Back to Technical Information Accessibility Maneuverability Home Use Obstacle Defeating Accessibility The WmegaTrac® is a very maneuverable chair. In its narrowest form, it is 24.5 inches wide and turns in a 30.5-inch radius. It is front-wheel-driven. This allows the climbing of obstacles like curbs, tree roots, driveway lips, thresholds, etc. The WmegaTrac® can jump curbs up to several inches and is usually limited by the footrest clearance. Some dealers who are ambulatory have taken the footrest off and jumped 8 inch curbs for demonstration. That is a pretty good jolt, so we do not recommend that anyone try it. Because of its small turning radius, access to small elevators becomes much easier than in conventional power chairs. The WmegaTrac® can make U turns in many elevators with the doors closed. While the technique is different than in conventional front-caster power chairs, the WmegaTrac® can make single motion turns from normal household hallways into normal 2'8"' doorways that are impossible with the front caster, rear-wheel-drive chairs. This is done by staying close to the side of the hall that the doorway is on and turning into the doorway as soon as the drive wheel axle has passed the door jam. In an WmegaTrac® riding shotgun in a minivan is done with the same ease. Just back in the right side and make a single turn into position. Driving from an WmegaTrac® is often easier than other configurations because there are no caster or dolly wheels up front to stop the user from pulling all the way forward. Top of the Document Maneuverability This characteristic is different for all powered wheelchairs as is its perceived and is of real importance. Flat-floor maneuverability is also different from irregular-surface maneuverability. In areas that have steps in the floor grade, such as is found in reconstructed buildings with overlapping instead of butting floor surfaces, rooms where ceramic tile lays above or below the carpet or wood floor, or where flagstone floors are used, twist-and-turn maneuvering will be far more difficult than on a smooth floor. In these cases, TRANSMISSION-STEERING gives the user the means to control positioning of the wheelchair. In chairs that have a left and a right drive motor, the wheel meeting the resistance stops or slows while the other wheel keeps moving, thereby altering the course taken by the chair. When more power is added to correct for the obstacle the chair farther veers off course until the obstacle is overcome, and then the chair lurches in the direction now being commanded by the user in their effort to correct the course deviation. In TRANSMISSION-STEERED powerchairs, the wheel meeting the resistance may also stop or slow as in two-motor drive systems, but the opposite wheel will do exactly the same thing, maintaining exactly the desired course while more power is added. This can be demonstrated by setting a wheelchair in slow forward motion with a rubber band to keep it going hands-off, and letting one drive wheel come up against a 2 by 4. The TRANSMISSION-STEERED chair will veer only by the extra distance up and down the board and the two-motor drive chair will deviate drastically from the desired course. Therefore the part of maneuverability that requires maintaining a desired course is far better served by TransmissionSteering™. The part of maneuverability that requires negotiating tight spaces is approached differently depending on whether the chair is Front-Wheel-Drive, Mid-Wheel-Drive, or Rear-Wheel-Drive. Turning radius plays a large role as well as overall width of the powerchair. Smaller radius and narrower overall width are better for maneuverability, but reduce static stability. RWD powerchairs have the largest turning radius and are less maneuverable. However, because of the long-standing directional stability problem in which no one knew how to solve the aft caster directional instability, persons were placed in these rear-wheel-drive chairs by prescribers because their teachers did so and their teachers' teachers did as well. By and large, this is still being done today, although the WmegaTrac® is gradually becoming known for having no directional instability. There are still the majority of prescribers who think that there is no front-wheel-drive powerchair that does not fishtail. It is like the story of the child that asked her mother why she cut the end off of the ham before cooking it. The mother said, "Because my mother did it". The little girl asked her mother why her mother did it. The mother said "we will go to grandma's house next Sunday and you can ask her". And so, on the following Sunday, the little girl asked her grandmother why she cut the end off the ham before she cooked it. The grandmother replied "because my mother did it to her ham". The little girl asked her why her mother cut the end off the ham and the grandmother said that next Christmas she could ask her great grandmother herself because they would all be together. And so it was, that the following Christmas, the little girl asked her great grandmother why she cut the end off the ham before cooking it and the great grandmother replied "because my roasting pan was too short". We have much the same situation in powerchairs. The therapist or other prescriber will carry on prescribing rear wheel drive power chairs for newly injured persons and that is what they get. Once a person gets accustomed to driving a rear-wheel-drive powerchair, it is harder for them to transition to front-wheel-drive chairs and they put up with the lack of maneuverability rather than go to the effort of making the jump. We are told by prescribers that persons who have never been in a wheelchair will learn the front-wheel-drive easier than the rear wheel drive. You may ask why all powerchair companies do not produce TRANSMISSION-STEERED powerchairs. There are two reasons. The primary reason is that TRANSMISSION STEERING is patented and is only produced by The TEFTEC Corporation. The second reason is that it costs considerably more to manufacture a steering transmission. While this may seem to put the WmegaTrac® out of reach for most, it is just the opposite. The longevity designed and built into the steering transmission makes it last for many years and ultimately is much less costly over the long run. The question that would naturally follow is "then you only manufacture TRANSMISSION-STEERED powerchairs for the rich? That is a fair question but the answer is surprising. The TEFTEC TRANSMISSION STEERED powerchairs are designed and constructed to last decades and are intended to be used throughout the life of the user. Early WmegaTrac® s are have been in use now (2001) for five years and will be for the next five, ten, and so on. All WmegaTrac® s are designed to be upgradeable. When a child gets his or her WmegaTrac® at preschool age, it will be upgraded to adjust the seat larger in a few years, again in middle school, and again in High School to the configuration for life or until obesity requires bariatric upgrading. No WmegaTrac® has been retired. TEFTEC's very newest upgrades can be carried to the chairs built 5 years ago. A same-as-new standard WmegaTrac® now costs about $4,000 per year. At the end of ten years, it will have cost about $2,000 per year. Gradually, insurers will start to realize what some in Medical in California have already found out. The WmegaTrac® is among the least expensive chairs for those who will be in a chair for many years. For those who eat chairs for lunch, this is particularly true. Even those, who pride themselves in destroying furnished chairs in 6 months or less, can not destroy an WmegaTrac®. And all the while, the user has had a safer, more capable chair, has had fewer secondary injuries, has had the most comfort, and the least mechanical failures. Top of the Document Home Use If power chair use in the home consisted of driving around in a 3,000 square foot dance floored area, almost any powered device could be made to work. However, this is the farthest thing from most in-home situations. In the majority of cases, the power chair users finds themselves in homes that were constructed with no thought of using powered mobility in them. There are step ups and downs, deep carpet with thick padding, narrow doors, and ramps up and down for adaptability, cook-top islands, pianos and other large pieces of furniture, small bathroom water closets, and combinations of these. In these situations, rear wheel drive wheelchair and two-motor-drive wheelchair users are at a distinct disadvantage. Rear wheel drive wheelchairs have a large turning radius that makes them require more room to negotiate complex turns and two-motor-drive wheelchairs have only an approximate ability to steer and track. Two motor drive systems are like two people pushing a shopping cart. As soon as something upsets the track that is being taken such as a thick carpet or step up that first affects one drive wheel and then the other, it does not take much contemplation to see why this is a difficult way to maneuver. Add to this a severe disability that would require sip and puff or chin control steering or a person with poor dexterity, and you can see that this is no small issue. Compound the difficulty of two-motor steering with rear-wheel-drive and its large turning radius, and we have a very poor arrangement for the disabled in confined surroundings. There are two conventional ways to make a vehicle track straight. One is to mount it on rails and the other is to steer the pivoting (steering) wheels. One can quickly see why rails are not a consideration, but some manufacturers attempted the steering of the caster wheels. The only ones that worked were a Stevens chair, made in the US and a Myera, made in Germany. These chairs could do well at straight-line tracking but could not turn around in anything smaller than a large empty room. All of this brings us to TransmissionSteering™. This was not listed above in the conventional ways to steer a wheelchair, because it was only invented in 1990 and is only available in the WmegaTrac®, BetaTrac®, and AlphaTrac® powered wheelchairs, all made by The TEFTEC Corporation which holds the patents on this new cutting edge technology. In TRANSMISSION STEERING, there is only one drive motor and another motor for steering. When driving straight, the steering motor is motionless and the wheelchair will not veer from straight unless the drive wheels actually skid. One can demonstrate this effect by rolling an empty thread spool on a non-skid surface like a foam rubber pad. The thread spool mimics the STEERING TRANSMISSION in which the drive wheels are geared together and cannot rotate independently except as mandated by the steering motor. If the pad is sloped and the spool is rolled at an angle to the slope, it will maintain that angle. If a tennis ball is rolled down the same slope, it will always go straight down and can not be coaxed to follow the thread spool that is rolled at a slant to the sloped pad. The tennis ball mimics the free casters of all other powered wheelchairs that do not have TransmissionSteering™ and like those wheelchairs, will roll approximately straight on a flat smooth floor. From this analogy, one can see that persons with no impairment to their use of their hands and that live in a place with hard smooth level floors with ample room, can use almost any powered mobility product. As these factors are taken away, the need for TransmissionSteering™ becomes more acute. By the time we reach goalpost type joysticks, head arrays, chin controls, or sip and puff control of steering, it makes no sense to use anything but TransmissionSteering™. Top of the Document Obstacle Defeating If you must be able to climb or jump obstacles such as a patio lip, curb without a cut, tall driveway lip, sidewalk discontinuity, differential floor heights, etc. and you can not or do not prefer to do wheelies each time this type of obstacle is encountered, then you must choose between front-wheel-drive wheelchairs, unless the maximum height you will ever encounter is no higher than a 2 by 4. In this case some of the large tired mid-wheel drive wheelchairs may also work for you, if you can stand the jarring. If you do not need to go inside with you wheelchair, you can use a powered wheelchair that does not have free casters. Chairs that steer the pivoting wheels just do not have the small turning radius to be used indoors. There are only two or three makes of these. Bear in mind that, except for the WmegaTrac® and its siblings, all non-rear-wheel-drive powerchairs with casters tend to fishtail and are difficult to impossible to drive at speeds higher than 4 mph. Chairs that are not front-wheel-drive have either front or rear anti tip bars depending if they are mid wheel or rear-wheel-drive. These anti-tip wheels will suspends the drive wheels helplessly in the air when dropping off a curb unless the anti tip wheels are adjusted so high as to be ineffective for anti tipping in the most adverse conditions. Chairs with non-powered front wheels on the ground will not be able to roll over objects that approach half the size of the wheel. Usually if the non-drive front wheel is 6 inches in diameter, the wheel cannot be made to roll over anything larger than 1-1/2 inches. The reason is that the wheel must rise to go over the obstacle, but when it strikes the obstacle, the chair is being pitched forward and the front down, just the opposite of what the wheel attached to the front of the chair needs to do. Top of the Document