Team was tasked to convert a hand powered wheelchair with off-road capabilities to an electric one with a bolt on kit that would not make major permanent changes to the chair. The schematics for the electrical and mechanical were done, but the project was not finished due to shipping delays for parts. Also we had to reinforce certain components to ensure reliability off-road which was completed.
Child has spinal bifida and parents want an all terrain vehicle that functions as both a wheel chair and an arm powered rowing system. This project was started in Spring of 2021 and mostly completed during the summer semester of 2021. Upon receiving this project in Spring of 2022 we decided that the bike would need seats and a new front caster wheel added. For the seats we determined that all we needed would be some padding and covering as the previous group had hard cutouts already made. To strengthen the front caster we decided that a complete new wheel as well as attachment method would be required. After we delivered the chair to the family, they told us they wanted to add electric motor controls to the chair to add more versatility to it.
The chair needs to be ADA compliant. It needs to be light enough for one person to load into a truck. The family requested that the electric system be a bolt on modification that can be reverted at anytime.
Since we inherited a previous project, most of our research was done by meeting with the previous designer of the chair to see what state the project was in and what the family wanted out of the project. We also thought about how waterproof robots are made, specifically the one in the Mechatronics lab and one that one of our team members had built for a previous competition.
Design one takes on the approach of modifying the current chair already assembled. The design has a waterproof box that would sit on top of the rear axle to keep the center of gravity in a manageable location. The box would house all of the electronic components required to electrify the chair. We would control the motors by a joystick on a plate mounted to one of the side purple plates. It would have all 4 degrees of motion coded with the motors via an Arduino. For braking, the best method would probably to put a disk and caliper between the gear and tires that is connected to a handbrake attached the joystick via a cable.
Design two takes on the approach of producing a new bike based on the current chair design with some quality of life improvements. First of all, the chair would now be powered by electric motors that control the speed and steering of the chair and would allow for reversible motion which the current chair lacks. This would be controlled by a joystick connected to the armrests of the chair. The chair also uses a disk brake system between the driving gear and rear tires of the chair in order so he can slow down the chair if need be. The seat has been made more easily adjustable with telescoping tubing to change back height instead of loosening and tightening four bolts. It also contains armrests and a much-needed safety strap that the current chair does not contain.
This design works on the principle of modifying the current chair. Using the framework from before we can add a insulated box that houses all electronics under the seat. The drive system would work on a 12 volt system using brushless motors, a 64:1 gear reduction, and a top speed of around 5 mph. This would mean there is plenty of torque available, but not so much that we’ll risk flipping the chair. This design leaves room to relocate the ratcheting system from the rear axle to the front. This would allow for forward and backward movement while using electric power, but still having brakes on the handles during manual power mode. The drive motor would be attached to an adjustable arm to allow the motor to be a tensioner, but when manual power is wanted it can be adjusted out of the way and add a static tensioner to the chain.
The third design was the one that we selected. It had accessibility and simplicity of use in mind. It used U-bolts and angle iron to attach the box to the chair and support the weight of the motors and batteries. The first design was similar, but missed crucial details as to how it worked, and the second design was not what the user wanted, but was another possibility though.
The concept design that we decided to go with was design number three. It aligned more with the wants and needs of the user, and had the ability to be installed easily, quickly, and by one person. It allowed room for the required electrical and mechanical components.
A joystick will be mounted on the arm rest and be accessible for the child so that it will be movable to the push arm handle for parents to control. The Inputs will then be run Arduino which will in turn send the information to the Motor controllers telling the motors what to do then will have the motor running into a gearbox then to the output shaft. All of this with the exception of the joystick and the driveshaft will be in a waterproof box mounted under the seat and around the support arm.
For the first engineering analysis, we ran calculations for the motor requirements and the circuit design. We used a formula to find the torque we would need from each motor with the 24inch tires on the chair. We then took that value to find motors and a gear box. We then found motor controllers and started to find batteries that could run the motors for an extended period of time.
Our project originally had two fabrication processes. The first was to strengthen and replace weakened parts. This included getting a new front caster that could hold the weight, and take a hit. Then making plates to weld to the chair frame to attach the caster to, and finally repainting the front of the chair where the new plates had been attached. The second fabrication stage was supposed to be converting from mechanical to electrical power, but due to shipping delays we were unable to complete this stage.
The project had a successful first fabrication process and design stage, but due to delays in shipping the second fabrication process was unable to be completed. If the project is revived in the future contact Nathen at email@example.com for the electrical side and Bradley at firstname.lastname@example.org for the schematics.