Group 9: Adaptive Trike

Abstract

To design a three-wheeled tricycle that meets the child’s needs and the family’s lifestyle.

Chris Dwyer, Jake Sparks, Jonathon Carpenter, Colton Jernigan

Problem Statement

The problem we are facing is to design an adaptive three-wheeled stroller that is well suited to the family’s needs. The first design aspect we have to consider is being able to have the stroller built for a child from years 1 and 2 all the way through early teenage years. The next aspect we have to consider is being able to have it adaptable to make sure it can handle sidewalks, trails, gravel, sand, and any other possible terrains. The biggest thing we are keeping in mind as we design and build this stroller is having it big enough to be well suited for the child and extra luggage, while also being small enough to fit in the van.

Design Specifications

Requirements

A three-wheeled stroller that is able to suit a young child for many years.
Has the ability to go on multiple terrain types.
Easy to use for one person.
Fit in the back of a van.
Belt/Harness to hold the child in the stroller.

Desires

Cupholder
Phone Holder
Miscellaneous Storage Tray
Bottom Compartment for bigger items.

Background Research

Identify existing tech that could meet, at least in part, some of the need, or inspires ideas.

Concept Design 1

Concept 1 focuses on the two options we have to make sure the three-wheeled stroller is able to be user-friendly and adaptable to the many different terrains the family may come across.

Concept Design 2

Concept 2 focuses on the different approaches to the front wheel and if we want it to be able to lock forward or not.

Concept Design 3

Concept 3 focuses on an overview of the things we want to implement into the stroller to make sure the family is able to take care of their child along with being able to bring along anything they may need and enjoy using the stroller.

Overview of Selected Design

Front Wheel

The current front wheel is a Carlisle tire on a steel wheel, which is wide enough for the application, but at 4 pounds just for the tire it is too heavy to be used on this stroller. We are currently waiting to hear back from Vipamat about dimensions for their wide stroller wheel so that we can load it into the drawing and adjust the frame for it.

Tube Size

We chose 1.5” OD 6061-T6 aluminum tubing for this project because of the strength and versatility of the material.

Rear Axle and Wheels

For the rear wheels, a 16” bicycle trailer wheel with a 3” tall and wide off-road tire was chosen because of the size and the wide contact patch of that size bicycle tire.
To make them work on a straight axle, we have chosen to make spindles out of 4140 steel alloy that would take place of half of the wheel’s existing hub, and would use the other half of the wheel’s hub and have a locking nut on the outside.

The 4140 steel alloy was chosen because of the strength of the material considering the small size of the shaft. These wheels are normally supported on each side, so something was needed that could support it being cantilevered out while supporting the weight of the stroller and child.

The center part of the shaft that the spindles screw into is another 6061-T6 aluminum tube, supported by custom made aluminum clamp blocks that clamp to the main frame.

Arm Rests and Hinges

The hinge pieces would be cut out of aluminum plate and then welded to the upper and lower frames. To lock the hinge in the open or closed position, a locking pin will be used.
The arm rest support pieces will also be cut out of aluminum plate. The main part of the arm rest will be CNC machined out of Delrin black plastic.

Floorpan

The floorpan will be made out of cut, bent, and welded sheet metal, and then welded to the bottom of the stroller. It also acts as a splash guard for the front wheel, and possible storage under the seat.

Seat

The seat will be made out of a heavy cloth material, such as canvas, that will be able to withstand many outdoor environments, hold up to years of use, and be washable.

Describe Design Details

This design is a stroller that will have the capability to go on and off road in multiple terrains with relative ease. It has large rear tires that can be aired down for sand or mud, and a front ski attachment for sand or snow.
The stroller folds in half to allow for easier storage, and the rear wheels come off with the push of a button to make it narrower or to service the wheels.
It has a 5-point harness to make sure the rider stays strapped in safely at all times during use.
It also has removable storage in the form of a basket and bag hanging off the back, and a cupholder on the side.
The rear axle can also be moved forward or backward to make adjustments for the center of gravity when the rider is onboard.

Engineering Analysis 1

Engineering Analysis 1: Distribution of forces on the wheels and frame of the chair. Assumed worst case scenario; that is maximum (assumed) weight of the child is applied at the absolute center of the frame. The lower to supports of the frame will bear majority of the weight. Therefore, Analysis was done as though those were the only supports. This analysis will help up find an ideal material that is strong enough to support the weight.

Bill of Materials

DOM-Bill-of-Materials_0.xlsx

Document Fabrication Process

Frame

One of the tubes was taken to a local shop to be tested for bending. It was found that bending would not work for our application, so we cut the tubes into pieces and sent them out to be welded together to create the upper and lower frames.
We welded in an extra crossmember in the upper frame for the harness.
Once all the welding was completed, we powdercoated the frame for styling and longevity.

Tabs/Hinge Plates/Arm Rest Supports

These pieces were plasma cut out of 1/8″ aluminum sheet, then cleaned up and had holes drilled in them, and were welded to the frame if necessary. They were powdercoated as well.

Arm Rests

These were cut and milled out of Delrin plastic.

Rear Axle

Instead of fabricating a custom axle with spindles, we got a pre-made axle with attaching wheels that only required slight modification of the axle and the clamp blocks.

Seat

We sewed together a “hammock-style” seat around the lower frame, same for the back of the seat on the upper frame, and wrapped the material around the padding for the upper and lower so that nothing falls in between the upper and lower portions.

Front Wheel

A small wheel was found for the front wheel with a bar going through it to use as an axle.

Ski for Front Wheel

A “cup” was 3D printed for the front wheel to sit in. It is mounted to a skateboard with no wheels using carriage bolts, and a strap across the top of the wheel.