MCP – autothrottle switch, part 2

After approximately a month the solenoid has arrived (a small drawback to the extremely low prices on aliexpress).
But as a cockpit builder there are always other things you can continue with, so I used the time to optimize my drawing in Inkscape and to continue with the throttle quadrant.

Similar to the method I used for fixing the toggle switch case to the 18 mm MDF spoiler board I created pockets in the spoiler board for the aluminum 20x20x2 mm U profiles that are used as frame for the switch and solenoid.


But first the CNC router was used to create the lever from 3 mm aluminum plate. To fit in the slot of the solenoid bar and small hole in the switch plate it had to be narrowed near the ends.
For the axis of rotation a piece of a silver steel axis of 4mm diameter was used that was left from a previous project.

Next the U profiles and 3 mm acrylic plates were processed and the screws that hold the solenoid were shortened (a precise job because the solenoid frame is quite thin and if the screws are too long the coil windings could be damaged).  At the opposite side of the solenoid there is no space left for nuts so I tapped M3 thread for the two screws in the U profile.

And then there was the moment of truth: will it work?
After assembling the construction I armed the switch, applied the 12V power and…..
found that the solenoid was too weak to toggle the switch.

I had been thinking about measuring the required force in some way, but don’t have such a nice force meter like we used to have in physics class.
I could have used a known mass and let gravity do the work, but too late.

As the lever wasn’t rotating as easy as I expected I tried to lubricate the joints, but that appeared not enough.

I also added a spring to the switch, but again not enough.
This spring was part of the collection that I bought for the fuel cutoff levers by the way. (Spring collection)

So I left the project alone for a day and thought of the 24V power supply that was left from my electromagnetic clutches.

Although the operating voltage of the solenoid is 12V it will be powered for a very short period of time, so I decided to just try to apply a short 24V pulse.
And hooray, it worked and kept working!!!

I’m still thinking about building a second version because for the first prototype I rotated the U profile 180 degrees for milling the holes and I noticed that the alignment of the holes for the axis of rotation is not perfect which could be the reason that the lever doesn’t rotate as easily as expected.
Also I could look for a stronger solenoid: the current one has 6N force and there are much stronger ones available, but most of those unfortunately don’t fit in the 20mm U profile.
But for the moment I’m just going to see how reliable it is with 24V.

The design of the switch in Inkscape SVG format can be found at the  downloads page.


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