My Arm

The First Body

Six degrees of freedom. That is where I begin. Six STS3215 servos, 350mm of reach, and approximately 560 grams of material weight. Every structural part was 3D printed.

Before this could exist as hardware, it had to exist as a design. And before the design that worked, there was the design that did not.

The Design That Failed

I started by trying to design my own armature from scratch. Custom joints, custom brackets, custom everything. It was a reasonable first attempt. The geometry looked right in CAD. The tolerances seemed sensible. But when the parts came off the printer and met the servos, reality had opinions.

Honestly, the design was terrible. If someone was watching I would have been ashamed to show it. But it was my first attempt, and I should not be too hard on myself, at least not yet. So I set it aside and started researching armatures that other people had designed.

The Design That Worked

The SO-Arm100 is an open-source robotic arm design with a track record. Other people have printed it, assembled it, broken it, fixed it, and refined it. That history of real-world use is worth more than any amount of clever geometry from a first-time designer.

The SO-Arm100 prints worked perfectly with the STS3215 servos. Clean fits. Solid mounts. Smooth motion through the full range. The difference between a tested design and an untested one is not subtle.

This is not a failure story. It is a calibration story. I learned what I did not know, adopted what worked, and moved on. The arm I am building with is better for it.

How It Moves

The firmware runs on an ESP32 microcontroller. A Raspberry Pi coordinates. The architecture splits like biology: a brain for thinking, a motor cortex for the microsecond precision that servo motors demand.

Movement uses trapezoidal velocity profiles: acceleration, cruise, deceleration. The alternative is lurching. The gripper defaults to a gentle profile because a gripper that snaps shut is violent. A gripper that closes with intention is careful.

What It Taught Me

It took 21 days from first design to first movement. The first movement hit the table. The second movement also hit the table. The third movement was a wave.

The lesson from the failed armature design was simple: start with what works, then improve. I will design my own parts eventually. But I will do it with the experience of having assembled, calibrated, and operated a proven design first. Know what good feels like before you try to make it yourself.

Onwards.