Author Topic: Brake input  (Read 484 times)

h106frp

  • Hero Member
  • *****
  • Posts: 1786
    • View Profile
Brake input
« on: March 07, 2018, 05:23:04 PM »
Does the brake control input displacement (joystick movement) emulate brake force directly or brake lever displacement?

Thank you

HornetMaX

  • Hero Member
  • *****
  • Posts: 5809
    • View Profile
Re: Brake input
« Reply #1 on: March 08, 2018, 07:37:23 AM »
I'd say input displacement dictates the pressure. Braking force then should also depend on discs temperature (iirc discs thermals have been implemented, if not, or in older betas, then input displacement dictates the braking force). Better if Pib can confirm though :)

h106frp

  • Hero Member
  • *****
  • Posts: 1786
    • View Profile
Re: Brake input
« Reply #2 on: March 08, 2018, 08:34:35 AM »
Thanks for the thoughts, at the moment changing master cylinder size does not appear to create the expected change in controller input. It is normal to consider that for a given system just changing to a smaller master cylinder will require more lever displacement, currently the reverse appears to be true so would support the idea that the control input is simulating pressure rather than lever displacement which makes some of the options for cylinder/lever a bit confusing compared to real life expected observations.

If this is the case it would be nice to have the option to simulate lever displacement instead.   

HornetMaX

  • Hero Member
  • *****
  • Posts: 5809
    • View Profile
Re: Brake input
« Reply #3 on: March 08, 2018, 09:39:19 AM »
Ideally, there's no lever displacement at all (after the initial displacement to put the pads in contact with the disc), it's just pressure from that point on.
Putting a smaller mc (again, ideally) would probably require more displacement to put the pads in touch (no braking force up to that point), so the mc setting should alter that sort of deadzone (to put the pads in touch), but it's probably a tiny detail and it gets messy with the brake input deadzone setting.
I'd be in favor of not overcomplicating this and consider that as soon as you move the stick, you're applying pressure to the discs (pads already in touch), unless you have configured a deadzone on the brake input, of course. It's already a bit hard to grasp (for casual players) with the mc and levrage settings :)


PiBoSo

  • Administrator
  • Hero Member
  • *****
  • Posts: 2433
    • View Profile
Re: Brake input
« Reply #4 on: March 08, 2018, 10:16:14 AM »
Does the brake control input displacement (joystick movement) emulate brake force directly or brake lever displacement?

Thank you

Brake input is directly converted to force on the lever.
Obviously your ambition outweighs your talent

h106frp

  • Hero Member
  • *****
  • Posts: 1786
    • View Profile
Re: Brake input
« Reply #5 on: March 08, 2018, 10:28:31 AM »
Thank you for the clarification.

So.. is the fact that a smaller MC needs to travel further to displace as much fluid as a larger cylinder accounted for? I am guessing that currently we are just simulating a proportional change in pressure with respect to the force applied by the lever so the smaller cylinder just starts to feel 'snatchy' or 'wooden' when IRL a smaller MC is used to create the reverse of this situation and give a more progressive feel at the lever.

Grooveski

  • Sr. Member
  • ****
  • Posts: 469
    • View Profile
Re: Brake input
« Reply #6 on: March 08, 2018, 01:07:55 PM »
Certainly feels counter-intuitive to me.  I understand that a larger m/c will require more lever force....

...but my mind equates joystick travel with lever travel - the thing in my hand that I'm moving in both cases.
...so if the brakes are reacting too quickly and I want to introduce more travel into the joystick I'd expect to be lowering the m/c bore size.

HornetMaX

  • Hero Member
  • *****
  • Posts: 5809
    • View Profile
Re: Brake input
« Reply #7 on: March 08, 2018, 01:46:36 PM »
IRL a smaller MC is used to create the reverse of this situation and give a more progressive feel at the lever.
To me it should be the opposite: smaller MC means you get more disc pressure (hence more force) for the same amount of lever pressure, so that is somehow less progressive no ?

Certainly feels counter-intuitive to me.  I understand that a larger m/c will require more lever force....

...but my mind equates joystick travel with lever travel - the thing in my hand that I'm moving in both cases.
...so if the brakes are reacting too quickly and I want to introduce more travel into the joystick I'd expect to be lowering the m/c bore size.
Ach, I agree on your 1st sentence but your last goes against it no ?
If brakes are reacting too quickly, you should increase the MC size (at lest in GPB).

Grooveski

  • Sr. Member
  • ****
  • Posts: 469
    • View Profile
Re: Brake input
« Reply #8 on: March 08, 2018, 02:08:59 PM »
Ach, I agree on your 1st sentence but your last goes against it no ?
If brakes are reacting too quickly, you should increase the MC size (at lest in GPB).

No, because the force and travel are related inversely.  Going to a larger master cylinder will require less lever travel but more force wheras going to a smaller m/c will require more lever travel but less force.

The more important sentence is the middle one.  When I pull back on my joystick I mentaly equate it to lever travel rather than force.
...so changing m/cs in GPB's pits has the opposite effect to what I'd expect to happen.
« Last Edit: March 08, 2018, 02:10:40 PM by Grooveski »

HornetMaX

  • Hero Member
  • *****
  • Posts: 5809
    • View Profile
Re: Brake input
« Reply #9 on: March 08, 2018, 02:20:25 PM »
Ach, I agree on your 1st sentence but your last goes against it no ?
If brakes are reacting too quickly, you should increase the MC size (at lest in GPB).

No, because the force and travel are related inversely.  Going to a larger master cylinder will require less lever travel but more force wheras going to a smaller m/c will require more lever travel but less force.
But unless GPB somehow simulates the "flexibility" of the hydraulic circuit (or the lever), there's no travel to speak of.
There's only force on the lever.

The more important sentence is the middle one.  When I pull back on my joystick I mentaly equate it to lever travel rather than force.
...so changing m/cs in GPB's pits has the opposite effect to what I'd expect to happen.
But as Pib said, this is not what GPB does: brake input = force on the lever (so pressure in the circuit), not lever travel.
So the change in MC size behaves correctly: smaller MC => less joystick travel for the same braking force.

Grooveski

  • Sr. Member
  • ****
  • Posts: 469
    • View Profile
Re: Brake input
« Reply #10 on: March 08, 2018, 04:50:33 PM »
But as Pib said, this is not what GPB does: brake input = force on the lever (so pressure in the circuit), not lever travel.
So the change in MC size behaves correctly: smaller MC => less joystick travel for the same braking force.

Yeah - funky - I know that now.   ;)

But the question is "Should it?" 
...or should joystick travel equate to lever travel?
....which to me would seem like the more intuitive way round.

Grooveski

  • Sr. Member
  • ****
  • Posts: 469
    • View Profile
Re: Brake input
« Reply #11 on: March 08, 2018, 05:31:35 PM »
But unless GPB somehow simulates the "flexibility" of the hydraulic circuit (or the lever), there's no travel to speak of.
There's only force on the lever.

Yeah I understand that too - but I'd argue that that flexibility is exactly what you're swapping master cylinders to fine tune in the first place - so perhaps it should be getting simulated.
...and that "no travel to speak of" is an oversimplification.  I prefer pretty soft levers(in real life) - not spongy but on the spongy side of normal.
...and there is most defiantly lever travel between on and full-on.

Grooveski

  • Sr. Member
  • ****
  • Posts: 469
    • View Profile
Re: Brake input
« Reply #12 on: March 08, 2018, 05:37:39 PM »
By the way - I have no problems with the brakes on GPB or the operation of them - I don't really think lever flex, hose expansion, caliper porosity, etc need simulated.

This whole thing is simply about swapping m/cs in the pits and  how a smaller m/c makes for what I'd consider a more wooden feel on the brakes - it just feels the wrong way round.

HornetMaX

  • Hero Member
  • *****
  • Posts: 5809
    • View Profile
Re: Brake input
« Reply #13 on: March 08, 2018, 05:46:31 PM »
But unless GPB somehow simulates the "flexibility" of the hydraulic circuit (or the lever), there's no travel to speak of.
There's only force on the lever.

Yeah I understand that too - but I'd argue that that flexibility is exactly what you're swapping master cylinders to fine tune in the first place - so perhaps it should be getting simulated.
...and that "no travel to speak of" is an oversimplification.  I prefer pretty soft levers(in real life) - not spongy but on the spongy side of normal.
...and there is most defiantly lever travel between on and full-on.
Yeah there is, but aren't better hoses (stainless, braided) just trying to avoid/minimize that ?
Also, I'm pretty sure your brain doesn't actually "reason" in terms of lever displacement: could you imagine a brake lever with a very light spring behind it (and no "hydraulic" feedback) work fine ? It would be tremendously hard to use. On a real lever, what you modulate is probably more the force you apply. The displacement is just a side effect. Zero displacement is probably a simplification and it may turn out to be a bit weird to use, but keep in ind that car-simmers do like load cells for brake pedals ...

This whole thing is simply about swapping m/cs in the pits and  how a smaller m/c makes for what I'd consider a more wooden feel on the brakes - it just feels the wrong way round.
I never swapped a MC in real life. What do you expect to happen in real file when you lower the MC diameter ?
Would you need to apply more or less force on the lever to get the same braking force as with the bigger MC ?

I'd expect less, hence the "wooden" feeling (or less progressive as h was saying before).

Grooveski

  • Sr. Member
  • ****
  • Posts: 469
    • View Profile
Re: Brake input
« Reply #14 on: March 08, 2018, 06:12:41 PM »
I never swapped a MC in real life. What do you expect to happen in real file when you lower the MC diameter ?
Would you need to apply more or less force on the lever to get the same braking force as with the bigger MC ?

I'd expect less, hence the "wooden" feeling (or less progressive as h was saying before).

As I said earlier:
Going to a larger master cylinder will require less lever travel but more force wheras going to a smaller m/c will require more lever travel but less force.

...and honestly, now that I know it's the force that's the being simulated it'll never be a problem again - but I'll always be thinking of it as the wrong way round in the pits when I go to change it.

Since we're chatting - here's another copy/paste from when h and I were blethering last night.   :)

Quote
The wee zxr is on it's fourth m/c.   :) 
The original was crap(right size(12.5mm)) - just a poor OEM unit that had no feel.
Fitted the Brembo off a Guzzi Daytona for a while.  12mm conventional design but a larger pivot length and longer barrel so a pretty good match.  About the same lever travel but much more feel - just a better manufactured piece of kit.
Was only a loan though so replaced that with an OEM Brembo Radial from an R1.  16mm but radials are measured different - the barrels are shorter so the bores have to be larger.  Felt much the same as the Daytona m/c.
...then changed my calipers to a set with bigger pads and pistons and to match them splashed out on a Brembo RCS19.  19mm radial with adjustable pivot length.  Far better quality than any of the previous units and you can feel it.

Having upped the pad size there was also less force required for the same bite.  Now it's 1 or 2 fingered loveliness.   ;D

...so while I've done a few m/c swaps, they've been more about improving the quality of the unit rather than adjusting the travel/lever force.  The earlier ones were all about the same size, had about the same travel and took about the same force.  It wasn't until the calipers were changed that there was less force required at the same travel.