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Enter your robot mass, wheel size, speed, grade, and 12 V motor data. The tool returns a ratio window, startup-current warning, and next action before the report explains the evidence and trade-offs.
| Source | How it is used | Boundary |
|---|---|---|
| Pololu 37D 12V Metal Gearmotors Checked 2026-07-28 | Anchors the 12 V 37D family as a common robot gearmotor option with 5.5 A stall-current class and 200 mA typical free-run current. | Catalog current is model-family data; final current margin must use the exact selected motor and gearbox. |
| Pololu 37D Metal Gearmotors category Checked 2026-07-28 | Provides the 6.3:1 to 150:1 37D ratio envelope plus continuous and instantaneous load warnings. | Pololu warns listed stall values are extrapolated and thermal damage can occur quickly near stall. |
| REV Robotics HD Hex Motor documentation Checked 2026-07-28 | Provides a 12 V robotics motor benchmark: 6000 rpm free speed, 8.5 A stall current, 0.105 Nm stall torque, and 15 W max output power. | Bare motor numbers require gearbox selection before wheel torque can be judged. |
| REV UltraPlanetary Gearbox Kit Checked 2026-07-28 | Confirms a common modular robotics gearbox reduction range from nominally 3:1 to 60:1. | Competition-style modular gearboxes are useful references but not always industrial-duty replacements. |
| REV DUO motor basics Checked 2026-07-28 | Defines stall torque/current, explains why free speed falls under load, and warns that stall heat can damage a motor. | General motor guidance; the exact safe duty point still comes from the selected motor supplier. |
| FIRST Robotics robot battery basics Checked 2026-07-28 | Supports the battery-sag warning: 12 V robot batteries drop voltage under load and high-current use changes usable capacity. | FRC uses a specific 12 V 18 Ah SLA battery; transfer the principle, not the exact pack rating, to custom robots. |
| ANSI/CAN/UL/ULC 2271:2023 Checked 2026-07-28 | Clarifies that light electric vehicle battery safety standards cover energy storage assemblies, not motor performance or reliability. | Only relevant when the robot product falls into a light electric vehicle or similar battery safety scope. |
| IEC 60204-1 wiring guidance summary Checked 2026-07-28 | Adds a wiring check: cable voltage drop from supply to load should not exceed 5% of nominal voltage in normal operation. | Use the applicable regional standard and electrical engineer sign-off for regulated machinery. |
| DFRobot mobile robot torque calculation tutorial Checked 2026-07-28 | Supports the force-to-wheel-torque workflow used in the calculator. | The page supports screening math, not final validation under shock, heat, and battery sag. |
| Maxon support: motor current measurement and protection Checked 2026-07-28 | Supports treating RMS current monitoring and thermal protection as validation items rather than deriving continuous-duty approval from stall data. | Controller protection settings still need exact motor winding data, sensor layout, and mission-cycle measurements. |
| Faulhaber: brushed and brushless micro motor trade-offs Checked 2026-07-28 | Adds supplier context for DC and brushless motor trade-offs so efficiency and thermal claims stay framed as selection trade-offs. | Motor-type guidance does not replace continuous torque curves, gearbox limits, or the final housing thermal path. |
These formulas explain the screening result and show where the page stops before supplier curves, controller logs, and thermal tests take over.
| Step | Formula | Decision use | Limit |
|---|---|---|---|
| Wheel speed | wheel rpm = speed / (pi * wheel diameter) * 60 | Converts the mission speed target into the wheel rpm that the gearbox must support. | The tool derates motor no-load speed by 18%; loaded speed still needs a bench or field check. |
| Traction demand | force = mass * g * sin(grade angle) + mass * g * Crr * cos(grade angle) | Separates grade force from rolling resistance so floor and ramp assumptions are visible. | It does not model impacts, caster scrub, soft tires, suspension bind, or wheel slip. |
| Wheel startup torque | wheel torque = force * wheel radius / driven wheels * startup multiplier | Shows how launches, direction changes, and ramps inflate the torque requirement. | Acceleration profile and controller ramp settings can change the real multiplier. |
| Motor torque and current screen | motor torque = wheel torque / (ratio * efficiency); startup current scales from the reference current and is capped at 3.5x | Compares the computed requirement with the entered reference torque and controller limit. | This is not a thermal model; RMS current, winding temperature, and gearbox load limits require measured validation. |
The table separates source-backed decisions from assumptions that still need supplier data or bench testing. Items marked as unavailable should stay as pending confirmation until the exact motor, controller, harness, and battery are tested.
| Conclusion | Public signal | Decision use | Known limitation |
|---|---|---|---|
| A 12 V label is not a fit decision. | REV defines operating voltage, free speed, stall torque, and stall current as interrelated motor metrics; Pololu publishes the same 12 V family across ratios from 6.3:1 to 150:1. | Screen voltage, no-load speed, gearbox ratio, torque, current, and battery behavior together before asking for RFQ pricing. | Public category pages rarely publish a complete thermal map, so sustained duty must be tested or requested. |
| Stall numbers are emergency boundaries, not repeated-use targets. | REV states stall is zero rpm at full stall current and warns heat can eventually cause failure; Pololu notes stalling is likely to damage the gearmotor. | Treat startup-current estimates as a warning trigger and validate current clipping with a real launch log. | The calculator estimates startup current from available motor inputs; it does not model winding temperature rise. |
| Gear ratio availability is discontinuous. | REV UltraPlanetary references nominal 3:1 to 60:1 configurations; Pololu 37D 12 V options list 6.3:1 to 150:1 ratios. | Use the result ratio window to find catalog ratios that actually exist, then check load limits and mounting. | A mathematically perfect ratio can still fail due to shaft support, gearbox load rating, or packaging. |
| Battery sag and cable drop can invalidate an otherwise correct motor calculation. | FIRST documentation notes 12 V battery voltage drops under load; IEC 60204-1 guidance summaries call out voltage drop limits in wiring. | For negative or tight current margin, compare 24 V architecture, larger conductors, shorter cable runs, and softer acceleration ramps. | Pack chemistry, connector resistance, and harness routing are project-specific and must be measured. |
| Battery safety evidence is separate from drivetrain performance evidence. | UL 2271 covers light electric vehicle battery energy storage assemblies and explicitly does not evaluate device performance or reliability. | Ask for both battery safety/compliance evidence and motor torque-speed-current evidence; one does not replace the other. | Whether UL 2271 is applicable depends on the finished product category and sales region. |
| 24V cuts resistive thermal losses by 75% for the same power vs 12V. | Joule heating (P_loss = I^2*R) means halving the current at 24V reduces winding and wiring heat by a factor of 4 if resistance stays equal. | If a 12V motor is failing thermal soak tests or requires thick, heavy cables, 24V is the mathematically required mitigation. | Assumes the 24V motor is wound to have an equivalent or acceptable resistance; controller and battery architecture must support 24V. |
| BLDC can improve sustained-duty margin, but it is not an automatic fit. | Faulhaber discusses DC and brushless motor trade-offs; Maxon support material reinforces that current monitoring and thermal protection must be checked against exact motor data. | Use BLDC as the first comparison when the 12 V brushed screen is current- or heat-limited, then request continuous torque/current curves before committing. | BLDC still needs driver tuning, EMC review, gearbox load data, and thermal testing; public type-level guidance cannot certify a specific motor. |
| Option | Ratio signal | Strength | Risk | Best for |
|---|---|---|---|---|
| 12 V brushed gearmotor | 20:1 to 150:1 common screen | Lowest control complexity and broad catalog availability | Brush wear, rotor heat near stall, and supplier-specific duty limits | Education bots, indoor AMRs, cost-sensitive prototypes |
| 12 V BLDC gearmotor | 10:1 to 80:1 typical short list | Higher efficiency potential and better sustained-duty comparison path when backed by curves | Driver tuning, EMI, higher integration effort | Long runtime platforms and speed-controlled mobile robots |
| Bare 12 V motor + modular gearbox | 3:1 to 60:1 reference range | Fast iteration and easy ratio swaps | Mounting stiffness and non-industrial duty uncertainty | FTC-style robots, lab rigs, early drivetrain experiments |
| Move to 24 V architecture | Same mechanical math, lower current for comparable power | 1/4 the I²R thermal losses in wiring for the same power | Battery, driver, safety, and charger stack changes | Continuous duty cycle AGVs or current-limited 12 V prototypes |
| Check | Pass signal | Fail signal | Owner |
|---|---|---|---|
| Launch-current log | Peak current remains below controller limit with margin during repeated starts and direction changes. | Brownout, controller foldback, fuse heating, or current peaks above the configured limit. | Controls engineer |
| Loaded speed test | Measured speed at payload and floor condition lands inside the target band after battery sag. | No-load rpm looked correct, but loaded wheel rpm falls below the mission requirement. | Mechanical and controls |
| Thermal soak | Motor, gearbox, controller, and wiring temperatures stabilize across the expected duty block. | Temperature keeps rising, gear grease odor appears, or controller derates during the run. | Test engineer |
| Harness voltage drop | Voltage at the controller/motor remains inside the allowed design window at normal load. | Cable length, connector resistance, or undersized conductors consume the current margin. | Electrical engineer |
| Supplier evidence review | Supplier provides original curves, duty rating, efficiency assumption, gearbox load limit, and test date. | Only headline voltage, speed, and marketing torque are available. | Procurement |