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View Full Version : FFB why both Fy and Mz scale ?



guntag
02-03-2016, 11:20
Fy and Mz both effect the strength and inducing restoring torque of the wheel.
I think Mz is a function of Fy (Fy is a function of slip angle and therefore amongst others corner speed)
plus the static and dynamic castor angle. So Fy scale should effects the restoring torque of the wheel at all.
But what is the reason that Project Cars has independent sliders for them ?
In what way should they be used and balanced ?

ex_
02-03-2016, 19:05
they can cancel each other out or overload and clip because they are both translated to the player using the left/right movement ofthe wheel, but they are modelling different physical forces, not the same.

F(y) is the lateral force, which is the force of the car pushing back against left/right maneuvers, ala Newtonian physics and the "equal and opposite reactions" effect.

M(z) is twisting motion of the wheel and its tendency to push back toward center due to the car's forward momentum. At lower speeds, for instance, you simply won't feel as much M(z) force transmitted to the player. People call this force "centering force" but it is not a comprehensive definition. That is why I call it the "twisting" force.

I hope this helps...

EDIT: To better understand these forces, turn off all of the cars' forces except one, then do the other by itself. The difference is very much apparent this way.

Krus Control
02-03-2016, 23:21
The reason that these are separated is to create more malleability in the FFB mixing system. By separating these, and all other individual force components, SMS has given us the chance to make FFB perfect in a number of ways. Anybody can find their sweet spot on any wheel and in any car. The FFB system is actually my favorite part of the game and the main reason I don't do other sims like rFactor 2 or Assetto Corsa.

MarleyMoo
03-03-2016, 00:45
My understanding is, Mz is Fy times pneumatic trail. Or maybe pneumatic trail was defined by Mz / Fy. Then the total torque on the steering column is Mz + Fy * mechanical trail. The Mz and Fy sliders therefore adjust the weight to each term.

Casey Ringley
04-03-2016, 14:13
They are very different things. Fy depends on lateral force and mechanical trail. Mz is primarily driven by pneumatic trail, what is going on within the contact patch and tire carcass. Important to remember that mechanical trail =/= pneumatic trail. The former is variable with car setup (caster angle, etc.) and steering angle while the latter is dynamically variable with what the contact patch is doing at that instant. Mz tends to peak right around peak slip angle and then fall off rapidly to even go negative as you pass peak. Fy is far less temperamental. It might fade slightly past peak slip angle, but since the force is still in the same direction and only slightly lower in magnitude, the effect on total FFB signal is largely the same.