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

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...

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 ] On 12 Mar 2002, Stefano Casillo wrote:

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> 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... > >