Best servo for a DIY robot arm
For most hobby and learning arms, the Feetech STS3215 is the best value: about $20 for a 12-bit magnetic encoder, bus wiring and real torque, and it is what SO-101, LeKiwi and XLeRobot are built on. Pick the 12V STS3215 or STS3250 if your arm is longer or carries more, and pick ROBOTIS Dynamixels when you want a polished ecosystem or are copying a Dynamixel design such as Koch or ALOHA.
What matters
- Position feedback: a bus servo that reports its angle is what makes teleoperation and learning from demos possible; plain PWM hobby servos cannot report position.
- Torque at the shoulder: the shoulder lift joint carries the whole arm, so size that one first and leave a wide margin over the stall rating.
- One voltage per bus: pick 5V, 7.4V or 12V servos and a matching supply; mixing classes on one supply burns servos.
- Copy a working design: buying the exact servos a proven build lists saves you from re-tuning gearing and brackets.
- Spare parts and sellers: a servo sold by several stores in your region is easier to replace at 2 a.m. when one dies.
Our picks
| Pick | Why | Where to buy |
|---|---|---|
| Feetech STS3215 7.4V (C001, 1/345) First arm, best price per joint | Stall torque 19.5 kg.cm at 7.4V with a 12-bit magnetic encoder for about $20. Runs the SO-101 follower and has the biggest LeRobot community behind it. | Seeed Studio: $20.00 Waveshare: $16.99 single; $16.99 to $21.99 across 7.4V and 12V options OpenELAB: EUR 23.57 RobotShop: $34.32 |
| Feetech STS3215 12V (30 kg.cm) Longer arms or heavier grippers on a budget | Same body and bus as the 7.4V version but rated 30 kg.cm at 12V, for about $2 more. Used in the SO-101 Pro follower, LeKiwi 12V and XLeRobot. | Seeed Studio: $22.00 RobotShop: $31.71 |
| Feetech STS3250 (C002, 12V) High-load shoulder or elbow joints | About 50 kg.cm at 12V in the same footprint as the STS3215, so it drops into the joints that strain most. Costs roughly three times as much. | OpenELAB: EUR 75.85 (unverified) |
| DYNAMIXEL XL330-M288-T Small, light 5V arms and leader arms | 18 g and 0.52 N.m stall at 5V with ROBOTIS's mature SDK and tooling. Too weak for a full-size shoulder, ideal for wrists, grippers and hand-moved leader arms. | ROBOTIS: $27.49 (unverified) single; backordered in snippet Generation Robots: EUR 40.20 RoboSavvy: GBP 27.20 |
| DYNAMIXEL XL430-W250-T Dynamixel arms that need more than an XL330 | The 12V workhorse in Koch v1.1's follower base and shoulder. Pairs with XL330s on the same protocol. | ROBOTIS: $27.50 Generation Robots: EUR 36.00 |
| DYNAMIXEL XM430-W350-T Lab-grade arms where budget is not the limit | Metal case and contactless encoder, used inside the Trossen arms of ALOHA. Over $300 each and often sold out, so it only makes sense for research builds. | ROBOTIS: $310.39 |
FAQ
Can I use MG996R or SG90 servos for a robot arm?
For a toy arm, yes. For anything you want to teleoperate or train, no: they have no position output, so the software cannot read where the arm is, and cheap clones vary a lot in torque.
How much torque does my shoulder servo need?
Work out the arm's weight times its reach to the center of mass, add the payload at full reach, then pick a servo whose stall torque is at least two to three times that. Servos run hot and lose accuracy near stall.
Feetech or Dynamixel?
Feetech gives more torque per dollar; Dynamixel gives better documentation, tooling and resale. Most new low-cost designs use Feetech STS3215s, while older research designs use Dynamixel.
Do I need a special controller board?
Bus servos need a USB to TTL bus adapter: a Waveshare bus servo adapter for Feetech, or a ROBOTIS U2D2 for Dynamixel.
Sources: huggingface.co · github.com · github.com · emanual.robotis.com · www.waveshare.com · www.seeedstudio.com · www.seeedstudio.com · openelab.io · github.com