Randolph A. Jones

Estimating Off-Road Ground Contact Forces for a Real Time Motion Simulator

Researchers at the US Army Engineer Research and Development Center (ERDC), working in the field of vehicle mobility, have developed methods to predict the physical interactions of vehicles with soil surfaces. This set of methods use research conducted at the ERDC over the last 40 years to predict the physical interactions of vehicles and terrain surfaces under all seasons. Methodologies to measure pertinent terrain properties and assess vehicle performance have also been developed. Much of the work focused on practical applications and is the result of extensive vehicle performance testing and the subsequent analysis of the test results. While there have been attempts to identify and characterize soil media properties using standard soil classification techniques and to assess their effects on vehicle mobility using classical soil mechanics and other theoretical approaches, the current state-of-the-art is such that these approaches have limited practical application. The ERDCs approach has been to quantify and relate a set of fundamental vehicle traction element performances to easily obtainable terrain properties. This empirical and lumped parameter approach has provided relevant and verifiable results for decades, but due to its nature, is difficult to extrapolate and manipulate mathematically. Nevertheless, the ease of obtaining suitable terrain properties, its historical success in vehicle performance predictions, and its maturity and broad validation database have made it an attractive choice for implementation into a simulated terrain mechanics model for real time dynamics vehicle simulators. This paper describes the algorithms selected for estimating longitudinal force coefficients for soils (frozen and non-frozen), snow, and ice, and the underlying assumptions.

Case Study of the Evaluation and Verification of a PackBot Model in NRMM

Abstract : The NATO Reference Mobility Model (NRMM)[1] is the primary mobility software used by the US Department of Defense, its contractors and NATO countries to evaluate various metrics of proposed vehicle systems for acquisition. The NRMM is a vehicle mobility performance model developed in the 1970s[2] that combines mobility related technologies into one comprehensive software package designed to predict the physically constrained vehicle and terrain interaction while operating in both on and off road environments. The empirically based relationships within NRMM are measurements taken from actual vehicles run over a variety of terrains and are geared towards vehicles weighing more than 1500 pounds. As the Army focuses on a lighter, faster and more mobile fighting force, standard military vehicles are decreasing in size with many new ultra lightweight autonomous systems being designed. This fundamental shift in the size and weight of military vehicle systems, questions, the NRMM predictions for on and off road performance. The following paper describes a case study comparing NRMM predictions of the current Future Combat System (FCS) Small Unmanned Ground Vehicle (SUGV), This paper defines required extensions in the existing data fields for the terrain and vehicle to support predictions of SUGVs in NRMM.

Application of an off-road mobility model to autonomous cross-country routing of unmanned ground vehicles

This paper describes the application of an Army-standard legacy off-road mobility model to cross-country route planning and negotiation by unmanned ground vehicles. A planned route is created from a movement map generated from existing terrain data. An unmanned ground vehicle negotiates the planned route and makes local routing adjustments based on a trafficability assessment of terrain features which are observed from the platform. This research leverages results from other work investigating the scalability of the existing legacy off-road mobility model to small vehicles (<500 kg). The legacy mobility model is the NATO Reference Mobility Model II (NRMM II), a standard for combat mobility modeling and procurement since the mid-90s.

Establishing UGV power requirements based on mission profiles

The propulsion systems employed on unmanned ground vehicle platforms in Future Force Units of Action will likely involve electric or hybrid-electric drive. Power storage systems for these platforms will therefore be driven largely by expected power depletion rates. Resistances that propulsion systems must overcome during maneuvers will be a major factor affecting power depletion rates, and the resistance forces will vary drastically depending on the mission. Therefore, realistic mission-related considerations need to be applied when defining power storage requirements. The US Army has developed numerous models and simulations that use terra-mechanics algorithms to predict maneuver capability for ground vehicles as limited by terrain and environmental factors, and the algorithms employed for predicting maneuver capability in most of these models and simulations are founded on the terra-mechanics algorithms contained in the NATO Reference Mobility Model. The NATO Reference Mobility Model uses physics-based force balancing algorithms with terra-mechanics relationships that were empirically derived from decades of vehicle-terrain interaction research, and it also incorporates proven methodologies for assessing mission effectiveness in terms of maneuver capabilities. The terra-mechanics algorithms and methodologies for assessing mission effectiveness that are implemented in this model and in other related software tools, such as those used for route analysis, can be used to generate realistic mission-related resistance profiles for defining power storage requirements.

Vehicle Gap Analysis Program

The Future Combat System Operational Requirements Document requires that manned and unmanned ground vehicles be capable of negotiating gaps 1.5- to 4.0-meters wide. Gaps include both natural and manmade obstacles. Overcoming battlespace gaps requires the ability to effectively conduct four tasks: prediction, definition, avoidance, and defeat. The inability to overcome gaps within the theater of operations will significantly impair the Future Forces responsiveness, agility, and sustainability. Researchers at the US Army Engineer Research and Development Center (ERDC), working in the field of vehicle mobility have developed methods to predict the physical interactions of vehicles with terrain mechanics. This physics-based simulation method uses research conducted at the ERDC to combine historical empirical laboratory and field evaluations with lumped parameter and numerical analysis to develop a simulated environment of the terrain. The terrain mechanics modeling is combined with a 2-dimensional vehicle dynamics model that predicts the traction required to maneuver through deformable terrains or gaps. The vehicle dynamics model is also designed to detect contact between the vehicle chassis and the terrain for vehicle and gap geometry analysis. The contact element is designed to provide both normal resistances during contact and act as a drag component representing the drag resistance between the vehicle chassis and the terrain. The combined terrain mechanics and vehicle dynamics models are called the Vehicle Gap Analysis Program (VGAP). This paper presents the application of the terrain mechanics research conducted in development of the VGAP and a verification of the VGAP.