Analysis of Direct Wheelchair to Shopping Cart Attachment (Question 2)

To address Question 2 from post “Direct Wheelchair to Shopping Cart Attachment“: What are the similarities and differences between the carts Gary will use (in Albuquerque)? I took a small sample of shopping carts and made several measurements:

(A) Distance between the shopping cart’s rear wheels (including any bolts or nuts that may extend beyond the wheel itself);

(B) distance from the back of the rear wheels of the shopping cart to the rear cart bar (RCB);

(C) height of the RCB.

The measurement (A) lets us know whether the front casters of a wheelchair can fit between the rear wheels of the shopping cart. If the front casters do not fit between this measurement, the attachment will need to be longer to span or reach over the distance (B).

From the picture in the original post, we can see that (C) may affect the placement of the attachment on the wheelchair frame. It turns out that the width of the RCB (in the original C measurements) is not relevant. This width is wider than (A) for most shopping carts and not a restriction in the placement of the attachment on the cart. Also, the diameters of the RCB’s sampled were similar (1/2 inch).

For our design efforts, we borrowed carts from La Montanita Co-Op Market (LMCM). There were two types of shopping carts. The larger of these was similar to the carts in our samples. We used this larger cart from LMCM for our prototype.

Small shopping cart from La Mantanita Co-Op Market.

Small shopping cart from La Mantanita Co-Op Market.

Large shopping cart from La Mantanita Co-Op market with measurements A (width at rear wheels: 20") and C (height of rear cart bar: 13.75").

Large shopping cart from La Mantanita Co-Op market.

 

Large shopping cart from La Mantanita Co-Op market with measurement B (distance from the back of the rear wheels of the shopping cart to the rear cart bar: 8").

Large shopping cart from La Mantanita Co-Op market.

Shopping cart samples: Home Depot, Walmart, Albertsons, Babies R Us and Best Buy.

Shopping cart samples: Home Depot, Walmart, Albertsons, Babies R Us and Best Buy.

We tabulated the measurements from our small sample and listed the measurements from LMCM last for easy discernment.

 A (width at rear wheels in inches)B (distance from bar to rear wheels in inches)C (height of bar in inches)
Albertsons20.54.0011.00
Babies R Us21.003.759.50
Best Buy21.504.009.00
Home Depot21.504.759.50
Walmart20.254.7510.50
Co-Op20.008.0013.75

The width of the rear wheels (A) of the carts from LMCM is 20.00 inches which is narrower than any of the other carts in our sample.  So if the front casters from a wheelchair fits between the rear wheels of a cart from LMCM, the casters will also fit between all of the carts in our sample.

Since the front casters of the wheelchair fit between the rear wheels of the shopping carts, our attachment will not have to span the distance from the back of the rear wheels of the shopping cart to the RCB.  Thus, we will not need to design accommodations for B.

At 13.75 inches, the RCB of the LMCM shopping cart is almost 5 inches higher than all the other carts in our sample.

If our prototype is able to attach Gary’s wheelchair to the large shopping cart from LMCM, we are almost done.  The final attachment will have to be able to accommodate for RCB height differences of about 5 inches (9 – 13.75 inches).

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3 Responses to Analysis of Direct Wheelchair to Shopping Cart Attachment (Question 2)

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