Background

This test is part of the ISO 7176-8 which consists of the Static, Impact, and Fatigue Strengths Testing. The Double drum, also known as multi-drum, evaluates the fatigue strength on a wheelchair by rolling the wheelchair during an extended period of time.

If you are going to complete the Fatigue multi-drum and curb drop tests, make sure to complete the Multi drum test before you proceed with the curb drop test.

Purpose

To determine the fatigue strength of the wheelchair by rolling the wheelchair over drums with slats to simulate a rough surface (International Organization of Standardization, 2014; Gebrosky et al., 2020).

Principle

This is a standardized test that requires the wheelchair to be rolled over the drums at a speed of 1.0 m/s for 200,000 cycles (Rentschler, 2002).

Apparatus

1. The drums should be aligned with the front and rear axles.
2. There are two flat obstacles (12.7 mm of height) placed opposite from each other on the drums to simulate rough surfaces.
3. Supporting structure. This structure supports the wheelchair attachment (see 4) which limits it from moving forward or backward but will allow the wheelchair to roll over the drums and to move vertically when hitting the slats.
4. Wheelchair Attachment. The attachment should be placed as close as possible to the drive wheels’ axle. This wheelchair attachment is not part of the wheelchair components and may need to be fabricated to fit the wheelchair’s axle. This attachment consists of two parts, one of them is in contact with the axle and the other is a fixed tube that is secured to the supporting structure (3). This attachment is one of the most important components of this test as it restrains the wheelchair from moving forward or backward.
5. Drum rotation counter/Cycle counter. This counter keeps track of the number of cycles completed during the test.
6. Test dummy. Use the maximum weight capacity as recommended by the manufacturer for the weight of the test dummy.
7. Straps and hooks. Use as many straps as needed to secure the wheelchair. The straps should not limit the movement of the wheelchair. Their purpose is to provide safety to the testers as these supports will hold the wheelchair and test dummy in case there is a failure that causes critical damage. For this reason, these straps should be loose enough to allow the wheelchair to move during the test, but tight enough to prevent the wheelchair and test dummy from falling when a failure presents.
8. Main structure. The structure provides support for the drums and allows the wheelchair attachment to be placed behind the wheelchair.

Test set up

Place the test dummy on the wheelchair and secure it with straps to prevent the weights from falling or moving during the test. The test dummy should have the maximum weight capacity as recommended by the manufacturer.

Secure the test dummy to the wheelchair.

 

 

 

 

Measure the distance between the front and rear axles of the wheelchair. This measurement should be used for the distance between the drums. The figure below shows how the axle wheels are aligned with the drums. However, make sure to place the drums at the appropriate distance before you place the wheelchair over the drums.

 

The wheelchair attachment restrains the wheelchair from moving front to back during the test. This attachment should be placed the closest to the axle as possible. Considering wheelchair models vary, it might be necessary to fabricate a custom attachment to connect to the fixed tube and supporting structure. As a recommendation, make sure the wheelchair attachment is level and it does not move.

A hoist will be needed to lift the wheelchair with the test dummy in place to be placed on top of the drums.

 

Secure the wheelchair by using straps. Use as many straps as needed to secure the wheelchair. The straps should not limit the movement of the wheelchair. Their purpose is to provide safety to the testers as these supports will hold the wheelchair and test dummy in case there is a failure that causes critical damage. For this reason, these straps should be loose enough to allow the wheelchair to move during the test, but tight enough to prevent the wheelchair and test dummy from falling when a failure presents.

 

Test 

Check possible damage to the wheelchair during and after the test. You may pause the test to tighten hardware, like screws. If a wheelchair part or component presents a failure type III, as it is irreplaceable, do not continue with the test and report the cycles completed before the failure happened.

This test is performed before the curb drop test to complete the Fatigue Strength Test.

The pass/fail result of this test is reported according to the completion of the 200,000

 

Two drum Video by Shonaquip SE

The following video was prepared by Dean Mubaiwa from ShonaquipSE for the ISWP Wheelchair Testing Centers Meeting on November 10th, 2021. This video shows the test set up, the apparatus and the test.

References

Gebrosky, B., Bridge, A., O’Donnell, S., Grindle, G. G., Cooper, R., & Cooper, R. A. (2020). Comparing the performance of ultralight folding manual wheelchairs using standardized tests. Disability and rehabilitation. Assistive technology, 1-10. doi:10.1080/17483107.2020.1754928

International Organization of Standarization. (2014). ISO 7176-8:2014 Wheelchairs — Part 8: Requirements and test methods for static, impact, and fatigue strengths. https://www.iso.org/obp/ui/#iso:std:iso:7176:-8:ed-2:v2:en

Rentschler, A. J. (2002). Analysis of the ANSI/RESNA wheelchair standards: A comparison study of five different electric powered wheelchairs. University of Pittsburgh (Unpublished).

Acknowledgements

We want to thank Dean Mubaiwa and Shona McDonald from Shonaquip SE for their presentation and the production of the video shared on this article. This is video was part of a presentation on November 10th, 2021 at the Wheelchair Testing Centers group meeting.

If you have any questions about the video, please contact Dean [email protected] at and Shona at [email protected]

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