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Thread: Why throttle notches?

  1. #1

    Default Why throttle notches?

    Why dont real engines have a variable throttle, like on a plane?
    Maybe because it would be too hard to match engine revs on trailing units?

  2. #2

    Default

    History, tradition, and solenoids.

    Speed control is managed on most engines by engaging combinations of solenoids, and the notches relate to which combinations get engaged. Some manufacturers had more notches than others, others less.

    Early versions of EMD diesels had four solenoids for throttle control, and could accommodate eight combinations. That then translated over to MU design -- four wires could be used to control four solenoids on any engine in the consist. That's where the eight notch "standard" came from with early EMD's and carried over to newer units with a control stand.

  3. #3
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    Speed control only uses 3 relays, the 4th relay is for engine stop ( or run )
    3 bits to the base 16 gives 8 numbers - 8 knotches
    The control stand has 9 notches, the 9th being off.
    Cheers
    Derek

  4. #4
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    Quote Originally Posted by chp56 View Post
    Why dont real engines have a variable throttle, like on a plane?
    Planes don't do MU.
    Cheers
    Derek

  5. #5
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    Interesting, that, about early EMDs. Makes sense. A few other thoughts:

    IIRC, GE U-series locomotives had 16-notch throttles. Presumably, when MU'd with EMDs, only every other notch actually mattered for MU purposes.

    Presumably, there were other arrangements for ancient locomotives like Baldwins, F-Ms, and the like. If it had an air throttle rather than electric, it would seem that the throttle would be continuous rather than notched - unless somehow it was equipped for MU with EMDs...

    Old electrics and streetcars all had "notches" too. They used resistor groups, not a rheostat, in almost all cases, because high-power-handling resistors existed, but rheostats (potentiometers) with similar power handling either didn't exist or were very expensive. Some had a lot more than 8 notches, so there could be finer speed control and comfort. How many notches were on a real GG1 controller? PCCs?

    What it really comes down to is that 8 notches, whether done with relay (solenoid) or semiconductor logic (or even software), is "good enough" for most purposes in the US. Because of how MU connections work, it has become a de facto standard where US practice prevails. Where US-standard locomotive MU isn't an issue (outside N. America, really old stuff, High Speed Rail trains that seldom get broken up, transit equipment with many more wires in the MU bundle or even CAN-like network connections - ever see a transit coupler with all the MU connections in it?), the throttle can have a different number of notches or even be continuous.
    Last edited by mikeebb; 10-09-2019 at 04:43 PM. Reason: fix reference to transit couplers

  6. #6

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    Quote Originally Posted by derekmorton View Post
    Planes don't do MU.
    That would be hilarious!

  7. #7
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    Quote Originally Posted by mikeebb View Post
    How many notches were on a real GG1 controller?
    If I remember right what I learned at the Strasburg Museum, 22 notches.

  8. #8
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    Quote Originally Posted by mikeebb View Post
    IIRC, GE U-series locomotives had 16-notch throttles. Presumably, when MU'd with EMDs, only every other notch actually mattered for MU purposes.
    No mu possible here, that is why the end 8 notch was made standard.
    Cheers
    Derek

  9. #9
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    Quote Originally Posted by chp56 View Post
    Why dont real engines have a variable throttle, like on a plane?
    Maybe because it would be too hard to match engine revs on trailing units?
    Passing a variable signal along several diesels would be subject to a lot of electrical noise and cause the power to jump around.
    Not a very reliable system.

    As the notch system is using relays, it is very reliable.
    I don't know why they stayed with 8 notches, 22 would have been better in my opinion.
    Cheers
    Derek

  10. #10
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    UK Class 60 and first generation diesels had a notchless throttle although it needed to placed from the "off" position to the "on" position before more power could be applied.

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