Actuator and wheel-motor interfaces

Checked 2026-10-25. Machine-readable copy: catalog/interfaces.json (keyed by catalog id). Vendor files: references/vendor/<catalog-id>/ with a SOURCE.txt in each folder.

How to read the tables.

• Units are mm, g, N and N·m.
• "PCD" is the bolt-circle diameter. "▼6" means thread depth 6.
• Output face is the rotating face the link bolts to. Case is the stator or housing.
• The source column says where each value came from:
  • drawing is the vendor's dimensioned 2D drawing. These are primary.
  • STEP means measured in the vendor STEP with OCP (cylinder faces grouped by radius, PCD and depth). STEP values are secondary and are used where the drawing is silent.
  • inferred gives its reasoning.
  • not found means the vendor publishes no value. Nothing here is guessed.
• Thread depth on the STEP models. RobStride, CubeMars and Damiao model tapped holes as tap-drill cylinders (3.3 mm for M4, 2.5 mm for M3, 4.2 mm for M5), sometimes with a cosmetic major-diameter body. A STEP depth is drill depth, so the drawing's ▼ value wins.

Short URL keys used in the tables:

Summary

Things that matter for the design

1. RS-03 strings decoded. Our catalog strings were 30.35x9x6 M4 and 98x8x8 M4. The drawing shows they are PCD × hole count × depth, but the counts hide something:

   • Output, 30.35x9x6. The "9" is 6 tapped M4▼6 plus 3 plain Ø4 (+0.1/0) dowel holes ▼7, all on Ø30.36±0.2.
     • The M4 holes sit at 30°, 90°, 150°…, 60° apart.
     • The dowel holes sit at 60°, 180° and 300°.
     • So the pattern is not 9 equally spaced M4 holes. A 9×M4 bolt circle will not fit.
     • The exact PCD is 30.36, not 30.35.
   • Case, 98x8x8. This one reads as written: 8×M4▼8 on Ø98±0.2, on the lug faces on the output side, at 22.5° + 45°·k.
     • The mounting face also has a Ø70 0/−0.1 male spigot, 2.5 mm high.
   • Do not use the website's "106 × 106". The STEP envelope is Ø100.5 over the lugs. The drawing gives no outside diameter.

2. The RS-03 output face is flush with a stationary ring. In the STEP, the Ø47 output flange face and the Ø59–70 housing spigot ring lie in the same plane, with zero axial gap.

   • A link plate larger than about Ø58 that bolts flat to the output will rub the housing.
   • The link needs a boss of Ø58 or less (Ø56 is suggested), or a relief.
   • RS-06 has the same arrangement: the Ø37 output sits flush with a Ø48–52 housing ring.
   • RS-04 and RS-02 sit only 0.5 mm proud.
   • Measured from the STEP, not stated in the manuals.

3. The RS-03 rear is 2.5 mm longer in the STEP than on the drawing: 56.6 mm in the STEP against 54.1 mm on the drawing. Use 56.6 for packaging until a real unit is measured.

4. The RobStride output bearings are thin-section deep-groove ball bearings, not crossed rollers.

   • RS-03: 45×58×7. RS-04: 61810, 50×65×7. RS-06: 35×47×7.
   • These come from the STEP part names and sizes.
   • RobStride publishes no axial, radial or moment ratings.
   • For cantilevered thigh and shank loads in a 19 kg robot, give the joint its own support bearing, or at least check the moment, before trusting the actuator bearing.
   • The DM-J8009P (crossed roller) and AK70-10 (crossed roller, C0 2520 N) are the alternatives with published or stated crossed rollers.

5. RS-04 and DM-J10010L look interchangeable but are not. Both are Ø120 with 10×M4 on Ø106 at the case and 9×M5 on Ø36 at the output, each with 3 pins on the output. The pins differ:

   • RS-04: Ø6 on Ø35.86.
   • DM-J10010L: Ø5 on a 19.5 radius (Ø39).

   One adapter could serve both only if it carries both pin sets.

6. Cables exit radially at the rear on every RobStride unit.

   • RS-03: two connector pockets on opposite flats of the Ø79.5 rear cover.
   • RS-00: on the side of the body.
   • RS-04: a fixed 310 mm harness through a silicone-sealed grommet.

   No hollow shafts are available in any of these parts, so cables cannot go through a joint axis. Plan an external service loop at each joint.

7. BotWheel.

   • Mount: single-sided on a fixed stator boss, Ø50 0/−0.04, carrying 4×M6 on Ø36±0.05.
   • The boss face sits 7.5±0.8 mm outboard of the tyre side.
   • The cable leaves axially through the centre of that boss.
   • The harness is 300±25 mm long and ends in JST WPJ (3-pin phase) and JST JWPF (8-pin feedback) waterproof connectors.
   • The leg bracket therefore needs a central through-hole for the cable inside the M6 pattern.
   • M6 thread depth is not published.

RobStride RS-03 (hip and knee, 4 per robot)

Drawing: RS03-man, section 1.1 (PDF page 10). STEP: references/vendor/robstride-rs-03/RS03.stp, a Creo assembly dated 2025-08-20 with 47 bodies, some of which are empty. STEP axis is +Z, with the output at +Z and the connector pockets at ±Y.

RobStride RS-04 (swap candidate)

Drawing: RS04-man §1.1 (PDF page 10). STEP: RS04.stp, a Creo assembly. Output at +Z.

RobStride RS-06 (tail lift)

Drawing: RS06-man §1.1 (PDF page 9). The STEP comes in two versions: RS06-new.step (Onshape, 2026-03, single body) and RS06.STEP (older multi-body). Both are 84.5 × 82 × 50.5.

RobStride RS-00 (tail wag)

Drawing: RS00-man §1.1 (PDF page 8). STEP: RS00.step, single body.

RobStride RS-02 (swap candidate)

Drawing: RS02-man §1.1 (PDF page 8). STEP: rs02.stp, single body. The IP67 variant has its own STEP, RS02-ip67-20261013.stp, which was not downloaded.

ODrive BotWheel (wheel hub motor, 2 per robot)

Drawing: BW-dwg, a dimensioned PNG on the shop page. It is in first-angle projection with Chinese labels. "视图A" means "view A".

CubeMars AK70-10 (swap candidate)

Drawing: https://www.cubemars.com/data/cms/202602/ak70-10-robotic-actuator-2d-drawing.pdf (first-angle). STEP: AK70-10 V2.0.STEP, taken from the 3D zip on CM-dl.

CubeMars AK10-9 V3.0 (swap candidate)

Drawing: https://www.cubemars.com/data/cms/202602/ak10-9-v3-0-robotic-actuator-2d-drawing.pdf (first-angle). STEP: AK10-9 KV60 V3.0-3D.STEP.

CubeMars AK80-64 (listed in the brief; 64:1, not QDD)

Damiao DM-J8009P-2EC (crossed-roller 8009)

Drawing: https://github.com/dmBots/DM-J8009P-2EC/tree/master/drawings/2d (8009-rau 5005-20240809.PDF). STEP: models/3d/8009-RAU_5005_外形尺寸-20240809.stp, saved locally as 8009-RAU_5005_outline-20240809.stp. Manual: manual/DM-J8009P-2EC Gear Motor User Manual V1.3 2026-09-10.pdf, read but not copied.

Damiao DM-J10010L-2EC

Drawing: https://github.com/dmBots/DM-J10010L-2EC/tree/master/drawings/2d (dm-j10010l-2ec-2D尺寸图.pdf, first-angle). STEP: models/3d/dm-j10010l-0730_1.STEP, 25 MB.

DM-J10010-2EC (non-L) also has a drawing and STEP in its repo (https://github.com/dmBots/DM-J10010-2EC). It was not processed because the catalog already prefers the L version.

Unitree GO-M8010-6 (basic only)

How comparable robots route leg cables

Nobody in this group routes through a hollow joint axis:

• Upkie daisy-chains power (XT30, 14 AWG, 42 cm leads) and CAN (JST PH-3, 26 AWG twisted pairs) from hip to knee to wheel along the outside of the legs. Its hip joint limit is set by "Cables fully stretched" (cables, electronics testing, upkie_description).
• DIABLO uses a parallelogram leg with the wheel motor flanged to the bottom link. "Some linkages are designed in an arched form to accommodate practical wiring considerations", which means external cables in a protected channel (arXiv 2407.21500).
• Ascento keeps the leg actuators (ANYdrive) in the body and drives the legs through four-bar linkages, so only the frameless hub-motor (Maxon EC90) cables run down the leg (arXiv 2005.11435).
• Unitree Go2-W and LimX TRON 1 routing is not publicly documented. TRON 1's tool-free swappable foot modules with automatic recognition imply a connector at the lower leg (inferred; New Atlas). A Go2 teardown notes only "meticulous cable management" (Simplexity).

None of these robots documents slip rings or cable carriers. With no hollow actuators in our candidate list, the practical pattern is the Upkie/DIABLO one: an external service loop at each joint, sized for the full joint range, plus a protected channel along each link.