[MOC] Corvette ZR1 Drivetrain Model

2GodBDGlory · June 1, 2022

Here's another drivetrain model for my series, this time a relatively simple one. It's a model of the drivetrain of the seventh-generation Chevrolet Corvette ZR1, and has a few different features. It's got a manually operated friction clutch, a realistic joystick-operated 7+R manual transmission, a friction-based adjustable rear differential lock, and a simple adaptation of the Corvette transverse leaf spring suspension.

Features:

V8 piston engine, driven by a PF L-motor

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Nothing fancy here, since Lego V8 engines are reasonably realistic. It'd have been interesting to try to eliminate the cross-plane crank (This ain't a C8 Z06!), but that's not really practical. I might have tried 3D-printed parts for the novelty, but I've got a long list of stuff for my printer to work through before I'll make time for that.

Worm gear operated friction clutch

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This is also pretty simple. The old tire is attached to the engine, and the DBG part is attached to the transmission. This part is connected via a driving ring switch, allowing it to slide freely on its axle. Some rubber axle joiners provide enough friction against the switcher that it stays put against the DBG part. The clutch is always on by default thanks to some rubber bands pulling a linkage that presses it together, but a worm gear mechanism in the base allows the user to push a Bohrok eye against that lever, disengaging the clutch.

Joystick operated 7+R manual transmission

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This is where it gets complicated. The goal was to keep the gearbox as realistic as possible, so I've got only two shafts of gears (plus the reverse idler), providing all seven speeds and reverse. Because of the lack of different sizes of clutch gears, my ratios were not quite ideal, with some rather small steps between 20:12 and 20:14 ratios. Yes, I'm using 14T gears again; I think they might be my favorite Lego element. In the end, the ratios are:

R=(16:20)(12:24)
7=24:8
6=20:12
5=20:14
4=16:16
3=14:20
2=12:20
1=8:24

As you may have seen, this requires that two of the driving rings be placed on one shaft, and two on the other, to ensure that they are always engaging with the bigger gear.

The part that is the most complicated is the shift linkages. I couldn't seem to find great information online about how the shift lever actually selects different gears, so I made an educated guess and landed on this system, where the lever is free to move side to side on its ball joint, through four different independently rotating parts. Whichever one it is engaged with will essentially lock with the lever, and rotate along with it, so that when the lever is pulled back, it will move forwards on the bottom, as if it were one piece with the lever. The bottom part then simply moves a beam forwards and back, engaging one of the four different gear selectors. Unfortunately, I had a hard time getting everything to fit in a small place, and my final solution made the shift lever attach quite precariously, so that if you had to apply much effort to it, it would just pop out. This makes this solution impractical, but as a proof of concept it's still interesting.

Friction-based adjustable rear differential lock controlled by worm gear

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The real car has an electronically controlled rear differential, which seems to mean that it can electronically, continuously vary between an open differential, different frictions of limited slip differentials, and a locked differential. To simulate this, I put a new 30mm tire and wheel on the axle next to the differential, with a small spring pressing it away from the differential. A 2L beam controlled by a worm gear in the base presses against the wheel, allowing me to press it against the differential at varying pressures, making it easier or more difficult for it to slip, with the highest friction being essentially a fully locked differential.

Transverse "leaf spring" double wishbone independent suspension.

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Corvettes have for a long time had an unusual suspension design, with independently sprung wheels sprung not by coil springs but by a transverse leaf spring. I wanted to try to model this, but because Lego isn't big on leaf springs, I tried to simulate it with some yellow beams. In the end, it works fine, but it's probably bending a lot of things other than the spring!

You may notice that this gearbox is really long, but that's really just a limitation of the Lego parts. For comparison, I think this might be a good opportunity to show off some of my 3D-printed gearbox parts. Using them, I could have made the gearbox only this long!