TECHNICAL SUPPORT
Published 2026-03-13
When we engage in product innovation, we often need to make some small parts move, such as making a smart car, a robotic arm, or adding aservocontrol to a model. At this time, the selection and 3D modeling of the steering gear became the number one problem. Especially for the most common microservolike Tower Pro MicroservoSG90, how to accurately "draw" it in CAD software and ensure that the designed shell and bracket can be installed tightly has become the first hurdle we must overcome.
When you get an SG90 servo, you may subconsciously think that if you just measure it with a ruler, everything will be fine. However, when you actually start to measure it, you will find that the way is not that simple. If there is only a slight deviation in the height of the holes on the steering gear ears and the shaft, the printed parts will not be able to be installed smoothly. Therefore, when measuring, the first step is to use a vernier caliper, which is the most basic tool for measurement. It is necessary to focus on measuring several key positions, such as the length, width, and height of the fuselage, the thickness and hole diameter of the mounting ears, and the height and diameter of the output shaft. Remember, when measuring, you must measure several points and take the average. This is because there are tolerances in the plastic parts themselves. Never measure it just once. If there is even a difference of 0.2 mm, you may need to use a file to deal with it after you get it.
Measuring these critical dimensions of the servo is an important step in ensuring subsequent parts fit. The length, width and height of the fuselage determine the space it occupies in the overall structure. The thickness and hole diameter of the mounting ears directly affect whether it can be accurately connected with other components. The height and diameter of the output shaft are also related to the smoothness of power transmission and connection. It’s these seemingly small size differences that can cause problems throughout the assembly process. Therefore, accurate measurement and averaging are the keys to reducing errors and ensuring perfect fit between the servo and printed parts. If a dimensional deviation occurs due to a measurement error, using files and other tools to correct it will not only increase the workload, but may also affect the accuracy of the part and the overall stability.
The easiest way is of course to download ready-made models online. However, the quality of the models online varies, many are drawn by enthusiasts, and the sizes may not be accurate. My first choice is usually to search for "SG90" on a professional model website like this to see the download volume and user reviews of the model. The one with the higher download volume is usually more reliable. In addition, you can also go to the official website of the servo brand, such as the official website of Tower Pro. Some manufacturers will provide official CAD models. This is like buying Lego. It is easier to put together using the original factory drawings than using knock-off ones, and it can save you a lot of time in later modifications.
If you can't find a suitable ready-made model, or if you want to have complete control over the design, you have to do the modeling yourself. In fact, the structure of SG90 is not complicated, it is just a cuboid plus a few cylinders. In CAD software, you can first extrude the main part of the fuselage, then draw the shape of the ears and extrude them. Next, create a cylinder on the ear and perform a Boolean subtraction operation to form the mounting hole. The most critical thing is that the position of the output shaft must be absolutely accurate, and the height of the small disc and shaft must be consistent with your actual object. The modeling process is just like building blocks. Break the servo into several simple geometric objects and put them together and you're done.
After the modeling is completed, the model needs to be carefully inspected. For example, check whether the connections between various components are tight and whether the dimensions are accurate and consistent with the actual object. After ensuring that the model is correct, it can be exported to a suitable format for subsequent use in 3D printing or other related applications. At the same time, in order to facilitate subsequent adjustments and optimizations, it is best to manage the model hierarchically and record each step and parameter. In this way, when problems are encountered, they can be quickly traced and modified, improving the efficiency and quality of the entire modeling work.
This is where things tend to go wrong the most. The SG90 servo has two common ear hole spacings, one is used to fix the servo itself, and the other is used to install the steering wheel swing arm. When drawing the mounting base, you must accurately measure the center distance between the two ear holes and the height from the base of the ears to the bottom of the servo. Many people only measure the diameter of the hole and ignore the distance between the holes. As a result, the screw can pass through, but the holes do not match up. You can first draw the hole on the mounting base as a waist-shaped hole 0.2 mm larger than the actual screw, so that even if there are errors in printing or processing, the position can be easily adjusted.
The output shaft is the key to connecting the swing arm. If the data is incorrect, the swing arm will not be installed, or it will not be centered after installation. The output shaft of the SG90 is made of plastic and has teeth on it, but we do not need to draw the details of the teeth in CAD, we only need to draw the diameter and height of the shaft. The diameter of the shaft is generally about 4.8mm (including the tooth profile). You can use a caliper to measure the outermost edge of the shaft. At the same time, don't forget the two small positioning bumps next to the measuring axis. They are used to prevent the steering wheel from turning. The position of these two points is also important in designs that require precise reset.
With an accurate servo model, all that's left is to "fit" it into your product design. My habit is to import the servo model as a separate part and then use it to "reduce" the installation space. For example, if you want to design a gimbal, you can first place the servo, and then use the interference check function of CAD to see if the surrounding parts will block the rotation of the servo. It's like decorating a house. After putting all the furniture in, you don't know whether the corridor is clear or not. Making good use of this virtual model can help you discover 80% of assembly problems in advance.
I hope what I talked about today can help you avoid some detours. What is the most troublesome problem you encounter when designing the steering gear installation structure? Come to the comment area to chat about your experience. If you find the content useful, don’t forget to give it a like and share it with more friends who need it!
Update Time：2026-03-13
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