Trike hinge design?

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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:
  1. rotated 45 degrees counter-clockwise around Z
  2. (maybe) rotated 45 degrees counter-clockwise around Y
Does that sound right?

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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I'm getting some answers from Emma/Twinkle and from DannyC. in other threads.

By the way, I think that, while fabrication (if not installation) of a suitable hinge is beyond my skill level at the moment, especially as during COVID lockdown I do not have my normal access to my local volunteer run nonprofit makerspace and its machine shop --

it also occurs to me that, once we figure out how it works, such a hinge could be retrofitted, in some instances, especially if one designs with the future hinge in mind.

In an Ice trike, the entire rear suspension is of a type that fits easily aft of the hinge. With a StreetFox rear triangle as I plan to use for now, it may not work as cleanly. I think I'd have either to:
(a) put the hinge forward of the seat tube, which supports the suspension's spring, or
(b) extend the rear with a suspension support separate from the seat tube.

I think that:
(a) would put the rear wheel further forward when folded (need to make sure rim & wheel fall forward of chainrings since they won't fall short of them)
(b) would change the steering geometry (as Warrior and StreetFox plans imply, the Ackerman angle depends on wheelbase)

So maybe it is not worth it. A hinge might make more sense on a Warrior-style or other fixed rear end.
On the other hand, I suspect that a rear suspension results in lower stress on the hinge.
 
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Suspension will indeed remove stress from a hinge though I'd think that the hinge is likely to be one of the last components to fail as it'll need to be so beefy to do the job that other components will be nearer the firing line for any failure. Why not try to acquire a folding bike on the cheap/free and cut the hinge out of that. You know it'll do the job as it's already doing the job. It's then a matter of welding it in at the angle you want.
 
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If I do see a cheap or free folding bike, I would love to take a hinge from it, as you suggest, Popshot. Also, if anyone has one and wants to offer me one, I hope to hear from them!

I do see the main challenge as to determine the orientation of the hinge. As I may have mentioned, I could always add the hinge later once I get one.

Emma just sent me some photos of an ICE rear triangle. I am not the most visually gifted (to determine from what angle the camera was looking, for instance) but when I make sense of the photos, they should help a lot.

I guess as a "scale model," I should be able to use any hinge that folds flat, and just "tubes" to it (even paper tubes), and play around!
 
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Good idea! So I just did post one. Can't hurt to ask.

However, where I live, when I post on Freecycle asking for anything of value, I've been offered bikes of the quality that our local nonprofit cooperative bike shop won't even accept (because they have to disassemble them before they sell as scrap metal). So, I will also try to find other hinges that may work or a fabrication technique for suitable hinges.
 
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OK, i did some rudimentary measuring of the hinge angle & placement.
With the keel at an almost horizontal level (my driveway has a run-off slope to it) the keel section before the hinge is essentially horizontal.


If you place a square on the hinge plate and measure the relative angle of the hinge to horizontal you get 5.91 degrees, so its probably fair to say that the hinge is laid back from vertical by 6 degrees.


The keel is effectively square and horizontal on top.


The hinge is oriented at 45 degrees to horizontal (as I said yesterday).


The hinge sits in the main keel approximately 39cm aft of the cross-beam.


...and 68cm ahead of the rear wheel axle.


There ya go! as promised.
 
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Thank you very much, DannyC!

Thanks also to Emma, who by email just now provided me with her measurements. She didn't have her "Project X" trike with her, and she took measurements (or estimates, I'm not sure) from an ICE trike. They are pretty comparable, as expected. Emma estimated:
8 degrees (to your 6),
50 degrees (to your 45), and
12 degrees. The 12 degrees is as seen from the top; the left side of her hinge is rotated forward by 12 degrees.

[Edited with Emma's measurements and diagram:
Emma's diagram drawn from ICE ]
 
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For anyone trying to visualise how the hinge for folding trikes works:

I just got through the first post in this thread and the following simple explanation occurred to me. I tried it and yes, it does work.

Take a square sheet of paper.
.Fold it diagonally in half, top right corner to bottom left corner.
Draw a vertical line on the paper, parallel to the left side. This line will represent the vertical rear wheel.
While holding the paper flat on the table or whatever, open up the fold and, looking through the paper, you will see that the line (wheel) is now horizontal.

The operation relies on the hinge pin being at 45 degrees.

Simple, ain't it?
 
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For anyone trying to visualise how the hinge for folding trikes works:

I just got through the first post in this thread and the following simple explanation occurred to me. I tried it and yes, it does work.

Take a square sheet of paper.
.Fold it diagonally in half, top right corner to bottom left corner.
Draw a vertical line on the paper, parallel to the left side. This line will represent the vertical rear wheel.
While holding the paper flat on the table or whatever, open up the fold and, looking through the paper, you will see that the line (wheel) is now horizontal.

The operation relies on the hinge pin being at 45 degrees.

Simple, ain't it?
Yes, wayyyyyyyyyy back when (on the old forum board) ...... as John (Sandman) was contemplating doing this we all had a discussion and the subject of folding undercarriage gear with a 45-degree joint came up.
While it is certainly a simple enough concept, it was "where exactly" you placed the joint in the keel so that the rear wheel ended up on its side parked between the 2 front wheels that taxed the brain more. ;)
Because he was "Solidworks Savvy" John modeled the whole trike & joint in SW so that he knew exactly where to put the joint.
 
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The position fore/aft is easy enough to determine, it's the height of the hinge and/or any twist in the hinge alignment that's needed that's the hard bit to work out. One if/but/maybe is if it clears the nearest front wheel as it folds and the track width and wheel sizes will be the biggest determining factors there. The other if/but/maybe is if the rear is horizonal or still twisted when it can fold no more. To achieve that the hinge must fold exactly 180 deg. There are a lot of determining factors that will affect that. The wheel will never go perfectly horizontal if the hinge is not 45 deg and it will only achieve that at 180 deg.

The issue of centrality
Just to throw another spanner in the works, if the hinge is not the same height as a line drawn between the centre of the rear axle and the centre of the rear axle when folded then at 180 degrees fold the rear will not fold to the centre of the fronts but to one side or the other and by the amount it's above or below that line. If the hinge centre is exactly on that line it will fold to the centre but given the hinge is likely to be offset to one side of the tube it intersects but is otherwise central to that line viewed from the side then the rear will fold horizontal but offset to the hinge side by twice the distance from the centre of the tube to the centre of the hinge measured horizontally. This may be of zero consequence.
 
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I realized part-way through that my plan to use a 26" rear wheel would also complicate folding. Emma pointed out that her ICE trikes have 20" rear wheels and maybe her Project X does too I am considering just using the implicit "hinge" of the StreetFox rear suspension to shorten the bike a bit to lower the profile while it sits somehow on my hitch-mounted rack. It would not be very compact at all and would not be a respectable "folding bike," but for cross-country travel (such as from Arizona to Massachusetts) I thought it might reduce drag somewhat.
 
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Popshot, I suspect at least two axes of the 3-D hinge rotations reported by DannyC (6/45/? degrees) and Emma/Twinkle (8/50/12 degrees) were meant as tweaks to get the wheel to end up in the right place, for precisely the reasons you just explained. The simplest 45-degree hinge would put the back end ~1.5" above and ~1.5" to the left of the front end -- at best, if it doesn't run into anything on the way.

What I gather so far, thanks to input from several great folks:
-A hinge in a trike is much more complicated than I'd have guessed initially (there is a very nice instructable about adding a hinge into an upright bike)
-There is probably no one-size-fits-all hinge or hinge placement -- clearances depend on the whole trike
-The folded-paper hinge is a great way to begin to understand.
-Emma suggests I get a regular hinge and some 2x2 lumber and experiment with that, an idea I like a lot. Might be worthwhile to model the whole trike in 2x2 lumber before fabricating a real trike with a hinge.
-It might be worthwhile to learn Solidworks (a license is free with Experimental Aircraft Association membership, $40/year), or Onshape, which is free for hobby use. I find it easier to get started in CAD programs when I can start with a model that embodies at least one feature I'm trying to build -- for instance, a hinge. I could perhaps model a whole trike around a hinge. In Onshape, at least, the hinge is the hard part. I have only sparse experience with CAD here and there since the 1980s. Lately it's mostly OpenSCAD and OpenJsCAD: Since I'm a programmer mainly, I like to use words to define shapes. I guess I've been attempting the same here and probabably not enlightening anyone much in the process; thanks for your patience.
 
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If you use the Streetfox suspension pivot as the hinge you can also use a Q/R skewer on the rear. A pin with R clip on one end of the suspension unit and it'll fold to a reasonable degree. Doing it that way you can fold it the other way - ie away from the seat so potentially not having to remove the seat. My first trike was sold to a chap who collected it with an estate car and folding / removing the wheel just like that got it in.
 
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Popshot, that's encouraging. I think I will do it just like that, at first!

Also, toward the future, the mechanical engineer who taught me an intro to Onshape (browser-based, free for hobby use, 3D CAD comparable to Solidworks) has replied to my query to him, with a simple model on which to elaborate! I made a copy here. Find the "Assembly 1" tab at the bottom, click to select that, then you can click on the rear end of the trike to drag it. (For some reason he has put the hinge through the boom rather than just outside it, and thus created lots of extra interference. But this can be changed.)

He also wrote:

"This looks like a pretty cool project. I think onshape would be pretty useful for modeling this. It looks like a plane of rotation coincident with the x-axis and rotated 45deg from the y-z plane would be what you need to rotate the front half of the boom 180deg and also get a 90deg rotation in the wheel. So I think you were right on your points 2&3 but possibly not 1 if I understood you correctly (though I'd have to think about it more to see if that would help). However, you'll get interference problems with the front and back half of the boom running into itself. This might be solved by making the back half of the boom curved up until the hinge. There are definitely other solutions to the problem like slightly changing the orientation of the rotation plane so that the boom doesn't quite make a 180deg rotation but the wheel still makes a 90deg rotation. I imagine the trike in the video uses a combination of a curved back half of the boom and a hinge that is not quite in (but close to) the plane that I described. I made a VERY simple onshape model that you can play with with the plane of rotation. You can see the current rotation and interference in the model in the "Assembly 1" tab. Also, the workspace is public so you can make a copy and work with that if you want to. Hope this helps. If you have any other questions definitely feel free to reach out. I'm just kinda busy so my response might take a day or two. Good luck! "

This was in reply to my message to him, in which my points 1-3, for reference, were:

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:

  • 2. rotated 45 degrees counter-clockwise around Z
  • 3. (maybe) rotated 45 degrees counter-clockwise around Y
 
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Hinge inside the boom just isn't a goer. It absolutely has to be outside.

Using the suspension pivot as the hinge, if you use a low height rear swing arm such as this:-

Rather than a more traditional shape triangle such as this:-

It'll keep the folded size smaller.
 
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Yes, what you said (that I'd said).

In my lazy way of using CAD programs I don't know very well, a model that has one wrong displacement still can save a lot of work. Onshape is parametric, so I should now be able to just edit the X and Y displacements of that hinge -- maybe -- my acquaintance M. was far too clever and went to a lot of work to put the hinge deep inside the tube. Dunno what to say; he is an MIT graduate and maybe doing it as shown in ICE's video was just too easy for him ;-)

In all seriousness, I think this illustrates a favorite rule of thumb of mine: Often those with the most experience with a particular problem can perform better in solving it than can a more-expert person working from general principles and limited time. In this case, you and I had already seen the answer, whereas I bet M. didn't even spend enough time watching that video to parse what he was seeing. Reminds me of how in the US healthcare system doctors are reimbursed for just about anything other than listening to the patient....
 
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From the experiences of other people with hinged trikes this is not as simple as putting the hinge in the right place.

When hinging you will have problems with both the chain and the cables , both routing them to get enough room for the fold and the effect the fold has on them ?
 
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