Freestanding Motorized Swing for Child up to Fifty Pounds

Designers: Amy Congdon and Jessica Foley
Client Coordinators: Linn Wakeford, Frank Porter Graham Childhood Development Center
Supervising Professor: Dr. Larry N. Bohs

Our client is a four-year-old boy with Cerebral Palsy. He has limited vision and mobility and is adult dependent. He enjoys motion, especially swinging. The goal of this project was to provide our client with a swing he can control himself. We designed and constructed a motorized swing that our client controls with a switch. This freestanding swing safely swings a child up to fifty pounds in weight, and provides appropriate support for our client as he swings.

How this project helped
Most of our client’s day-to-day activities require that he depend on adults. There are very few things that he can do on his own. His limitations in play behavior make it difficult for his parents and therapists to create play opportunities for him that are both enjoyable and allow him to develop independence. Linn Wakeford, our client’s occupational therapist, believes that “the swing will offer him the opportunity not only to do something he really likes, but also to control that activity to some extent. He can rely more on his own desire to engage, rather than on an adult’s desire that he play with something.” She added that the swing “really will enhance his quality of life.”

The overall swing is pictured in Figure 1. It includes the swing frame, seat, drive mechanism, motor speed control and power supply. The swing drive mechanism is shown in Figure 2. A drive plate (1) is attached to the motor (3). A drive pin, surrounded by a cylindrical bearing and mounted on the drive plate, rides in a channel of the swing drive arm (2). As the motor spins the drive plate, the drive pin causes the drive arm to move in an oscillatory manner about a crossbar (4). The drive arm is rigidly attached to the swing arms (6), which freely rotate about the crossbar.

The swing seat attaches to the swing arms with four ropes, which decouple the drive mechanism from the swing pendulum sufficiently to allow the swing to start from rest without a push. Horizontal cross-supports are added to the base of the swing frame, which was purchased commercially (Sammons Preston), for added stability. The frame is further stabilized by filling the lower legs and these cross-supports with sand. The motor mechanism is mounted with a custom plate and six ¼” bolts to the crossbar at the top of the frame.

The motor is a 12V DC, 37 RPM, 1/5 HP gearmotor. A pulse-width modulated speed controller is mounted in a control box, and adjusted to match the motor speed to the natural frequency of the swing pendulum. 12V DC is provided with a computer power supply, mounted next to the control box on the swing frame. A relay in the control box allows an external switch with a 1/8” plug to actuate the swing. A bypass plug allows the swing to be used without the external switch.

Materials for the swing cost approximately $950.00; machining costs were approximately $600.

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