One of the most critical components in this project is what I call the "sub-frame". It is essentially a cradle that sits inside the engine bay and seats each of the Power Pack modules. It is also the most difficult to standardize, and the prototype version will definitely be a one off, custom piece.

Knowing that I wanted to make the design as flexible, and easy to construct, as possible. This piece acts as an interface between the existing engine bay, which was designed for a very specific footprint, and packaging scheme. The bottom of the sub-frame may be able interface with existing engine mounts which could increase the vehicle rigidity and allow for the weight of the modules to be distributed more evenly across the chassis, instead of through the ends of the 3 cross tubes which are currently intended to be welded to the chassis.

Another element I have given a lot of consideration to is how to properly secure the enclosures. Using foam padding along the front plate and square tube support members will dampen road vibrations that will transfer through the structure and reach the module packs. To ensure that the modules will not fly out of the slots, however, I believe the best option is to use a rotary latch like the one shown below, produced by Southco. It can be electrically actuated to release the module, but also includes a manual override in case of emergencies.

Image and product listing can be found at http://www.southco.com/en-us/r4-em

One big area of exploration is how this addition will change the way the vehicle deforms in the case of a crash. If the cradle is filled with lithium modules, the weight in the engine bay will far exceed that of a normal combustion engine. In that instance, this will dramatically change how the vehicle behaves in a crash scenario and may cause sever injury or death to the driver and/or passengers. Before proceeding further I definitely want to think about how to do scale tests and how the design of the cradle can be done to mitigate or prevent any problems.