Once more before I start this discussion, I am in no manner disparaging the DF Goblin or stating that Lonny and his team provide an unsafe product. A lot of engineering went into the design of the Goblin and it has been proven as a safe, capable, and durable kit car as delivered. My modifications to my Goblin are made on my own cognizance and are not intended to point out any potential short comings of the DF Goblin kit car. All changes are made to increase the performance potential of the basic kit and satisfy my personal needs for safety.
Warning: this will be an extensive addition into my build log.
Okay, time to dig into the details of my frame improvements project. I anticipate this will require several posts in my build log to get all of the photos and information explained enough so that anyone can replicate parts of or this whole project. Please note in my explanations I will use 'X', 'Y' and 'Z' axis terms - 'X' is left to right (lateral axis), 'Y' is front to back (longitudinal axis), and 'Z' is up and down (vertical axis) - just to be sure everyone understands the narrative. I will try to list everything I did, but as with any other project that has taken months to complete, I may miss somethings. IM me with any questions.
The main goal of this project was to increase the safety of my Goblin (reasons are expressed above in my build log and in other forum conversations - RIP Zack). The most important area of the frame is the main cockpit area between the A-pillar (windshield area) and the B-pillar (rollbar). This area of the frame must remain rigid and intact not only for optimum vehicle operation, but also in an impact for survivability. As a bonus the increased safety also creates a stronger/stiffer frame - by somewhere between 40-45% overall. This figure is based on the 2 different structural programs (my archaic frame program and an aerospace program for designing rocket structures) to define the best locations to install the frame improvements.
It should be noted the DF frame cockpit area is already strong by design - the track frame is about 30% stronger than the city frame (for obvious reasons) - and the frame can provide good protection when it remains intact. My biggest concern that pushed me into this project is the need to help make sure the frame remains intact. Reinforcement of the critical frame welds helps ensure this happens. I will point out in the narrative which added pieces make the biggest improvements in frame safety and stiffness.
A quick rehash of the materials purchased to make the improvements:
3 inch saddle gussets - X2 sets (20 pieces total) - all used
1.25 inch saddle gussets - X2 set (20 pieces total) - 16 used
2 inch plate gussets 60 degree - X2 sets (12 pieces total) - 10 used
2 inch plate gussets 90 degree - X2 sets (20 pieces total) - 18 used
2 & 3 inch plate gussets 90 degree - X1 set (25 pieces total) - all used
4X12X0.125 inch steel plate - X1 piece - fabbed 4 large plate gussets
8X12X0.65 inch steel plate - X1 piece - fabbed 1 large & 2 medium saddle gussets
1.5X0.95 inch round steel tube - X2 4 feet pieces used
1.25X0.83 inch round steel tube - X1 4 feet piece used
1.0X0.65 inch round steel tube - X2 4 feet pieces & X1 1 foot piece used
All of these parts can be purchased from eBay, Amazon, or other vendor supplying steel fabrication materials.
First, an explanation of the areas that surfaced as needing improvements became evident when using the frame programs. These are the areas that I focused on with this project.
From analysis the floor is the weakest part of the frame, but is also the least susceptible to experiencing an impact in an accident. Discussion with a coworker - who is a structural engineer -found that replacing the tunnel and 1 inch square tubing in all locations with at least 1.25 inch diameter cross tubes and eliminating the tunnel from the middle of the structure would be the best change. There is inherent problems with doing this kind of major frame surgery and not wanting to completely tear out the changes I had already made, the alternative was to reinforce the existing pieces. The changes I made kept all of the original floor components and I added triangulation pieces - which had been posted in the past in my build log - and reinforcement gussets that made about a 15-20% improvement in the floor. I will explain this in detail further on in the posts.
The 'base' (bottom) of the rollbar does not have a dedicated solid crossbar. The rearmost 1 inch square cross tube is the closest cross piece (5 inches offset), but it is subject to the same issue defined above for the floor and is not a good 'base' for the rollbar. The bolted in subframe frontmost cross member is too far rearward (about 12 inches) to function as the 'base' to the rollbar in stock form and it is not located in a B-pillar connected rigid structure. The reason for this is the 'ears' the subframe is bolted into behind the B-pillar - good 'Y' and 'Z' axis rigidity but not good 'X' axis rigidity. The improvements I made to reinforce the rollbar and increase support to the 'base' area enhances rollover safety and adds about 10-15% torsional stiffness. This will be explained further in the posts.
The open area above the footwell in the cockpit is inherently a weaker area of the frame, it is essentially an open top box susceptible to twisting forces and is easier to collapse in a diagonal direction in an impact. I personally like my legs and feet (especially my feet) and reinforcing this area was important to my project. The front frame is also flexible in torsion (twisting) that can allow front suspension geometry changes when loaded in hard turns. The changes I made increased front torsional stiffness by 75-80% and reduced the tendency to collapse in a diagonal or side impact. Explanation of the improvements will be posted.
The rearmost parts of the frame, behind the rear strut mount towers is also a weaker part of the frame. This area is not directly a safety item, but can benefit from improvements that help reduce deformation from impact forces. The installation of the cross bar and triangulation at the rear greatly improves frame strength, especially with the application of 'X' axis suspension forces that can affect the suspension geometry under dynamic conditions. The changes I installed increased the stiffness by 70-75%, especially for the rearmost frame to subframe mount locations. I have gone over this before in my build log and what I did to resolve this, but I will review this information in the posts.
Enough with the explanation ramblings (Racer X was my editing help), time for photos.