42 replies to this topic

[Steve Okeefe]

This is for the Old Geezers (like me)...  Your opinion is solicited.

 

 

If you are sure you know a slot car drop arm when you see it;

 

1. What are the defining characteristics of a drop arm?

 

In the 1960s, drop arms were standard feature on virtually all pro cars, but by 1974, they were all gone...

 

2. What purpose does (or did) the drop arm serve?

 

And the $64,000 question: It is accepted that drag racers were the first to install drop arms or their cars.  However:

 

3.When did the "drop arm" first appear on road cars?

 

 

To get this going, I'll start:

 

1. A drop arm is an isolated mass with a transverse hinge on one end and the car's pickup-guide on the other.

 

2. The drop arm separates the function of the pickup-guide from the function of the front wheels.

 

3. Mid 1962.

 

What say you?

[don.siegel]

In response to 2, I would put it more like: 

 

A drop pickup is designed to keep the guide/pickup brushes in/in contact with the slot/tape independently of the attitude of the front of the car. 

 

Agree with your other answers. 

 

Don 

[Steve Okeefe]

Don,

 

Good!  Thanks!

 

Anybody else...  Or do I have this nailed?

[Don Weaver]

A drop arm was used because of rough tracks and those that had built-in bumps like the American Red and the original Orange..  Besides, they're just kool!

 

Don Weaver

[Steve Okeefe]

Don W,

 

Kool they are, no question.  Slot cars are all about electro-mechanical kool-ness, and the more mechanical and electrical they are, IMHO, the better.

 

Your observation about rough tracks and tracks with built-in bumps illustrates, I believe, one of the key differences between tracks of the 60s and current tracks, which are waaaay smooth by comparison.

 

Cars running on rough tracks, etc. need the drop arm (regardless of what year it is) to help keep the pickup-guide in the slot and in contact with the tape/braid while the front wheels bounce around on that rough surface or leave the track suface altogether when going over the bumps.

 

Conversely, when running on smooth surfaces, the drop arm doesn't really have a lot to do (except look kool), so many years ago builders eliminated it from their designs because it no longer served any purpose.  On a super smooth surface that is almost true, modern Retro-Racers demonstrate this at every race, but what kind of bugs me is that there are a few folks out there who go on to presume the drop arm NEVER served any purpose, which is wrong.

 

Thanks for the input, Don

[SlotStox#53]

Drop arms do serve a purpose , they R definitely Kool as you and Don both rightly say Steve

but also still to this day on some club tracks that have hills or humps their mechanical purpose in helping braid contact and the whole front wheel thing are both still relevant

Nothing like a nice slab of heavy brass sitting there in drop arm guise that's what's missing in retro chassis !

[Don Weaver]

Drop arms from brass rod with a brass weight on top of them are way kooler than from brass "slabs".......

 

Don Weaver

[Pablo]

Random thoughts:
-It allowed wheelies.
-It allowed the marshal to see the flag in order to position it in the slot.
-It allowed the flag to stay in the slot when the front wheels hit bumps.

Greg Gilbert owns a Foamy retro chassis that is a winner and has a plate droparm.
It is just one more point where the chassis is de-coupled and allowed to move.

[Duffy]

Hm. Pretty happy you guys're institutionalizing the "kool" factor, it's the real reason we do this in the first place!

 

I wanna observe, tho: on a bumpy track, every bit of mass is subject to the elevation changes, including the big brass collar. The concept that it's gonna obediently follow the ups&downs of the track contour while the rest of the chassis is launching into clean air is just wishful thinking.

 

We geeky types actually discussed this in '65 in Santa Rosa CA. For a while there was a lot of experimentation with light springs on the drop arm, not near enough to push the front up (we told ourselves) but enough to have a delaying effect on the droparm's launch. It probably contributed more to mini-wheelies than anything positive.

One thing I do remember in this same venue (a real Slots-engineering backwater I guess, since all the real action was happening in LA), we tried flimsy front axles: The idea was, there's more reactive mass in the tyres than just about anywhere up front, so if we delay the reaction of those we can spread out the reaction in the chassis.

This actually came out of Mickey Thompson's memoir, where he talked about putting the axles in solid in Challenger I - 'cause the wheels would be several yards down the road before the mass started to react to a bump. Okay, it's not really that way, but we were talking about allowing the guide to move with the slot while the tyres crushed and moved later, damping some of the input.

The fashion was 1/16" drop axles soldered to a four-rail tube space frame, & the app for a flexier axle was two 1/32 wires soldered in tandem & a 1/16" tube capping that for the wheels.

Who knows if it worked. We believed in a lot of magic feathers back then.

 

Duffy

[Tex]

Whether "good" or "bad", I built a couple chassis' for Da Sano II(I think) with drop arms. when pushing the car beyond it's limitations, the inside front end would lift off the track while the guide flag remained in the slot... at least for a brief period before the 2-wheeling became an actual deslot. But I had that brief period in which to see the car trying to lift out before it actually deslotted. Sometimes I gathered it in, sometimes I didn't.

[Gator Bob]

  ISO ala 'Cuc' is a pseudo drop ... no?

 

 

 

 

 

[Gator Bob]

Whether "good" or "bad", I built a couple chassis' for Da Sano II(I think) with drop arms. when pushing the car beyond it's limitations, the inside front end would lift off the track while the guide flag remained in the slot... at least for a brief period before the 2-wheeling became an actual deslot. But I had that brief period in which to see the car trying to lift out before it actually deslotted. Sometimes I gathered it in, sometimes I didn't.

 

 

** Anyone doing Wheelies will be warned **

 

** All four wheels must touch the track, violators will be de-slotted **

[Steve Okeefe]

Duffy,

 

In the world of Newtonian physics, your statement "every bit of mass is subject to the elevation changes" is unquestionably correct.  In the world of Quantum physics however, the pickup-guide is both in the air and in the slot at the same time -  go figure.

 

The most dramatic example of how correct you are is that notorious launching ramp that formed in black and purple lanes right before the big bank on certain tracks.  At full-tlit boogie the cars would lose the slot just as the banked turn began and travel at multi-sonic speed across all six or seven other lanes (hopefully missing all the other cars), off the end of the track, ten feet up the wall (at my home track it was paneled) and either stick in the ceiling tile or pop the tile out of its frame.

 

You are absolutely right, however at this point I should like to submit for your consideration an observation of my own; although most people involved in slot racing are not degreed engineers or scientists, as a lot they are some of the smartest people I have ever met.  They tinker and experiment until they find a novel combination that works, sometimes without having a clue why it works, and exploit that discovery free of doubt and fear of failure because the BA, MS and PhD "experts" never got around to telling them it was not possible.

 

The historical record includes the fact that from 1966 through 1973, the percentage of total chassis weight either in, on or hinged off the drop arm (i.e.: plumber rails and floppies) steadily increased.  During this same period, lap times dropped by half.  Surely chassis design was only part of the reason for the improved performance, nevertheless Bob Emott once remarked that as he kept making his drop arms wider and wider, his cars went faster and faster.

 

Wishful thinking aside I have no idea why concentrating chassis weight in, on or hinged off the drop arm tends to enable the car hold the slot better.  I only know it works.  It's a mystery.  I'm guessing it has something to do with absorbing and/or delaying the chassis' total reaction to that bumpy track.

 

Respectfully,

 

Steve

[Steve Okeefe]

Tex,

 

What I think I hear you saying is that the presence of a drop arm on your chassis improved the car's handling by making it just a tiny bit more forgiving, or put another way by making the absolute limit of road (slot) holding actually visible.

 

Two points for the drop arm?

[Gator Bob]

Well stated Steve....

 

 

R U Faster then a physicist or Redneck rum runners.

 

3" wide drop arm . .... ** This is Not a pro car** but a post 1974 build.

Conforms to Rule 3. - 2. above.

 

http://slotblog.net/...-34#entry425818

[Duffy]

Steve: Very nice, every word; especially the bit about the non-scientist tinkerers, that's US.

And:

"I'm guessing it has something to do with absorbing and/or delaying the chassis' total reaction to that bumpy track."

That's all there is.

 

Duf

[Steve Okeefe]

Gator Bob,

 

Yes, you could call ISO ala 'Cuc' a pseudo drop arm, but I tend to think of it as more of a "special case" drop arm.

 

The Cox Cucaracha Iso-Fulcrum chassis (presumably the term means "Isolated Fulcrum") was a primitive first iteration Iso design, and yet it included the main architectural feature that made it work; the pickup-guide was separated, or decoupled in engineer-speak, from the front wheels.  It served exactly the same purpose as a true drop arm, without actually being a drop arm.

 

A true drop arm (in my definition) has a transverse hinge at the aft end and is a separate part distinct from the center section.  In the case of the Cuc, the functional hinge is the rear axle and the drop arm and center section are one in the same.

 

Later Iso chassis (example: the TonyP Iso) featured a more sophisticated design in that the side pan body mount (and body) was now hinged off the front end of the chassis center section and the front wheels & axle were the only parts on the end of the hinged sub-section.  It worked the same way only better.  Damn uneducated tinkerers...

[Tex]

Tex,

 

What I think I hear you saying is that the presence of a drop arm on your chassis improved the car's handling by making it just a tiny bit more forgiving, or put another way by making the absolute limit of road (slot) holding actually visible.

 

Two points for the drop arm?

 

I don't think it really made it handle better; it's just that I could see a deslot in the making a little easier. I'm not sure that was a good thing... made my heart skip a beat every time I saw it starting to tilt. Maybe "Ignorance is bliss" is applicable here... don't SHOW me you're going to deslot... just DO it and get it over with.

[Gator Bob]

Gator Bob,

 

Yes, you could call ISO ala 'Cuc' a pseudo drop arm, but I tend to think of it as more of a "special case" drop arm.

 

I'll go ahead and put this out there for ya ... I am a special case too.

 

The Cox Cucaracha Iso-Fulcrum chassis (presumably the term means "Isolated Fulcrum") was a primitive first iteration Iso design, and yet it included the main architectural feature that made it work; the pickup-guide was separated, or decoupled in engineer-speak, from the front wheels.  It served exactly the same purpose as a true drop arm, without actually being a drop arm.

 

A true drop arm (in my definition) has a transverse hinge at the aft end and is a separate part distinct from the center section. 

True .. but ... it's like what are 'thingies'?   *There are experts in this kind of thing.*

 

In the case of the Cuc, the functional hinge is the rear axle

Not true.

and the drop arm and center section are one in the same.

True

 

Later Iso chassis (example: the TonyP Iso) featured a more sophisticated design in that the side pan body mount (and body) was now hinged off the front end of the chassis center section and the front wheels & axle were the only parts on the end of the hinged sub-section.  It worked the same way only better.  Damn uneducated tinkerers...

 

Kinda like a Dynamic hinge .... no ?

IMO, Tony IS the expert and many just follow on. 

 

[Steve Okeefe]

Gator Bob,

 

Oops!  Perhaps I should ammend that part about the functional hinge being the rear axle on the Cuc; there's not enough words there.  It should say: "the functional drop arm hinge is the rear axle".

 

Even though when you pick the car up the center section appears to pivot around the Iso hinge, when you put the car down on the track, the center section rests on the two rear tires and the guide, such that if the guide were to come up out of the slot, the center section would be rotating around the rear axle.  With the car still sitting on the track, the front-wheel / body-mount section in turn pivots around the Iso hinge.  Sorry about the confusion.

 

In the case of the Dynamic hinge, I would have to say "no" it is not the same as an Iso; the pickup-guide is NOT decoupled from the front wheels.

 

About my definition of a drop arm, you wrote: True.. but... it's like what are 'thingies'? *There are experts in this kind of thing.*

 

Hmmm...

 

Government guy: "We have top men working on it right now..."

 

Indiana Jones: "Who...?"

 

Government guy:  "Top... men..."

 

Would that be experts in what a thingie is, or experts in what a drop arm is?  My definition of a drop arm is neither true or false, it is just my definition.  If you disagree I would be genuinely pleased to hear your definition, your opinion is solicited, and even more pleased to hear definitions rendered by TonyP or anyone else.  No hassle at all; it will enhance the narrative, which is my stated goal. 

 

Steve

[gascarnut]

  In the case of the Cuc, the functional hinge is the rear axle...

 

Only true for the 1/32 La Cucaracha. The 1/24 car had a separate hinge between the axle and the motor.

 

Personally I would not classify an iso-fulcrum frame as a drop arm, since the weight of the motor lies on the hinged segment of the frame, and is not supported by the front wheels, which is the case with a true drop arm.

 

As I recall, Cox explained at the time that "Iso-Fulcrum" meant "one hinge".

[TSR]

The ISO chassis with the whole front-end hinged ahead of the motor, introduced by Jan Limpach in 1972, was the first step in exposing drop arms as an obsolete and ill-conceived idea. Jan's design showed that a rigid center was much more efficient against heavy glue, but could still launch and was still a bit fragile in construction. It still used a front axle that could easily get deranged. Ohren followed that design but Monty's ISO chassis were never that successful compared to "L"-arm chassis.
The day when I built the first successful pro-racing car doing away with the drop arm altogether and making the front wheels no longer a unit with the guide and independent from each other (August 1972) is when cars stopped launching on the King and Red tracks straightaway hills, and reduced their lap time by nearly 1/2 second, a huge step forward at the time.

Drop arms were a cute idea for bumpy tracks but as a general rule, never worked as well as a solid center section on a well balanced chassis. The well known "Dynamic hinge" worked better than drop arms because it carried the weight of the front axle and wheels. But an identical Dynamic chassis with the solid tongue ALWAYS handled the bumps better, assuming that the body used on the car did its job of keeping the nose down.

 

I have PAGES in my new book, of pro races lost because cars fitted with drop arms launched in the straights and self destroyed. I also know that as soon as drop-arm springs were introduced, the more the pressure on the spring, the less the cars launched. When I was first to used dual springs with greater tension, launching became a thing of the past. Eliminating the drop arm altogether was the next logical step and it worked.

[Gator Bob]

First Data point:

The drop arm can compensate for varying braid depths from lane to lane, track to track, smooth or undulant.

Next Data point:

The drop arm maintains a percentage of the CG for a longer period of time as the balance of the mass is rising.

Next Point:

I know what a drop arm is.

 

 

Gator Bob,

 

Oops!  Perhaps I should ammend that part about the functional hinge being the rear axle on the Cuc; there's not enough words there.  It should say: "the functional drop arm hinge is the rear axle".

 

The functional hinge is the rear axle (if rear wheel drive) even without a drop arm.*

 

Even though when you pick the car up the center section appears to pivot around the Iso hinge, when you put the car down on the track, the center section rests on the two rear tires and the guide,

 

I don't think we would want it any other way or someone would have to come up with a new name. 'Appears to' yes .. because it does.

 

such that if the guide were to come up out of the slot, the center section would be rotating around the rear axle. 

 

Why, of course ... see above.*

 

With the car still sitting on the track, the front-wheel / body-mount section in turn pivots around the Iso hinge. 

 

Why of course, Yes ... sitting on the track too.

 

Sorry about the confusion.

 

Well I hope you are clear on the subject now,

 

In the case of the Dynamic hinge, I would have to say "no" it is not the same as an Iso; the pickup-guide is NOT decoupled from the front wheels.

 

Just checking.

 

About my definition of a drop arm, you wrote: True.. but... it's like what are 'thingies'? *There are experts in this kind of thing.*

 

Hmmm...

 

Government guy: "We have top men working on it right now..."

 

Indiana Jones: "Who...?"

 

Government guy:  "Top... men..."

 

Would that be experts in what a thingie is, or experts in what a drop arm is? 

 

C - both ... final answer.

 

My definition of a drop arm is neither true or false, it is just my definition. 

 

I did see that you used the word true ... so I follow, but ... not often.

 

If you disagree I would be genuinely pleased to hear your definition, your opinion is solicited,

 

You got it.

 

and even more pleased to hear definitions rendered by TonyP

Yes, for sure.

 

or anyone else.

 

 Cute

 

No hassle at all; it will enhance the narrative, which is my stated goal. 

 

Steve

[Steve Okeefe]

Hi Dennis,

 

First I must apoligize for and attempt to quell the growing confusion surrounding my feeble attempts to describe the functions of the Cox Iso-Fulcrum chassis.  I am either using the wrong words or putting them in the wrong order, or something... I don't know what.  The English language is a marvelous thing but it's endless adaptability can also become a serious impediment to the very communication it is intended to facilitate!

 

Yes the 1/24 Cuc had a separate hinge between the axle and the motor.  Yes this separate hinge was the point about which the two chassis sections rotated.  Yes I agree that the Cox Iso-Fulcrum chassis is NOT an example of a true drop arm.  You are completely right and I concur regarding all these things.

 

Please however consider this: if you were to separate the two sections at the hinge and set the front-wheel / body-mount part aside, then set the center section (which includes the motor mount and pickup-guide) on the track, then manually lift the pickup-guide out of the slot, around what part of the center section would the rotation occur?  What I have been trying to suggest is that the actual rotation occurs around the rear axle; it HAS TO because we've removed the front-wheel / body-mount part of the chassis from the equation and the rotation still happens, unaffected by the missing chassis section.

 

I'm pretty sure what's happening here is that we both understand how the Iso-Fulcrum chassis works but are describing it from different points of view.  Long ago I came to the realization that the front-wheel / body-mount section is a secondary part of the chassis that is hinged off the primary part, the center section (the part that includes the motor mount and pickup-guide); not the other way around.  The part of any chassis that includes the pickup-guide, the motor and the driving wheels is always the primary part; everything else is along for the ride.

 

I sincerely hope I'm making sense with my explanation and not further confusing things.  I've considered and re-considered the functions of the Cox Cuc chassis many times and keep coming to the same conclusion.

 

Now back to the subject of the thread.  We seem to agree about what a drop arm is and what purpose it serves, yes? 

[Steve Okeefe]

Gator Bob,

 

Yes, I am clear on the subject now, thank you for your input.