i'm pretty sure the honda rs 125 track tail piece is close in shape to the gp one to give you a starting point
Also, I have an idea of what I'd like the bike to look like; This rendition of yours is just too beautiful! I wish Ducati would build this. Are you sure you not working under cover for MV Agusta?
Hello good folks of Ducati land, time for another update. I'm not really sure how much detail to go down, It'll bore most people to death I think, graphs aren't very sexy unfortunately! So feel free to skip all this nonsense I'm at the stage now where I'm starting to manafacture the three chassis'. The final matierial i went for was based on this: a small amount of data. I've tested 7 different chassis designs each optimised from the last, and coordinated that with a reverse engineering of Pierbons X85R mk1 and 2. The inital topology optimization study didn't do as i hoped it would and honestly was a waste of time, but playing the academic game for uni it looks fancy enough for a few extra marks hopefully. I mentioned it briefly before but to really analyse a chassis you need to figure out four things: 1) Strength, This is fairly self explanatory... But knowing the maximum loading is a little more difficult. Normally when optimising any product you have a maximum load case and work towards some factor of safety to give yourself a little space for unusual circumstances and engineering whoopsies. For the case of a bike chassis the basic maximum loading is usually considered to be maximum braking force, which can be found be either using accelerometer data or by calculation. The maximum braking is limited in two ways: tyre friction and tip over, any kid with a strong front brake on a bicycle knows that usually tip over is the limiting case (stoppie). So in essence you can only stop as fast as you can keep the rear wheel on the ground. Traction limited braking can be thought of as weight of the vehicle (downward force due to gravity) multiplied by the co-efficent of the tyre and works out as roughly 3200N, do a bit of newtons second law with the weight of a panigale and rider and your rate of deceleration is 11.5m/s^2 (warm day, racing tyres). Pretty fast. However, you would very quickly be thrown over the front end with that level of braking force. By using some equations from Motorcycle Dynamics - Vittore Cossalter on front and rear tyre loads, you can calculate the maximum force the bike can take before starting to stoppie, this takes into account wheelbase, center of gravity and mass. This is around 2750N or 9.8m/s^2. But of course at 180mph drag is quite substancial and stops you stoppie'ing, so your rate of decelleration at those kinda speeds is utterly incredible. Part of a university assignment was to simulate a laptime base on accelerations of a chosen bike below is mine on a 1199s ridden by Michel Neeves. The orange trace is purely a microsoft excel calculation, blue is real data measured throughout a lap of donnington. You can see how close the the angles of those curves are (accelerations), proving that these forces are fairly realistic. My calculations show the bike braking harder and accelerating faster, Micheal was on a borrowed bike and obviously wasn't riding to the bikes maximum potencial, he also had road tyres on with sub optimal british weather (pissing down, only a few dry sessions) So thats it? if the chassis can survive that, it'll be good right? nope. What happens if you slam down a wheelie? or hit a big pothole? Those are the killer forces, and very awkward to realistically find out. But I've seen chassis' break from slamming down wheelies, so I would assume the manafacturers don't design for it, or it happens to not be as high as other dynamic forces. For my project, its not really important what the maximum force is.
2) Rigidity This is interesting, The titanium model is stronger than the steel one but it bends more. Rigidity is the combination of the matierial properties and the structure (what the frame looks like), so with two identical frames one made with steel and one with titanium, the titanium is stronger but less rigid. Which is a strange concept. I ideally I want three frames with identical stiffness, but with different matierials. As explained before in an earlier post the chassis acts as a spring at high lean angle to absorb bumps in the road, as that spring 'unwinds' and releases that energy, the natural damping of the matierial is realistically the only thing stopping that oscilation. But to achieve matching stiffness the strengths will be all over the place, its not possible to have the same stiffness and strength without changing the structure shape of the frame, something i dont want to do... its too time consuming, and I doubt its actually possible. You can see above the siffness of each of my designed chassis made from grade 9 titanium 3AL-2.5V, BS4T45 steel and a combination of 6063 and 6082 alumnium both in T6. The titanium will be slightly less stiff, I just couldn't source the appropriate size of tubing and don't quite have the budget to get something custom ordered. But you can see that the outer diameter of the titanium is the same as the alloy, which naturally makes no sense! The titanium has almost have the youngs modulus of steel, its floppy. The only way to get that stiffness back was to massively over engineer the whole frame, in those braking tests in the early designs it has factor of safety of something stupid like 19. The aerospace industry uses around 1.3, its daft. That graph shows the steel to be chromoly Cr25Mo4, thats what the Pierobon X85R's are made from, Ducatis steel GP bikes and KTM dirt bikes are made from. It does need to be heat treated after welding even though I was planning to avoid that due to only using thin walled tubing, But the biggest reason i didn't was the price. In America or europe its very available, in the UK its.... not. So hence the T45, which is actually better as its more weldable and its only marginally different in terms of stiffness. So above are the final designs and wall thickness' (again...T45 not Cr25Mo4).
3) & 4) Modal analysis I'm not going to go into any detail, this is the subject for my masters degree and honestly.. I don't know enough about it. Basically, you dont want to design a chassis that has any resonance in the usable dynamic range.
BUT THATS BORING! So heres my new lathe! If I've going to be heavily in debt when I leave uni I might aswell have something to show for it rather than a pretty piece of paper. Its a beautiful 1968 Colchester student mk2, I was planning to do the maching in the uni but apparently some people have been rather unwell around the world and thats sadly ended my plans to borrow university equipment. I'm terrible at grinding tools and prefer to just get kit that works so I got some CNMG insert tooling with inserts for steel, alloy and titanium, along with a boring bar and a parting tool. I didn't want to get a little sh** chinese lathe, I've had enough with crap tools nowadays, i'd rather pay more the first time. It definetly paid off, I had to machine a new backplate to fit my 4 jaw chuck, hows this for accuracy: Not sure if you can see, but the new part is exactly on the money down to 100th of a mm. Thats good enough for me! Luck may have been a part of this....
I've made start on the Aluminium frame and already made an arse of it This ^^ was the piece for the top and bottom head stock, I was using second hand telescope gauges which weren't at all accurate and I overshot the inference fit. Not all bad though, I learned alot about feeds, speeds and surface finishes which was good. I also came across some titanium bar and thought I'd have a crack at a little project to get turning on some Ti, wedding bands for my wedding if that ever happens... I was a good boy for valentines day this year! "can you put diamonds on it?" - was not a well received piece of feedback.
My grandad had this sitting around so I thought I'd machine it up and make it fit mine. Lathe milling was definetly not part of the plan, but.. needs must in times of corona virus! I currently have everything I need for the alloy chassis and the tubing for the Ti and T45 one. I need to find some EN14 for the hard mounting points but I'm struggling! Only quote I have for a 100mm diameter of EN14 was £650 + shipping + VAT for a 3m long section, which is a bit scary and of course I can't find anywhere that will sell me a smaller section. I believe EN14 chrome plate round stock is what they make hydraulic rams from? I may be wrong, and no way am i messing around trying to turn down chrome plate round stock! I believe the Uni has a large chunk of 6al-4V grade 5 Ti which i'd like to use for the Ti chassis, but I'll need to wait til it opens back up again to get access to it. Worse case I can get an eBay cut off, its very available which is good.
That was not even close to boring. Love the read, best post I've seen in ages, maybe ever. Loved every minute of it, hope you keep doing these posts!
Every days a school day!!! ..... very educational, and exceptional attention to detail I’m from an engineering background, turning, grinding, milling etc. Eventually making the transition into the latest and greatest CNC machinery. So keep it coming Great work.
It's nice to see people are interested in the techy side of this project, I'm a bit obsessed with it! I feel like I need to stress that if you're just making a custom bike chassis that's not performance orientated this is a little too far to go, I'm eager to see if I can feel any difference between the chassis'. The new design should be alot less stiff than the OEM cast one laterally (side to side), so I'd hope I can feel a very very slight difference. But again.. this is getting to levels that (as a rider) I'm just not at, I don't race and I'm not a WSBK champion. But I think that's also kinda the point, does this stuff even matter for the average trackday rider? It obviously does for MotoGP but those bikes are closer to aircraft than standard road bikes, and they have so much power that they probably don't handle very well, more like drag bikes than nimble 250's of yesteryear. So I'm keen to try this out and validate it with a real arse on a seat.
Fascinating! but way above my level of engineering knowledge (such as it is). Please keep updating us.
Finished the jig to make the frames on, it was a little awkward to make as you have to be able to get the chassis out at the end! I opted to make the lower headstock section removable so I can use the original engine to frame hardware. The clearance for the bolts is very large. The bolts are 12mm and the holes are around 13mm, I assume due to the single sided swingarm having no wheel alignment adjustability they designed the clearance so the frame can pivot do alignment from there. ...or my frame is royally f**ked. The headstock is out of round by around 0.04mm I doubt that's from machining, it's most likely from a crash, but it's very negligible anyway. I decided to put dowels in so that removable part is in exactly the right place everytime for all three chassis. You'll also see the two weld plugged holes, the jig moved quite substantially after welding so I had to redo the dowel location. Knowing me I'd end up putting the dowels in the wrong holes and have a duff chassis at the end! I'm starting to worry a little about distortion in the chassis, chassis guru Tony Foale recommends welding the headstock parts last so any movement will be done before that, so engine mounts to headstock distortion should be minimal. We'll see how it goes. Weirdly after welding I heard a 'chink' sound, and couldn't figure out what it was, once I went to weld again I figured out the ceramic cup had shattered.. strange as I hadn't dropped it or anything! I'm seriously impressed that the capton tape survived the last part of welding too! I machined the first parts too, so I guess I've officially started making it? I dunno.. The headstock inserts are a bearing fit, I can't remember if I measured the OE chassis diameter or used the engineers black book to calculate the fit. Either way, it could fit in on the machined parts out it would take a bit of force which is good. If it's too tight later I can use a scotchbrite wheel and polish in some clearance.
FYI from an amateur machinist, the bore gauge is definitely the way to go, way more repeatable results compared to the telescope gauges.
It makes me wonder what the Ducati MotoGP team are missing. Given their lack of corner speed. This thread is very interesting/ enlightening. To say ‘well done’ is an understatement. Fascinating, keep it coming.
I'd love to talk to a corse engineer and find out! My theory is that they play it a little safe with the road bikes (and hence sbk) and don't do anything too drastic, apart from the panigale frame.. that was really really different. But with the GP bikes they go really far in a direction to try it out, essentially making much bigger changes. It's very difficult to validate what you have done in terms of rider feedback, it's going to be a very small change even with a large change in stiffness, so track temperature, tyres, riders mood, brakes, engine... So much comes into it that it's difficult to single out the chassis. If you look where the 's' is you can see Suzuki's hybrid chassis system. These 'engine hangers' can be replaced with various thicknesses of carbon or aluminium, that's what the research paper was about. They can choose lateral stiffness on demand (how much flex at high lean angle) whilst maintaining the geometry of the structure so well that longitudinal stiffness is unchanged (braking axis). I had a similar idea years ago in college of just bolting bits on to change stiffness, it's a great idea! It's basically just like changing the spring rate in the suspension based on which track you are at.
