Methods of Construction

May 22, 2024

Introduction

Our final design works to prevent the tipping wheelchairs used by Shriners Childrens’ Hospital due to the weight imbalance of the halo traction equipment attached to the back of the device. Our design features a 3D-printed clamp that fits around the bottom frame of a wheelchair that connects to the frame of the wheelchair via screws. The cutout of the hole within the roof and underside of the clamp is ovular, enabling the clamp to fit around varying sizes of steel frames that the wheelchairs may be constructed with. 

The following document will provide instructions to construct and set up our design in a safe and efficient manner. The instructions are divided into the following sections:

• Materials and equipment

• Theory of operation

• Directions for device construction and assembly

These instructions are intended for physicians and medical staff acquainted with the function and setup of halo traction equipment.

Materials and Equipment

Materials List

Equipment

• Cura 3D printer

• Band saw

• Drill press

• Hot glue gun

Theory of Operation

Our final design features a 3D-printed clamp that fits around the bottom frame of a wheelchair. The height adjustment mechanism features a ⅞” Nut and bolt, which is welded onto the top of the steel frame of the 3”-tall rubber caster wheel. The 3D-printed clamp has a horizontal protrusion that houses the bolt, enabling it to move up and down only. The clamp will be connected to the frame of the wheelchair via ¼” screws. The cutout of the hole within the roof and underside of the clamp is ovular. This ovular shape enables the clamp to fit around varying sizes of steel frames that the wheelchairs may be constructed with. Since the radius of the ovular cutout is ~1.5 larger than the radius of standard frames, it will be able to still clamp around the frame, regardless of whether the size is a perfect fit. Our final design can be visualized in Figure 1 and 2 below. 

Figure 1: Complete anti-tip wheel design

Figure 2: 3D printed lamp design with nuts and bolts

When attached to the halo-traction wheelchair, the finalized design should operate in a manner similar to that of a training wheel on a bicycle. Utilizing the adjustable screws on both the clamp and wheel, the wheel should maintain a parallel position to the existing larger wheelchair wheels and sit perfectly on the ground with little to no room for upward or downward movement. In addition, the clamp, which is connected to the silver rods near the rear of the wheelchair, should fit tightly and securely, with little room available for possible movement. This setup is visible in Figure 3 below. 

Figure 3: anti-tip wheel setup

The addition of a smaller support wheel restricts the tipping of the halo-traction device and wheelchair as the weight is more effectively distributed throughout the back of the device through multiple contact points with the floor. 

Directions

Directions for 3D Printing of the Clamp

• Download the CAD from Solidworks in STL file format

• Import the STL file into Cura

• Send the printing information to the Cura 3d printer with infill settings set to 95%

• Wait approximately 50 hours for the print to complete

• Apply a smooth layer of hot glue to the interior of the clamp cutout (approximately ⅛”) as referenced in Figure 4 below

Figure 4: Hot Glue Additions

• WARNING – when using a hot glue gun, be sure to proceed with caution as touching hot glue may result in burns or other injuries

Directions for Setup

Gather all materials and equipment, including the 3D printed clamp onto a solid surface clear of any additional items. 

Wheel/Bolt Assembly

• Take a small section of a ½” polycarbonate sheet and outline the shape of the wheel attachment using permanent marker, as well as the holes on either side of the middle used for attachments. Reference Figure 5 below. 

Figure 5: Wheel Plate Outline

• Using the band saw, cut out the outlined shape as demonstrated in Figure 6 below

Figure 6: Bandsaw

• WARNING – when using the band saw, be careful not to place any bodily parts in proximity to the moving saw. If you are unsure of how to use this device, consult an experienced professional to assist you

• Take this piece and drill a ⅞” hole into the center of the piece using the drill press as referenced in Figure 7 below

• Drill two more ¼” holes into the previously outlined holes as referenced in Figure 7 below

Figure 7: Drill Press

• WARNING – when using the drill press, be careful not to place any bodily parts in proximity to the rotating drill. If you are unsure of how to use this device, consult an experienced professional to assist you

• Insert the ⅞” bolt through the ⅞” hole in the piece

• Place the center of the wheel plate below the bolt head, and align the holes in the plastic plate and the metal plate of the wheels

• Insert one ¼” screw through each of the holes, through the top of the plastic plate, into the metal wheel plate

• Securely tighten one ¼” bold onto each of the screws

Figure 8: Wheel/Bolt Attachment

• WARNING – ensure that the wheel is secure and no movement is possible between the wheel and the ⅞” bolt to prevent possible safety concerns after the installation of the device on the wheelchair

Clamp Attachment

• Thread a ⅞” nut through the ⅞” bolt

• Thread the bottom piece of the 3D printed clamp onto the ⅞” bolt

• Thread another ⅞” nut through the ⅞” bolt, on top of the clamp attachment

Figure 9: Bottom Clamp Attachment

• Place the top piece of the 3D printed clamp on top of the bottom piece

• Insert a ¼” bolt through each of the holes in the clamp through from the top piece through the bottom piece

• Thread a ¼” nut through each of the bolts 

Figure 10: Full Wheel/Clamp Assembly

Directions for Wheelchair Attachment

After the device is properly assembled and all necessary materials gathered, lay out the pieces on a solid surface clear of any additional items, along with the halo-traction wheelchair the device will be installed onto. 

Clamp Attachment

• Separate the two pieces of the 3D printed clamp

• Hold the upper plate in place on top of the rear wheelchair rod closest to the ground

• Fit the bottom piece (has a lip and ovular hole) to the bottom of the rear wheelchair rod closest to the ground so that it is in line with the upper plate

• Thread the head of a ¼” bolt into each hole in the bottom of the clamp, going through the openings in the top of the clamp as well

  • Note: 4 ¼” bolts total should be used

• Thread a ¼” nut through the top of each ¼” bolt until secure

  • Note: 4 ¼” nuts total should be used

• WARNING – ensure that there is little to no excess room available for the possible movement of the clamp along the wheelchair rod. If there is excess room, thread the bolt further through the upper portion of clamp and securely fasten the bolts at the tightest setting possible

Wheel Adjustment

• Adjust the height of the clamp attachment on the ⅞” bolt as needed, until the wheel just touches the ground

• Thread the ⅞” nuts on both the top and bottom of the clamp until they are secure around the clamp attachment

  • WARNING – ensure that the nuts are secure around the lip of the clamp attachment to prevent device failure

Figure 11: Attached Device with Adjusted Wheel