I'm very fond of gyroscopes and I like artificial horizons like the Smiths H6 Director Horizon. Michel from France made a video about the Sperry 313 gyroscope. This video is shown below. The vertical gyro is(/was) widely used in several air planes like the Boeing 737. And I wanted to replicate this setup as shown in the video.
Source: Video: Le Labo De Michel
Since this gyro model is rather expensive, I looked for a while on the internet to find a affordable one. And halfway the year 2023 I found a Honeywell/Sperry 311 vertical gyro in the USA for my budget. (Part number 2587335-11 or VG-311.) The 313 and 311 seem te be rather similar except for the 'missing' second connector. Since it had to be shipped to the 'other side of the world' the price including shipping and taxes wasn't very low, but good enough. After a couple of weeks the box arrived. Yey! The bad thing is that the box was torn, there were holes in the box and the contents was 'floating around' in de box. On the gyro is written: "Handle with care!" and "Delicate instrument!" But still the gyro was packed very very bad. To make everything even worse, the metal cap was dented seriously. So the packaged was dropped from a serious height and landed upside down. The metal cover was dented that it now touches the inner frame. Since the metal lid is rather thick and shaped (to obtain more mechanical strength) the impact had to be serious. It probably no surprise that I was not happy... I contacted the (eBay) seller and he acted very emphatic and responsible. He handled this very professional, so kudos for him!
The damaged lid is shown below. The right bulge should be at the same height as the left bulge. The difference in height is rather clear... The good thing is that there's no visual damage found. Although it's rather likely that the precision bearings are compromised due to the impact. The glass 'spirit level' tubes are also undamaged. My plan is to use a hydraulic press to restore the original shape of the lid.
Since this 311 gyro looks similar to the 313 one, it's likely that this one is pin compatible. Michel mentioned that the power pins are pins  and . With some 'probing around' on the circuit board, this seems likely. I applied 115 VAC 400 Hz to pins  and  and the 400 Hz hum is heard and the motor moves, but not spin up. After a measurement it turns out that my power supply (modified audio amplifier) can't handle the load so the voltage limits at 55 VAC. So it's likely that the pinout matches but that the current draw is too much as Michel in his earlier video's mentioned. Hopefully I can find/receive the service manual for this 311 gyro and in the meanwhile I have to think of a way to generate more 115 VAC 400 Hz current... 20231106 - Luckily I found some more information about the pinout. More information will follow later on, but here's the first important information:
power input: '46' = 115 VAC 400 Hz power input (also linked to '44') '47' = 115 VAC return/common ground (also linked to '1')
roll data output: '7' = synchro output X (115 VAC) '8' = synchro output Y '9' = synchro output Z
pitch data output: '5' = synchro output X (115 VAC) '4' = synchro output Y '6' = synchro output Z
26 VDC output (intended to be used for error flag control): '24' = +26 VDC at startup/not operational condition '12' and '45' = +26 VDC at normal operational condition '47' = 115 VAC return/common ground (also linked to '1')
error flag control relay: '19' = relay common '20' = relay NO contact
interlock relay (switch at normal operating conditions): '15' = common '14' = NO contact (normal operational condition) '16' = NC contact (normal operational condition/startup)
interlock relay (switch at normal operating conditions): '17' = common '18' = NO contact (normal operational condition)
interlock relay (switch at normal operating conditions): '19' = common '20' = NO contact (normal operational condition)
After removing a set of screws I lifted the lid off the housing. The gyroscope mechanics is now revealed. This is shown on the image below. The gimbal frame is shock mounted in the red/orange rubber mountings. On top of the (outer) roll gimbal and the (outer) pitch gimbal are two glass tubes mounted. These are for detecting the (desired) initial vertical position. There's a transparent liquid inside the tubes. A drop of mercury was more logical since mercury conducts and acts as a switch. Since mercury (and it's vapour) is (very) toxic this is likely replaced with some other solution. Maybe the liquid is conducting or the capacitance changes resulting in the same position detection. This needs some more investigation...
Specifications and features
Name: Vertical Gyro Model 311 Part number: 2587335-11 Aternative part number: VG-311 Connector: 50 pin circular Cannon connector pin size #20
Specifications Height: 9.563" = 24,29 cm Width: 10.125" = 25,72 cm Length: 10.719" = 27,23 cm Power supply: 115 VAC / 400 Hz Temperature range: -55°...+70° C = -68°...+158° F Weight: 14.8 lbs = 6,71 kg
Bank (roll): Full 360 degrees freedom Climb and dive (pitch): Approximately 85 degrees freedom (mechanical end stops) Operating temperature: -55...+70 degrees C / -68...+158 degrees F Erection system: Liquid levels and torque motors Vertically error: 0,25 degree maximum Flight controls/system signal output data: Three wire pitch an roll synchro transmitter (115 VAC) Flight director/radar stabilisation/comparator recorder signal output data: Two wire transformer type (three outputs per axix) Gyro compartment: Pressure sealed
Features Low erection rate and response sensitivity to eliminate any tendency of the aircraft to oscillate in high-speed flight. Electrically driven gyroscope. Roll cut-off switch automatically disables roll erection while aircraft is in a turn. Pitch erection is restored automatically after three minutes even if cut-off switches continue to indicate acceleration.
On the images below is the gyroscope unit shown. The housing consists of a sealed aluminium housing with a rubber seal and a aluminium lid. The unit is mounted using four mounting holes. There's a specific bond for a (flexible) ground strip for proper 'grounding'. At the bottom of the die cast housing is a shielding cover placed to protect the control electronics.
At the bottom end of the housing is the electronic circuitry placed. After removing three machine screws can the protecting cover be removed. On the image below is also a moisture absorber visible. The moisture absorber is a plastic cylindrical housing containing silica beads. The goal is that moisture in the gyroscope housing is absorbed by the silica to protect corrosion to the sensitive gyroscope mechanics.
After removing five machine screws, the aluminium panel with electronics components can be tilted since there are hinges installed. The panel can be tilted to access the bottom part of the movable panel and the rest of the electronics.
Interesting is that there are no printed circuit boards installed. The base if the electronics are aluminium panels with white plastic insulators and connecting pins. All the electronics components like resistors, capacitors and so on are connected to these connecting pins. Component leads can share a connecting pin and also wiring can be soldered to the connecting pins. The aluminium panels are divided into squares. Eacht line has an identification starting with A, B, C and so on for horizontal lines and 1, 3, 5 and so on for vertical lines. This 'coordinate system' makes is easier to locate components during service ans repair. The good thing about this mechanical style design is that it's built for heavy duty use like large mechanical stresses due to vibrations and large gravity forces. Interesting though is that it seems that carbon composite resistors are used. Carbon composite resistors are known for it's noisy performance. I assume that these resistors where the industry standard back in the day, but nowadays these type of resistors are not recommended to used. Probably the resistor performance won't affect the function and usability of the gyroscope tough.
On the image below is the circuitry seen with the movable lid tilted away. The larger board is more dense 'populated' and designed with high efficiency. At the right bottom part of the left board can the green connector be seen that links these electronics to the electronics in the gyroscope compartment. This is an airtight connector to prevent access of dust and moisture to the rather sensitive gyroscope mechanics.
After removing a lot of mechanical bolts, the lid and rubber gasket can be removed. The view of the inside is shown on the image below. The gimbal with the gyroscope components are fitted in a metal frame. The frame is suspended with the remarkable orange rubber dampers.
The mechanical parts of this gyroscope is a masterpiece of engineering precision. Every movable part moves easy with no play.
On top of the gimbal are two glass envelopes shown which are used for detecting the gimbal's position. At startup of the gyroscope is the orientation detected by these glass envelopes and the electronics controls the (big orange ring shaped) torque motors. The torque motors are powered to send the gyroscope to it's vertical position. In the glass vials is a liquid present wit electrical contacts. The liquid is unknown to me by I expect that the liquid is conducting or the electrodes and liquid have some significant capacitance change that can be used by the electronics circuit. The blue 'studs' are just interconnecting points for the electrical wiring.
On the image below is movable multi contact visible. The inner gimbal has a movement of 170 degrees. One part of the contacts (left) are connected to the inner gyroscope housing and the other part (right) is connected to the middle gimbal housing. This design results in a low friction solution that's rather durable. Note that the orange plastic housing of the torque motors an be seen well here.
On the image below is the gyroscope housing visible in the middle. (The gyroscope axis is not in it's usual upright position here.) The photo is focussed on the red(dish) copper wire coil. This coil is outer part of the synchro transmitter that sends the position information of the gyroscopes position. The other half of the synchro transmitter is in the middle of the outer coil. By applying an AC voltage to the rotor coil, three voltages are induced in the three stator coils. By rotating the angle of the axix, the amplitude and phase changes. This makes it possible to detect the angular movement of the gyroscope with high precision. There are two synchro transmitters installed; one for each axis (roll and pitch).