Spider (+ chainrings) and FD during shifting

[wheelsONfire]

i have a question for the technical minded, talking mechanics and efficiency.

If we look at the rear derailleur, we can agree on this. The chain is moved with the cage to line up to each cog (- YES)!

If we look at the chain on the chainrings, the front derailleur cage move the chain without the chain have any traction to the cogs in the lift.
It is pushed side ways and perhaps a small controlled throw (- YES)!

If you look at the best efficient way, it's that of the RD that we all know.
It's under load all the time and also and probably during shifting.
The chain in front handles better if you can have a certain timing during load and chain move.

How about looking at what the chain does (just like a tire on the ground it needs contact, not losing traction.
Chainline is relevant as front and rear tire is in line). We don't throw the front tire by force and no grip to ground)

Why isn't the RD, the FD and spider with chainrings like a unison brain?
Moving the spider (chainrings) instead?
The axle of the crankset is larger and will handle that stress i would guess (the axle to the cassette has no way near same stress).
It would require a motor that moves the spider and chainrings, that handles the stress.
But talking traction and chainline it could be optimized?
Or am i wrong here?

All updates and revisions always mention speed of shifting.

Typical complaints, Sram VS Shimano is shifting speed and front derailleur reliability.
Both really revise current and an old way of doing same thing now as it did, well always.
It's really not a big progression as long as we talk electrical groupsets.
Just chaining RD speed the rest is always about keeping traction, lowering friction.will be most efficient and lowering friction should be a big deal

But how about looking more at the FD and spider (+ chainring) from another view?

Just a thought and i am sure there is a reason for doing this as it does, instead of like i ask?

[TobinHatesYou]

SRAM and Shimano have both patented technologies that will adjust the chain line at the chainrings. Shimano’s implements a sliding member over the spindle while SRAM’s is even wilder with what effectively is a hinged, half floating chainring.

SRAM has also patented an integrated FD built into the chainrings themselves. A section of the big ring slides inboard in order to pick up the chain.

https://patents.google.com/patent/US202 ... 0200140035