servo actuated autothrottle for f14

[Gareth Barry]

So, after having 3d printed my stick for the f 14, which works great ( I used the thrustmaster t16000m and simply replaced the shell), I am looking to make my own  f 14 throttles. Some of the shapes are simplified by my limited CAD skills. Anyways, what I am really hoping for is help in making the throttles and wing sweep mechanism to be servo actuated using DCS bios. Seems simple at first, until I started thinking about the actual mechanics of this. My understanding is that in the f14, auto-throttle is immediately disengaged if the pilot exerts any pressure on the throttles. So a mechanism needs to be made that allows for this without the servo gears breaking from being worked against when auto-throttle is not engaged, which seems complicated to my small brain.  At the moment, I am thinking of a system of 2 servos, one for actually moving the throttle, and another one to lock the first servo in place. Then maybe using a force sensing resistor, to sense the hand pressure of the pilot 'resisting' the position of the throttle, which would then be used to A) power down the throttle actuating servo as well as B) use the 2nd servo to 'unlock' the first servo to allow it 'float' in its movable base.  This might seem like a lot of work to make a moving auto-throttle but heck, it seems fun!

Perhaps others have more elegant solutions to this problem, ie a moving auto-throttle that disengages with hand pressure, without ruining the gears of the servo when being moved by hand. Other ideas that I have seen on the net involve slip clutches, but those seem crazy expensive to me.

Keen to hear what others think of this.

Edited April 24, 2023 by Gareth Barry
grammar

[No1sonuk]

Maybe couple the throttles to the servos with springs. Like "servo savers" that are designed to protect servos if the mechanism jams.

Then drive the servos to the position you manually select so that they follow the manual input.

I don't know how DCS defines the throttle servo position, but if it's no different from manual input, that driving part could be as easy as just using the throttle position output.

The only problem I see is that the servo moving the physical throttles might disengage the auto mode because it thinks you're trying to override it. 

[Gareth Barry]

Thanks, interesting suggestion - however, I would think that any spring between the servo arm and the throttle lever would be hinderance toward the goal of getting a true-to-life version of how auto-throttle disengages, ie when the pilot exerts hand pressure on the throttle quadrant. So in essence, the system needs to detect either a force exerted on the throttle quadrant, or else detect a mismatch between the servo position and the actual position (due to pilot had pressure) and then use that to disengage. Hence my suggestion of a force-dependent resistor with a voltage across it which could feed and input to the arduino and act as a switch for the servo. 

Another thought is maybe to use a solenoid instead of an RC-plane type servo, and maybe have quite a low gear ratio, so that moving the throttle quadrant against the gears when the solenoid is switched off doesn't harm the gears too much. This would reduce the complexity compared to my initial idea of having a servo fixing in place another servo which operates the throttle quadrant. 

[Vinc_Vega]

I already had the idea to mis-use some kind of motor driven linear potentiometer and capacitive input for AT but did not realized it yet.

https://www.adafruit.com/product/5466

 

Regards, Vinc

Edited April 24, 2023 by Vinc_Vega

[No1sonuk]

Coupling the servo and lever with a spring doesn't preclude detecting a mismatch in the servo and lever positions.

And don't limit your definition of "servo" to purely RC devices. You could easily make a suitable servo with a geared motor or even a stepper motor...

[Gareth Barry]

No1sonuk - I hear you, although I think i am going to go with Vinc_Vega's suggestion- seems elegant and simple. I was thinking mainly in terms of RC servos since I am familiar with them, but I hear what you are saying. If Vince_Vega's suggestion doesn't work out for some reason, I might go with a low geared motor and hall sensors.

Vince_Vega - Being a gigging musician who is used to digital mixing desks, I am ashamed that I didn't think of this! I see they come in both the rotary as well as linear varieties. For the f14 the rotary variety will be easier. These things seems to have a clutch mechanism and everything all built in

rotary;

Alps Rk16812mg Dual Potentiometer 10k Ohm Lin Taper Pot Motrorized Rk16 for sale online | eBay

linear;

8x Alps Fader Motorized Rsa0n11m9 Touch Sensitive 10k Linear Slide Potentiometer for sale online | eBay

So the next step will be finishing up the cad models, and then 3d printing the parts. Will be posting the progress as I go, as I am going to need a bunch of help with DCS Bios etc.

Thanks everyone.