BACKGROUND

Amy is a teenage girl with cerebral palsy (CP), a neurological disorder that affects the brain and reduces motor control. Amy has Athetoid CP, which is characterized by spastic and involuntary movements of the body. Involuntary movements interfere with her ability to walk, speak, and reach for objects. An assistant must often help transport her, interpret her speech for others, and carry out actions for her. Though Amy mostly relies on others to perform basic tasks for her, her cognitive abilities and interests are the same as those of a typical teenager. One activity she enjoys is riding her tricycle in the neighborhood. Amy rides a standard Schwinn Meridian Tricycle that was modified by her family to accommodate some of Amy’s needs. Her family attached a torso brace and a pair of foot sandals to secure her on the tricycle. When riding, Amy has trouble braking the tricycle herself; she cannot use the conventional brake levers because she has difficulty reaching them quickly and squeezing them with enough strength. Someone else must stop her by pulling backwards on a strap attached to the back of the tricycle. Thus, Amy would like to have a braking system that allows her to control the brakes herself.

PROBLEM STATEMENT

Because Amy cannot use the conventional brake levers, an alternative method of braking and brake activation must be developed. The previous braking method where an assistant pulls backwards on a strap attached to the back of the tricycle compromises Amy’s riding independence because Amy does not have direct control over the brakes and because someone else must always follow her. Therefore, Amy needs a customized brake system that will enable her to easily and independently brake the tricycle.

METHOD

Meetings with the client were held to better identify and understand Amy’s abilities and limitations. Ideas for suitable brake activation triggers and brake system types were brainstormed and evaluated by analyzing their advantages and disadvantages. Activation triggers considered included using buttons, gear shifters, and pedals. It was found that rotary hand motions were the quickest, easiest, and most comfortable actions for Amy. Therefore, the initial design incorporated gear shifters or grip shifts as the brake activator and the use of gears for mechanical advantage. However, Amy did not have the strength to use standard grip shifts, and, consequently, a device similar to a motorcycle throttle was considered instead because it requires less strength to use. Nevertheless, the second design, including a throttle-like device for brake activation and gears for mechanical advantage, was also revised due to its unnecessary complexity. The final design involves a customized handlebar that allows for brake activation by a 90- to 120-degree rotation of the hands and a modification of the brakes using levers to provide mechanical advantage. At least two prototypes of each the custom handlebar and the adapted brakes were constructed to refine the design and to test and verify their function.

RESULTS

The tricycle brake system was modified to address Amy’s needs by attaching a custom handlebar and adapting the existing brakes. The custom handlebar is clamped horizontally onto the existing handlebar, which is similar to one on a cruiser bicycle. The custom handlebar consists of two concentric stainless steel cylinder tubes of differing lengths and diameters: the outer rotating cylinder and the inner support shaft. The rotating cylinder (1.5” outer diameter, 18.25” length) is the handle that Amy holds with both hands and uses for steering and brake activation. The cylinder contacts the support shaft only on its ends, which are capped with custom-made Teflon bushings. The Teflon provides a bearing surface with low friction and prevents binding in the two cylinders. Shaft collars around the support shaft prevent lateral movements of the rotating cylinder. The brake cable is attached halfway down the length of the rotating cylinder by drilling two holes 45 degrees apart and threading the brake cable through the holes. The stopper on the brake cable end is larger than the drilled holes and, therefore, secures the cable to the cylinder. Non-adhesive foam strips are wrapped around the cylinder as handgrips, and the area surrounding the secured brake cable is left unwrapped. The support shaft (1” outer diameter, 3’ length) provides the axis of rotation for the rotating cylinder and allows the custom handlebar to be clamped onto the tricycle. A stainless steel bracket with an adjusting barrel is attached to the existing handlebar to fasten the brake cable housing to the tricycle frame.

The existing band brakes on the back wheels of the tricycle were adapted to provide mechanical advantage during brake application. Because the band brakes are activated by pulling a lever, force amplification is achieved by attaching an metal bracket that extends the lever length 2.5 times, which amplifies the applied force by 2.5 times. A brake cable anchor bolt secures the end of the brake cable to the lever extension. A second metal bracket is fastened on the trike frame almost parallel to the lever extension. The second bracket includes an adjusting barrel to keep the brake cable in place.

DISCUSSION

With the custom handlebar, Amy is able to apply the brakes without changing the position of her hands and by twisting the rotating cylinder forward. Mechanical advantage from the adapted brakes allows Amy to brake the trike with her reduced hand strength. On average, Amy can produce 5 lbs of linear force from each of her hands, and it takes 20 lbs of linear force to brake the trike. Using both hands to activate the brakes corresponds to 10 lbs applied in brake activation. The 10 lbs are increased 2.5 times by mechanical advantage incorporated in the brake modifications, resulting in 25 lbs of total force available to brake the trike. Plus or minus 5 lbs of uncertainty in the total force is included to ensure that Amy will be able to brake the trike and to allow for unpredicted losses in energy.

The system is designed to be operated on flat or moderately-sloping areas, which are similar to the terrain in Amy’s neighborhood. The system works as expected and has been tested by Amy for leisure riding on areas with moderate or no hills. There were two ways that Amy used the custom handlebar. She either placed both hands on the rotating cylinder, using both hands to brake, or she placed one hand on the exposed support shaft and the other hand on the rotating cylinder, using one hand to brake the trike. The latter method provided better steering as Amy transitioned to using handles in an unfamiliar position. However, as expected, braking was not as effective when only one hand was used because, in theory, she was applying 12.5 lbs of force, which is not enough force to fully stop the trike.

CONCLUSION

The goal of this project was to design and construct a custom tricycle brake system that a teenage girl with cerebral palsy could use easily to independently and directly brake her trike. The solution involved attaching a custom handlebar and adapting the existing brakes. The custom handlebar allows her to apply a rotational force from her hands to activate the brakes. Mechanical advantage in the brake adaptations allows her to brake the trike using less strength. Not only can the custom trike braking system be useful to other teenagers and adults with cerebral palsy or with diseases that reduce motor control, but it can also be useful for elderly adults with weakened hand strength. The custom brake system would be would cost under $300, which is affordable compared to other types of adaptive trikes costing $1,000 or more (1). In conclusion, this custom brake system would provide more riding independence to riders with reduced motor control and reduced hand strength at an affordable price.