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  • Writer's pictureOkan Saçlı

Real 400Hz Gyroscope in operation

Updated: Jun 30, 2023

Environmental ambience of a real home simulator can be achieved by using various sound files which adds a lot in terms of realism. In a previous post, I have already written a blog on controlling relays and contractors with PROSIM (which is available via this link). Using real heavy duty contactors linked to various electrical bus gates, I simulate the contactor closing and opening sounds which is much better and realistic than the sound functionality of PROSIM. PROSIM allows addon (additional) sounds to be triggered via gates (which can be configure from PROSIM SYSTEM) which is also a very usefull function to realism. I have been using the gyro sound set provided by Ben Lim from , which has three components; the first component is the gyro start phase sound, the second set is the gyro running sound and the third set is the gyro stopping sound set which lasts for many minutes. All sounds can be configured in PROSIM by the fade-in (ie. the gyro start phase sound) and fade-out (ie. the gyro stopping sound) functions.

As an engineer who gets excited about things that no one else cares about, I was looking for options to run a real gyro motor (powered by related electrical bus). So I decided to buy from ebay a used gyro or gyro motor. I came across 6BB/2305 16347-0 Birmal Navigation RAF Vintage Aircraft Gyro from ebay and purchased it (knowing the risk that it may or may not work, no idea on power requirements and/or wiring etc). Below is a photo of the gyro motor purchased from ebay.

This motor had three wires coming out, so a star-connected 3 phase motor. Measuring the resistance between each wire gave out 78 Ohms. Knowing that this is an aviation product it must be a 400 Hz unit. But I had no clue if it runs on 28VAC 3ph or 115VAC 3ph. How idea on power requirements (200 Watts ? 500 Watts? ) So I started to look for aviation power supplies which would convert a dc power to 400Hz 3phase ac supply, but i just could not spot the correct unit.

I decided to build myself a suitable power supply. I could generate a 400Hz PWM signal via Ardiuno , then using opamps (operational amplifiers) and differential comparators I should be able to generate a ~12VAC 3ph 400Hz power supply which then should be stepped up to either 28VAC or 115VAC (no idea which one) via self designed step up transformers.

The photo below shows my delay calculations for a 400Hz PWM signal for the Ardiuno coding.

The circuit desing is shown below (I had to modify some parts of it). For the opamps I worked with LM358 and for the comparators I used LM311 (for over current protection).

Using a breadboard I made some prototypes, measuring signals at various point of the circuit. Many nights spent as seen below, correcting things, changing connections. Nightmare

Anyway, I was able to produce a ~12VAC 400Hz 3phase powersupply with all the work and headache. But I parked this project as it needs a lot of work for the step up transformers, which will continue in the future (hopefully)

In the meantime I discovered that I could achieve converting a monofaze 220VAC powersupply (home outlet) to a 3PH AC output with varying frequency using a simple VFD (variable frequency drive) . I found a rather cheap (around 75 EURs) DELTA VFD drive VFD004L21A, which has a single phase 220VAC mains input, 400W and has all the necessary configuration parameters (ie. 400hz). If needed I can glady share which parameters I've changed for the gyro unit to run.

Below is a video published on youtube on the initial run. The full spool up when powered takes arond 35-40 seconds. When unpowered it takes about 10 minutes for the gyro to come to a complete stop. Very interesting device.

The VFD unit and the gyro motor were installed in an electrical junction box as seen below (later I have added some sound insulation to decrease the level of the sound) The start function comes from the closing of DCESS power bus contactor.

The video belows shows a cold and dark cockpit with Ground power available. The ground power is activated all relevant contactors close, the screens come alive and the you can hear the starting up of the 400Hz gyromotor in the background. Very joyfull

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