bpaar
|
| posted on 3/1/06 at 11:27 PM |
|
|
quote:
Yes - a transverse mid-engine layout will have a more rearward mass centre for the drivetrain than a longitudinal one.
I am not sure this is true, conventional wisdom would seem to indicate longitudinal is better but run the numbers and there is very little difference
for a locost. I think the answer is "it depends".
For example, my donor is an esprit and it has the traditional inline (north-south) engine arrangement. The transaxle weighs ~150lb (69kg) and is 23
inches (58cm) long. The bellhousing takes up a third of the length so the mass is almost all behind the axle (tranny center of mass is 7inchs behind
the axle). This almost negates the advantage of having the engine further forward. With my engine weight of 275 lbs (125kg) there was only a ~10lb
difference on the rear wheels when I calculate for both layouts.
If I tilt a transverse engine forward 10 degrees the center of mass is identical.
If I used the lotus 907 engine engine (45 degrees of tilt) the transverse layout is superior.
If I install a heavier or longer engine (v8) the longitudinal design is (much) better.
When aero is a big concern, inline has a distinct advantage but I am only considering mass centre here.
Bill
|
|
|
|
|
kb58
|
| posted on 4/1/06 at 01:51 AM |
|
|
I don't think anyone disagrees with the above, but "locost" budgets don't allow for "real" transaxles. Where is
this transaxle going to come from? Where is the expensive adaptor plate coming from?
Since this thread is for a mid-engine Locost, there is only one clear choice, use an existing FWD drivetrain in the back of the car.
This is exactly what I said at the top of the thread, everyone has *their* idea of what makes a Locost midi... and many seem unwilling to bend to a
common view.
Well, as self-appointed dictator, I say the only *realistic* solution is an existing FWD drivetrain. Here's the whole design, use all
Miata parts at the front and the FWD drivetrain, axles, uprights, and brakes at the back. There, Lord Kurt has spoken, so let it be written, so let
it be done. Now stop squabbling and get to work designing it!
[Edited on 1/4/06 by kb58]
Mid-engine Locost - http://www.midlana.com
And the book - http://www.lulu.com/shop/kurt-bilinski/midlana/paperback/product-21330662.html
Kimini - a tube-frame, carbon shell, Honda Prelude VTEC mid-engine Mini: http://www.kimini.com
And its book -
http://www.lulu.com/shop/kurt-bilinski/kimini-how-to-design-and-build-a-mid-engine-sports-car-from-scratch/paperback/product-4858803.html
|
|
|
TheGecko
|
| posted on 4/1/06 at 02:44 AM |
|
|
Hmmm,
No post from me with render etc last night as I got home and found my PC dead  Hopefully it's just the power supply because I can replace
that pretty cheaply. However, work pressures mean that won't happen for a day or two.
Some comments:
Brian (Ratman) - Yes, wishbone front ends are getting rarer. For that matter, undriven front ends are rare (ie RWD rather than FWD/AWD). Van
spindles are a possibility athough everything I see and hear suggests that they're pretty heavy (reflecting their commercial vehicle origins).
The Gemini/Chevette parts are lovely and light and have a nice bolt on caliper mount, making brake upgrades even easier. They are also 20+ years old
and getting rarer, even in Australia. That said, I was given (for free, nada, zip, gratis) three sets, complete with brakes and racks 
[MonsterGarage] FREEBIES [/MonsterGarage]
I agree with Kurt (kb58) that the Miata parts are eminently suitable. However, whilst they may be common in North America, the wrecking yards are
definitely not littered with MX-5s here. Japanese parts importers do have them but they're usually pricey (eg $300-$500). And the rack mounts
at an odd angle (I'm told).
The other possibility is modifying strut type uprights, in the same way the Steve Graber, Alan B, and Kurt have all done. Steve and Alan are both
using Mk1 MR2 uprights which are effectively E8/E9 series Corolla parts with the CV/axle replaced with a big bolt to hold the bearings in. It's
not a big step further to do that yourself. Using FWD uprights modified in this way, even by just having the CV cup turned off the spindle in a
lathe, would open up a vast supply of parts.
crbrlfrost - With regard to central tub stiffness (oo'er missus!) - the Gecko has twin top rails on each side of the cockpit, braced back to the
bottom rails and panelled. This effectively makes each side a triangular 'pontoon' structure, adding strength well away from the central
axis where it can be more effective, as well as improving the side impact performance (hopefully that part will never get tested!  ). The outward
sloping lower sides are echoed by the upper sides behind the seatback, which slope in at the same angle, adding a bit of visual interest and stopping
it looking too slab-sided there. The little sausage shaped vents break up the big flat part too.
Bill (bpaar) - Thanks for those numbers - they're very interesting. I only have my transverse drivetrain to measure so I wasn't
able to make any real quantitative statements about inline ones. I definitely hadn't thought about how much of one of those transaxles hangs
behind the axle line. Somewhat deflates Phillipe's argument about transverse drivetrains sitting over the axles
Just out of interest, what are you building? The idea of using an Esprit as a 'donor' sounds wild to my Australian sensibilities. I see
Esprit's much less often that I see Ferrari's (and I don't see them very much - maybe once or twice a month).
That's probably enough for now but I'm enthusiastic about how much good discussion this thread is evoking - thanks to Phillipe for kicking
it off.
Dominic (who needs to go shop for a ATX-P4 power supply now)
|
|
|
bpaar
|
| posted on 4/1/06 at 05:20 AM |
|
|
quote:
Just out of interest, what are you building? The idea of using an Esprit as a 'donor' sounds wild...
An esprit daily driver. That means swapping in a reliable modern engine and controls, redesigned rear suspension and reducing the weight. A small
project compared to the excellent ground up builds seen here. The project car I found is locost, once I sell off the extra bits I should show a small
profit on the donor. I looked 2 years for the right car, so I wasn't lucky, just patient.
Bill
|
|
|
Ratman
|
| posted on 4/1/06 at 08:36 AM |
|
|
Front wishbones... yes Gemini/Chevette. Some kit cars use these here in NZ. Also, these exchange with early Viva parts. And.. in our local
"pick-a-part" wreckers I found an Isuzu Piaza (or something) sports version of the Gemini with exchangable parts and ventilated front
disks. Also had a disk rear axle and my friend used this to upgrade his Gemini based MG looking kit car. For a midi these are not light weight... but
what is? the sacrifice is only a very few kg and it is much easier to get certification on the build for road registration if the suspension
components have not been modified. It's hard enough to get a car built that you don't want any unnecessary hassels with "the
system".. Cheers, Brian
|
|
|
crbrlfrost
|
| posted on 4/1/06 at 02:37 PM |
|
|
I didn't mean to imply that the rear box with central tunnel would be ideal unto itself, however, it is still very doable, but a complete
redesign of the rear bulkhead area. I personally like the idea of twin sidepods carrying most of the load, but it presents issues such as
ingress/egress, doors, arguably dangerous fuel location if used such, etc etc. Just another compromise in my book, only depends on who you're
marketting to. As far as uprights go, at least in the states it may be interesting to scrounge up modern light duty truck uprights, since they seem to
be the source of most SLA's in this country. With the vastly different roles they market to, perhaps one or a few of the models would be
suitable. Otherwise, it may be possible to fabricate/machine relatively simple uprights on the cheap and use a donor spindle (one of the many press
fit variety) seeing as they are the more difficult to machine. Or, if using enclosed body work, it would be possible to get away with the ubiqitous
honda sla upright, although it limits wheel size and perhaps raises the cowl (not as much as a strut does though). Well, horses for courses. Cheers
|
|
|
iank
|
| posted on 4/1/06 at 02:46 PM |
|
|
It's often possible to use another set of 'normal' FWD front uprights with the driveshaft/CV removed. This has been done since the
60's on mid engine kits based on the mini (GTM etc).
That would open up the Honda Civic which IIRC uses double wishbone suspension assuming the uprights are suitable.
|
|
|
kb58
|
| posted on 4/1/06 at 03:09 PM |
|
|
Not sure about the Civic, but the Prelude upright is a huge S-shaped affair. Way too tall IMO. Oh and the calipers weight 15lbs each...
Mid-engine Locost - http://www.midlana.com
And the book - http://www.lulu.com/shop/kurt-bilinski/midlana/paperback/product-21330662.html
Kimini - a tube-frame, carbon shell, Honda Prelude VTEC mid-engine Mini: http://www.kimini.com
And its book -
http://www.lulu.com/shop/kurt-bilinski/kimini-how-to-design-and-build-a-mid-engine-sports-car-from-scratch/paperback/product-4858803.html
|
|
|
TheGecko
|
| posted on 6/1/06 at 07:34 AM |
|
|
Bit slow getting back with a reply to this one - my home computer is still dead (motherboard and/or CPU) and won't be fixed until this weekend
because of work and other pressures 
Re: converting FWD uprights. Although the later Civic's etc have double wishbone fronts Kurt is right on the money when he points out that the
uprights are a VERY odd shape and would look quite strange on the front of a Locost-ish car. The top balljoint, on the variants that I've
looked at at least, is above the tyre. This does make for a very nice KPI and small scrub offset etc but a cycle guard underneath the
balljoint is going to look a litle strange
As well, from memory, the Honda SLA front suspension is arranged in a somewhat non-conventional way too. That is, the wishbones are very different
sizes and the pivot axes aren't 'aligned' with each other. Not very amenable to our purposes I suspect.
I was thinking more along the lines of older Corolla (E8/E9/E10) or, even better, Suzuki's like the Swift. The 4x100 PCD is almost universal on
small FWD's now and the little Suzuki's tend to be more lightly built and, thus, possibly more suited to our purposes. As well, because
these uprights need to fit inside 13" wheels in the native environment, there should be plenty of space to do the Mac strut to ball-joint
adapter shuffle that AlanB & SteveG have done. Brakes should be more than up to the job with lighter overall weight and a much more rearward
weight bias.
In the unlikely even that I find myself with some spare time, I'll have a look at the wreckers and see how big/small and adaptable (or not) the
uprights from Suzuki's and the other small FWD's are.
Dominic
|
|
|
akumabito
|
| posted on 6/1/06 at 02:22 PM |
|
|
I know this is of little to no use for people outside the EU, but I was wondering if the uprights of the old Fiat Panda could be converted to fit a
wishbone-type suspension?
It would pretty much be the cheapest donor vehicle ever, since people are often giving them out for free when they become too rusty...
And light too, of course!
|
|
|
