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.
Unfortunately I haven't got the connection information for this device nor the schematics/service manual. I know there's a service manual, but I haven't got a reaction from him. (https://www.eevblog.com/forum/chat/sperry-311-honeywell-vg-311-gyro) 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...
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
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.