LocostUSA.com

So, starting this thread because I want to have a functional version of this death trap this autocross season and having input from experienced builders would be brilliant.

Build Progress
- Framework for cockpit tack welded
- Engine Mounts Mocked Up
- Working on a-arm design
- Swing arm pivot drawings sent to machinist

Have/Need?

Parts List
- Motor 2001 CBR 600 F4i (from totaled race bike milage unknown)
- 4x 2001 CBR 600 F4i Rear Swing arm Coilovers (and linkage)
- 1991 Miata Front Spindles/Brake Calipers/New Slotted Rotors/New Hawk HPS Pads
- 2001 Yamaha Banshee 350 Rear Bearing carrier/axle hubs (stock)
- Wilwood Dual brake Master Pedal

Parts to order soon
- Brake Hard Line
- Kart Steering Wheel + Quick Release
- Desert Kart 14" Steering Rack (+ possibly quickener)

Project has 2 important requirements I will not compromise on.
- Must Be a Single Seater
- Must Conform to Current SCCA A-Mod Rules
However... Due to my fantasies of being able to drive this thing on the street in race configuration in VA
- Swing arm rear (To allow this vehicle to convert into a reverse trike for road use)

So, here's a roughly to scale drawing of the structure I wish to have by this autocross season. (I am 5' 11" that's what the boxes are for)



Critical comments welcome. I'm currently going back to school for Mechanical Engineering (classed as a freshman again), previously an Industrial Design Major and this vehicle I plan to make an evolving project as I learn more and grow as an engineer.

Research - So far I'm half way into Carroll Smith's Tune to Win and I plan on picking up some more of his books.

The first thing that came to mind when reading your post, and something you should steal ideas from, is CalPoly SLO's 2008 FSAE car.

Can your feet be forward of the front axle centerline like that?

nick47 wrote:Can your feet be forward of the front axle centerline like that?

Is that a question on is it physically possible or is it a question of should you be doing that? there is room, currently.

Letze wrote:

nick47 wrote:Can your feet be forward of the front axle centerline like that?

Is that a question on is it physically possible or is it a question of should you be doing that? there is room, currently.

He might be asking as regard competetion rules. IIRC, in trhe SCCA GCR book, feet fwd of the front axle is prohibited in the sports racer classes, but I don't think it matters for Solo1 or 2. Other sanctioning bodies might have diferent requirements.

generally, feet fwd of the axle is considered a no-no, because in any kind of fwd crash scenarion, well, the human foot/lower extremity makes a really bad crash-absorption structure. two feet arent' really much better.

robbovius wrote:IIRC, in trhe SCCA GCR book, feet fwd of the front axle is prohibited in the sports racer classes, but I don't think it matters for Solo1 or 2. Other sanctioning bodies might have diferent requirements.

It's the front edge of the wheels, not the axle centerline. I also don't think it matters for solo but, if it were me, I'd ask the Solo Events Board for a clarification before I started cutting tubes.

It doesn't matter for solo (the solo rule book never prohibits it) and the GCR only really applies to road racing or solo classes using GCR legal road racing cars or where referenced in the solo rule book.

Well I'm back on front suspension and steering geometry.



Since I'm using the miata hubs, I stayed close to the miata Geometry

Targeting 6 degrees of caster and 1.5 degrees of camber in the front with adjustment for +2/-2 the a-arm design. Camber adjustment will affect caster but given my fabrication limitations and engineering understanding I have right now I'm willing to live with it until the second or third iteration of this vehicle.

One thing I'm currently debating is steering, I was considering the DesertKart.com steering rack, I was familure with it from my time on the BAJA SAE team, our kart ran their rack with a steering quickener and the solution worked for a slow vehicle like our baja buggy. However, during a recent driver training session with one of the old buggies. I was reminded of the slop, this buggy has only done two competitions and there's a relatively pronounced slop in the rack that would be unnerving above 40 mph.

This kart's primary activity will be short autocross runs, and I'm wondering if there's something I'm missing or under estimating by going with a steering setup without gearing. I'm used to endurance karting at tracks like Summit Point and VIR, but most of these karts; peak at 35 mph and have no suspension, have small diameter tires, and have significantly less mass which I believe makes the comparison moot.

Cons:
- Pronounced feedback from road surface (counter with steering dampener?)
- requires more force to turn
- Greater driver fatigue

Pros:
- Simpler to implement
- Quicker Ratio
- Cheap...

With the solid rear axle this car will be prone to understeer and snap oversteer. something else to consider.

what a coincidence I ran across this, I've recently had thoughts along the same lines as this, but with a driving position more like a Locost or a front engined 750 Formula car, using a big single or a ~650cc twin as the powerplant rather than a 600cc sportbike motor.

Have you thought of offsetting the motor/swingarm (if you're using an actual ATV-derived swingarm) to one side, offsetting yourself to the other side and moving the seat rearward in the car? That would solve the issue of your feet being forward of the front axle centerline without lengthening the wheelbase, and from what I've read, moving your head rearwards relative to the center of the wheelbase makes a tail happy car feel a tad more comfortable to drive, since a slide is felt less as a yawing motion and more as an actual sideways motion if you're further back and thus you notice it earlier and can correct for it quicker. it will make the chassis wider and it will make the car feel and look less like a baby formula car and more like, well, a really tail happy locost, but it might be worth looking into, and if you're open to it, it would make packaging a lot easier since you'd have more room to work with within the same width and wheelbase.

Also, being a swingarm rear end, I'm not certain it will understeer quite as much as you may think, even with no diff and sticky race slicks. you've got infinite geometric roll resistance at the back (ignoring any rear end roll that results from tire deformation), so if the chassis is going to roll at all, it has to come from the front end, which is going to make the inside rear tire VERY light and very likely cause it to lift off the ground completely, like a lot of the front wheel drive ST_ class AX cars do. This will definitely help with understeer, since the rear tires will no longer be fighting each other, but you'll have to take it into account when choosing your rear tire sizes in addition to static f/r weight distribution. To keep the car from feeling like it's falling over on the outside front, I'd be tempted to place the front roll center fairly close to the CG height, that way you get more geometric roll resistance (lower front roll couple) without having to run a HUGE front swaybar or super stiff springs. If the front roll center seems like it's going to dive a lot under braking and you can't design that trait out of the car, consider adding a little bit of front anti-dive, otherwise the car is going to want to fall over on the outside front if you trail brake into a turn, which could make the car VERY sensitive to turning and braking at the same time.

This looks like an awesome project and I would love to see where it goes!

Thanks, I was working on the front end this weekend with a friend of mine, we managed to build the two sections where the front suspension will mount however we didn't get a chance to mate them together. This should be ready shortly with plenty of photos come this weekend. One element of my build will amuse and confuse some folks the build table, more on that this weekend.

the only portion of the swing arm from the ATV I'm using is the baring carrier mount, I'm fabricating a new arm portion to fit my application more adequately since the static height and shock angle are going to be quite different from a banshee.

I have consider having the motor beside the driver, much like it is in a Mini Sprint car however given my axle choice it was going to be an engineering feet I wasn't prepared for just yet. This vehicle will be a learning platform for me, I foresee it getting hacked up and modified while i'm going to school. though considering I have too many spare motors for my R6's I may just build a second that way I can learn/develop both platforms. luckily once I resume full time classes next year I'll be able to really be able to stretch my capacities.

I think I'll still maintain the goal of making the vehicle a "convertible" as the main design principle even though it introduces interesting problems, but that's what engineering is about, solving problems.