Motors

de:volt models three motor types: a brushed DC motor, a hobby servo, and a 4-wire bipolar stepper. Each is electrically simulated and reports a live mechanical readout (speed, angle, or step position) alongside the circuit.

All three are inductive loads. Drive them with an H-bridge (L293D, TB6612) or, for a bare transistor switch, add a flyback diode to suppress the inductive kick.

DC Motor

A generic brushed DC motor, modelled as a series R+L winding with a back-EMF source proportional to rotor speed (Vbemf = Ke × ω). Winding current produces torque (Tm = Kt × i), and the rotor follows J × dω/dt = Kt×i − b×ω − loadTorque.

Pinout

Defaults

These can be overridden via the Inspector properties panel.

How it behaves

Speed is proportional to applied voltage. As the rotor speeds up, back-EMF rises and opposes the supply, so current falls. At standstill (ω = 0) there is no back-EMF, so the current is highest — the stall current equals V / windingR. With the default 5 Ω winding and a 6 V supply that is 1.2 A.

The simulator reports rotor speed (ω in rad/s) and RPM in the readout. The speed value drives the back-EMF source only; it is not mechanically coupled to any external load.

Drive method

Use an H-bridge for bidirectional control: connect M+ to OUT_A and M− to OUT_B for forward rotation, then reverse the drive signals for reverse. Reversing the terminal polarity reverses the spin direction. A bare transistor switch needs a flyback diode connected anti-parallel across M+/M− to clamp the voltage spike when the transistor turns off.

Example circuit

Arduino D5 ─── IN1 ┐
Arduino D6 ─── IN2 │  [L293D]  OUT1 ─── M+
                   │           OUT2 ─── M−  [DC Motor]
              5V ──┴── VCC / VS

Hobby Servo (SG90)

A PWM-controlled rotary position actuator. A pulse HIGH time of 1–2 ms on the signal pin commands the shaft to a position between 0° and 180°. The servo holds its last commanded angle between pulses.

Pinout

The connector is polarised: signal first, power centre, GND last. Do not reverse it.

Defaults

How it behaves

The signal pin is a high-impedance input (modelled as 1 MΩ to GND); it reads HIGH when V(sig) − V(gnd) ≥ 2.0 V. The power pins draw a small idle current (default load 330 Ω, roughly 15 mA at 5 V).

On each pulse the sim measures the HIGH time and maps it to an angle:

angle = minAngle + (pulseMs − minPulseMs) / (maxPulseMs − minPulseMs) × (maxAngle − minAngle)

So a 1 ms pulse gives 0°, 1.5 ms gives 90°, and 2 ms gives 180°. The commanded angle is reported in the readout and held between updates.

Drive method

Drive the signal pin with a 50 Hz PWM signal — use the Arduino Servo library, which generates the 1–2 ms pulses for you. Power V+ from a 5 V rail that can supply the stall current (about 700 mA); for more than one servo use a separate supply rather than the Arduino 5 V pin.

Example circuit

Arduino D9 ─── Signal
       5V  ─── V+   [Servo SG90]
       GND ─── GND

Bipolar Stepper Motor (NEMA 17)

A 4-wire bipolar stepper with two independent coils (A and B). Energising the coils in the 4-phase full-step sequence advances the shaft one step at a time. Default: 200 steps/rev (1.8°/step).

Pinout

Defaults

How it behaves

Each coil is a series R+L load. Stepping is detected from the sign of the committed coil currents after each solve (±1 mA deadband), giving four phases:

Advancing one phase (mod 4) moves one step forward; stepping back one phase moves one step back. A non-sequential jump holds position. The simulator reports the accumulated step position. There is no back-EMF in this model.

Drive method

Cycle the full-step sequence with an H-bridge. With an L293D, wire OUT1→a1, OUT2→a2, OUT3→b1, OUT4→b2; with a TB6612, AO1→a1, AO2→a2, BO1→b1, BO2→b2. Each phase transition is one step (1.8° for a 200-step motor). Reversing one coil reverses the rotation direction. Bare-transistor drivers need a flyback diode across each coil — the L293D/TB6612 handle this internally when VM is powered.

Unipolar/ULN2003 5-wire steppers are not modelled in this version.

Example circuit

Arduino D8 ─── IN1 ┐           OUT1 ─── A1 ┐ Coil A
Arduino D9 ─── IN2 │  [L293D]  OUT2 ─── A2 ┘
Arduino D10 ── IN3 │           OUT3 ─── B1 ┐ Coil B
Arduino D11 ── IN4 ┘           OUT4 ─── B2 ┘  [Stepper NEMA 17]