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#26 blue&orange

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Posted 27 March 2020 - 09:01 AM

To the best of my knowledge a centerline hinge was never used on the scratch built chassis' in the 1966 to 1968 time frame. Which is the time period the modern IRRA cars are emulating, but not necessarily duplicating. In fact even hinges running in directions 90 degrees to each other weren't a feature on the inline cars of that time frame and only came about with the anglewinders of the late 60's. Note that there could be an exception or two built by someone somewhere to what I've said above but I believe that it is true to a great extent. 

 

BTW... A centerline hinge is indeed possible and was a feature that many of the late '90s and early 2000s Eurosport cars had, definitely not retro in the IRRA sense.

 

Re:  no hinges until anglewinders. Car Model magazine, March 1968, shows the inline Jail Door car of Jerry Cowan that won the fifth Car Model Race with hinged "outriggers." Yes, stay-at-home is a good time to re-read old mags.


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#27 Dallas Racer

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Posted 27 March 2020 - 10:00 AM

I'm sure not the only one to think about this: Why do chassis' need movement in the first place? Modern tracks are super smooth. Motors are balanced. Where's the vibration coming from?

 

The only thing I can think of is the inside rear tire going over the slot when the rear end swings out in a corner and returns to center after the corner. Since the braid is recessed, it creates a gully. The inside tire drops into that, and pops back out of it, as the rear end swings across the slot. And does it again as the rear end swings back across the slot exiting the corner. So that happens twice every corner, at least it does on flat corners that are not sweepers. That has to really upset the chassis and create a lot of vibration. This would possibly explain the effectiveness of a center hinge and/or torsional flex.

 

Or so it seems to me. What do y'all think?


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#28 crazyphysicsteacher

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Posted 27 March 2020 - 11:33 AM

I am following this very well. The question is why the rotating center rail, well it only rotates on one end. That means it does not effect the rotational stiffness but will allow for more stiffness and bite in the longitudinal direction the rail can also be adjusted to change where that happens. You can do the same type of tuning by placing wire at points along the rail. If that wire pushes against the pans under acceleration it can stiffen the chassis that way but will not change the rotational flex.

I have been using tuning fork chassis's now for my coupe and can am cars and have some pretty good success on flat tracks with them because of how I can better tune the flex.

Now, you can also gain control of flex by using brass rails instead of steel. You get the damping effect since the brass does not have the same spring as steel. Retro lets you try many different ideas, kinda the appeal of it.


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#29 old & gray

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Posted 27 March 2020 - 01:40 PM

I'm sure not the only one to think about this: Why do chassis' need movement in the first place? Modern tracks are super smooth. Motors are balanced. Where's the vibration coming from?

 

First consider the problems which occur with a solid axle going around a corner. The tires are trying to twist the guide toward the inside of the turn when the weight transfers to the outside rear tire. (Unequal forces acting on the center of gravity.)

 

The inner tire slips (less force, less traction), if this slip were linear this would not be a problem; however the tire stretches and contracts as the traction grabs and slips which results in vibration.

 

Additionally we need to look at the gear drive; while gears can be extremely forgiving examining the actions of two gears in mesh will show that during the contact period there is rolling and sliding contact. There will also be a small variation in speed as the tooth engagement moves from the outer to inner point of contact. These issues decrease as the number of teeth engaging increases (48 to 64 to 72 pitch) but other issues occur.

 

This is not an entire picture vibration in a slot car but should help explain some of the problems.


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#30 MSwiss

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Posted 27 March 2020 - 02:20 PM

I certainly know chassis theory, but I think it's important to also keep an open mind, because slot cars don't always make sense.

An example is the FCR. How do they run as well as they do, with zero movement?

Granted, if one had an articulated FCR chassis, it most likely would handle a bit better.

But how does it get (adequate) bite? It's stiffness is in another stratosphere compared to just about any slot car chassis.


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#31 tonyp

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Posted 27 March 2020 - 02:32 PM

The weight.


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#32 MSwiss

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Posted 27 March 2020 - 02:47 PM

I'm going to say "No," and guess you have never driven an FCR.


Mike Swiss
 
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#33 Cheater

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Posted 27 March 2020 - 02:51 PM

I agree with you, Mike.

 

I was amazed the first time I drove a properly set-up FCR and I also have no idea how that chassis can work as well as it does when correctly tweaked.


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#34 MSwiss

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Posted 27 March 2020 - 03:17 PM

I wouldn't rule out voodoo. LOL.


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Inventor of the Low CG guide flag 4/20/18
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#35 Bill from NH

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Posted 27 March 2020 - 03:50 PM

The 4.5" FCR runs pretty good when set up right. The 4" FCR chassis always seems like it has a virus.

 

Back on centerline hinges, not every using them has the hinge in the same position. Sometimes, they're placed just ahead of the motor box, other times they're upfront, immediately behind the guide post. It's still a popular item to put on 1/32 scratchbuilts. Look at some of the proxy race cars.


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#36 JerseyJohn

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Posted 27 March 2020 - 04:55 PM

The primary reason is that the creators of the IRRA rules in 2007 sought to simplify chassis construction, and not to permit overly complex chassis designs with a multiplicity of movements and elements, with the idea being to lower the time needed to scratchbuild a chassis to run under that ruleset, and thereby to lower the barriers to participation.

 

LOL you haven't seen a Bonanno chassis, Greg. Nothing simple about it. Might be time to revisit that rule...

 

90697956_2508375062761429_3813780583453032448_n.jpg


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#37 MSwiss

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Posted 27 March 2020 - 05:41 PM

J.J.,

 

No need to revisit the rule. There are legal chassis out there way more complex.

Just like the paint jobs, racers can make them simple or complex.

They just can't have a center hinge.

BTW, that's an Andrew Ford design.


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Eight-time G7 King track single lap world record holder

17B West Ogden Ave., Westmont, IL 60559, (708) 203-8003, mikeswiss86@hotmail.com (also my PayPal address)

Note: Send all USPS packages and mail to: 5858 Chase Ave., Downers Grove, IL 60516


#38 tonyp

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Posted 27 March 2020 - 06:16 PM

Nothing on Jeff’s chassis comes close to skirting the rules.


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#39 MSwiss

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Posted 27 March 2020 - 06:35 PM

The only thing I notice (unless I'm missing something) is that it looks like it's going to drag the brass squares in the front of the chassis.

Below is a pic of Greg Mayer's super-sano version of Andrew's Moonshine Special.

post-173-0-81822900-1581476651.jpg

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Note: Send all USPS packages and mail to: 5858 Chase Ave., Downers Grove, IL 60516


#40 crazyphysicsteacher

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Posted 27 March 2020 - 07:36 PM

JJ, those chassis are designed around a different principle. I have talked with some and they are designed to separate the body movement from the drivetrain. Kinda like the famous two-in-one Lotus Formula One chassis of the past. I just rebuilt one of mine to a similar strategy after talking with one of the Retro East racers. I am hoping my mods help.


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#41 Cheater

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Posted 27 March 2020 - 08:57 PM

LOL you haven't seen a Bonanno chassis, Greg. Nothing simple about it. Might be time to revisit that rule...


J.J.,

My thinking at the time, and I feel the same way today, was that we should define a restricted 'envelope' of allowable constructional parameters within which builders would be permitted to innovate. I felt that would be a better approach than letting builders do as much and go as far as they might want.

 

The history of Retro so far makes me believe it was indeed the correct approach. YMMV.


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#42 Jay Guard

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Posted 27 March 2020 - 10:12 PM

I like the more basic chassis designs.. .like my Weightshifter v3.0, just like in the '60s. :-)

 

IMG_2028.JPG


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#43 Dallas Racer

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Posted 27 March 2020 - 10:37 PM

That's really clever, Jay! :good: 


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#44 Cheater

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Posted 27 March 2020 - 10:56 PM

Don't encourage him, Phil. He's already having trouble finding hats big enough...


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#45 JerseyJohn

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Posted 28 March 2020 - 01:20 PM

My point was not all about the physics or the reasons for a center hinge. or why Jeff and Andrew build their wild machines. It just seems to me that the reason it is banned is because they need to ban something so let's take something that no one really uses and ban it. So as to say, see, we do not allow everything. 

 

How about you hold out on pillow blocks instead LOL. I would love to try a center hinge chassis and see what it does.

 

To me it's like banning plastic straws but it's legal to burn out your lungs by smoking drugs. LMAO.

 

I am done on this topic.. next!


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#46 Cheater

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Posted 28 March 2020 - 01:27 PM

“I can't give you a sure-fire formula for success, but I can give you a formula for failure: try to please everybody all the time.” 

 – Herbert Bayard Swope


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Never forget that first place goes to the racer with the MOST laps, not the racer with the FASTEST lap


#47 MSwiss

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Posted 28 March 2020 - 01:45 PM

My point was not all about the physics or the reasons for a center hinge. or why Jeff and Andrew build their wild machines. It just seems to me that the reason it is banned is because they need to ban something so let's take something that no one really uses and ban it. So as to say, see, we do not allow everything. 
 
 I would love to try a center hinge chassis and see what it does.

 

Wrong, J.J.,

 

You were not privy to our rules discussions, so I find your "the man is just trying to keep us down" post, ill-informed, comical, and rude.
 
Center hinge chassis did not get banned. They were never allowed to begin with.
 
The "no center hinge" is just a carryover from the original SoCal D3 rules Paul Sterret (and others?) came up with.
 
The founders of IRRA found wisdom in that rule, were fine with it, and kept it.
 
Feel free to build a center hinge chassis. Feel free to build anything.


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Mike Swiss
 
Inventor of the Low CG guide flag 4/20/18
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Note: Send all USPS packages and mail to: 5858 Chase Ave., Downers Grove, IL 60516


#48 JerseyJohn

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Posted 28 March 2020 - 02:08 PM

LOL Mike i can always count on your entertaining sarcastic responses. I had no plans of ever building a center hinge although im interested in its performance. My curiosity was more the reasoning in it not being allowed.. I never met a argument i didn't want to jump into. usually when people so vehement apposed to something it is because they are afraid of it. What are you old guys afraid of ????


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#49 MSwiss

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Posted 28 March 2020 - 02:18 PM

I already explained in my post that it's a carryover from the beginning of Retro, from someone who passed a 5+? years ago.

Did you miss that, or just fell asleep before you got to that part? LOL.


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Mike Swiss
 
Inventor of the Low CG guide flag 4/20/18
IRRA® Components Committee Chairman
Five-time USRA National Champion (two G7, one G27, two G7 Senior)
Two-time G7 World Champion (1988, 1990), eight G7 main appearances
Eight-time G7 King track single lap world record holder

17B West Ogden Ave., Westmont, IL 60559, (708) 203-8003, mikeswiss86@hotmail.com (also my PayPal address)

Note: Send all USPS packages and mail to: 5858 Chase Ave., Downers Grove, IL 60516


#50 Cheater

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Posted 28 March 2020 - 02:18 PM

J.J., who are you calling old? You ain't no youngster yourself, you know... LOL.

 

The IRRA rules were created with specific goals in mind, as was previously related. For myself, I can accept the fact that you may not understand, agree with, or support those goals. See again my post #46.


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Gregory Wells

Never forget that first place goes to the racer with the MOST laps, not the racer with the FASTEST lap






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