• Welcome to MX Bikes Official Forum. Please login or sign up.
 
September 22, 2020, 11:40:12 PM

News:

MX Bikes beta14e available! :)


beta6 bug list

Started by Asdrael, March 17, 2017, 11:38:17 AM

Previous topic - Next topic

Bj Slice

Simple as kinetic energy of a spinning wheel is being transferred to the whole bike through the bite of the rear brake and anything that connects to it, thus makes the rotation of the whole bike to the direction of the spin of the wheel. If the wheel does not have enough spin, the bike, as a whole won't rotate.
"Practice not until you get it right. But practice until you can never get it wrong, and make it a routine"


CSchmied986

Quote from: Asdrael on April 06, 2017, 12:28:00 AM
Quote from: NorCal 986 on April 06, 2017, 12:17:27 AM
Most people do not understand is that when you hit the break/ throttle in the air, you are actually effecting the front wheel very little. Hitting the rear break in the air does not bring the front end down, it bring the rear end up, and the opposite goes for the throttle.

"So if I hit rear break then front brake then rear brake I'll reach the moon? No, hitting the rear brakes makes the front end go down."

Can you use actual physics to explain your theory? From studying physics, and learning about torque, angular momentum, and Newton's Second Law, I'm just having a hard time understanding how torque and angular momentum around the center of gravity of spinning mass would effect another object (front wheel) instead of altering the angular momentum of the object which is creating the energy.  ??? Unless it is some sort of theoretical Quantum effect that I just don't understand.

Bj Slice

April 06, 2017, 02:41:59 AM #62 Last Edit: April 06, 2017, 03:11:12 AM by Bj Slice
Regarding the rear brake tap and its effect to the front and rear end, it's not a question of whether the front or rear is raising or dipping, cause it does both. It's a question however of how much it raise and how much it lowers depending on the bikes angle when you jump. The rear wheel is the center of rotation, but it is not hard-mounted to anything, thus is still subject to rotation because the front and the rear wheels are mounted on a chassis and the swingarm. Imagine a see-saw but not mounted. They move up or down or only the front is lowering but how it would look like would depend on how you see it perspective-wised.

Anyway, I noticed that the pit board info (your position and timing) are not for the current lap. it is from the previous lap. Another thing about it is that the pit board comes out before or after the finish line (way after). Is this known? Thanks!
"Practice not until you get it right. But practice until you can never get it wrong, and make it a routine"


CSchmied986

Quote from: Bj Slice on April 06, 2017, 02:41:59 AM

Anyway, I noticed that the pit board info (your position and timing) are not for the current lap. it is from the previous lap. Another thing about it is that the pit board comes out before or after the finish line (way after). Is this known? Thanks!

Ya, it is to simulate real life, so the thought is that your mechanic can't give you your laptime until you go by him on the next lap, and the weird placement of the lap board is because that is the designated 'mechanic area'. But ya, I'm not a huge fan of it either, and for many people it makes it confusing on where the actual finish line even is.

HornetMaX

Quote from: NorCal 986 on April 06, 2017, 02:24:01 AM
Quote from: Asdrael on April 06, 2017, 12:28:00 AM
Quote from: NorCal 986 on April 06, 2017, 12:17:27 AM
Most people do not understand is that when you hit the break/ throttle in the air, you are actually effecting the front wheel very little. Hitting the rear break in the air does not bring the front end down, it bring the rear end up, and the opposite goes for the throttle.

"So if I hit rear break then front brake then rear brake I'll reach the moon? No, hitting the rear brakes makes the front end go down."
Can you use actual physics to explain your theory? From studying physics, and learning about torque, angular momentum, and Newton's Second Law, I'm just having a hard time understanding how torque and angular momentum around the center of gravity of spinning mass would effect another object (front wheel) instead of altering the angular momentum of the object which is creating the energy.  ??? Unless it is some sort of theoretical Quantum effect that I just don't understand.
No quantum effect, it's called angular momentum conservation.

Idealized situation (to keep it very simple): bike flying forward at constant speed, perfectly horizontal, rear wheel spinning.

The angular momentum of the entire bike (relative to the rear wheel axle) is given by the rear wheel inertia (along its rotation axis) times its angular speed, as the rest of the bike is not rotating relatively to the rear wheel axle.
When you hit the rear brake, the angular speed of the rear wheel will go down, so its angular momentum too. For the total angular momentum to stay constant, something else must start rotating and the only option is that the bike starts rotating around the rear wheel axle. Its rotation speed depends on the initial total angular momentum, on how much the rear wheel slows down and on the "bike minus rear wheel" inertia around the rear wheel axle.

The heavier the rear wheel the more the effect is noticeable. The heavier the bike (minus rear wheel) the less the effect is noticeable.

If you want an easier way to visualize this (guess Asdrael will call this the TL/DR version :) ): when you hit the brake the pads squeeze the disc and that generates friction, i.e. a force that tries to slow down the wheel. By reaction, an equal and opposite force will try to "accelerate" the brake caliper, to drag it along with the disc rotation. As the caliper is tied to the swingarm (itself tied to the bike frame), the bike will start rotating around the rear wheel axle, as in the air the bike is not supported by anything.

teeds

Quote from: geofanatec on April 06, 2017, 01:03:18 AM
The softer compounds do have more grip than the hard compounds that is on OEM models? So not sure why you think/say this?

This bugged me at for ages but pretty sure it's not representing compound in MXB (although they are different). A Soft tyre in MX is for soft ground, the nobbles are more spaced but the rubber is a harder compound. Hard tyres are for hard surfaces they have more of a contact patch with less space between the nobbles for a bigger contact patch but would be a softer compound.

http://www.motosport.com/blog/the-difference-between-soft-intermediate-and-hard-terrain-dirt-bike-tires

I wondered why you were describing the tyres with rolling resistance due to compound  :o
"Damn dirt bikers!" - Bubba

teeds

Quote from: geofanatec on April 06, 2017, 01:03:18 AM
A softer tyre may grip better (and does), BUT because it is softer and does grip better you have more surface area contacting the ground.........thus more resistance :)

Probably should have included this line in the quote above.

A soft tyre with MX tyres does not have a bigger contact patch, a hard tyre does.

I have asked before ages ago but got no response from Piboso about what exactly the tyre names represent, but I find it hard to believe he would use rubber compounds and not the real world meaning. Might be why i didn't get an answer as it's obvious? But If i'm correct about this your "Goes" tyres are probably going in the wrong direction and might explain why i'm finding them terrible compared to the stock ones on certain surfaces.

Can you show any real world info about rolling resistance with dirt bike tyres? I'm sure it exists technically but isn't something I've ever heard mentioned or have read about as I suspect it's negligible.

Need to clarify this.....
"Damn dirt bikers!" - Bubba

Asdrael

If you take one example out of Piboso tires -
"Hard" has significantly more grip on compact, soil and soft than "Soft" tyres. Less on sand. They have the same roll resistance. On certain surface, they will present a better grip overall than Geo tyres (in particular when wet and on sand).

As for Geo Tyres, the grip <-> roll resistance balance was just a temporary solution while trying to get a clue how the rest works as far as I know. I think he's now coming out with much better bike behaviour now, a few more tweaks and I think it'll be time to properly move to surface specific tyres, hopefully keeping the roll resistance rather low. Ideally, we'd have 5 or so different "surfaces" tyres to chose from (from soft soil to hard packed), and 2 different width at least for the rear - which will in that case give grip at the cost of "power" (or more resistance). Would seem like the right way to go, and pretty close to how stuff works IRL. There is no way currently to space out the pattern to prevent dirt jamming etc as far as I know.

And yeah, real tyres roll resistance is kinda low - the problem is the surface roll resistance. Sand being obviously more resistant than asphalt, etc.
Donate to me -> feed my coffee addiction -> get more mods!
OEM bikes pack
MXBikes Discord

Asdrael

Quote from: geofanatec on April 06, 2017, 03:14:33 PMNow, there is only 1 item in the "magic formula" that I have not messed with yet. It is q_sy1 and is the only value in the formula that changes from hard to soft. So I don't know if this has anything to do with knob spacing or what? Would love to know, but thre could be something there.

If PiBoSo follows the Matlab package implementation names, Qsy1 is the Rolling resistance torque.

I have got an idea to make the transition from the current Geo Tyre to a v2.0 with surface tyre choices being the pivotal choice (instead of a tentative compound softness). I'll move this to the GeoTyre thread because I'm losing hope for bug reports here now :p
Donate to me -> feed my coffee addiction -> get more mods!
OEM bikes pack
MXBikes Discord

HornetMaX

Quote from: Asdrael on April 06, 2017, 03:29:15 PM
Quote from: geofanatec on April 06, 2017, 03:14:33 PMNow, there is only 1 item in the "magic formula" that I have not messed with yet. It is q_sy1 and is the only value in the formula that changes from hard to soft. So I don't know if this has anything to do with knob spacing or what? Would love to know, but thre could be something there.

If PiBoSo follows the Matlab package implementation names, Qsy1 is the Rolling resistance torque.
Very likely, that's what's in Pacejka's book (Tire and Vehicle Dynamics, 2nd edition, there's a 3rd out now) which PiBoSo follows AFAIK.

It's not a torque by itself, more of a coefficient, a % if you want. The book says it's "typically 1-2%", but at the same time the book mostly deals with cars' tyres and I can't grant this translates well to bike's tyre (or even less to mx tyres). At any rate, if you have it at 0.5 (50%) that would make my eyebrow rise :)

Personally that's not the 1st parameter I'd play with, especially if we don't know how it relates to soil type.