build diary

January 6, 2006:
I figured out enough SolidWorks to put together a line drawing of the suspension that lets me bounce things up and down.
Whee, this is fun! I need to double-check the dimensions of the various parts though. While the suspension movement looks familiar, my control arms ended up more parallel than they do in pictures.
entry 1091

January 9, 2006:
You know, I really should choose one thing and focus on it.
I seem to be suffering from vehicular ADD again. A fresh load of Mini magazines has me thinking of cool, fun things to do with the Mini. I've started to get the itch to run my Land Rover, Basil again. I want to start working on my house again. And of course there's the Seven. I have a long list of things I'd like to do. And one I don't - the hood.

I'll measure the car up again tonight to see if I can figure out how the front suspension works. I really hope my Solidworks model isn't correct. It shows a camber curve that isn't enough to compensate for body roll, putting the tires into positive camber immediately. Well, if anyone wants a set of dimensions for a suspension that has a whole bunch of bad habits, I'd be pleased to oblige.

Meanwhile, I've been considering the other laundry list of modifications. One is to move the battery up to the front of the car. Space is a little tight, so I'm considering a little Odyssey PC680 or the Hawker G16. I can get one for around $80 and it has the same long-lived construction that I'm used to seeing in Miata batteries. It's also only 15 lbs. Granted, I've had to jump the Seven a couple of times with my current Miata battery but that's because it wouldn't start for other reasons - fouled plugs. I figure a set of jumper cables are now standard issue for going to the track. There's also the matter of the fender. A tempting solution would be Coveland's aluminum fenders. There's also a good rear view mirror that would come in handy at Mirrors for Sevens. I saw one on the RMSC car at Aspen. Argh. Concentrate! Concentrate!
entry 1092

The first model of my current front suspension, with a few degrees of roll.
I need to recheck the dimensions, but check out what's happened to the camber! Nothing good.
entry 1093

January 10, 2006:
Lots of SolidWorks fun last night.
I spent some time learning how to animate the model properly and discovered some interesting things - then realised I was using some measurements from the rear. Argh. With my new knowledge it only took a moment to change the dimensions (this is so cool!) and the car immediately picked up enough positive camber to look like a VW Beetle jacked up in the air. Obviously something isn't right. I'll need more measurements. I have a front upright on my desk right now and the car suspension is easy to check once I get home. Playing with my incorrect model did teach me a few things about the interaction of the various parts, though. Of course, I also spent some time trying to figure out how to put 10" wheels over my 8.4" brakes on the Mini...
entry 1094

A better model of the front suspension with fewer errors, but not yet error-free.
entry 1095

January 11, 2006:
A friend pointed out that there's a CMC car like mine on eBay.
I had a brief email exchange with the owner about diff mount design last summer but that's all I know. It'll be interesting to see if this car fetches more than it would cost to build. It's fun to look at the pictures - looks as if his fender stays were always crooked like my original ones were. There's a lot of static camber in the front wheels which implies he discovered some of the difficulties with the suspension although there's not much roll in the pictures online. I have an idea of what the final price will be, let's see how close I am.

On a similar note, there's a new CMC Miata kit that's still for sale. Rod Lingren has been trying to move this one for a while and is now asking $4000 for it. He can be reached at 619 787 2412. It's the basic kit - frame, suspension, aluminum panels, 'glass body panels (no hood) and the MSO documentation from CMC. Some modification will be required to the diff mount!
entry 1096

January 13, 2006:
I measured up the front suspension upright again and came up with slightly different numbers, but not different enough to make the suspension look like the one on my car.
I need to check the measurements of the car for the third time then I think I'll have it. So far, it's looking as if I lose 2 degrees of camber with 4 degrees of roll. Not so good.

To ensure further distraction, I bought a number of painting supplies today. It's time to learn how to paint my own cars. Maybe I'll start with the spare nose cone.
entry 1097

January 17, 2006:
I took a battery from a power supply home.
It's pretty close in size to the Odyssey I've been considering. Wow, the packaging options are good. I can tuck it up against the passenger's feet, right near the starter, alternator and my main power distribution block and a grounding point. That alone will probably make the price worthwhile, allowing me to move some weight up front while shedding 10 pounds plus cabling. I'll have to open up the transmission tunnel again to remove the old cable but I think it will be worth the effort. It's nice to see something make the car lighter for a change. I'll add in a battery cutoff switch for security, safety and ease of working on the car.

I've been learning about hood manufacturing. Those who are in the business of making metal change shape have been sitting back and laughing at my floundering around. It appears that I could make a hood in a few minutes with access to the right tools. It would also help if I started with the right alloy of aluminum.

And now, the suspension. I've given up on SolidWorks for the time being (cool stuff, I'll come back to that) and I'm using an Excel spreadsheet that someone worked out to determine my suspension behaviour. It's not telling me any good stories - camber loss of 1.8 degrees with 2 degrees of roll. Ouch! The rear looks a bit better, losing about 1 degree. That explains why the car turns in nicely but then understeers in sweepers. I'm still guessing at ride heights from the way my control arms looked at rest. Interestingly, the front roll center appears to be right at ground level and the rear is pretty close as well. No indication from the spreadsheet about how it moves around. I might try entering the numbers for the stock Miata rear suspension to see how it behaves. I'm tempted to stick that in the back without modification and build a front setup that has similar behaviour to the stock Miata front. Ah, who knows. I'll probably hear about a track day and scramble to just reassemble everything.

One note about the aluminum fenders from Coveland. They weigh 1.7 lbs for a 9.75" wide front and 2.8 lbs for a 11.75 lbs rear. I'll have to pull mine off to compare, but right now I'm thinking I'd rather put the aluminum rears on instead of trying to repair my battered unit. Or maybe I'm just scared of a bit of work.
entry 1098

January 18, 2006:
Okay, I've managed to confuse myself.
I modelled the front suspension of the Miata in the spreadsheet and came up with camber curves even worse than my own. I double-checked that against some measured curves and while it's not 100% accurate (that front upright is a bugger to measure) it's close enough to confirm that maybe I don't want the suspension to keep the wheels from changing camber in roll. After all, the Miata setup works pretty well. Argh. I know that too much camber change wreaks havoc with the braking and acceleration behaviour. Maybe the key is just to keep the thing from flopping all over the place - the same tack that Heikki has been taking. So I decided to play with my pushrod design instead. Ahh, that's a lot more interesting to do. I think I've worked out how the math is meant to function. I need to spend some time in the garage with the real pieces to see if what I'm working out onscreen makes sense at all, but I'm getting somewhere.

I've seen comments that I'm really dissatisfied with the handling of this car. Those who don't believe in IRS suspensions (or indoor plumbing I guess) seem to take my car as an example of how it shouldn't be done. I don't know about that - I already know the car's competitive on the track with a Caterham and I do still hold the track record here in town as far as I know. So it's not all that bad. I just know it could be better.

Oh, some news. My new muffler has finally shipped.
entry 1099

Size comparison of an Odyssey-sized vs stock Miata battery.
It's not as if the Miata part is huge, it's that the Odyssey is tiny!
entry 1100

January 19, 2006:
The muffler arrived today.
It looks like a good size, 4" x 22". Hopefully it will hush the beast a little. It's about 9" longer than the current one. For those who are confused as to the muffler saga, I started with a chambered muffler. It blew apart after a backfire. When it was working, it was pretty good but had a rasp at low throttle. It was replaced with a resonator that sounds great at part throttle and is ear-splitted at full bore. This new one should keep things a bit quieter at full throttle due to the extra length but still have nice sound when puttering. Let's hope so! It's certainly free-flowing - I can drop a squash ball right through it. The battery has also been ordered, that should show up soon. The old Miata battery that's in the car right now will probably end up in my Mini.

I finally figured out how to find motorcycle suspension rockers on eBay. They're called "shock linkages". There's quite a variety available, usually along with the shock. Busa parts might work well, although I'll make a journey to our local motorcycle wrecking yard to get some dimensions first. Odd that there should be so many high-performance motorbikes being parted out...
entry 1101

The Solidworks doodle of the pushrod suspension.
It's obviously extremely stylised, but these parts allow me to move the wheel up and down and measure the change in angles and shock compression. I could also work out a math-intensive spreadsheet to do the same thing but this is more fun!
entry 1102

January 20, 2006:
The battery arrived.
It's so cute! It appears I have some fabrication ahead of me. Time to stop screwing around then.

We have a smashed up 2005 Mazdaspeed MX-5 at the shop right now so I'm helping to disassemble it. We decided to simply lift the car right off the drivetrain. It was a lot of fun - but the drivetrain sure looks like it's just waiting for a new chassis. Oh the temptation!

To help other builders, I've put together a PDF of the stock Miata subframes.
entry 1103

The new muffler.
Hopefully this will be it!
entry 1104

January 21, 2006:
Instant diet for a Miata!
A Mazdaspeed gets taken apart. You know, it wouldn't be that hard to make this thing driveable...
entry 1105
The new battery, with cat to scale.
A fat cat yes, but it is a small battery regardless! Those floor tiles are 12" x 12".
entry 1106
A drawing of the rear Miata subframe.
Exciting! A higher-quality version with indications for mounting points is available on scalable PDF.
entry 1107

January 23, 2006:
I spent some cold time in the motorcycle graveyard yesterday and came back with a whole pile of dimensions.
Turns out these linkages are right at the bottom of the bike so they're a little awkward to measure. The good news is that the owner offered them to me for $20/pair. Now, if only they have more than one of each bike! I think there are a pair of Kawasakis, I might pick those up just so I have something to play with as I ponder this. One thing that just popped to mind is that I need to be able to bolt it to my shocks, which means a clevis on the linkage - hopefully I'm using the proper terminology there! The problem is that the motorcycle units like that don't tend to have a central bearing which makes life a little more complex. Otherwise I could just make my own out of two plates of aluminum. That's how Yamaha does it on the R1. What I need is something just like the one used on Fraser cars. They never answered my question about where that rocker came from. It may be a custom piece. Alternatively I could mount the bearing to the frame. Or go custom myself. Ducati has a part that's suitable and so beautiful it hurts.

I've decided that I'm just confusing myself with suspension geometry. My insistence on camber curves that matched roll doesn't make sense and is over-simplified. So maybe I'll just concentrate on cutting down the roll for now. That means bringing up the roll stiffness either through sways, stiffer springs or my pushrod setup. Heikki has already gone this way and stiffened his springs. I've become fixated with solving a good pushrod setup so I think I'll continue along that way for a while. The real trick is figuring out what the ratio between the spring and the wheel should be. I have 3" of shock travel. That's not a lot of wheel travel but it's about what I have in the rear. I've also done some thinking about how to keep the suspension from developing a falling rate. That's important!
entry 1108

January 28, 2006:
A view of the damage to my rear fender.
All the black bedliner will have to come off for a good repair. Sigh.
entry 1109

January 31, 2006:
A set of 10" wheels with 165/70-10 Yokohama A008 tires arrived today.
They're for my Mini, but they're just so cute! A grille for the Seven also arrived courtesy of my friend Chris. Thanks! I'll fit it to the nose of the car tonight and Eric will be filled with joy. Now if only I'd stop being such a baby and get to work on the 'glass repair. It's really just a matter of a few messy hours in the shop. This weekend, I promise.

There's a big project coming up. Eric and I are planning on running the Targa Newfoundland race in 2007. I don't know exactly what we'll be driving yet but I do know it won't be the Seven. Maybe in 2008 after we've had a chance to see what the road surfaces look like.
entry 1110

Finally, some braces for the Seven's open mouth!
This grille was given to me by Chris Fiaccone. Thanks Chris!
entry 1111
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