Lotus E21 construction report part 14

Gearbox and Underbody Manufacturing

After finishing the Renault RS27-2013 engine, I started to design the gearbox (my usual process chain: monocoque-engine-gearbox-underbody-systems-suspension-wings-bodywork-wheels). The Lotus’ gearbox is a bit of a pain to do as they are one of the last teams, not to use a Carbon composite housing. It’s a cast Titanium structure. Williams is the second team in the grid not using a Carbon gearbox (Aluminium). To rebuild metal structures from paper is always very difficult. Anyway, it’s (almost) done and I can be pretty satisfied with it.

The whole suspension stuff is located within the gearbox. That’s a trend which appeared about three years ago. Before, most of the suspension stuff (dampers, springs) was mounted outside the housing beside the gear cluster. With the aero development over the last years, the teams started to locate all this stuff inside the housing in front of the gears, to get a tighter ass. I don’t know, if I’ll add all this stuff inside the gearbox. I will do the ARB and the drive shaft definitely but I won’t do the gears.

This week I also started with the underbody design.


Front bulkhead of the gearbox. The starting point of the design. You can clearly see the six pick up points to mount the gearbox to the engine. At the real car, this is realized by six M12 studs.


First attempt for the basic structure. The shape is pretty trivial. I just needed one try to get it done. Very important is the integration of the studs into the structure. They have to pick up the whole load. It’s the first gearbox, where I do it this way. My previous gearboxes were just bonded to the rear face of the engine. The advantage here is a much higher stiffness between the engine and gearbox.


The first try to fit the gearbox to the car. Even without glue, the connection is so stiff, that I can carry the car just by holding it on the gearbox.


Finished gearbox housing mounted to the car and pre fitted underbody.


From the top you can see how tiny the gearbox is. There’s loads of space between the wheels and the gearbox for aero tweaks.


Gearbox removed from the engine.


Rh side of the gearbox housing. The hole that you can see at the lower front of the housing is for the ARB. The top front one for adjusting the heave damper. You can also see the angled rocker. At the rear you can see the fixing point for the rear crash structure.


Lh side of the gearbox housing. At the rear below the final drive, the oil pump will be located.


My gearbox drawing. I had to stretch the gearbox by about 3mm compared to the drawing to reach the correct whelbase.


With the gearbox mounted, the cars current length is at 458mm. With the rear crash structure attached it will reach its full length of 508mm.


Top view of the car with mounted gearbox.


Current state of the underbody. There’s still a lot of work left to do. Note the blown starter hole in the diffuser area. That’s to prohibit a flow separation. More on this later on during the build of the underbody.


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About paulsf1

My name is Paul Bischof. I’m a student in mechanical engineering at the Technical University of Graz in Austria, expected finishing in February 2016. Since I was eight years old, I am building model planes out of paperboard. Since 2004 I scratch (that means building without an assembling set) Formula 1 and sportscars in 1:10th scale. The average time I need for such a car is around 400 to 700 hours within 4 to 8 months. One car has around 3500 up to 5000 single components. On this blog, you can take a look on my work and later, after my studies, hopefully you can see me in Formula 1.

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