Autothrottles & servos disconnect

[mauriceb]

Hi,

I am building a 737 throttle assembly with A/T servos and I have come up with a way to disconnect the servos when the A/T is not active so that you can move the throttles manually. I made a drawing that describes how I plan to do it and I'm wondering if my idea will work or if I have missed something crucial.
I would appreciate any comments from anyone who thinks this might or will not work for whatever reason.

Thanks,
Maurice

http://i32.photobucket.com/albums/d3...rvoswiring.jpg

[alandyer]

Maurice,

Your design has been used by a number of builders.
i.e. using A/T arm status to control power to servo.

Using 8/8/8 to control Phidget 0/0/4 (relays) is redundant.
Phidget 0/04 is already digital output.
i.e. will respond directly to A/T Arm status.

Regards,
Alan.

[mauriceb]

Maurice,

Using 8/8/8 to control Phidget 0/0/4 (relays) is redundant.
Phidget 0/04 is already digital output.
i.e. will respond directly to A/T Arm status.

Regards,
Alan.

Hi Alan,

I realize that, but A/T arm status is not the only variable here. I need A/T arm AND either IAS or Mach inputs to actuate the relays since I don't want power to the servos just when I arm the A/T. Arming is not the only thing that is needed befofe the A/T functions. You still have to turn on the IAS switch or the Mach switch, otherwise the A/T does nothing.

Am I out to lunch here ?

Thanks,
Maurice

[alandyer]

Maurice,

One thing missing from your diagram is input for servos.
i.e. THROTTLE POSITION

Your servos would be tracking throttle position in MS-FS, right ?
i.e. your real throttles will track virtual throttles.

When your virtual autopilot (controlled by real IAS/Mach and N1 switches) changes virtual throttle your real throttles will track.

Design consideration: When should real throttle track virtual throttle ?
All the time ? Nope. Hence, requirement for Relay to disengage virtual world from real world. You understand this, Neo

The answer that most designers arrive at:
When virtual autothrottle is driving virtual throttle levers !

Add a block for virtual AUTOPILOT in your diagram.
If you are super fastidious you might put a dotted line through that block and label one half MS-FS and the other half PM MCP/PM CDU.

Digital input for MACH/IAS and N1 will run to that block.
Coming out of that block will be THROTTLE POSITION controlling servo.
Coming out of block will by A/T ARMED controlling relay to servo power and possibly electromagnetically controlled clutch.

Regards,
Alan.

[mauriceb]

[QUOTE=alandyer]Maurice,

One thing missing from your diagram is input for servos.
i.e. THROTTLE POSITION
QUOTE]

Hi Alan,

Just some clarification to my earlier question. I already have the servos & the throttle handles moving in response to the A/T and that is working great thanks to Rob Howard's excellent article AND your excellent software. So, what is 'missing' from my diagram was intentional since all I am really concerned about at this time is how to disconnect the power to the servos when A/T is turned off. The diagram wasn't meant to show all the wiring necessary to achieve the full A/T or manual operation.

I'm not going to try & use a clutch or some other mechanical way since this would complicate things un-necessarily in my opinion. I have the powered throttles working OK with A/T control; all I need is to disable power to the servos when flying manually. I still think my diagram allows me to do that (I will add the N1 input).

So, I really hate to question your answer again , but I'm still not sure that I need to do anything else if all I want to do is cut-off the power to the servos when I don't want the A/T to control the throttle.
Sorry if I am too dense :confused: , but can you please look again at my diagram and let me know exactly what you think may be wrong with it based on this new information.

Thanks again
Maurice

[alandyer]

I would use A/T ARM offset to control power.

SPEED, N1 and VNAV are inputs to virtual A/T (MS-FS and/or PM).
These set the mode for A/T unit (virtual in your case).
A/T in turn manipulates power levers which you track with servos in real world.

When A/T is disengaged it does not matter what the mode is.
i.e. A/T is not driving power levers.

[mauriceb]

I would use A/T ARM offset to control power.

SPEED, N1 and VNAV are inputs to virtual A/T (MS-FS and/or PM).
These set the mode for A/T unit (virtual in your case).
A/T in turn manipulates power levers which you track with servos in real world.

When A/T is disengaged it does not matter what the mode is.
i.e. A/T is not driving power levers.

Alan,
I'm sorry but I have no idea how your reply relates to my question in any way. Obviously, I haven't made myself very clear and I don't know how else I can put it.
Anyway, I don't want to waste any more of your time. Thank you for trying anyway.

Best regards,
Maurice

[imported_farrokh747]

Hi M - did you find the answer to this one yet? I'm guessing the power would have to be switched off somehow when any none of the at modes are active - ie, the at thrust annunciation in the fma is blank - what happens if you have the porwe to the servo running, but are not in any AT mode on your set up? Will the servo hold the last position it was in?

cheers,

FC

[mauriceb]

Hi M - did you find the answer to this one yet? I'm guessing the power would have to be switched off somehow when any none of the at modes are active - ie, the at thrust annunciation in the fma is blank - what happens if you have the porwe to the servo running, but are not in any AT mode on your set up? Will the servo hold the last position it was in?

cheers,

FC

This is how I resolved my problems. This works perfectly for me and although it may not be the best solution, it does everything I need it to do.
Basically, power is supplied to the servos if the autothrottle switch is on and if either TOGA, Airspeed or Mach hold are on. The A/T disconnect on my throttle assembly turns off the autothrottle and that automatically removes power to the servos and allows me to move the throttle handles & control the power manually.

The spare inputs to the OR gate can be used if there are other conditions that require power to the servos, but so far I haven't found any (I'm sure there must be other times when that would be required, and if I find out what it is, I will use the spare inputs).

http://entertainment.webshots.com/ph...51510320bvfAHE

Regards,

Maurice

[imported_farrokh747]

Hi maurice - thanks for the diagram - will see how I can make it work for me -

Happy New Year -

c

FC