The foregoing
When I participated in an electronics competition in school, I solved the topic related to stepper motors. I was full of confidence when I was doing it, but in the end I got a three-point saving and a shameful one-P. After the competition, there were a lot of unused stepper motor kits in the laboratory. I got a piece of kit from the competition and was thinking about using these stepper motors to make up for it. I discussed it with my classmates and decided to make a writing robot.
Structural part
The structure refers to Zhihui Jun’s open source project X-Bot, and the motors are placed in the center instead of on both sides. Advantages: The central placement makes the whole more compact and the wiring is neater. Disadvantages: It needs to drag two motors every time it moves, which is a bit heavy.
Use 3D printing to produce relevant parts, and cooperate with parts such as optical shafts, linear bearings, synchronous wheels, and synchronous belts to achieve movement in the XY axis.
The Z-axis uses a servo and a spring to realize the pen lifting and pen lowering movements.
Hardware parts
Main control: ESP32-WROOM-32D
Motor: 42-type stepper motor
Driver chip: TMC2209 silent driver
Power supply method: 12V power supply (DC05-female socket)
Voltage stabilizing chip: MT2492
Servo: MG90S
Limit: micro switch - with handle - bent foot
software part
Port the 0.9J version of GRBL to ESP32 and add support for servos. Bluetooth wireless communication is implemented on the basis of serial port communication. In this way, you only need to plug in the 12V power cord on the motherboard, and there is no need to connect the serial port line. Developed using vscode+platformio, Arduino platform.
Overall physical picture
The above is the overall structure diagram of the actual object. It was a hot day, so I just put it somewhere where it could be exposed to the sun. As a result, the 3D printed parts were yellowed and the blood was lost. The left and right sides are support brackets, which also have the function of triggering the limit switch. Two non-toothed synchronization wheels are installed on the rear part for transmission, and the front structure is equipped with a servo to realize lifting and placing the pen.
There are two PCB boards between the stepper motor and the 3D printed parts, one is used for heightening, and the other is the main board for wiring. The power supply, main control, limiter, motor interface and so on are all on it.
The self-drawn TMC2209 driver board can be placed just at the bottom of the stepper motor and connected to the motherboard using a PH2.0 cable. The mainboard and servo are connected using FPC cables.
This is the most critical 3D printed part and also the most expensive one. There are linear bearings embedded inside, two each for the X-axis and Y-axis, and there are toothed synchronization wheels on both sides. As you can see from the picture above, the two ends of the timing belt are stuck on both sides of the pen lift structure. Because I often pull it out and squeeze it in during debugging, the whole thing is very loose. I will fix the timing belt later when I have time. It is best to tighten it with screws.
Font drawing effect
Above are the fonts drawn using Micro Engraving Butler, all of which are outline fonts.
This is a single line character drawn using ChiWi.
Shortcomings and improvements
In the entire system, I feel that the pen clip structure on the front side has the greatest impact on the drawing effect. It uses an optical axis and a linear bearing. However, the gap between the optical axis and the linear bearing is too large, and the pen tip can shake up, down, left, and right with just a hand. It very, very, very, very affects the drawing effect. When the force is uneven during drawing, the pen tip will deviate, and the curve that should be closed is not closed. I must change this in the future if I want to correct it.
There is also the problem of the tightness of the synchronous belt. After working for a period of time, the synchronous belt will feel loose. The two ends of the synchronous belt are clamped to both sides of the pen-lifting structure. Over time, it will become loose. If the clamp is not tight, it must be changed. Use screws or other means to tighten it instead.
There is another problem. The whole thing will be top-heavy. If the pen-clip structure extends far away, because the pen is relatively heavy, the whole part of the pen-lifting part will tilt downward. Sometimes it is in the pen-lifting state, but The tip of the pen touched the paper, so I had to raise the pen again.
I feel that this kind of structure can be made small, but not suitable if it is large. If it is really big, it is better to use aluminum, which is strong and stable.
Conclusion
This project is suitable for personal DIY learning, studying GRBL algorithm, learning PCB drawing, etc. If you want to make one that can be used for taking notes, I suggest you get one from Big Fish at Station B. Other people’s ones are very stable. I’ll use this one as a toy.
If you use the serial port, you need to connect it through the pin header reserved on the motherboard. There is no silk screen on it. You can see the PCB file. To use Bluetooth, the computer needs to first connect and pair the Bluetooth slave of the ESP32 (name: Writing_robot). After the connection, the computer will have several more ports, and you can use one of them to achieve Bluetooth communication with the ESP32.
The schematic diagram and PCB drawn with AD will be uploaded to the attachment below. The source code will also be uploaded, but the writing is very rubbish, just take a look.
I originally recorded a video, but found out that I can only upload 50M in size, which is enough for what I'm doing, that's all.
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