arm horns; see servos.
I
I²C
A two-wire bus (SDA data, SCL clock) where each device has an address. On Strido: PCA9685 0x40, LSM6DSOX 0x6A, INA260 0x41 at 400 kHz; see buses.
IMU (inertial measurement unit)
A sensor measuring acceleration and rotation rate. The LSM6DSOX gives the robot its orientation (Mahony filter on the XIAO); see sensors.
INA260
Texas Instruments' current/voltage/power monitor with an integrated shunt (Adafruit 4226). It reports pack voltage for the low-battery cut-off; the firmware will not drive without it; see sensors.
Infill
The internal fill of a printed part, given as a density and a pattern (kit: 30 % gyroid); see 3D printing.
Interference check
The gate that tests the assembled CAD for parts that overlap in space; report in verification/interference.md.
ISO 4762 / DIN 912
The standard for socket head cap screws, the only screw head type in Strido; see fasteners.
J
Joint limits
The safe range of each joint, from a collision sweep of the full assembly (e.g. calf −150…−45°), shared by firmware, gait and simulation; see kinematics and gaits.
K
Kinematics
The geometry that relates joint angles to foot positions (forward) and foot positions to joint angles (inverse); see kinematics and gaits.
Knee crank
The arm on the knee servo that drives the knee linkage; its angle maps non-linearly to the calf angle; see mechanics.
L
Layer height
The thickness of each printed layer; 0.2 mm in the kit, half the 0.4 mm nozzle; see 3D printing.
LiDAR
A sensor that measures distances with a rotating laser. The Slamtec RPLIDAR C1 publishes /scan at 10 Hz from the top pedestal; see sensors.
LiPo (lithium polymer)
The rechargeable battery chemistry of the robot's 2S 5000 mAh pack: high power, but dangerous if shorted, overcharged or over-discharged; see batteries.
Lock nut (DIN 985)
A nut with a nylon insert that grips the thread, used at moving joints so they can turn freely without the nut backing off; see fasteners.
Loop key
A shorted XT60 plug that arms the servo branch when inserted in the arming port; pulling it is the servo kill; see safety.
M
mAh (milliampere-hour)
Battery capacity: 5000 mAh can supply 5 A for one hour. With 7.4 V nominal it stores about 37 Wh; see batteries.
Mahony filter
A lightweight algorithm that fuses gyroscope and accelerometer data into an orientation estimate; runs on the XIAO for /imu/data; see sensors.
Manifold (closed)
A mesh with no holes or loose faces, so it has a well-defined inside; every kit STL is checked to be closed; see CAD as code.
Microcontroller (MCU)
A small single-chip computer for real-time tasks. The XIAO ESP32-S3 is Strido's MCU; see microcontrollers.
MJCF
MuJoCo's XML model format; models/mujoco/strido.xml is generated from the CAD; see simulation and RL.
MuJoCo
A fast physics simulator used for the walking demo and reinforcement learning; see simulation and RL.
N
Nav2
The ROS 2 navigation stack. It talks to the robot through /cmd_vel and /scan, so it runs unchanged on Strido; see ROS 2.
NT-X
The robotics platform Strido integrates with through the strido-ntx extension; see NT-X integration.
N·m and kg·cm
Units of torque. Servo makers quote kg·cm;
O
OE (output enable)
The PCA9685 pin that switches all 16 outputs off when high. The XIAO holds it high until armed, and a 2.2 kΩ pull-up keeps it high during resets; see safety.
Overhang
A surface printed over empty space. Beyond about 45° from vertical it usually needs supports; the print list gives each part's overhang share; see 3D printing.
P
PCA9685
A 16-channel, 12-bit PWM driver on I²C. It generates the 12 servo signals at 200 Hz but carries none of the servo current; see buses.
Perimeter
An outline line of a printed layer; the kit prints 3 perimeters (≈ 1.2 mm wall); see 3D printing.
PETG
Polyethylene terephthalate glycol: a tough, heat-resistant filament and the kit profile's material; PLA+ is the alternative; see 3D printing.
Pilot hole
A hole smaller than the screw, into which a thread-forming screw cuts its thread (about 0.8 d after printing); see fasteners.
PlatformIO
The build system for the firmware: pio run to compile and upload, pio test -e native for host unit tests; see firmware.
PLA+
A tougher variant of PLA filament allowed by the print list as an alternative to PETG; see 3D printing.
Plate
A ready-arranged 220 × 220 mm build plate (3MF file); the kit has 10 graphite and 3 lime plates; see 3D printing.
Policy
A learned controller that maps observations (IMU, command, previous action, gait clock) to joint actions; stored as policy.npz and run with numpy; see simulation and RL.
PPO (proximal policy optimisation)
The reinforcement-learning algorithm used to train Strido's walking policy in MuJoCo; see simulation and RL.
Print kit
The package of oriented STLs, slicer profile, parts sheet and plates; build one on the print kit page.
Printability gate
The check that slices every part and plate with PrusaSlicer and scans wall thickness; report in verification/printability.md; see 3D printing.
Pull-up resistor
A resistor that holds a signal at a defined high level when nothing drives it, like the 2.2 kΩ on PCA9685 OE; see buses.
PWM (pulse-width modulation)
A signal whose pulse length carries information. Hobby servos read the position from the pulse width: 500–2500 µs for 180° on the SPT5435LV, 1500 µs being the centre; see servos.
R
Range of motion (ROM)
How far each joint can move without collisions; the ROM sweep produces the joint limits; see kinematics and gaits.
Raspberry Pi 5
The robot's main computer (4 GB) running Linux and ROS 2; see Linux on the Pi.
REP-103
The ROS convention for units and frames: x forward, y left, z up, SI units; see ROS 2.
Reinforcement learning (RL)
Training a controller by trial and error in simulation, rewarding good behaviour; see simulation and RL.
ROS 2
Robot Operating System 2: a middleware where nodes exchange messages on topics. Strido runs ROS 2 Jazzy; see ROS 2.
ros2_control
The ROS 2 framework for controllers and hardware interfaces; in Gazebo it consumes /leg_controller/commands; see ROS 2.
S
Service loop
A deliberate length of free cable between two ties that lets a cable cross a moving joint without pulling on its terminations. Strido's thigh and knee servo leads cross the hip joint with 36 mm and 40 mm loops, at least 1.2 × the largest tie-to-tie distance over the hip range; see cable management.
Servo (hobby servo)
A motor, gearbox, position sensor and controller in one case that moves to the angle given by a PWM pulse. Strido uses twelve SPT5435LV-180W, without position feedback to the controller; see servos.
Slew limit
The maximum speed at which the firmware lets a commanded joint angle change (6 rad/s), to avoid violent jumps; see firmware.
Slicer
Software that turns a 3D model into printer instructions (G-code) layer by layer, e.g. PrusaSlicer; see 3D printing.
SLAM
Simultaneous localisation and mapping: building a map while tracking the robot's position in it, here from /scan; see ROS 2.
Smoke test
The first power-up with the loop key out: check boot, /battery_state, /diagnostics and the OE voltage before any servo can move; see safety.
Snug
Tightening a screw only until the head seats and the parts stop moving, the rule for screws into printed parts; see fasteners.
SPI
A fast synchronous bus with clock, data and chip-select lines. The XIAO drives the ST7789 LCD over SPI, with an extra DC (data/command) line; see buses.
Spiral wrap
A plastic spiral wound around a bundle of cables that holds and protects it while letting single cables branch out anywhere. Strido puts it on every bundle of three or more cables (spiral_wrap); see cable management.
Stall torque / stall current
The torque a motor produces and the current it draws when blocked. SPT5435LV: about 3.43 N·m and 3.5 A at 6 V; see servos.
Stand-off
A threaded spacer that lifts a circuit board off the deck (M2.5 × 6 mm and M2 × 8 mm brass, female-female); see fasteners.
STEMMA QT
Adafruit's 4-pin JST-SH I²C connector system. Two STEMMA QT → female-socket cables connect the IMU to the PCA9685 (W18; the IMU sits too close under the Pi for Dupont housings) and to the INA260 (W19); see buses.
STEP, STL and 3MF
STEP: exact CAD solids (the upstream Yertle assembly). STL: triangle meshes for printing. 3MF: a package of meshes plus arrangement, used for the plates; see CAD as code.
Strain relief
Anything that keeps pull and bending away from a wire's termination: the insulation grip of a crimp, heat-shrink over a solder joint, a cable tie close to a connector. It matters most where solder has wicked into the strands and made them stiff; see cable management.
Supports
Temporary printed structures under overhangs, removed after printing; the kit uses snug supports on listed parts; see 3D printing.
T
TF
The ROS 2 transform system that tracks coordinate frames (odom, base_link, imu_link, lidar_link); see ROS 2.
Thread-forming screw
A screw that cuts or forms its own thread in a plain pilot hole. 78 of Strido's screws do this in printed parts; see fasteners.
Threadlocker
An anaerobic adhesive that stops screws from loosening. Medium (blue) strength is used on screws into metal horns; see fasteners.
Tibia
The lower leg link (calf). Each leg has an inner_tibia and outer_tibia printed half with a 633ZZ bearing each; see mechanics.
Topic
A named ROS 2 message channel, such as /cmd_vel, /joint_states or /battery_state; see ROS 2.
Trot
A gait in which diagonal leg pairs (front-left with rear-right, front-right with rear-left) move together; see kinematics and gaits.
U
udev rule
A Linux rule that gives a device a stable name when it is plugged in; 99-strido.rules names the XIAO and LiDAR; see Linux on the Pi.
Upstream (Yertle)
The original open-source Yertle robot whose STEP and STL files Strido builds on, kept unchanged in upstream/yertle/; see design.
URDF / xacro
The ROS robot description format (URDF) and its macro language (xacro); strido.urdf.xacro is generated from the CAD; see simulation and RL.
USB CDC
USB's communication device class: the XIAO appears as a serial port to the Pi, carrying the COBS-framed protocol; see firmware.
uv
A Python package and workspace manager; Strido's Python packages are a uv workspace; see CAD as code.
V
VitePress
The static site generator that builds this documentation site.
W
WAGO 221-415
A five-way lever connector (32 A, 0.2–4 mm², strip 11 mm) used to build the servo power bus in the front and rear cavities; see cable management.
Watchdog
A timer that triggers a safe action if no command arrives: no joint command for 200 ms → hold, 2 s more → relax; see firmware.
X
XIAO ESP32-S3
Seeed's thumb-sized ESP32-S3 board: the robot's motion controller, talking USB to the Pi and I²C/SPI to the PCA9685, sensors and LCD; see microcontrollers.
XT60
A two-pole power connector (Amass XT series) rated 30 A continuous, used for the battery input (under the deck), the arming port and the loop key; describe halves by pins or sockets, not male/female; see power.