5 ms·

Author here for all your mechanical computer questions :-)

by kens 3y ago

CamperBob2 3y ago
I'll point out that reverse engineering the CADC is not as easy as you might expect. Well, there goes that illusion. :) An amazing piece of work as usual, Ken. Thanks for sharing your hard-won insights on this gadget. The linear-endpoint wraparound hack was worth learning about all by itself. I'm surprised it took until 1954 before someone got around to patenting that, as it seems like a valuable general-purpose control technique. I can imagine a CORDIC-like algorithm that takes advantage of something similar to avoid clamping. You have to find a way to power this thing up as a static demonstration piece.
- kens 3y ago
  Thanks! We're powering up the unit piece by piece. CuriousMarc got a vintage pitot tube vacuum simulator so we'll use that to simulate the different pressures.
mgsouth 3y ago
Based on a quick search, it looks like air impedance (the mysterious air density x speed of sound calculation) affects turbine stability. So needed for engine control?
- kens 3y ago
  Thanks, that makes sense. Do you have a link that discusses this?
  - mgsouth 3y ago
    Wow, what a rabbit hole... I started by searching for "turbine air impedance". Seems to be a common topic, but maybe just for design modeling? And maybe an outdated parameter to use? One of the front-page hits is a recent (2021) paper from Whittle Laboratory [1] "Modeling Turbine Acoustic Impedance" [2]. Abstract says in part "Impedance boundary conditions are an influential yet uncertain parameter in predicting the thermoacoustic stability of gas turbine combustors...A parametric study of turbine stage designs using the analytical model shows acoustic impedance is a weak function of degree of reaction and polytropic efficiency. The design parameter with the strongest influence is flow coefficient, followed by axial velocity ratio and Mach number. We provide the combustion engineer with improved tools to predict impedance boundary conditions, and suggest thermoacoustic stability is most likely to be compromised by change in turbine flow coefficient." Many search iterations later [5], I found a recent paper discussing "fuel flow rate fluctuations which depend upon the air side impedance at the fuel injection location" [3]. Maybe it's for controlling inlet shock waves? However, I couldn't find anything obiously linking "Air inlet control systems" to "air impedance". Here's one paper discussing such a system, with an extremely detailed transfer function [4]. Maybe it's using another term for impedence, or something close? Edit: Considering this was cutting-edge control hardware for military equipment, I guess some lack of public details is to be expected. On the other hand, on Ebay there's a Fuel Control Unit for a J-79 engine as used in the B-58 Hustler [6]. [1] Yes, that Whittle. https://en.wikipedia.org/wiki/Whittle_Laboratory https://en.wikipedia.org/wiki/Whittle_Laboratory [2] https://www.mdpi.com/2504-186X/6/2/18 https://www.mdpi.com/2504-186X/6/2/18 [3] "Analytical modelling of flame transfer functions for technically premixed flames" https://journals.sagepub.com/doi/full/10.1177/17568277221094403 https://journals.sagepub.com/doi/full/10.1177/17568277221094... [4] "Complex Control System for an Aircraft Supersonic Inlet" http://www.wseas.us/e-library/conferences/2009/rodos/SYSTEMS/SYSTEMS75.pdf http://www.wseas.us/e-library/conferences/2009/rodos/SYSTEMS... [5] Just so you know, "b-58 engine computer" only brings up automotive stuff. [6] https://www.ebay.com/itm/325676156863?_trkparms=amclksrc%3DITM%26aid%3D777008%26algo%3DPERSONAL.TOPIC%26ao%3D1%26asc%3D20230823115209%26meid%3D5af4cefff0304c96bd723aeb9765b577%26pid%3D101800%26rk%3D1%26rkt%3D1%26sd%3D325676156863%26itm%3D325676156863%26pmt%3D0%26noa%3D1%26pg%3D4375194%26algv%3DRecentlyViewedItemsV2SignedOut&_trksid=p4375194.c101800.m5481&_trkparms=parentrq%3A0c6fc5d618b0ab9711f1f22affff6958%7Cpageci%3Ae1b69473-6567-11ee-bb79-8eca912930b8%7Ciid%3A1%7Cvlpname%3Avlp_homepage https://www.ebay.com/itm/325676156863?_trkparms=amclksrc%3DI...
    - kens 3y ago
      Thank you for the detailed response! This is way more than I expected :-)
  - akira2501 3y ago
    Seems also to be related to https://en.wikipedia.org/wiki/Rayleigh_flow https://en.wikipedia.org/wiki/Rayleigh_flow
dekhn 3y ago
Are the synchros in this similar to what the Rosenblatt Perceptron used to adjust and show weights: "This machine was designed for image recognition: it had an array of 400 photocells, randomly connected to the "neurons". Weights were encoded in potentiometers, and weight updates during learning were performed by electric motors.[2]: 193 "
- kens 3y ago
  I couldn't find details on the Perceptron's motors, but I expect they were DC motors, rotating the potentiometers higher or lower as needed. The synchro is useful if you have a rotation in one location and one to match the rotation at another location. But with the Perceptron, you don't have a specific rotational angle you want, just "more" or "less".
cesarb 3y ago
How are these "zeroed"? That is, how did they make sure that the "zero" position for all gears is correct when assembling the device?
- kens 3y ago
  I'm not sure how the devices were zeroed. This will probably be an issue when we put it back together. I think some of the gears could be loosened on the shaft so they could be rotated to the correct point. The manual defines the zero points for all the synchros, i.e. 0° means X pressure or Y temperature, so I guess you'd adjust everything to those points.

Author here for all your mechanical computer questions :-)

by kens 3y ago

Author here for all your mechanical computer questions :-)

I'll point out that reverse engineering the CADC is not as easy as you might expect. Well, there goes that illusion. :) An amazing piece of work as usual, Ken. Thanks for sharing your hard-won insights on this gadget. The linear-endpoint wraparound hack was worth learning about all by itself. I'm surprised it took until 1954 before someone got around to patenting that, as it seems like a valuable general-purpose control technique. I can imagine a CORDIC-like algorithm that takes advantage of something similar to avoid clamping. You have to find a way to power this thing up as a static demonstration piece.

kens 3y ago
Thanks! We're powering up the unit piece by piece. CuriousMarc got a vintage pitot tube vacuum simulator so we'll use that to simulate the different pressures.

mgsouth 3y ago

Based on a quick search, it looks like air impedance (the mysterious air density x speed of sound calculation) affects turbine stability. So needed for engine control?

kens 3y ago
Thanks, that makes sense. Do you have a link that discusses this?
- mgsouth 3y ago
  Wow, what a rabbit hole... I started by searching for "turbine air impedance". Seems to be a common topic, but maybe just for design modeling? And maybe an outdated parameter to use? One of the front-page hits is a recent (2021) paper from Whittle Laboratory [1] "Modeling Turbine Acoustic Impedance" [2]. Abstract says in part "Impedance boundary conditions are an influential yet uncertain parameter in predicting the thermoacoustic stability of gas turbine combustors...A parametric study of turbine stage designs using the analytical model shows acoustic impedance is a weak function of degree of reaction and polytropic efficiency. The design parameter with the strongest influence is flow coefficient, followed by axial velocity ratio and Mach number. We provide the combustion engineer with improved tools to predict impedance boundary conditions, and suggest thermoacoustic stability is most likely to be compromised by change in turbine flow coefficient." Many search iterations later [5], I found a recent paper discussing "fuel flow rate fluctuations which depend upon the air side impedance at the fuel injection location" [3]. Maybe it's for controlling inlet shock waves? However, I couldn't find anything obiously linking "Air inlet control systems" to "air impedance". Here's one paper discussing such a system, with an extremely detailed transfer function [4]. Maybe it's using another term for impedence, or something close? Edit: Considering this was cutting-edge control hardware for military equipment, I guess some lack of public details is to be expected. On the other hand, on Ebay there's a Fuel Control Unit for a J-79 engine as used in the B-58 Hustler [6]. [1] Yes, that Whittle. https://en.wikipedia.org/wiki/Whittle_Laboratory https://en.wikipedia.org/wiki/Whittle_Laboratory [2] https://www.mdpi.com/2504-186X/6/2/18 https://www.mdpi.com/2504-186X/6/2/18 [3] "Analytical modelling of flame transfer functions for technically premixed flames" https://journals.sagepub.com/doi/full/10.1177/17568277221094403 https://journals.sagepub.com/doi/full/10.1177/17568277221094... [4] "Complex Control System for an Aircraft Supersonic Inlet" http://www.wseas.us/e-library/conferences/2009/rodos/SYSTEMS/SYSTEMS75.pdf http://www.wseas.us/e-library/conferences/2009/rodos/SYSTEMS... [5] Just so you know, "b-58 engine computer" only brings up automotive stuff. [6] https://www.ebay.com/itm/325676156863?_trkparms=amclksrc%3DITM%26aid%3D777008%26algo%3DPERSONAL.TOPIC%26ao%3D1%26asc%3D20230823115209%26meid%3D5af4cefff0304c96bd723aeb9765b577%26pid%3D101800%26rk%3D1%26rkt%3D1%26sd%3D325676156863%26itm%3D325676156863%26pmt%3D0%26noa%3D1%26pg%3D4375194%26algv%3DRecentlyViewedItemsV2SignedOut&_trksid=p4375194.c101800.m5481&_trkparms=parentrq%3A0c6fc5d618b0ab9711f1f22affff6958%7Cpageci%3Ae1b69473-6567-11ee-bb79-8eca912930b8%7Ciid%3A1%7Cvlpname%3Avlp_homepage https://www.ebay.com/itm/325676156863?_trkparms=amclksrc%3DI...
  - kens 3y ago
    Thank you for the detailed response! This is way more than I expected :-)
- akira2501 3y ago
  Seems also to be related to https://en.wikipedia.org/wiki/Rayleigh_flow https://en.wikipedia.org/wiki/Rayleigh_flow

dekhn 3y ago

Are the synchros in this similar to what the Rosenblatt Perceptron used to adjust and show weights: "This machine was designed for image recognition: it had an array of 400 photocells, randomly connected to the "neurons". Weights were encoded in potentiometers, and weight updates during learning were performed by electric motors.[2]: 193 "

kens 3y ago
I couldn't find details on the Perceptron's motors, but I expect they were DC motors, rotating the potentiometers higher or lower as needed. The synchro is useful if you have a rotation in one location and one to match the rotation at another location. But with the Perceptron, you don't have a specific rotational angle you want, just "more" or "less".

cesarb 3y ago

How are these "zeroed"? That is, how did they make sure that the "zero" position for all gears is correct when assembling the device?

kens 3y ago
I'm not sure how the devices were zeroed. This will probably be an issue when we put it back together. I think some of the gears could be loosened on the shaft so they could be rotated to the correct point. The manual defines the zero points for all the synchros, i.e. 0° means X pressure or Y temperature, so I guess you'd adjust everything to those points.