Making sense of the Regulations...

Now, I know that I'm supposed to make sense of regulations, or at least try and find all the useful loopholes in them, but the RACMSA 'Blue Book' makes about as much sense as a bucket of chocolate frogs. I'm trying to work out how small I can make the tubing for the spaceframe chassis, and depending on which interpretation of the rules you like. Section Q covers all the safety features you could or should fit on a car and paragraph 1.3 mandates CDS steel tubing, with a minimum yield strength of 350 MPa and either 45x2.5 mm or 50x2mm diameter and wall thicknesses. Yet paragraph 1.5.2 for Sports racing cars says a minimum of 48.3mm with a wall thickness of 2.6mm and 1.5.4 (b) for non-standard cars says 32x1.5mm. Which is right? I think we should be a Sports racing car rather than a 'non-standard' car, but there are significant weight penalties for using thicker than necessary tubing.

So if we look at the cross-sectional areas of the four options we get values of 333mm², 301mm², 373mm² and 143mm². The maximum compressive force that these members can take before starting to permanently deform (for those who remember A-level physics, the equation is of course Force = Stress x Area), varies between 50 kN for the lowest member and 130kN for the largest area. So which is adequate and which will give you a few short microseconds of terror before a basilar skull fracture puts you out of your misery for good?

The human resistance to acceleration was found out in nicely empirical fashion by Dr John Stapp of the USAF who strapped himself to a rocket sled and pulled 46.2G in a frontal deceleration. Using Newton's second law (Force = Mass x Acceleration), if we get our car down to the minimum weight of 560kg, we get an impact force of 254 kN. If that impact force is suddenly applied (and you can bet it is), the initial impact stress is actually double that (so effectively we can only use half the limiting impact force if we want no margin of safety). I'm vastly oversimplifying the reality, but SolidWorks doesn't come with a copy of DYNA3D or PAMCRASH, which is what the automotive industry use for this sort of thing.

Anyway, if we have two roll hoops, with extra front and rear stays, we'll have 8 struts resisting an impact force.
If we use the smallest diameter tubing the cage will yield under such loading, whereas if we use the largest tubing we have a factor of safety of around 2. Is it really worth saving weight if you get one of those once in a lifetime accidents - and you want to be around to tell the grandchildren all about it? I'd be inclined to use the lightest of the large tubing (which has other advantages, such as being less likely to buckle than the thinner diameter - so that's 50mmx2mm thickness round tubing.

For frontal impacts we can trade deformation for force - i.e. limiting the force and hoping the car stops before the metal tubing makes contact with our delicate feet. F1 expects a peak rate of deceleration of 10g for the first 150mm of deformation, and 20g for the first 60kJ or energy absorption. For our car 20g and assuming that our non-CDS metal tubing (so a yield strength that could be as low as 275 MPa) will yield under such an impact, we need an impact force of 110 kN and thus a cross sectional area of about 400mm². There will probably be 4 frontal force members here (and a nice big chuck of energy absorbing honeycomb to keep the force at those levels for at least the initial phase of the impact). So each tube needs a cross-sectional area of 100mm². So it's a case of running through the sizes to work out what tubing will work in these areas. A quick bit of maths lets me know that I need tubing that weighs around 780 g/m. In circular tubing that means 7/8"x16g, in square that means ¾"x16g and in rectangular we can use 1"x½"x16g.

I finally got out to measure someone's chassis and bodywork at the weekend and the picture at the top is a quick revision of the chassis, less the back end and using thinner tubing. With a 50mm diameter cage on the top, but using only ½" round tubing, the whole lot weighs around 34kg. The chassis was using 1" tubing and had a lot of extra tubes knocking around (it was originally a prototype chassis), so weighed considerably more. Even with a ramping up in tube size, I reckon we can get significant weight savings in place to get the car close to (or even below) minimum weight.

Safety

Now no racer would ever imagine that they're going to have a really BIG accident, and certainly one where they impact the rollbar at a really nasty angle. I spent the thick end of a decade investigating RTAs and I've seen the impossible happen quite a lot. So, I wanted to see what my allegedly natty rollbar design really would do in the event of a shunt. I've loaded the top part of the rollbar with 10kN (effectively a tonne) and at the same time applied the same level of force horizontally - sort of landing upside-down while sliding into a brickwall with just the rollbar taking the loading. This is nowhere near as sever as F1 for example, which expects loading of 90kN through the rollover structure.

With this loading the rollbar only just survives - the factor of safety, i.e. the ratio between yield stress and max stress, is 0.97 so some parts of the rollbar would just start to bend. Dynamic crush testing is way beyond my knowledge of Cosmos, but I'm more certain than ever that I'll want either front stays on that roll bar or a full roll cage tying the rollbar to another roll hoop around the steering wheel area. Once I've got the rest of the chassis, I'll repeat the analysis and see what the whole car will do. I'll also see if I can get some dynamic analysis done using Cosmos.

The other thing I want to do is have sensible impact protection to the front and sides. Aluminium honeycomb is your friend here and I've got both Hexcel's design document and the F1 regulations as an input value:

"For the purposes of this test, the total weight of the trolley and test structure shall be 780kg and the velocity of impact 15.0 metres/sec.The resistance of the test structure must be such that during theimpact:
- the peak deceleration over the first 150mm of deformation does not exceed 10g;
- the peak deceleration over the first 60kJ energy absorption does not exceed 20g ;
- the average deceleration of the trolley does not exceed 40g ;
- the peak deceleration in the chest of the dummy does not exceed 60g for more than a cumulative 3ms, this being the resultant of data from three axes.
Furthermore, there must be no damage to the survival cell or to the mountings of the safety belts or fire extinguishers."

There's similar for side impact as well. I'll see what sort of volume of expanded honeycomb is required and see where it can be fitted in. I've seen some nasty intrusions into spaceframe chassis over the years and it's a risk I'd like to design out as much as possible.

Making progress...

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 humanlymachinely possible. While I'm waiting to go and measure (work is intervening for the rest of this week), I'll get the modal suspension finished off...

More integration...

and a lazy way to do calculations. The Educational edition of Solidworks has the full-on CosmosWorks designer built in to it, and FloWorks, but I'm fairly sure I don't have enough processor cycles in my PC to sanely do any meaningful CFD studies. I thought I'd check out the possibility of integrating the body-side mounting of the heave spring into the big lump of metal that slides from side-to-side when the car rolls. A quick analysis later (and it took less than a minute to cue it up and run it - far, far better than when I used to use FEA in the days before Pentiums - I first used PAFEC on a Vax and IBM CAD on a mainframe) and you get the picture above. This is the von Mises plot, which is effectively a combinational stress criteria for yield (if you get yield when you combine the stresses in all three dimensions using the von mises formula, it'll probably yield in real life) when 5000N (a bit more than 500 kg) of loading is applied to the bolt hole. If you click on the drawing you'll get a better view, but the safety factor (i.e. the ratio of actual stress to peak stress) is just over three, so even if shock loading was applied, you'd still not cause that lump of metal to yield.

So, knowing that I'm not overloading the lump in question, I can clean the design up a bit, which gives the picture you see below:


I've shortened the guide rails as much as possible (I'll be running the geometry again to see what motion ratios I have and how much roll travel I actually need) to limit the bending moment on them and put a simple framework around that can be bolted onto the chassis in the most appropriate place. I'm now almost ready to start designing the chassis. Adrian has offered to let me measure his bodywork, so I know what space I have to play around with, and I've got a copy of the Blue Book to tell me what I can and can't do, so I'll start with the rollbar and go on from there.

Coming Together...

OK, the picture above is the central gubbins of the modal isolation suspension system. You have a central block which carries a normal coil spring on one side and a coil-over unit on the other. For the purposes of mock-up, I've modelled a Sachs Race Engineering damper, although at the eye-watering costs of these units, I can't imagine I'd ever actually use one. This central unit slides left-to-right on linear bearings (You could probably get away with plain bushes, but I'd want as little stiction in my suspension linkages as I can get away with, hence the posh guide bearings) when the car rolls. The big bearings at the bottom of the picture are to support a bell-crank that will rotate around the lower guide rail to give displacement control in bump. At the moment these are standard roller bearings, although it'll make more sense for them to be tapered to allow for the axial loads as the roll displacement works.

The only outstanding issue is to work out the sort of springs rates needed for this unit and to find someone prepared to do a 1:1 bump:rebound damper. Because of the mounting angle, we need a mono-shock damper and it's pretty rare to get a 1:1 ration for rebound forces as you normally want softer bump (which controls the wheel mass relative to the body) than rebound (which controls the body relative to the wheel mass). If it proves to be completely unfeasable (unlikely), there's nothing stopping you using two coil-over units mounted back to back across the central bar.

Update
I've put the bellcrank (I haven't put the bolt holes for location the two pull/push rods yet) in position with a second coil-over unit to show the heave spring mechanism as well. I was originally planning to attach the heave unit to the body directly and put some sort of guide bush in to deal with the side-to-side movement, but it seems possible to locate it onto the same central bracket that holds the roll coil-over. The only issue is that you want the guide rails then to be as short as possible to manage the bending loads they'll be undergoing as a result. If the loading all looks a little severe then I can still attach the heave coil-over to the body, I'll just have to tweak the mountings so there's sufficient articulation in the bushes.

Time to hit the calculator and work out if the attractive looking method will work...

Monoshocks and modal isolation...

Running on from yesterday's slightly cryptic post about modal isolation and the joy of being able to get exactly the right amount of damping in particular modes (getting the right amount of spring stiffness is usually easy). I thought I'd better elaborate. The picture above is from a Force hillclimb chassis (you can tell it's a hillclimber by the absence of just about everything in the search for stuff-all weight) and is about the best photograph I could find of a monoshock suspension. You can see that the two pushrods operate a single bellcrank. When both pushrods are displaced upwards, the crank rotates and moves the coilover unit in bump. When there is differential movement, the crank displaces along its 'axle' against the action of stacks of Belleville washers.

The design shown has two major design issues. There's very little roll movement possible and that movement is undamped. This isn't an issue in a wing-equipped car because you actually want very little roll else your expensive carbon fibre is going to be none-to-gently abrading itself on the tarmac. The absence of damping is an issue. At the end of the day these cars are going to be driven by amateur racers (gifted or not) and it's worth trading a few tenths of a second for driver confidence in the car. A car vibrating around in roll does not normally give a driver confidence.

So, how can we get around these two problems. Firstly we can replace the Belleville stack with normal helical coil springs. With more movement we can get more roll at less loading. With more lateral movement comes more side loading of the coilover unit which is bad, but this is easily curable by using a wider yoke rather than a clevis connect the coilover to the bellcrank. The only way to introduce damping is to fit a damper unit for the lateral movement. I'm thinking of having a Y-shaped bellcrank with a secondary inner arm. This inner arm would be static relative to the rotation of the bellcrank and move linearly with the roll movement. You can then fit a damper to the inner arm, connect it to the body and hey presto, properly damped, modally isolated suspension. and with little weight penalty over conventional two coilovers plus anti-roll bar.

The only other thing I'm considering is to put all this gubbins on the floor of the chassis and operate it by pullrods rather than push rods. A saving in centre of gravity height. In fact the only downside I can see is that corner weighting will be slightly harder as you'll have to preload one side of the roll springs relative to the other to transfer the weight. You do however get very easy ride height adjustment.

So I have a mental picture of how it'll all go together (I don't do visuals except in CAD becuase I'm quite possibly the World's worst sketch artist. I've got to sketch up a couple of dampers and some linear shaft bearings (well I say sketch, when I really mean drag them off of 3dContentCentral - thank you OnDrive) and then I can do a concept model for your general delectation.

Modal Isolation

Sorry for the absence of a post yesterday, but I was flat out on the CAD preparing for my evening class. They're going to be making a pipe vice, a mill stop and a plumb bob (or at least parts of them) as assessed pieces, so they all have to be modelled in CAD and then dimensioned up as 2D drawings before being cross referenced to the specifications of the qualification units. Anyway, here's a couple of quick renders of the two main items:
But getting back on with the car, I've been thinking long and hard about modal isolation, mainly because this month's issue of Racecar Engineering has a review of the Formula SAE/Student/FISITA World Cup events - annual competitions for university undergraduates to build their own deathtraps 600cc racing cars. Back when I was just a sprog in ride and handling terms, I worked closely with a certain British sports car manufacturer on fitting an active suspension system to a tank. The system worked on the principle of modal isolation. In other words instead of each wheel station having a spring and damper rate associated with it the overal vehicle was considered to have four specific spring and damper rates: roll, pitch, heave and warp. Warp was effectively torsion of the chassis, but that's probably better known to racecar engineers as either Roll Moment Distribution (if you read Milliken & Milliken) or Magic Number (If you've been trained by Claude Rouelle). Sitting in a car with a laptop you could change any of these rates and make either a dream handling vehicle or one that would disappear off into the undergrowth at the prod of a key. In fact if you had a half-decent egotist test driver you'd prod the key mid corner while trying desperately not to laugh as you sailed off into the undergrowth.


So, where does this come in for us - I'm hardly likely to specify an active ride system (especially as they cost around £500k - Moog servovalves tend to be around 10K each and you need at least eight per car). Well, on most cars the spring and damper units have to do all the work for all four modes and as a result you tend to have a bit of a pigs breakfast when it comes to getting an optimum solution, especially in damping of modes other than wheel heave. If you could have separate springs and dampers for everything, you could make large gains in handling without compromise.


Such systems are fairly popular on racecars - F3 have been using monoshock systems for over a decade, although these don't have any roll damping whatsoever. I'd be looking for a system that replaces the two coilover units and an antiroll bar with a pair of coilover units and a set of linkages and bellcranks. I've got a couple of ideas that I need to get modelled up so I can check the kinematics with Solidworks. I would ordinarily start designing my own rotary roll damper but I reckon that would be overkill so an extra bellcrank might be the order of the day. The basic idea is to have no ride springs and a T-type anti-roll bar connected between a pair of bellcranks operated by pushrods (or pullrods, for the benefit of my other reader). A coilover unit would be connected between the chassis and the centre of the T-type bar and thus be operated in heave. A second damper would be connected between a floating frame on the anti roll bar and the bar itself to give separate roll damping. It's the latter part that's causing some grief at the moment, mainly because the whole application lends itself wonderfully to rotary damping but chucks up a load of interesting kinematics problems when it comes to linear dampers.

Oh well, time to get the back of the fag packet out and start sketching...

Something other than cars...

I'm running an evening class for wannabe machinists, starting in September. One of the would-be master craftsmen asked a question about Stirling engines, which then segued into the little beast shown above (click on the picture for a larger view). For those who know their Stirling engines, it's a 'Ringbom' type that uses air pressure to move air between the hot and cold sides of the displacer rather than running the two pistons off a common crank arrangement.

Actually, it's probably a little complex to use for assessment pieces (not least because it's only around two inches high) - the qualification is at 'level 2' which is sort of equivalent to GCSE. That said, I'm hoping there'll be plenty of time available during the year and we can build one anyway. If we do, I'll re-engineer it (lets just say the person who designed it doesn't expect anyone trying to make it to have access to CNC machinery) for quicker manufacture.

Now back on with the car. I'm debating whether to install the spherical rod ends for the uprights in a pseudo-vertical or a pseudo-horizontal plane (by which I mean the axis of the hole). If I install them vertically, I'll have no issues with steering lock, but I might have articulation issues under bump. For a horizontal installation, it's vice-versa. I've been using the Aurora Bearings catalogue to try and make my choice and their rod ends would have around 35 degrees of articulation. If you look at yesterday's picture, you'll see that the joints are already relatively inclined, so I might have issues with wheel travel. I doubt that I'd need to use 35 degrees of articulation with turning. The tightest bend I know (the hairpin at Mallory) needs around 10 degrees of steering lock at the wheels to negotiate for a neutral steered car, which leaves plenty in reserve. I'll do some calculations and let you know the results.

Back to Geometry

With the information garnered from the upright model, I've been able to return to SusProg and try and finalise the suspension geometry, so that I can then engineer the chassis hardpoints and then get on with the design of the chassis itself. The picture above shows the (theoretical) final positions for the suspension arms, together with the best location for the steering rack to give minimal bump steer. For those who want a feel for the scale of the drawing, the thicker grid lines are 200mm apart and you're looking rearwards from the front centreline of the car.

I've rolled and bumped the suspension and got some feel for the geometry. As expected, there's very little change in roll centre height during roll, something of the order of 0.08 degrees inward for both wheels at 2 degrees of body roll. As I've said earlier, the net result of putting the instant centre on the centreline of the car is that you get a relatively shorter equivalent swing arm length (695mm in this case) compared to having less inclined suspension arms. According to SusProg, at 40 mm of bump travel, there's 3.5 degrees of negative camber. The roll centre doesn't move at all during roll, and is fixed at 132 mm above the ground.

Using SusProg to do all the hard maths for me has resulted in a total bump steer of 0.15mm toe-in at 100 mm bump, and around 10 microns over the range of +/-40mm wheel travel from static. One thing that I havn't considered up to now is the amount of Ackerman that the car will have. Ackerman is the method by which the inside wheel turns more than the outside when cornering. It's especially useful on circuits with tight corners, such as the hairpin at Mallory Park. At the moment the tie rod end is effectively outboard of the virtual kingpin, so the car has anti-Ackerman (277% for those who like meaningless numbers) and the outside wheel turns more. If I had sensible tyre data, I could actually work out if this was a bad thing or not. I don't and I doubt anyone will give me £200,000 to do some testing at CALSPAN, so I'll put it in the 'to be determined' pile for now. It's not an enormous issue, as I can do the same job on the steering arm as I did with the top rose joint mounting to offset it inward. In fact doing it that way would enable a range of Ackerman to be easily engineered and you could have a different geometry for Mallory than for Thruxton or Silverstone.

All done for now...

I think the upright is finished. One side effect of building the upright in two main parts, which I'd forgotten, is that there is no need to have two separate designs for nearside and offside. Those of you who look carefully at the finished design will spot the method for joining the two bits together. The aim is to mill a round-ended slot in the upright and have an identical mortice in the top extension. Ideally this will be a light interference fit (one of the joys of CNC is that you can do this sort of thing without the need for extensive grinding) which is further located by a pair of dowel pins for added strength. The cutaway below shows the joint a little better:



According to SolidWorks, that complete assembly weighs around 4 kg (and in reality probably less because the calliper has more volume than the real-life item. That's not too shabby, especially since the FEA results are looking fairly reasonable. I'm tempted to use a bit more mass and reinforce the upright slightly by reducing the size of the central hole in the purple bit. Now all that's together I can hit SusProg and get on with firming up the suspension geometry. After that should come the suspension hardpoints on the chassis and the chassis itself.

Back on track...

OK, 24 hours later and things are looking a bit better. I've changed the design for the upright by rotating the mounting holes through 45 degrees and then sending spurs off in the right direction for the various attachments. I've also come to a decision about manufacturing. While the idea of machining the whole thing out of solid billet has great appeal, the inward spur on the upright for the top wishbone mounting is going to be the thick end of 80-100mm inside the rest of the upright. This means that were this to be made out of billet around 85% of the billet would be converted into swarf. It seems to make a lot more sense to have a multi-part upright so that anyone with a milling machine can make the bits cheaply. I need to do some analysis on the loadings but I imagine that a properly designed joint is going to be no weaker than the billet method, and will be quicker and easier to manufacture, and cheaper to boot.

I decided to extend the method to the brake calliper mounting as well, as you can see in the complete assembled upright. This has the added side effect that other callipers can be easily accommodated for the unit without having to design and build new uprights every time. Now everything fits together and doesn't clash. I just need to do some FEA work to make sure the upright is meaty enough (the Mk I eyeball says it is, but I want to see what sort of safety margin I have when I've got 1.5g of cornering acceleration, a bit of downforce and 1.5g of braking applied too) and isn't going to fail like a US road bridge at the first sign of abuse.


Once I've satisfied myself with that, the I can get back to SusProg and finish the front suspension geometry off. I definitely want the zero camber change in roll, combined with zero bump steer (SusProg can calculate the position for the steering rack for me to achieve this)

Reasons not to be cheerful...

part one! Following on from the stress-free design of the front hub unit yesterday, I cracked on with the design of the upright that's going to glue all those miscellaneous parts to the rest of the virtual car. So, combining the basic dimensions I'd clubbed together from SusProg for my default upright, I set to work. The first, and most obvious problem was that I'd need to shift the lower mounting inboard by around 50mm so that it wouldn't foul on the brak disc. Susprog works on individual points and doesn't allow for such piffling considerations as the diameter of the rod ends that will actually be in use. Not a big issue, but I'll have to revisit the location of the upper mounting as well to keep the zero offset kingpin inclination I want. Still, it's only software and time rather than swearing in the garage 'cause you've mucked up another set of calculations.

So, next job was to make a mounting for the hub unit - nice and easy and there's a nice big hole in the middle for weight saving purposes. After giving it a nominal 25mm thickness, I did a quick and dirty check with CosmosWorks (the inbuilt FEA) package which reckoned on a safety margin of 8 with a 250kg load on the mounting bolts. I then added extensions for the lower mounting and the steering arm which gives the object shown above.

Final task of the day was to start building up a complete upright design so that I can be sure that I'm not doing anything silly with clearances. Yep, you've guessed it - I've manage to clash the steering arm with the brake calliper itself, and not by a small amount either:

So I have two choices:

1. Move the steering arm or calliper to the front to remove the clash - nice and easy, although I did flirt briefly with the idea of installing the calliper at the bottom of the wheel for c of g lowering purposes until I realise that I'd then be clashing with the lower mounting eye instead
2. Move the steering arm further inboard to avoid the clash - again easy to do in virtual space but a right bugger for anyone who actually wants to make the thing

I think 1 makes more sense and I'm more inclined to move the calliper than the steering arm because I want to leave the far front of the car free for a crushable structure and the radiator (if I can't get enough cooling using side ducts) rather than filling the space up with a steering rack.

Oh well, back to the coal face...

I love SolidWorks...

because it links in with 3dContentCentral. Anyone who does a lot of designing will tell you that if you haven't got decent backup from suppliers then you spend an inordinate amount of time reverse engineering standard components to be able to insert them into your virtual assemblies. Yesterday I was talking about designing my own hubs so as to be able to press on with the upright design. SKF have their complete bearing catalogue online within 3dContentCentral so it was a case of dragging components off-the-shelf and putting them into the design. So a quick 15 minutes (and I'm not kidding here) later, we have a nice working hub design that I can now use for reference. If all comes to the worst, I can simply get those manufactured and sold.
The hub isn't perfect yet - I haven't made the central spindle long enough to fully engage with an M20 nut; there's no dust cap for the bearings, although given the lack of usage and (hopefully) the attention to detail of most racers, it's probably not necessary; the tolerance issues haven't been ironed out (everything is a perfect sliding fit with 0.000000mm of clearance) and I'm not sure it'll be gold anodised if ever I manufacture it. Pimpy looking components do sell a car and I'm reliably informed by people with more taste (i.e. everyone) that purple is the new gold.

Still, it's something to be going on with...

More on uprights...

OK, I've started bolting things together virtually. By putting the calliper and brake disc together, I've worked out that in order for the brake disc to line up with the centre of the contact patch we'll need wheels with an offset of 42mm (luckily that's a nice common offset) and then everything will fit comfortably under the 13" rims.

The next task is to take the data from SusProg in terms of the location of the upright mounting. Luckily SusProg is sensibly designed so that the uprights aren't measured relative to the vehicle datum (i.e. measured from a virtual point at the intersection of the vehicle centreline and the front axle centreline) but relative to the mounting face on the upright. This saves a lot of unnecessary trigonometry, although I must make sure to subtract the width of the disc mounting face as this is effectively a spacer between the upright and the wheel.

The thing that is holding me back from finishing this first component is that I haven't had time to measure up a suitable hub yet. I'm still toying with the idea of doing my own, but for now I'll just mock up an estimated hub and go from there. The joy of CAD is that it's inordinately easy to change something right at the top of the model and let all the changes percolate through. I'm a really lazy person at heart if I can be...

The picture above is a very quick mock-up - I put the calliper and disk together with a basic plate so I could measure up how much space there was between the calliper mounting bolts and the back face of the mounting bell. With that number (it's 49.5 mm for anyone interested), I can get everything else together.