Today we will talk about how [Adam Bäckström] took a DS3225 servo and rebuilt it to improve accuracy, then built a high-precision robotic arm with those custom servos to show how much improvement it has — up to 36 times better positional accuracy. If this is feeling déjà vu, it’s because we covered his last demonstration video in an article a few weeks ago, but now there’s more. In a month since the last video came out, [Adam] took it to the next level, showing us how the change was made and how to do it ourselves, in a newly released video embedded below.
After ordering replacement control boards designed by: [Adam] (assembled by your PCBA service of choice), disassemble the servo and carefully set the gearbox aside. Stripping the stock control board is the obvious next step, but from there you don’t just drop the new PCB – there’s more to getting a perfect servo than this, you’ll also need to add extra sensing. First you need to print a spacer and cover for the control board, as well as a new base for the motor. You should also print (or maybe laser cut) two flat encoder disks, one black and one white, with the white one being eccentric. It only escalates from here!
Both discs go into the engine. That is, you need to pry apart the servo’s DC motor, take out the base with brushes, and then put in the encoder disks. Next, cut and file away the plastic parts from the base to free up as much space as possible in the motor base, and add the optical encoders into the space you’ve cleared. Once that’s done, solder the motor, optocoupler, and potentiometer connections to the new controller board and reassemble the motor.
After you are done with the operation, you need to calibrate your servo, for which [Adam] shows how to set it up mechanically correctly, provides the code you need to run, and even nice GUI tools with controls to adjust servo parameters – its firmware gives us far more power than we could ever expect from a servo like this one. All available buttons and sliders to control coefficients, limits and curves show us [Adam] really understand what makes for good servo movement. Sufficient care is taken in the documentation, explanations and tools for this modification process so that we don’t have to worry about being left behind if we want to follow these steps ourselves!
In a robotic arm, small accuracy errors at the base are scaled to large errors at the tip of the arm. If what you crave is high accuracy on a budget, and you have some time to spend adjusting stock servos, this approach may be just what you need, and [Adam] has in fact laid all the foundations for you. The last time we talked about these servo tweaks, one of our commenters suggested that this could be a viable successor to the OpenServo project’s goals, and we’re definitely seeing where they come from. What if you want to go even cheaper than this? You could then build a servo out of junk DC motors with a “3 cent” microcontroller.
we thank [sarinkhan]† [Diede] and [BaldPower] to share this with us!
This post Servo surgery teaches us DIY encoder implants
was original published at “https://hackaday.com/2022/04/03/servo-surgery-teaches-us-diy-encoder-implants/”
