Throttle Quadrant

On internet many DIY-projects can be found for building a Boeing 737 Throttle Quadrant.
Most of them use a sandwich construction of 11 wooden plates connected with 8 mm full threaded rods.
The throttle, flaps and speedbrake handles rotate around a central rod and switches and potentiometers are attached to the wooden plates.

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When checking one of these TQ projects on www.thair.nl I noticed that the design of the plates could be requested as a DWG file.
Using the DWG to DXF converter on www.autodwg.com/dwg_dxf_converter I had this converted to a DXF file so that I could open and modify it in Inkscape.

For the wooden plates I purchased a 244 cm x 122 cm x 6 mm MDF plate and had it sawn in 29 cm wide strips that nicely fit on my CNC router table.
In Inkscape I had to do some processing of the converted DXF design so that Estlcam was able to trace the outlines of the panels (no gaps) and create G-code for each panel so that it could be milled with the CNC router.

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As I don’t have a lathe I purchased a complete set of knobs for all levers at cockpitsimparts.co.uk (‘Boeing 737 Throttle full handle set’)
These knobs appeared to be solid, so I’ve used the CNC router to make holes in the throttle knobs to fit the pushbuttons for the autothrottle disengage function.


Also I modified the design of one of the throttle handle plates a bit so that it better matches the notch in the knob.

Many throttle quadrant projects found on the internet are ‘passive’ implementations, that is, they’re not motorized.
I’d like to have the levers moved automatically by the autothrottle however.

After some more searching on the internet I found a very instructive YouTube channel ‘Buildaboeing‘.
A couple of the videos on this channel show various aspects of the construction of a motorized throttle quadrant using servos.
Most important difference with many other DIY throttle quadrant implementations is that all functions are motorized: not only the throttle handles and stab trim wheels, but also the speedbrake, parking brake and stab trim indicators.

There are some cockpit builders that have created very realistic implementations for the throttle handles with motors and a clutch so that even under autothrottle control the handles can be manually overridden, but these are expensive solutions. I decided for the somewhat less realistic, but cheaper implementation with servo motors as seen in the Buildaboeing videos.

Another difference with other projects is that instead of ‘normal’ potentiometers driven by gears Peter from Buildaboeing uses sliding potentiometers moved via levers by the throttle handles.
Instead of two microswitches at the outer limits of the reverse thrust handle paths he used potentiometers with gears: according to him this more closely resembles the original reverse thrust handles: when moving them they only trigger after halve of the rotation.

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Something he mentions in one of his videos but didn’t implement is that the reverse thrust handles in real life can only be moved when the throttle handles are in idle mode.
It was an interesting challenge to see if I could find a solution to add this to my implementation.

For driving the trim wheels I used a solution with bike chains as found in some other implementations. I want to use cheap derailleur jockey wheels that can be bought at Aliexpress for just over a euro a piece.
I spent some time finding suitable, small and narrow enough chain tensioner wheels. Until I read the annotations on the pictures in the document ‘How to build a B-737 300/800 throttle quadrant’ by Francisco Gago of February 2004 where I found that the ‘K’NEX Hub/Pulley Medium‘ is very suitable for this.

 

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trim wheel

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Fuel cutoff handle with two microswitches

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Interesting links:

www.737ngproject.be
Youtube kanaal Buildaboeing
www.buildaboeing.com
www.737flightsim.com
www.737ngxca.com/throttle.html

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