{"id":8344,"date":"2021-11-24T07:59:54","date_gmt":"2021-11-24T12:59:54","guid":{"rendered":"https:\/\/dronebotworkshop.com\/?p=8344"},"modified":"2023-04-12T07:05:21","modified_gmt":"2023-04-12T11:05:21","slug":"custom-servo-motor","status":"publish","type":"post","link":"https:\/\/dronebotworkshop.com\/custom-servo-motor\/","title":{"rendered":"Build a Custom Servo Motor with a DC Motor"},"content":{"rendered":"\n

\"Download \"Parts<\/a> \"View<\/a> \"Download<\/a><\/p>\n

What do you do when you need a big servo motor but don\u2019t want to spend a big amount of money? Make your own, of course!<\/span><\/p>\n

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Introduction<\/span><\/h2>\n

Servo motors are essential components when working with robotics, model aviation, and other animated projects. They are used in all kinds of industrial applications as well.<\/span><\/p>\n

Servo motors, for those not familiar with them, are motors whose shaft position can be precisely controlled by an external signal. Unlike stepper motors, which also have controllable shaft positions, servo motors don\u2019t need a reference point to start with. You just specify the angle of shaft rotation, and the servo motor will oblige by moving into that position.<\/span><\/p>\n

Large industrial servo motors use sophisticated controllers and cost quite a bit of money. Smaller, hobby-grade servo motors (sometimes called \u201cRC Servo Motors\u201d) are much more affordable, but they have their limitations.<\/span><\/p>\n

The biggest limitation with hobby-grade servo motors is the amount of power, or torque, they can provide. \u00a0 The larger the motor, the greater the torque, but this gain comes with a corresponding price increase.<\/span><\/p>\n

Another limitation is the range, or degrees of rotation, that these motors are made for. The most common hobby-grade servos rotate 180 degrees, some models are available that have 270 degrees of rotation.<\/span><\/p>\n

But what do you do if you want a smaller, or larger, amount of rotation? It\u2019s entirely possible that you might want to rotate more than 360 degrees. And what if you need a large amount of torque, greater than that provided by inexpensive hobby servo motors?<\/span><\/p>\n

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The answer, of course, is to make your own servo motor. A custom design, based upon your specific needs.<\/span><\/p>\n

In fact, I know someone who requires a custom servo motor.<\/span><\/p>\n

Jeremy Fielding<\/span><\/h2>\n

I\u2019m sure most of you are already familiar with <\/span>Jeremy Fielding through his YouTube Channel<\/span><\/a>.\u00a0 For the few of you who are not familiar with Jeremy’s work, he is a mechanical wizard who builds amazing projects in his workshop, many of them using 3D-printed or reclaimed materials. If you want to know anything about mechanical engineering or working with motors, then Jeremy is the fellow you need to know.<\/span><\/p>\n

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Jeremy and I were chatting, and he mentioned that he required a very large servo motor for one of his projects.\u00a0 Not only does it need to have a lot of torque, it also has to be able to turn two full revolutions (720 degrees) instead of 180 degrees.\u00a0 All driven by a signal intended for a standard hobby-grade servo.<\/span><\/p>\n

So we decided that the easiest way to meet his requirements was to build a custom servo motor, using a high-torque DC motor.<\/span><\/p>\n

Now, of course, your requirements may differ from Jeremy\u2019s, and that\u2019s fine – this custom design can be tailored to just about any application.<\/span><\/p>\n

Before we get into the design and the hardware, let\u2019s just review how a servo motor actually works.<\/span><\/p>\n

Servo Motors<\/span><\/h2>\n

As I\u2019ve already mentioned, a servo motor is a motor whose shaft position can be set using an external control signal.\u00a0\u00a0<\/span><\/p>\n

With a standard hobby servo motor, that control signal is a logic-level PWM waveform. The pulse width of the PWM waveform is how the servo position is controller.<\/span><\/p>\n

The width of the pulses ranges between 1000 and 2000 microseconds. At 1500 microseconds the servo is in its Top Dead Center (TDC) position, on a standard 180-degree servo motor this is the 90-degree position.<\/span><\/p>\n

Internally, a servo motor consists of a DC motor driven by a controller. The controller takes in the PWM signal. Measures its pulse width and turns the motor accordingly.<\/span><\/p>\n

The key to making all of this work is that the motor shaft is coupled to a sensor, which reads the motor position. This position information is fed back to the controller, which then makes the appropriate adjustments to the motor speed and direction.<\/span><\/p>\n

This diagram illustrates how it all fits together.<\/span><\/p>\n

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Note that the controller can be either a digital or analog design, as both types of circuits are used in modern hobby servo motors.<\/span><\/p>\n

So by building our own controller and position sensor, we should be able to turn just about any brushed DC motor into a servo motor.<\/span><\/p>\n

Controller Design Consideration<\/span><\/h2>\n

Here is a summary of what we would need to build our own custom servo motor:<\/span><\/p>\n