DME

Blog posts of '2019' 'August'

Power Wheelchair Suspension: What you need to know and look for?

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Over the past 2 weeks we have talked about drive wheel configuration and some tips on how to decide which option is right for you. This week we are going to discuss power wheelchair suspension.  The suspension can vary from chair to chair even within each manufacturer, but there are some key points that we should discuss. 

Most power wheelchairs on the market are going to use compression springs for their suspension. There are two types of compression spring that are typically used: Linear and Non-linear.

Non-linear springs as seen in the photo below allow for changes in compressive load at different points of the range.  What this means is that you can have the looser spring coils at the beginning phase to help with climbing over obstacles.  The trade-off will be that you will lose some of the overall stability of the chair when not climbing.  Many manufacturers will use one non-linear spring as their suspension.

Linear springs on the other hand allow for consistent stability throughout the compression range.  For Permobil, these springs are also adjustable. The factory will set the suspension spring resistance based on the weight of the user and then the supplier or manufacturer representative will have the ability to further adjust depending on the needs of the user. With the Permobil M and F series, the suspension will be composed of multiple linear springs to achieve optimal traction and suspension.

 

Why does this matter?  The shape and the coil distance have an impact on how a spring works and effects the user.  The better the suspension, the greater the decreased forces on the end-user. This could lead to increased seating tolerance, pain management, spasticity management, and decreases the risk for loss of balance or position in the wheelchair.  One of the biggest points that I think about is driving over any uneven terrain whether it is just a sidewalk or grass at a park. It is important that as the chair goes over each bump that this bump is not felt by the user or limited as much as possible.  If each bump is transmitted up to the user, then the user will likely not maintain their seated position.  They will also feel all this vibration.  According to one study by Wolf and colleagues in 2007, this vibration can lead to many impairments including fatigue and pain.  

 

 

The final thought that I believe is one of the most crucial points to make is that the suspension on the wheelchair should always be there for you or your client.  We know how important suspension is and the negative impact that not having this suspension could be to our clients.  Therefore, we need to make sure that the wheelchair will maintain its suspension in any position and over all surfaces.  No matter what position the user takes the Permobil power wheelchair to, such as elevate, posterior tilt, active reach, or standing, the suspension remains the same.  If you want to drive your wheelchair in elevate, active reach, standing, or other positions, you want to be sure that your suspension will continue to support you in those positions and not lock out. 

It is important to know that each manufacturer will have different suspension set up on their chairs.  As a client, therapist, or carer make sure you ask about the suspension to determine which option is best for you.

 

Rachel

 

 

Part 2: Power Wheelchairs - Where is my Drive Wheel and Why Does it Matter?

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The drive wheel on a power wheelchair is the larger wheel if you are looking at your wheelchair or client’s wheelchair.  The location of this drive wheel can have a large impact on how the power wheelchair drives and manoeuvres in different environments.

There are three main types of drive wheel configurations on power wheelchairs: front-wheel drive, mid-wheel drive, and rear-wheel drive. In this blog today, we will focus on mid-wheel drive. 

 Mid-Wheel Drive:

The mid-wheel drive power wheelchair is the most recent technology developed for power wheelchair bases. It attempts to combine the positive aspects of front-wheel and rear-wheel drive into a hybrid product. Mid-wheel drive has many benefits.  The most well-known benefits being the small turning radius and intuitive driving.  The mid-wheel drive power wheelchair has the smallest 360  ĚŠ turning radius which can improve manoeuvrability for many individuals in their home or smaller spaces.  The intuitive driving benefit is due to the placement of the drive wheel. Typically, in the mid-wheel drive, the client will be sitting directly over the drive wheel, which is where the chair will turn/rotate from.  This axis of rotation being directly under the individual is what makes the driving intuitive or often people will say “easier to learn”.  It is important to remember that in some cases the mid-wheel drive may not line up directly below the client and therefore may lose some of that intuitive driving.  The final benefit to discuss for mid-wheel drive is the stability.  Because a mid-wheel drive wheelchair has 6 wheels on the ground, this chair will offer superior stability. This can be the case whether ascending, going up, or descending, going down, ramps or inclines. 

 

While there are many benefits for mid-wheel drive power wheelchairs, there are a couple considerations when deciding if mid-wheel drive is right for you or your client.  In being a superior option for stability, the 6 wheels on the ground also means that more energy from the ground is transferred to the client. Imagine going over a bump, because there are 6 wheels you could feel that bump 3 times versus the 2 of the front-wheel drive.  This could potentially limit the ride comfort for the individual in the chair.  Luckily, depending on each manufacturer, we have suspension to help decrease the impact of having 6 wheels on the ground.  I LOVE talking about suspension and we will have a blog post coming soon to talk all about suspension in power wheelchairs and the importance of the suspension.  The other comment I hear about mid-wheel drive power wheelchairs is the potential for “high centring”.  This term is used to describe when the centre drive wheels lose traction and may not be able to move in certain situations. This is particularly a risk with uneven terrain and was previously the biggest disadvantage of the mid-wheel drive power wheelchair. However, depending on your manufacturer, newer technologies and suspension can compensate and have greatly decreased the risk of this occurring.

The mid-wheel drive power wheelchair is the most popular drive wheel configuration and for good reason.  As technology continues to progress, the mid-wheel drive continues to have greater benefits with less limitations. 

Keep in mind that not everyone will benefit from the same drive wheel configuration and it is important to ask questions and complete an evaluation to determine which drive wheel would be best for you or your client. 

 

Rachel

 

 

Power Wheelchairs - Where is my Drive Wheel and Why Does it Matter?

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The drive wheel on a power wheelchair is the larger wheel if you are looking at your wheelchair or client’s wheelchair.  The location of this drive wheel can have a large impact on how the power wheelchair drives and maneuvers in different environments.

There are three main types of drive wheel configurations on power wheelchairs: front-wheel drive, mid-wheel drive, and rear-wheel drive. In this blog today, we will focus on front-wheel drive. 

 Front-Wheel Drive:

The front-wheel drive power wheelchair is typically going to be good for maneuverability indoors and optimal for outdoor use.  This is because of the larger drive wheel being the first wheel to overcome the uneven terrain versus the smaller casters.  Because the front wheels are connected to the drive motors, these pull the casters over obstacles and through various terrains versus if the casters were the front wheel.  In the case of the casters being in front, the casters are being pushed, the force generated is forward and downward.  This would be similar to a plowing effect and can increase the likelihood of becoming stuck in certain situations. For individuals looking to go over all terrains, the front-wheel drive wheelchair may offer the best solution.

Another benefit of front-wheel drive is the smoothness of the ride.  Look at how many wheels are on the ground.  In the case of front-wheel drive there are four wheels versus the six wheels with a mid-wheel drive chair. This means that as the end-user goes over a bump in a front-wheel drive chair, they would feel the force of that bump two times versus three in a mid-wheel drive. This can also be important for individuals that may easily lose their positioning when going over any uneven terrain.

We could talk about front-wheel for hours, but the final benefit to mention is the front-wheel drive chair’s smallest front turning aspect.  In all the configuration options, the chair will turn on its drive wheel.  The photo below shows an example of a bathroom.  In this bathroom the sink is positioned against the wall.  Because the wheelchair turns on its drive wheel and the end-user can only pull themselves so close to the wall before turning, we can see the only chair to gain full access to the sink is the front-wheel drive.  Does this mean that everyone should have a front-wheel drive wheelchair?  No, but it does mean that it is important for clinicians, suppliers, and clients (end-users) to consider the environment that the client lives in. 

 

  

Often, I hear that people stay clear of front-wheel drive because it doesn’t have as small of a turning radius as mid-wheel drive and it is harder to learn to drive.  Both of those statements are true.  The front-wheel drive will have a slightly larger 360 degree turning radius, but as you saw above it has the smaller front turning aspect which may be utilised more than someone turning in a full circle.  Front-wheel drive may be less intuitive to learn how to drive versus mid-wheel drive, but with a little practice and a few key tips, many users find front-wheel drive to be just as easy to learn as mid-wheel.  The two key points I like to teach someone when learning to drive a front-wheel drive wheelchair is:

  1. Hug the corner.  When going through a doorway the end-user will want to “hug” the corner or keep a tight turn.
  2. Turn towards the problem. For example, when positioned adjacent to a wall/barrier, turn toward the wall/barrier, then slightly reverse to allow the rear casters clearance for turning in the desired direction.  This might sound complicated, but if you remember to turn into the problem you will easily maneuver away from the problem.

Keep in mind that not everyone will benefit from the same drive wheel configuration and it is important to ask the questions and complete an evaluation to determine which drive wheel would be best for you or your client. 

 

Rachel