Lower voltage electric screwdriver principle
Electric motors are designed to combine batteries, motors, gears, and switches into an extremely compact and powerful tool. Let's take apart a screwdriver and see what's in it! This is the screwdriver we are going to disassemble today:When you take off the outer cover, you will find that all the basic components of the screwdriver are in a straight line extending from one end to the other. You will see:A rechargeable battery, a switch, an electric motor, a double planetary gear system, a simple chuck locking device, the chuck itself, which holds the screwdriver
The contact of the motor is in the middle of the gap of the switch contact. When the switch is in neutral position, the motor contacts do not touch anything. In this picture, the position of the motor contact is indicated in square green:When the user presses the switch to the side, the current flows from the battery to the motor contact. In this picture, the direction of the current is indicated by a red arrow:Electric motorThe electric motor here is a standard DC motor. See the motor works to see the actual internal structure of the electric motor. The top of the motor is fitted with a small 8 gear. This gear is fixed at the center of the planetary gear system, as shown in the following figure:The gear system is the core of all electric screwdrivers. The electric motor itself is a rather weak device. You can easily hold the rotating shaft of it and stop it turning. But if you apply the gear system to the electric motor, it will have enough power to screw the screws effortlessly into the board. The reduction ratio of the double planetary gear system of the electric screwdriver is 68:1. At this reduction ratio, the motor rotates 1 turns at 68 rpm. This means that the speed of the chuck is much slower than that of the motor, but the torque of the chuck is very large (because the force of the gear ratio is 68 times as much as that required for the motor to stop spinning). The gear system actually has two layers, and you can only see one of the second gears in the figure below:When the motor rotates 8.25 times, the top of the gear system turns a circle. The second layer is exactly the same, that is, the top of the gear system turns 8.25 turns each time, and the second layer turns a circle. That makes the total gear tooth ratio about 68:1.
One trick of this screwdriver is that the manufacturer uses a design that reduces production costs. There are no screws or connectors in the lid - all parts are fixed in place by casting the notches or bumps on the lid. When you take the parts out of the lid, they come apart naturally because there is practically nothing to fix them together:Switch blockThe switch block has three functions in this screwdriver: it prevents the current from flowing into the motor at the center position. It can provide any polarity current to the motor, so that the motor can rotate in two directions. The bottom of the switch is provided with a charging contact, so the switch block also provides a charging power source for the battery.
