Addendum: Deep-Dive VBar Vibration Analysis & Diagnostic Spectrum Guide

While standard Mikado documentation states that the VBar Vibration Analysis tool displays a continuous FFT (Fast Fourier Transform) spectrum sampled every two seconds over a 0.1-second window, practical field diagnostic requires translating raw frequency peaks into physical component failures.

1.

The Mathematics of Frequency Isolation

The VBar spectrum analyzer plots vibration amplitude against frequency in Hertz (Hz) or rotational speed in RPM (1 Hz = 60 RPM). Every rotating mechanical subsystem on an RC helicopter operates at a distinct gear ratio relative to the main rotor.

To pinpoint the source of a vibration peak, calculate the expected operating frequencies using your airframe's exact gear mesh profile:

Main Head Frequency (Hz) = Target Head Speed (RPM) ÷ 60
Tail Rotor Frequency (Hz) = Main Head Frequency (Hz) x Tail Gear Ratio
Motor / Pinion Frequency (Hz) = Main Head Frequency (Hz) x Main Gear Ratio
2.

Frequency Range Mapping Table

Use this reference table to match live spectrum peaks against physical component groups during bench or flight logging:

Frequency Band Typical RPM Range (700 Class) Primary Mechanical Suspects
Low Frequency
(20 Hz - 50 Hz)		 1,200 RPM - 3,000 RPM
  • Main rotor blade out-of-track or spanwise imbalance.
  • Bent main shaft or warped main gear/hub.
  • Notchy or failing main shaft radial bearing blocks.
Medium Frequency
(100 Hz - 250 Hz)		 6,000 RPM - 15,000 RPM
  • Tail rotor blade imbalance or bent tail spindle.
  • Torque tube whip or worn tail drive bearings.
  • Damaged tail pitch slider, hub, or bent tail output shaft.
High Frequency
(300 Hz - 800+ Hz)		 18,000 RPM - 50,000+ RPM
  • Motor pinion/main gear mesh tight or tooth damage.
  • Failing motor bearings or imbalanced motor rotor can.
  • High-frequency ESC current switching / motor pole electrical noise.
3.

Practical Field Isolation Procedure (Step-Down Teardown)

When the VBar log triggers a "High/Extreme Vibration" warning, follow this systematic teardown procedure to isolate the faulty part:

  1. Step 1: Motor-Only Baseline Test

    Disengage the motor pinion from the main gear (or drop the main belt). Run the motor up through your flight throttle curves while connected to the VBar analyzer. If the spectrum remains clean (low noise floor), the motor and bearings are eliminated as suspects.

  2. Step 2: Main Mechanics Test (No Blades)

    Re-engage the motor, remove both main and tail blades, and spool up to operating RPM. If a spike appears in the 100 Hz-250 Hz range, the vibration originates in the tail assembly or torque tube/belt system.

  3. Step 3: Tail Rotor & Main Rotor Incremental Testing

    Install tail blades first and test. A sudden spike confirms tail grip dynamic imbalance or a bent tail hub. Finally, install main blades to evaluate overall flight line tracking and damper seating.

4.

References & Sources

This technical guide synthesizes official manufacturer documentation and field research across the following industry repositories: