BLDC Motor Sizing Guide for AGV Applications
Choosing the wrong motor for your AGV means redesigning the drive train, delaying production, and eating margin on rework. This guide walks through the complete sizing process — from load calculation to final motor and gearbox selection — so you get it right the first time.
Step 1: Calculate Your AGV's Drive Requirements
Every motor sizing exercise starts with load. For an AGV, the key numbers are:
- Gross vehicle weight (GVW): AGV chassis + battery + maximum payload. A typical warehouse AGV runs 200–500 kg loaded; heavy-duty transporters reach 1,500–2,000 kg.
- Wheel diameter: Directly affects torque-to-force conversion. A 200mm wheel generates 2× the traction force of a 100mm wheel at the same motor torque.
- Rolling resistance coefficient: 0.015 for smooth concrete, 0.03 for rough factory floors, 0.05 for outdoor pavement.
- Maximum grade: Most warehouse floors are flat (0°), but ramps and outdoor AGVs may see 3–5° inclines.
- Target speed: Typical warehouse AGV: 1.0–2.0 m/s. Outdoor transport: 2.5–5.0 m/s.
Step 2: Calculate Required Motor Torque
The drive motor must overcome two forces: rolling resistance on flat ground and gravitational pull on inclines.
Flat Ground Torque
Rolling resistance force: Froll = m × g × μroll
Example: 500 kg AGV on smooth concrete (μ = 0.015): Froll = 500 × 9.81 × 0.015 = 73.6 N
Torque per wheel: τ = Froll × r / (N × η)
Where r = wheel radius (m), N = number of driven wheels, η = drivetrain efficiency (~0.90 for planetary gearbox).
With 200mm wheels, 2 driven wheels: τ = 73.6 × 0.1 / (2 × 0.90) = 4.09 Nm per motor
Incline Torque (if applicable)
Fincline = m × g × sin(θ)
5° incline: Fincline = 500 × 9.81 × sin(5°) = 427 N
Total required force = 73.6 + 427 = 500.6 N
τ = 500.6 × 0.1 / (2 × 0.90) = 27.8 Nm per motor
The difference between flat ground and 5° incline is 6.8× — always factor in your worst-case slope.
Step 3: Match Motor Power to Your Requirements
AGV Motor Sizing Quick Reference
| AGV Type | Payload | Recommended Motor | Gear Ratio | Output Torque |
|---|---|---|---|---|
| Light warehouse | 100–300 kg | 48V 400W BLDC | 15:1 | 15–20 Nm |
| Standard warehouse | 300–500 kg | 48V 750W BLDC | 15:1 | 25–35 Nm |
| Heavy warehouse | 500–800 kg | 48V 1000W BLDC | 15:1 / 20:1 | 45–60 Nm |
| AGV tractor/tugger | 800–1,500 kg | 48V 1500W BLDC | 20:1 / 30:1 | 70–110 Nm |
| Heavy transporter | 1,500–2,000 kg | 48V 2000W Geared | 30:1 / 50:1 | 120–180 Nm |
Power check: P = τ × ω, where ω = (v/r) × gear_ratio (rad/s).
For the 750W motor at 1.5 m/s with 15:1 ratio and 200mm wheels: ω = (1.5/0.1) × 15 = 225 rad/s ≈ 2,150 RPM — within the motor's rated speed range.
Step 4: Gearbox Selection
BLDC motors run at 2,000–4,000 RPM — too fast for direct wheel drive. A gearbox converts high-speed low-torque into low-speed high-torque.
- Planetary gearbox: Best for AGV drives. Compact, high efficiency (88–92%), coaxial input/output. Our default recommendation. See BLDC planetary gear motors.
- Worm gearbox: Self-locking (prevents backdriving on inclines), but lower efficiency (60–70%). Use for safety-critical stops. See worm gear motors.
- Right-angle gearbox: Space-constrained AGV designs where the motor mounts perpendicular to the axle. See right-angle DC gear motors.
Always add a 15–25% safety factor to your calculated torque to account for dynamic loads during acceleration and emergency stops.
Step 5: Controller and Battery Matching
A well-sized motor is useless without a proper drive system:
- Controller: FOC (Field-Oriented Control) for smooth low-speed operation and regenerative braking. Trapezoidal control works for basic point-to-point AGVs. See 48V BLDC motor controllers.
- Battery: Match voltage to motor rating. For 48V motors, use 13S/14S Li-ion or 16S LiFePO4. Size for full-shift operation: a 48V 750W motor running 8 hours at 60% duty draws ~60Ah.
- Feedback: Hall sensors are standard. Add a 1000-line encoder for precise speed control in docking and positioning applications.
Real-World Sizing Example: 600 kg Payload Warehouse AGV
Requirements
- AGV self-weight: 180 kg (chassis + battery)
- Max payload: 600 kg → GVW = 780 kg
- Two driven wheels, 250mm diameter, two free casters
- Target speed: 1.5 m/s on smooth concrete
- Max incline: 3° ramp access
Calculations
- Froll = 780 × 9.81 × 0.015 = 114.8 N
- Fincline = 780 × 9.81 × sin(3°) = 400.3 N
- Max force = 114.8 + 400.3 = 515.1 N
- τmotor = 515.1 × 0.125 / (2 × 0.90) = 35.8 Nm per motor with direct drive
Selection
With a 15:1 planetary gearbox, motor torque required = 35.8 / 15 = 2.39 Nm — well within the 48V 750W motor's 2.4 Nm continuous rating. This provides a 2× safety margin for acceleration loads.
Final configuration: 2× 48V 750W BLDC motors with 15:1 planetary gearboxes, FOC controllers, 48V 80Ah LiFePO4 battery pack. Estimated drive system cost: $800–1,200 FOB.
Get Your AGV Motor Sizing Right
Shenghe's engineering team reviews your AGV requirements and recommends the exact motor-gearbox-controller combination. We provide a detailed torque-speed curve and integration drawing before you order. Most AGV drive system proposals are delivered within 48 hours.