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Where can you find real life bike data ?

Started by h106frp, December 05, 2015, 11:42:56 PM

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h106frp

Playing around with bikeED and interested in the effect that moving the 'center of mass' has on the observed bike handling.

Curious if there is a source of data for bikes like the Honda to compare to the GPB bikes models. I always though it would be around the crank somewhere but this assumption does not seem to be correct from what i can see.

Thanks

Hawk

That sort of data I found almost impossible to find or acquire. Though I've only really searched for the old classic bike data.

I've also tried emailing bike companies and some classic racing guys for real bike data and Dyno Chart copies, but all I got back from those, that bothered to replied, was that they were not allowed to release that sort of technical information and my best bet was to actually go to classic race meets and talk to the riders and mechanics about it.

If your lucky you can find data that some have posted online, but centre of mass data I really cannot see anyone posting info like that, but there must be a mathematical formula for calculating that if you can obtain the other figures about the weight of the chassis, swingarm, etc, etc needed? Other than that you could just use trial and error testing until it feels right.  ;)

Maybe Max would know the CM formula?

Hawk

h106frp

Trial and error is what got me scratching my head  ;)

I was just playing with the new Honda and found that moving it close to the crank centre makes the bike much more 'flickable' at high speed and generally nicer handling all round, but most of the bikes have it positioned higher and further back so trial and error might be misleading.

Keep reading about 'mass centralisation' but cant find any useful info.

tseklias

I don't believe you can find the centre of mass with just a formula. I mean the vertical point, cause the horizontal you can find it easy. I'm very curious though to learn how they find the centre of mass cause i was doing a research myself lately... let's wait and read opinions.

h106frp

December 06, 2015, 09:19:29 AM #4 Last Edit: December 06, 2015, 09:29:35 AM by h106frp
Quote from: tseklias on December 06, 2015, 06:39:22 AM
I don't believe you can find the centre of mass with just a formula. I mean the vertical point, cause the horizontal you can find it easy. I'm very curious though to learn how they find the centre of mass cause i was doing a research myself lately... let's wait and read opinions.

It seems quite critical with the way the physics are calculated in game - it makes a major impact to way the bike 'feels' when turning/accelerating/stopping etc. If you want bikes that feel definitely different and unique to each other rather than Mura clones this seems to be effective.

Pictures of the newer Ducati without its fairing would suggest it is very low and forward, virtually no bike in the area with the 'classic' mass point.

This is an older bike, but with the lightweight clutter removed where would you now place the centre? I would have guessed somewhere near the crank  ???


HornetMaX

The CoG of a body can be computed with a formula, knowing the exact geometry of the body and the density of the material at each body point. You can look it up on wikipedia (https://en.wikipedia.org/wiki/Center_of_mass).
You basically can't do it by hand, except for trivial bodies (e.g. sphere, disc, rod etc). So most of the time this is done numerically.

Given a body, there are ways to localize its CoG experimentally (i.e. you can "measure" it).

Given he CoG of two bodies, computing the CoG of the resulting assembly of the two is trivial. So if you have the CoG (and mass) of each body, it's easy to compute the COG of the bike.

Keep in mind that GPB bike is an assembly of multiple bodies: front and rear wheel, rear swingarm, steering head, chassis and rider (plus the CoG of the fuel in the tank, which of course varies with time).

Notice however that the CoG varies in time too, not only due to the fuel, but also (and mostly) due to the fact the bodies move relatively one to the other (swingarm, steering head and, of course, the rider).

Hawk


HornetMaX

Quote from: h106frp on December 06, 2015, 12:17:33 AM
Keep reading about 'mass centralisation' but cant find any useful info.
This is related to inertia: a bike that is slimmer (less wide, e.g. a v4 vs a 4 in-line) has a smaller inertia along the longitudinal axis so it will be easier to flick.

HornetMaX

Forgot to add: moving the CoG fwd/backward and up/down alters the load transfer (and other things). This dictates how hard you can accelerate before the front lifts up.

@h106frp: V.Cossalter, "Motorcycle Dynamics". That's all you need man :)

h106frp

December 06, 2015, 08:14:29 PM #9 Last Edit: December 06, 2015, 09:30:38 PM by h106frp
Thanks,
I think that's useful  ;) Anyone lend me a GP bike so i can measure it  ;)

@MaX actually something you could explain that has puzzled me about the inertia boxes;

steer
{
   Mass = 11
   InertiaBox = 0.4, 0.8, 0.2

The second value appears to fix the top yoke in the longitudinal axis of the bike, reducing it allows it to visibly move. Fair enough that must be how fixed points are tethered in the model

but;
rear_suspension
{
   Mass = 8
   InertiaBox = 0.4, 0.2, 0.6

seems to contradict this, surely the rear pivot should be rigid in the longitudinal axis as well.

Just puzzled  ???


Now i can pan and zoom in biked i can see easily that chassis center mass position varies greatly between mod bikes, back to trial and error i guess  :)

Centre is quite a bit higher on the motogp15 Honda MOD than on the PB Mura which has it in the area (crank) i ended up with on the Honda by trial and error - lucky coincidence?. Noticed on the CBR250R it is very high   ???

C21

December 07, 2015, 08:26:52 AM #10 Last Edit: December 07, 2015, 08:49:19 AM by C21
QuoteKeep in mind that GPB bike is an assembly of multiple bodies: front and rear wheel, rear swingarm, steering head, chassis and rider (plus the CoG of the fuel in the tank, which of course varies with time).
And each of it has an influence of the bike handling....including fuel mass, chassis mass, aero pressure point :o
That´s the "problem" modding new bikes AND let them behave different.
It´s easy (more or less) to make a new Muru Clone....but to make the clone an individuum it´s harder and sometimes the art of try and error. ;)
You can make the bike oversteer, understeer, wheelie , bottomed, changing the values......in the right or wrong direction.
Then we have the steering damper and PID controller which can mess up good bike physics when improperly set.

QuoteV.Cossalter, "Motorcycle Dynamics". That's all you need man
That´s the bible.....but not for everyones mind (too much formulas)  ;)
# Member of the CAWS Racing Team #


HornetMaX

Quote from: C21 on December 07, 2015, 08:26:52 AM
QuoteV.Cossalter, "Motorcycle Dynamics". That's all you need man
That´s the bible.....but not for everyones mind (too much formulas)  ;)
True, but there's only one way to understand it for good.

If one needs something a bit easier on the maths, there's this: Motorcycle Handling And Chassis Design by T.Foale

C21

QuoteMotorcycle Handling And Chassis Design by T.Foale
i find that one more practicable then the Cossalter one.
Cossalter is very theoretical but it´s the mathematical view of Foale´s book.
# Member of the CAWS Racing Team #


HornetMaX

I'd say more the other way around, the Foale book is the "practical" view of the Cossalter :)

The problem is that in some occasions, you do need a formula to do the job.

h106frp

Might be some guidance, its for the road bike version but i guess they would be similar mass distribution