As promised, I've got back onto SusProg to work out important things like position of pullrods, spring rates and the like. First problem was that pull rods simply weren't going to work as a triggering mechanism. Where I've put in the zero roll suspension there was effectively bugger all motion translated from the pullrod into the monoshock assembly to get any meaningful translation of a coil spring. This is not a good thing. I actually want the suspension to move, and more importantly, move under control and 10 mm of spring travel could be taken up by stiction, clerances and poor manufacturing.
So, pushrods it is, albeit at the expense of a little increase in centre of gravity height. That said, SolidWorks is reporting that the current unit is around 10kg, so I'm not unduly concerned with that minor growth. I used SusProg to work out suitable spring rates. I've gone for a ride frequency of 2 Hz which requires a spring rate of 310 lbf/in in this instance. 2 Hz is about the upper limit for ride frequency until you start getting ridiculous amounts of downforce, and I'll probably stiffen up the rear ride frequency by around 10% more. That can wait until I've actually got some ballpark weights to play with, rather than the 'pick a number out of the technical regulations and use that' option.
The picture at the top shows the layout of the front suspension in SusProg. SusProg can't actually calculate values for a monoshock, so it's really two separate bellcranks with coincidental spring and damper units. Still, it looks pretty and gives me some values, which is all-important. The key value is that for 50mm of bump and droop travel, I actually need around 85mm of damper travel, so the 40mm travel damper I've been playing with will need to be replaced. Creating a new damper is not of itself a major issue as all I have to do is change one number in Solidworks, but I now have the lead on issues of changing everything else to fit the central guide rail. The only ray of light is that the equivalent suspension travel in roll is going to be about an inch either way, so I'll be able to keep the guides very short and limit the bending moments on the shafts.
So, I've pretty much got the front sorted out now and we can think about putting the chassis together. Unlike certain 3D solid modellers, SolidWorks has a built-in facility for 'weldments'. That's spaceframes made out of random tubes to you and me. You simply have a separate drawing of the tube profile and a 3d wireframe sketch of where the tubes have to go, marry the two together and you get something like this:
You can even add mounting plates, weld fillets (there's a few on the drawing where I've joined said plates to the tube) and trim tubes so they don't appear inside each other. All-in-all, something pretty much designed to make a chassis designer's life easier. Of course until I measure the bodywork, I can't really put a design together, but that mockup meets the MSA requirements and weighs 12.3 kg. The basic concept for the chassis is to use that heavy rollbar to link into the engine mounts at the front and the differential and suspension pickup points at the rear to reduce weight as much as
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