179 replies to this topic

[Pablo]

Plumber's Nightmare - pans hinged with .032 wires, managed with .055 independent bite bars and .032 down stops, giving about 15 thou tilt

 

[eshorer]

So... the front wheels go up, the guide stays down, the body tilts as it goes around a turn, but shakes off any stress as it loosely holds onto the side pans...  I'm starting to get it.  :-)  What does that "shaker square" in the middle of the pic do? I remember it's on the Lola, too. I just forget what the theory is. A plumber's nightmare, but a driver's dream?  

Eddie

[Pablo]

So... the front wheels go up

 

Technically correct, they can move up in relation to the center section. The La Cucaracha design was called Iso-Fulcrum and it was about a mile. To make the design work correctly, the movement is minimal. You aren't really trying to lift the front wheels. If true, I'd just raise the wheels up in wheelie position and win the race.

 

Front wheels don't exist on wing cars because a super hi-downforce body keeps the car in the slot. Slot cars don't need front wheels to turn; the flag in the slot is what turns it. Front wheels can be the worst enemy of a good handling scale car, especially on old, bumpy tracks. The wheel hits a bump and lifts, lifting the flag out of the slot. The ISO design removes the negative aspects of front wheels by allowing them to "float" independent of the flag. On an ISO center section, the entire weight of motor, main rails, flag, chunk, tongue, etc. is all resting on the flag - and the fronts are allowed to wiggle and flex and lift if they want.

 

the guide stays down

 

Yup

 

the body tilts as it goes around a turn, but shakes off any stress as it loosely holds onto the side pans...  

 

It may tilt a little but tilting isn't really the goal. Greg Wells calls it "de-coupling" and if you look at the history of chassis evolution of scale cars, the best designs de-couple many different things. One area in a slot car you DON'T want flex or movement is the drivetrain. You need some flex in the main rails to get grip. Too much flex the car can't drift right. Not enough flex and you get a spooky handler that tilts out of the slot. Tilting pans are just one of the things it was discovered to work by de-coupling the body and pans from the center section.

 

Look at a top fuel dragster or a funny car going down the strip in slow motion - everything in and on that car is flexing like a living animal. Look at a Cheetah running in the wild, in slow motion - every muscle is moving separately with one shared goal - speed. Same way with a slot car chassis.

 

A SOCAL BP chassis guru gave me great advice for the BP flat track before I started building my Lola - he said "de-couple as many parts of the chassis as you can, and make it heavy".

 

Shakey body mounts are simply another de-coupling. If the body is able to wiggle a little, it won't act like a lever (as much) to influence the car to de-slot.

 

What does that "shaker square" in the middle of the pic do?

 

Just one of those designs that works. It adds weight in a good spot. The reason it needs to be de-coupled is because you don't want to cross-connect your main rails in that area where you need flex. Mike Steube soon discovered split and/or floating bite bars worked better on D3 cars because they don't cross-connect the main rails. He had a car that wouldn't punch the BP King donut. He Dremeled the bite bar in half right in the middle. Instant donut punch. It's in the video, Eddie 

 

A plumber's nightmare, but a driver's dream?  

 

Let's hope so 

[Pablo]

Eddie told me exactly how he wanted the body/chassis relationship to work before I even started.

And it made sense. Similar to the Lola body mount design, but different in the details.

He is the man on the ground and he feels what his track likes.

 

Let's see if the builder guy with the pencil, Sharpie, and calculator with a hot Weller can make it happen.

The owner/driver has to be confident he can put the Lotus on the podium.

 

Mounting the body is probably the hardest part of this build because the body is opaque    

Sharpie dots mark the target spots for axle alignments and body pin holes

 

 

 

My plan for the tubes is similar to a method I used before on a heavily modified Cucaracha chassis

 

 

 

 

[Pablo]

At the risk of sharing my body mount plan and have it not work to my satisfaction and or people being certain I've lost my mind, I'll go ahead and tell you, Eddie 

 

The pan widths are 2 1/4. The body skirt inside widths are 2 3/8. So the pan outer edges at ground zero will not be touching the body hard - it can wiggle.

 

The body mount 1/4 x .032 strips bend up 90 degrees at the pans outer edges. Given the extreme curvature of the body skirts, absolutely nothing is going to touch the body except an .063 retainer at each mounting point. Pins will stick through .063 body holes into the 1/16 tubes which are flopping around inside the .078 holes in the strips. The tube pieces are governed with retainers as shown in the Cuc photo above.

 

The tricky part is, I can't get my eyes or my hands in there to adjust how far out the tubes must extend to meet the body. Here is the math. Men in white coats will be arriving soon with a straightjacket, so enjoy the ride while it lasts   

 

By fiddling with 1/16 tubing, I found the inside length of pin location to pin location in front to be 2.640. Rear is 2.675.

Measured the strips outside to outside, front is 2.295, rear is 2.270.

Fwd math, 2.64 - 2.295 = .345/2 = .1725

Rear 2.675 - 2.27 = .405/2 = .2025

 

Conclusion is, fwd tubes need to extend .1725 and rears .2025 past the outer edges of the strips. We shall see here today .....

[Pablo]

All four gizmos are ready to install on the chassis. I got smart and made four 1/4" long 3/32 spacers so the outer retainers wouldn't get hot and move. See my 3 thou steel spacer tool gizmo?  

 

 

Gizmo installations complete. I checked the measurements, they are +/- a couple thou so I'm happy.

See the droop? That's the magic slop that I'm looking for

 

 

Next step: drill pilot holes in the body and take a peek to see if my math worked   

[Pablo]

Thank God it all worked out fine, not going to the loonie bin after all    Well, not yet, anyway 

Turns out my measurements were right and of course math doesn't lie

 

 

The body is easy to pin and she floats and wiggles just like I planned

 

 

[eshorer]

Looking sharp! Looks like the body's gonna "just be along for the ride," exactly how I like 'em. 

Eddie

[SpeedyNH]

nice work! 

[dc-65x]

Nice work Pablo. You nailed that body mounting.  

 

 

 

 

[SpeedyNH]

hey Pablo, where'd you get the little retainers? i remember those. 

thanks 

Speed 

[Pablo]

Thanks guys

 

Speedy, those retainers are a common item, most all slot car parts places stock them.

 

I set the wheels (.82 front/.93 rear) in place at 2 3/4 widths. Clearances are ok, but the front axle may need to be redone. One side rides slightly lower than the other. Metal moves around and Cox gears aren't the best choice for jig wheels - easy fix. Gives me a second chance to make the wire wraps prettier LOL

 

Despite all my attempts to measure how wide we can make the wheel widths on this car without breaking the rules, another hurdle to jump comes into play - 2 3/4 isn't going to work. Maybe 2 5/8.

 

 

So I have more work to do. Hey, if it was easy your Aunt Sally would be doing it 

[eshorer]

 

Despite all my attempts to measure how wide we can make the wheel widths on this car without breaking the rules, another hurdle to jump comes into play - 2 3/4 isn't going to work. Maybe 2 5/8.

So I have more work to do. Hey, if it was easy your Aunt Sally would be doing it 

 

All the more bragging I get to do if I can get it on the podium with something built at such a narrow disadvantage (starting to milk it ahead of time...). 

 

I didn't have an Aunt Sally, but I'm sure Aunt Gertie couldn't have done any better!  

 

Eddie

[Pablo]

I know what you mean, when a build gets this close to completion, I start thinking "this thing is going in the tumbler tonight" but there is always something that needs tweaking to perfect.

 

In this case, the BB's need to be installed, new front axle wrapped, rear wheels need more trimming, etc.

 

I get PM's all the time from guys saying, "Hey, thanks for showing the working details on your builds, I learn something every time". In this case, my followers may like this failure and fix of my front axle to meet my Q/A standards.

 

When I placed the front wheels on the 3/32 piano wire axle for a clearance check, the left front was a couple thou too low. The RIGHT way to fix it is, sacrifice the wire axle, install a new one. It's not a drill blank axle, it's just a piece of wire. No love lost.

 

Slice and dice with the Dremel

 

 

Apply acid and a hot Weller gun, remove the goober

 

 

Soder-Wick the uprights clean again

 

 

Ready for a new piece of 3/32. This is where I'm glad I make my uprights perfectly 90 degrees vertical - the new one will slip right in no problemo

 

[Pablo]

No matter what I do, I'm back at the start - this little body is just not going to accept big wheels at 2 3/4 widths.

The Pro-Tracks simply won't work. So I'm switching to JK plastic hubs with the hubs flush with the inner sides.

They are only .840 so they need new JK natural donuts installed

 

 

Next hurdle to overcome - outer main rail on right side is now in the way. I tried carving it a little but no go.

A piece of that rail needs to come off. I'm getting good at this "slice n dice" stuff, eh? 

 

[Pablo]

New upright secured and wrapped. Still ugly LOL

 

 

JK hubs narrowed to 13/32 will give me a new (narrower) width of about 2 3/8

 

 

 

[Bill from NH]

Finer ga.. tie wire might pretty up the joints. Next time your at a veterinarian, ask for 10' of their surgical stapling wire. It will be SS.

[Don Weaver]

I've used strands of wire from a lamp cord successfully.

[Bill from NH]

You won't find copper wire much finer than that. I keep lamp cord around, but I'll have to remember slot car uses. Thanks Don.   

[Pablo]

More bracing for the BP Platform legs, new axle up front wired and with inner retainers set for 2 3/8. If the body allows more than that, I can add spacers later

 

 

 

A pair of .025 wires push down atop the ISO management gizmos to soften the front axle/pans lift

 

 

 

[Pablo]

Eddie, this is important for you when you present an ISO car to tech inspection:

In the photo an .055 wire passes way under the rear no problem with the .92-ish OD wheels.

(Pro-Tracks shown for illustration only)

Up front a 15 thou wire passes under the outer rails with lots of room to spare.

BUT the wire BARELY passes under the center section - due to the ISO design.

This is something the tech inspector is going to need to be aware of

 

 

Mid-America ball bearings soaked in lighter fluid to remove any possible factory grease - and there was none

 

 

To me that's a good sign. They soldered up to the tubes real nice

 

 

Inner front axle retainers faced with Magnehone tool

 

 

Front axle ends acid tinned before tumbling. That way the outer wheel retainers can be soldered on afterwards sans acid

 

 

 

 

[Bill from NH]

The ISO centersection replaces not having a drop arm. Not to put words in anyone's mouth, but BPR should tech the centersection clearance the same way  they check drop arm clearance.

[Pablo]

Bill, I understand your point, but this has nothing to do with drop arms.

My chassis has no drop arm and I have not seen any drop arms in BP hardbody classes. 

 

BP hardbody rules are very clear and I do not want to challenge or change them. 

All I want is for my ISO chassis to be understood for what it is. 

 

An ISO chassis prevents track damage better than any other design. That's what tech inspection for clearance is for, isn't it? LOL

[eshorer]

Eddie, this is important for you when you present an ISO car to tech inspection:

In the photo an .055 wire passes way under the rear no problem with the .92-ish OD wheels.

(Pro-Tracks shown for illustration only)

Up front a 15 thou wire passes under the outer rails with lots of room to spare.

BUT the wire BARELY passes under the center section - due to the ISO design.

This is something the tech inspector is going to need to be aware of

 

 

 

I'm not sure what the point is regarding tech. My understanding is the minimum clearance as stated in the rules is the minimum clearance, regardless of drop arm, ISO, shaker pods (Gonzo's), or whatever. If it's teched, and it's too low, it will need larger tires. Am I missing something?

 

I think track damage is the reason the track owner wants to enforce a minimum clearance rule, but I think it's the racers who want it enforced to keep anyone from having an unfair advantage. 

 

Eddie

[bbr]

Use guide washers to space center section for track clearance.
Robert Ahulli built an iso chassis, when racing starts again, check out his chassis.
Marco's chassis had "suspension" front wheels. Static wise they pass tech, but under load the front clearance maybe not. Under braking the car is amazing partly due to the chassis being in a lower cg situation.