By Lt Col Narendra Tripathi (r)

Exoskeletons are a technology that captivates roboticists, military strategists, and medical professionals alike. The term often conjures images of war machines from movies like Avatar or The Wandering Earth 2, where humans seamlessly control robots with movements that mimic natural human motion. However, this vision remains quite distant from current reality.

Exoskeletons, or exo-suits, are wearable devices that act as external skeletons, enhancing a soldier’s strength and abilities. Worn over a uniform, they use powered mechanisms and AI to boost performance, allowing faster movement and heavier load carrying. Exoskeletons are classified as Active or Passive. Active exoskeletons use advanced technology to improve physical abilities, offering soldiers tactical advantages. Passive exoskeletons, powered by self-actuation-like springs, are less advanced but valuable for rehabilitation. Exoskeletons can be designed for specific tasks: Upper-Extremity Exoskeletons enhance arm movements, while Lower-Extremity Exoskeletons improve leg motion and load capacity.

About Exoskeleton Technology and its Challenges

Before advancing further, it’s important to understand the origin and challenges of exoskeleton development, especially active or powered exoskeletons. These wearable devices are designed to move in sync with the user’s body, with actuators that provide necessary motion based on each body part’s movement. While the concept seems straightforward, creating an effective exoskeleton, particularly for military applications, presents significant challenges. The human body operates through a complex system where the brain signals muscle cells to contract and expand, resulting in limb movements around joints like the hip, shoulder, or elbow. These movements are not simple; they follow unique patterns known as the GAIT cycle, with each person having a distinct motion signature. For an exoskeleton to effectively augment a user’s movement, it must mimic this natural pattern.

Actuators, the components responsible for movement within the exoskeleton, are placed at key joints and can be rotational or linear, depending on the design. However, replicating natural joint movement is critical, as each joint has a different degree of freedom (DoF). For example, the knee joint alone has six degrees of freedom, allowing movement in six different ways, which complicates the task of accurately replicating this in an exoskeleton. This complexity extends to other joints like the hip, which also have multiple DoF, making the design of an effective exoskeleton a challenging endeavour.

Once the complex movements of the human body are mechanically replicated by the exoskeleton, the next challenge is controlling the actuators with precision. The exoskeleton must receive accurate signals to determine when and how to move. These signals can be derived from the brain using electroencephalography (EEG) or from muscles using electromyography (EMG). However, translating these biological signals into mechanical movement is a significant challenge. The system must accurately interpret these signals to provide the right amount of power, ensuring that the exoskeleton’s movements align perfectly with the wearer’s natural motion.

Another major challenge is the weight of the exoskeleton itself. As a wearable metal superstructure, it inherently adds weight to the user, which could be counterproductive for soldiers by increasing their physical burden. Therefore, the exoskeleton must be designed to be self-balancing, using mechanisms like force-torque balancing with springs to cancel out its own weight. This would ensure that the exoskeleton feels almost weightless, not adding to the wearer’s effort.

The most pressing challenge, however, is providing a constant and reliable power source for the exoskeleton. The actuators require power to function, which can be supplied by batteries, engines, or fuel cells. Finding a power source that is both powerful enough to meet the exoskeleton’s demands and lightweight enough for extended use in the field remains a significant hurdle in its development.

World trends in exoskeletons

Globally, countries have been investing in exoskeleton technology for their soldiers for decades. While the potential advantages of this technology are significant, the development of active exoskeletons faces considerable challenges, particularly in terms of cost and technological complexity. Although passive exoskeletons have seen successful implementation, the dream of fully functional powered exoskeletons remains elusive. These systems must replicate the full range of human motion, accommodate the unique GAIT patterns of individual users, manage power efficiently for extended use, and, importantly, be cost-effective—an area where current solutions fall short. Despite their benefits in reducing soldier fatigue, the exorbitant costs make widespread deployment of powered exoskeletons impractical especially for developing countries like India. Globally, through extensive research numerous prototypes and products have been developed for rehabilitation, military, and industrial applications. 

(a) The Chinese military has developed an advanced powered exoskeleton suit, the Portable Ammunition Support Assist System, designed to enhance soldiers’ ability to carry ammunition. This suit provides 20 kilograms of assisted strength, reducing over 50 percent of the load and lowering the risk of waist injuries. Powered by a motor, it helps users stand more quickly after bending. Previously, in 2020, the People’s Liberation Army (PLA) deployed a passive exoskeleton suit for border defense troops, effective in high-altitude environments like Tibet for tasks such as supply delivery and patrols. The PLA’s progress in exoskeleton technology was highlighted during the 2019 “Super Warriors” competition, where over 50 prototypes competed in various categories.

(b) Lockheed Martin has developed the Human Universal Load Carrier (HULC), a hydraulically powered exoskeleton that enables soldiers to carry up to 91 kg with minimal strain by transferring the load’s weight to the ground through titanium legs, reducing the risk of musculoskeletal injuries. Weighing 24 kg without batteries, the untethered HULC allows a full range of movements like squatting, crawling, and lifting. An onboard micro-computer adjusts to the user’s movements, supporting both front and back payloads. It can be customized with mission-specific attachments and offers a range of 20 km on level terrain, with speeds up to 16 km/h. 

(c) The Berkeley Lower Extremity Exoskeleton (BLEEX) was developed by U.C. Berkeley’s Human Engineering and Robotics Laboratory, funded by DARPA, to help soldiers carry heavy loads with minimal effort across any terrain. First demonstrated in November 2000, BLEEX features two powered legs, a power unit, and a backpack-like frame for carrying loads. It securely attaches to the wearer’s feet, allowing a wide range of movements like squatting, bending, and running while carrying equipment. BLEEX enhances the wearer’s ability to carry heavy loads over long distances without losing agility. In case of power failure, the powered legs can be easily removed, converting the system into a standard backpack.

(d) Hybrid Assistive Limb (HAL) from Japan is the world’s first technology designed to enhance, support, and regenerate the wearer’s physical functions based on their intentions, earning it the title of “Wearable Cyborg™.” When a person attempts to move, the brain sends signals to the muscles to initiate the action. These signals generate faint bio-electrical signals on the skin’s surface, reflecting the wearer’s intention to move. HAL uses sensors attached to the skin to detect these signals, allowing it to execute the desired movements in response to the wearer’s voluntary commands.

(e) The XOS 2, also known as the “Iron Man” suit, is a second-generation robotic exoskeleton developed by Raytheon for the U.S. Army. It enhances a soldier’s strength, agility, and endurance using high-pressure hydraulics, allowing them to lift heavy objects at a 17:1 weight ratio without fatigue.

Evolving from DARPA’s 2001 program, the XOS 2 features improved materials and performance, weighing about 95 kg. It can support up to 200 pounds on one foot, reducing physical strain on soldiers. Though tethered, it offers logistical advantages by lowering manpower needs and operational costs. Additionally, the suit’s internal combustion hydraulic engine provides up to 200 kg of force per square centimeter, enabling soldiers to lift 50 pounds with each arm.

Soldier demonstrating XOS2 at Utah, Pic Source: https://www.army-technology.com/ 

The Present Status of Exoskeleton Development for Military Usage in India

India’s development of military exoskeletons, led by DRDO laboratories, is advancing rapidly with contributions in biomechanics, robotics, cognitive technologies, and human-machine interfaces. These innovations promise to enhance soldiers’ strength, endurance, and cognitive abilities. DRDO’s Defence Bioengineering and Electromedical Laboratory (DEBEL) has been gathering data to analyze musculoskeletal components, while the Ministry of Defence is investing in upgrading wearable gear to meet modern combat challenges. Research by various defence R&D units, academic institutions like IIT Kanpur, and private industry aims to create exoskeletons tailored to Indian soldiers’ needs. These suits are expected to increase load-carrying capacity by 100 kg for up to 8 hours, with 3 to 5 hours of battery backup. They will also assist soldiers in high-altitude terrains by reducing fatigue and the risk of injuries, making significant contributions to operational effectiveness.

India is advancing in passive exoskeletons with positive field results. DRDO is developing more advanced powered exoskeletons for future combat. Current passive systems like the JaipurBelt and ArmMax, used by the Indian Army, Air Force, and National Disaster Response Force, support weightlifting by 5 to 35 kg (11 to 77 pounds). The JaipurBelt aids the back and spine, while ArmMax supports the arms. These lightweight, self-powered exoskeletons feature an innovative hinge mechanism that conserves energy for heavy lifting. They enhance soldier mobility in challenging terrains and offer protection against injury and extreme weather.

DRDO has been extensively researching exoskeleton technology to enhance soldier safety and efficiency, though operational deployment is still pending. Significant progress has been made, with DRDO leading efforts in developing exoskeletons to boost soldiers’ capabilities and endurance. Various DRDO labs are working on bioengineering, biomechanics, and control systems to strengthen Indian soldiers.

The primary focus is on augmenting soldiers’ logistics capabilities, with DRDO analyzing the biomechanical demands of tasks like transporting goods across diverse terrains. They are developing exoskeleton systems for specific military logistics applications such as bending, lifting, and walking with payloads. The exoskeletons are being designed in two approaches: passive (unpowered) exoskeletons using springs and dampeners, and active (powered) exoskeletons with actuators to reduce energy expenditure. DRDO’s multi-pronged approach, involving deep tech and various labs, aims to make advanced exoskeletons a reality soon.

Biomechanical Characterization and Psychophysiological Evaluations:

The Defence Bioengineering and Electromedical Laboratory (DEBEL) is focused on biomechanical characterization and psychophysiological evaluations for exoskeleton development, ensuring they enhance physical capabilities while respecting soldiers’ physiological limits to prevent fatigue and injury. DEBEL collaborates with the Research & Development Establishment (Engineers) (R&DE(E)) and the Institute of Nuclear Medicine & Allied Sciences (INMAS) on brain-computer interfaces and cognitive technology, including brain-mapping integration, threat warning systems, and EEG-based controls for military applications.

Actuators, Control Systems, and Robotics Integration:

The integration of actuators and control systems is crucial for the development of full-body, hybrid, and soft exoskeletons. DEBEL has taken the lead in designing these systems, ensuring that the exoskeletons can mimic natural human movements while providing additional strength and endurance. Robotics integration is also a key focus area, allowing for the development of sophisticated systems that respond accurately to a soldier’s movements. R&DE(E) is also contributing to this field by developing exoskeleton-based soldier augmentation systems. These systems aim to improve the operational effectiveness of soldiers by reducing the physical strain of carrying heavy loads over long distances, among other enhancements.

Cognitive Exoskeletons and Human-Machine Interfaces:

Cognitive exoskeletons are the next frontier in this technology, with DEBEL exploring ways to enhance both physical capabilities and cognitive functions like situational awareness and decision-making. A key component of this development is Human-Machine Interfaces (HMIs), which DEBEL is working on to enable intuitive control and operation. This includes HMIs for full-body, hybrid, and soft exoskeletons, ensuring adaptability across various military applications.

Passive Exoskeletons for Load Carriage:

For soldiers involved in missions requiring extensive physical endurance, passive exoskeletons offer significant benefits. The Defence Institute of Physiology and Allied Sciences (DIPAS) is working on developing passive exoskeletons specifically designed for military load carriage. These exoskeletons do not require power sources and are engineered to redistribute weight effectively, reducing the strain on soldiers during long marches or in combat situations. DIPAS also has a mandate for Creating data sets for bioeffects of RF/MW/DEW/ammunition/nanoparticles/bird-strike/noise & vibrations.

Sensors, Smart Textiles, and Soft Exoskeletons

The integration of advanced sensors and smart textiles is another area where DEBEL is making progress. Sensors are essential for monitoring the performance and condition of the exoskeleton, while smart textiles provide comfort and additional functionalities such as temperature regulation. These innovations are particularly important for soft exoskeletons, which are designed to be lightweight and flexible, providing support without restricting the wearer’s movements.

Exoskeletons for Soldier Augmentation

Exoskeletons designed for soldier augmentation are at the core of India’s military exoskeleton development program. These systems are being developed to enhance the physical capabilities of soldiers, allowing them to carry heavier loads, move faster, and endure longer periods of physical exertion. The combination of robotics, sensors, and cognitive technologies in these exoskeletons promises to significantly improve the operational effectiveness of Indian soldiers. 

DEBEL organized an international workshop on the Emerging technologies and challenges for Exoskeleton “IND-EXOS 2024 at Bengaluru on 16-17 Apr this year to bring together stakeholders from defence, industry, rehabilitation, and R&D fields to brainstorm over the agendas of advancement in exoskeletons globally, Musculoskeletal modelling and simulation, bio mimic sensing, mechanics and structure, neuromuscular control, human-machine interface (HMI) & regulatory standards.

Conclusion

Exoskeletons have the potential to transform both military and civilian sectors by enhancing human capabilities and improving interactions with autonomous robotics. In the military, these devices could adapt to soldiers’ behaviour patterns, proving invaluable for combat and logistics. As R&D advances, their impact is expected to expand across various applications.

However, developing active exoskeletons faces significant challenges, including mimicking human joint movements, translating biological signals into mechanical actions, achieving self-balancing, and ensuring reliable power sources. Additionally, addressing production costs, chip development, and understanding human anatomy are critical hurdles.

Future innovations, such as bullet-proof armor, integrated weapons, and jetpacks for aerial mobility, promise to extend exoskeleton use beyond the military to civilian applications like freight handling. Overcoming current technical and cost challenges will be key to unlocking the full potential of exoskeleton technology, leading to more efficient and versatile designs powered by fuel cells and AI-driven actuators.

Lt Col Narendra Tripathi (r) is an alumnus of IIT Kanpur with research in Exoskeleton. He is also an SME and independent consultant in military technology.