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Functions of chassis design question(s)?


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#1 Shruska55

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Posted 21 March 2020 - 12:23 PM

When I raced 1/24th scale in the late 60s early 70s, everything was anglewinder. We played a bit with pure sidewinder chassis, but since I was 14, I used the chassis guide sheet Parma distributed and copied that chassis design when building my own kit. It had hinges EVERYwhere. And, again, at 14, I did not spend enough time understanding the physics of the sport at the time. Then, life got in the way and slot cars faded because, well, I discovered girls.

 

That said, 50 years on, chassis performance dynamics have changed. Physics hasn't however So...Is there a thread or link to a page which has a Chassis Performance Dynamics for Dummies? Something that explains terms such as 'slider', 'shaker', 'torsion', 'fixed' et al and how they apply to performance issues in language that a neo-chassis builder will understand? Assumptions here are (but not limited to): The type of track. e.g flat, speed, twisty, long straights etc., driving style and the 'and all other variables which apply' caveat.

 

I also understand that physical forces affect directional motion of the car. I've read the tripod threads, length to guide flag recommendations, understand the front axle outrigger et al. I've watched Tony Ps youtube vid, bought the MIke Stuebe vid, scoured SlotBlog and other sites for information. While there is quite a bit of knowledge out there and fantastic, (and fantastical) chassis designs, it is presented n my opinion, with the added assumption that one understands the underlying principles of why the builder chose a specific design ethic.

 

What I want to understand before I cut that first piece of piano wire is very basics of design concept, if that is possible. (..and only in 1/24 scale for THIS iteration!). F?Y: I'll probably be looking for a Chassis Tuning for Dummies How-To down the track.so to speak.

 

If this info is out there and I've missed it, please accept my mea culpa and point this heretic to the source.

 

Thanks,

ScottH


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#2 Ramcatlarry

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Posted 21 March 2020 - 12:59 PM

Technical guides may have 'truths' at a point in time.  Over the years, track design, tires, traction compounds, and especially racing organizations rule changes what are 'better designs'.  It is still up to the driver to be able to make the difference in driver skills and now - new controller differences.

 

It seems to me that each classic body style has unique chassis designs that work for them.  If we limit the design elements to just the current design parameters of 'retro racing' of can/am and F-1, then it is easier to focus on design elements.


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#3 Don Weaver

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Posted 21 March 2020 - 01:58 PM

The only "primer" I know of is experimentation using a winning design at your track as a starting point.  If you follow the Scratch Building forum here you'll see how designs have progressed over the years, i.e., 1 & 2 rails of 055 or 063 to multi-multi rails of 039, 032 and even 025 as an example.  Jim Fowler's and CMF3's threads are also a good place to see how changes affect performance.

 

Don


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#4 Pablo

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Posted 21 March 2020 - 04:04 PM

May I be so vain as to recommend my personal subforum as one source of explanations?

I have made many different syles of custom and race cars over the years, and I always try to explain what and why I do things.

 

I learned from all the masters. Feel free to read my sandbox and if you don't understand something send me a PM for further explanations. Or you can immediately begin by building a replica of 1969 era pro car; by the time you finish you will know all about motors and chassis, etc.  :D

 

http://slotblog.net/...-pablos-builds/


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#5 Bill from NH

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Posted 21 March 2020 - 08:02 PM

Scott, if you have access to the vintage Car Model magazines, or know someone who does, there were some articles by Pete von Aherens (NJ) & Mike Morrissey(CA) that might help answer some of your questions. These magazines also had many chassis build articles from those with simple designs to others which were more complex. None of this old information is apt to make you an immediate race winner today, but it'll provide a good foundation if that's what you want to achieve. As a worst case, you can learn how to construct some good running slot cars.


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#6 Shruska55

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Posted 21 March 2020 - 10:11 PM

Thanks to all for the inputs and Bill H, yes, I want a good foundation to build better cars in the future! Of course, I need to figure out how to build that first one...

 

I'll soldier on and see what I can discover along the way!

 

All the best,

ScottH


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#7 Greg VanPeenen

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Posted 21 March 2020 - 11:16 PM

Scott, 

 

If you want to see Retro Chassis that show no race results to show they are not just Perfect (LMAO) and pretty.  Look at some on this blog. Not all but some.

 

On the other hand, if you want to see Chassis Designs that really win big races, look at the Race Reports on this blog and the other Blog. That way you can see what is being built that really works and wins races. 

 

I wish you the best of luck if you start building. But remember pretty does not always win races but a superior design does, Oh yea, and if it don't go chrome it. 

 

Regards,

Greg VanPeenen

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#8 Bucky

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Posted 22 March 2020 - 08:02 AM

Coming up on 24 hours, and there's no actual theory being shared. I'm not sure if that's due to guys trying to keep their knowledge secret or just evidence that it's trial and error for all of us.

I wish I had more to add, but I'm more of a trial and error guy. Even when I've had good results building and testing I couldn't tell you why the design worked.
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#9 Pablo

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Posted 22 March 2020 - 09:31 AM

Lots of great info here also:

 

http://slotblog.net/...scratchbuilder/


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#10 Dominator

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Posted 22 March 2020 - 09:32 AM

Now that I was able to pry the laptop away from my daughter I can try to give some of my points on design.

 

Vertical and rotational articulation goes in hand.  Small changes can make a huge difference.  Regardless if your building for fun or for weekly/series racing the following will get you on the right track.

 

In general the most common rail configurations used in a straight line are the following based on inline motor designs:

  • single rail of .078 (one rail per side)
  • two rails of .062 (two rails per side).  Some will also use use a .062 and .055 rail per each side.  This will allow a little more vertical flex.
  • Eight rails of .047 (four rails per side).  With this design most add a piece of .025 wire about 1" long just in front of the motor bracket to limit the vertical flex.
  • As a rule of thumb when you down side in rail diameter you need to add a minimum two rails.  So the next step down from .047 would be 10 rails of .039.

When assembling a chassis some builders will leave the middle portion of a multi-rail design un-soldered.  This will all the chassis to have more rotational flex but still have almost the same vertical flex as the same rail configuration that is soldered from end to end.  When using .047 wire or smaller it is necessary to add a limiter of some kind to limit the vertical flex so the car does not bottom out on higher speed tracks.  Placement and length of the wire can affect the vertical flex.  Here is an example of my F1 design with eight rails of .047 that has a .025 wire at the rear of the bracket to limit the vertical flex.  The .025 wire is un-soldered in the middle.

 

82215629_493061091347810_462016946360025

 

Wish bone designs are also popular but a little more tricky to build.  Here is one of my wishbone designs that uses six rails of .047.  The wishbone is joined using 1/4" wide .016 brass with .062 rails.  The .047 rails by themselves would have too much flex both rotation and vertically.  The wish bone limits the vertical and while giving optimum rotational flex.  This design just happened to work well right out of the box. 

 

81451895_493061154681137_755187315297694

 

These rail configurations are the most commonly used.  Guide leads (measured from center of guide post to center of front axle) are usually 15/16" or 1". Wheel base (center of front axle to center of rear axle) are usually 3-15/16" or 4". 

 

What does a shorter guide lead do?  A longer guide lead will be easier to drive into the turns.  Sometimes with F1's I have found they can be a little loose coming out of the turns. 

 

What does a a longer wheel base do?  Longer can be more forgiving especially on flatter style tracks.  Shorter wheel bases can be faster exiting the turns and on higher speed tracks. 

 

If you look under the parts counter you can download my build tutorials for each of my designs which can be applied to most any build. 

 

Pablo's builds are also very well documented and Tony P's.  


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#11 scaleuser

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Posted 22 March 2020 - 09:37 AM

if the chassis is all one piece it has a single resonance so all forces act on it as a whole. The force against the guide in a corner is unified. Breaking the chassis up in pieces means each piece has its own resonance. The hope/assumption is that they essentially cancel each other. Really helpful would be damping yet there is no viscous damping. Metals are springy and the only suspension is the undamped tires. Mixing brass and piano wire probably helps. People are using vibration tape to create damping. Twist-O flex is important yet again it has to be damped. I'd say this is the idea behind the wish bone where the the tubes along the sides of the motor are not soldered to the rods inside them. Those slip joints tend to damp the twisting along the center axis.

 

Also inline layout is a huge equilizer. If you look at winning chassis pics you see a pretty big variey in basic apperance. Some have wings ahead of the front wheels some have nothing up there. The main rails are not all the same some have the wish bone and some don't.

 

Turning the motor sidways must put the gryroscopic stability cross the chassis evidently a huge improvement. Yet I totally understand the desire not make it about speed but keep Retro about the pure creativity of working with the inline and recreating the Can Am period.

 

I'd like to see Retro anglewinders strictly as a Flat Track class.

 

Of course wing cars are all one piece which is why they only stay in the slot at speed, where the massive aero trumps all other forces. Down force increase exponentially with speed it's not a miracle.

 

 

I'll leave it here before some prolific builder weighs in.

 

Too late. Great specific info from Pablo and Dominator. 


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#12 tonyp

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Posted 22 March 2020 - 05:13 PM

Short cars are faster on a high bite track. A longer car is more forgiving and easier to drive on a bumpy or slicker track.
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#13 Shruska55

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Posted 25 March 2020 - 06:34 PM

Great tips as always!

 

For me, in any development project, having a baseline from which to experiment/proceed is what I look for first. Each of the above comments have been helpful and filled the baseline requirement.

 

I doubt I'll ever race wing cars. My brain doesn't move that fast anymore! Flat tracks are my bag. I've seen quite a few variations on theme with the tuning fork, but also simple flex designs. Now that I have a handle on this, I need a Retro F! chassis. Guess where I'm going to start this adventure?

 

I'll post some pics along the way and would very much appreciate critiques. I'll note if it doesn't run well and feedback as to possible causes is welcome as well.

 

Thanks again for the inputs!

 

ScottH


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#14 MSwiss

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Posted 27 March 2020 - 02:11 PM

Knowing basic chassis theory is very important, but also keep in mind 2 important laws in slot racing.

1-slot cars don't always make sense.

2-the timer is all that matters.

A sample of slot cars not always making sense would be an FCR.

How does it get any bite?

It's a stiff, solid board, but yet it runs fine, and gets plenty of bite.
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#15 Tim Neja

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Posted 27 March 2020 - 03:25 PM

Knowing basic chassis theory is very important, but also keep in mind 2 important laws in slot racing.

1-slot cars don't always make sense.

2-the timer is all that matters.

A sample of slot cars not always making sense would be an FCR.

How does it get any bite?

It's a stiff, solid board, but yet it runs fine, and gets plenty of bite.

Well Mike---like a wise man once said----"IT'S ALL ABOUT THE RUBBER" :)  :)


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She's real fine, my 409!!!

#16 Shruska55

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Posted Yesterday, 04:11 PM

Thanks MIke,

 

The bumblebee shouldn't fly, but it does. We don't know why though new studies give hints! 

 

The reason I'm asking for basics and functions is to honor that idea...that something just shouldn't do what it's doing...

 

The way to find out what something shouldn't do, is to find out fundamentally what that something Should be doing.

 

Once I figure that out, I can shake my head and run a fast race with my new and improved bumblebee chassis design. .LOL

 

Scott


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#17 Dominator

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Posted Yesterday, 08:35 PM

Scott, one more thing I thought of to add to this discussion is motor bracket width.  The narrow the motor bracket the more rotational flex the chassis will have.  The most popular sizes are .750", 1", and 1.365.  Chicago Land recently introduced a .875" wide bracket. 

 

Using a .750 bracket with say 8 rails of .047 (4 per side) will have more rotational flex than a 1" wide bracket with the same name of rails. 

 

The below chassis has a 1.365" motor bracket and a rail configuration of .062 inside rails and .055 outside rails.  The original design had the .062 rails on the outside and .055 on the inside.  I was at my first fall brawl and found I needed a little softer chassis.  So I build one of these during the F1 race on Saturday to run Can Am on Sunday.  Moving the smaller rail to the outside gave the car slightly more flex and made it more driveable on Speed Zone's Engleman.  I qualified 6th and I think finished 6th in the main.  Proof small changes make a big difference. 

 

73056843_439605846693335_708119191755109 


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#18 Shruska55

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Posted Yesterday, 11:21 PM

Dominic,

 

That is gorgeous! 

 

If I'm understanding things correctly, the side pans and, what in my words, the center pan, all slide front to back? No 'shakers' on this chassis?

 

Also, the smaller gauge on the outside offsets the rigidity of the wider motor mount? The chassis then has the stability of the wider rear wheel base with the flexibility of a narrower motor mount, if I understand correctly.

 

Most impressive to me is building that beauty in between heats! Not certain I'll ever get there.  :dash2: But then...there is that bumblebee thing...
 

Thanks,

Scott


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#19 Dominator

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Posted Today, 07:41 AM

Scott,

 

The side pans have .002"-.003" of front to back movement.  The up and down movement is limited using a piece of .055 wire (pan stop) inside of 3/32 square tubing.  This give the pan about .020" of vertical movement. 

 

The center weight or pan has some front to back movement and is held in place with a standard straight body pin.  The vertical movement is limited like the side pans. 

 

You are correct on the rails and on the wider bracket.  When retro began 10+ years ago most used a 3/4" or 1" bracket with an axle tube (7/32" O.D.) length of 1.4" which ran through the bracket.  The down side to this is adding adequate bracing for strength which is difficult with a 3/4" bracket.  The tubes needs to be braced well not only crashes but to ensure speed is not lost in the turns when the chassis flexes.  Using the 1.365 bracket give better strength and offers similar rail configurations.  If I remember correctly, Bryan Warmack and John Gorski were the first to use a wide bracket.  I think I remember a Retro East report from season 1 or 2 where Gorski used a wide bracket in a F1.  Chicago Land (Mike Swiss) was first to mass produce these. 

 

Thanks for the compliments on the chassis.  Where my chassis are machined instead of stamped I can usually have a completed chassis in about 2-2.5 hours.  Lot's of great kits out there to work with and get idea's from. 


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#20 Shruska55

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Posted Today, 11:28 AM

Dominic,

 

Thank you for the detailed explanation. The old lightbulb above my head is beginning to show a glimmer of shine. 

 

Lastly, (for a while anyway!) a specific rules related question which is open to everyone.

 

The following is from the currently published IRRA Rules and is the same for the non-Pro Retro Can-Am and F1 classes in which I currently participate.

 

 

4. Hinged Movements: Other than a drop arm, all hinged movements must be oriented in only one direction on any individual chassis.
4a. A chassis may have transverse hinges (examples: Iso-fulcrum hinges and plumber hinges) or it may have longitudinal hinges  (example: side pan hinges) but the chassis may not have both types.
4b. The number of individual hinges is not

restricted.
4c. Centerline hinges are not allowed.

 

Based on this IRRA rule, your beautiful chassis would be legal based on the fact that all of the hinges used are longitudinally oriented. Is that correct? The chassis would become illegal based on this IRRA rule if a transverse hinge(s) were added, for example, to the front of the pans? The Pro Retro rules allow that mod BTW.

 

I used the mod option for illustration purposes only. The reason for asking, however, is that I want to build my competitive chassis legally under the Class(es) rules where I race. Experiments and prototypes are a whole different thing.

 

Please feel free to continue adding your thoughts. I encourage other builders to contribute as well. I believe that other Members are interested in this topic. for example

 

Now to put this information to work.

 

Thanks for taking the extra time to explain. I appreciate it!

 

ScottH


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