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I've been tinkering with the top bay door, pondering how I want to set it up for servo control, and more specifically how to hinge the door.
Here's a simplified cross section of the bay, as if you are looking from the front of the droid toward the back (so port is to image right and and starboard is to image left). Any dimensions specified here are accurate to the real model. The black part is the door.
![[Image: 20230621-hinge-geometry-01.png]](https://www.niflheim.net/droidbuilding/images/LD-F1/20230621-hinge-geometry-01.png)
There are three types of hinges that I have been pondering:
If I wanted to place a hinge on the starboard side of the door, then the only thing that will work is the tape hinge. The door sits directly on plastic with no gap between to allow for a compact metal hinge or for the mounts for the R-series hinges. Also, the R-series hinges would extend into the interior cavity of the head, and on the starboard side, that'd likely be a problem because the existing head mechanics are right there. And yeah, hinging the narrow side of the door would look a bit odd.
Putting the hinge on the port side of the door (which was my intent from the start) won't have quite as many limitations. Obviously the tape hinge is still the simplest here. But now a compact metal hinge could also work, but it would have to be shaved down on whichever side is attached to the bay wall (each side is (13/2) = 6.5 mm, and the wall is only 5.155 mm high.
As for the R-series hinge, this is problematic for a number of reasons, mostly because there are some tight constraints on where the pivot can be located. If you drew an arc that represents the desired path of the lower corner of the door from its closed position to its maximum "open" position, then the center of that arc is the necessary pivot location.
The ideal pivot placement for LD-F1's situation would allow the door to rise faster than it travels horizontally (at least until it clears the top of the opening). That means that the pivot would best be placed nearer the corner of the door vertically than it is horizontally. If you imagine the pivot's rotation circle as a compass, it'd be best if the pivot were between East and East-by-Southeast from the door, or as a clock, between maybe 3:15 and 4:30 ... ideally closer to the 3:15 end.
Unfortunately, that's not very practical. If you look at the dimensions given above, the pivot has to be at least (1 + 5.155 + 2) = 8.155 mm below the upper surface of the head, plus some offset from the inside surface (1 mm in this model). That's dimension B in the next image. Horizontally, on the other hand, anything more than 6 mm away from the port inside wall of the bay, will place the pivot axis inside the shorter section of the head. That could be problematic. It's 4.5 mm in this model, dimension A.
If the pivot fits the constraints given above (as A and B do), it will always be nearer the corner horizontally than it is vertically. Have a look at this diagram:
![[Image: 20230621-hinge-geometry-02.png]](https://www.niflheim.net/droidbuilding/images/LD-F1/20230621-hinge-geometry-02.png)
In the above image, the dashed circle represents the path of the lower corner of the door. You could only rotate the hinge about 6 degrees before it strikes the head, and by the time you've rotated more than about 24 degrees, the door would have reached the apex of its movement and would be moving further into the head (having never actually cleared it).
As for the dashed line coming off the bottom the pivot, then going left, and then going back up to the door, this is roughly the shape of the R-series style hinge arms that would be needed, and the lengths of those dashed lines are determined by where the pivot is. For example, since the bottom dashed line rotates upward to become a vertical line as the door opens, its length must be >= dimension B plus some extra for clearance as well as the thickness of the arms perpendicular to it (represented as 0.5 mm in this example, but probably a fair bit larger).
There is another small problem that would make the pivots for the R2 style hinges harder to place because of the way I designed the head. Below is the relevant section in CAD from a high angle to the side (the white shape shown in the head opening here is the ridged reinforcement pattern I'm likely adding to the bottom of the door itself. It is currently a separate model so I can check clearance.):
![[Image: 20230621-top-bay-hinge.png]](https://www.niflheim.net/droidbuilding/images/LD-F1/20230621-top-bay-hinge.png)
The main problem is the magnet mount (the protrusion beneath the top edge of the opening in the head, with the circular recesses for holding magnets) and how close it'll be to one of the hinge arms. Here's the view from a lower angle:
![[Image: 20230621-top-bay-underside.png]](https://www.niflheim.net/droidbuilding/images/LD-F1/20230621-top-bay-underside.png)
And the bottom view:
![[Image: 20230621-top-bay-bottom.png]](https://www.niflheim.net/droidbuilding/images/LD-F1/20230621-top-bay-bottom.png)
I should have centered the magnet mount rather than putting it so far toward the rear of the head. Notice how close the highlighted rectangle in the last image is to that horizontal rectangle. The pivot has to be closer to the top edge of the image than the highlighted rectangle is, which implies that the pivot on that side will end up directly adjacent to (and probably overlapping) that magnet mount). It's also possible the new antenna mechanism could interfere, since it's in the area at its highest point, but i havent checked specifically.
So the upshot is that the R2-style hinges have several problems, and I would likely have to go with one of the other two options.
Edit: Upon further consideration, the other two also have a problem. If I leave the black door overhanging the port wall of the bay; then the door protrudes beyond the port side of the pivot point on that image, which means that the protrusion would rotate downward. Since it's already in contact with the lip the door sits on, it would be blocked from rotating at all. In order to avoid that, the pivot point ideally needs to be as close to the actual bottom right corner of the black door in that image as possible, and even that wouldn't strictly be enough. I'll have to think on it more. Might end up needing to embed a pivot directly into the wall of the bay.
Here's a simplified cross section of the bay, as if you are looking from the front of the droid toward the back (so port is to image right and and starboard is to image left). Any dimensions specified here are accurate to the real model. The black part is the door.
There are three types of hinges that I have been pondering:
- A living hinge type of arrangement. Think "piece of tape along the side of the bay and the underside of the door". It is the most compact, cheapest, and easiest to implement, but it will look the worst.
- A compact metal hinge, such as this antique type from amazon or something similar, arranged much the same way as the living hinge above. I don't really think this would fit the aesthetics of the droid, even painted, and it would have to be glued on rather than attached with screws.
- U-shaped hinges akin to those often used for R-series Astromech panels (astrogreeblies, Seth's hinges, etc)
If I wanted to place a hinge on the starboard side of the door, then the only thing that will work is the tape hinge. The door sits directly on plastic with no gap between to allow for a compact metal hinge or for the mounts for the R-series hinges. Also, the R-series hinges would extend into the interior cavity of the head, and on the starboard side, that'd likely be a problem because the existing head mechanics are right there. And yeah, hinging the narrow side of the door would look a bit odd.
Putting the hinge on the port side of the door (which was my intent from the start) won't have quite as many limitations. Obviously the tape hinge is still the simplest here. But now a compact metal hinge could also work, but it would have to be shaved down on whichever side is attached to the bay wall (each side is (13/2) = 6.5 mm, and the wall is only 5.155 mm high.
As for the R-series hinge, this is problematic for a number of reasons, mostly because there are some tight constraints on where the pivot can be located. If you drew an arc that represents the desired path of the lower corner of the door from its closed position to its maximum "open" position, then the center of that arc is the necessary pivot location.
The ideal pivot placement for LD-F1's situation would allow the door to rise faster than it travels horizontally (at least until it clears the top of the opening). That means that the pivot would best be placed nearer the corner of the door vertically than it is horizontally. If you imagine the pivot's rotation circle as a compass, it'd be best if the pivot were between East and East-by-Southeast from the door, or as a clock, between maybe 3:15 and 4:30 ... ideally closer to the 3:15 end.
Unfortunately, that's not very practical. If you look at the dimensions given above, the pivot has to be at least (1 + 5.155 + 2) = 8.155 mm below the upper surface of the head, plus some offset from the inside surface (1 mm in this model). That's dimension B in the next image. Horizontally, on the other hand, anything more than 6 mm away from the port inside wall of the bay, will place the pivot axis inside the shorter section of the head. That could be problematic. It's 4.5 mm in this model, dimension A.
If the pivot fits the constraints given above (as A and B do), it will always be nearer the corner horizontally than it is vertically. Have a look at this diagram:
In the above image, the dashed circle represents the path of the lower corner of the door. You could only rotate the hinge about 6 degrees before it strikes the head, and by the time you've rotated more than about 24 degrees, the door would have reached the apex of its movement and would be moving further into the head (having never actually cleared it).
As for the dashed line coming off the bottom the pivot, then going left, and then going back up to the door, this is roughly the shape of the R-series style hinge arms that would be needed, and the lengths of those dashed lines are determined by where the pivot is. For example, since the bottom dashed line rotates upward to become a vertical line as the door opens, its length must be >= dimension B plus some extra for clearance as well as the thickness of the arms perpendicular to it (represented as 0.5 mm in this example, but probably a fair bit larger).
There is another small problem that would make the pivots for the R2 style hinges harder to place because of the way I designed the head. Below is the relevant section in CAD from a high angle to the side (the white shape shown in the head opening here is the ridged reinforcement pattern I'm likely adding to the bottom of the door itself. It is currently a separate model so I can check clearance.):
The main problem is the magnet mount (the protrusion beneath the top edge of the opening in the head, with the circular recesses for holding magnets) and how close it'll be to one of the hinge arms. Here's the view from a lower angle:
And the bottom view:
I should have centered the magnet mount rather than putting it so far toward the rear of the head. Notice how close the highlighted rectangle in the last image is to that horizontal rectangle. The pivot has to be closer to the top edge of the image than the highlighted rectangle is, which implies that the pivot on that side will end up directly adjacent to (and probably overlapping) that magnet mount). It's also possible the new antenna mechanism could interfere, since it's in the area at its highest point, but i havent checked specifically.
So the upshot is that the R2-style hinges have several problems, and I would likely have to go with one of the other two options.
Edit: Upon further consideration, the other two also have a problem. If I leave the black door overhanging the port wall of the bay; then the door protrudes beyond the port side of the pivot point on that image, which means that the protrusion would rotate downward. Since it's already in contact with the lip the door sits on, it would be blocked from rotating at all. In order to avoid that, the pivot point ideally needs to be as close to the actual bottom right corner of the black door in that image as possible, and even that wouldn't strictly be enough. I'll have to think on it more. Might end up needing to embed a pivot directly into the wall of the bay.