1. What is a Brushed Motor Speed Calculator?

Definition: This calculator estimates the rotational speed (RPM) of a brushed DC motor based on electrical and mechanical parameters.

Purpose: It helps engineers, hobbyists, and technicians determine motor performance under different operating conditions.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( RPM \) — Rotational speed (revolutions per minute)
• \( V \) — Supply voltage (volts)
• \( I \) — Current draw (amps)
• \( R_m \) — Motor resistance (ohms)
• \( K_v \) — Motor velocity constant (RPM/volt)
• \( \Phi \) — Magnetic flux (Webers)

Explanation: The numerator calculates effective voltage after IR drop, while the denominator converts this to RPM based on motor characteristics.

3. Importance of Motor Speed Calculation

Details: Accurate speed estimation is crucial for system design, performance prediction, and troubleshooting motor-driven applications.

4. Using the Calculator

Tips: Enter all electrical parameters. Typical values:

• Small hobby motors: R_m = 0.1-1Ω, K_v = 1000-5000 RPM/V
• Industrial motors: R_m = 0.01-0.1Ω, K_v = 100-1000 RPM/V
• Flux (Φ): ~0.001 Wb for small permanent magnet motors

5. Frequently Asked Questions (FAQ)

Q1: What if I don't know the motor resistance?
A: Measure it with a multimeter or check manufacturer specs. For estimation, small motors are often 0.1-1Ω.

Q2: How does load affect the calculation?
A: Increased load raises current (I), which decreases speed due to IR drop.

Q3: What's the difference between K_v and K_t?
A: K_v relates speed to voltage, while K_t relates torque to current (K_t ≈ 1/K_v in SI units).

Q4: Why is flux (Φ) needed?
A: It accounts for magnetic field strength which affects motor performance. For PMDC motors, this is constant.

Q5: Can this be used for brushless motors?
A: No, brushless motors use different equations. See our Brushless Motor Calculator.