Wheel-legged robot packaging survey (2026-10-26)

Goal: concrete packaging lessons for condensing Gyropup (20–26 kg, 200/200 mm thigh/shin, Ø180 wheel, 2 × RS-04 per leg, hub wheels, J501 Orin box, ~14S pack, foam-dart turret). Specs already covered in reference-robots.md are not repeated; this file is about layout.

Tags: [derived] = we computed it from a public CAD/URDF/SDF or from physics (inputs given); [inferred] = our reading of mass/geometry data, not stated by the maker; [unverified] = seen only in a search excerpt or a single secondary source, or the primary could not be opened.

1. At a glance

2. Robot notes

2.1 DDT Diablo — the closest analogue

Sources: DIABLO paper, arXiv 2407.21500 (DDT co-authors; Fig. 2 = mechanism, Fig. 3 = motor exploded), DiabloSTLSDF (STL + SDF, no licence), video.

• Table I: 22.90 kg; width 0.540 m, length 0.371 m, height 0.491 m standing / 0.260 m creeping; links L1 0.090, L2–L4 0.140 m; wheel R 0.0935 m. Resellers print the same numbers as "L × W"; the SDF confirms the paper (wheel outer faces at y = ±0.272 m → 544 mm) [derived]. Our earlier notes and the mech review compared Gyropup's width with "Diablo 371 mm"; the right figure is ≈540 mm.
• "The hip motor is flanged to the knee motor, resulting in a series connection that requires less torque from the motors when the same force is applied at the foot, as compared to a parallel coaxial arrangement." The SDF shows it: Motor0 (body → Leg0) drives a carrier with a 90 mm crank pin; Motor1 sits on that carrier and drives the thigh; a 140 mm rod runs from the crank pin to the shank, 90 mm below the knee. So crank ∥ shank and rod ∥ thigh, a true parallelogram [derived]. The force transmission angle at the knee equals the interior knee angle: it is best at 90° and goes to zero only at a straight or fully folded knee.
• Virtual work for a stance with the ground force through the hip [derived]:
  • Diablo layout: the hip motor holds ≈0 and the knee motor holds |Q_knee|.
  • Both stators on the body (Gyropup today, mech review A2): both motors hold |Q_knee|.
• Packaging (SDF/STL):
  • Body 370 L × 175 W × 245 H mm [derived], hip axis at mid-height.
  • Body CoM is 12 mm ahead of and 7 mm below the hip axis. The body is 6.7 kg of the 19.7 kg SDF total.
  • Lateral stack from the centreline: body face 88 mm → two pancake motors → thigh plane 176 → shank 215 → wheel centre 246 mm.
  • Hip range in the SDF is −3.53…+1.96 rad (≈315°).
  • Links are "arched … to accommodate practical wiring".
• The body ("head") houses battery, main board and IMU (IMU at the midpoint between the hip joints), plus a mini PC (4-core A53, 5 TOPS). Four rollers under the head support crawl mode (80 kg payload crawling, 4 kg standing).
• No abduction; roll comes from differential leg length (roll controller). 6 × M1502D direct drive (2.6 kg, 9.6 N·m rated).
• Manual (v1.1c) has "Description of Tail Lights", a tail warning light, an e-stop switch and a detachable upper cover [unverified: search excerpts of device.report; the PDF returned 403].

2.2 DDT TITA (successor, with abduction)

Sources: top3dshop, TITA_Description URDF (no licence).

• URDF: abd ±45°, hip pitch, knee, wheel. Thigh 200 mm, shank 200 mm, wheel Ø185 × 34 mm.
• Body collision box 470 L × 300 W × 190 H mm, 13.2 kg (48 % of the URDF total) [derived].
• Abd axes at y = ±89.5 mm inside the body. The hip-pitch joint is 142.6 mm outboard on the 2.06 kg abd link. Track 567 mm, overall ≈600 mm [derived]; spec 510 × 590 × 490 mm (axes unlabelled).
• The thigh is 3.10 kg with its CoM 28 mm from the hip; the shank is 0.57 kg. So the knee actuator sits at the hip and drives the knee remotely [inferred].
• Base CoM is 20 mm ahead of and 19 mm above the abd axis.
• Sensors are flush in the body's front face: stereo cameras at ±75 mm, two SPAD ToF and an ultrasonic, all at x ≈ +0.22…0.24 m inside the 0.235 m half-length. Nothing protrudes.
• Two hot-swap batteries (≈1 h each, 43.2 V); Orin NX 16 GB.
• "Integrated indicator light bars" show status.
• Accessories mount on the "TITA Bridge" on the back plus three bridges on top; 10 kg moving payload.
• Only an "automatic safe stop" is listed; no physical e-stop. Magnesium-alloy structure per a press release [unverified] (IoT M2M Council).

2.3 Ascento (ETH 2019 → Ascento Robotics)

Sources: ICRA paper arXiv 2005.11435 (Fig. 2 = leg), RA-L WBC arXiv 2005.11431, video, MYBOTSHOP Ascento manual.

• 2019: 10.4 kg, 310–660 mm tall.
  • One ANYdrive SEA (40 N·m) per leg "installed in the hip of the body". The linkage is optimised so the wheel path is near-vertical through the CoM; RA-L calls it a four-bar.
  • Torsion springs in the inner joints carry the weight. Maxon EC90 frameless hub motors keep the wheel compact.
  • SLS PA12 topology-optimised parts. "A body that houses all electronics": NUC i7, 4 × 3S motor pack, 4S compute pack. ToF jump sensors sit next to the wheels.
• Commercial R&D unit (manual):
  • 30–35 kg; 550 L × 600 W × 550–750 H mm; base height 0.3–0.8 m.
  • 50.4 V 12S5P 17.5 Ah pack "integrated inside the robot's body" (weatherproof), >7 h balancing; Orin NX; D435i, Livox Mid-360, thermal and IR cameras; dock charging.
  • Handles on top of the main body. The power key is in a slot underneath; you tilt the robot to reach it.
  • Lights: flashlights blink at power-up; headlight and hazard light on separate commands; status LED colours are white = OK, orange = soft e-stop, red = error, blue = other. The "eyes blink red" when homing is needed.
  • Soft e-stop damps the motors so the robot "gently falls"; there is a separate hard e-stop.
• Guard: 50–90 × 70 × 50 cm, <30 kg (Robot Report). Guard 2.0 has "spotlights three times brighter" and up to 8 h (Robot Report). Leg actuation of the commercial versions is unpublished.

2.4 LimX TRON 1 (wheel-foot)

Sources: spec, robot-description WF_TRON1A (Apache-2.0, URDF/MJCF/STL), New Atlas.

• Spec: ≤20 kg; 392 × 420 × 845 mm; 48 V actuators (30 N·m rated, 60 N·m peak); 46.8 V 4.5 Ah quick-swap pack (≈211 Wh by V × Ah; New Atlas says 240 Wh).
• "E-Stop button" on the robot plus a remote E-Stop. Peripheral port gives 24 V / 100 W, USB 3 and GbE, and there is a mounting point.
• URDF: thigh 300 mm, shank 300 mm, wheel Ø254 × 50. Abd axes at ±105 mm; base 9.59 kg (43 %).
• "Pelvis" layout [derived]: the base mesh is 287 L × 344 W × 337 H mm and the abd axes are 260 mm below its top, so the hip cluster sits in the lower part and the electronics box (collision 270 × 260 × 190) sits above. Track ≈297 mm: the wheels tuck under the body width.
• The thigh (2.3 kg) has its CoM 48 mm inboard of the hip and its mesh reaches 108 mm inboard; the shank mesh has a lever 41 mm above the knee. So the knee actuator is coaxial at the hip on the thigh and drives the knee by a rod, quadruped-style [inferred].
• An optional D435 sits in the pelvis nose, pitched 61° down (commented out in the URDF).

2.5 Tencent Ollie

PMC paper, IEEE Spectrum (photos).

• ≈15 kg, floating base ≈11 kg, height 0.33–0.70 m.
• Eight motors: four at the hips (five-bar, "without actuators on the knees"), two in the tail, two wheels.
• The tail is used only for specific motions (flips); the controller assumes it is fixed. Link and wheel sizes are unpublished.

2.6 RoboMaster balance infantry (平衡步兵) — most similar mission (two wheel-legs + pan/tilt launcher)

• Rules (RMU 2024 spec manual V2.0):
  • Size and mass: Standard robot ≤25 kg with battery, excluding the referee kit (2.60 kg on balancing robots). ≤600 × 600 × 500 mm initial and ≤800³ mm expanded. Balancing robots carry two large armour plates.
  • Light indicators (S115–S118): mounted firmly on the chassis, illuminant ≥200 mm above the ground, fully visible from at least one horizontal view.
  • Bumpers (S128): teams "should design safety rods" so armour does not hit walls.
  • Power (S113): the power-management module switches chassis, gimbal and launcher outputs separately, and the launcher (flywheels, feeder, solenoid) must lose power whenever the ammo-booster port is off (PM01).
  • The balancing class was dropped for 2025 (per SJTU's report below), but teams kept wheel-leg chassis.
• Community-standard five-bar: motor spacing 150 mm, thigh 150 mm, shank 270 mm. It appears identically in HKUST 2024, ZJUI (8.2 kg, Ø124 CyberGear hubs) and Multivac11.
  • Joint motors sit on the chassis: Unitree A1/Go1, HT-04, DaMiao, CyberGear.
  • Wheels: DDT M1505B direct-drive hubs, LK hubs or geared M3508.
• WIT 2024 (post + SolidWorks .7z):
  • 18.4 kg; Ø200 wheels on Unitree Go1 motors; jumps 30 cm.
  • Shortened links (machined thigh adapter) and compressed body height and width.
  • Planned next: a smaller geared wheel, lower the leg set, and "move the joint motors to the body's lower deck to free the upper deck for the gimbal".
  • Climbs steps by extending the legs, bumping the step, then retracting.
• HKUST 2024 (post, technical report PDF):
  • Size and drive: 21.8 kg; 445 × 445 × 780 mm expanded; HT-04 joints; DDT M1505B hubs; 3.5 m/s.
  • Standing needs 6–7 N·m per joint motor. A tension spring per side cut that to ±1 N·m and about doubled runtime: hook 22 mm from the joint centre at 68° to the thigh, k = 4000 N/m.
  • The thigh is carried by a CNC hub on a large bearing. Bolting it straight to the motor output (3 × M4 + 3 × Ø4 pins) "broke legs" on jumps.
  • Frame: 1 mm-wall aluminium tube filled with low-infill prints; the outer tubes tie straight into the glass-epoxy shell. Joint stops are printed in TPU 95A, and the light-bar brackets are TPU so they survive falls.
  • A wiring "belly" opens with two M4 thumb screws for access to power and wiring.
• DGUT ACE 2024 (post): 20 kg; 598 × 442 × 490.5 mm initial (772.5 mm tall expanded); 4 × A1 joints, 2 × M3508 wheels; bicycle-headset joints.
• SJTU 2025 "serial-leg" (post + PDF + CAD zip):
  • Why they left the five-bar: steps can be climbed by collision-then-retract, and a 360° hip lets the robot right itself.
  • Of three coaxial layouts they kept the "similar linkage": kinematically a five-bar with zero motor spacing, which splits load evenly between the two motors. The "simplified linkage" gave uneven load and worse control.
  • Thigh shorter than shank so the knee clears the ground when crouched; nitrogen gas springs for jumping.
  • Hip drive: motors drive the hip through chain (slotted mount plus a printed wedge for tension) into a nested two-stage hip shaft on two headset bearings. A 30 mm-bore slip ring gives continuous hip rotation.
  • Frame: 1 mm aluminium tube in a "#" grid, ≈2 kg. The hip blocks carry the gimbal frame. "Adjust parts so the CoM is near the geometric centre."
  • Turret: the magazine moved into the chassis to cut yaw inertia; the mini-PC rides on the turret.
  • Quick-release head: 4 screws, XT30 and DB9 through two breakout PCBs, 5 minutes to separate (was over an hour).
  • Protection: hinged sacrificial bumpers and guide wheels at the front-lower corners protect the core frame; ToF sensors are tucked beside the front armour.
  • Mass came down from 23 kg to under 20 kg.
• Joint hardware (bicycle-headset note):
  • Shoulder screw + flanged bearing + PTFE washer joints loosened under jumps, bound when tightened, and let heavy offset wheels splay ("外八").
  • The fix is headset-style angular-contact cups: SJTU machined their own; DGUT uses stock 44 mm OD / 41 mm bicycle headsets.
• Licence: forum CAD is for RoboMaster teams only and non-commercial. Use it as reference, do not copy.

2.7 Upkie (open source)

• Sources: parts (Apache-2.0, FreeCAD/STL), BOM.
• ≈5.3 kg (URDF sum); serial leg with the knee motor on the leg; 112 mm wheel.
• The battery (RYOBI 18 V) sits inside the torso case on a printed stud with leaf-spring contacts.
• Optional bearing hip and knee supports "protect knee actuators from radial load"; handle and camera brackets are add-ons. v2 uses a fork lower leg with cables run outside.
• No e-stop and no lights in the BOM.

2.8 Unitree, RobStride, HighTorque, other kits, Disney

• Unitree: no wheel biped found. Its wheel-legged products are quadrupeds: Go2-W, B2-W, A2-W, and AS2-W, announced 2026-07-24 (secondary source).
• RobStride (robstride.com/open-source):
  • The page renders in JS. Per our crawl in robstride-open-source-2026-10-26.md it has 8 entries: the EL-A3 arm, reBot arm, K-Bot humanoid (4 × RS-04), LeRobot humanoid and 4 toolchain repos.
  • None is wheel-legged. No public RS-04 wheel-legged build was found.
• HighTorque: no wheel-legged kit found. Its documented robots are humanoids (π, π+, Hi) (RoboCup AP 2025).
• Other kits:
  • StackForce mini: 540 g, 4 servos + 2 × 2208 gimbal wheels, URDF/STL/schematics open.
  • XGO-Rider (micro:bit) and Rider-Pi (CM4): desk scale.
  • Tsinghua ARX-6: an open wheel-legged manipulator; files not checked.
  • DDT sells its M1505B hubs to RoboMaster teams (HKUST and HKU credit it).
• Disney: no wheel-legged robot found. BD-X (15.4 kg biped) is still relevant for packaging and character:
  • Torso: battery module, comms board, IMU. Head: PC, radio, show board.
  • The removable battery gives ≥1 h.
  • LED-array eyes, a head lamp and antennas are used for expression.
  • A controller "motion stop" freezes the joints standing.

2.9 Hobby / student builds with CAD

• Skythinker616 (GPL-3.0, SolidWorks): desk scale, a closed linkage driven from the body.
• Venus-1 (GPL-3.0): four-bar, CyberGear, FR4 plates. Geared-wheel backlash made it jitter.
• Multivac11: five-bar 150/150/270, A1, 12.9 kg.
• ZJUI: Fusion; no licence.
• huoyiwei4 (MIT, SolidWorks + STL, not validated on hardware).
• N-B-Studio (Apache-2.0, "fully 3D-printed 8-DOF"; details sparse).
• Flamingo (MIT; Isaac Lab sim-to-real; hardware undocumented).

3. Cross-cutting packaging patterns

3.1 Body proportions (D = wheel diameter) [derived]

Relative to its wheel, Gyropup's body is half as long and half as tall as Diablo's or TITA's, and its stance is the widest. Anything that does not fit in a 181 × 206 × 112 box ends up bolted outside, which is the "box out front".

There are two archetypes:

• Side legs (Diablo, TITA, Ascento, RoboMaster): the hip axis passes through the body's mid-height and the wheels sit outside, giving 2.6–3.1 D track.
• Pelvis (TRON 1): the electronics box sits above a hip cluster, the legs hang under the body and the track is ≈1.2 D. It needs abduction and long (300 mm) links.

3.2 Battery and compute

• Inside one shell, between or under the hips. Diablo puts battery, board and IMU in the body; Ascento's pack is integrated in the body; TRON 1 stacks electronics above the hips; RoboMaster keeps battery and supercap in the chassis.
• Body CoM within ~20 mm of the hip axis (Diablo, TITA).
• Service: quick-swap packs (TRON 1, TITA ×2), a belly cover on thumb screws (HKUST), every part reachable in 5 minutes (SJTU).
• Compute: RoboMaster mounts the mini-PC on the turret near the camera (SJTU, HKUST). BD-X puts its PC in the head. Diablo and TITA keep compute in the body.
• No front box anywhere. Sensors sit flush in the body's front face (TITA cameras/ToF/ultrasonic, TRON 1's D435 in the pelvis nose, SJTU's ToF beside the armour). Accessories go on top or back interfaces: TITA Bridge, TRON 1's 24 V/100 W port, Ascento's top payload.

3.3 Lights

• Integrated, not pods: TITA light bars; Ascento headlight, hazard light, colour-coded status LEDs and "eyes" that blink red when homing is needed; Diablo's tail warning light [unverified]; BD-X eye arrays and head lamp.
• Mounting rules from RoboMaster: on the chassis, ≥200 mm high, visible horizontally, on TPU brackets (HKUST) because rigid brackets break in falls.

3.4 E-stop

• TRON 1: a physical button on the robot plus a remote stop.
• Ascento: a soft stop that damps the motors and sits the robot down, plus a hard stop. The key switch is underneath.
• RoboMaster: separate switched rails for drive, turret and launcher; the launcher dies whenever the turret rail does.
• Diablo: rollers under the body give it a safe resting posture.
• None of the sources documents where the e-stop button sits on the body.

4. Ranked recommendations for Gyropup

1. Adopt Diablo's leg topology; keep the rod. "Pushrod vs parallel linkage" is a false choice: Diablo's knee is a rod in a parallelogram. The difference is in three details:
   • Series flange. Bolt the knee RS-04's housing to a carrier on the hip RS-04's output, coaxial.
   • Crank ∥ shank. Put the rod's lower pin on the shank below the knee (Diablo: 90 mm crank, 90 mm below the knee) and run the rod parallel to the thigh. The transmission angle then equals the knee angle: best near the 90–100° stance and zero only at straight or fully folded. This removes mech-review A1 (dead point at 90°). Rod force = T / (r·sin γ).
   • Stance load on one motor. The knee RS-04 alone holds the stance: ≈10–15 N·m per leg at the 60 % pose for 20–26 kg [derived]. Today both motors hold it (A2). The cost is a knee-motor cable crossing the hip joint; Diablo routes it along arched links.
   • Reject the RoboMaster five-bar for us. Its 270 mm shanks reach fore and aft, which limits hip rotation and steps; SJTU left it for exactly this. In this survey no ≥15 kg robot drives the knee by belt (SJTU uses chain only at the hip).
2. One body shell that swallows everything; no external front box. Target ≈2 D long × 1.0–1.3 D tall (≈360–450 × 190–235 mm for D = 180).
   • Hip axis through the body's mid-height (Diablo).
   • J501 (206 × 192 × 112) ahead of or above the actuator block, pack behind or below, all within one shell.
   • Balance so the body CoM falls within ~20 mm of the hip axis with the turret fitted (Diablo/TITA).
   • Cameras, ToF and lights flush in the front face (TITA). Leave the J501 an air path (intake low, exhaust high or back): none of the surveyed robots documents compute cooling, so this is ours to design.
3. Pack low and central, swapped from the rear or bottom. Use a slide-in pack with a latch (TRON 1/TITA quick-swap). Put power electronics on a removable belly tray held by thumb screws (HKUST), and aim for "every part in 5 minutes" (SJTU).
4. Narrow the stance to ≈2.6–3.0 D (470–540 mm track). Recess the hip RS-04 inside the body wall and keep the knee RS-04 on the carrier outside. With thin link planes and the wheel just outboard of the shank this gives ≈540 mm overall [derived, rough]. Stacking both motors outside a 206 mm body gives ≈630 mm, no gain on today. TRON 1's pelvis layout is narrower still but needs abduction.
5. Joints like the RoboMaster teams build them.
   • Bearings carry the link; the actuator flange carries torque only (HKUST, SJTU, Upkie supports).
   • Headset-style angular-contact cups, or double-shear forks, at the knee and the carrier (SJTU/DGUT; fixes A3).
   • TPU end-stops.
6. Turret as a quick-release module. Four bolts and one connector panel through a breakout PCB (SJTU). If yaw inertia matters, move the magazine into the body (SJTU lower-feed).
7. Lights integrated and meaningful.
   • Headlights recessed in the body nose, or in the turret face so they follow aim (BD-X head lamp).
   • An RGB status band or "eyes" using Ascento's code (white OK / orange soft-stop / red fault).
   • A rear tail or hazard light (Diablo/Ascento).
   • TPU mounts, ≥200 mm high, visible from the side (RoboMaster).
8. E-stop architecture.
   • A latching button on the body (our suggestion: top-rear, reachable from behind) plus a remote (TRON 1).
   • A soft stop that damps and sits the robot onto skids, rollers (Diablo) or the tail before the contactor opens (Ascento).
   • Separate drive, turret and launcher rails, with the launcher always dropping with the turret (RoboMaster S113).
9. Fall furniture. Skid rollers under the body (Diablo); sacrificial bumpers and guide wheels at the lower front and rear corners (SJTU, RoboMaster "safety rods"); top handles (Ascento, Upkie).
10. Springs only if heat or runtime needs them. RS-04 holds the stance at ≈25–35 % of rated [derived], but a tension or gas spring (HKUST ±1 N·m and 2× runtime; Ascento; SJTU) is cheap.
11. No abduction in v1. Diablo, Ascento, Ollie, RoboMaster and Upkie balance without it; TITA and TRON 1 pay for it with two actuators and width. Roll comes from differential leg length (Diablo).

5. Open items and unverified

• Diablo: tail-light and e-stop placement (manual blocked). TITA: battery location and knee transmission. TRON 1: knee rod (inferred from URDF). Ascento commercial: leg actuation. Ollie: link and wheel sizes. RoboMaster rules: we read 2024; the 2026 manual was not checked.
• Licences: DDT models (Diablo STL/SDF, TITA URDF) have no licence; RoboMaster CAD is restricted to teams. LimX descriptions are Apache-2.0 and Upkie parts are Apache-2.0, so those two are safe to reuse.