- By YIKONG
- 2026-07-04 14:36:02
- Technical
AGV Drive System Selection Guide: Dynamic Calculation Method for Drive Wheels, Low Voltage Servo Motors and Servo Drives
Preface
The operational performance of AGVs (Automated Guided Vehicles) and AMRs (Autonomous Mobile Robots) largely depends on whether the drive system is properly designed.
In a complete mobile robot drive architecture, the AGV drive wheel provides traction force, the low voltage servo motor delivers torque output, the gearbox performs torque amplification, and the servo drive ensures precise motion control. Together, these four components determine acceleration capability, climbing performance, positioning accuracy, and long-term operational reliability.
In practical engineering applications, many drive system issues are not caused by insufficient motor performance, but by incomplete vehicle dynamics calculations. A common mistake is selecting motors based solely on rated payload without considering rolling resistance, slope resistance, acceleration inertia, and wheel-ground adhesion. This often leads to startup failure, motor overload, wheel slippage, or reduced system efficiency.
As an early developer in mobile robot drive systems, Yikong Intelligent has long been focusing on AGV drive wheels, differential drive systems, low voltage servo motors, servo drives, and integrated motion solutions. Based on engineering practice and mechanical design principles, this article systematically explains the dynamic calculation methodology for AGV drive systems, providing a reference for system design and selection.
1. AGV Vehicle Driving Resistance Analysis
For industrial AGVs operating at speeds typically below 1 m/s, air resistance can be neglected. Therefore, the total driving force must overcome three main resistances:
Rolling resistance
Slope resistance
Acceleration inertia resistance
The basic force balance is:
Fdrive ≥ Ff + Fθ + Fa
Where:
Symbol
Description
Fdrive | Total traction force (N) |
Ff | Rolling resistance (N) |
Fθ | Slope resistance (N) |
Fa | Acceleration inertia force (N) |
Only when the driving force exceeds the total resistance can stable motion be ensured.
2. Rolling Resistance Calculation
Rolling resistance is generated by elastic deformation between the wheel and the ground and is the most fundamental resistance during continuous motion.
Formula:
Ff = (f × G) / r
Where:
Parameter
Description
Unit
Ff | Rolling resistance | N |
f | Rolling resistance coefficient | m |
G | Vehicle weight | N |
r | Wheel radius | m |
Typical Engineering Values:
Wheel & Surface Condition
f Value
Polyurethane wheel + epoxy floor | 0.0018–0.0025 |
Polyurethane wheel + concrete floor | 0.0020–0.0030 |
Steel wheel systems | 0.0010–0.0015 |
Engineering Note:
Some reference materials still define rolling resistance coefficient in centimeters (cm). It must be converted into meters (m) during calculation, otherwise the result may deviate by up to 100×.
3. Slope Resistance Calculation
Industrial AGVs are typically designed for a 2% slope capability.
For small angles:
sinθ ≈ tanθ ≈ slope ratio
Therefore:
Fθ = 0.02 × G
Example:
For a 500 kg AGV:
G = 500 × 9.81 = 4905 N
Fθ ≈ 98.1 N
For larger slopes, trigonometric functions should be used for higher accuracy.
4. Acceleration Inertia Resistance
Frequent start-stop operation introduces significant inertial loads.
Formula:
Fa = M × a
Where:
Parameter
Description
M | Vehicle mass (kg) |
a | Acceleration (m/s²) |
Recommended Design Values:
Application
Acceleration
Standard logistics AGV | 0.4–0.6 m/s² |
Human-robot collaboration | 0.2–0.3 m/s² |
Heavy-duty AGV | ≤ 0.2 m/s² |
Higher acceleration improves responsiveness but increases peak load on the drive system.
5. Total Resistance Calculation Example
5.1 Design Parameters
Item
Value
Vehicle mass | 500 kg |
Wheel radius | 65 mm |
Rolling coefficient | 0.002 |
Slope | 2% |
Acceleration | 0.5 m/s² |
5.2 Calculation Results
Resistance Type
Result
Vehicle weight G | 4905 N |
Rolling resistance Ff | 150.92 N |
Slope resistance Fθ | 98.10 N |
Acceleration resistance Fa | 250 N |
Total resistance ΣF | 499.02 N |
5.3 Design Conclusion
The maximum required traction force is approximately:
499 N
For engineering design, a safety margin of 20%–50% is recommended to account for startup shock, ground variation, and long-term operational losses.
Engineering Insight:
Drive system failures rarely occur under steady-state conditions. Most failures happen during transient states such as startup, slope climbing, and acceleration peaks. Therefore, peak resistance must always be used for system sizing.
6. Drive Wheel Torque Calculation
The output torque is generated by the low voltage servo motor through a gearbox.
Formula:
Twheel = Tm × i × η
Where:
Parameter
Description
Twheel | Output torque (Nm) |
Tm | Motor rated torque |
i | Gear ratio |
η | Gear efficiency |
Typical efficiencies:
Planetary gearbox: ~0.85
Worm gearbox: 0.60–0.70
Different gearbox types must not be mixed using the same efficiency assumptions.
7. Traction Force Calculation
Torque is converted into traction force:
F = T / r
For dual-drive systems:
Ftotal = 2 × F
Example:
Motor torque: 0.4 Nm
Gear ratio: 30
Efficiency: 0.85
Wheel radius: 65 mm
Output torque ≈ 10.2 Nm
Single wheel traction force ≈ 157 N
This value directly determines whether the AGV can overcome system resistance.
8. Maximum Speed Calculation
Theoretical speed is determined by motor speed and gear ratio:
V = (2 × π × r × n) ÷ i
Where n is motor speed (rpm).
Example:
2500 rpm
Gear ratio: 30
Wheel radius: 65 mm
Theoretical speed ≈ 34 m/min (≈ 0.57 m/s)
Speed and torque must always be balanced during system design.
9. Motor Power Verification
Formula:
P = (T × n) / 9550
Example result:
≈ 0.105 kW
Engineering Recommendation:
Torque safety margin: 1.2–1.5×
Power margin: 20%–50%
10. Wheel Adhesion and Preload Force
To prevent wheel slippage:
μ × FN ≥ F
Therefore:
FN ≥ F / μ
Example:
Single wheel force: 157 N
Friction coefficient: 0.54
Required preload force ≈ 291 N
Recommended spring preload: ~320 N (including fatigue margin)
Typical Surface Friction Coefficients:
Surface
μ
Dry epoxy floor | 0.75 |
Wet concrete | 0.35 |
Dry gravel | 0.65 |
Dry soil | 0.54 |
Wet surface | 0.30 |
Ice/snow | 0.25 |
11. AGV Drive System Selection Workflow
Define vehicle mass, speed, acceleration, slope
Calculate rolling, slope, and acceleration resistance
Determine total traction force
Calculate single wheel load
Derive required output torque
Select gearbox ratio
Match low voltage servo motor
Verify servo drive capacity
Check speed performance
Verify adhesion and preload force
12. Engineering Considerations
Rolling resistance coefficient and friction coefficient are fundamentally different parameters and must not be confused.
Gearbox efficiency varies significantly depending on structure.
Motor and servo drive selection must consider continuous duty cycles and peak loads.
Multi-wheel systems must ensure sufficient ground contact force to avoid slippage and positioning deviation.
Conclusion
AGV drive system design is not only motor selection, but a comprehensive engineering process involving vehicle dynamics, mechanical transmission, electrical control, and system integration.
From resistance modeling to torque calculation, and from servo motor selection to gearbox and drive wheel design, every parameter directly affects system performance and reliability.