Hi. I'd like to build a recumbent tadpole trike, like Warrior or Streetfox, but that folds, like that of Emma/Twinkle, which was built by the late John Price/Sandman/Marengo, whose other two similar trikes are now owned by DannyC. The tubing is square, and the rotation is all in the hinge, right? And the hinge has just one pin, one axis of rotation?
I'm trying to visualize how it works. I am forming a hypothesis that I will then test in a scale model or maybe in SolidWorks or Onshape. (A CAD model may take me a while, because although I had a small Onshape intro some years ago, I haven't used it since, and I haven't tried using my SolidWorks license yet. BTW, you can join Experimental Aircraft Association for under $40/year and that gives you a SolidWorks license.)
For those who haven't seen it, such a hinge allows the rear half of a recumbent tadpole (two wheels in front) tricycle to fold up 180 degrees while also rotating 90 degrees, so that the wheel lays flat, like in this video by ICE:
Since I think the hinge has just one pin, and that the trick is in the orientation, I am trying to determine the orientation. Please feel free to help me think this through -- or even just share plans if you have them!
Because I don't know any other system, for this post I'll call:
"X" the horizontal center line of the trike (viewed from behind)
and "the boom" the main longitudinal structural member that runs along this axis
"Y" the transverse horizontal axis (also the wheel axle's axis) (viewed from left)
"Z" the vertical axis (viewed from above)
Angles 0-360 degrees. 0 degrees is "top" in X and Y, or "front" in Z. Angles are indexed clockwise when viewed as indicated.
First, it seems clear from photos that, whatever the orientation of the plates, the hinge itself is in the "upper left" quadrant when viewed from behind. Compared to a "top hinge," the hinge is:
1. rotated 45 degrees counter-clockwise around X
Right?
But I suspect that also, the plane of the hinge plates is, compared to an orientation perpendicular to X:
Or are the latter two (if they both exist) maybe just 22.5 degrees each? Or any combination that adds to 45 degrees?
My intuition says somehow these three angles, or their projection (?) onto a plane around X? (the X-rotation component of their overall rotation)
should add to 90 degrees, to get the end result of a 90 degree twist in X.
The hinge itself does achieve a 180 degree fold or close to it. But it seems as though at least some of the twist comes from the hinge's orientation with respect to the boom.
Some of the trikes using round tubing (Titan?) do rely on a tube-in-tube rotation near their hinge. Since I want to insert a hinge into my trike, which will be made of square tubing, I hope to make hinge placement do all the tricks.
Thoughts?
Also, since I am not skilled in MIG welding yet, let alone 16-gauge steel, I had in mind to add lugs to my hinge, so that I don't need to rely on a butt joint for this, which I anticipate being a very high-stress joint. Make sense? Maybe put slots or holes in the lugs, so that I can weld more beads? Or, just weld butt joints and then build up after the fact with more flat stock around it, flush and/or angle bracing?
I'm trying to visualize how it works. I am forming a hypothesis that I will then test in a scale model or maybe in SolidWorks or Onshape. (A CAD model may take me a while, because although I had a small Onshape intro some years ago, I haven't used it since, and I haven't tried using my SolidWorks license yet. BTW, you can join Experimental Aircraft Association for under $40/year and that gives you a SolidWorks license.)
For those who haven't seen it, such a hinge allows the rear half of a recumbent tadpole (two wheels in front) tricycle to fold up 180 degrees while also rotating 90 degrees, so that the wheel lays flat, like in this video by ICE:
Since I think the hinge has just one pin, and that the trick is in the orientation, I am trying to determine the orientation. Please feel free to help me think this through -- or even just share plans if you have them!
Because I don't know any other system, for this post I'll call:
"X" the horizontal center line of the trike (viewed from behind)
and "the boom" the main longitudinal structural member that runs along this axis
"Y" the transverse horizontal axis (also the wheel axle's axis) (viewed from left)
"Z" the vertical axis (viewed from above)
Angles 0-360 degrees. 0 degrees is "top" in X and Y, or "front" in Z. Angles are indexed clockwise when viewed as indicated.
First, it seems clear from photos that, whatever the orientation of the plates, the hinge itself is in the "upper left" quadrant when viewed from behind. Compared to a "top hinge," the hinge is:
1. rotated 45 degrees counter-clockwise around X
Right?
But I suspect that also, the plane of the hinge plates is, compared to an orientation perpendicular to X:
- rotated 45 degrees counter-clockwise around Z
- (maybe) rotated 45 degrees counter-clockwise around Y
Or are the latter two (if they both exist) maybe just 22.5 degrees each? Or any combination that adds to 45 degrees?
My intuition says somehow these three angles, or their projection (?) onto a plane around X? (the X-rotation component of their overall rotation)
should add to 90 degrees, to get the end result of a 90 degree twist in X.
The hinge itself does achieve a 180 degree fold or close to it. But it seems as though at least some of the twist comes from the hinge's orientation with respect to the boom.
Some of the trikes using round tubing (Titan?) do rely on a tube-in-tube rotation near their hinge. Since I want to insert a hinge into my trike, which will be made of square tubing, I hope to make hinge placement do all the tricks.
Thoughts?
Also, since I am not skilled in MIG welding yet, let alone 16-gauge steel, I had in mind to add lugs to my hinge, so that I don't need to rely on a butt joint for this, which I anticipate being a very high-stress joint. Make sense? Maybe put slots or holes in the lugs, so that I can weld more beads? Or, just weld butt joints and then build up after the fact with more flat stock around it, flush and/or angle bracing?
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