Since figuring out the door seperation locations in the design, with both ingress and egress in mind, needed to re-examine the roll cage or roof structure. This isn’t a full cage meant for racing, but it is meant to act as the start of a full cage that would be required by various sanctioning bodies if the owner ever decides to go racing in one of these. The goal of the roof structure is to provide protection to the driver and passengers, as well as mounting points for the doors.
This is the 2nd revision of the structure here, with an X bar setup. This portion weights around 37lbs including the gusset and bracketry. Here shown with a 5000lb/ft load on the front corner of the windshield (the weakest point).
In this plot you can see the displacement from that load, exaggerated in the screenshot to illustrate weak points, shows around an inch of displacement from that load.
The main reason for running these quick rudimentary tests were to compare the relative strength and rigidity of the 2 designs. Here you see the next revision in the cage, which weights slightly less than the first version around 36lbs.
This version actually ended up being inferior in this particular test, showing almost 8% more displacement from the same load. For now I will continue to pursue the first option, which suits me fine as there are less tubes, less coping and easier to construct.
I will experiment with moving the X position forward more as well which will allow me to attach it closer to the radius of the windshield top corners.
I made a conscious decision on this design as well to use 2 bent members in an X (2 L shaped tubes) versus 2 straight members which would require one to be cut and coped in the center. This design has been used in motorsports for door bars for some time as it’s seen to be safer in the event of an accident. With shorter welded tubes meeting in the center, during a bad crash they could detach and become spears directly above the drivers head.
The bends aren’t exactly straight forward for these bars, but will be likely getting these done by CNC from an external company to save time and ensure accuracy. It’s important that these bars tuck up under the roof composite panel as close as possible for the best driver safety, and head room.