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Enter your chassis conditions first to get ratio, torque, and shaft-fit direction. Then use the report layer to validate boundaries, compare options, and avoid interface mistakes before RFQ lock-in.
These summary blocks are decision-first. They convert tool outputs and evidence boundaries into practical procurement direction for 10 kg class mobile robot builds.
Run calculator to generate a ratio recommendation and sample window.
Use this as a candidate window, not a final procurement lock.
Traction feasibility is unresolved until friction coefficient and motion targets are entered.
If demand exceeds mu*N grip limit, torque sizing alone will not prevent wheel slip.
12 mm is a common baseline for this class, but direct fit still depends on hub geometry and tolerance.
Do not assume direct fit without checking hub standard and retention method.
Shaft-stress risk is unresolved until required torque and shaft diameter are entered.
High startup torque or undersized shaft pushes fit from pass to watch/fail quickly.
Public data is enough for screening, not enough for fatigue sign-off.
Complete sign-off still needs supplier curves and instrumented endurance runs.
| Condition | Applicable | Not applicable | Action |
|---|---|---|---|
| Ratio screening | Candidate window inside 8:1 to 220:1 | Required ratio above 220:1 | Raise motor torque or lower speed/grade demand. |
| Shaft interface | Native hub standard with verified shaft retention | Mixed parts without tolerance-verified adapter | Use validated adapter and runout check. |
| Startup transient | Measured startup within controller/battery limits | Unknown or repeated overcurrent protection trips | Tune ramp and gather current traces before RFQ. |
| Traction limit | Traction demand stays below estimated µN boundary | Traction demand reaches or exceeds µN limit | Increase grip or reduce launch demand before final ratio lock. |
| Deployment safety scope | Safety case reviewed separately from drivetrain sizing | Calculator output treated as deployment approval | Route to ISO/Risk assessment workflow before field deployment. |
| Evidence quality | Supplier curve + endurance data available | Catalog-only numbers with no duty test evidence | Require bench report and thermal run before sign-off. |
Scenario zones summarize where teams usually move from speed-first designs to torque-reserve designs. Treat this as routing logic, then confirm with your own duty-cycle telemetry.
New evidence gain (stage1b): similar-mass robots still use different shaft/hub standards. Do not infer compatibility from weight class label alone.
| Platform | Hub size | Official fitment evidence | Decision impact |
|---|---|---|---|
| Pololu 37D ecosystem | 6 mm motor shaft + optional 12 mm hex adapter | Category related products list compatible shaft adapters | Mass class alone does not imply direct-fit hub size; adapter stack must be verified. |
| maxon GPX42 configuration | Configurable shaft geometry (length/flat/key options) | Catalog configuration fields enumerate shaft optioning | Interface compatibility is a configuration decision, not a default. |
| Cross-vendor mix (general case) | No universal 10 kg standard | No reliable public unified standard found | Treat cross-vendor shaft/hub pairing as pending until tolerance and retention are validated. |
If your ratio window is clear but shaft interface or startup risk is still uncertain, send the current inputs now. We can map a short supplier-ready candidate list before you commit bench budget.
This layer explains how the tool result is constructed, what is known vs unknown, and what trade-offs matter when choosing a planetary ratio and shaft standard for 10 kg class robots.
| Step | Equation | Why it matters |
|---|---|---|
| Traction force | F = m(a + g sinθ + Crr g cosθ) | Captures acceleration, slope load, and rolling resistance in one force target. |
| Wheel torque | T = F x r | Converts force demand into drivetrain torque demand at the wheel. |
| Ratio by torque | Ratio = (Twheel x SF / eta) / Tmotor | Protects against under-torque sizing when load spikes or duty drifts. |
| Ratio by speed | Ratio = motor rpm / wheel rpm | Prevents selecting ratios that cannot reach target vehicle speed. |
| Shaft stress screen | tau = 16T / (pi d^3) | Flags early shaft-overload risk before detailed fatigue analysis. |
More stages can provide higher ratios but can reduce net efficiency and push thermal demand upward. New dataset check: maxon GPX 42 UP stage data (2025) extends ratio reach to 1526:1, but with lower efficiency and larger package size.
New factual increment (checked 2026-05-17): same-family stage data shows where higher ratio availability trades against efficiency, backlash, and package mass.
| Stage | Ratio band | Max efficiency | Avg backlash | Max cont. torque | Max radial load | Length | Mass | Decision note |
|---|---|---|---|---|---|---|---|---|
| 1-stage (UP) | 3.9:1 to 5.3:1 | 96% | 0.3° | 45 Nm | 350 N | 48.0 mm | 400 g | Lowest loss and smallest package, but limited ratio reach. |
| 2-stage (UP) | 16:1 to 35:1 | 93% | 0.4° | 80 Nm | 525 N | 67.0 mm | 540 g | Balanced for many builds; moderate size and loss increase. |
| 3-stage (UP) | 62:1 to 231:1 | 90% | 0.5° | 120 Nm | 750 N | 86.0 mm | 660 g | High ratio access with clear backlash and packaging penalties. |
| 4-stage (UP) | 243:1 to 1526:1 | 87% | 0.6° | 120 Nm | 750 N | 104.5 mm | 790 g | Counterexample to the 220:1 planning window; feasible but usually heat- and size-sensitive. |
| Scenario | Mass | Target speed | Grade | Likely ratio zone | Outcome note |
|---|---|---|---|---|---|
| Indoor AMR transfer bot | 9-10 kg | 1.6-2.0 m/s | 0-5% | 18:1 to 35:1 | Prioritize runtime and smooth start profile over peak speed. |
| General 10 kg rover | 10-11 kg | 1.8-2.4 m/s | 10-15% | 30:1 to 60:1 | Balanced zone for torque reserve and manageable thermal load. |
| Ramp-heavy inspection duty | 10-12 kg | 1.0-1.8 m/s | 20-28% | 55:1 to 120:1 | Use lower speed and higher ratio; watch gearbox efficiency drop. |
| Coarse terrain + strict launch time | 11-13 kg | 1.6-2.2 m/s | 20%+ | 90:1 to 180:1 | Upper boundary zone; verify startup current, thermal rise, and shaft stress. |
| Tracked payload mover | 10-14 kg | 0.7-1.4 m/s | 30%+ | 120:1 to 220:1 | High-ratio envelope where packaging and heat become the gating risks. |
| Option | Ratio band | Shaft interface | Known strength | Main risk | Best fit |
|---|---|---|---|---|---|
| Brushed DC + planetary (2WD) | 20:1 to 80:1 | 10-12 mm keyed or clamped output | Lower BOM and straightforward control stack | Higher brush wear under long duty cycle | Cost-sensitive indoor transport bots around 10 kg |
| BLDC + planetary (2WD/4WD) | 12:1 to 60:1 | 8-12 mm shaft with encoder-ready stack | Better efficiency and controllability at variable speed | Controller tuning and EMI integration complexity | Longer runtime and dynamic speed profiles |
| High-ratio crawler stack | 70:1 to 220:1 | 12 mm output with reinforced hub | Strong climb torque and low-speed control | Speed ceiling, efficiency loss, and thermal loading | Ramp-heavy or rough-terrain missions |
| Hub motor + chain/belt reduction | Custom external reduction | Wheel-integrated motor with external stage | Packaging flexibility and modular replacement | Open drivetrain contamination and chain tension drift | Teams that can maintain mechanical tuning regularly |
New decision-critical guardrail: this table uses published Pololu 37D 12V 50:1 data to show why startup telemetry matters before final ratio lock.
| Condition | Published value | Risk if ignored | Action |
|---|---|---|---|
| Continuous torque planning (Pololu 12V 50:1 example) | Recommended upper continuous load: 10 kg·cm (~0.98 Nm) | Sustained operation near stall heats motor/gearbox quickly and shortens life. | Hold routine duty near validated thermal zone and log motor-case temperature every cycle block. |
| Short burst / transient event (same model example) | Instantaneous upper load: 25 kg·cm (~2.45 Nm) | Repeated burst use can drive rapid wear or abrupt failure under shock loads. | Allow only short bursts and add controller torque/current clipping for repeated events. |
| Startup current screen | Model stall current: 5.5 A at 12 V; first-pass screening target: <=25% stall current for repeated duty | Battery sag, current foldback, and unstable acceleration make ratio results look better than reality. | Log current and battery voltage during launch; rerun tool with measured startup multiplier. |
New factual increment (checked 2026-05-17): published current guidance and DC motor linearity explain why a ratio can pass on paper but still fail on battery/controller limits.
| Check | Published point | Boundary meaning | Execution action |
|---|---|---|---|
| Voltage family choice (same gearbox family) | Pololu 37D category: 12 V and 24 V families have similar nominal speed/torque; 24 V draws about half current. | A ratio that looks fine on torque can still overload a low-voltage current budget. | Screen controller and battery current margin together with ratio; do not validate ratio in isolation. |
| Continuous vs stall screening | Pololu guidance: continuous load 10 kg.cm, instantaneous 25 kg.cm; brushed DC recommendation <=25% stall current. | Repeated launches near stall current can cause second-level thermal damage and short lifetime. | Set current clipping and log launch traces before RFQ freeze. |
| Linearity assumption for first-pass model | FAULHABER technical note states near-linear load-speed and current-torque relation for DC motors. | Tool interpolation is useful for screening, but constants must come from the selected motor curve. | Replace generic assumptions with vendor torque-speed-current points for final sizing. |
Decision boundary clarification: this page uses 220:1 as default screening envelope, but published counterexamples exist. Use them only when trade-offs are explicitly accepted and verified.
| Condition | Published counterexample | Trade-off signal | Validation gate |
|---|---|---|---|
| Need high climb torque at low top speed | maxon GPX 42 UP 4-stage offers 243:1 to 1526:1 published ratios. | Same table shows efficiency/backlash/size penalties versus lower-stage options. | Treat >220:1 as deliberate exception and run thermal + packaging sign-off, not default path. |
| Thermally constrained duty cycle | FAULHABER duty guidance separates continuous and intermittent capability. | Intermittent peaks can be feasible while continuous operation at the same point is not. | Document duty cycle explicitly and verify winding temperature during real launch profile. |
| Noise / vibration limits in application | Pololu Rev 1.2 notes first-stage helical pinion used to reduce noise/vibration and improve efficiency. | High reduction can solve torque but may still violate NVH targets if drivetrain stack is unmanaged. | Add NVH check to candidate comparison, not only ratio/torque check. |
This hybrid page now marks compliance scope explicitly: drivetrain sizing remains an engineering input, not a deployment safety approval.
| Boundary | Standard signal | Not covered | Action |
|---|---|---|---|
| Driverless truck / AMR safety verification | ISO 3691-4:2023 abstract defines safety requirements and verification for driverless industrial trucks. | The same abstract states requirements for power sources are not covered. | Use this page for drivetrain screening only; maintain separate safety and power verification workflow. |
| Operating-zone dependency | ISO abstract states operating-zone condition significantly affects safe operation and references Annex A preparation. | Zone prep details are not available from the abstract page alone. | Do not claim deployment readiness until zone hazards are mapped in your safety case. |
| Out-of-scope deployment contexts | ISO abstract excludes public-road and certain severe-condition contexts. | This calculator does not assess those excluded contexts. | Flag out-of-scope conditions early and route to domain-specific safety standard review. |
Evidence-discipline update: where public evidence is insufficient, we explicitly mark pending status instead of overstating certainty.
| Boundary | Current rule | Evidence status | Next step |
|---|---|---|---|
| Fit-band shaft stress thresholds (watch/fail MPa) | Watch >70 MPa, fail >100 MPa (screening gate only) | Pending (needs material-specific validation) | Replace with material-specific allowable stress from your shaft cert and fatigue case. |
| Default ratio window padding | Recommended ratio x 0.85 to x 1.20 for candidate sweep | Pending (no reliable public universal multiplier data) | Use at least one speed-priority and one torque-priority neighbor then bench-compare heat/current. |
| Traction feasibility rule | Watch >80% of mu*N limit, fail >100% | Pending (depends on tire compound, contamination, and weight transfer) | Replace default mu with measured slip-threshold data from your surface and payload. |
| Risk type | Trigger | Impact | Mitigation |
|---|---|---|---|
| Misfit ratio | Torque ratio and speed ratio diverge too much | Either overcurrent or top-speed miss | Sample three adjacent ratios and run load trace. |
| Traction shortfall | Required traction force approaches or exceeds µN limit | Wheel slip, unstable acceleration, and degraded path tracking | Increase tire grip or reduce launch demand, then rerun with measured µ. |
| Interface slip | Mixed shaft/hub standards without verified fit | Backlash growth and steering drift | Use verified adapter stack and runout screening. |
| Shaft overload | High startup multiplier + small diameter shaft | Plastic deformation or early fatigue | Increase shaft section or reduce startup shock. |
A practical hybrid-page workflow: use tool output for immediate direction, then add evidence until the decision is robust enough for procurement lock-in.
| Source | Use | Scope | Checked | Confidence |
|---|---|---|---|---|
| DFRobot: How to Calculate the Motor Torque for a Mobile Robot | Supports force -> torque -> power workflow for wheeled mobile robots. | Primary reference for the structure of first-pass sizing equations. | 2026-05-17 | Primary |
| Pololu 37D Metal Gearmotors category | Confirms common catalog ratio envelope and encoder availability. | Reference ratio window for first-pass candidate screening. | 2026-05-17 | Primary |
| Pololu 37D Metal Gearmotor datasheet (Rev 1.2) Published: Rev 1.2 PDF | Provides ratio-specific no-load speed and stall-torque examples. | Used as benchmark data for 10 kg class scenario bands and startup checks. | 2026-05-17 | Primary |
| Pololu 37D 12V 50:1 gearmotor (item 4743) | Adds published guidance on continuous load, instantaneous load, and stall current. | Used for current and duty-cycle guardrails in the tool interpretation layer. Caveat: Numbers apply to this model family only; replace with your chosen motor curve before release. | 2026-05-17 | Primary |
| maxon GPX 42 catalog page EN-405 (2025) Published: 2025 catalog page | Provides stage-by-stage ratio range, efficiency, backlash, and package trade-offs. | Used to quantify what changes when a 10 kg robot spec pushes into high-ratio territory. Caveat: Do not treat this single-vendor trend as universal across every planetary gearbox platform. | 2026-05-17 | Primary |
| FAULHABER DC-Motors Technical Information | Adds linear speed/torque/current relationships and duty/lifetime caveats for brushed DC motors. | Used to explain why current-limited launches and duty point selection change real output. Caveat: Coreless micromotor guidance is directionally useful, but motor-family constants must still come from your selected datasheet. | 2026-05-17 | Primary |
| Physics LibreTexts (OpenStax): Friction model | Anchors static friction upper bound fs(max)=mu_s*N and example mu ranges. | Used for traction-feasibility boundary so torque results are not interpreted as guaranteed ground force. Caveat: Surface contamination, tire compound, and transient load transfer can shift effective mu away from textbook values. | 2026-05-17 | Secondary |
| ISO 3691-4:2023 abstract page Published: Edition 2 (2023-06) | Defines safety-verification scope for driverless industrial trucks/AMRs and lists exclusions. | Used to mark where drivetrain sizing is necessary but not sufficient for deployment readiness. Caveat: This page cites abstract scope only. Full requirement clauses require licensed standard text. | 2026-05-17 | Primary |
| Engineering ToolBox: Rolling resistance coefficients | Provides first-pass Crr range references by surface/material pair. | Used only for initial estimate when measured rolling-loss data is unavailable. Caveat: Surface state, tread, and pressure change Crr substantially; prefer measured field data. | 2026-05-17 | Secondary |
| NIST Handbook 44 (2026), Appendix C length conversions Published: 2026 edition | Anchors inch-mm conversion used in shaft-interface checks. | Reference conversion: 1 inch = 25.4 mm. | 2026-05-17 | Primary |
| RoyMech: Torsion equations for solid and hollow shafts | Provides the solid-shaft torsional shear equation used in boundary checks. | Secondary sanity check for tau = 16T / (pi d^3) modeling. Caveat: Equation is first-pass only and does not include keyway notch, fatigue spectrum, or shock factors. | 2026-05-17 | Secondary |
| Evidence gap | Status | Checked | Reason | Action |
|---|---|---|---|---|
| Controller current foldback vs battery sag in real launch events | Pending | 2026-05-17 | Open product pages rarely include foldback curves across battery voltage droop and temperature. | Capture launch telemetry (voltage, current, speed) with your target pack and ramp profile. |
| Gearbox efficiency map at 10 kg duty profile | Pending | 2026-05-17 | Vendor catalogs provide limited spot points and not a full map by torque, speed, and oil temperature. | Request bench map from shortlisted suppliers and validate against your mission cycle. |
| Rolling coefficient for actual terrain, tire pressure, and tread | Pending | 2026-05-17 | Public Crr values are broad estimates and drift significantly with load and surface condition. | Measure coast-down or force-draw on your real route to replace default Crr assumptions. |
| Universal torsional-stress pass/fail threshold across shaft materials | Pending | 2026-05-17 | No reliable public dataset maps one MPa threshold across all steel/aluminum shafts, keyway forms, and duty spectra. | Treat MPa gate as screening only; confirm with supplier material cert + fatigue test before release. |
| Trackable friction coefficient under launch load transfer | Pending | 2026-05-17 | Public mu tables are environment-level references and do not capture tire wear, contamination, or dynamic weight transfer. | Measure slip threshold with your exact tire, payload, and surface; replace default mu in this tool with measured value. |
| Safety-clause mapping from ISO abstract to site-specific SOP | Pending | 2026-05-17 | Open abstract confirms scope/exclusions but not project-specific clause interpretation and verification method. | Map your use case to the full standard text with safety engineering review before field deployment. |
FAQ is grouped by what engineering and sourcing teams actually need to decide next.
This hybrid page gives immediate directional output and the evidence context to avoid premature lock-in. If you want a supplier-ready stack, send your result and we can map candidate motors, ratios, and shaft interfaces to your actual duty profile.
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