I’ve made quite some progress in designing the front battery box, therefore now it’s time to also work on the rear box. Earlier I made a prototype and did some designing and after further developing that design I knew it had to fit. Only keeping the original tow bar would be a challenge. Another original tow bar for the wagon that I bought did not give me more space unfortunately Well in worst case scenario I’ll have to modify or even build one.
In the back I need to install 5 modules, a stack of 3 modules and another one of 2 weighing 125 kg together.
I sketched the box itself but not yet decided on how to mount the modules. Having a self supportive box will become quite heavy given the side. Therefore I decided to explore the possibility of a supporting frame.
My idea was to have a slot in the first and last frame in which I could slide the module. I bought some 15x15x2 square tube and used my mill to add the slot.
Fits nice and tight onto the module.
I measured how far I could push it on and what the overall width would become and continued digitally. The challenge is whether I will be able to actually tilt the modules in. Added a small strip to level the mounting rail.
On top of that there will be a 40x15x2 aluminium tube which then is the basis for the rear module.
I added props that lock the aluminium tube sideways and provide additional overall stiffness. After the module another strip and a top strip.
Tightening the modules is still an open question. Current idea is to use M6 and weld nuts.
The lenght I need to mount two modules and the aluminium tube is bigger than the available room to move in a bolt. I see two options:
1. Socket bolt
In the support above drill a hole that allows a socket bolt through combined with an open weld nut. Disadvantage: the hole needs to be 10 mm which weakens the tube.
PS. the hole on the right hand side is 6 mm and is intended to the module just above.
2. Use a threaded end
In the support above add a 6 mm hole which allows a M6 threaded and through which then can be fastened in a closed weld nut using two nuts. Advantage is: less weakening of the tube. Disadvantage: more screwed connections and nuts to handle (with the risk of dropping one).
Update: it will become option 2
It does requires some extra attention when securing everything but in the end the frame is stronger.
So with all modules, strips and supporting tubes it will look like this:
After that I used the ‘sheet meta’ function in Onshape to add the outside.
Technically this are three parts which can be fabricated by welding and bending. I can generate drawings and have the panels laser cut.
If designed the parts in such way that I can bend them on my own press brake.
After that I assembled everything in context with the car and tow bar. Seems to exactly work out with the original tow bar.
The box (made of 1 mm steel) weighs 20 kgs which includes the frame.
I’m not sure what kind of material I want for the outer box. Stainless steel is the best option but also the most expensive and most difficult to produce.
I did start working on the frame a bit already.
To be continued!