Servo Surgery Teaches Us DIY Encoder Implantation

Today we will talk about how [Adam Bäckström] Taking a DS3225 servo and modifying it to increase its accuracy, he then built a high-precision robot arm using these modified servos to show how much of an improvement he achieved – a 36x increase in position accuracy.If this brings Already seen It feels like, that’s because we’ve covered his servo modifications before, but now, there’s more. It’s been a year since the last video was released, [Adam] In the newly released video embedded below, we take it to the next level, showing us how to make modifications, and how we can do it ourselves.

After ordering a replacement controller PCB designed by [Adam] (Assembled by the PCBA service of your choice), you disassemble the server and carefully set the gearbox aside for now. The next step is obviously to tear out the stock control board, but from there you can’t just put a new PCB in it – there’s a lot more that needs to be done to get a perfect servo, you also have to add additional sensing capabilities . First, you have to print the gaskets and covers for the control board, as well as the new base for the motor. You will also have to print (or possibly laser cut) two flat encoder discs, one black and one white, with the white one off-center. Things will only escalate from here!

Both disks are located inside the motor. That means you have to pry open the servo’s DC motor, take out the base with the brushes, and insert the encoder disk. Then, cut and file off the plastic parts of the base to free up as much space as possible inside the motor base, and add the optical encoder in the freed space. Once completed, solder the motor, optocoupler, and potentiometer connections to the new controller PCB, then reassemble the motor back together.

After the surgery is complete you have to calibrate your servos, for this [Adam] Shows how to get the mechanical setup right, provides the code needed to run it, and even has a nice GUI tool with controls for adjusting the servo parameters – his firmware gives us more than we would expect from a servo of this type more features.All the knobs and sliders available to control coefficients, limits and curves show us [Adam] Really understand how to achieve correct servo motion. The documentation, explanations, and tools for this modification process are given enough attention that if we follow the steps ourselves, we don’t have to worry about being left behind!

In a robotic arm, small precision errors at the base magnify into large errors at the end of the arm.If what you crave is high accuracy on a budget, and you have some time to devote to modifying the stock servos, this approach may be just what you need, and [Adam] Basically all the foundations have been laid for you. Last time we discussed these servo modifications, one of our commenters suggested that this might be a viable successor to the OpenServo project goals, and we definitely know where they came from. What if you want to go cheaper than that? Well, you could build a servo system out of a crappy DC motor with a “3 cent” microcontroller.

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