Topic: CB750k7 Project: Operation Street Fighter (On the Road, Carb tuning in progress)

[laminaytrap]

Hi I'm Jon and I'm a modaholic.

I have a problem with not leaving vehicles as they were designed, I compulsively change them.

Most of this as happened with my many cars over the years, and this familiarity and confidence was enhanced when I had the opportunity to help design and fabricate a few racecars.

So the history.

I bought the bike in 2007 from a friend's dad, who had bought it from another friend's dad. I was just out of high school and severely cash strapped as well as lacking the necessary skills to tackle this kind of project. The bike was missing a few things and already having the ambition (not the skills) I began to change things.  The bike had a charging issue that had been its downfall, and the reason for the two previous owners discarding it.

Luckily although 17 year old Jon lacked fabrication skill, he did have a good amount of electrical knowledge. Prior to getting the bike working properly (read: at all) 17 y.o. Jon shipped off to school and almost forgot about this bike tucked away in the back yard. At this point the bike ran, but not well, and still didn't charge.

So far my only regret is that I don't have any pictures of the bike when I first picked it up, or even before I started working on it, so all I have is more current pics.

Fast forward 5 years, 7 cars, two race cars, and significant engineering experience. Summer of 2012 is coming and the current project car goes sour after some old lady runs a stop sign turning a perfectly straight Rx-7 FC with a built motor waiting into a bent piece of junk.



This is after it was all hammered back out

So one afternoon I took a truck up and picked up the bike, it was missing a few things (muffler, rear lights, charging system, etc). Luckily one of my buddies had a few boxes full of ZX6-R parts and 17y.o. Jon was bang on for the required parts to build a solid state regulator and rectifier. After replacing the field coil and going over the diagrams I wired up my component rectifier and ford truck regulator and it all worked! First try too!

So with this worked out I fitted a CBR? LED tail light with signals, ZX6 Muffler, ZX6 Brake Master (old one leaked), and some new tires.

The result, I know most of you didn't bother to read all this, is this! (Late April)







This was just the get it rideable build, plans for modifications to commence as soon as the snow flies. Next post will cover a few issues I've had and maybe ask some questions.

Hope some of you enjoyed the read, and others the pics.

[Mugen_Stumpo]

I have a problem with not leaving vehicles as they were designed, I compulsively change them.

count me in the group

[laminaytrap]

So i finally got some time to sit down with CAD and do some geometry layout.

so i mocked up the frame and critical points, plotted a tank and tires for reference and away we go.

So Basic Stock setup



And Modified setup.

Looking to run a 17in front wheel, zx6r forks, custom tees, and a monoshock rear. Dropped seat is shown on both drawings.



Will be working on this a little more soon, looking mostly at rake/trail, front end height and monoshock location.

All dimensions in mm

[laminaytrap]

So if anyone wants to jump in on this,

I am thinking about making custom triples as i have some access to CNC equipment.

I'm thinking of something like these, i like the clamp design and the adjustable offset.



So my question is what offset or set of offsets should i be shooting for, I understand that offset, rake, and trail are all related and are affected by ride height front and rear.
I have a CAD Model that evaluates all these settings and the swingarm angle/length to pump out rake and trail values.

Any ideas what would be ideal?

I was thinking about shooting for a sportbike style geometry, or at least head that direction, but I've also read that the swingarm to steering head length/angle are an important factor as well, but I don't quite know why that is or what other lines i can draw on the model to determine various handling characteristics.

As for adjustable offset I can either modify the ZX6-r trees with inserts etc. or make new ones.

Finally is the steering head angle to tree angle. Is this something that is commonly done? I've seen it in some choppers but i don't think i've ever seen it on a sport bike/ street bike.

[brandEn]

subscribed.

btw, the link to the pic above is broken.

[laminaytrap]

fixed

BRB, reading 500 pages of Motorcycle Handling and Chassis Design... ok maybe not right back.

[laminaytrap]

So by the book


Will work out some more stuff before i post further, but I think this is the right track...

[laminaytrap]

So basic geometry is covered in the first ~60 pages of Motorcycle Handling and Chassis Design. Since I don't yet own a copy I used the preview on google books, which only has selected pages.

Basically there doesn't seem to be a whole lot to it.

Wheelbase
     Should be in the range of 1350-1450 for handling reasons, longer means more stable (larger turning radius).

Normal Trail (Real Trail)
     ensure this is a reasonable value and that it stays positive through suspension travel and steering.

There's a lot more to it than that, but it comes down to those basics. Beyond that tire size (front vs. rear profile) seems to be the largest contributing factor to handling and overall road stability. The rake angle affects bumps and braking, as well as the overall tire diameter in the front. The larger 19in rim would handle bumps better, but otherwise not a huge concern.

Armed with that knowledge and the fact that i can do what i want to do with the stance of the bike I moved on to rear suspension geometry. I don't have the bike or the swap parts here right now so I won't be able to start on front end cad work till i move everything.

I realized that most newer sport bikes have a bellcrank/rocker setup in the rear to increase the rear spring rate as the squat is increased, and since i now have unlimited machine shop and welding access I think fabricating a new rear swingarm is a feasible plan.

Most modern bikes have the rocker at the bottom, but as it is already pretty busy down there and the top of the frame will be getting modified/reinforced anyways it seems logical to place the bellcrank under the seat. This will also allow me to run the shock at the same angle as the rear frame tube, offset to the rear, which i think is a good look.

Below is a GIF of the basic model I drew up.



The bellcrank mount would go between the to rear tubes integrated with rear chassis bracing.

The GIF Shows a suspension travel of 8 degrees (64mm, 2.5in) and a spring compression of 16.5mm (0.65in) at a rising rate. The rate is controlled by the separation of the mounting points and the bellcrank arm length ratio, meaning multiple points could be left on the swingarm/bellcrank for quick spring/damping rate changes when doing setup. this could also facilitate rear ride height changes, given two bellcrank mounting positions, for a variety of setups for each given spring, preload, rebound combination.

Must be cautious though, as it is the rear end and as Tony Foale said "if you give people adjustability, they'll manage to arrive at the worst possible setup".

[iron_worker]

I'm a Mechanical Engineer so I love where this is going.

I would love to do a build like you're doing some day. No "infinite access to machine and fab tools" like you though so much more difficult for me. lol

Keep this thing updated!

IW

[laminaytrap]

Thanks for the compliment.

My Grandpa way back in the day used to sign up for evening machining "classes" at his local community college/high school for the express purpose of getting machine shop access. It's nice to own your own tools (expensive), but even nicer to walk into a fully stocked machine shop and just setup your stuff He would just pay the bill and go do whatever he wanted for 2-3 hours. And if you get to know the instructor real well you might find you can go to other "classes" different days of the week.

Until i get my bike and part into my garage the CAD work will continue I hope to work out:

Frame gussets/Braces/Rear shock mount
Seat bracket/tubes/Seat
Rear Suspension Geometry
Removable Top tube section (I've seen some people do it as below, but i'm thinking about an engineered member to increase steering head stiffness and give me more height near the carbs, while being bolt in)
Increase carb angle (bolt on intake?)
Front end swap (waiting to see how my parts will fit up, either adapters or new tees)
ZX6r brakes (along with the forks)
Axles/wheels/adapters (want to run spokes, probably stock rear maybe front)

Adjustable clipons?
Bar end Turns?
Carbon fibre fenders?
Frame Sliders?
Rear Sets?

Oh and a motor build.

May have bitten off more than I can chew, but only time will tell.

[MJL]

I'll be watching this, it's nice to see something other than a cafe done.

[laminaytrap]

So i drew up a swingarm model. 0.095 wall sheet and 1x2 box tubing, it has two braces under the shock mount for now. This is a first attempt.

The stress analysis looks good, need to eliminate some stress points but factor of safety for a 1ft drop into wheelie with a solid rear shock looks like factor of safety of 1, which is probably good enough. Later i'll take a look at the cornering forces applied and how the twist looks. This is assuming a 700 pound weight x 3 = about 10000 N.

Hidden Lines drawing


Stress Drawing


I believe for cornering forces i should be using about 1g lateral, only a component of which will result in twist. Again i will attempt to look at it in a worst case scenario, so 1g in a wheelie

So using similar forces applied to the wheel 3xMassxgravity, Multiplied by the component of force in the direction of twist (0.707) then applied at both the top and bottom of wheel to negate sideways movement.



The image shows where the factor of safety is below 10, which indicates that the swingarm will be quite torsionally stiff, as i don't think i've ever seen a motorcycle do a 1ft drop into 45 degree lean (except Guy Martin in the Isle of Man TT) and i don't plan on running stick race tires.

Shown Below is an exaggerated displacement diagram (17x) showing a maximum of about 1-1.5 mm at the ends of the swingarm in worst case scenario.

[laminaytrap]

Well the CAD continues,

Can't see spending $400 on rear sets, so I think I can make them too.

Still looking for a source for small tapered bearings for the levers, but it looks like the bracket and arm are fairly simple, offset levers are possible too. I think welding a mounting plate to the frame in the desired position is the way to go, maybe with some equally spaced holes for a bit of adjustment if i want to do so in the long run, or if the bike is going to be ridden by someone taller.





Wow, so many posts in "theory" and nothing in "really" I need to get my bike down here asap!

Last one for now, need to write some reports...



oh no.... figured out photoview... so hard to get real work done...

[Retro Rocket]

I'm in , i just love your attention to detail, i think i'm in love.....

[Viktor.J]

I believe for cornering forces i should be using about 1g lateral, only a component of which will result in twist. Again i will attempt to look at it in a worst case scenario, so 1g in a wheelie

So using similar forces applied to the wheel 3xMassxgravity, Multiplied by the component of force in the direction of twist (0.707) then applied at both the top and bottom of wheel to negate sideways movement.





Shown Below is an exaggerated displacement diagram (17x) showing a maximum of about 1-1.5 mm at the ends of the swingarm in worst case scenario.

Long time since I did any "strength of materials" and CAD simulations. But I have some thoughts.

according to this simulation the axle is going to bend first, if you want to really know the strength of the swingarm shouldn't you make the axle stiff also ? Or have you already made the axle and given it correct mechanical properties ?
The maximum displacement here is at the top of the wheel, which is far greater then the swing arm due to the axle is shot.

OR I just took another look at the latest picture and maybe the swingarm is twisted also, it's quite hard to tell from that picture. If so, then skip some of what I just said
But still, even though the axle may be shot before the swingarm shouldn't you calculate that it will not. To rule out "other factors" and to be sure on your point !

And make sure that all your displacements are in the elastic deformation area with a great safety factor as you don't want to drive around with a bent frame/swingarm/forks etc.

Great work man !

[laminaytrap]

"Or have you already made the axle and given it correct mechanical properties?"

Answer: No

I had the model mostly mocked up, but the axle is both small and the wheel thinner than the actual bearing spread on the bike, I just threw a disk in there since i was already doing simulations I just changed the points of force. So yes, I should have/ will in the future throw in a large tubular axle or to test further.

But i was mostly concerned with the parts i was making (the swingarm) I figure the axle supplied by Honda has sufficient strength to handle the normal operations of the bike, so I try not to worry about parts that were already engineered and not considered a weak point after 30+ years and millions of miles of road.

Good eye though, I wasn't going to post till i'd redone them, but i figured most people are distracted by the pretty colours

Hopefully have some new content up tomorrow, too much to do today!

Jon

[stuartni]

this should be interesting 

[iron_worker]

The axle will also pick up some strength from the rigidity of the hub itself as well. But ya, I've never heard of anyone breaking an axle on a bike so you're probably fine. lol

IW

[Viktor.J]

My point was more that, if you want to solely want to see how much deformation you'll get on the swingarm you shouldn't calculate with a deformable axel since some of the energy that should twist/deform the swingarm now is used to deform the axle.Now you get the deformation with swingarm + axle, but thats OK to, but you said you wanted to see only swingarm stresses. But in real life it's obviously a complex combination of forces where the axle etc works with and against each other

So my point was never if the axle would be strong enough, As you say guys that would be my smallest problem

BTW which program are you using? SolidWorks ?

[snowman]

I would be interested in the triple trees and I was looking into a boxed swing arm and would also be interested.

Looking great.

[iron_worker]

Good point Viktor... if that is your real name. lol

IW

[laminaytrap]

Solidworks, Yes.

So in a real like test scenario like you said it's important for the fixtures to greatly exceed the strength of the component being tested.

BUT, in SolidWorks simulation express it will not calculate permanent deformation/plastic/nonlinear etc. so when you run a sim with a part that will obviously fail in real life that is not important, as the simulation continues beyond the yield strength of the part in question if applicable.

So in the case of the axle although it deformed in both testing scenarios all of the force is still being transmitted to he swingarm with  out any of the real life "energy loss" associated with deforming/breaking a component.

You are still right that it is better to have the most accurate representation of the part possible but, as you can see in the original post of the bending test, Solidworks continues to calculate stress and deformation well beyond (and in some cases, many times" the Yield strength of the material.

I'm going to do a more complete model in the future, just wanted to make sure 2x1 box would be strong enough so I could move on to the finer points and worry about the optimization and bracing later.

Just one more comment, I don't really trust FEA in solidworks as fact, it's nice to get a ballpark (+/- 1 FOS) but when I was doing FEA on footpegs this morning it's pretty all of our footpegs have already broken off, and if you have aluminum pegs you wouldn't even be able to get on the bike. Food for thought.

You're making great points though! And don't quote me on this stuff. It's my hobby, not my job


EDIT!!!

In the interest of getting to the bottom of this I'm running new tests...



So with a beefier Axle and a wide hub this bending test came up considerably stronger, the whole part shows Factor of Safety > 1

and do the twist.

Stress


Displacement



So now we've learned something about solidworks...

By beefing up the axle and the hub there is now a portion of the twist stress that is being countered by the axle, as it is a strong tube and most importantly

SOLIDWORKS SOLVES ONLY MERGED SOLID MODELS!

So although in real life the axle would slip around and wiggle in the slot, allowing the swingarm to bend independantly, in the solid model version it counts as a solid structural beam between the two sides, equivalent to having the back of the swingarm welded together.

That's why in the twist model there is a significant increase in strength, whereas in the bending model it is more moderate.

That's what i get from this anyways, more comments/opinions are welcome, cause at the end of the day nobody wants their parts to fail!

I guess if we're going to do this right we would resolve the moments into the ends of the swingarm and test the twist with....

oh f*ck it.

It's good

(at this point my spoked wheel would be a prickly, rubbery mess on the road behind me, oh well.)

[laminaytrap]

So, rear sets.

Make 'em?
Buy 'em?
Adapt parts off sport bike?

I'm looking at making the rearsets, as posted earlier, but i'm wondering if it's really worth the trouble, or if i should just pick up a set of used OEM sets off a modern bike, and build the appropriate bracket to fit 'em.

I can't see that that would even cost me more than material/ bearings/ rod ends etc.

anyone done this with anything other than universal sets?

They go for 100-150 around here, and although I could do custom, I am also interested in saving time...

[laminaytrap]

got bored



thanks to Oette for the idea!

wish my bike lived where I live

[Retro Rocket]

What gauge is that.?   Speedo as well