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Teardown and Analysis of a Tornado-S Missile Pendulum Accelerometer
0:00:04 Introduction: Introduces a pendulum-type accelerometer, identified as part of the Inertial Measurement Unit (IMU) from a Russian Tornado-S missile.
0:00:29 Condition: Notes that finding working units is difficult due to ground impact shock; one functional unit (out of three shown) is available for teardown.
0:00:48 Initial Disassembly: Reveals a hybrid electronic module dated 2023 (Part УОС090 562) mounted on a small PCB.
0:01:17 Servo Amplifier PCB: The small PCB contains the servo amplifier circuitry, featuring conformal coating, with connections identified for the voice coil (2 wires for force feedback) and the optical zero detector (4 wires for LED & sensor).
0:02:13 Internal Mechanism: Removing the top cover exposes the core components: an optical zero detector (LED on top, sensor below), and a voice coil positioned between two adjustable magnets.
0:03:04 Magnets & Voice Coil: Strong, adjustable magnets, similar to those in loudspeakers, create a magnetic field for the voice coil. The voice coil assembly, suspended by tiny flat pivot wires, acts as the proof mass.
0:04:08 Operating Principle: Acceleration exerts a force on the proof mass (voice coil). The optical zero detector senses any displacement, and the servo amplifier drives the voice coil to generate an opposing electromagnetic force, keeping the pendulum precisely centered. The coil current required is proportional to the acceleration.
0:04:36 Zero Detector Details: The detector assembly uses an LED (likely infrared) and what appears to be a differential photodiode pair to precisely measure the pendulum's position relative to its null (center) point.
0:05:08 Zero Detector Test: Testing the detector shows it outputs a current (~+/- 150µA observed within a +/- 200µA range) proportional to the displacement of a plastic flag between the LED and sensor, passing through zero current at the exact center point.
0:06:02 Electronics Reverse Engineering: The process begins by mapping external passive components and the connections between the PCB, the hybrid module, the feedback (voice) coil, and the sensor.
0:06:33 Proposed Hybrid Circuit: Based on external connections, the hybrid is hypothesized to contain a transimpedance amplifier (for the photodiode signal) followed by a second op-amp stage driving the voice coil. An external resistor likely allows gain adjustment.
0:08:55 Hybrid Internal View: After removing a conformal coating, the decapsulated hybrid module reveals two operational amplifier dies and other discrete components (resistors, transistors).
0:09:32 Final Schematic: Detailed reverse engineering confirms the hybrid contains a two-stage op-amp design: a transimpedance amplifier followed by an output driver stage, largely matching the hypothesized circuit.
0:09:58 Circuit Analysis Findings: Analysis of the final schematic reveals potential design curiosities or anomalies, including unexpected resistor values (30k vs. ~15k expected for bias compensation) and seemingly incomplete input bias current compensation on the first op-amp stage (missing input resistor).