Steven Georges, Joval Shamsoum, and Michael Carter
For drivers with minimal or no leg function, operating automatic transmission vehicles is their only practical option. This is due primarily to limited or no availability of adaptive driving equipment for a manual transmission vehicle. The goal of this project was to design a system that operates the clutch of a manual transmission car with the hand rather than the foot. In this design, the clutch pedal is connected to two servo motors, which are controlled by a finger trigger. Our auto clutch system is called Automated Clutch Control System (ACCS). The inspiration for this project came from one of the authors, Steve Georges, who has cerebral palsy and saw the need for this type of vehicle operational system.
For many years, driving aids have been on the market for persons with reduced leg function. One of the most common driving aids is hand controls. This is a device that operates the gas and brake of a car using the driver’s hand rather than the foot. It is mounted under the steering column and is directly connected to the gas and brake pedals. Located under the steering wheel is a bar that is connected to the hand control that the user moves in two different directions to push the gas and brake pedals. Common methods are to push to brake and pull down to accelerate or vice versa. This system is normally operated by the left hand, while the right hand controls the steering through the use of a steering knob on the steering wheel. Since this type of hand control system has only two functions, operating the gas pedal and the brake pedal, it works only on vehicles with an automatic transmission.
A solution may seem to be the semi-automatic transmission, which is a manual transmission that does have a clutch, but one in which the driver is not required to operate in a traditional fashion. The clutch is controlled by a computer via electronics, pneumatics, and/or hydraulics, and the driver has the option to use hand paddles behind the steering wheel to change gears if they desire. Although current hand control systems can be adapted to semi-automatic transmissions, the catch is these systems are extremely expensive and are found only in newer high performance sport and luxury cars.
When selecting a car, drivers who do not require hand controls have the choice between driving either one of two options: an automatic or manual transmission vehicle. For drivers who require hand controls, however, the only current option is a vehicle with an automatic transmission, due primarily to current adaptive diving equipment availability. While most of these drivers are satisfied with operating an automatic vehicle, the driving enthusiast, who desires total gear-change control in a vehicle, is not.
The problem our design project focused on was that drivers with reduced leg function, who require hand control modifications on their vehicles in order to drive them, are limited to driving automatic transmission vehicles. Not every person requiring hand controls has hundreds of thousands of dollars to spend on a car with the hand-control adaptable, semi-automatic transmission if they want more precise control of the transmission. Another factor to consider is the situation in which a person may suddenly lose leg function in one or both of the legs due to an accident or medical condition. Some of these drivers may already operate a manual transmission car and suddenly cannot drive it any longer due to limited driving adaptive equipment on the market today for manual transmission cars. There is a system on the market today that can automatically actuate the clutch pedal, but this system is meant for a driver with one functional leg and is extremely expensive. For these reasons, there is a need for adaptive hand controls for a manual transmission car.
We acquired a manual transmission vehicle that would be inexpensive and easy to equip with our system. The car is a 1993 Honda Civic hatchback. The car was fitted with a normal set of hand controls, this type is push to brake and pull down to accelerate. To allow the necessary clearance for the hand controls, an aftermarket steering wheel was installed. The gear shift lever was extended up twelve inches and angled towards the driver and the steering wheel to allow the driver to have a better grip. A short shift linkage was installed to compensate for the extra length of the shift leaver.
The two servos used were Hitec HS-M7990TH mega torque high-voltage magnetic encoder servos (Figure 1). They were selected because of their high torque output (611 oz./in. or 44 kg./cm.), as well as their strong titanium gears. These servos have eight O rings on each servo to prevent dirt and water particles from contacting internal components. This type of servo is programmable, enabling the user to set the end points. The servos also feature integrated heat sinks to dissipate heat though continuous operation.
The first step was to design and make the mechanical components and hardware. All the components were made by hand on a mill. The entire clutch pedal assembly was removed from the vehicle, and a template was made of the assembly. This template was used to make a main bracket that would house the two servos used operate the clutch pedal. The main bracket was positioned above the clutch pedal. On the main bracket, the two servos sit parallel to one another. They have U brackets to secure the servos to the main bracket. Each servo has an arm that rotates about 90 degrees. These arms are attached to a connecting rod that is also connected to the clutch pedal. Figure 2 shows the finished assembly. As the servos activate, the arms move the connecting rod which then depresses the clutch. Figure 3 helps to illustrate how the system operates.
The next step was to design a wiring harness for the system. The power wire is connected directly to the battery of the car. This wire has a fuse built in to protect the system if there is an electrical short. The power wire is routed through the driver’s side of the firewall and is connected to a main power switch with a light on it. The switch is mounted on the dashboard. After the switch is a voltage regulator. This regulator takes the car’s normal output of 12-14 volts and drops it down to 8 volts and allows up to 40 amps of current to go to the servos.
From the regulator, two groups of wires split off: they go to the servo controller and the servos. The servo controller is mounted on the dashboard and generates the control signal that goes to the servos. Connected to the controller is a finger trigger that is mounted to the hand controls (Figure 4). The finger trigger is made from a modified Xbox 360 controller. The finger trigger is set up so that it is in a direct one-to-one ratio with the clutch pedal for movement and speed. If the trigger is fully depressed, the clutch pedal is as well. If the trigger is depressed halfway, the clutch pedal is also. If the trigger is pulled or released at a given speed, the pedal follows.
Once all the components were assembled and installed in the car, the servos were then tuned. The whole assembly must be in the car to tune because the clutch pedal must be connected to the hydraulic line of the transmission in order to locate the precise clutch engagement point. The servo control box is hooked up to a computer and a servo tuning program from Hitec. Two points for each of the servos are set: a rest and end point.
Our goal was met, and our team successfully built a system to control the clutch pedal of a manual transmission car with only the use of the driver’s hands (Figure 5). It does not take much effort to learn how to operate this system but practice is needed. The prototype was tested in a large parking lot with minimal to no other cars. In this parking lot, team member Steve Georges was first taught how to drive a manual transmission car by team member Joval Shamsoum. After stalling the car two times, Steve successfully got the car moving on the third try. Using the Automated Clutch Control System, he learned how to shift through the gears properly using the hand controls. Once diving in the parking lot was mastered, driving was then conducted on back roads and then on main roads as well.
After fine-tuning the servos, the operation of the ACCS works as designed. In evaluating our project, it has met and exceeded our expectations. The system gives the user precise and smooth control of the clutch pedal.
Tuning the system to get the servo arms in parallel rest and end positions was difficult and took a lot of time. If they were off by a millimeter, the servos would fight each other and not allow the system to function properly. In depth research was done by the team prior to starting this project to ensure the reliably and performance, which paid off in the end. Special attention was given to the design of the brackets, so that they do not flex or fail from applied force.
The ACCS is the solution to the need of a device that allows a driver to control a manual transmission car with just his or her hands. It is recommended that the driver receive some training with the ACCS before operating the vehicle on the roads.
Consumer feedback is important for any prototype. The ACCS is currently being used by team member Steven Georges in his manual transmission car, and he is pleased with its design and happy that he finally is able to drive a manual transmission car.
Servo controller: $40
Finger trigger unit: $12
Aftermarket steering wheel: $100
Shift knob and boot: $21
Hand controls: $1050
Wiring and other electrical components: $67
Recycled scrap metal for brackets: free
Whole project Total: $3930
ACCS system total: $459
There are a couple of things that could have been done differently to improve this project. Instead of two small servos, one large servo would have made the system easier to set up and tune the rest and end point. Designing the brackets and connecting rods on a computer program such as solid works and then making them on a computer operated mill would have saved a lot of time and would have made the parts fit a lot better. Plans are coming together to make upgrades to the system such as one larger servo and more precisely designed brackets.
We would like to thank our project advisor, Dr. Ma-moun Abu-Ayyad, Assistant Professor of Mechanical Engineering, and Mr. Bill Moody, Engineering Lab Supervisor.
50 Cranfield Court
Elizabethtown, PA 17022