Custom Tricycle

Designers:  Alex Feng, Lola Xie, Jessica Zinck
Supervising Professors: Kevin Caves, Richard Goldberg

Our client, an 8-year-old boy with Thrombocytopenia Absent Radius (TAR) Syndrome, cannot use a standard tricycle independently because his arms are weak and very short.  Braking is difficult due to his limited ability to squeeze a hand brake.  Additionally, his right leg has limited range of motion and he cannot effectively pedal with that leg.   We modified a commercial tricycle intended for older children so that he could ride it easily.  We made modifications to the steering, braking, and the hub.

The client’s mother commented, “No one who has normal children ever realizes how much it breaks your heart when your child says to you ‘Mommy and Daddy, I want to ride a bike like my brother and sister’ and they are physically unable to do this due to special needs.   These students and North Carolina Sports for Special Kids (NCSSK), have made this a possibility for [my son].  This bike has enabled him to become just a ‘normal’ kid in one aspect of his life and that is something that is so valuable to our family that few will ever know.”

The handle bars were removed from a commercially available Triaid tricycle and replaced with a four-bar linkage steering mechanism (Figure 1). The four-bar linkage moves the point of rotation of the handlebars back, so our client can use his considerable trunk rotation to steer the bike.  The steering system was fabricated from 7/8” aluminum square tubes due to their light weight, low cost and corrosion resistance.  A round, hollow vertical stabilizing rod made of the same aluminum alloy was added to the tricycle to stabilize the 4-bar linkage at the center horizontal bar.  Both the vertical stabilizing rod and the long steering bars are adjustable in length to accommodate the client as he continues to grow.  Finally, mountain bike hand grips were added to the ends of the steering mechanism to provide a larger surface for the rider to push against and stabilize himself by gripping with his hands and fingers.

Because the client has poor range of motion on his right leg, he could not use the right foot to pedal.  We removed that pedal and put a platform in its place to rest his foot.  In addition, the client is not able to effectively use hand brakes, so we connected one end of the brake cable to that platform.  When he presses on the platform, it pulls on the brake cable to activate the cantilever brakes.  This allows the client to brake using his right foot, while pedaling with the left foot.  In addition, the rear gear sprocket was changed to a smaller, free wheel system to allow the bike to move faster and to coast like a standard bicycle. The overall design focused on ease of use, independence, versatility, cost-effectiveness, and aesthetic appeal.

Figure 2 shows the client using the Custom Tricycle. Cost of the commercial tricycle was covered by a donation from NCSSK.  The cost of the parts for the modification of the steering, braking and gearing was approximately $300.

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