Figure 1: All Terrain Power Chair
Abstract
Power chairs provide important advantages to elderly and handicapped people, especially those who are not ambulatory. There are thousands of indoor and outdoor power chairs on the market that are manufactured with state-of-the-art electronics and battery technologies. However, there currently are no power chairs available that are capable of performing indoors, outdoors, and posses the ability to function in rough off road terrains.
The product has been designed, built, and tested to be capable of climbing a thirty percent grade, maneuver seamlessly though a common doorway, climb a standard curb, and maintain at least six inches of ground clearance while providing a top speed of seven miles per hour.
The All Terrain Power Chair is driven by tracks thereby replacing the wheels on traditional wheel chairs, consequently increasing its stability and traction on all terrains. The device is controlled electrically with a user-controlled joystick, as well as a wireless enable option. The unit is also furnished with twin twelve-volt batteries connected in series, which power two DC electric gear reduction motors as well as a linear actuator used for seat adjustment.
Figure 2: All Terrain Power Chair Final Prototype
Background
Unlike manual wheelchairs, power chairs do not require physical strength to move, and they provide a wide variety of additional perks for those who struggle to get around on their own.
The purpose of a power chair is to significantly improve a person’s independence and quality of life. They are made to increase independence both within and outside the home, while still easy to use.
There are thousands of power chairs on the market with state-of-the-art electronics and battery technologies. However, there currently are no power chairs available that are capable of performing indoors, outdoors, and posses the ability to function in rough off road terrains which still compact in width.
Project Description
The purpose of the device is to enable mobility impaired consumers. The device will transport the user while traversing various terrains.
More importantly, the device will be designed to easily climb a standard curb, travel seamlessly though a common doorway and keep the device weight low.
Design Description
Unit Features
The All Terrain Power Chair (ATPC) will substitute the traditional wheelchair wheels with a track design, to increase stability and traction on all terrains.
The device is controlled electrically with a user-controlled joystick, and also offers a wireless option. The unit is also furnished with twin twelve-volt batteries connected in series, which power two DC electric gear reduction motors as well as a linear actuator used for seat adjustment.
Safety Features
The safety features incorporated within this device, include a hip belt as well as some possible lower body positioning, such as a calf belt, as lower body positioning affects the position of the pelvis, balance, and freedom of movement of the upper body.
Design Specifications and Constraints
Specifications
A standard size seat is controlled with an electronic linear actuator; an accessible flip up footrest is also attached to the track assembly frame.
The ATPC will be constructed to climb a 30 percent grade, maneuver through a common doorway, climb a standard curb, maintain at least 6 inches of ground clearance while providing a variable top speed of 7 miles per hour.
Constraints
The constraints associated with the All Terrain Power Chair design are composed of:
- Transporting a passenger of weight up to 300 pounds.
- Suitable to fit thought a standard 36 inch door way.
- Able to climb up a standard curb.
- Capable of climbing a thirty percent grade incline.
- Total weight of the device must less than or equal to 300 pounds.
Schematic Diagrams and Physical Models
Control Systems
Figure 3 shows the set up of the All Terrain Power Chair’s control system. This following configuration encompasses both a user controlled joystick and wireless enable option.
Figure 3: Control Systems Wiring Diagram
Providing multiple control options allows the user to adapt the product to their specific situation and need.
Track Information
The modeled track and track drawing can be seen in Figure 4 below.
Figure 4: Motiondynamics™ Track Model
Motiondynamics™ track descriptive information:
180mm (Width) x 72mm (Pitch)x39 (Links)
Circumference= 110.6 inches = 9.2 ft.
Motors
Figure 5: 13:1 Gear Reduction Servo Motor
Testing shows these motors to perform at approximately a quarter horsepower under a theoretical current draw when the motor is stalled.
Sprockets
Figure 6 displays the aluminum sprocket dimensions, designed to perform optimally in the Motiondynamics™ tracks.
Figure 6: Aluminum Sprocket Drawing
Track Assembly
Figures 7 and 8 show the All Terrain Power Chair’s track assembly modeled in ProE®.
Figure 7: Track Frame Assembly Model: Isometric and Top View
Figure 7: Track Assembly Drawing
It can be seen in figure 7 that the overall with of the design is 29″, it should be taken into account that the tracks are not attached in this drawing, but there is still ample space once added to maneuver through a standard 36 inch doorway.
Design Analysis
Seat Frame Design
The seat frame operation design for the All Terrain Power Chair was designed with maximum operator comfort in mind, especially when climbing and descending grades such as a common staircase or a standard curb.
The seat is designed on a linear linkage actuated by a linear actuator; this design consideration will give the operator a significant comfort enhancement when climbing or descending grades as well as when added assistance for semi-ambulatory operations when they need assistance entering and exiting the operator station.
Figure 9: Linear Actuator Configuration
The primary design considerations for the linear actuator that was chosen for this operation include: stroke, length and total cycle time. The actuator within this unit is a twelve-inch stroke, one inch per second with a 1500-pound load capacity. The capacity is larger than necessary, but the stroke and cycle speed are within the design constrain for this application.
Motor Location
The position/location of the motors was compared and evaluated based on a pros and cons list, as well as constraints that have been placed upon the unit.
Figure 10: Motor Placement Pros and Cons
Track Geometry
Numerous designs were considered for the track geometry.
Figure 11: Track Geometry Design Options and Decision Matrix
However, the team had to use the constrains of the actual track when determining the final geometry.
Discussion and Conclusion
The team managed to design, build, and test a device that is capable of transporting a passenger of weight up to 300 pounds, suitable to fit through a standard 36 inch doorway, able to climb a standard curb, and climb a thirty percent grade, while still providing a variable top speed of 7 miles per hour. The device is also easily adaptable for individual user safety needs. Future efforts consist of optimizing battery run time by adding a solar charge panel to the device – allowing for a longer run time between complete charges. The team would also like to see an independent suspension incorporated in the design, allowing the tracks to move independently of each other. Another future effort consists of custom designing the tracks. this would allow for more geometry design options as well as reducing the size of the model, but also the weight. Overall, the All Terrain Power Chair is capable of performing indoors, outdoors, and posses the ability to function in various off road terrains while still maintaining a compact width.
Acknowledgments
This project would not have been possible without funding from Geller Automotive (Minneapolis, MN), flow jetting from Industrial Machine & Engineering (Brookings, SD), powder coating from Twin City Fan (Brookings, SD), and donated tracks from Motion Dynamics (Newburgh, IN). The team would like to extend a thanks to Mr. Harvey Svec, Mr. Douglas Peters, and Dr. Kurt Bassett for their endless support and guidance.