Connecting trike front suspension to frame

Continuing my recumbent trike front suspension project, this is the previous post:

https://bkhome.org/news/202403/considering-heim-joints-for-wheel-knuckles.html

Getting close to putting it together, decided today to post about an aspect of the project that is rather weird...

My trike is a TrikExplor/Motrike with a "320" frame. There are various models based on this frame, for example:

https://www.motrike.com/product-item/rear-suspension-recumbent-trike/

So, there is a central frame tube, and a cross-beam to which the wheels are attached. Where the weirdness comes in, is the cross-beam is attached to the central frame at a hinge-point, complete with ball bearings ...except, it doesn't actually hinge. If you look carefully at the above photo, there is another member coming out from the cross-beam and attached to the central-frame, locking the cross-beam at 90 degrees to the central-frame.

Hinging, that is, steering, occurs at the wheels, as is done for all recumbent trikes.

So why the ball-bearing join, when it doesn't hinge? The only reason I can think of is that the 320 frame was designed as a basis for many different trike designs, including the possibility of swivelling the entire cross-beam.

When I bought this, I hardly knew anything about trike design. Soon after buying it, I was thinking, if starting again, I would buy a more "normal" trike frame; however, most trikes weld the cross-beam onto the main frame, so I would have had to cut it off, then weld new framework. Messy; at least this 320 frame, though weird, does make it easy to detatch the cross-beam and fit something new.

I think that a lot of these have been sold in the USA, so if someone reading this can obtain a secondhand one cheap, with a view to modifying it, then this blog post provides some useful information.

What I needed is a tube that will slide into the ball bearings, with some means of attaching a framework. This is what I put together:

The tube is 30mm OD aluminium, which is a perfect fit. Well, not quite. It is a perfect fit for the top-most bearing, but there is a very slight sloppiness sliding through the bottom bearing. Reason is, the tube needs to be painted, then the bottom bearing becomes a snug fit.

When I inserted the tube and pulled it out, the bottom bearing came out, that you can see in the photo. To the immediate right of the bearing, there is an adapter-ring that I took off the trike. Then to the right of that is an aluminium sleeve that I cut to length, so as to fine-tune the height of the suspension-frame relative to the trike-frame. That sleeve is 30mm ID, 40mm OD, but I had to sandpaper the inside a bit to get it to slide over the 30mm OD tube.

Here are where I obtained the parts:

The 30mm pipe clamps. But, I see right now they are out of stock. Perhaps there are metal ones elsewhere in Aliexpress. There are plenty of plastic ones available, which would probably be strong enough. This is where I got mine:

https://www.aliexpress.com/item/1005005478071535.html

I purchased 30mm OD, 20mm ID, 240mm length aluminium pipe. Length is exactly right. Thicker wall than really needed. From here:

https://www.aliexpress.com/item/1005004347889082.html

The aluminium sleeve is 40mm OD, 5mm wall thickness, 100mm length, from here:

https://www.aliexpress.com/item/1005005964994480.html

I spray painted the tube with an etching primer, followed by a red gloss enamel. Just one thin coat of each.

A bit of a hassle attaching to the trike frame, but probably better than having to cut off a cross-beam and weld new framework. Hmmm, but I am going to end up needing a bit of welding to the trike frame anyway.

The actual front suspension is just about ready to be put together; that will be a future blog post. That piece of pine is misleading; there is a lot more to it, with metal reinforcing.    

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Considering heim joints for wheel knuckles

Yesterday I considered ball joints on the wheel knuckles:

https://bkhome.org/news/202403/considering-ball-joints-for-wheel-knuckles.html

At the workshop today, I constructed another design, using two heim joints top and bottom:

The orientation of the heim joints has the advantage of allowing any amount of vertical displacement of the wheel relative to trike frame.

The downside is weight. It has the original m12 bolt, inserted through a steel tube with brass sleeve insert. I cut off the head of the bolt and welded it to the cube, as can be seen on the left of the photo. I didn't weigh yesterday's design when assembled, but estimating by weighing the parts, today's design is about 330g heavier. For both sides, that is 660g (0.73 Imperial pounds).

With the original trike suspension, that I had almost completed, I found that the weight had got much higher than desired. A bit of extra weight here and there; it adds up. In particular, the sprung part, the wheel knuckle, should be as light as possible. So, I am not going to take today's design any further.

I'll be back at the workshop after Easter, want to try one more design variant. Oh yeah, Easter has rolled around again. Happy Easter guys!    

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Considering ball joints for wheel knuckles

I posted about three different types of ball joints that I purchased for comparison:

https://bkhome.org/news/202403/heim-versus-ball-joint.html

Today I was at the workshop where retired guys get together and work on little projects. Lots of good equipment there. Thinking about what ball joints to use with the wheel knuckles.

Back in early January I was working on the wheel knuckles, intending to fit them to the cheap swing-arms that I purchased from China:

https://bkhome.org/news/202401/construction-of-wheel-knuckle-hinges-and-learning-to-weld.html

Various problems with those swing-arms. Sloppy pivots is the main problem, but also the design became very big and heavy; not really what I want for a trike. While my thumb has been healing, have rethinked the design; hence purchase of the ball joints for consideration.

The workshop has some old 40x40mm steel square tube, and I cut out some cubes. Actually that square tube is fencing post, available from Bunnings, but I found an old length to cut up. Here is the first consideration:

...the cubes are just balanced in place, to see how it will look. I won't rush into doing it this way, as it will be a one-way process; the cubes will have to be welded onto the wheel knuckle.

Any downsides? The main one will be limited vertical displacement, restricting how big a bump can be handled.

The spacing between the ball joints is ok. I looked at it with SolveSpace:

...notice that 390mm distance; that is the height of the trike frame above ground. That is intended to be the rest position, with someone sitting in the trike. The distance between the wheels on the ground is 650.99mm.

If the trike frame is pushed down, which would be the same as riding along and both wheels hitting a bump, this table shows how the wheel spacing (on the ground) varies:

Height	Spacing
390	650.99
380	651.93
370	652.28
360	652.05
350	651.23
340	649.85

...wheel scrubbing is at most 1.3mm (0.65mm per tyre); negligible. Snapshot from SolveSpace, at height of 340mm:

...looks good. The ball joints could handle a bit more vertical displacement; just looking at it in SolveSpace, it seems the height could go down to about 320mm, at which point the shock absorbers would also be reaching their limit -- 70mm vertical displacement, a little bit under 3 inches. That's a pretty big bump.

Next-up will consider the wheel knuckle with heim joints.   

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Heim versus ball joint

A few weeks ago, I admired Tomek's "Street Fox" DIY recumbent trike front suspension:

https://bkhome.org/news/202402/trike-front-suspension-using-tie-rods.html

Those type of joints are known as "Heim" joints, as distinct from normal ball joints. These are also known as "Rose" joints in Britain.

There is at least one trike manufacturer using the same technique; Stein Trikes (based in Serbia). See video about the "Wild One" trike front suspension and a snapshot from the video:

https://www.youtube.com/watch?v=-TBdcZqQ_g0

I did some reading-up on Heim joints. Two major problems; they do not have high axial strength, and secondly they can wear out quickly.

That bottom joint is the main concern. You can imagine, if the wheel hits a bump, there will be a severe upward force, that the lower swing-arm will resist due to the shock absorber, hence strong axial force trying to rip the joint apart.

Then riding in inclement weather, rain and dirt will get into the joint. On dry dirt roads, dust will get in.

So, it seems to me, that bottom joint will have a limited lifetime. But does that matter if the joints are cheap?

I purchased three different types of joints, to compare. Firstly, Heim joint:

I bought the cheapest, m10 thread and hole diameter, they cost only about AU$3.50 each and AU$2.50-ish postage. Postage remainded about the same for bigger quantity. Ha ha, compare with RS Components here in Australia, they are asking AU$45 each (plus postage?). eBay AU vendor wants AU$25 each plus AU$10 postage.

Maybe these ones from Aussie vendors are higher quality. Perhaps they have higher axial strength. The couple that I purchased from Aliexpress look okay, just eyeballing them.

I also purchased this ball joint:

As far as I can make out, it looks like the ball has been inserted from the bottom, which means that it cannot be pulled out. That is an important point for the bottom joint in the swingarm that you can see in the Stein Trike photo.

I found, however, that the join is incredibly stiff, and when I did get it to move, it did so very jerkily. It would probably loosen up in time, I suppose. The Heim joint, in comparison, moved freely, without feeling loose.

The third one I purchased is this:

Also a bit stiff to move, but again I suppose it will loosen up with usage. I pulled that little spring clip out, thinking that would allow the ball to be pulled out; but no, it is locked in, as shown in this section view:

I don't think that this would last if used upside down. For that bottom joint in the swingarm, there would have to be a bracket so that the joint can be bolted on right-side-up.

Both of those last two have rubber boots, so very good protection from water, dirt and dust.

Having a respite from the DIY trike project while my thumb heals; it has been an opportunity to rethink the design. Lots of thoughts, will post when something definite is decided. Definitely don't want to start from scratch; will use parts already constructed, such as the steering knuckles.

One very interesting bit of information; Stein Trikes did design a full-suspension leaning trike about 9 years ago, named "Wild Wave". There were prototypes but it never went into production. From a couple of short videos, it looked like the leaning was purely by body lean, not via the steering mechanism.   

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Trike front suspension using tie-rods

I'm always on the look-out for ideas for simple construction of front suspension for a recumbent tadpole trike. A few days ago, came across this:

"Evolution of my Street Fox trike to full suspension e-trike"
https://www.youtube.com/watch?v=KOeiWURsPlA

Tomek has built his own trike, "Street Fox", and in the above video has shown how he converted to full suspension.

It is a very simple design, using tie-rods. These are readily available, in various lengths. Here is a snapshot from the video:

...welded the tie-rods together, and he has swing-arms! Very nice.   

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Construction of trike front suspension pivot

Continuing the recumbent trike project, here is the previous post:

https://bkhome.org/news/202401/starting-assembly-of-trike-front-suspension-frame.html

The two shock absorbers meet at a central point, and that is where it gets very interesting. The design is such that the trike can be tilting or non-tilting. If tilting, it can be achieved by either balancing, like on a bicycle, or by linkage with the steering. The idea is to experiment with all three.

In November 2023, I posted how the central pivot of the shock absorbers will work:

https://bkhome.org/news/202311/two-shock-design-with-swinging-steering-linkage.html

Reproducing the drawings here:

...if that pivot is locked in place, then it is a non-tilting trike. If allowed to swing, it becomes a tilting, or leaning, trike:

I don't have a nice drawing of that pivot, but have taken a snapshot of a rough sketch, that should give enough detail:

This is where some welding is required. Here are the two parts of the pivot:

...the welding is not pretty, but looks strong enough. Small bushes have been inserted where the shock absorbers are attached:

The bushes are 8mm inside, 10mm outside, 6mm long, ordered as "d8D10L6" from here. The pivot tubing is 14mm OD, 10mm ID, mild steel, from here.

I did a temporary assembly, to determine the weld-point for joining the two parts of the pivot:

Consequently, the two parts were welded together:

This pivot design is very experimental, and it is going to be a fascinating experience to test it and compare the three modes; non-tilting, free-tilting and tilting linked to the steering. Progress is slow, and cannot say when the trike will be basically operational. Ha ha, as I learn, keep getting ideas about a trike "mark 2" version.     

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Starting assembly of trike front suspension frame

Here is the previous post, of the recumbent trike front suspension conversion project:

https://bkhome.org/news/202401/construction-of-wheel-knuckle-hinges-and-learning-to-weld.html

As already mentioned, the swing-arms and knuckle came as a go-kart front-suspension kit. Which has proved to be a challenge, mostly due to the sloppy pivot points. I mentioned in the previous blog post that brass bushings were inserted to reduce the sloppiness.

The swing-arms have m10 bolts, but the hole they slide through is about 11mm. So, as for the knuckle, inserted brass tubes to act as bushes. In this case 11mm OD, 10mm ID, 0.5mm wall thickness, bought from here. I didn't buy enough brass tube, so mixed with some aluminium tube purchased from here. Brass would have been best I think, from the point of view of wear and less likely to corrode when wet and in contact with iron.

The m10 bolts supplied with the kit were not long enough, so bought 200mm length off eBay. That was the longest that I could find, stocked anywhere in Australia. I thought that could get away with that length; however, it is still not enough:

...only about 5mm before the thread starts, whereas want 9mm. Even worse, want to put in some nylon spacers. I hunted on Aliexpress and found some longer ones, a vendor that sells m10 up to 300mm. So, there will be a delay while waiting for them to arrive. In the meantime, there are other jobs to do...

Notice one thing in the above photo; the plastic plugs at each end of the swing-arms is, I thought, not a very good fit. So I epoxied them firmly in, using metal-repair epoxy, which is epoxy with silicon and iron powder. It is available all over the place, got it from here.

The SolveSpace design of the front suspension frame is here. It has a false ".gz" appended, so just rename the file. Exported as PNG:

It is only a 2D design; how it goes together is in my head, but this photo should help:

...the swing-arm hinge-points have brass bushes, that can be seen in the above photo. The holes in the aluminium are 12mm and the bushes are 10x12x10x18, sold here. They are a firm fit and needed to be hammered in.

To show what it will look like, here is a partial assembly, with the swing-arms attached:

As will become clear in future blog posts, the design is adaptable to different implementation strategies. For example, it can be tilting or non-tilting. Next-up, plan to install the shock-absorbers, which will involve some welding.   

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