Interactive engineering worksheet
Calculate RMS torque, braking peak and motor speed for a repeated AGV mission. Review the assumptions before selecting hardware.
Live results per motor. Edit the illustrative inputs to calculate your mission.
Each cycle has one linear acceleration, level cruise, constant-speed uphill cruise, one level deceleration and unpowered dwell. Set absent cruise, ramp or dwell segments to 0. Acceleration and deceleration durations also determine acceleration force.
Preliminary estimate: no thermal or safety approval. Equal tractive sharing, an editable 1.08 inertia allowance, level starts/stops and zero powered holding are assumed. Ramp launches, steering loads and grip require separate review. Read calculation limits.
| Segment | Time (s) | Avg speed (m/s) | Avg motor rpm | Wheel torque (Nm) | Motor torque (Nm) | Avg shaft power (kW) | Avg DC current (A) |
|---|---|---|---|---|---|---|---|
| Acceleration | 1.20 | 0.75 | 89.52 | 38.92 | 38.92 | 0.36 | 8.35 |
| Level cruise | 15.00 | 1.50 | 179.05 | 3.82 | 3.82 | 0.07 | 1.64 |
| Ramp cruise | 4.00 | 1.50 | 179.05 | 11.47 | 11.47 | 0.22 | 4.92 |
| Deceleration | 1.00 | 0.75 | 89.52 | -38.30 | -38.30 | -0.36 | -6.81 |
| Unpowered dwell | 7.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
Estimated average motor + inverter loss: 9.5 W under constant efficiency. Winding temperature is unknown without a loss map and mounted thermal data.
Decision summary
| Finding | Decision | Evidence / boundary |
|---|---|---|
| Peak and RMS answer different questions | Check pulse torque and repeated loading separately; include negative braking torque. | Motor-sizing method [1]; actual torque-speed and thermal limits still need the selected motor data. |
| DC bus current is not motor phase current | Use power / bus voltage for a preliminary DC estimate. Use the winding torque constant and drive convention for phase current. | Controller power conversion [2]; voltage alone does not reduce torque-producing phase current. |
| Active-time share is not an S3 approval | Send the full profile, starts per hour, braking and inertia to the supplier. | Duty definitions [3], current IEC catalogue [4]; frequent starting or electric braking changes the classification question. |
| Motor topology does not prove fit | Compare mounted torque, wheel envelope, bearings and total installed cost. | Project-specific engineering comparison below. Public data here do not establish a universal axial-flux size or efficiency advantage. |
The worksheet is a first-principles screening model. Let m be gross vehicle mass, n the driven-wheel count, r the effective wheel radius, G the speed reduction ratio, ηg transmission efficiency, v maximum speed and θ = atan(grade / 100). Tractive demand is divided equally by n; this division does not establish the actual vertical load on a driven tire.
| Quantity | Equation | Meaning / limit |
|---|---|---|
| Level rolling force per drive | Frr = (m / n) × g × Crr | g = 9.80665 m/s²; Crr must represent the actual tire and floor. |
| Acceleration force per drive | Facc = (m / n) × k × v / tacc + Frr | k is an editable rotating-inertia allowance, not a validated drivetrain inertia. Acceleration is level only. |
| Uphill steady force per drive | Framp = (m / n) × g × (sin θ + Crr cos θ) | Constant speed; no uphill launch, steering scrub or towing drag. |
| Deceleration force per drive | Fdec = Frr − (m / n) × k × v / tdec | Usually negative (regeneration). A sufficiently gentle stop can still require positive drive torque. |
| Shaft torque | Twheel = F × r; Tmotor = Twheel / (Gηg) when positive; Twheelηg / G when negative | Gear losses oppose power flow. No-load gear drag and efficiency variation are excluded. |
| Motor speed | rpm = v × 60G / (2πr) | Acceleration and deceleration are linear between 0 and this maximum; ramp cruise uses this same speed. |
| RMS and peak | Trms = √(Σ Ti²ti / Σti); Tpeak = max |Ti| | Only segments with nonzero duration contribute. There is no added design margin. |
Load, inertia and RMS torque are separate checks in the manufacturer sizing method [1]. The wheel-force equations above are this worksheet’s analytical adaptation, not an IEC certification procedure.
Illustrative inputs: 650 kg gross mass, two equal traction drives, 160 mm wheel, 1:1 direct drive, Crr 0.015, inertia allowance 1.08, speed 1.5 m/s and 3% uphill grade. One cycle has 1.2 s acceleration, 15 s level cruise, 4 s uphill cruise, 1 s deceleration and 7 s unpowered dwell.
The wheel radius is 0.08 m. Level rolling force is (650 / 2) × 9.80665 × 0.015 = 47.81 N per drive. Acceleration is 1.5 / 1.2 = 1.25 m/s², giving wheel torque (325 × 1.08 × 1.25 + 47.81) × 0.08 = 38.92 N·m. At 1:1 and unity transmission efficiency, motor and wheel torque are equal.
| Segment | Duration (s) | Signed motor torque (N·m) |
|---|---|---|
| Acceleration | 1.2 | 38.92 |
| Level cruise | 15.0 | 3.82 |
| Ramp cruise | 4.0 | 11.47 |
| Deceleration | 1.0 | -38.30 |
| Unpowered dwell | 7.0 | 0.00 |
Square each torque, multiply by its duration, sum, divide by 28.2 s, then take the square root: 11.95 N·m RMS per motor. Absolute peak is 38.92 N·m and maximum motor speed is 179.0 rpm. Select the warehouse example in the tool and export its CSV to reproduce all assumptions. These are demands to compare with hardware data.
These are constructed scenarios, not customer installations. Each card uses the same calculation engine as the tool. Choosing its example mission loads the complete parameters; the CSV includes every input. Do not transfer a result between vehicles based on payload alone.
2 driven wheels · 160 mm diameter · 1:1 ratio · 1.5 m/s · 3% grade.
Acceleration / cruise / ramp / deceleration / dwell: 1.2 / 15 / 4 / 1 / 7 s.
11.95 N·m RMS · 38.92 N·m absolute peak · 179 rpm per motor.
Next check: mounted continuous torque and measured floor rolling resistance.
2 driven wheels · 200 mm diameter · 5:1 ratio · 1.2 m/s · 5% grade.
Acceleration / cruise / ramp / deceleration / dwell: 1.8 / 20 / 6 / 1.5 / 12 s.
6.85 N·m RMS · 17.17 N·m absolute peak · 573 rpm per motor.
Next check: gearbox peak torque, reverse efficiency and bearing loads.
2 driven wheels · 125 mm diameter · 1:1 ratio · 2.2 m/s · 0% grade.
Acceleration / cruise / ramp / deceleration / dwell: 0.8 / 8 / 0 / 0.7 / 4 s.
5.98 N·m RMS · 18.43 N·m absolute peak · 336 rpm per motor.
Next check: repeated pulse duration and docking control at low speed.
4 driven wheels · 250 mm diameter · 8:1 ratio · 1.4 m/s · 8% grade.
Acceleration / cruise / ramp / deceleration / dwell: 2.5 / 25 / 10 / 2 / 15 s.
7.59 N·m RMS · 15.25 N·m absolute peak · 856 rpm per motor.
Next check: unequal traction sharing, tow resistance and actual wheel adhesion.
Per segment, mechanical power is T × ω. During linear acceleration or deceleration, mean speed is half the maximum. The DC estimate is P / (Vη) while motoring and Pη / V during regeneration, with regeneration shown negative. For a linear current ramp from 0 to Ipeak, the integral of current squared is Ipeak² × duration / 3; using half the speed in an RMS calculation would underestimate that contribution.
Peak motoring DC current and regeneration peak are shown separately. Multiply synchronized drive currents by the number of motors for an approximate traction-only battery total. Add steering, controls, lift, communications and auxiliary loads separately. Coincident loads, sag and ripple require measurements before cable, battery or protection selection.
maxon’s controller explanation [2] distinguishes supply-side current from motor current. Doubling bus voltage at fixed power approximately halves DC current; it does not halve the motor phase current required for unchanged torque and winding. Phase current cannot be calculated here without the chosen motor’s torque constant and its RMS/peak convention.
RMS torque helps screen repeated loading when torque tracks current, but does not predict winding temperature. Iron loss, AC winding loss, speed, ambient, stator-to-case resistance and mounting affect the thermal result. The tool’s constant-efficiency loss estimate covers motor plus inverter and cannot be assigned entirely to the stator.
| Duty concept | Distinction | Action for an AGV |
|---|---|---|
| S1 | Continuous running at a load long enough to reach thermal equilibrium. | Check the mounted continuous operating envelope. |
| S3 | Repeated load and de-energized rest; starting heating is insignificant. | Do not assign from active-time percentage alone. |
| S4 / S5 | Starting is significant; S5 also includes electric braking. | Supply starts per hour, inertia, braking and complete time history. |
| Nonperiodic missions | Variable routes may not repeat the five-segment example. | Provide measured time series for supplier assessment rather than forcing an S3 label. |
The S3/S4/S5 distinctions are described in ABB’s duty guide, Annex D [3]. The IEC catalogue [4] lists IEC 60034-1:2026, edition 15, published 13 March 2026; the 2022 edition is revised. The public catalogue confirms edition and scope; it does not validate a particular motor, insulation temperature margin or vehicle duty rating.
| Architecture | Potential benefit | Cost / integration check |
|---|---|---|
| Direct-drive axial flux hub | No gearbox stage; a disc-shaped package may suit the available wheel envelope. | Motor must supply wheel torque at low speed. Check radial envelope, bearings, seals, winding cost and assembly tolerances. |
| Geared axial flux drive | Reduction lowers required shaft torque while increasing motor speed. | Include gearbox cost, losses, reverse efficiency, lubrication, backlash and replacement access. |
| Geared radial-flux module | Established module options may reduce integration and service effort. | Compare actual installed axial length, bracket loads, torque-speed curve and maintenance against the custom option. |
| Higher DC bus voltage | Can reduce supply current at the same input power. | Check battery, inverter, insulation and auxiliaries as a system. Motor phase-current capability still depends on the winding. |
These are engineering tradeoffs, not a product ranking. Request drawings, comparable mounted tests, prototype and production quotations, and a service plan before committing. Wheel diameter alone cannot prove that an axial flux hub fits.
Regenerative torque requires an accepting electrical path. At high state of charge, low battery temperature or a disconnected BMS, review whether the pack can accept current and whether the bus requires a suitable buffer, brake chopper/resistor or a different controlled stopping strategy. The manufacturer’s four-quadrant guide [6] explains the possibility of returning energy during braking.
For a transparent energy illustration, a 650 kg vehicle at 1.5 m/s has ½mv² = 731.25 J of translational kinetic energy before rotating inertia is included. This is not the recovered energy or resistor rating: slope, conversion losses, pulse duration and repeated stops matter. DC capacitance absorbs only ΔE = ½C(Vmax² − Vnom²), using the actual allowable voltage range.
ISO 3691-4:2023 [5] covers driverless-truck safety and verification. This page does not derive protective-field dimensions, stopping acceptance limits, safety performance levels or compliance from its catalogue abstract. Verify the applicable edition, complete requirements and scanner/brake manufacturer instructions with the vehicle safety engineer.
| Risk / unknown | Why it matters | Minimum mitigation or alternative |
|---|---|---|
| Ramp launch or powered hill hold | The level-start and zero-holding assumptions can understate demand. | Supply a measured/custom slope and hold profile; size the brake and drive separately. |
| Grip and vertical wheel loads | Equal traction sharing does not establish adhesion or bearing capacity. | Measure wheel loads and floor friction, including wet floors and weight transfer. |
| Tire compound / cold storage | Rolling loss, traction and durability vary with load, temperature and surface. | Request compound-specific dynamic load-speed-temperature data. No universal hardness change, loss tangent or blowout temperature is established here. |
| Rotating inertia and towing drag | An assumed multiplier can miss substantial reflected inertia or trailer resistance. | Use measured inertia and force data; switch to a full drivetrain model where needed. |
| Thermal pulse capability | RMS below a nominal rating does not guarantee acceptable pulse temperature. | Use supplier thermal time constants, loss maps and mounted duty tests. |
| Custom integration cost | Prototype tooling, tolerances and qualification may dominate unit savings. | Compare total installed and service cost with a proven geared module before production release. |
Torque, shaft power and DC current results are per motor under equal tractive sharing. Synchronized traction currents can be summed across drives; auxiliaries and unequal wheel loading require separate assessment.
RMS accounts for squared torque over time and helps screen repeated thermal loading. Absolute peak includes braking and checks pulse demand. Neither result alone establishes the mounted motor temperature or allowable peak duration.
No. Active-time percentage describes the entered profile. S3 assumes insignificant starting heating; significant starts or electric braking require a different duty discussion. Ask the motor supplier to classify the complete profile under the applicable IEC 60034-1 edition.
At the same input power, a higher bus voltage reduces DC current. It does not automatically reduce the phase current needed for the same motor torque. Compare the complete battery, inverter, winding and auxiliary system.
No. The drive converts voltage and current. Phase-current selection needs the motor torque constant, current convention, torque-speed curve and controller continuous and pulse limits.
Results and filled exports are withheld until every required input is within its displayed range. Correct the marked fields, restore the warehouse example, or use the blank worksheet for an engineering review.
Each is the actual time between zero and maximum speed in this cycle. Shorter times increase inertial force. The same duration is used in force and RMS calculations; there is no separate hidden acceleration time.
No. Cruise, ramp and dwell can be omitted with zero duration and then contribute no torque, power or RMS load. A complete modeled motion cycle still requires positive acceleration and deceleration times.
No. Starts and stops are level; ramp cruise uses the entered maximum speed. Supply a custom measured profile for simultaneous incline acceleration, downhill braking, steering scrub, trailer drag or powered hill holding.
It scales translational inertial demand to approximate rotating components. The default 1.08 is illustrative, not a measured universal value. Replace it with a drivetrain-specific estimate; reflected motor and gear inertia may require a detailed model.
No. It uses constant motor-plus-inverter efficiency to estimate average conversion loss. Winding temperature needs motor loss maps, thermal resistances, time constants, mounting conditions and a representative duty test.
Fit depends on the actual motor and wheel drawings, bearings, brake, seals, air gap and load path. Disc geometry may help packaging, but no universal thickness, wheel size or torque advantage is established by this worksheet.
No. Confirm battery and DC-bus energy acceptance and independent braking behavior across payload, slope, temperature and battery extremes. Vehicle safety verification needs the applicable ISO 3691-4 requirements and component instructions.
Send the filled CSV, installation drawings, measured wheel loads, tire and floor data, rotor and gearbox inertia, ambient range, bus limits, phase-current ratings, powered holds, ramp starts and intended acceptance tests.
By CustomAxialFlux Engineering Editorial. Substantive review: . Manufacturer guides support methods; standards catalogue pages establish identity and scope. Illustrative calculations and architecture comparisons are the worksheet’s engineering analysis, not measured product claims. Full standard clauses and hardware certification are outside the evidence available here.
Send the calculated profile with installation and thermal details for a project-specific review. Motor dimensions, peak duration, temperature margin, cost and delivery timing require confirmation for the chosen design.
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