Autonomous ground vehicles (UGVs,
Unmanned Ground Vehicles) are increasingly taking on tasks in agriculture,
municipal services, logistics, and industrial applications. Therefore,
developers often face the fundamental decision of whether the vehicle should be
tracked or wheeled – one of the most important decisions in the design of such
vehicles.
Both concepts have proven successful in
practice. The optimal solution depends heavily on the requirements of the
specific application. In addition to mobility and traction, the design of the
electric powertrain plays a crucial role. While many military, industrial,
rescue, and logistics platforms use tracks, wheel drives are frequently seen in
agricultural robotics.
Wheels and tracks pursue different optimization goals.
Tracked undercarriages were originally developed to optimize the movement of heavy vehicles on difficult terrain. The large contact area reduces ground pressure and increases traction on soft ground.
Wheeled systems on the other hand, often pursue different goals:
· High energy efficiency
· Low mechanical losses
· Higher travel speed
· Easy maintenance
· Lower system weight
Mobility and Traction
Scientific studies show that tracked vehicles can often transmit higher tractive forces on soft surfaces than comparable wheeled vehicles. At the same time, the larger contact area reduces the risk of sinking.
However, on firm or moderately soft ground, modern wheeled undercarriages can achieve very similar mobility performance. Wide tires, low-pressure tires, and controlled individual wheel drives have significantly improved the performance of wheeled vehicles in recent years.
The crucial question is often what type of terrain actually needs to be traversed. Many agricultural robots work in tramlines, on plantations, or on prepared terrain with low obstacle heights, where the advantages of a tracked vehicle are less pronounced and the ability to work efficiently and precisely for many hours is more important.
Energy efficiency as a key factor
With increasing electrification, energy consumption is becoming increasingly important. While wheels move by rolling, tracks incur additional losses due to deflection, deformation of the track, slippage during steering, and weight.
This directly impacts battery capacity, vehicle weight, operating time, and charging cycles for electric vehicles. Therefore, the longer a vehicle is intended to operate autonomously, the more crucial the efficiency of the entire powertrain becomes.
The Role of Modern Electric Drives
Regardless of whether a vehicle uses wheels or tracks, the demands on drive technology are constantly increasing. Modern drive systems for UGVs are characterized by the following attributes:
· High torque density
· High efficiency
· Compact design
· High reliability
· Easy integration
· Low maintenance
These requirements have led to the development of highly integrated drive systems.
Integrated Wheel & Drive Systems as a Platform for Modern UGVs
I&W systems combine the motor, transmission, brakes, and sensors in a single drive unit. This creates a compact and robust platform that offers significant advantages for both wheeled and tracked vehicles.
· Maximum compactness: Installation space is one of the most valuable resources for autonomous vehicles. By integrating multiple functions into a single unit, the required installation space can be significantly reduced. At the same time, mechanical interfaces are minimized.
· Integrated transmission: UGVs typically require high torque at low speeds.
· An integrated approach significantly simplifies assembly and maintenance.
· High robustness under real-world conditions (water, dust, etc.) can be guaranteed. High availability is particularly important for UGVs.
· The integrated parking brake makes a significant contribution to functional safety.
Conclusion
There is no clear winner in the "wheels or tracks" debate. Tracks offer advantages in traction and mobility on challenging surfaces. Wheels often impress with higher efficiency, higher speeds, and lower maintenance requirements. However, for developers of autonomous vehicles, another aspect is becoming increasingly crucial: the integration of the powertrain.
Modern drive systems enable a compact, robust, and highly integrated vehicle architecture. By combining the motor, transmission, brakes, and sensors in a single unit, both wheeled and tracked vehicles can be efficiently implemented.
This means that the actual optimization task is increasingly shifting from the pure choice of chassis to the question of how mobility, efficiency, reliability and integration can be optimally combined.
Sources
Wong, J.Y.; Huang, W. (2006): Wheels vs. Tracks: A Fundamental Evaluation from the Traction Perspective. Journal of Terramechanics.
Shamah, B. (1999): Experimental Comparison of Skid Steering vs. Explicit Steering for a Wheeled Mobile Robot. Carnegie Mellon University.
Mandow, A. et al. (2007): Experimental Kinematics for Wheeled Skid-Steer Mobile Robots.
Wong, J.Y. (2017): Tracks or Wheels: Perspectives and Aspects in Agriculture.