# Design Considerations Concerning an Innovative Drive System for a Manual Wheelchair
## 1 Introduction  
In its World Report on Disability, the World Health Organization (WHO) demonstrates that the issue of disability, in its broadest sense, affects around 1 billion children and adults, among whom the proportion of people experiencing severe functional difficulties is between 2.2% and 3.8%. As pointed out by the WHO, the negative median increase in the issue is also accelerated by the ageing population trend [1]. Thus, one can conclude that there is a great need for the research and development of devices that facilitate the daily functioning of people with disabilities. Based on the current technology, several types of wheelchairs can be distinguished, depending on their driving force source [2]. The first and most popular group are manual wheelchairs, both with pushrim and crank systems [3]. They are characterized by a very good traction/stability ratio, simplicity of design while maintaining ergonomics, low weight and ease of transport. Due to the nature of the use, these wheelchairs are available in variants focused on active lifestyles, sports or driving over difficult terrain. A significant limitation for manual wheelchairs is overcoming infrastructure obstacles, such as stairs, kerbs, damaged pavements, unpaved surfaces or uphill climbs, as well as traveling long distances. An alternative to manual wheelchairs are electric or hybrid wheelchairs [4; 5], which are a combination of a manual wheelchair with additional assistance via an electricdrive unit [6]. The advantages of these wheelchairs are that they dramatically increase the distance that can be covered without straining the upper limbs, and that they can be used by people with mobility issues involving the upper body as well [7]. Another advantage of this type of wheelchair may be the additional systems that allow it to overcome various types of architectural obstacles, such as kerbs or stairs, although these modifications are often associated with reduced performance in covering longer distances [8]. Disadvantages include the fact that due to the electric motor power system including a battery, these vehicles have a much higher weight compared to traditional wheelchairs, and reduced maneuverability, as well as control inertia due to the delay of the signal transmitted from the operator, through the control module, to the actuator [9; 10]. A significant disadvantage of electric wheelchairs is also that they are difficult to transport in cars [11]. Paradoxically, the electric drive system, which is intended to facilitate use by replacing muscle power, results in a decrease in physical activity for people with disabilities, which may contribute to exacerbated health issues [12]. A development direction worth noting as an alternative to classical solutions is the power assist device [13; 14]. These systems serve as an adaptive module for manual wheelchairs, mounted directly onto the wheelchair frame. The user controls the speed of the drive wheel via a controller, which can function as either an auxiliary or primary drive. This solution significantly reduces the number of push strokes, thereby substantially decreasing the strain on the upper limb muscles [15]. The device's weight, ranging from 6 to 8 kg, also represents a reasonable compromise given the benefits gained. Unfortunately, such devices are still new to the market and have a relatively high price. Given the advantages, disadvantages and limitations of current wheelchair solutions, and the increasing needs of wheelchair users, it makes sense to conduct research aimed at developing manual drive systems. Their most important features include lightweight, ability to fold, enabling an increase in distance travelled, making it easier to navigate uneven and unpaved terrain as well as facilitating the overcoming of architectural obstacles.