Hallo from England - sometimes Saxony !

[beachcomber]

I thank you for your interest Carsten. The overall idea is completed in my head ............. now I just have to make it happen.

Michael - I tried to keep my ideas simple on this forum - not everybody has an excellent grasp of the English language as you - and your technical knowledge. My initial thoughts were more like "thinking aloud" to invite response [ like yours ! ]

Please allow me to take a little time to explain.

I have been a design engineer / manufacturer for over 40 years with many new and sometimes novel designs in my portfolio.

There are 3 phases in any design / development

1. The ideas [ the "what if" ] where there are maybe 3 or more solutions for your project.

2. The P.O.C. [ Proof of Concept ] phase where the shortlisted ideas are given precise thought as to if they will work
1 & 2 usually go together.

3. The actual detail design of the selected "what if", and again - 2 & 3 are connected.

My "what if"s were
 
1. the Banana styling cue [ not the function ], 
2. the Indian style with a leaf spring out front, 
3. and something like the H-D sliding pillar in front of the main fork.

As you quite correctly state - the banana fork tube must move parallel to the Bantam USD fork - which can only move vertically. And for that to happen - the top of the tube must be secured so it will have a similar vertical [ and parallel ] action as the Bantam.

The POC here is that to get the "look" .......... however, there is not enough room at the top of the banana tube to allow the forks to be turned before hitting the tank !

 That leaves the H-D style which will work as it moves parallel to the Bantam tubes and the top end can be secured via a sliding pillar with barrel springs. On the H-D it is big and UGLY.

The Indian style - with leaf spring out front is not a favourite of mine as it looks very agricultural ! That would be very simple.

So now with more thinking - there is another possibility, like the Vincent with the main blade [ in my case - the Bantam forks ] and a slim dampener unit at the rear. Similar to the Blue Norton with Vincent inspired forks. I have this option on the Bantam forks [ see where the green garden hose is ! ].

So - another reason that is a good idea [ using a gas strut at the rear ] - the Bantam forks do not have any hydraulic dampening ! I have only just found this out once my secondhand forks arrived.

Once I have decided which style to use I will draw up a couple of sketches - much simpler than a load of words.

With the H-D style of fork I have the option to include a normal rear damper type of unit - or even coil over. I must be clever to hide the modern parts !

So - I apologise to any of my German cousins who are interested, but I think it was necessary to clarify my thoughts, and please keep your comments coming !! .

[Michael]

Hi TJ,

thanX for pointing this out !

I am really sorry, but any fork version that has a short (rotating) swingarm or any kind of (rotating) trapezoidal arrangement can't be combined with "parallel/linear" movement of the Bantam fork.
To strengthen the fork and add damping, rear shock absorbers may be used, even if they are intended for bicycles (downhill racer / mountain bike (MTB)).
The bicycle staff is small / slim / short and may fit much better than standard motorbike rear shocks with approx 30 cm / 10 inch length.

There is a hype about old-style "Beach Cruiser" bicycles, maybe they use old-style shock absorbers in chrome or black as well ?
(Just an idea, without any specific recommendation). 
At least MTB market provides a lot of this stuff in modern style. 

The other thing is to avoid the shok absorbers from tilting away at the lower end, when they are pushed by the "banana tube".
I expect the lower end of the shock absorber to be welded to the banana tube or 
at least to use any kind of mechanical fixing (square holes?), 
to avoid any "escape" movement (to front or rear), 
to avoid bending the "banana tube" and 
to keep it in place for parallel movement with the Bantam fork.

Here a simple drawing of what I have in my mind:

TJ boardtracker fork1.jpg

All the best,
Michael
Keep on rocking ! 

[bikeorslk]

Hi,

..in the end, I could not withstand...to understand...the fork stand circumstances... uah!

Honestly, I had some trouble to follow your discussion (as I am not familiar with all the different fork types), but in the end, I am a bit more sure to have an idea of TJ's planning.

And, sorry, Michael, I am not with you: A linear movement can be supported by a rotating construction (look at any piston/crankshaft-ensemble!)

I sketched it here.

IMG_3331.JPG

Very important: ALL links need to be rotational and there is of course an absolute need for the rocker arm in the middle.

Or did I completely get wrong now?

All the best

Carsten

[beachcomber]

Carsten - Picasso would be proud !!! 

Yes - essentially that is it - and you are BOTH correct as I did not mention to Michael the link !

Michael - I thank you also for your sketch !

Carsten your sketch also shows why I cannot use that system [ the one I prefer ] because the springs would not allow the steering to turn before hitting the tank. Altering the 110 year old tank is NOT an option !!

I really do not like the Indian style with the leaf spring -  so it will be my version of the H-D springer.
 
Michael this is similar in principle to your sketch, except the new vertical tube will be parallel to the Bantam fork tube [ like the H-D ], and you are quite correct to point out to avoid the rotation - maybe some version of a rose jointed link. The RAMSHOX is a very substantial item.

I have worked out a way that I can use one RAMSHOX and still maintain sufficient travel [ 100mm minimum ]. The shock will be hidden mostly. That is a perfect solution as the spring platform is adjustable on the RAMSHOX - and I have fully adjustable dampening at the click of a button. We also checked the Bantam forks more closely - they are VERY basic ! However, the RAMSHOX will now be doing the work of the spring and dampener - just like the version RAM sells for the BMW Oilheads. I can fine tune the spring rates and dampening to suit the finished bike. I can also shorten the fork bottoms by around 50mm to improve the "look". The adjustability will be useful at Glemseck  ?

I am now happy - and again thanx to everyone for the feedback.

This bike is being designed by Z750Twin forum !!!!

[bikeorslk]

Ok, just for brain-massage:

And what about a pull-spring solution? (I wonder whether something compatible exists at all, but it would at least solve your 110 problem

IMG_3332.JPG

Greets

Carsten

[beachcomber]

OK ............... we go with the H-D springer style !! 1st picture. By the way - these forks are from India and £1020 !!!

 Imagine lighter and more elegant [ ! ] and imagine this with a single coil over like the second picture. The RAMSHOX unit is perfect - it is fully adjustable and will just fit through the lower fork clamp and mount through the top. This will allow a full 100mm + travel. The shocker is available with a pin mount, or a bar mount that would be quite stable. I will look at using a pivoting link as well to reduce the rotation.

We are still at P.O.C. - but with everyone's input I am happy this is the best solution.

[Michael]

Hi TJ,

sounds good.

I am still not confident with the lower shock absorber mounting.
To avoid this from tilting, means moving forward  instead of upwards / bending the banana tubes, something must be there to "fix" them and only allows the parallel movement.

Just a thought:
The RAMSHOX have a large thread to adjust the spring preloading.
Can this thread be used to screw it in a heavily modified and strengthened upper holder (upper triple tree) ?
This can be supported by a set of stock adjustment nuts to secure it.

That will hold the shock absorber in the parallel" position and no enhancement of the banana tubes would be required to avoid tilting.
Would fit in solutions with one or two shock absorbers.
Not sure about the length of all that stuff and if it will match 

Attached the pic with the RAMSHOX included.

TJ boardtracker fork2.jpg

Cheers, Michael

[beachcomber]

Michael

i thank you for your continued feedback.

The "banana" fork will only work cosmetically as in the Motobecane position.

So .... I have decided to go with the H-D style springer. This uses a straight upright and it will move completely parallel to the bantam main fork tubes [ see sketch ].

HOWEVER - you have come up with a viable solution to remove ANY possibility of tilting [ I was going to use a bellcrank link ].

That is - using the main threaded part of the RAMSHOX body as the top mount anchor ! 

I can have a shock assembled without the eye mounting on one end [ see 2nd pic with black bracket - simply remove the bracket ] and then use two of the spring platform locking rings to attach the shock through a suitable mount. That way the shock CANNOT move or tilt. The body is made from Aircraft quality 6262 material and is bulletproof !

As we [ RAM ] have the shox made specifically to our design I can order any combination of open length, travel, and what fittings I want. That's the perks of being the original development engineer for these products !

I did say this project was being overseen by the forum members !!!! That is what I love about these forums - the free interchange of ideas - and I thank you for the solution.

[beachcomber]

More Cad-Cam   mock up.

[Michael]

Hi TJ,

ok, now I'm convinced that the fork will work.
Well done !

Your last pic is taken by a Live-CAM, isn't it ? 

Cheers, Michael