Calculator
Example Data Table
| Use case | Total servos | Idle mA | Moving mA | Stall mA | Active average | Peak servos | Duty % |
|---|---|---|---|---|---|---|---|
| Micro pan tilt | 2 | 8 | 120 | 650 | 1 | 1 | 30 |
| RC steering | 1 | 25 | 700 | 3200 | 1 | 1 | 20 |
| Robot arm | 6 | 20 | 500 | 2500 | 3 | 2 | 40 |
| Walking robot | 18 | 15 | 350 | 1800 | 6 | 3 | 45 |
Formula Used
Loaded moving current = Idle current + (Moving current - Idle current) × Load percentage.
Average current = Total servos × Idle current + Active servos × (Loaded moving current - Idle current) × Duty cycle + Controller current + Accessory current.
Peak current = Peak servos × Stall current + Remaining servos × Idle current + Controller current + Accessory current.
Recommended supply current = Peak current × (1 + Safety margin) ÷ Regulator efficiency.
Runtime = Battery capacity × (1 - Reserve) × Efficiency ÷ Average current.
Wire resistance limit = Allowed voltage drop ÷ Peak current.
How to Use This Calculator
Enter the number of servos in your project. Add the number that move during normal operation. Add the number that may stall or surge together.
Enter current values from a datasheet or bench test. Use milliamps for idle, moving, and stall current. Enter the servo rail voltage.
Set duty cycle for motion time. Set load percentage for normal mechanical load. Add regulator efficiency, safety margin, battery capacity, reserve, and extra electronics current.
Press Calculate. Use average current for runtime. Use recommended supply current for the regulator, BEC, battery, switch, fuse, connectors, and wiring.
Servo Current Draw Guide
Why Servo Current Changes
A servo can draw a calm idle current at one moment and a sharp peak current in the next. This matters when a robot, arm, gimbal, camera mount, or RC model uses several servos together. A weak supply may reset a controller. Thin wires may drop voltage. A small battery may look fine on paper, then fail during loaded motion.
What the Calculator Estimates
This calculator estimates those demands from practical values. Enter the supply voltage, servo count, idle current, moving current, stall current, active servos, duty cycle, load level, efficiency, and safety margin. The tool separates average current from peak current. That is important. Average current helps estimate runtime. Peak current helps size regulators, BEC units, fuses, connectors, and wiring.
Average Current Method
The average method starts with idle current for every servo. It then adds the extra moving current only for the servos that are active. Duty cycle controls how often that extra current is present. Load percentage scales the moving current between idle and rated moving current. This gives a useful planning value for mixed motion.
Peak Current Method
Peak current is different. It assumes some servos may hit stall at the same time. That can happen during startup, blocked linkage, hard acceleration, or a mechanical end stop. The calculator adds stall current for peak servos and idle current for the rest. A safety margin is then applied. Efficiency is also considered, because regulators waste some energy.
Testing and Design Tips
Use measured current whenever possible. Datasheet values may be optimistic. Stall current is often missing, so testing with a current limited supply is wise. Do not intentionally stall a small servo for long. Heat rises quickly. Gear damage may also occur.
For reliable builds, choose a supply that can handle the recommended current. Keep servo power separate from sensitive logic when needed. Join grounds correctly. Use short wires for high current paths. Add bulk capacitance near servo rails. Check voltage during real movement, not only at idle. The best design is based on peak demand, thermal limits, and safe wiring.
Final Check
This calculator is a planning aid. Final designs need testing under load. Mechanical friction, linkage binding, cable length, and battery age can change results. Always leave margin for harsh starts and unexpected stalls. Use this estimate before buying components early.
FAQs
1. Which current value should size my supply?
Use the recommended supply current. It includes peak demand, safety margin, and regulator efficiency. Average current is better for battery runtime planning.
2. Why is stall current important?
Stall current is the worst normal electrical case. It can occur when a linkage blocks, a servo hits an end stop, or motion starts sharply.
3. Can a microcontroller power servos directly?
Usually no. Most controller pins and onboard regulators cannot supply servo surge current. Use a separate servo supply and share ground correctly.
4. What safety margin should I use?
A margin of 20% to 50% is common. Heavy robots, unknown loads, and cheap servos may need more margin.
5. What if my datasheet lacks stall current?
Measure it carefully with current limiting, or use a conservative estimate. Larger servos can draw several times their moving current.
6. Does voltage affect servo current?
Yes. Higher voltage can increase speed and torque, but current behavior depends on the servo design and load. Stay within rated voltage.
7. Why include regulator efficiency?
Regulators are not perfect. Efficiency accounts for power losses, heat, and the extra input energy needed to deliver servo output current.
8. How can I reduce current draw?
Reduce friction, balance loads, avoid binding, lower duty cycle, use stronger servos, shorten wires, and avoid holding torque near stall.