I Introduction
In order to learn more about the electric screwdriver we had to dissemble the parts to show is the different systems inside. The reverse engineering experiment was performed to allow us as future engineers to see the mechanical and electrical systems and how they are used together to accomplish a given task.
II Mechanical System
A. Gearing System
The gearing system in screwdriver changes a high-speed low torque 3.6-volt electric motor into a 180-RPM High Torque output. The combination of gears and gear holders increases torque at the cost of reducing speed. This is called a tradeoff, the torque must be powerful enough to drive the screws into wood but not too fast. The torque should not be so powerful it breaks your arm when you use it to drive in a screw.
The gear assembly works as follows: (From chuck to motor)
Chuck fits into an internal lubricated needle bearing assembly. Internal bearing serves as a chuck carrier. Exterior bearing serves as a planetary gear carrier.
Needle bearings serve as an automatic locking mechanism by holding the chuck in place by locking against the top edge of the arc of the chuck when torque is initiated from the chuck end of the assembly. The sun gear for the first planet gear is attached to a planet carrier for a second set of planet gears. The sun gear for the second system of planet gears is the rotary gear of the motor.
B. Operation of Automatic Lock
The automatic lock mechanism works by reversing the direction of thrust. When a turning force is placed into the gear mechanism. The chuck is held in position by needle bearings and when the motor drives the chuck they are held in position and rotate with the chuck assembly. When the torque comes from the chuck end of the gear assembly the bearings are pushed up against the arc of the chuck housing. The arc of the chuck holds the bearing from turning and locks the chuck against the housing.
C. Switching Mechanism
The switching mechanism works by making a DPDT Switch using the motor contacts as the outputs of the switch and two eighteen gauge wires as the input. The rotating of the assembly changes the positive and negative terminals on the motor. When the Orange button is pressed the circuit is closed allowing the motor to operate.
III. Electrical System
A. Wiring Battery, Motor
The wires are all eighteen gauge they are all rated for three hundred volts and ninety degrees Celsius. The three batteries are all Nickel Cadmium rechargeable with a power rating of 1.2 volts. They are connected in series for a total power rating of 3.6 volts. The motor is a 3.6-Volt DC motor that reverses the drive-shaft by reversing direction. The manufactures is (Johnson?)
B. Charging System
The charging system consists of an AC adapter that lowers the voltage to charge the battery. The docking station outputs an AC current to the screwdriver. The screwdriver changes the AC to a positive pulse with a rate of 60 times a second to charge the battery by placing a diode across the charging terminal and the positive battery terminal. This diode makes a basic rectifier to provide the DC necessary to charge the battery pack. The diode also prevents accidental discharge if any metal objects should happen to short out the metal charging contacts.
(
geocities.com/yosemite/trails) (
geocities.com/yosemite)