and speaking of hard work, this frame design is probably the 6th refinement i have come up with. it took my third attempt for structural software to accept the frame.

and i am going to try a major variation in the frame. by try, i mean make it in 2d using autocad, making sure the numbers are what i want. then make it in 3d in autocad. using those dimensions, make it in 3d in the structural software. just to see if its any better / worse than this one.

had to learn 3 softwares, and spend weeks learning about frames and motorcycle dynamics.

all this while doing my university postgrad assignments.

it does take a special madness.
but its worth it. i dont understand why more people dont do this kind of thing. most just adapt or copy whats already done. if you want to stand proud as an Indian in the international arena, you cannot replicate what has been done.

I am not sure but .5mm seems a bit too much.

ah finally i caught hold of your thread abhi. By the time you're down in november we must have hopefully landed a good frontend from one of the SBK guys around.

Got in touch with the tube and metal angles dealer. Should be easy to get the required tubes and even get them cut professionally on a single axis rotating cnc pipe cutting device. Need to figure out a good weld setup and we're good to go

Also, have you finalized on tapered roller bearings for the swingarm axle or is it gonna be phosphor bronze bushing? Phosphor bronze bushings will be a cake to fabricate. You can easily get tapered roller bearings for the conseset/tstem, but you'd be better off getting them abroad..not many options in those bearings here..I checked up for the RD and not there

What wheels do you intend to run for the setup?

Im not sure you'd need to do this but wont you need to consider the flex of the frontend as well? I could be wrong

I would also suggest a ali subframe since its gonna be a single seat.

What about the fairing? Or gonna retain the naked bike look?

Cheers to your madness abhi

Atul

@OP - nahin re, i am enjoying reading every post and info being posted. great to know someone is taking the pain of getting so technically insightful! best of luck. ill keep chipping in from time to time!!

Nice mods there mate!

abhijeet, 0.5mm deflection when i load one point on the frame by ~200kg is ok i feel. i think the way i am using the software at the moment, it is not giving perfect numbers. time permitting, i will feed in the stock frame and have it for comparison.

and atul, mate you are a lifesaver. the single axis pipe cutter is going to be a major help. what i am trying to do is have everything ready by the time i come back so we can start knocking as many things together as we can in 2 months.

Now...
here is the thing about the chassis...
the layout i have shown here is not working very well in some load situations. an older option of mine is performing better, but that option did not have the quality of packaging in it.
coupla days back i realized to my amusement that i had accidentally made a chassis that was perfect for a double wishbone (with an unsprung steering stem) front end... like the britten bike.

analyzed the double wishbone in detail for the first time, and its a way better design than the telescopic fork. i will not go in detail about what it does better but here is a list...
1. progressively changing rake and trail during front wheel travel.
2. very high rigidity for the weight and complexity
3. lack of momentary wheel unloading due to braking, as opposed to telescopic forks.
4. the stanchions connecting the axle to the steering stem are much smaller, making them lighter and stronger.
5. better aerodynamics due to the very low front of the bike.


then it is obvious to ask why is this design not in widespread use?
we motorcyclists are a suspicious bunch. the manufacturers have developed the telescopic fork to such a level that its hard to mach it for its outward simplicity.
but for my application, i see a double wishbone to be as good as a telescopic fork only if the fork has come from a R6 or something. and i think its worth doing the wishbone thingy... out of spite.

will put up pics tomorrow or later today

in essence i need 2 sbk rear suspension units.

for the wheels and tyres..
we are still limited by the alignment of chain. that means, we can only go for the fattest tyre you can fit on the stock bike without it rubbing the chain. unless we use an offset sprocket. but i think thats unnecessary.
by what i hear, a 140 is the largest you can use and thats plenty big enough.

i like the the ninja 250 wheels, brakes and tyre combo. lets see if we can get that.

flex at the front end, of course. the wishbone takes care of that too. better than the telescopic forks.

the fairing... will come to it later, but it will not be naked.

rear swing arm pivot...
phosphor bronze bushings are not an option. the sbks use needle roller bearings and the taper roller bearings is my idea. its a pain to figure out an assembly for that, but if its too much pain, we will just go with needle bearings.

the welding...
MIG welding for sure due to its low ~ heat ~ spreading qualities. but most the DOM tubing i see is 2.1 mm wall thickness... more than the weld penetration of the MIG welding. but i have a trick up my sleeve



this is no longer a mod, no longer a replacement frame, but a new bike where i happen to use an rd engine.

more tomorrow
cheers

did a lot of number crunching last night...
and after 13 attempts, landed a front end geometry that has a progressive change in rake and train exactly as i want it.

let me elaborate...
lesser the rake an trail, easier it is to turn into corners and maintain the ability to tighten your line mid-corner.
a regular bike reduces trail when you brake by pitching its nose down. you can use the reduced R&T (rake and trail) for corner entry by trail braking.

but once you are leaned in a corner (provided you have done it smoothly) a mid corner bump will reduce the R&T further which is undesirable.

My geometry deals with this.
the R&T decrease sharply for the first 50% of the wheel movement (braking) and then the numbers remain pretty much constant. so a mid corner bump has no effect on the R&T.

i am not going to let out the exact geometry or numbers as i feel that info is worth a patent as this has never been done before with this goal in mind.

but the basic structure is a double wishbone with a floating steering stem.
will put up the 3d pics when its done.

^^ So it will not have a conventional front end? How does it look?

i will put up the 3d once its done, probably tomorrow. but it is a modified double wishbone setup which was there on the britten bike.

the headstock is unsprung and to imagine how steering is accomplished, look at aircraft nosewheels.

its not the layout thats radical, its the actual geometry that matters.

the way i am looking at this, is a system that has all the performance of the r6 front end, plus a bit more, without the inherent shortcomings of the telescopic forks.

its not absolute gold... there is a unsprung weight penalty but that can be controlled by design and material choice. its not a built-in disadvantage.

hot isn't it?
but a long long way to go. lots it interference in the tubing... the lower A arm to frame, engine heads to frame and such.
will take a good amount of resolving. but it looks fundamentally ok from my point of view.

but an idea is like good wine. takes some time in the cask to get it right.

what do you think folks?

Wow!!!!!!
Gr8 going Abhi best of luck.Radical is all i can say. And I envy you a lot. wish i did the stuff in my BE days. Best of luck with the project

the detailing for the bearing assemblies is eating my head. what i want for the steering pivots, no one makes them.

how hard is it to make your own bearing races? considering i can get access to a cnc lathe.

looking into surface hardening of stainless steel. if that turns out to be beyond my reach, the backup plan is ready using normal bearings but thats a compromise and i dont like it.

all the best bro,
that front end looks cool,
just wondering what kinda response will it give under hard braking!!

Kinda raging bull...nice initiative there

it will give a way better rigidity and feel than telescopic forks. and learning from bikes that have had a similar setup, this will at least be on par with sbk forks, if not better.
i have elaborated in some previous posts.

i like the raging bull analogy.