I'm back with the second MOC in my drivetrain model series, after my Koenigsegg Jesko one. I've always been very inspired by Sheepo's old Porsche 911 model and its amazing gearbox. Sadly, I've been able to learn very little about the working principle of this gearbox, with only one image available of a part of its structure plus a text description. Anyways, I've always wanted to emulate its dual-friction-clutch 7+R design with the secondary motor for applying the clutch pressure (I have made dual-friction-clutch designs with the entire shifting done by one motor. This was in my early days, before rotary shifters!), and I have done so here, taking advantage of newer parts to (I assume?) make a smaller design than Sheepo did. The overall model consists of the engine, the transmission, and the differential, plus a stand with four motors, four switches, and a rechargeable battery box inside to control the functions.

The four motors control:

Drive

Shifting

Clutches

Differential lock

 

Drive: A PF L-motor drives the drivetrain, branching off to run the large-scale boxer-6 engine, which has the  correct crankshaft design allowing the opposite cylinders to extend and retract at the same time, unlike most Technic engines, and 120 degrees of offset between each set of cylinders, which is more realistic than it could be, but probably not completely realistic. The other branch goes to the gearbox.

Spoiler

 

 

 

Shifting:

I have tried to explain the gearbox and its operation, but it is very complicated and hard to explain in text. If you really want to understand it, it may be more helpful to watch my video below.

 

The gearbox, as a dual-clutch design, is split into two nearly symmetrical halves (Reverse throws off the symmetry). The drive axle from the gearbox directly runs one of the clutches, while a 14:20:12 gearing runs the second clutch (directly above the first one) at a very slight speed increase. After the clutches, I have a 28:24 ratio from each clutch to its respective gearbox. The use of 20 and 16T clutch gears in these gearboxes provides one speed difference, and the fact that the axles holding the driving rings are connected to each other by a 16:12:20 gearing (using quarter stud spacing) makes for another difference. The gearbox connected to the slightly slower clutch has the slowest gear reversed, making the gearbox a 7+R. After these gearboxes, a 8:16:12 ratio (more odd spacing) connected each gearbox to the output shaft. Shifting was done with two rotary shifters hard-coupled to each other and connected to a PF L-motor in the base. This also ran an eccentric mechanism at a speed 4x faster than the shifting (Thanks to 12:24X12:24 reduction to the primary shifting), which slid a large assembly back and forth to select the correct clutch. More on that later.

Spoiler

The eccentric for selecting clutches.

The even/reverse half of the gearbox

The odd half

T

The 14T gears are the gearbox input, and the blue 20T gear runs a black 12T gear above it to run the other clutch.

Some of the weird gearing.

Clutch:

There were two separate friction clutches, composed of two sets of 30mm tires being pressed against each other. To engage the clutch, a tan 4L axle with central stop was pushed by a long lever. The axle then pushed a black 4L L-beam into the one wheel, engaging the clutch. These two long levers were engaged by a pair of black wedge belt wheels which slid back and forth due to the eccentric on the shifting drive, causing first one clutch to be engaged, and then the other. A PF M-motor could also rotate the entire assembly with the wedge belt wheels in order to engage or disengage the clutches. With the clutches disengaged, the car would be in neutral (though the differential usually rotated intermittently and weakly because of friction between the technically disengaged clutches).

Spoiler

Clutches

The two long LBG beams going vertically at the center operated the clutches. The tan axle in the lower center is pushed by the DBG 2L beam attached to one of the LBG levers, and then pushes in the clutch. You can see the black wedge belt wheels engaging the right lever, which engages the nearer of the two clutches.

 

Clutch assembly disengaged

Clutch assembly engaged

Differential lock:

Another PF M-motor operated a very simple rear differential lock through a linear clutch. 

Overall, I was pleased with the model, though the clutches didn't really move far enough to engage as much as they could have or disengage as much as they should have. Otherwise, though, I was pleased with the complexity and unusual mechanism for shifting between clutches.

More images at: https://bricksafe.com/pages/2GodBDGlory/porsche-911-drivetrain-model

Edited October 25, 20213 yr by 2GodBDGlory

Looking at your creations is like reading McElroy's Women and Men - you have no idea what hit you but you know it was stellar.

I just downloaded the pics from your Bricksafe page and I'm going to gaze at them every time I need a shot of awesomeness.

23 hours ago, suffocation said:

Looking at your creations is like reading McElroy's Women and Men - you have no idea what hit you but you know it was stellar.

I just downloaded the pics from your Bricksafe page and I'm going to gaze at them every time I need a shot of awesomeness.

Thanks a lot!