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Bodie Legs

Team 6

Edward Lin, Niko Aquino, Steven Meissner, Clifford Miranda

Objective

Dog paraplegia, caused by serious spinal and hindquarter injury or disease, occurs with greater frequency than one might think. For example, the prevalence of Intervertebral Disk Disease (IVDD) is as high as 19% in some breeds. Loss of ambulation is often compounded by full or partial loss of bladder and bowel control. If the dog needs to relieve itself, it cannot move on its own to do so. If the dog has an accident, it will soil the bed, itself, and the family home. Thus, these “down dogs” require extra caretaking. Some owners opt for euthanasia due to the misconception that the dog will be miserable, or because they lack the support and resources to care for the animal. “Dog carts” are available, and allow pups to move on their own. However, placing the dog into current cart models is inconvenient, and the carts can only be used for brief spells. Dogs cannot sit, lie, or rest comfortably once put in the cart.The objective of this project is to design, build, test, and document a mobility device for down dogs. The device should be usable for extended periods of time by recovering the dog’s ability to alternatively stand/rise, move, and lie down on its own.

Design Solution

In order to address the functional requirements of the cart, the design created was a foldable cart with assisstive springs In order to allow the cart to fold and bend, a pivot point was used to translate Bodie’s horizontal motion into a vertical motion. The spring system was used to assist Bodie’s lack of control in the rear half of his body. Finally, to make the cart durable and easily cleanable, the design was to utilize an aluminum frame made from flat 6061 aluminum bars.

2. Brake Dimensions:

Overview

The wheel-brake system allows the device to engage in two directions: a backward sitting direction and a forward standing direction. When engaged in the backward direction, the device is able to collapse, allowing Bodie to lay down while the cart is still attached. Triggered by a forward dragging motion, the cart will be able to return to a standing position.

Functional Requirements

The following are the functional requirements of the wheel-brake system:

• • Allows cart to pivot and collapse when moving backwards going from standing to sitting position

  • Allows cart to pivot and open when moving forwards going from sitting to standing position

Comparison of Designs Considered

• • Pivot system (shape of rubber stopper)

    • Use a cylindrical shaped rubber stopper (linear surface contact with floor)

    • Use a rectangular box shaped stopper (rectangular surface contact with floor)

    • Large radius arched (constant rectangular surface contact with floor)

  • Wheel-brake system

    • Wheel utilizes bike hub motion to prevent movement in backwards direction

Justification of Final Design Choice

The wheel-brake design is sufficient to allow Bodie to stand and sit. Refer to Appendix B for analysis on brake coefficient of friction. Analysis of rubber on a variety of surfaces show that the brake has sufficient friction to prevent the cart from backwards motion but rather use it as a trigger to engage the folding mechanism pivoting the leg bars with respect to the side bars causing the cart to fold into the sitting configuration. The necessary dimensions and angles were derived by the analysis below, by using the cart dimensions to optimise brake engaging angles.

W = Weight of Bodie’s rear ≅ 44.48 N (10 lb)

d = Leg bar length = 20.32 cm (8 in)

d2 = Rigid link attached to pivoting leg bar (L-Extension)

P = Coordinates of spring anchor with respect to the origin

θ = Angle between L-extension & x - plane

Φ = Angle between L-extension & leg bar

r = Position vector of leg bar where reaction force from weight W is applied

r1 = d (-isin (Φ+θ),-jcos(Φ+θ))

f1 = Force vector on pivot leg bar at center of wheel

f1 = W(0i,1j)

→ f1 = (0i,Wj)

r2 = Position vector of L-extension where spring force is applied

r2 = d2 (-isin(θ),-jcos(θ))

f2 = Force vector provided by spring

f2 = fs ᐧ f'2

where f'2 = unit vector for the spring force vector

→ f'2 = (xp - xr2) + (yp - yr2)(xp - xr2)2 + (yp - yr2)2

Ls = Spring length

Ls = (xp - xr2)2+(yp - yr2)2

Use moment equations:

r1 ⨉ f1 + fs ᐧ (r2 ⨉ f2) = 0

→ fs = -r1 ⨉ f1r2 ⨉ f '2

By changing the parameters for the initial angle of the L-extension, there is a change directly correlated to the spring force required to keep Bodie’s rear supported. Since the spring needs to apply little to no force in the sitting to lying down region, the curve can be manipulated to make the given spring profile weaker than it is required to be. From Figure 3.9, which shows a 110° initial angle, at a spring length of 18.733 cm (7.375’’) - a sitting angle of 45 degrees - the spring force required to lift Bodie is 97.861 N (22 lb). From Figure 3.13, which shows a 150°initial angle, at a spring length of 19.685 cm (7.75’’) - a sitting angle of 45 degrees - the spring force required to lift Bodie is 111.206 N (25 lb). This indicates that a larger angle will not provide as much force in Bodie’s sitting position because there is less of a moment arm working on the system.

Final Product and Results: