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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