Calculator Inputs
Example Data Table
| Input Case | B (T) | L (m) | I (A) | Mass (g) | Target (mm) | Move Time (ms) | Expected Use |
|---|---|---|---|---|---|---|---|
| Lens stage | 0.75 | 2.40 | 1.80 | 85 | 8 | 40 | Fast precision travel |
| Small shaker | 0.60 | 1.90 | 1.20 | 120 | 5 | 60 | Controlled vibration |
| Scanner actuator | 0.90 | 3.10 | 2.20 | 70 | 10 | 30 | High acceleration scan |
Formula Used
Force constant: Kf = B × L. If a tested Kf is entered, the calculator uses that value.
Motor force: Fm = Kf × I.
Spring force: Fs = preload + k × x.
Damping force: Fd = c × |v0|.
Net force: Fnet = Fm − load − friction − Fs − Fd.
Acceleration: a = Fnet ÷ m.
Travel: x(t) = v0 × t + 0.5 × a × t².
Final velocity: v(t) = v0 + a × t.
Voltage demand: V = I × R + Ke × |v|.
Copper loss: Pcu = I² × R.
Thermal rise: ΔT = Pcu × duty × thermal resistance.
Electrical response: τ = Lcoil ÷ R, and 95% rise time is about 3τ.
How to Use This Calculator
Enter magnetic and electrical data first. Use measured force constant when available.
Add moving mass, target travel, stroke, spring, load, friction, and damping values.
Set move time, duty cycle, thermal resistance, ambient temperature, and current rating.
Press the calculate button. Review movement, voltage, heating, and safety margins.
Download the CSV for spreadsheets. Download the PDF for reports or lab notes.
Electrical Motion Planning
A voice coil motor moves because current flows through a coil inside a magnetic field. The calculator estimates that motion by combining electromagnetic force with mass, load, spring force, damping, and thermal limits. It is useful for lens stages, speakers, scanners, small pickers, and precision linear actuators.
Why Movement Changes
Movement is not set by current alone. The same current gives different travel when the moving mass changes. Friction reduces usable force. A spring can pull against the stroke. Damping can slow fast moves. Back EMF adds voltage demand during speed. Coil resistance turns current into heat. These details decide whether the actuator reaches the requested position.
Design Checks
Start by entering the flux density and active wire length. Or enter a tested force constant. Add the desired current, resistance, inductance, and supply voltage. Then define the mass, stroke, spring rate, preload, friction, damping, initial speed, and move time. The result shows motor force, net force, acceleration, estimated travel, final speed, voltage demand, copper loss, current rise time, heat rise, and useful margins.
Using Results Safely
Positive net force means the coil can accelerate the load in the selected direction. A negative value means the load, spring, or friction is higher than the motor force. Travel greater than stroke is clipped by the mechanical limit. Heat rise is based on steady duty heating, so short pulses may be safe while long pulses may not. Always confirm with manufacturer data, sensors, and temperature tests.
Practical Notes
Use total active conductor length inside the magnetic gap. Do not use total wound wire length unless it is all active. Keep current below continuous rating unless pulse limits are known. Add safety margin for bearing drag, cable force, alignment error, and magnet temperature. For accurate servo design, also check controller bandwidth, current loop response, position feedback resolution, and end stop energy. This calculator is a planning tool, not a replacement for lab validation.
Example Workflow
Run the example first. Change one input at a time. Watch force margin, stroke margin, and temperature rise. If travel is low, increase current carefully or reduce moving mass. If voltage demand is high, reduce speed, resistance, or back EMF losses before selecting hardware or drivers.
FAQs
What is a voice coil motor?
It is a direct drive actuator. Current in a coil reacts with a magnetic field. The result is smooth linear or rotary force.
What does active wire length mean?
It is the conductor length inside the magnetic gap. Only that part creates useful Lorentz force. Do not count inactive wire.
Should I enter B and L or Kf?
Use Kf when it is measured or listed by the maker. Otherwise, estimate Kf from flux density and active wire length.
Why is my net force negative?
The load, spring, damping, and friction exceed motor force. Increase safe current, reduce resistance forces, or choose a stronger actuator.
Why does voltage demand rise with speed?
Motion creates back EMF. The driver must overcome coil resistance and speed voltage. Fast moves can need more supply voltage.
Is the temperature result exact?
No. It is a planning estimate. Actual temperature depends on mounting, airflow, duty shape, coil materials, and nearby heat sources.
Can this calculator size servo control loops?
It helps with first motion estimates. Servo tuning also needs sensor resolution, bandwidth, controller limits, and real dynamic testing.
What safety margin should I use?
Use larger margins for unknown friction, flexible cables, changing temperature, and production variation. Test the final design under load.