Even with years of planning, actually making Godiva has never really been a very linear process, where each step is well planned in advance and flows smoothly from one stage to another. Instead it has been very much like a long staircase in a grand old building where there are pauses along the way to look at the sights and to get your breath back. Recent developments have shown the current period to be one of rapid movement, followed by a pause to look around!
You can see in the images that a build table was constructed as per issue eight along with a few changes. The two additional cross members to support the open areas were wisely added by Laurie and Bill. The welding was limited to reduce the chance of distortion (there appears to be about a 1mm dip in the middle over the whole length) and the castors welded to the bottom of the supporting legs. These castors need to have spacers added underneath if the floor is uneven as even a frame such as this will distort.
Twenty two millimetre thick MDF was placed on top of this frame and screwed down to form a flat surface on which the chassis could be mocked up on. The MDF overhang at the sides was removed where the wheels would normally be at each corner, so that mock-up wheels could be used to help position components. With the MDF in place, a need for a centre line to measure from was obvious. Initially this was drawn with a pencil down the middle of the table. I thought that this was not ideal as even if the line was drawn in indelible ink it would require care to ensure that the placement of the tape measure was accurate in the centre. In addition, I also felt that the line would become obscured or more difficult to access as the build progressed. The solution was straightforward: a groove was very carefully cut with a circular saw, 5mm deep 4mm wide down the centreline. This groove cannot be easily damaged and the end of the tape measure catches nicely in the groove, making measurement easy and accurate. The width of the groove adds to the centreline and this is accommodated into the measurement by adding 2mm to the total. To make sure that the measurements were marked off square to the centreline a 40cm length of ‘T’ section aluminium extrusion was glued to a large metal square as in image XX. This ‘T’ section then runs in the groove and any angle drawn off the square is at 90 degrees to the groove…simple and very easy to use.
After working all of this out, the decision was made to start the mock-up proper. One line was drawn across one end of the table to represent the rear axle line and every 100mm from this a line was drawn across the board out to 2650mm (the maximum anticipated wheelbase). Doing this reinforced how useful the groove and square arrangement was.
The engine and transmission was then lifted onto the table with the engine crane and the driveshafts were lined up with the notional axle line and checked on both sides. This then placed the engine and allowed a much better visual understanding of the engine bay space needs, particularly the placement of the rear bulkhead/firewall.
At this point, a trip to my local hardware store resulted in my return with around ten, three meter lengths of 32mm and 42mm square, primed pine and 50mm PVC water pipe. Great care was taken to select the straightest lengths of wood. The 32mm wood exactly replicates that which is planned for the front and rear sections of the space frame and the 42mm combined with the 9mm MDF reasonably replicates the 50mm square SHS and 1mm Aluminium sheet (the outside skin of the honeycomb panel) planned for the side structure and front and rear bulkhead.
The 42mm square wood was laid across the line where the rear bulkhead was planned and this then became the start point for the cabin area of the chassis. From here I estimated the amount of spacing required to keep my posterior off the floor of the chassis. This included 32mm for the steel of the chassis, another 8mm for the seat (shell and padding) and 5mm clearance between seat and chassis, to make a total of 45mm. Thus I sat myself on a 45mm thick piece of wood, spaced 50mm from the centreline and measured the amount of width required to house my body and the anticipated amount of room required for the seat, plus an amount of room for arm movement. The 50mm from centreline measurement was to accommodate the centre tunnel that will house the coolant/brake pipes etc. This then gave the basic space requirements to house the driver. The base layer side tubes were then laid down and glued into place with a hot glue gun (which as it turned out was not the wisest thing to do!). From here the second cross tube behind the driver was glued into place as well as the cross tube at the drivers knee level, which is the forward most point for the side tubes.
I then needed to estimate how wide the front structure of the car was going to be. As I noted in a much earlier Godiva article, the front suspension design is greatly influenced by the dimensions of the uprights, but there is also another significant dimension in the width of the steering rack. We want to ensure that we have no or absolutely minimal bump-steer and the easiest way of doing this is to line up the inner suspension joint points with the steering rack that I intend to use. This sounds easy, does it not? Well, it is not, for the simple reason that the suspension is not yet designed and all the final components (rack/uprights etc) to be used are not yet finalised.
I had a power rack from the donor Mitsubishi 380, which seemed almost the right size and since it was there and matched the steering column, I decided to go ahead with this as the base for the mock-up. The advantage of this rack of course is that it perfectly matches the strut bottoms from the 380 that I had intended to convert (for Short-Long-Arm (SLA) suspension) for all corners of Godiva. The steering arms on the 380 strut are quite low and at the back of the strut. This meant that the steering rack would need to be mounted on top of the base layer tubes, at be bottom of the bulkhead in front of the driver’s feet. This places the rack at a very stiff part of the chassis and makes it easy to accommodate the lateral loads from the steering rack. The need to mount the rack low also meant that there was no real need for substantial structure to mount the rack elsewhere, thus saving a small amount of weight. With the rack mounted so low it also allowed for the possible lower suspension points to be predicted to occur within a certain amount of space. Because of this the base level of the mock-up could be fully laid out. At this point I added the rear bulkhead and the side tubes to see how it felt with respect to drivers arm room and ease of entry, given the height of the ‘sills’. This was also the start of working out how long the doors needed to be. I have a database of such information taken from a range of production sports cars and of course I have my own car to practice getting in and out of. In the end a piece of wood was cut so that it would replicate the high sill of Godiva and this was placed in the door opening of the family Falcon. I found that I could get in, but getting out would be more of a challenge. However this ‘test’ did show that a 90cm door opening is a functional length. Note that this is the door aperture length and not the door itself. This length was measured from the front of the box section that houses the tank, which is behind the driver/co-driver and simply forms the rear-most part of the functional cabin. So measuring 90cm forward from this point gave us our ‘A’ pillar base point, which also matched the chassis as laid out. At this point I was starting to feel pretty smug that things seemed to be going so well…however things did not go as well this might make you believe.
I decided at this point that I needed a real windscreen to go much further as its rakes greatly influences the door aperture and I wanted to clarify the dimension chosen. The windscreen from a Mitsubishi FTO was ordered from National Screens for the grand sum of $135.00. This screen was ordered because it has a nice rake (the angle it leans back from vertical) and it has a nice curvature in plan (both these features were felt to be important for the cabin architecture to achieve a good aerodynamic performance). In addition I wanted an easily available screen from a production model, just in case a screen was broken on an event….plus they are cheap. The added bonus of using a production windscreen is that I can use a complete windscreen mechanism from a production car, which saves a lot of mucking around and will help keep the certifying engineer happy, which is always a good thing!
The screen is also important as the chassis width at the drivers knee level is set by the width of the windscreen base – the ‘A’ pillars (assuming you want to keep the chassis sides vertical and easy to manufacture, flat sides are very important) and as it turns out I was inaccurate by 10cm, a relatively huge amount! Simply put it all had to be taken apart and widened and then the driver fit checked again. This was not as bad as it might seem as the steering rack did not work out either, as the pinion shaft was on too steep and at an angle pointing away from the centreline of the car. As previously noted the rack width sets up the base level front structure, so all of that had to come apart too, which affected the rest of the base level tubes.
The steering column seemed quite heavy and no doubt there are lighter ones out there, but at this point I do not have the time nor funds to chase a different column. In addition the 380 column combines with the wiring loom I hope to modify and use, so I will do without the complication of changing this component!
The pause section then began. I had to find a new steering rack – a manual rack of 2.5 turns lock to lock (TLTL). This was very hard as all current (i.e. produced in the last 15 years) manual racks are 3.0 TLTL or more. I had a good look at the recent power steering units that are 2.5 TLTL (Volvo V70, Alfa, MX5 etc), but they are complex things, having their own ECU and sensor system and they are definitely not cheap. In any case the need for a power rack was much discussed and I finally decided that it was not required, given the overall weight planned, the width of the front tyres and also the desire to maximise front end feedback, which I personally feel could be an extremely important driver aid. So despite my initial misgivings a Ford Escort rack seemed the obvious solution. It can be modified to have the desired ratio at 2.4-2.5 TLTL (or even 2.2 if required), it can be sourced as a new part and the pinion shaft was almost straight, which would aid the coupling to the column.
The other option was the Suzuki Mighty Boy steering rack, which is 2.6 TLTL and I have been told that this is popular with Sports Sedan racers. However it is from a very light car with minimal grip and steering loads. Unlike a Sports Sedan, I intend to run Godiva on the road and I have more confidence in an Escort rack. So, a new Escort rack it is. At the time of writing, the Escort rack had not arrived. Consequently, the front end mock-up is somewhat in limbo, which is not such a bad thing, as the complete suspension design is yet to be started.
Whilst this steering rack deliberation was going on, the rear structure was being mocked-up. As with the front end, the suspension design was by no means close to being finished. Instead the reason to mock-up the rear structure was simply to see if the structure would fit as planned around the engine. To do this successfully the fist step was to inspect the ‘uprights’ and to estimate the wheel dimensions, which were based on the 255/40R17 tyres notionally selected for the rear. These have a diameter of 636mm and thus the height of the wheel centre will be half of this minus a 4-5mm for the distortion at the contact patch. This wheel centre height will give the outer driveshaft height and the lower suspension arm outer ball joint’s height relative to the ground. The ball joint height virtually sets the inner pivot height, assuming that I intend to have a horizontal lower suspension arm. This was the assumption made for the sake of this mock-up and thus the base level rear chassis height was also set. It is my belief that the chassis should be constructed around the suspension points and not the reverse. The inner pivot location required the rear chassis structure to be raised 70mm at the rear, which then introduced the first compromise in the rear structure. On the pulley side of the engine all seemed as though it was going to work out well, but not so on the gearbox side. The gearbox is wider than the opposite (pulley) side and the gearbox intruded into the space where the tube ‘should’ run if it were to exactly match the opposite side. The pragmatic solution is to use much thicker wall tubing on the gearbox side at this point, with a bend in it to clear the gearbox casing. This is theoretically not ideal, but it is a practical solution at this point in time.
The other problem that was alluded to previously is the difference in height between the level of the output from the gearbox and that required for the uprights. In response, I have tilted the engine and gearbox approx. 12 degrees forwards and this has almost equalised the heights and the driveshaft is almost level.
Another compromise in the chassis is in this rear section at the firewall. You can see that the inner diagonal tubes run to the middle of a tube that makes up the firewall. One of the cardinal rules of a spaceframe is to never feed loads into the middle of a tube. This is simply because the tube will be in a bending moment instead of tension and bending introduces all sort of compliance issues in a structure you want as stiff as possible. However, all is not as it seems at first glance when looking at Godiva. The tube, in bending, is backed up by a second tube running parallel, which in effect creates a substantial beam across the rear of the car, both at the base layer and also at the mid layer. It is still not ideal in any theoretical sense, but I feel the beam will be more than substantial enough for the loads and such a design compromise allows the rest of the design to proceed as planned (having said that, if anyone has any better solution I am happy to hear it!). This beam structure is also part of the tubular structure to locate the honeycomb panels that make up the main transverse box. This box running across the cabin area houses the fuel tank, adds to the cabin area stiffness and creates an important high strength area immediately behind the driver’s torso that the ROPS will locate to.
Where to from here? The cabin area will be firmed up when we get a proper race seat from one of the manufacturers and the steering rack arrives. The front and rear structure will be fully mocked up when the suspension is roughed out and this will start next issue.