Another status update of the throttle quadrant.
Meanwhile I’m working on the outer panels with the flaps, speedbrake, parking brake and stab trim functions.
After checking more TQ projects photographs and videos on the internet I noticed the two ‘stops’ on the aluminum flaps guide, which are not always present on the throttle quadrants that are found on internet. A nice challenge to see if I could add this level of detail. The new design can be found in the Downloads section of this blog.
Although they’re small and there is not so much room to mount them to the flaps guide it appeared not too difficult. But it required a new version of the flaps guide because the notches at the stop positions have a different shape than the other ones.
The parking brake did not give too much problems: originally I preferred to have the rotation point higher like in “the real thing”, but in that case the rods that keep the panels together block the joint between the parking brake handle and the clutch/servo.
Something that gave a lot more problems is the speedbrake. In videos I saw that even if it is not in the armed position it can be automatically moved to the up position. So I created a plexiglass lift mechanism similar to what I’d seen in other solutions and added notches in it for all speedbrake positions.
In this way when the plexiglass arc is in the uppermost position, in manual mode the speedbrake handle latches in 3 possible positions.
By lowering the arc a bit the automatic mode doesn’t need to override the notches.
So far the theory, but when I mounted the parts some problems appeared:
– as the speedbrake handle slides along the arc when lifted it requires quite some force to lift it. Initially I wanted to use a solenoid, but I replaced this by a servo for more power and because it has more than just two possible positions.
– the first notch for the ‘armed’ position in the arc was exactly in the sliding path, so when lifted the speedbrake handle got stuck in this notch.
– because the notch for the ‘up ‘position is close to the rotation point it is hardly lowered when the plexiglass arc moves to the lower position, so in automatic mode the handle still locked in the notch and was difficult to override.
To overcome these problems I extended the ‘down’ position of the handle a bit further to the back, so that the upwards movement is more perpendicular to the plexiglass arc which makes it easier to lift the handle.
I also removed the first and last notches from the plexiglass arc as these match with the start and end positions of the handle anyway.
The extra servo for lifting the speedbrake handle brought the total number of servos to 7, 1 more than the number of servo outputs of an OpenCockpits servo card.
Adding an extra card for just 1 servo is expensive, but the nice video of Andreas Haug where he showed the internals of his authentic throttle quadrant and explained that the left and right trim indicators are coupled came to the rescue.
In my original design I had two separate mini servos for the left and right stab trim indicator. Which even where mirrored, so difficult to synchronize.
Instead of this I decided to replace the two mini servos with a bigger servo in the middle of the TQ and connect both the left and right stab trim indicator to the servo arm with a M3 threaded rod.