Variation couple appliquée sur la transmission

Nombre de messages : 3807 Localisation : IdF Date d'inscription : 21/04/2010

Ok, merci pour l'explication.

Nombre de messages : 9 Localisation : France Date d'inscription : 31/10/2019

Frits Overmars a écrit:: An engine with two contrarotating crankhafts, like the Aprilia RSW /RSA racers, is not a V-twin if you ask me. I would rather call it a W-twin.
W-twins can have perfect primary balancing if both cylinders fire simultaneously, but this will mean a heavy load on all transmission parts.
Anyway, I think that calculating transmission stresses based on the combustion torque fluctuations is futile because gear shifting can generate unpredictable but much fiercer torque fluctuations.

Well, i start thinking the same way, i just did the same work for the Ducati 1098 and, wow, the peak torque are insane, well from my simplify calculations. So how did the engineer to build these gears ? They just take the mean torque, multiply by 3 and try it ? I know that a 500 V2 two stroke engine put less stress than a 1098, so i can approximately use the dimensions of oem Ducati gears and adjust them to my need. Atleast i tried Very Happy

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According to you, is it better to build a 0° engine, simple balancing but more stress on the transmission and less grip, or a 90° engine with the invert benefit ? This engine won't rev up a lot, and i feel like the 90° ignition timing is uselful (about the grip) at high rev only, where the inertia momentum is predominant.

Nombre de messages : 1832 Localisation : GE-CH Date d'inscription : 04/01/2016

Pends un vieux rotax tandem en exemple!
Regarde le post de Francis Payart, son moteur est très bien décrit.
Si tu ne fais pas un tandem, les problèmes de facteur d’équilibrage décrits par Frits vont arriver à vitesse supersonique et la taille de tes pignons sera le cadet de tes soucis!
Si tu cales à 90’ les embases, il est inutile de faire 2 vilos séparés, il vaut mieux en copier 1 de Honda RS mais alors tu ne couperas pas à l’arbre d'équilibrage ET au facteur d’équilibrage.
Tout est affaire de choix et de compromis!

Nombre de messages : 9 Localisation : France Date d'inscription : 31/10/2019

J'ai regardé au tandem, ça revient au même avec le Vé à 90, on peut équilibrer parfaitement l'ordre 1 et il reste de l'ordre deux si je me trompe pas. Le choix de deux vilos séparés prend aussi en considération les capacités machines que j'ai à disposition, le 250 RS Honda c'est la même architecture que le 250RGV ? Je vais y réfléchir Wink

Max, if you want to continue with two contrarotating crankshafts, I would not choose a V-configuration, but the beautiful layout shown by Francis Payart (well OK, it is a very narrow-angle V). This would mean two cylinders firing simultaneously, so I would strongly recommend a transmission shock absorber built into the clutch.
In fact I would recommend a transmission shock absorber for any engine.
Otherwise you could follow the layout of the Honda RS500, with one crankshaft, which has the advantage of lower torque peaks, and the option (almost the obligation) to use reed valve induction.
Either way, you do not have to re-invent the wheel; both layouts are well proven and documented.
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Nombre de messages : 9 Localisation : France Date d'inscription : 31/10/2019

Well, i will use YZ250 cylinder, reed valve induction, and in case of a tandem it won't really work. I chose some common parts, with some benefits and drawbacks. The clutch system i intend to use has a shock absorber built in. What is the problem with an engine like a Rotax 258 ? The space between the vé is useful to put the intake system, it fits pretty well in my frame, but i have to agree the last engine picture is better (seems compact, light, and 90° firing order i suppose ?) but involve more work to machine the crankcase. Thanks for your sharing.

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