rec.autos.simulators

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"Dog" rings.
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This is a side view of two racing transmission gear engagement "dog"
rings with straight cut teeth. One rotates with the engine and the other
with the differential (rear wheels).  When a gear is selected they are
brought
together and the teeth engaged. It may be possible to disengage them
without lifting off the throttle and when the teeth start to wear they may
slip
out of engagement (Trans. "pop" out of gear).
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These are "undercut" dog rings. The teeth are cut at an angle to
give more positive engagement and prevent slipping out of gear.
Nearly all new transmissions have this type. The teeth can not be
disengaged unless power is reduced by either a slight lift on the throttle
or an ignition cut out switch on the gear shifter.

Both of these types of dog ring require "Blipping" or raising the throttle a
slight
bit on downshifts to match rear wheel dog ring speed to engine dog ring
speed
for a smooth engagement. Different types of pedal setups and foot sizes may
use different methods of "heel and toe" to blip the throttle.
Dog ring are usually the first thing to wear out in a transmission because
of
not matching the rpm's to the rear wheels. You probably don't have to worry
about
this in a racing sim unless it has a transmission damage setting.

D Sport Racer #74

  Correctomundo!   I let literalness get in the way...the concept was right the
explanation was way off.   Thanks for the correction
dave

I think the "official" line while in the school is to use the clutch,
but from off-the-record discussions with instructors, they almost
universally approved of clutch-less upshifts for everyone who wanted
to and understood vaguely what to do.

(You also can do clutchless downshifts, which is worth practicing for
the day you lose clutch hydraulics, but expect to spend plenty of your
early downshifts stuck in neutral hunting for a gear, and making lots
of ugly sounding noises.)

---Jim

Sorry this is a little late... been away from my copy of Pine for a few
weeks!

Keeping it floored whilst smacking the clutch is called 'powershifting',
and was used extensively in Touring Cars until recent years.  It works
best with a rev limiter.

Clutchless shifting requires a brief cut in power.  This is now achieved
in all Touring Cars and many other classes by cutting the ignition for a
split second (F1 engine management does a similar trick).

If you're driving an endurance race you should be both lifting the
throttle and using the clutch - you'll break something otherwise.

Jonny
---------------------------------------------------------------------
|                 Jonathan Hodgson | TTech Predator                 |

|  than win by two laps            | LSU Archery Club and Orchestra |
---------------------------------------------------------------------

You "can", and you'll even get the gearbox to engage sometimes, but
you'll be putting maximum fully-reversed stresses on the drivetrain,
and you can expect to see the insides of the gearbox on a VERY regular basis.

In order to match revs (and have the gearbox/drivetrain have a
chance), the most elementary analysis reveals that you have to lift to
match revs (barring drive-by-wire computer controlled shenanigans).

It's still *** the clutch and drivetrain when there is no
computer-controlled integration (other than a rev limiter) intervening
on behalf of the driver.

There's some differing schools of thought on that topic. Matching revs
on shifts and not declutching may in fact create the highest
probability of finishing an endurance race, particularly if the clutch
is the weak link.

School #1:
Use the clutch to get underway from rest and from the pits and leave
it alone otherwise; you can design a fairly light-duty (low
reciprocating mass) clutch and pressure plate that can start the car
once an hour. In modern endurance cars with purpose built gearboxes, I
would predict this is a lower-risk approach (given talented drivers)
than banging the clutch each time.

School #2:
Others (in the business) will claim that declutching every time is a
win. (Probably depends on the drivers, and you can design the cars
around the drivers' talents and educate the drivers around the limits
of the machine to a certain extent.)

---Jim

(good stuff snip)

  IMO, School#3

Use the clutch when downshifting, to make sure the back end does'nt come
around and bite yer feet off:-) "Heel & Toe".

At the closest track to our workshop, there is a *tight* 2nd/1st gear
bend leading onto the pit straight. Approaching this bend, you are
flashing over a crest in a little S-turn, 4th gear, then you try to find
a somewhat straight line towards the Apex to brake/downshift.
One of my fav time wasters (when I am a spectator, that is!) is to sit
and watch people handle this challenge. The F3 guys are the most fun to
watch, too busy steering to use the clutch or listen to the
revs-,approaching the bend at well over 110MPH,*** on the brakes,
and start to downshift;

Whiiine--crash !! the dog rings shout
Wheeee-pop-pop  the engine goes
Screech-screech  the locked rear wheels shout

And sooner or later (in about 3 laps), they arrive at the turn looking
*away* from the Apex!
But they learn...., crawling out of their tire-stained Dallaras:)))

Pardon the wacky sound effects!:))

Matt

--
Matthew Knutsen

Cheek Racing Cars
http://www.racesimcentral.net/~kareknut/

That would be Rudskogen Raceway you`re talking about right :-)

If so, braking for that left IS difficult to get right !

I`ve driven enough laps in my roadcar to know THAT (I clutch both on the
upchange AND the downchange btw :-), especially the first laps I did
with my new engine, I suddenly had a "few" more mph coming over the
crest :-), locking the right front because it is lightly loaded AND
stone cold since it doesn`t do much work and then ask that same wheel to
do the turn in for you, yeah right

I`ve never gotten it quite right, although I don`t think I`ve ever lost
it totally either, but I HAVE been in the sandtrap on the exit trying to
get a jump on those darn Cosworths, it ain`t easy for them to get it
right when you have that Turbo-lag :-), if I get it reasonably right I
can usually tag onto their tail coming out of the carousell and onto the
main straight, then it becomes a question of who is the most stupid when
we brake for that righthander at the end, I HAVE been pretty far into
the sandtrap there :-)

Btw, do you do setup work on roadcars Matt ?

I have some ideas for a 4 link rear suspension for my trusty old Opel
Manta, but I`m not sure about lenghts and angles and stuff for the
linkages.

Beers and cheers
(uncle) Goy
UncleGoy on TEN

I'm getting into things like suspension geometry (I've run model race cars
for the past nine years) so I'll see if I can manage a few pointers
(though it's complicated - best do some reading up.  Does Milliken and
Milliken cover it?)

Lower wishbones want to be as long as possible, for best control.  They
generally should run about horizontal as a first approximation.

Top wishbones should be shorter (~1/2 - 3/4 as long) and should be angled
downwards and inwards.  They'll converge (if you imagine them extended)
with the lower arms at a point somewhere the other side of the vehicle.
The length out to that point is the swing axle length.  A longer SAL
is better in squat (acceleration) whilst a shorter one keeps the outside
wheel more upright in roll (cornering) - like everything, it's a
compromise!

Bring a line from this point (the instantaneous roll centre) back to the
centre of the tyre contact patch.  Where this new line crosses the vehicle
centreline is your rear roll centre.

An equivalent construction can be made for the front, and in general the
rear RC should be higher than the front - perhaps the front one at ground
height and the rear a couple of inches higher?  Don't know what Manta
front suspension is...

If you want maximum learning value, design brackets with several
alternative mounting holes and move things around to feel what it does!

I'm crossposting this to rec.autos.sport.tech - it might be an idea to
move the discussion there, if you're serious about getting some answers!

Jonny
---------------------------------------------------------------------
|                 Jonathan Hodgson | TTech Predator                 |

|  than win by two laps            | LSU Archery Club and Orchestra |
---------------------------------------------------------------------

For Racing Purposes only!
The top links should be close to the same length as the lowers and to
stay parallel to each other.
The shorter the top links are cf the lowers the closer to the center of
the axle (assuming the manta stillhas its live axle).

The reason is mid corner or bump steer, causing snap oversteer.
For reference see two simliar road cars the pre 86 Mazda Rx7 and the pre
86 Corrolla AE86 16V GT rwd.

Both have 4 link rears (ok 5 with watts on RX and pan*** AE86).
Both setups are similar with top links under 50% of lowers.
The AE86 ties the top links to eitherside of the diff housing and has
excellent handling for road.
The RX7 ties them to the outer ends of the axle, causing serious
wheelbase changes on the compressed side of the car after about 4 degs
of roll!
Mind you the lively feel adds to the cars 'character'!

The panhard rod solution is simpler than the Watts and nearly as
effective, though theoretically watts is better.  The RX7 however has a
questionable unequal length implementation.

Another car to look at is the simpler design of the UK Rover SD1
1976-86.
This has long lower arms, and mount on an extended diff nose.  A li ecan
be drawn through the chassis mounts of the arms and the chassis mount of
the diff mount.  The diff mount is designed to give the axle a slight
nose down attitude.  A watts linkage (equal length) provides the lateral
control.

I race an RX with the standard tail...the clerks of course are getting
peed off with my spinning....the car of course...it couldn't be the
driver!

PS.  the back end of the Manta isn't bad anyroad.  Best options for
modification are to lok at the Tarmac rally spec Manta 400

IanC

Hi Jonny

Thanx for the input and the tip about the other newsgroup as well, but I
have the feeling that you are talking about a "double wishbone" setup
here, but I was talking about adding two more linkages to my "live axle"
setup.

Although I`d love the idea of your suggestion, that would really be out
of my league

Beers and cheers
(uncle) Goy
UncleGoy on TEN

I think I`ll go for the Corolla setup then :-)

From what I`ve read, as long as the suspension doesn`t give TOO much
wheel travel, there isn`t THAT much to be gained from converting to
watts linkage anyway

I`ll check at the breakers, but there not many of those cars here in
Norway, not Corolla AE86 GT`s or RX7`s either for that matter

Of course not :-)

Manta 400 HAS 4 link suspension, rear axle from Opel Commodore with
modified (?) linkages, a friend of mine once owned an Ascona 400 and I
rember with joy how that one used to squat down at the rear when
applying power through a corner, my car however raises the rear end and
starts spinning the inner wheel in low-mid speed corners, luckily the
LSD is only 40% or I`d have some really scary moments :-)

The 400`s also uses modified front suspension angles (there are
different wishbones for the 400`s, I`ve checked) wich means that even if
I could get a good look at the rear suspension, there is the possibility
that I could get it all wrong anyway and end up with something that
handles badly, wich my car doesn`t do at the moment, it just doesn`t get
the power down

A friend of mine has a rear axle from an Opel Rekord/Vauxhall Carlton
lying around, which is a 4 link setup, and it`s this axle that will be
the base of my design, unless someone comes up with something better.

There is the question of cost here too, I can`t go to a race shop and
say; "Here are the keys to my car, sort out the suspension and send me
the bill" :-), besides, a lot of the enjoyment comes from doing it
yourself with the help from others of course, I know my limitations
(roughly :-)

Beers and cheers
(uncle) Goy
UncleGoy on TEN

With wheels on the ground, and with the car preferably stationary (vbg)
measure all the suspension components and then draw them up on paper

On a rear wheel drive car we normally want the front inner to lift
before the rear.

If you don't get squat under straight line power, then the geometry is
giving you anti-squat.  This normally means that the lower arm is higher
at the front than rear. Measure how much.

Put 50Kg of weight in the boot and try again!  Repeat until squat
occurs.  this should happen within 150kg.  Infact I'm sure an Opel Manta
Berlinetta I drove always squatted.  Might be worth looking for siezed
components such as dampers.

Once squat occurs test cornering, given the additional weight, and add
weight to the front passenger foot well to lower front of car.

Alternatively call PMC in UK and get a standard suspension kit.
Changing the rear axle is a bit radical for DIY.

If the dampers aren't damaged you basically need to lower the car.  If
ride height is important, lower the car and put larger wheels/tyres on.

You guys need two sets of wheels any way so the summer wheels/tyres
could be the standard 195/60/14 and the winters 195/70/14.

IanCT

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Just a helpful note: Milliken and Milliken is fine on theoretical stuff,
but I think you'll find more practical information in Herb Adams' book
on chassis and suspension design, as well as Forbes Aird's "Race Car
Chassis Design and Construction", Allan Staniforth's "Competition Car
Suspension", and even the venerable Carroll Smith's "Tune to Win".

But please...not in rec.autos.simulators -- unless you're planning a
chassis-design add-on to one (or more) of the current or future
racing.sims. If that's so, please keep me informed!

Bart Brown

The Manta has what is called a "torque-tube" which goes from the diff
housing and forward some distance and is then mounted to the body, this
tube is what prevents "wind-up" in the axle when I apply power.

This is a cheap way of locating the axle and works very well whith the
original engines, once we get more power however, the picture changes. I
now have enough power in the car to actually generate lift through that
"torque-tube", not a big problem in a straight line on dry surface, but
on loose surface and in corners, forget it

I`ve never messured the length of it, but it is of course roughly the
same lenght as the suspension linkages themselves

Will do

You`ve seen Ari Vaataanen drive Escorts on tarmac, haven`t you :-)

Haven`t thought of that, but from my answer below, I`d say it wasn`t

The car is lowered with progressive springs up front (40mm) and modified
originals at the rear, yellow Konis all around and stiffer suspension
***s will be fitted soon. I also have a stiffer anti-roll bar at the
front.

The car is slightly lower at the rear than at the front for better
weight distribution/transfer

Don`t really want to lower it any further because then I`d limit the
suspension travel too much, the rear bottoms out every now and then as
it is

Na, enjoy these things alot, ported the cylinder head on one of my
previous engines myself with good results, although with afterthought
I`d never do it again, at least not without the proper tools, too many
hours wasted when you can get it done fairly cheaply even here in Norway

See above

I run 195/50/15, good compromise between grip, durablity (price) and
comfort

Basically my suspension is in good working order, or will be as soon as
I get those ***s changed, there is nothing seized or rusted.

The only other thing I can think of is the weight ditribution, the car
weighs 1100 kg, about 550/450 front/aft, but unless I add a lot of
weight at the rear there isn`t a whole lot I can do about that without
going to extreme meassures, and this is a road car after all

Thx again for taking the time

Beers and cheers
(uncle) Goy
UncleGoy on TEN