What are the different drive wheel configurations in a power wheelchair?
In power wheelchairs, we have three different types of drive wheel configurations: front-wheel-drive where the drive wheel is in front the client's pelvis; rear wheel drive where the main drive wheel is just behind the client's pelvis; and then center or mid-wheel where ideally the client's pelvis is right above that drive wheel. How do we know which one to pick?
Rear Wheel Drive
The main advantage of a rear wheel drive configuration is that it is very stable on a variety of terrains. It tends to handle going downhill, such as a sloped street or ramp, with better control at higher speeds. There is a wide range of choices in this category of chairs. It works really well for people who use a chair a lot outside and at fast speeds. It also has a lot of suspension.
A drawback of rear wheel drive configuration is that this has the largest turning radius of the three. It is easy to see how long and wide this chair is. People are often worried about accessibility with these. Most of these chairs can get through a doorway in your house. The trick is the turning radius and navigating around furniture and obstacles in the home.
As the front wheels pivot during turns, oftentimes they interfere with the foot rest hanger. If this foot plate is placed too low, as the wheel turns around during turning maneuvers, it is going to hit and jam against the footplate. Due to this we might be more limited on what type of front rigging or foot rest hanger that we can use.
Front Wheel Drive
Front wheel drive has been around for a long time. We have some more options available than we used to. Front wheel drive has primarily, until recently, been available on one main manufacturer’s chair and that is Permobil. The drive wheel, since it is in front of the client, tends to pull the chair rather than push the chair. In this case, our casters are actually behind the client and they pivot as the client completes turns. Due to the larger front wheel, it can help get over lower obstacles. We do not have to worry about footplate interference, and so it is possible to get someone's feet right underneath their knees. If we are dealing with tight hamstrings and we need a 90° knee angle, we can easily do that on a front-wheel-drive. It has a fairly small turning radius.
There are some drawbacks though. These tend to be a little less stable going downhill. If the client is driving very quickly down a sidewalk or street, the back of the chair might tend to fishtail just a little bit. This is much better than it used to be, but that can feel disconcerting to the client. If the client tends to step on that foot rest during transfers, even if we tell our clients not to, the chair might tip forward a little bit. It will not tip over, but it might move enough that the client is suddenly not very stable. These chairs do not go quite as fast as other drive wheel configurations. There are some options in the electronics to improve that. None of these options do very well with curbs, but in some rear wheel drive chairs, if a caregiver steps on the back of the chair, it pops up the front a little to negotiate a curb. This is not really recommended way of getting over curb. However, because of this large front wheel in this model, sometimes it can actually climb over a curb a little bit. The suspension is generally not as high in front-wheel-drive.
Center Wheel Drive
The main drive wheel is just about underneath the client's pelvis. Most consumer level chairs are mid-wheel drive. This has the smallest footprint in most cases; footprint meaning the actual space taken up by the wheelchair base itself. It also tends to have the smallest turning radius. Many people consider this to be the most intuitive driving platform, because as a client is turning, there are turning on their own center and that makes it more intuitive. These are also pretty stable.
Center wheel drive, however, does not always perform as well on aggressive outdoor terrain. There is also a very significant difference between consumer level center wheel drive and rehab level. In a complex rehab level center wheel drive, there are a couple things that have been added to help these perform better. When these first came out and were still in some of our consumer level chairs, when the client moved forward initially, the chair would tend to tip rearward onto the back caster just a little bit. That could be very scary for the client. When the client stopped, the chair would also tend to rock forward onto the front caster. That is not the case with the complex rehab center wheel drive. There is technology built in to prevent that from happening. Though some of them still do move back-and-forth a little bit if the client is using a lot of force or perhaps during transfers. If the client was moving up a steep incline, like a ramp, sometimes the drive wheel would actually lift right off of that surface and the client would be high-centered and stuck on these four separate casters. There is technology on these chairs now that drive this center wheel down during those maneuvers so that does not occur. With that said, these chairs do not always do as well on more aggressive outdoor terrain.