Crankshaft rotation direction

[Vini]

http://forum.piboso.com/index.php?topic=2951.0


So, if you rev Manu's M1 while standing still, the rear suspension compresses.

Shouldn't it be the other way around due to the reverse rotating crankshaft?


....Haven't tested it for other bikes.

[HornetMaX]

GPB can't sim a rev rotating crankshaft, as far as I can tell from the physics files.

[Vini]

But it simulates a regular one?
That's not good.

What about dual counter-rotating cranks (Cagivca C594 for example)?

[HornetMaX]

But it can simulate a regular one?
That's not good.

Reported a long time ago: http://forum.piboso.com/index.php?topic=596.msg4930#msg4930 by me (just noticed that in the request I mentioned fwd rotating instead of backward rotating, fixed now). Check out also what was the 2nd suggestion

The problem is that with backward rotating engines you have an additional shaft/gear (with his own inertia and gearing), so the physical model is slightly more complex. If you want to do things right, GPB engine model should have to allow this additional shaft/gear.

First sight I think GPB could cheat a bit and allow modders to set a flag to specify if the engine is fwd or backward rotating. Depending on the flag GPB can then generate an engine reaction torque with the correct sign. This allows to have a common engine architecture (crankshaft + primary shaft + secondary shaft) and "simulate" fwd rotation. But it's a bit of a dirty trick.

I'm not 100% sure, but I don't think the Yam is today's only backward rotating engine. Anyway it's nothing new/recent: there were backward rotating 2-strokes.

P.S.
The engine reaction torque has been introduced in beta7.

[Vini]

First sight I think GPB could cheat a bit and allow modders to set a flag to specify if the engine is fwd or backward rotating (or dual crank ). Depending on the flag GPB can then generate an engine reaction torque with the correct sign. This allows to have a common engine architecture (crankshaft + primary shaft + secondary shaft) and "simulate" fwd rotation. But it's a bit of a dirty trick.

Same thing I would suggest.
...Especially if the only problem is that one small additional shaft has to be simulated. The influence it has on the bike is probably negligible.

Otherwise, no engine reaction torque for bikes like the M1 or Varese would still be better than how it currently is.

[HornetMaX]

Could make sense. Option for forward / backward / dual crank impacting engine reaction torque and angular momentum:

• forward (classical): reaction torque favoring wheeling, angular momentum in the same direction with respect to the (rear) wheel
• dual crank: no reaction torque, no angular momentum
• backward: reaction torque countering wheeling, angular momentum in the opposite direction with respect to the (rear) wheel

[h106frp]

How would it calculate the reaction as i have not seen an engine component mass declarations in the physics files?

[HornetMaX]

How would it calculate the reaction as i have not seen an engine component mass declarations in the physics files?

I think you don't need it: the reaction torque on the crankcase is equal to the torque produced by the engine on the crankshaft (but in opposite direction, of course).

[h106frp]

Ok, I follow the logic but it has made me wonder why the crank mass and position relative to the CofG is not considered for the physics calcs.

[HornetMaX]

Ok, I follow the logic but it has made me wonder why the crank mass and position relative to the CofG is not considered for the physics calcs.

Because you don't need them. The reaction torque is applied to the whole engine and the crank mass is included in the engine weight (which is part of the chassis weight).