rec.autos.simulators

Car Physics: Open differential, the way I do it.

Stefano Casil

Car Physics: Open differential, the way I do it.

by Stefano Casil » Thu, 14 Mar 2002 00:16:03

Well,

If someone out there...Ruud, Doug or Sebastien has 10 mins... read
this out and tell me if Im missing something in this approach...

I've modelled everything using torques..let's focus on the
differential..we've Te (torque from the engine) T1 and T2 (torque from
the wheels)...

Im doing this in steps...first I use engine torque then wheels...
So, for the engine is simple...the torque is split 50% on both
sides...and that should be indipendent from wheels rotational speed...
so the wheels are accellerated by this torque..

Then I get the feedback torques... now if they have the same signs, im
using the "common module" to to feed back the engine... the difference
is then transfered to the less resistent wheel...

Example... if I have T1=50 and T2=20 ... I send 40 (that is 20*2) back
to the engine and 30 across the differential to the less resistent
wheel...with fipped signs...

If the feedback torques are opposite in signs...nothing goes to the
engine but everything is sent across the axles (always the difference
of curse, flipped signs)...

Now I have well counter spinning if u apply a torque on a wheel...
everything is looks fine...

Does anybody see something wrong? It looks so simple (too simple
actually..compared to Gregor solution used by Ruud)...

I still havent plugged it into the main code...

Feedback'll much appreciated..

Ciao..

P.S. Doug I've spent weeks looking at that "lever" analogy in your
book...still doesnt make any sense to me... sometimes I feel so
stupid...

Doug Millike

Car Physics: Open differential, the way I do it.

by Doug Millike » Thu, 14 Mar 2002 07:34:48

Well,

Sorry that the levers don't help you, some others seem to like them.
When we did RCVD, I really wanted to include something more than just
the standard picture of the gears in an open diff, so I came up with
the levers to simulate opposite teeth on the spider gears.

I found it hard to follow your words below, but if you have an open diff
without friction, then the torque in the two axle shafts will always be
equal.  So if your model does this correctly you have solved at least part
of the problem.  Of course in the real world nothing is perfect, so the
torques won't be exact, but they are close.

--  Doug Milliken
    www.millikenresearch.com/olley.html   <--new book now available!
          [ New book won't help with differentials, sorry ]



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