Re: [Flightgear-devel] gear numbering

[Josh Babcock]

OK, I guess I'm just confused about the brake numbering.  I was assuming 
that brake[0] went with the leftmost wheel, and brake[1] went with the 
next one to the right et cetra, and that when I hit "," the entry in 
keyboard.xml literaly means "turn on the brake on wheel[0]".  Looking at 
a bunch of files, I see that you have to hand map this for each wheel.  
It just seems a little confusing that on a big plane with say, 5 gear 
units that /controls/gear/wheel[1]/brake is what controls braking on 
wheel[5].  I can see the value of having seperate braking channels, in 
this case there are two, but the property names seem to imply that they 
are linked to particular wheels, which they are not.  I think I'm 
straight now.  I'll just put the appropriate mapping in my .xml files.

Josh

Jon S Berndt wrote:

On Mon, 05 Jan 2004 07:12:21 -0800
 Andy Ross <[EMAIL PROTECTED]> wrote:
But the hard part is that this only works for YASim.  I think the other
FDMs get their control inputs indirectly, via the FGControls C++ 
class, instead of out of the property tree.  This code would have to
be modified before they could use such a system (Jon/Tony/David 
should correct me if I'm wrong here).

Andy


In JSBSim.cxx (the JSBSim instance of FGInterface - the FDM/FlightGear 
bus), we do this in the copy_to_JSBSim() function:

...
FCS->SetLBrake(FMAX(globals->get_controls()->get_brake(0), 
parking_brake));
FCS->SetRBrake(FMAX(globals->get_controls()->get_brake(1), 
parking_brake));
FCS->SetCBrake( globals->get_controls()->get_brake(2) );
...

In our JSBSim aircraft (and for quite a few years) we have defined a 
gear object as follows,

The gear parameters that can be specified are as follows, IN ORDER OF 
APPEARANCE:

AC_GEAR
<name>                          name of gear entry - no spaces allowed
<X> <Y> <Z>                     location in aircraft body coords in 
inches
<spring constant>               spring constant in lbs/ft
<damping coefficient>           damping coefficient in lbs/ft/sec
<dynamic friction coefficient>  sliding friction coefficient
<static friction coefficient>   "onset" friction coefficient
<rolling friction coefficient>  rolling friction coefficient
<steerability attribute>        One of <STEERABLE|FIXED|CASTERED>
<brake group membership>        One of <LEFT|CENTER|RIGHT|NOSE|TAIL|NONE>
<max steer angle>               Maximum steerable angle in degrees
<retraction attribute>          <RETRACT | FIXED>
-->

AC_GEAR NOSE -6.8 0.0 -20.0 1800 600  0.5 0.8 0.02 STEERABLE NONE 10 
FIXED
AC_GEAR L_MN 58.2 -43.0 -17.9 5400 1600 0.5 0.8 0.02 CASTERED LEFT 0 
FIXED
AC_GEAR R_MN 58.2 43.0 -17.9 5400 1600 0.5 0.8 0.02 CASTERED RIGHT 0 
FIXED
AC_GEAR T_SKID 188.0  0.0 8.0 20000 1000 0.2  0.2 0.2 FIXED NONE 0 FIXED
AC_GEAR L_TIP 43.2 -214.8 59.4 10000 2000 0.2 0.2 0.2 FIXED NONE 0 FIXED
AC_GEAR R_TIP 43.2  214.8 59.4 10000 2000 0.2 0.2 0.2 FIXED NONE 0 FIXED

We've modeled left and right gear for years, so I'm not sure what the 
problem is.  I know I can steer using differential braking on the 
C-172.  I'm not sure I understand the problem.

Jon

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