Abstract
In AGV and AMR development, engineers usually focus on critical components such as drive motors, reducers, control systems, and navigation technologies. However, one important mechanical factor is often underestimated - the suspension design of the drive wheel system.
For four-wheel AGVs equipped with four drive wheels and steering functions, suspension is not simply an optional accessory. It plays a critical role in maintaining balanced wheel loading, reducing steering resistance, preventing excessive motor current, and improving long-term system reliability.
This article presents a real customer case from Plutools, analyzing how the lack of suspension caused uneven wheel loading, abnormal steering current, and motor overheating on a four-wheel AGV. Through on-site testing and engineering analysis, the actual cause was identified, providing valuable insights for AGV chassis design.
Project Background
A customer developed a heavy-duty AGV with a four-wheel drive and four-wheel steering structure.
The AGV was equipped with four sets of Plutools PLT310 Vertical AGV Drive Wheels. The vehicle did not include auxiliary wheels, and the drive wheel system was designed without a suspension mechanism.
The PLT310 Vertical AGV Drive Wheel features a compact structure, high load capacity, precise steering performance, and excellent reliability. It is designed for heavy-duty AGVs, AMRs, and industrial mobile robot applications that require stable driving and accurate positioning.
During the initial commissioning stage, the AGV operated smoothly at the customer's factory.
Since the commissioning area had a relatively flat floor condition, the vehicle demonstrated good steering performance. Based on this environment, the customer believed that a suspension system was unnecessary.
From an engineering perspective, however, we recommended keeping the suspension design to improve adaptability to real-world operating conditions and maintain balanced wheel loading.
Although the AGV performed well during factory testing, unexpected problems occurred after deployment at the final application site.
Steering Problems Appeared at the End User Site
After the AGV was installed at the customer's final site, several issues occurred:
The AGV had difficulty performing in-place rotation;
Steering current frequently reached the 80A current limitation of the controller;
In certain areas, the AGV could not complete steering;
The steering motors became extremely hot after continuous operation.
Based on these symptoms, the customer initially suspected that the steering system lacked sufficient torque.
They believed that the solution would require:
A larger steering motor;
A gearbox with a higher reduction ratio.
This assumption was understandable because high current and failed steering are often associated with insufficient motor torque.
However, after analyzing the actual operating conditions, Plutools engineers believed that the root cause might not be related to motor power.
A detailed on-site investigation and data analysis were required.
On-Site Investigation and Root Cause Analysis
Plutools engineers visited the end-user site and conducted a comprehensive inspection of the AGV chassis.
The four PLT310 Vertical AGV Drive Wheels were installed in a standard four-corner configuration:
Wheel No.1 and Wheel No.4 formed one diagonal pair;
Wheel No.2 and Wheel No.3 formed another diagonal pair.
During inspection, we found that the floor flatness at the final application site was significantly worse than the customer's commissioning environment.
More importantly, the deformation of Wheel No.1 and Wheel No.4 was noticeably greater than the other two wheels.
This indicated that the four drive wheels were not sharing the vehicle weight evenly.
Due to uneven ground conditions, one diagonal pair of drive wheels was carrying excessive vertical load, while the other diagonal pair was carrying much less load.
For a four-wheel AGV without suspension, this imbalance can significantly increase steering resistance and create abnormal motor loading.
Steering Current Test and Data Verification
To verify our analysis, Plutools engineers performed a real-time monitoring test on the steering current of all four PLT310 Vertical AGV Drive Wheels.
First, the AGV was tested in the area where steering failure occurred.
During the test, one diagonal pair of drive wheels quickly reached the controller's 80A current limit, but the AGV still could not complete the rotation.
This indicated that the steering system was experiencing excessive mechanical resistance rather than insufficient motor output.
After that, the AGV was moved to an area where all four drive wheels could rotate smoothly. The steering current of each drive wheel was measured again.
The test results showed:
Wheel No.1 and Wheel No.4: approximately 70–80A steering current;
Wheel No.2 and Wheel No.3: approximately 5–15A steering current;
Total starting current of the four steering motors: approximately 170–180A.
These results provided strong evidence.
If the steering motor capacity was insufficient, all four steering motors should have approached the current limitation simultaneously.
However, the actual situation was completely different:
Only one diagonal pair of drive wheels was operating under high load, while the other pair was carrying significantly less load.
Therefore, the problem was not caused by insufficient steering motor torque or gearbox capacity.
The actual cause was uneven wheel load distribution caused by the lack of suspension compensation.
Why Does the Lack of Suspension Affect AGV Steering Performance?
Many engineers assume that a four-wheel AGV can naturally distribute the vehicle weight evenly among all four wheels.
In theory, this is true under ideal conditions.
However, real industrial environments are rarely perfectly flat.
Even small differences in floor height can create uneven loading when the AGV chassis passes through different areas.
For a four-wheel AGV without suspension, the chassis cannot effectively compensate for these ground variations.
As a result, the following situation may occur:
One diagonal pair of wheels carries most of the vehicle weight;
The other diagonal pair has reduced contact pressure;
The overloaded wheels experience greater tire deformation;
Steering resistance increases significantly;
Steering motor current rises rapidly;
Motor temperature increases;
The AGV may eventually fail to complete steering.
Therefore, the actual issue is not that the motor cannot generate enough torque.
The real problem is that excessive mechanical resistance is created by uneven wheel loading.
Load Distribution Analysis
The relationship between steering force and motor current can be considered approximately proportional.
During the field test, when the AGV could barely complete steering, the average steering currents of the two diagonal wheel groups were approximately:
Group A: 10A;
Group B: 80A.
Based on current distribution, the approximate load distribution can be calculated:
Group A:
Total load × 10 / (10 + 80)
≈ 11% of total load
Group B:
Total load × 80 / (10 + 80)
≈ 89% of total load
This means that the load ratio between the two diagonal wheel groups was close to:
1 : 8
In other words, one pair of diagonal wheels was carrying nearly eight times the load of the other pair.
When the AGV reached a more uneven area where steering completely failed, the load imbalance became even more severe.
This calculation further confirmed that the key issue was not the power capacity of the PLT310 drive wheel system, but the uneven distribution of mechanical load.
Solution: Adding Suspension to the PLT310 Drive Wheel System
After identifying the root cause, Plutools did not replace the steering motors or modify the gearbox configuration.
Instead, the solution focused on improving the mechanical structure:
A suspension mechanism was added to all four PLT310 Vertical AGV Drive Wheels.
With the suspension system installed, each drive wheel could automatically compensate for small floor irregularities and maintain more balanced contact pressure.
After the modification:
The AGV regained smooth in-place rotation performance;
Steering current was significantly reduced;
Motor temperature returned to a normal range;
The vehicle operated reliably at the end-user site.
This case demonstrated that improving mechanical load balance can be more effective than simply increasing motor power.
Engineering Summary
Many AGV projects perform well during factory testing but encounter unexpected problems after deployment.
The reason is often not insufficient component performance, but the difference between the commissioning environment and the actual operating conditions.
For four-wheel AGVs, steering performance depends not only on motor torque and gearbox selection, but also on wheel load balance.
This case shows that even minor floor irregularities can cause severe load concentration in a four-wheel AGV without suspension, resulting in:
Increased steering resistance;
Excessive motor current;
Higher motor temperature;
Reduced system reliability;
Possible steering failure.
For four-wheel AGV chassis design, Plutools recommends:
Evaluating suspension requirements based on real application conditions, not only commissioning environments;
Considering the worst-case operating conditions during chassis design;
Performing wheel load distribution analysis before finalizing the mechanical structure;
Using suspended drive wheel solutions for heavy-duty AGVs and continuous operation applications.
Suspension is not simply an additional mechanical component.
It is an important design element that ensures stable operation, balanced loading, and long-term reliability of AGV drive systems.
Through professional drive wheel technology and engineering experience, Plutools continues to provide reliable AGV mobility solutions for global intelligent manufacturing and logistics applications.
