with standard wheels to match the capabilities of the wheelchair to the current activity. mobility scooters mobility scooters share some features with powerchairs, but primarily address a different market segment, people with a limited ability to walk, but who might not otherwise consider themselves disabled. smaller mobility scooters are typically three wheeled, with a base on which is mounted a basic seat at the rear, with a control tiller at the front. larger scooters are frequently four-wheeled, with a much more substantial seat. opinions are often polarized as to whether mobility scooters should be considered wheelchairs or not, and negative stereotyping of scooter users is worse than for manual or power-chair users. some commercial organisations draw a distinction between power-chairs and scooters when making access provisions due to a lack of clarity in the law as to whether scooters fall under the same equality legislation as wheelchairs. single-arm drive wheelchairs one-arm or single arm drive enables a user to self-propel a manual wheelchair using only a single arm. the large wheel on the same side as the arm to be used is fitted with two concentric handrims, one of smaller diameter than the other. on most models the outer, smaller rim, is connected to the wheel on the opposite side by an inner concentric axle. when both handrims are grasped together, the chair may be propelled forward or backward in a straight line. when either handrim is moved independently, only a single wheel is used and the chair will turn left or right in response to the handrim used. some wheelchairs, designed for use by hemiplegics, provide a similar function by linking both wheels rigidly together and using one of the footplates to control steering via a linkage to the front caster. reclining and tilting wheelchairs a standing wheelchair with electrical 4-wheel drive and standing functions reclining or tilt-in-space wheelchairs have seating surfaces that can be tilted to various angles. the original concept was developed by an orthotist, hugh barclay, who worked with disabled children and observed that postural deformities such as scoliosis could be supported or partially corrected by allowing the wheelchair user to relax in a tilted position. the feature is also of value to users who are unable to sit upright for extended periods for pain or other reasons. in the case of reclining wheelchairs, the seat-back tilts back, and the leg rests can be raised, while the seat base remains in the same position, somewhat similar to a common recliner chair. some reclining wheelchairs lean back far enough that the user can lie down completely flat. reclining wheelchairs are preferred in some cases for some medical purposes, such as reducing the risk of pressure sores, providing passive movement of hip and knee joints, and making it easier to perform some nursing procedures, such as intermittent catheterization to empty the bladder and transfers to beds, and also for personal reasons, such as people who like using an attached tray. the use of reclining wheelchairs is particularly common among people with spinal cord injuries such as quadriplegia. in the case of tilting wheelchairs, the seat-back, seat base, and leg rests tilt back as one unit, somewhat similar to the way a person might tip a four-legged chair backward to balance it on the back legs. while fully reclining spreads the person's weight over the entire back side of the body, tilting wheelchairs transfer it from only the buttocks and thighs (in the seated position) to partially on the back and head (in the tilted position). tilting wheelchairs are preferred for people who use molded or contoured seats, who need to maintain a particular posture, who adversely affected by sheer forces (reclining causes the body to slide slightly every time), or who need to keep a communication device, powered wheelchair controls, or other attached device in the same relative position throughout the day. tilting wheelchairs are commonly used by people with cerebral palsy, people with some muscle diseases, and people with limited range of motion in the hip or knee joints. tilting options are more common than reclining options in wheelchairs designed for use by children. standing wheelchairs a standing wheelchair is one that supports the user in a nearly standing position. they can be used as both a wheelchair and a standing frame, allowing the user to sit or stand in the wheelchair as they wish. some versions are entirely manual, others have a powered stand on an otherwise manual chair, while others have full power, tilt, recline and variations of powered stand functions available. the benefits of such a device include, but are not limited to: aiding independence and productivity, raising self-esteem and psychological well-being, heightening social status, extending access, relief of pressure, reduction of pressure sores, improved functional reach, improved respiration, reduced occurrence of uti, improved flexibility, help in maintaining bone mineral density, improved passive range motion, reduction in abnormal muscle tone and spasticity, and skeletal deformities. other wheelchairs provide some of the same benefits by raising the entire seat to lift the user to standing height. sports wheelchairs a modern racing wheelchair a range of disabled sports have been developed for disabled athletes, including basketball, rugby, tennis, racing and dancing. the wheelchairs used for each sport have evolved to suit the specific needs of that sport and often no longer resemble their everyday cousins. they are usually non-folding (in order to increase rigidity), with a pronounced negative camber for the wheels (which provides stability and is helpful for making sharp turns), and often are made of composite, lightweight materials. even seating positions may be radically different, with racing wheelchairs generally used in a kneeling position. sport wheelchairs are rarely suited for everyday use, and are often a 'second' chair specifically for sports use, although some users prefer the sports options for everyday use. some disabled people, specifically lower-limb amputees, may use a wheelchair for sports, but not for everyday activities. us vs. france, fipfa world cup, tokyo, japan, october 2007 powerchair football while most wheelchair sports use manual chairs, some power chair sports, such as powerchair football, exist. e-hockey is hockey played from electrical wheelchairs. wheelchair stretchers wheelchair stretchers are a variant of wheeled stretchers/gurneys that can accommodate a sitting patient, or be adjusted to lie flat to help in the lateral (or supine) transfer of a patient from a bed to the chair or back. once transferred, the stretcher can be adjusted to allow the patient to assume a sitting position. all-terrain wheelchairs tracked all terrain wheelchair all-terrain wheelchairs can allow users to access terrain otherwise completely inaccessible to a wheelchair user. two different formats have been developed. one hybridises wheelchair and mountain bike technology, generally taking the form of a frame within which the user sits and with four mountain bike wheels at the corners. in general, there are no push-rims and propulsion/braking is by pushing directly on the tyres. a beach wheelchair a more common variant is the beach wheelchair (beach-going wheelchair) which can allow better mobility on beach sand, including in the water, on uneven terrain, and even on snow. the common adaptation among the different designs is that they have extra-wide balloon wheels or tires, to increase stability and decrease ground pressure on uneven or unsteady terrain. different models are available, both manual and battery-driven. in some countries in europe, where accessible tourism is well established, many beaches have wheelchairs of this type available for loan/hire. smart wheelchairs a smart wheelchair is any powerchair using a control system to augment or replace user control. its purpose is to reduce or eliminate the user's task of driving a powerchair. usually, a smart wheelchair is controlled via a computer, has a suite of sensors and applies techniques in mobile robotics, but this is not necessary. the type of sensors most frequently used by smart wheelchairs are the ultrasonic acoustic range finder (i.e. sonar) and infrared red (ir) range finder. the interface may consist of a conventional wheelchair joystick, a "sip-and-puff" device or a touch-sensitive display. this differs from a conventional powerchair, in which the user exerts manual control over speed and direction without intervention by the wheelchair's control system. smart wheelchairs are designed for a variety of user types. some are designed for users with cognitive impairments, such as dementia, these typically apply collision-avoidance techniques to ensure that users do not accidentally select a drive command that results in a collision. others focus on users living with severe motor disabilities, such as cerebral palsy, or with quadriplegia, and the role of the smart wheelchair is to interpret small muscular activations as high-level commands and execute them. such wheelchairs typically employ techniques from artificial intelligence, such as path-planning. technological developments recent technological advances are slowly improving wheelchair and powerchair technology. a variation on the manually-propelled wheelchair is the leveraged freedom chair (lfc), designed by the mit mobility lab. this wheelchair is designed to be low-cost, constructed with local materials, for users in developing countries. engineering modifications have added hand-controlled levers to the lfc, to enable users to move the chair over uneven ground and minor obstacles, such as bumpy dirt roads, that are common in developing countries. it is under development, and has been tested in kenya and india so far. the addition of geared, all-mechanical wheels for manual wheelchairs is a new development incorporating a hypocycloidal reduction gear into the wheel design. the 2-gear wheels can be added to a manual wheelchair. the geared wheels provide a user with additional assistance by providing leverage through gearing (like a bicycle, not a motor). the two-gear wheels offer two speed ratios- 1:1 (no help, no extra torque) and 2:1, providing 100% more hill climbing force. the low gear incorporates an automatic "hill hold" function which holds the wheelchair in place on a hill between pushes, but will allow the user to override the hill hold to roll the wheels backward if needed. the low gear also provides downhill control when descending. a recent development related to wheelchairs is the handcycle. they come in a variety of forms, from the road and track racing models to off-road types modelled after mountain bikes. while dedicated handcycle designs are manufactured, clip-on versions are available that can convert a manual wheelchair to a handcycle in seconds. the general concept is a clip-on front-fork with hand-pedals, usually attaching to a mounting on the footplate. a somewhat related concept is the freewheel, a large dolley wheel attaching to the front of a manual wheelchair, again generally to the footplate mounting, which improves wheelchair performance over rough terrain. unlike a handcycle, a wheelchair with a freewheel continues to be propelled via the rear wheels. there are several types of hybrid-powered handcycles where hand-pedals and used along with the electrical motor that helps on hills and large distances. a wheelchair with a lightweight power add-on attached the most recent generation of clip-on handcycles is fully electrical wheelchair power add-ons that use lithium-ion battery, brushless dc electric motor and light-weight aluminium frames with easy to attach clamps to convert almost any manual wheelchair into electrical trike in seconds. that makes long-distance journeys and everyday tasks much easier and keeps wheelchair users hands clean. there have been significant efforts over the past 20 years to develop stationary wheelchair trainer platforms that could enable wheelchair users to exercise as one would on a treadmill or bicycle trainer. some devices have been created that could be used in conjunction with virtual travel and interactive gaming similar to an omnidirectional treadmill. this convergence of virtual reality and a treadmill have been used for pediatric and adult rehabilitation to regain walking skills. in 2011, british inventor andrew slorance developed carbon black the first wheelchair to be made almost entirely out of carbon fibre recently, epfl's cnbi project has succeeded in making wheelchairs that can be controlled by brain impulses. interest in electric-powered wheelchairs that are able to climb stairs has increased over the past twenty years. therefore, many electric wheelchairs with the ability to climb stairs have been developed. electric-powered wheelchairs with climbing ability need to be stronger and have greater movement in comparison to an electric-powered wheelchair that cannot climb stairs. they must also be stable in order to prevent injury to the wheelchair user. there are currently a number of electric powered wheelchairs that