LocostUSA.com

Learning how to build Lotus Seven replicas...together!
It is currently June 23, 2017, 1:04 am

All times are UTC - 5 hours [ DST ]




Post new topic Reply to topic  [ 195 posts ]  Go to page 1, 2, 3, 4, 5 ... 13  Next
Author Message
PostPosted: January 7, 2009, 9:32 pm 
Offline
User avatar

Joined: July 22, 2007, 10:58 pm
Posts: 388
Location: Zagreb, Croatia
ok, after a while lurking on the forum, I feel it is finally time to start a build thread, so here it goes..

please forgive me for long introduction but I feel it might be beneficial for some to read my thought process as it might help others in the build.. so I will tend to go in depth with regards to all the decisions I am making during the build..

also, after toying with the idea of producing the beast commercially, I got scared of liability issues and decided to make the build Open source... so anything I do, will be available to everyone to use.. I will post all the data and files online after I feel satisfied with them.

While preparing for the build, I consumed lots of books, including a certain kimini book.. :) I have yet to find a “all in one book” but I have my favourites... and those are the Miliken book, and The Racing & High-Performance Tire: Using Tires to Tune for Grip & Balance


a brief history...

First, something about myself... by vocation I am an electrical engineer,... used to study digital electronics.... and did some work on a standalone ECU I constructed long time ago.. :) However, I found much more enjoyble life as a professional photographer and graphic designer, specialising in automotive clients... among others I work for the croatian edition of EVO magazine, as a photographer nad journalist, so I get behind some interesting machinery.. (At-om and BMW formula junior for example.. :) ) my portfolio can be found here:
http://smg.photobucket.com/albums/v723/ ... portfolio/


after toying with various cars, at one point I decided to restore my Lancia Delta integrale 16V... at first I wanted just to fix the shell and seamweld it with some reenforcements, so I bought a MIG and made a dolly for he shell, with reinforcements so that it would keep the shell from twisting during the welding.... and also so that I could tip it on the side when working underneath...

Image

But soon I started tinkering with the idea of making a cage... then I got introduced to solidworks and I made a rough sketch of what I wanted... one thing led to another and I was on my way to making a spaceframe chasis for the grale..

Image

This project never got anywhere, mostly because I had no real space to do it in.... however I did buy some 175 kg of 4130 (25Crmo4) seamless tubing in various sizes.. more of that later... :)
Oh, and I also sold the shell and the rest of the car in pieces, and bought a mitsi EVO9... great car.. :)

Right in the middle of all this, I met some university students who were working on our first FSAE car.... Since I had all these lovely books on the automotive engineering subject, I helped them a bit with the literature and a bit of my knowledge in the subject of ECU’s and engine electronics.. I also had fun time watching all the work they did and some great (chain diff) and not so great (suspension..) solutions they came up with..
Their car worked, got them to the UK for the competition,... had enormous flex in the suspension, but the first time I saw it in the flesh and heard them go trough the gears, I was hooked... :)


Image


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: January 7, 2009, 9:34 pm 
Offline
User avatar

Joined: July 22, 2007, 10:58 pm
Posts: 388
Location: Zagreb, Croatia
So, the idea was born... motorcycle engine, and a simple tube frame, like a big cart, for fun.. :) I had a bit of a look in the papers for R1 and R6 engines and that was it, wouldn’t think much more of it.... however, here comes the scary part. Just about that time, I meet a client and a friend of mine... all plastered up... had a BIG crash on the track, fell from his 2007 GSX-R 1000... so I mention to him that I have a customer for his engine, if he decides to break it apart, and not much more than 3 months later I was a proud owner of a GSXR engine... :)

Time to decide what to build...

Bike engined middy was the obvious choice... I always dreamed of light powerful engines and sequential boxes, and on my desk I had a 175 HP engine weighing at only 64 kg, box included.. :)

Second decision was that it would have minimal bodywork... There are a couple of reasons for this:
1. I did not want to get bogged down loosing too much time on bodywork, as it really never interested me much
2. I wanted that open in yer face feeling you get on a bike
3. messing with the body meant messing with the aerodynamics and I and no time and interest in that.
4. less bodywork means less weight...

Single or two seater? SINGLE!
I feel that with a relatively modest amount of power a BEC has, getting two people in the car means too big a change of power to weight, so you really loose the effect. Also, I never like driving other people in anger, so why bother with all the negatives of a two seater build (wrong weight distribution....) when I will never really use the second seat..

Frame material...
Well, my basement is full of 4130 tubing... no point in making an alu monocoque. :)

Dimensions?
I first wanted to use the wheelbase of my hot hatch (pug 306 gti) which was around 2300 mm, with a wide track... I had a look at At-om dimensions also, so this was my first ballpark figure. 1600 mm track.

Wheels?
for me this was the most important decision. Because 13 inch tires are available in europe, but mostly because they are so light, I went with 13 inchers... but modest, 185/60 (55 or 50 would have been better but those are rare) on 6 inch wheels... for starters all 4 corners the same. I do not want excessive grip...
Major design idea was to have the uprights as far inside the wheel as possible. Bearings should be as close to the centerline of the wheel as possible.


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: January 7, 2009, 9:39 pm 
Offline
User avatar

Joined: July 22, 2007, 10:58 pm
Posts: 388
Location: Zagreb, Croatia
So the design started from the wheels.
After looking long and hard at various wheel manufacturers I decided on compomotive as they were the only ones to give me a cross section of the wheel. I had a quick sketch, and figured that with a custom offset I could pack my custom made upright well inside.. and have space for the disk brake. In the rear, I went for inboard discs because due to open design they would have enough airflow..

So I ordered a set of light CXR’s, with Ford fittment and custom 22 mm offset. Ford fittment was chosen after finding out that Fiestas have really nice small and light CV joints available, so I could buy fiesta front hubs and use them in the back.

Image



The availability of the wheel cross section enabled me to play with the brakes. I found out that I could fit nice small wilwood 4 pot calipers under the wheels and use a xxx mm disc. However, wilwood did not have a suitable disc for the use, mostly because they have 6 mounting holed that interfere with my wheel bolt pattern.

Image

I will post the cross section drawings later...

So I went out to find a OE flat non vented disc that I could machine to my spec... and lo and behold, here it is. Alfa Sud front disc (which incidentally is mounted inboard) has nice 4 holes which can be modified for floating mount, and is just the right size... I might cut down the diameter a bit..

Image

Image

I then calculated the brakes I need for the car.. Using some assumptions on the final weight distribution, I made a small EXCELL sheet for brake bias calcualtion.
I will post it for download when I get to work..

I ordered 4 wilwood calipers, all the same 4 pot powerlites, with smaller pots for the rears.

I also bought a floor mounted pedal box as it is such a good value product, some master cylinders following the results of my excell calculator and the slave cyl for the clutch as I find the hydraulic clutches to be nicer in operation especially on short throw snappy clutches...

Image



Speaking of brake calculations.. I did a calculation for the pedal force for 1 G stop. I used 33 kg to be my rough target for the pedal force, thinking that it would be enough for firm pedal ( I do not like over servoed brakes) but not too heavy.... Since that, I had the pleasure of driving a BMW formula junior car (little formula car with aero, bmw 1200 cc motorcycle engine and hewland box... AWESOME!) and that uses really major forces on the pedal for the full stop. We could not get used to it for the whole day... I’d say I was pushing that pedal with 90 kg at least...

Image


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: January 7, 2009, 9:42 pm 
Offline
User avatar

Joined: July 22, 2007, 10:58 pm
Posts: 388
Location: Zagreb, Croatia
The diff decision
well, transversly mounted mid engine is the natural choice, so for simplicity I went with a chain diff.

My FSAE friends did this really nice aluminum box that housed the FSAE diff (in reality an AUDI torsen unit) and positioned the diff in the centre with equal length outputs, and held the oil and was used for suspension pickups, but I wanted a simpler solution.

Initially I wanted to buy the quaife unit, but that is expensive, and since I was in Lancia Integrale waters at the time I remembered that car had a torsen diff in the back, so I just bought a whole diff for the lancia and removed that one from the casing. One other good thing about it is that it uses standard LOBRO 100 mm joints on the output axles.

Now I need to make a housing for it but such that will keep everything in the centre but allow the sprocket to align with the engine sitting in the centre of the car.. No mean feat, but more of it later...

Frame design. V1
Frame is designed with suspension in mind first, but I wanted to make a simple design exercise just to see what kind of torsionall stiffness I could get.

Image

First came the simple box with most frame flex in the cockpit area. I then added simple triangular tubing on the outside, and whoa, frame stiffness went up 4x. So, this would be a design feature.

Image


Image

Image

Also, no curved tubing. It might be an exoskeleton car, but I am no fan of At-om frame, and like efficient design with all the tubes ending in common points, for maximum efficiency.

Image

of course, the frame was too short at this point.. :)


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: January 7, 2009, 9:45 pm 
Offline
User avatar

Joined: July 22, 2007, 10:58 pm
Posts: 388
Location: Zagreb, Croatia
Now it was time for some suspension design. In general terms, double A arms on both ends with pushrods.

Why pushrods?
1. because I can get 1:1 motion ratio on the dampers
2. because I can adjust the ride height separately from the damper, leaving the damper in the ideal position
3. pushrod is thinner than a damper, so in the front I can place the lower pushrod rod end closer to the lower outer ball joint (it will in fact be a spherical joint) minimising the bending in the A arm. In fact the geometry of the joint is such that there is minimal bending in the lower ball joint.

Pullrods were attractive but I just could not package them with such a narrow lower suspension mount, as the pullrod geometry was all wrong and put too much stress on the Upper A arm.

I choose 12 cm ride height, because I want to use it on the road. Springs and dampers will be finalised when I confirm the final weight distribution, but from the suspension travel, which is: 175 mm including 25 mm bump stop, which is divided in 90 mm bump and 60 mm drop +25 m for the bump stop.
For the purposes of the design I needed a shock, so I found some nice AVO shocks, with double or triple adjustment, which hare small and are available with 7 inch travel. This gave me the important shock length at ride height, which in the case of this shock, (which is 19 inches fully extended and 12 inches fully closed) is 395 mm, and this was used in the simulation software.
Now, I might buy it in the end, and I really want a double adjustable shock, but I will try contacting proflex to see what they can offer.


Image


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: January 7, 2009, 9:47 pm 
Offline
User avatar

Joined: July 22, 2007, 10:58 pm
Posts: 388
Location: Zagreb, Croatia
Suspension geometry. V1
First came the uprights. From the wheel measurements I got an idea of what I can fit under the wheel. Existing uprights were out of the question so I decided on a custom build from steel tubing.
At first, I wanted zero king pin angle, zero scrub. This was not possible, as I could not fit the disc and the upright in the same space. :) KPI gives the possibility of running zero scrub, but also too much KPI will give negative camber in the turn. Castor angle, on the other hand can be used to combat the negative camber in a turn, but will also give some trail.

Now, as I see it, trail gives me steering info on the ammount of grip in a corner, while scrub can give me info on the grip level during braking, and I really want both informations, even thought it will give me heavy steering. I decided to keep trail and scrub roughly the same, as to balance the ammount of informantion I get trough the steering.

Then came the inboard points. There is lots of talk about the suspension software but no one really talks about what one wants in a suspension. Generally, I wanted long A arms, to limit the angle of the spherical joints, as well as keeping relatively long suspension travel.
Also, I wanted my camber to loose the inclination at a slower rate than the vehicle body roll, without excessive camber gain in bump. I do not subscribe to the staniforth roll centre theory, and I did not want to get into the force diagrams, so I decided to use the roll centres as a factor in my build and try to fix them in both bump and roll. After some experimentation I got what I wanted, even thought my RC’s are above ground, but there came a time when I had to sto pexperimenting with the software and just continue with the build... Also, lower suspension mounts came up 4 cm above the frame floor, so I ended up with a “high” nose design..

front suspension V1
Image

Image

rear suspension V1
Image


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: January 7, 2009, 9:50 pm 
Offline
User avatar

Joined: July 22, 2007, 10:58 pm
Posts: 388
Location: Zagreb, Croatia
Of course, after you make a design, you have to check if it will fit, and on some occasions I got interference at maximum bump + steering angle (35 deg) so I had to move the upright points, etc...


Image

For the purposes of speed, I decided to use the same suspension geometry in the back, and try putting togeather a “final” frame design which I tried to optimize in torsion by using various tube diameters and thickness. Major parts are to be made from 40mmx1.5 as I have rather lots of it, with some reenforcements in 40mm x 1mm but I will have to get some 20x1.5 and 25 / 30 x 1.5

Image

Image

Image



Working in solidworks is nice, but I do not relate easily with the available human models so in paralel I built a frame from wood, just to see if it would fit.

Image

the build table is under there.... when the MDF is removed, the heavy frame underneath is used for the build..

Seat fittment was a major concern, as I firstly used an improvised “seat” and I could not decide on the inclination I wanted. At the same time I got into a red bull F1 car.. :) and saw that I could live with a radically low angle..

So, this was the first frame design.. as you can see, the rear mounts for the front suspension are around the legs. While my feet are behing the front axle, I really did not like this solution as I felt the frame was not supported propperly in those points.. I’d much rather see a cross brace between both front suspension mounts, and bit more space for the legs.

The shocks ended up high, almost horizontal. This is ok if you use monoshocks, but I’d much rather see them lower down.

So, time for V2.... and this looks like something I will finally build..
just to add, there will be some bodywork... a nose cone of course, and a side pod with the radiator... and an airbox on top of the engine

more pics and updates very soon.. :)


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: January 7, 2009, 11:19 pm 
Offline
User avatar

Joined: September 17, 2007, 10:36 pm
Posts: 209
Location: Montreal, Canada
Wow, talk about a good first update!!! It reminds me of the Formula cars that I've worked on.

This has to be stickied! 8)

_________________
Concordia University FSAE - Chassis
00 Impreza OBS - RIP
81 Rabbit 1.6D
95 525i


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: January 7, 2009, 11:35 pm 
Offline
Always Moore!
User avatar

Joined: November 9, 2007, 3:40 pm
Posts: 3857
Location: Fort Worth, TX
Nice looking start to your build. I'm really digging the brake set up and wheel packaging.

_________________
-Andrew
Build Log
Youtube


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: January 8, 2009, 12:04 am 
Offline
User avatar

Joined: October 11, 2006, 4:49 pm
Posts: 499
nice, looks rigid, keep us posted.

Andrew

_________________
build log http://locostusa.com/forums/viewtopic.php?t=2142


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: January 8, 2009, 12:43 am 
Offline
The voice of reason
User avatar

Joined: January 10, 2008, 4:47 pm
Posts: 7305
Location: Massachusetts
KiKi, glad to see you starting a build log.

I like the way you got stiffness around the cockpit. I have a hard time explaining how to triangulate outside around the frame rail and you have done a very simple and clean job of it.

Congrats on your progress so far, look forward to following your project...

_________________
Marcus Barrow - Car9 an open design community supported sports car for home builders!
SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
Car9 Roadster information - models, drawings, resources etc.


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: January 8, 2009, 4:34 am 
Offline
User avatar

Joined: July 22, 2007, 10:58 pm
Posts: 388
Location: Zagreb, Croatia
thx, I will put up some FEA numbers for the frame with and without the triangulation on the sides, you'll see the difference is dramatic..

I put the brake balance calculator on my site, you can download it here:

www.bib-nakladnistvo.hr/x1000/brake balance upgraded sheet.xls


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: January 8, 2009, 3:44 pm 
Offline

Joined: August 6, 2008, 9:40 am
Posts: 532
Location: Greenville/Charlotte NC
Sweet project! I love how tight those calipers and rotors fit in those little wheels :D

_________________
+442E, SR20det, Thunderbird/Markviii IRS with clutch lsd, R1 suspension all around, Mustang II 2" drop spindles, Woodward steering rack


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: January 9, 2009, 12:41 am 
Offline
Auto Motive, My friends call me Motive
User avatar

Joined: October 23, 2007, 11:56 pm
Posts: 270
Location: Spanish Fork, UT
How you did the triangles on the outside is very similar to what I am doing in my build! Great minds must think alike! Not a new idea though.


Attachments:
gullwing_chassis_175.jpg
gullwing_chassis_175.jpg [ 237.78 KiB | Viewed 25235 times ]
Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: January 9, 2009, 3:29 am 
Offline
Weight watcher
User avatar

Joined: March 7, 2006, 6:15 pm
Posts: 2392
Location: Northridge, CA
But, what about the poor Lancia?
The Delta Integrale is still one of my favorite street cars.

Good job on the middy 8) .

moti

_________________
Moti

My R1 powered Locost build log

Visit the Blackbird Fabworx Facebook Page!


Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 195 posts ]  Go to page 1, 2, 3, 4, 5 ... 13  Next

All times are UTC - 5 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
POWERED_BY