June 21, 2012
Some real progress on the suspension. We actually managed to build shock mounts for the front end, and somehow got them welded in without ruining the frame. Since these are probably the most critical welds in the entire Locost, we took our time, and welded them on the top, bottom, and sides. I'm confident the mounts will not only support the weight of the car, but also any additional downforce generated by flying down the Mulsanne straight.
The shock mounts aren't the standard "book" brackets, but are instead the more popular cantilevered brackets that give you a better motion ratio and therefore in theory better handling and ride characteristics. To counteract the twisting forces imparted to the J-tubes (upper frame rails), the mounts extend to the S and T triangulation braces, and we also drilled holes in the tops of the mounts and welded in blind nuts so we can attach a bar between them later on to help even more with the twisting. If we're lucky, we may be able to use the bar to mount the headlights. We'll see how that works out.
The blind nuts we used are specially-made for welding. They're super easy to install, and they melt really well. They're not exactly what I'd call highly structural items, but if you're lazy like me they can make installing things a snap. We got a couple of bags of them in different sizes from McMaster-Carr, so we'll be looking for more places to use them in the future. Probably not the roll bar. Or the engine mounts.
We reinforced the lower rear pickups. We were concerned about the ability of these brackets to resist the stresses they'd see, particularly at Le Mans, but we weren't sure whether it would be best to add gussets or a cross tube. So we did both, which looks a little over-the-top, but the brackets won't be going anywhere. And the tube is removable, so if it interferes with anything, like for example the engine, we can remove it and throw it away, and then grind down the gussets so it doesn't look like we tried to do anything stupid like adding a cross brace.
So we're now able to hang the front A-arms on our cool wooden shocks, and we could actually set the front of the car on the ground if we had wheel bearings and hubs. Wheel bearings can be ordered from Moss Motors, but the hubs are a bigger obstacle since we have to clean and paint them, and then wait for the paint to dry. In any case we still have a lot of work left to do on the rear suspension, and having the front end on its wheels with the rear dragging on the ground would look silly.
It's not like we're avoiding working on the rear suspension, although that would be totally justified on the basis of having to drain the differential oil alone, but with the front suspension in place we thought it might be a good idea to start looking at the steering rack arrangement. We are completely on our own here of course, in unexplored territory, being probably the first M.G. Locost builders in history to incorporate built-in caster.
The book mounts for the steering rack won't work. They place the rack only an inch or so above the bottom frame rails. With our rack sitting on 3 two-by-fours, it's still too low. Ideally you want the tie-rods parallel to the ground at normal ride height. So our rack has to be about 5" above the bottom frame rails, and it's probably not going to work to use two-by-fours. So we need some kind of mount, probably made out of metal, and we're starting from scratch, which means we'll have to do some a) engineering and b) fabrication, which of course exposes us to yet more derision and ridicule.
Luckily we don't have to do any of this right away, since the rack is still too long and despite our earlier optimism we don't yet have any clue as to where or how to get it shortened. To keep bump-steer to a minimum, the inner tie rod joints need be in line with the upper and lower A-arm pickups, and right now they're about two inches outboard of that location, so shortening the rack 4" should do the trick. Then we'll have to lengthen each tie-rod by 3", although I've heard you can buy extensions for these, which sounds technically feasible if not entirely believable.
So with that issue tabled for now, we can move on to routing the steering column. This might actually be easier than we thought, since the steering wheel end of the column is firmly mounted to the firewall, and needs only a short extension to connect it with the rack column. We can calculate the length of this extension by measuring the distance between the column ends, and subtracting the length of the universal joints that connect them, however only in very few universes do these sort of calculations turn out to match what you actually need. Luckily we can only buy extensions an even number of inches long, so our calculated length of 9-3/8" means we should probably be okay with a 10" extension.
The short length of the extension means we can get away with a single support bearing for it. How we mount that support bearing is another issue we may need to table, since there are several different types of bearings, with different ways to mount them. The cheapest and therefore the best support bearing looks like a simple rod end with a 3/4" hole in it for the column. We could probably mount it to a short length of 1/8" steel strip welded to the upper frame rail, if we weren't concerned that it would then be free to flex like a popsicle stick. Clearly more thought is needed here. Maybe we'll drain the differential oil first.
Our Build Log
Search log entries
|Home Previous Entry Next Entry Latest Entry|