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Recumbent trike front suspension Mark-3

June 01, 2024 — BarryK

I posted about Mark-2, with a photo mounted on the trike frame:

In the last few days, posted about tackling steering linkage for the Mark-3 design:

In the last several days, have been constructing the Mark-3 frame. This is welded, using 20x20mm, 1.6mm wall thickness, carbon-steel tube. As I am a beginner-welder, I have found that thin steel to be a challenge; it is too easy to burn a hole right through it. The workshop that I go to, has a lot of scrap metal, and I since found some 20x20 with 2.5mm wall thickness, that I started to use after having constructed most of the frame.

In that last link above, I posted a drawing of the end-view of the frame. A slight modification when I constructed it; moved the piece shown in yellow down a few millimetres:

img1

...one of the pipe-clamps will be bolted onto that cross-piece and I decided to give it a bit more distance from where the Heim joints will be bolted on.

After welding these two end-frames, to make sure that the holes are aligned, I clamped the two frames together and drilled through, as shown:

img2

...note, the four holes for the Heim joints are 10mm, the one shown being drilled is for the shock-absorber pivot and is 12mm.

The side-pieces are 90mm long, and to get them reasonably accurately in place, I inserted m10 bolts, then turned the whole thing on the side (bolt heads on the bench), inserted the side-pieces, clamped, then welded. This shows the inserted bolts:

img3

Here are the measurements for the side-pieces:

img7

...the bottom side-piece is special; although welded to sloping off-vertical end-frames, it is oriented with sides horizontal and vertical.

Fully-welded frame:

img4

...the red lines show holes drilled for mounting the pipe-clamps (actually, I drilled 6.5mm holes, though the bolts are only m6). The holes for the bottom pipe-clamp are right against the side wall of the square tube, so I welded some small pieces to strengthen the side-walls and also welded a backing-plate, as shown by the blue lines. The reinforcing is probably unnecessary; I'm just being ultra-cautious to make sure it is going to be strong enough when taking a pummelling.

Notice that the bottom side-pieces have a 6m hole in the middle. That is for the steering linkage, and more details will be forthcoming.

The shock-absorbers mount on a pivot, that can optionally convert the trike to be tilting. Here it is temporarily inserted:

img5

...alongside the Mark-2 frame. The phone wide-angle lense gives the mistaken impression that the Mark-3 is about the same size as the Mark-2; in fact, the Mark-3 is quite a bit smaller. I have designed the Mark-3 to be as small as possible; one problem that arises is that the shock-absorber pivot will require something more to lock it in place. The photo shows its height:

img6

...a flat plate is required to go across horizontally, though which a m10 bolt can be inserted to lock the pivot, for a non-tilting trike. The ends of that plate will have to be bent down and welded to the frame. I intend to do that at the workshop on Monday.

Note, I constructed that shock-absorber pivot for the Mark-2, in late-January. Here are the details:

...I could have built another, a bit smaller for Mark-3, but it is OK, using it as-is.

I temporarily attached the pipe-clamps, to show how the frame will fit onto the trike:

img8

...due to the smaller size of Mark-3 frame, the 30mm aluminium tube is too long; it will need to be cut off. Flush with the pipe-clamp, to allow enough space for the bolt to which the shock-absorber pivot is mounted. Another job for Monday.

A bit more work required on the frame; when finished will probably paint it flat-black to hide the sins of my welding. Note, there will be some extra bracketing to attach the frame to the trike tube, so not relying totally on just those pipe-clamps.

Here is the SolveSpace design of the Mark-3 frame, file renamed with false ".gz":

https://bkhome.org/news/202406/images/frame-14g.slvs.gz     

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