platform comparison mwd, fwd & rwd · take rwd as the example to make the point: • rwd is...

Platform Comparison – MWD, FWD & RWD

Comparing Function & Performance Characteristics of

Power Wheelchair Platforms

© Permobil Corp. | www.permobil.com

The presentation will start at the top of the hour.

• This session is being recorded and you will be provided with access to the recording.

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• You can submit questions at any time in the "Ask A Question" console. A Q&A session with the speaker will also be held at the end of the session.

Platform Comparison – MWD, FWD

& RWD

• Comparing Function & Performance

Characteristics of Power Wheelchair Platforms


• Indoor

• Outdoor

• Stability

• Driver Positioning

• Smooth Ride

• Intuitive/Likeability?

Note: This information is not scientific!

It is based on experience!


PLATFORM COMPARISONS

Six General Areas of Function and Performance

• Eco System

• Individual situations

• Using common sense


Not a „Pure‟ Science

• About weight distribution and Center of Gravity

• About maximizing the positives and minimizing the negatives related to WD

& C of G

• About driver weight

• Group 3 with Powered Seating


Impact of Weight Distribution and Center of Gravity

Key characteristics important to indoor performance include:

• Overall turning radius/circumference

• Distance between pivot (rotating) point and furthest point on base

• Overall Width


Indoor Performance

• MWD is the superior platform indoors

• It edges out FWD because of the 360 degree turning circumference which is

significantly smaller than all other platforms

• A MWD turning circumference can be towards half of all others


Indoor Performance

• The results of a study (*VA, U of P, Cornell) surprisingly showed that FWD actually navigates more easily than the other platforms around tight corners

• But FWD does have a significantly larger 360 degree turning circumference than MWD

• You may more easily negotiate a tight turn with a FWD but if you need to rotate in that space, make certain there is enough space for the FWD

• RWD has the largest turning circumference of the 3 platforms*Info available on demand


Indoor Performance

PLATFORM TURNING PERFORMANCE

FWD – End of Hallway

Drive Wheels

Casters


MWD – End of Hallway

Casters

Casters

Drive Wheels


RWD – End of Hallway

Casters

Drive Wheels

Characteristic Bad Better Best Platform

Overall turning circumference Smaller MWD

Distance between pivot

(rotating) point and furthest

point on base

Smaller MWD

Length located in front of driver

(turning radius)

Shortest FWD

Length located in front of driver Longest RWD


Indoor Performance



Indoor Performance

Key Characteristics important to Outdoor performance:

• Larger wheels and casters

• Larger leading wheel particularly if it is the drive wheel

• Wider tire/caster profile

• Good Weight Distribution / COG

• Ground clearance

• Adequate power/torque & efficiency


Outdoor Performance

OBSTACLES

Hard, Vertical Obstacle

OBSTACLES

Continuous Soft Obstacle

Continuous obstacles appear

like a ramp to the wheel.

FWD performs superior outdoors for 3 fundamental reasons:

1. The large front drive wheels (Monster Trucks prove it at every

performance)

2. Weight Distribution tends to be over the drive wheels

3. It is easier to „pull‟ casters over obstacles (a FWD characteristic) versus

„pushing‟ casters over obstacles (a RWD characteristic)


Outdoor Performance

Characteristics that work against the RWD & MWD platforms:

1. RWD - Pushing often „loaded‟ casters over soft / resistive surfaces can

cause the drive wheels to dig in

2. MWD platforms are designed to transition obstacles as high as 3”

forwards. That is the limit

3. MWD architecture is sensitive to „high centering‟ on rough / soft surfaces


Outdoor Performance

High Centering:

• Unique to MWD Platforms

• Most common cause of „stranding‟ MWD Platforms


Outdoor Performance


3” Climbing Forward

Characteristic Bad Better Best Platform

Driving Wheel In front FWD

Larger leading wheel In front FWD

Caster & wheel Diameter Larger Various brands

offer solutions

Ground clearance Higher All

Adequate power/torque More All

Sensitivity to Weight Distribution & Center of

Gravity

Lower MWD/FWD

Tire and wheel width Greater Optional from

some

manufacturers


Outdoor Performance



Outdoor Performance

Factors which create stability include:

• Ideal COG Location

• Ideal Weight Distribution characteristics

• W D / COG „friendly‟ architecture

• Anti tip capability


Stability (Fore/Aft)

Positive Platform Characteristics:

• FWD architecture is „accommodating‟ of good W D & COG positioning

• MWD architecture is also „accommodating‟ of good WD & COG

positioning

• MWD has the front and rear casters



Factors which create instability:

• Poor WD and COG positioning

• Narrow band for safe COG/WD location

Take RWD as the example to make the point:

• RWD is easily unbalanced to the rear

• Corrective actions can cause it to become front „tippy‟

• RWD incorporates „unfriendly architecture‟

– Significant weight (battery‟s) behind the rear wheel plane

– Has a long distance between center of rear wheel which limits driver location options



Characteristic Bad Better Best

Platform with the least sensitivity to ideal distribution of

weight and balance and C of G

RWD FWD MWD

Weight Distribution / COG friendly architecture RWD FWD/MWD

Anti Tip Characteristics RWD FWD MWD

Maintaining stability during Tilt or Recline RWD FWD/MWD

Maintaining stability Up and Down ramps etc. RWD FWD MWD





Stability (fore/aft)

MWD and FWD are generally more stable than RWD:

Their architecture provides more options for ideal „positioning‟ of the driver

and „location‟ of the powered seating system. The front and rear anti tips of

the MWD are a plus factor

Rule of thumb for weight Distribution: (Check with each manufacturer to obtain specific recommendations)

Platform Drive Wheels Casters

RWD 60% to 70% 40% to 30%

FWD 55% to 65% 45% to 35%

MWD 60% Plus 20% / 20% or less



Factors which provide good seating and driver placement:

• Unencumbered 90 degree foot space

• Not having to compromise driver/seating location to compensate for WD

or COG while reclining or tilting


Driver Positioning

Factors that create a bad „environment‟ for driver positioning:

• Platform geometry that forces compromise of driver & seating location


Driver Positioning

FWD and MWD score well in this area:

• FWD has no casters and the most open space for lower extremity positioning including 90 degrees

• MWD does have casters but due to architecture they are generally less intrusive than the RWD platform


Unencumbered space including at 90 degrees RWD MWD FWD

Ability to position Powered Seating without compromising

stability

RWD FWD MWD

The ability to maintain ideal Weight Distribution and C of G

regardless of seating and lower extremity needs

RWD FWD MWD


Driver Positioning



Driver Positioning

Key factors that help create a „smooth‟ ride:

• The ability to reduce jolts, bumps and vibrations

• The ability to traverse diverse surfaces and reduce/limit rocking and

bouncing

• Larger wheels and casters

• Pneumatic wheels and casters


Smooth Ride

Both FWD and RWD platforms are more amenable to independent

suspension on all wheels:

• Typical MWD architecture does not provide independent suspension on all

6 wheels

• This makes the difference between the platform ratings


Smooth Ride

• Both FWD & RWD fare best due to the lower wheel count and the potential to add independent suspension on all wheels and casters


The ability to absorb/reduce bumps, jolts, vibrations MWD FWD/RWD

The ability to provide a stable seat (reduced rocking and

bouncing)

MWD FWD/RWD


Smooth Ride



Smooth Ride

What is it?

• „Intuitive Feel‟ is used to describe the response that drivers have

to the „feel‟ and sense of „connection‟ with the vehicle

• A strong positive sense of intuitiveness/likeability is a very

powerful factor in a selection decision

• Most drivers can develop control of a platform given time


Intuitive Feel (Likeability)

What is it?

• Being quickly „intuitive‟ to drive and control impact this reaction positively

• This is more significant to individuals who have experienced independentmobility through ambulation, driving an automobile or having prior drivingexperience with a particular platform

• If the intuitive feel is not instant, some drivers may not accept a particularplatform selection regardless of all other factors and contra indications

• An example of this is the individual who spends significant time outdoorson rough terrains where a FWD (rates highest - Outdoors and SmoothRide categories) would be the objective choice assuming access in thedwelling is a non factor. However the individual much prefers the feel of aMWD. All we as practitioners and advisers can do is ensure the choice ofproduct is made with full knowledge of the facts



Two characteristics appear to be the main drivers of this reaction:

• Having the turning pivot point close to the driver‟s head delivers a more natural/intuitive feel and typically shortens the learning curve

• The ability of the vehicle to access tight spaces is another positive contributor

• Although FWD may require a longer learning curve, it ultimately scores high due to its superior maneuverability (relative to RWD) in confined spaces


Pivot point at or close to driver‟s head FWD MWD/RWD

Maneuverability in confined areas RWD FWD MWD





Intuitive Feel – ‟likeability‟



Combined View

MWD

FWD

RWD

• In the combined view one could conclude that FWD is hands down the „best

all around‟ choice and for many drivers that may be the simple fact

• However when you „weight‟ the 6 areas recognizing that some are generally

more critical; the result changes


“Weighting” The Results

Two of the areas are „generally‟ more significant:

1. Indoor Performance

2. Intuitive / Likeability


“Weighting” The Results

Steps:

1. Do an „equipment needs‟ evaluation

2. Objectively prioritize the „needs‟

3. Match the platform performance characteristics to the prioritized needs

4. Review with client and adjust if needed

5. Wherever possible have client experience performance first hand in

environments as close to real life as possible particularly the most

challenging areas expected


Relating the Information to Life

• What is it?

• The „Form‟


“Equipment Needs” Evaluation


“Equipment Needs” Evaluation



Platform Selection

Front, Mid or Rear, make the selection based on a detailed

„life/equipment‟ evaluation:

• Real life information

• Realistic expectation



Q&A

Questions?

• Please use the “Ask A Question” section to the left to submit your

questions to our speaker.

THE POWER OF MOBILITY

www.permobil.com

(800) 736-0925

[email protected]

platform comparison mwd, fwd & rwd · take rwd as the example to make the point: • rwd is...

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