Unicorn on the Ocean - 1120AF Coming to Canada

[whomisi]

Small update, big satisfaction, it's driving again


Started up with a whole new fuel system, for the first time in 9 months, like it was running yesterday. What a beast, purred right into life.

Interior layout getting quite well designed now, need to be ready to cut some holes once there is a box on the back.



Arguably overly complicated subframe components being laser cut and formed in the next week or so, will be a big job welding up the whole frame flat and true. I've got the right tools and know an awesome welder to get things close enough. Although the two main box sections have a 5mm lateral bend in them which I'm not sure how to straighten. I guess we'll see.

 

[whomisi]

One of those big days where things come together instead of just staring and scratching my head. The subframe is tacked together and came out very close to flat. Although I've come to realise that flat is just a concept to be aimed at, but never achieved. According to the laser, I'm within a couple of mm over the whole length. Not sure how much things will move when my the final welding is done. I guess we'll find out, luckily for me a very experienced and highly qualified welder is going to burn it in for me, so it's got the best chance of staying flat.

I'll lift it off the chassis for the final welding, save splattering holes in all the fresh paint and fuel lines!

 

[camprr]

That is some real progress there, must be nice to have it done! Have you decided on how and where to pivot the subframe on the truck frame?

 

[whomisi]

That is some real progress there, must be nice to have it done! Have you decided on how and where to pivot the subframe on the truck frame?

I'm going for rail on rail for highway manners and robustness for the chassis. I've got a variety of die springs so I can tune the hold down tension and preload along the length. As well as limit the travel if required. Starting point is 6" of travel at the front.

You can see the hold downs below, just a bolt in the image as I was setting it up for welding.

I had to drill out the chassis hold down rivits and replace them with countersunk bolts for clearance to the springs. The springs are 30mm OD.

There's 1/4" rubber between rail and chassis to keep the noise down.

I know this still leaves some torsion in the box, but on balance it's a better fit for how the truck will be used, and simplicity.

 

[camprr]

Are you welding some 'angled tabs' in to guide the frame back into the right position when they meet up again?

 

[whomisi]

Are you welding some 'angled tabs' in to guide the frame back into the right position when they meet up again?

Sort of, bolted to the frame but same idea. Taller than the maximum travel, adjustable height to set them snug to the frame. And with a UMHW slippery plastic plate to save the paint. 5/16 steel, formed and welded, silly strong.

 

[camprr]

Nice! The frame of frames.

 

[whomisi]

And for completeness, this is the bracket I designed for holding the rear of the subframe to the chassis. This connects close to some diagonal braces that connect to the rear cross member. The factory cross member is welded to the chassis as well.
This is part of the winch extra structure so it should tie everything together nicely.
Four 5/8 bolts per side, grade 8, torqued FT.

I didn't put it right at the very back as I didn't want the box flopping around too much, it's halfway between the rear and the rear spring hangers. Tough balancing act for highway manners, off road articulation, and limiting box torsion.

 

[GR8ADV]

Great stuff. I could never do this.

Curious, and maybe I missed it. By extending the frame rail from 3.65 to 4.2, the bending stresses (roughly speaking) in the beam rail increase by about 30-35% +\~ over what it was designed for. Did you have to strengthen the frame rail itself to account for this. Or is it covered elsewhere.

If you have addressed this and I missed it I apologize.

I (we all) really appreciate you taking the time to post all of this

 

[whomisi]

Curious, and maybe I missed it. By extending the frame rail from 3.65 to 4.2, the bending stresses (roughly speaking) in the beam rail increase by about 30-35% +\~ over what it was designed for. Did you have to strengthen the frame rail itself to account for this. Or is it covered elsewhere.

Good question. Mercedes provides a guide, which can be found on their website through the "Builders Portal", on how to extend/shorten the chassis and that includes adding reinforcing profiles inside the frame.



It also gives pointers like if you extend beyond the longest standard wheelbase, then increase strength. These screenshots are from the guide which I translated.


There are also requirements for cross member spacing, as well as maximum length that one section of driveshaft can be before a centre bearing multi part driveshaft has to be used.

On top of this (literally) is the subframe, which spreads the load along the length of the frame reducing the bending forces on the extended section of chassis. For reference, I have used subframe box sections that are 3x6x0.188 in approximately the same grade of steel as the chassis, which is stronger than your regular mild steel. The cross member and the reinforcing parts are also this same steel, laser cut and formed from 1/4 plate.


This reminds me why it's taken two years from buying the truck to getting back to a driving chassis cab.... now I don't feel so bad about the slow progress!