Mobile Base Architectures — Family Index

Comprehensive catalog of ground-mobile robot base topologies: every wheel arrangement plus tracked, legged, hopping, ball, and air-bearing variants. Cross-referenced to product families and research platforms. Companion to [[Robotics/mobile-base-wheeled]] and [[Robotics/legged-robotics]].

1. At a glance

Ground-mobile bases group by contact mechanism and by holonomy.

Contact-mechanism categories

• Wheeled: differential drive, skid steer, Ackermann, tricycle, mecanum, omni, Swerve, caster-drive.
• Tracked (continuous-track): rigid track over road wheels with sprocket drive.
• Legged: quadruped, biped, hexapod, octopod, wheeled-leg hybrid.
• Hopping: single-leg dynamically stable (Raibert).
• Omni-tracked: tracked module with omni rollers on segments (rare research).
• Ball / spherical: balances on a single sphere, 3-DoF planar.
• Hovercraft / air-bearing: lift via plenum or porous-media bearing.

Holonomic vs non-holonomic

A holonomic base can command any planar velocity (Vx, Vy, ω) instantaneously without first re-orienting. Non-holonomic bases are subject to rolling-without-slip constraints that couple linear and angular velocity.

• Holonomic: mecanum, omni (3- or 4-wheel), Swerve (when modules pre-aligned), ball-bot.
• Non-holonomic: differential drive (can spin in place but cannot move sideways), Ackermann (cannot spin in place), tricycle, skid-steer (planning-treated as diff drive with slip).

2. Differential drive

Two coaxial drive wheels plus 1 or 2 passive casters for static stability. Kinematics:

• v = (v_R + v_L) / 2
• ω = (v_R − v_L) / L, where L is wheel separation (track).

Cheap, mechanically simple, can pivot in place (zero-radius turn). Non-holonomic — no sideways motion. Most common research base.

Exemplars

• iRobot Roomba (consumer vacuum, since 2002).
• Pioneer 3-DX (MobileRobots / Omron Adept legacy research platform).
• MobileRobots PowerBot (heavier-payload Pioneer sibling).
• Fetch Robotics Freight 100 / Freight 500 (logistics).
• Robotnik RB-1 Base (mobile-manipulator base for collaborative arms).
• ROS TurtleBot 1 (iRobot Create), TurtleBot 2 (Kobuki), TurtleBot 3 (Burger / Waffle), TurtleBot 4 (Create 3).
• Stretch by Hello Robot (lift-and-arm research robot).
• KUKA KMR iiwa in differential mode (some variants).

3. Skid-steer (4-wheel, 6-wheel, tracked)

Both sides driven, no steered wheels. Turning by left/right speed differential, requiring tire scrub. Treated kinematically like differential drive with an effective track wider than physical (slip factor). Robust outdoors; high tire wear; heading drift from slip-dominated turns.

Exemplars

• Clearpath Robotics Husky A200 (4-wheel outdoor research UGV).
• Clearpath Jackal UGV (smaller indoor / mixed).
• ARGO J5 / J8 / Atlas XTR (amphibious 6- and 8-wheel skid-steer).
• Nuro R2 (last-mile delivery, sidewalk-class).
• Boston Dynamics LS-3 / BigDog tracked-augment prototypes (legacy).
• Lynx UGV-2 (Roboteam).
• Bobcat S70 / T-series (industrial loaders — not robots, but the kinematic archetype).
• Coco Robotics delivery (sidewalk skid-steer).

4. Ackermann steering

Front wheels steered, rear wheels drive (or 4-wheel drive). Inner and outer steered wheels follow concentric arcs about an instantaneous center on the extended rear axle (Ackermann geometry). Minimum turn radius constrained:

R_min ≈ L / tan(δ_max),

where L is wheelbase and δ_max the maximum steer angle.

Non-holonomic and cannot zero-radius turn. Dominant for any base derived from a passenger vehicle.

Exemplars

• Waymo (Chrysler Pacifica, Jaguar I-Pace, Zeekr platform).
• Cruise (Chevy Bolt, Origin shuttle).
• Tesla Autopilot / FSD (production passenger).
• Mobileye SuperVision / Chauffeur.
• F1Tenth racing platform (1:10 scale autonomous-vehicle research, Traxxas chassis).
• MIT RACECAR (Jetson-based 1:10).
• CARLA Simulator default vehicle model.
• John Deere autonomous tractor (8R Autonomous, 2022).
• Pix Moving / Neolix autonomous delivery vans.

5. Tricycle

Single steered + driven front wheel and two passive rear wheels (or inverse). Compact; common in forklifts.

Exemplars

• Hyster / Yale / Toyota electric counterbalance forklifts in narrow-aisle config.
• Linde reach trucks with single steered drive wheel.
• Various older outdoor mobility scooters used as robot test platforms.

6. Mecanum wheel

4-wheel arrangement using passive rollers angled at 45° around the rim (Ilon, Swedish patent 1973; US 3,876,255 granted 1975). The angled rollers convert each wheel’s normal traction into a force at 45°; by combining four wheels in mirror-image pattern, the planar net force can be commanded in any direction. Holonomic 3-DoF in the plane (Vx, Vy, ω). Inverse kinematics:

• v1 = Vx − Vy − (Lx + Ly)·ω
• v2 = Vx + Vy + (Lx + Ly)·ω
• v3 = Vx + Vy − (Lx + Ly)·ω
• v4 = Vx − Vy + (Lx + Ly)·ω

(wheel order FL, FR, RL, RR; sign convention varies by source).

Drawbacks: high slip on dirty / uneven floors, low efficiency, audible roller noise, sensitivity to seams and ramps.

Exemplars

• KUKA omniMove (KMP 200, KMP 600, KMP 1500, KMR iiwa) — high-payload industrial mecanum.
• Robotnik RB-MECA / SUMMIT-XL Mecanum.
• Vetex SWAT, OTSAW O-R3.
• Festo Robotino XT and MecanumBot (educational).
• Andymark / VEX educational mecanum kits.

7. Omni-wheel (3-wheel, 4-wheel, 8-wheel)

Wheels with passive rollers around the rim oriented perpendicular to the wheel axis. A single omni-wheel acts like a normal wheel along its driven axis and like a free roller orthogonally. Common configurations:

• 3-wheel symmetric at 120°: simplest holonomic geometry. Forward kinematics relates body-frame Vx, Vy, ω to wheel speeds v_i = R·ω_i.
• 4-wheel cross-pattern (X / +): more wheels for higher payload distribution but redundant — one wheel velocity is dependent.

Exemplars

• Festo Robotino (3-wheel omni, education).
• Adept Lynx (legacy logistics, now Omron LD-series moved to diff drive).
• KUKA youBot (4-wheel mecanum, sometimes operated as omni).
• DEKA iBOT (medical mobility, omni / balance modes).
• Various RoboCup small-size league robots (4-wheel omni at corners).

8. Swerve drive

Each corner is an independently steered and independently driven module. Holonomic when modules can be coordinated, with full tractive force at every wheel (unlike mecanum, where most traction is wasted at 45°). Coordinated control: each module computes a target velocity vector from base (Vx, Vy, ω); modules steer to align then drive at the magnitude. Singular when wheel speeds approach zero (heading discontinuity).

Exemplars

• FIRST Robotics Competition (FRC) modules: Swerve Drive Specialties MK4, MK4i, MK4c, MK4n; REV Robotics MAXSwerve; West Coast Products (WCP) Swerve X / X2 / X-Flipped.
• ANYbotics ALMA (Sherpa wheeled-leg variant uses driven steered wheels).
• KUKA omniMove (some variants use swerve over mecanum).
• Saderet modular Swerve drive units (industrial AGV).
• Otto Motors Otto 100 / 600 / 1500 (mix of swerve and dual-Ackermann across generations).

9. Caster-drive

Drive wheels plus passive casters. Caster wheels swivel about a vertical axis with trail, allowing them to align passively with motion direction. Encountered when adding an active drive wheel to a cart already on passive casters (warehouse hand-cart conversion).

Exemplars

• Otto-Bock and Toyota Material Handling caster-drive carts.
• Some AGV conversions retrofitted onto passive carts.

10. Tracked / continuous-track

A flexible rubber-or-steel track wraps over sprocket-driven drive wheels and idlers, contacting ground over a long footprint. High ground-pressure spread, excellent obstacle climb. Drawbacks: high friction, high power draw, maintenance (tensioning, debris), turning scrub.

Exemplars (military and rescue)

• iRobot PackBot (later FLIR / Teledyne) — bomb disposal and recon.
• QinetiQ North America Talon / FoxX (TALON IV).
• Endeavor Robotics / FLIR Centaur and Kobra.
• ReconRobotics Throwbot XT (small).
• Boston Dynamics LS-3 tracked option (legacy).

Exemplars (industrial / construction)

• Bobcat T7X autonomous electric tracked compact loader.
• Built Robotics LDR (large dozer retrofit).
• Robotnik RB-EHS tracked outdoor research platform.

11. Legged — quadruped, biped, hexapod, octopod

Covered in depth at [[Robotics/legged-robotics]] and [[Robotics/Tier3/legged-morphologies]]. Summary list:

• Quadruped: Boston Dynamics Spot, ANYbotics ANYmal C / D, Unitree A1 / Go1 / Go2 / B1 / B2, DEEP Robotics X20 / Lite3 / Jueying.
• Biped: Agility Robotics Digit, Boston Dynamics Atlas, Apptronik Apollo, Tesla Optimus, Figure 01 / 02, 1X Neo / Eve.
• Hexapod: PhantomX, Hexapod-Mark by Robugtix.
• Wheeled-leg hybrid: Ascento (ETH), ANYmal on Wheels (ALMA), Boston Dynamics Handle (legacy).

12. Hopping / single-leg / wheeled-leg hybrid

Active dynamic stability — the robot is balanced through controlled bouncing or balancing.

• Raibert hopper (CMU 1980s, MIT Leg Lab) — original active-dynamics platform, Marc Raibert’s planar hopper that informed all later legged work at Boston Dynamics.
• Disney Imagineering bouncing characters (hopping demo robots for theme parks).
• Ascento (ETHZ) — wheeled biped that balances on two wheels with extending legs for steps and jumps.
• Salto-1P (UC Berkeley) — single-leg jumping robot.

13. Spherical / ball-bot

Balances on a single sphere driven by mecanum or omni rollers. Holonomic 3-DoF planar, expressive (can lean), inherently unstable like an inverted pendulum so requires continuous active balancing.

Exemplars

• Rezero (ETHZ, 2009) — first ETH ball-bot, balanced and expressive for HRI demos.
• CMU Ballbot (early prototype).
• Murata Manufacturing “ANT-USHI” and miniature ball-bot demonstrators.

Mostly research and demonstration; payload is low and floor must be flat and clean.

14. Hovercraft and air-bearing

Lift the platform off the ground with a plenum or porous-media air bearing. Effectively frictionless within the bearing’s stroke; used for emulating zero-gravity dynamics.

• Tronair / Aerofloat air-bearing dollies (cargo).
• Naval Postgraduate School and NASA Marshall free-floating air-bearing test beds for satellite-emulation research (servicer-target docking experiments).
• Hovercraft prototypes for amphibious robots (less common).

15. Wheel propulsion sub-axis: passive vs active suspension

• Passive suspension: Clearpath Husky uses passive 4-wheel independent compliance; some ANYmal-related wheeled prototypes use elastomer compliance.
• Active suspension: Boston Dynamics Spot has 12-DoF active legs that effectively form an active suspension on every step; ANYmal similarly.
• Rocker-bogie: NASA Mars rovers Sojourner (1997), Spirit / Opportunity (2004), Curiosity (2012), and Perseverance (2021) use a passive 6-wheel rocker-bogie mechanism that keeps all wheels in contact over uneven terrain without springs. The rocker pivots about a body-mounted bearing; the bogie carries the rear two wheels in a sub-linkage.

16. Comparison table

Architecture	Holonomic?	DoF planar	Typical max payload	Typical floor	Exemplar product
Differential drive	No (can spin in place)	2	1–500 kg	Indoor flat	TurtleBot 4, Pioneer 3-DX
Skid-steer 4-wheel	No (slip-turning)	2	75–500 kg	Outdoor rough	Clearpath Husky
Skid-steer 6-wheel	No	2	250–1500 kg	Outdoor rough	ARGO J8
Ackermann	No (no zero-turn)	2	100–3000 kg	Roadway	Waymo Pacifica
Tricycle (steered drive)	No	2	500–5000 kg	Warehouse	Linde reach truck
Mecanum	Yes	3	100–1500 kg	Indoor flat clean	KUKA KMP 1500
Omni-wheel 3	Yes	3	5–80 kg	Indoor flat	Festo Robotino
Omni-wheel 4	Yes	3	50–250 kg	Indoor flat	RoboCup SSL bots
Swerve drive	Yes	3	50–800 kg	Indoor / mixed	FRC SDS MK4i
Caster-drive	No (constrained)	2	50–500 kg	Indoor flat	Custom AGV
Tracked	No (skid-turning)	2	50–5000 kg	Off-road	iRobot PackBot
Quadruped	Effectively yes	3+	5–50 kg	Mixed terrain	Spot, ANYmal
Biped	Effectively yes	3+	5–30 kg	Mixed	Digit, Atlas
Hexapod	Effectively yes	3+	1–20 kg	Mixed	PhantomX
Ball-bot	Yes	3	5–20 kg	Indoor flat	Rezero
Rocker-bogie 6-wheel	No (slip-turning)	2	100–900 kg	Off-road	Curiosity rover
Wheeled-leg hybrid	Effectively yes	3	5–50 kg	Mixed	Ascento, Handle
Hovercraft / air-bearing	Yes (low friction)	3	Variable	Smooth	Air-bearing dolly
Hopping (Raibert)	Effectively yes	3	<10 kg	Flat	Raibert planar hopper
Single-leg jumper	No	1	<2 kg	Flat	Salto-1P

17. Power and speed envelopes

• Roomba: 0.3 m/s, ~10 W drive.
• Warehouse AGV MiR 250 / MiR 600 / MiR 1350: 1.2–2.0 m/s, 200–1500 kg payload.
• Otto 100 / 600 / 1500: 1.8–2.0 m/s, 100–1500 kg payload.
• Mobile manipulator (UR + base, e.g., Robotnik RB-1 + UR5): 1.0–1.5 m/s.
• Outdoor security patrol (Knightscope K5): 1.4 m/s.
• Sidewalk delivery (Starship): 1.6 m/s ground speed.
• Autonomous delivery van (Nuro R2): 40 km/h max (~11 m/s).
• Robotaxi (Waymo Chrysler Pacifica, Cruise Bolt): 80 km/h urban (~22 m/s).
• Military UGV (PackBot): ~2 m/s.
• Spot (Boston Dynamics quadruped): 1.6 m/s walk-trot.
• ANYmal C: 1.0 m/s.
• Atlas (Boston Dynamics): ~2.5 m/s walking, ~4 m/s running in demonstrations.

18. Wheel and tire materials

Wheels (industrial AGV)

• Molded polyurethane (Trelleborg, Stellana, Blickle, Hamilton) — non-marking, high static and rolling load, common for indoor AGV.
• Vulcanized rubber on iron core — heavy-duty industrial floor truck.
• Pneumatic rubber (inflated) — outdoor AGV, agricultural, off-road.
• Foam-filled solid-core — puncture-proof outdoor (Husky, ATX), heavier and harsher ride than pneumatic.
• Sponge-rubber (Roomba) — light consumer.

Tracks

• Vulcanized rubber with slot-grouser tread (e.g., Spot in tracked add-on, PackBot).
• Reinforced rubber with embedded steel cable.
• Steel link (military, mostly outside robot scale).

Casters

• Bayer, Faultless, Albion, Colson, RWM — nylon, polyurethane, phenolic, rubber.
• Polyurethane tread is the AGV / clean-floor default; nylon for high load with low rolling resistance on hard floor.

19. Selection heuristics by use case

• Indoor flat-floor pallet transport, 1000 kg → diff-drive (MiR 1000 / 1350) or differential AGV; if lateral motion needed, mecanum / swerve (KUKA KMP 1500, Otto with swerve).
• Warehouse fork-tine pallet → AGV forklift (Linde MATIC, KION Dematic, Toyota Material Handling Autopilot, JBT) — Ackermann or tricycle.
• Confined-aisle cube mover or mobile-manipulator in dense cell → mecanum (KMP-series, Robotnik RB-MECA).
• Outdoor security patrol on paved or compacted surfaces → 4-wheel skid-steer or Ackermann hybrid with sealed pneumatic / foam-filled tires (Knightscope K5, K3).
• Rough-terrain inspection (utility, mining, oil-and-gas) → tracked or quadruped (Boston Dynamics Spot, ANYbotics ANYmal C / D).
• Sidewalk delivery → 6-wheel skid-steer or 4-wheel Ackermann (Starship Technologies, Coco Robotics, Serve Robotics).
• Autonomous taxi on public roads → Ackermann with redundant brake and steer (Waymo, Cruise, Tesla, Mobileye).
• Research racing → Ackermann 1:10 scale model (F1Tenth, MIT RACECAR).
• Construction-site excavator / dozer → tracked autonomous (Built Robotics LDR, Bobcat T7X).
• Agricultural row-crop with rigid row geometry → Ackermann or 4-wheel-steer Ackermann (John Deere 8R Autonomous); free-row weeding → diff-drive (Naïo Oz, Naïo Dino).
• Lab and clean room → diff-drive plus caster (Robotnik RB-1, MiR 100 plus collaborative arm).
• Search-and-rescue rubble → tracked (PackBot) or quadruped (Spot with Search-and-Rescue payload).
• Holonomic motion in a tight machine-tending cell → mecanum or omni (KUKA KMP, Robotnik RB-MECA).
• Human-robot interaction demo with balance and expressive lean → ball-bot (Rezero) or unicycle prototype.
• Hospital logistics on tile floor → diff-drive (Aethon TUG, Diligent Robotics Moxi).
• Last-yard outdoor delivery on mixed terrain → 6-wheel skid-steer (Starship) or tracked.

20. Cross-references

• [[Robotics/mobile-base-wheeled]] — kinematic equations and control details.
• [[Robotics/legged-robotics]] — quadruped, biped, hexapod families.
• [[Robotics/multirotor-design]] — aerial counterpart to ground mobility.
• [[Robotics/mobile-manipulation]] — mounting an arm on a mobile base.
• [[Robotics/Tier3/legged-morphologies]] — Tier-3 family index for legged.
• [[Robotics/Tier3/motor-families]] — drives that power these bases.
• [[Robotics/Tier3/sensor-families]] — perception sensors typically paired with each base class.

21. Citations

• Siegwart, Nourbakhsh, Scaramuzza. Introduction to Autonomous Mobile Robots, 2nd ed., MIT Press, 2011.
• Bengt Erland Ilon. US Patent 3,876,255 — “Wheels for a course-stable self-propelling vehicle movable in any desired direction on the ground or some other base”, granted 1975 (Mecanum wheel).
• Marc H. Raibert. Legged Robots That Balance. MIT Press, 1986.
• Clearpath Robotics product catalogs (Husky, Jackal, Warthog).
• Mobile Industrial Robots (MiR) datasheets (MiR 100 / 250 / 600 / 1000 / 1350).
• Otto Motors product line (Otto 100 / 600 / 1500).
• KUKA omniMove technical brochures (KMP 200 / 600 / 1500, KMR iiwa).
• Boston Dynamics technical references (Spot, Atlas, Handle).
• ANYbotics ANYmal product documentation.
• FIRST Robotics Competition Swerve drive technical references (SDS MK4i, REV MAXSwerve, WCP Swerve X).
• NASA / JPL Mars rover engineering papers on rocker-bogie suspension.