This post was last edited by yang_alex on 2023-5-14 10:02
I had received a portable electric drill for the event before, and I took the time to analyze it thoroughly before I started preparing to hand in the assignment.
First, take a look at the overall picture of the portable hand drill:
It looked fine. But after a closer look, I found that the electric drill's three-jaw chuck was rusted, and I couldn't get it open after using WD40 to remove the rust for five or six days.
The nameplate on the drill is very clear. From this, we can know that this is a 12V dual-speed drill that supports 10~32mm drill bits.
Just above the drill is a dual-speed switch for low and high speed:
The black one that looks like a pistol trigger is the speed switch. There are three battery indicator lights next to it. The black button with two triangular arrows next to it is the forward and reverse switch. Turn it to the left for forward rotation (clockwise rotation), turn it to the right for reverse rotation (counterclockwise rotation), and turn it to the middle for safety to prevent accidental start.
Remove the battery pack by pressing the tabs on both sides of the drill handle.
From the nameplate of the battery pack, we can see that the battery pack is 10.8V 1.5Ah.
Inside the battery pack. It's too simple, there's no over-discharge or over-charge protection. The batteries are simply connected in series, and the charge and discharge contacts are connected (using an external charger). It can't even charge evenly. No wonder one of the batteries is starved to death (over-discharge damage, can't be charged, and the voltage is always 0V).
The battery pack is made up of three 3.6V lithium batteries connected in series. The corresponding voltage is 10.8V1.5Ah.
Then remove the buckle inside the handle shell to disassemble the electric drill handle. The electric drill is relatively easy to disassemble, with a total of a few screws, which can be opened after removal.
Now you can see the inside of the drill. There is already a lot of debris mixed in.
Take out the movement. From left to right, there are the motor, reduction gear set, and chuck. Closely below the reduction gear set is the lighting and speed indicator panel, in the middle is the speed control switch, and at the bottom is the plug for the battery pack.
Here is a close-up of the speed control switch. Front: You can see that it supports 7.2~24V 5~15A DC speed control.
Reverse side: The aluminum plate fixed with screws is the heat sink for the speed regulating MOSFET.
The speed control switch is disassembled as shown below. The white plastic part on the top is the forward and reverse switching mechanism. Through different channels (as can be seen in the picture below taken from top to bottom), the mechanical contacts (upper left part of the picture) are pushed to cross-switch the positive and negative poles of the regulated DC power to achieve forward and reverse rotation.
Looking from top to bottom, there are two grooves, corresponding to forward and reverse rotation. When stopped in the middle, the speed control switch is prevented from being pressed to prevent accidental triggering.
Take out the circuit board of the reverse speed control switch, and you can see the mechanical structure behind it. It mainly consists of two groups of contact switches, the upper group is the power on-off switch, and the lower group is the speed control group switch. Through different positions, resistors of different resistance values are connected to achieve speed control. The circuit board corresponds to the PCB contacts. I have to sigh that in the era when electronic technology was not developed, the mechanical structure design was ingenious! Now with the development of electronic technology, many of these ingenious mechanical structures have been replaced by electronic circuits (including the forward and reverse mechanical structure mentioned above).
The front of the speed control switch circuit board was originally thought to be a common universal 555 DC speed control circuit, but it is not. In fact, it is a special circuit commonly used in electric drill speed control.
I searched for a long time to find the circuit diagram (I am a bit lazy, I didn't draw the schematic diagram myself). I added a chip manual, and interested netizens can take a closer look.
GS069.pdf
(242.93 KB, downloads: 1)
The lighting and speed indicator circuit of the electric drill. The lighting is the larger white LED on the top, which starts to illuminate when a certain voltage is reached. The three red, yellow, and green LEDs on the right indicate different speeds through a voltage comparator made of two TL431 (this chip can be used in many ways!) (yes, the higher the voltage, the faster the speed, simple and crude. 
)
My own schematic:
Because I used violent disassembly methods when disassembling it (mainly because the things were too bad and had no use value. ), I will not restore it here (the actual reason is that my craftsmanship is too poor and it cannot be restored. 
).
This concludes the disassembly.
Now with the development of electronic technology, many mechanical structures have been replaced by electronic circuits, such as the commutation structure of the motor. The original (including the disassembled one) was a brushed DC motor, which used the brush as a mechanical structure to achieve continuous rotation of the motor, and the external electrode commutation structure mentioned above to convert the positive and negative electrodes of the motor, thereby achieving forward and reverse rotation of the motor. Today's brushless DC motors use power semiconductor devices in the circuit to achieve motor drive and commutation, which is much simpler (in fact, the responsible work is integrated or completed by software.), and the life and performance are enhanced.
Additional content (2023-5-14 10:11): The low-speed and high-speed dual-speed gear switch is connected to the reduction gear set directly above the electric drill. The low-speed and high-speed are switched through the mechanical structure. The development of electronic technology now enables electronic stepless speed regulation.
提升卡
变色卡
千斤顶
京公网安备 11010802033920号
