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When it comes to 6-wheel power wheelchairs, make no mistake, they defy common logic toward climbing small curbs and thresholds. After all, front-wheel drive power wheelchairs have large drive wheels to pull the power wheelchair up obstacles, and rear-wheel-drive power wheelchairs can wheelie up to boost the front casters up an obstacle. However, how is it that a 6-wheel power wheelchair can get its seemingly small front casters up obstacles that even large drive wheels struggle to surmount?

Physics and engineering, that’s how. Advanced 6-wheel power wheelchairs share a common trait: The front caster arms raise and lower in response to motor torque and movement, lifting the front casters precisely when needed to surmount obstacles.  

To understand how a 6-wheel power wheelchair’s motors and caster arms interrelate, let’s consider a mechanism you may recall from your childhood, a teeter-totter.  In a very simple illustration, picture a teeter-totter, where when one end of the teeter-totter travels down, the other end goes up, and vice versa – this is the same elementary concept as the relationship between a motor and a caster arm with a pivot point in-between, meaning that when the motor torques itself downward, the caster arm travels up. Of course, very complex, proprietary designs and geometry come into play from one power wheelchair model to the next, and the motion isn’t as direct as a teeter-totter (some using linkages), but the base concept is truly that simple, where if one were to press downward on the motor like one end of a teeter-totter, the caster arm would raise up.

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Going back to our original principle that motor torque lifts the caster arm, it’s important to understand how the process occurs, how the internal power of a motor can literally move the motor and caster arm up and down. If a motor is fully anchored to a power wheelchair, the torque of the motor exclusively transfers power to the drive wheel – and, if one stalls the wheels, preventing them from spinning, it stalls the entire power wheelchair. However, on an advanced 6-wheel power wheelchair, the motor isn’t fully anchored to the power wheelchair, but mounts via a pivot point, linked to suspension and the caster arm, and it allows the motor to pivot up and down like one end of a teeter-totter.  Now if one stops the drive wheel, as with stalling the power wheelchair against an obstacle, the motor, itself, wants to keep turning the axle, but since it can’t, it intrinsically rotates itself slightly, forcing the motor downward on its pivot. Motor torque, then, creates vertical motor movement on a teeter-totter type of arc.  

To truly understand how advanced 6-wheel power wheelchair technology functions, let’s move through an everyday situation. When one pulls up to an obstacle, as with a small curb, and places the front casters against it, the power wheelchair is initially merely driving the casters straight into the obstacle’s blunt face, which is an entirely ineffective way to climb. However, as one accelerates from a dead stop with the casters against the obstacle, the power wheelchair strains, demanding more motor torque, and as motor torque increases, it begins pivoting the motor, lifting the caster arm, raising the caster over the obstacle, allowing the power wheelchair to climb the obstacle.

For users, it’s vital to note that in order for an advanced 6-wheel power wheelchair to do its job toward climbing, the user must take care in placing the casters against the obstacle at a complete stop, then accelerate, allowing the motors’ torque to raise the casters. One should never hit an obstacle at speed, as the power wheelchair will simply drive the casters into the obstacle, rebounding the entire power wheelchair, likely damaging the power wheelchair and harming the user. Again, the most effective obstacle climbing technique is to pull up to an obstacle, stop, then accelerate, letting the motor torque serve its function, allowing a safe, controlled climb.

In some instances, when one places a power wheelchair’s casters against an obstacle, and accelerates, the casters may not lift high enough to climb an obstacle. In such cases, the obstacle simply proves too tall or awkward for the power wheelchair to climb – every power wheelchair has its limitations, and cannot surmount every obstacle it meets depending on conditions. Further, some users have greater success than others do with obstacle climbing, where skill, balance, and level of disability can effect climbing abilities. Nevertheless, some 6-wheel power wheelchairs feature adjustable suspension that controls how easily and how high the caster arms raise, so if climbing performance is notably less than expected, one should contact the service provider for possible adjustment.

Advanced 6-wheel power wheelchair technology has consumed the high-end mobility marketplace, where if you’re a power wheelchair user, you’re likely using a 6-wheel system. The next time that you pull up to an obstacle, know that there are some complex physics and engineering principles at play when your casters seem to intuitively rise up a blunt obstacle, taking you where you need to go.

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Published 11/2010, Copyright 2010, WheelchairJunkie.com