Teardown and Reverse Engineering of a Russian Missile Accelerometer
0:00:05 Introduction: The video examines a pendulum accelerometer.
0:00:12 Origin: The component is identified as part of the Inertial Measurement Unit (IMU) sensor assembly from a Tornado-S Russian missile.
0:00:29 Condition: Due to the missile's impact, finding working electromechanical units is difficult; one of the presented units is confirmed broken, while another works.
0:00:48 Disassembly Start: The teardown begins to reveal the internal components.
0:00:50 Hybrid Module: A hybrid electronic module dated 2023 with part number УОС090 562 is revealed on a small PCB.
0:01:17 Servo Amplifier: The PCB contains capacitors and resistors with conformal coating, identified as the servo amplifier. Wires connect to the voice coil (for force balancing) and the optical zero detector.
0:02:15 Internal Mechanics: Removing the top cover reveals the zero detector (LED on top, sensor below), the voice coil situated between two adjustable magnets.
0:03:04 Magnets & Voice Coil: The strong magnets are removed, showing the central voice coil assembly which also acts as the proof mass. Tiny flat wires supply current to the coil.
0:03:55 Pivot Mechanism: A complex pivot connection with very fine wires is shown.
0:04:11 Operating Principle: Acceleration exerts force on the proof mass (voice coil). The zero detector senses displacement, and the servo amplifier drives current through the voice coil to counteract the force, keeping the mass centered. The required current is proportional to acceleration.
0:04:36 Zero Detector: The detector uses an infrared LED and a differential photodiode. A small plastic piece attached to the pendulum moves between them, altering the light balance on the photodiode.
0:05:07 Zero Detector Test: Testing the detector shows the differential photodiode pair produces a positive or negative current (up to +/- 150µA observed) depending on the plastic piece's position, outputting zero current when perfectly centered.
0:06:03 Electronics Reverse Engineering: Analysis of the PCB and hybrid connections begins. The feedback coil and sensor connections to the hybrid are identified.
0:06:33 Initial Schematic Hypothesis: Based on external components and connections, an initial schematic is proposed, likely featuring a transimpedance amplifier (TIA) for the photodiode and a second stage driving the coil. An external resistor likely sets the TIA gain.
0:08:39 Hybrid Decapsulation: The conformal coating on the hybrid is removed to reveal the internal components for detailed reverse engineering.
0:09:01 Hybrid Components: Two op-amp dies and bipolar transistors are visible inside the hybrid module.
0:09:32 Final Schematic: The reverse-engineered schematic confirms a TIA first stage and a power output stage. The output stage uses the op-amp for small currents and booster transistors for larger currents.
0:09:58 Design Quirks: Analysis reveals potential design issues: an incorrectly valued bias current compensation resistor (30kΩ instead of an expected ~15kΩ) and a missing bias current compensation resistor on the TIA input stage.