ATP Series

Power Base Priorities

How Evolving Technology Is Impacting Power Wheelchair Choices

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Like almost everything in life, power wheelchair designs have changed…as have drive-wheel configurations. Seating and mobility teams have a wealth of choices… so how should they decide on an optimal system for a particular client?

How Power Bases Have Changed

Historically, front-, mid-, and rear-wheel drive configurations have each had distinct advantages and disadvantages, the latter including the fishtailing seen in frontwheel-drive power chairs and the high centering seen in mid-wheel-drive chairs.

With design evolutions, are these challenges still a concern? Are today’s power base configurations more alike than they used to be?

Julie Piriano, PT, ATP/SMS, is VP, Clinical Education/Rehab Industry Affairs and the Compliance Officer for Quantum Rehab.

“I don’t think the three traditional drive-wheel configurations are any more alike today than they were in years past,” Piriano said. “However, there are more hybrid configurations and center-of-gravity adjustments that can be made to benefit from the advantages of two base configurations when the drive wheel is slightly forward or rearward of the client’s center of mass. It would also be correct to say that the engineering advancements and design evolution of modern power wheelchairs have mitigated or at least significantly minimized many of the disadvantages of each drivewheel configuration that were known to be true of their earlier versions.”

For example, “Fishtailing has by and large been eliminated on front-wheeldrive chairs with enhanced electronics capabilities and the use of technology that measures angular velocity and revolutions per minute data, senses an imbalance and corrects it to allow the chair to move smoothly, even at higher speeds,” Piriano noted. “In addition, advanced programming and drive algorithms can be set up to automatically slow a chair down when entering a turn and then accelerate out of it to prevent the backend whip that used to occur.

“The intuitive nature of driving a mid-wheel-drive chair is a huge advantage, especially for an individual who was previously ambulatory. But the jolting/vibratory forces that were often felt by the end user, coupled with the concern of high centering while negotiating obstacles and inclines, were often two significant deterrents to recommending this drive-wheel configuration. Again, for manufacturers that have made design innovation a priority, their engineering teams worked the problem and created improvements to the chassis design, suspension systems and motor technology that significantly reduce the terrain’s effect on the end user, keep all six wheels on the ground, and virtually eliminate these two issues.”

Improvements to Rear-Wheel Drive

That leaves rear-wheel drive, known for its longer turning radius and often thought to be less maneuverable.

“I think a lot of us who’ve been in this industry for a long time have gravitated toward or had a soft spot in our hearts for rear-wheel drive,” said Brad Peterson, VP of Sales for Amylior. “Having been with Quantum [Rehab] when mid-wheel drive was really starting to grab more marketshare, people kind of forgot about rear-wheel drive because of the maneuverability that the mid-wheel drive base gave… but they forgot about why they liked [rear-wheel drive] in the first place.”

Amylior’s version of rear-wheel drive makes many people do a double take: “The first time I saw the Amylior R3, I [thought] ‘That’s a mid-wheel-drive chair,’” Peterson said. “You see the casters on the ground in the rear, not an anti tip. You see the shortened wheelbase, and it looks more mid-wheel drive.

“I think when you look at other bases — are there more choices or less choices, is there kind of a homogenization of some of the different technologies? — and look at the [R3], it does look like a mid-wheel drive. But the R3 definitely has a lot of traits that set it apart from not only rear-wheel drives, but also other chairs that are saying they’re hybrids. The patented dual-action suspension in Amylior products is really what makes the chair unique, because it allows the chair to react to the ground, but also stay amazingly stable in multiple environments, configurations and weights. So we don’t use locks, we don’t use gas cylinders, we don’t use any kind of a cable mechanism to give stability to the chair. It’s just the mechanical workings of the suspension in addition to the geometry of the chair.”

The distance from the drive wheel to the front caster, Peterson added, makes a difference: “It’s much shorter than a traditional rear-wheel-drive chair. Most rear-wheel-drive chairs have that really big distance from the rear wheel to the front caster, which gives them that big turning radius or that big swing. By shortening the wheelbase and then spreading out the load over the entire chassis, we have a very stable, very comfortable, maneuverable chair. When people get into that chair, folks I’ve known forever who have tried pretty much everything, they’re blown away by the comfort of it and where it will go. It has that nice outdoor performance, and it will go places that other chairs won’t go — but most importantly, it’s how well it maneuvers in elevators, indoors and how tight the turning radius can be if it’s set up correctly.”

How Technology Has Leveled the Playing Field

Tracking technology and suspension systems have improved the overall power chair experience, regardless of drive-wheel type.

Peterson referenced Ben Leclair, a member of Amylior’s marketing team and a professional wakeboarder who sustained a C3 spinal cord injury in 2016. Leclair now has a mid-wheel-drive Amylior M3 and a rear-wheel-drive R3.

“He prefers the R3,” Peterson said, “because he feels less fatigued throughout the course of the day. He feels more comfortable in the Hybrid Wheel Drive — that’s what we’re calling it now, an HWD, not a rear-wheel drive. He doesn’t have as many issues with his tone or spasticity as he does in a center-wheel drive. I think it’s the suspension; I think it’s also where he is on the base. He’s not sitting on top of the drive wheel; the drive wheel is kind of behind him. Benjamin also uses a drive wheel with a 14x4" tire, which is the larger-diameter tire for outdoor performance, and that gives him more shock absorption as well. He’s in aggressive urban environments and outdoors on trails, outdoors in the woods. He likes to be outdoors.”

Peterson added that while power chair literature often highlights the big numbers — how high an obstacle a power chair can climb, for example — consumers often have different concerns.

“People say, ‘It’s not uncomfortable for me to go over a curb cut, it’s not annoying for me to go over a huge gap in pavement. It’s uncomfortable and annoying for me to go over bricks, cobblestones, those constant vibrations day to day.’ That causes them to have more stress, more tone, more fatigue. So with the dual-action suspension on the R3 and the M3, we have two facets of the suspension. The first is what reacts to the ground, so that’s what keeps your front and rear casters and your drive wheels on the ground and helps keep them level. But the second part is that rear spring that ties the base to the seat, so you watch that spring absorb shock and try to keep the seat as level as absolutely possible. When we keep the seat level, that means we’re dissipating a lot of the shock before it gets up to the consumer.That helps maintain their position and conserve energy.

“I think suspension absolutely has improved, so we’re of course dealing with energy conservation. If someone’s not fighting against gravity or the ride of the chair is such that they can navigate normal obstacles without moving their body as much as they would in older chairs, it’s going to help them stay out of bed much longer. Maintaining a functional position by not having the body moved, not having tone or spasticity kick in that will move them, helps them to stay out of bed longer and helps them stay in their technology longer.”

Taking in the Whole Picture

So maybe choosing the best power chair is less about obsessing over drivetrains and more about taking in as much information as possible about the consumer.

“Diagnosis alone has never driven my consideration for wheelchair base configuration, as the physical, functional, and environmental considerations of each person are far too varied,” Piriano said. Instead, she focuses on factors such as how the client’s weight is distributed, the seating and accessories that will be needed, current and future medical conditions or progressions (ventilator, cough assist?), and how the client transfers.

Peterson agreed that details are crucial. “It’s tracking technology,” he said. “It’s also the ability to dial in simple drive parameters and drive settings so you’re not constantly giving those commands to maintain a straight line. It’s also the setup of the chair. So if the chair is set up well, where you don’t have really aggressive caster swings or aggressive movement of the base, it’s going to preclude the use of a lot of movements of the joystick.

“The tracking and suspension — they’re big parts, but they’re small parts of the overall picture. It’s the caster size, it’s the caster type. It’s where the person is centered on the chair, center of gravity wise. It’s the cushion they’re sitting on. It’s the armrest support, it’s the footrest support. Tracking technology and suspension are parts that can really make it better, but they’re not the only things.”

In the end, nothing is more important than knowing the power chair user. “Having had the benefit of working with so many different types of power chairs and talented ATPs, there’s almost nothing we can’t do with the technology that’s out there today,” Peterson said. “We have the ability to do so much, from an electronics standpoint, from a setup standpoint, from an easy setup standpoint — center of gravity that moves, really optimizing the balance and performance of a chair. I just hope we all take the time to ask those extra questions that may make the difference between a chair that someone lives in for five years and a chair that someone thrives in and finds new independence and function for five years.”

This article originally appeared in the Sep/Oct 2021 issue of Mobility Management.

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