The modified servo being calibrated on the left half of the screen, with some graphs of its operation being shown on the right half.

Servo Surgery Teaches Us DIY Encoder Implants

Today, we shall talk about how [Adam Bäckström] took a DS3225 servo and rebuilt it to improve its accuracy, then built a high-precision robot arm with those modified servos to show just how much of an improvement he’s got – up to 36 times better positional accuracy. If this brings a déjà vu feeling, that’s because we’ve covered his servo modifications before, but now, there’s more. In a year’s time since the last video came out, [Adam] has taken it to the next level, showing us how the modification is made, and how we ourselves can do it, in a newly released video embedded below.

After ordering replacement controller PCBs designed by [Adam] (assembled by your PCBA service of choice), you disassemble the servo, carefully setting the gearbox aside for now. Gutting the stock control board is the obvious next step, but from there, you don’t just drop the new PCB in – there’s more to getting a perfect servo than this, you have to add extra sensing, too. First, you have to print a spacer and a cover for the control board, as well as a new base for the motor. You also have to print (or perhaps, laser-cut) two flat encoder disks, one black and one white, the white one being eccentric. It only escalates from here!

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Watch The Snappy, Insect-like Moves Of This DIY Quadruped Robot

Some legged robots end up moving with ponderous deliberation, or wavering in unstable-looking jerks. A few unfortunates manage to do both at once. [MusaW]’s 3D Printed Quadruped Robot, on the other hand, moves in rapid motions that manage to look sharp and insect-like instead of unstable. Based on an earlier design he made for a 3D printable quadruped frame, [MusaW] has now released this step-by-step guide for building your own version. All that’s needed is the STL files and roughly $50 in parts from the usual Chinese resellers to have the makings of a great weekend project.

The robot uses twelve SG90 servos and an Arduino nano with a servo driver board to control them all, but there’s one additional feature: Wi-Fi control is provided thanks to a Wemos D1 Mini (which uses an ESP-8266EX) acting as a wireless access point to serve up a simple web interface through which the robot can be controlled with any web browser.

Embedded below is a brief video. The first half is assembly, and the second half demonstrates the robot’s fast, sharp movements.

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Drive Big Servos With Ease

CNC machines of all types are a staple here at Hackaday, in that we have featured many CNC builds over the years. But the vast majority of those that we see are of relatively modest size and assembled in a home workshop, using small and readily available components such as small stepper motors. These drives are a world away from those used in industrial CNC machines, where you will find high-voltage servos packing a much greater punch. With good reason: driving a small low-voltage motor is easy while doing the same with a high-voltage servo requires electronics that have hitherto been expensive.

STMBL (for STM32 microprocessor and BrushLess motor) is a servo driver for STM32F4 microcontrollers that is specifically designed to use in retrofit projects to industrial CNC machines that have those high-voltage servos. When assembled, it takes the form of two PCBs arranged in a T configuration over a heatsink, with high-power connectors for the motor terminals, and RJ45s for feedback and serial control. In fact each of the boards has its own STM32, one on the high voltage side and the other on the low voltage, to enable only the simplest of isolated serial connections between them.  A significant variety of combinations of motor and feedback system is supported, making it as versatile as possible a module for those whose CNC needs have escaped their home bench setup. We’re sure we’ll see this module pop up in quite a few builds we show you over the coming years.

Thanks [Andy Pugh] for the tip.

FoTW: LED Strips Make Awful Servo Drivers

We must all have at some time or another spotted a hack that seems like an incredible idea and which just has to be tried, but turns out to have been stretching the bounds of what is possible just a little too far. A chunk of our time has disappeared without trace, and we sheepishly end up buying the proper part for the job in hand.

[Orionrobots] had a conversation with a YouTube follower about LED strips. An LED strip contains a length of ready-made PWM drivers, they mused. Wouldn’t it be great then, if each of the drivers on a strip could be connected to a servo, making the strip a ready-made single-stop SPI servo driver. With a large multi-servo robot to build, he set to work on a strip of WS2801s.

If you are in the Soldering Zone and have elite skills at the iron, then soldering a wire to a surface mount driver chip is something entirely possible. For mere mortals though it’s a bit of a challenge, and he notes just how much extra time it’s added to the project. The fun starts though when the servo is hooked up, the best that can be said is that it vibrates a bit. On paper, the LED drivers should be able to drive a servo, because they can create the correct waveform. But in practice the servo is designed to accept a logic level input while the driver is designed to sit in series with an LED and control its current. In practice therefore the voltages required for a logic transition can’t quite be achieved.

He concludes by recommending that viewers splash out on a servo driver board rather than trying an LED strip. We applaud him for the effort, after all it’s a hack any of us might have thought of trying for ourselves.

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