23 replies to this topic

[Steve Okeefe]

February 1967

Warmack 4 Rail Sports Car

Drawing by Steve Okeefe

 

[endbelldrive]

This is the design that epitomizes the classic jaildoor chassis IMHO.

[Champion 507]

Bob, I agree with you 100%

[tjallen]

Is there an article or text info to go with this chassis drawing?

 

I see the Bryan Warmack car pictured in the race report, http://slotblog.net/...d-race-1967-02/

and a similar Warmack chassis again in the next report: http://slotblog.net/...d-race-1967-04/

 

Thanks!

[Steve Okeefe]

Hi Jim,
 
It's good to hear from you again, and good to know you have not lost interest in the hobby (or scratchbuilding ).
 
I'm going to guess (when you ask about an article or text info) that you mean a construction article.  Unfortunately, I don't think I did one for this chassis. In fact, I don't think I actually built any of this one; at least if I did I cannot find it in my collection.
 
Maybe I should build a Vintage-style version... what do you think?

[tjallen]

Steve, so good to hear from you, especially since I need your calming reassurance that I'm not completely confused. (Again!)
 
I needed to draw a rear view of a classic chassis, and this seemed a good candidate. I kept redoing my math, thinking I had some error. Every time I calculated, it seemed the Russkit bracket would result in a chassis where the motor sat 1/8 inch off the ground, rather than the rules-minimum of 1/16 inch. Am I confused? Here is a cut & paste of some of your artwork, to illustrate my question:
 

 
First, I checked your rule sets for the Car Model races - all but one specifies a track clearance of 1/16 inch.
 
Next, I looked at cars in my own collection, and it turns out I have two distinct types of chassis built with the Russkit bracket:
 
1. Cars where the chassis runs at 1/16 inch track clearance with a motor mounted 1/16 higher than the chassis, at 1/8 inch.
 
Picture of a car where the motor is mounted 1/16 above the chassis:


 
2. Cars where the motor is built flush with the bottom of the chassis, but the whole package rides at 1/8 inch of track clearance!
 
Chassis and motor built flat, with 1/8 track clearance.


 
These must be obvious points to the classic scratchbuilder, but in all my time, I hadn't noticed or thought about this. I don't remember discussing this or reading it before, but maybe I was just blind to it all along. I know normally the motor centerline and the axle centerline must match to get good gear mesh. So it seems strange that the rules specify a tire size that raises the standard motor above the minimum clearance.
 
Hope you can enlighten me!
 
Jimmy

[grooverunner]

Hi Jim,

 

I recently CNC machined out a few copies if the Russkit bracket for some builds I'm going to do myself and noticed it was set up for 1/8'' clearance with 7/8'' dia tires myself, and I have meant to ask Steve the same question. I was scratching my head also..

 

 

Ken

[tjallen]

I can see this is a "feature" of the rules set, combined with the standard motor size, and not the fault of the Russkit bracket. Maybe the rule makers wanted to allow larger motors, or motors with a 1/16 pan under them. Still, it is something I never noticed.
 
Can we assume that the pro chassis in the CM races were all like the first one I pictured above (two levels)? Can I assume the Warmack chassis is 1/16 inch track clearance, but with 1/8 inch clearance for the motor?

[Eddie Fleming]

Were any of those cars built with the front end of the motor down like the angled brackets used in Retro today. I remember seeing Russkit cars with angled motors I think.
 
With them being endbell drive it would make the heavy end of the motor down just as you would want.

[Steve Okeefe]

Jim,
 
No, you are not confused.  Here is the logical progression:
 
Full size car tires range in size from about 24 to about 27 inches in diameter. There are larger and smaller sizes to be sure, but that is a typical range. In 1/24 that would be 1" to 1-1/8". In the early '60s that is what scale model slot cars had... big tires.
 
Towards the mid-'60s, builders and drivers were beginning to understand that slot cars require the lowest center of gravity you can give them in order to handle well, and 1" to 1-1/8" tires are just too tall. Large tires like that (and the gears that go with them) also tend to behave as flywheels, slowing down acceleration and braking.
 
So the rules makers conceded by allowing 15/16" diameter rear tires in 1966, and 7/8" diameter rear tires in 1967. By 1971 they further conceded 13/16", and eventually 3/4" rears. But we are talking about the Warmack car, which is from early 1967, so it would have had 7/8" (.875") diameter rear tires.
 
Keeping that in mind, Mabuchi FT-16 and FT-16D motors happen to be about .645" tall; that's the way Mabuchi made them without any concern whatever for what slot racers might want.
 
The scratchbuilders job is to marry these two things together (.875" diameter tires and .645" tall motors) so they work properly. Doing the math we find that if you center the motor shaft on the axle, and keep the motor parallel to the track, you get .115" under the motor.  .115" is very close to 1/8", so your calculations are quite right.
 
Prefab motor brackets, regardless of who makes them, are supposed to keep the motor shaft and the rear axle aligned - that is their job.  In 1967 it was assumed the correct and best alignment (in an inline set-up) was to have the center lines of the shafts intersect (and at 90 degrees!) That is not strictly necessary in slot cars, as builders and racers eventually discovered, but we're talking about 1967.
 
The next step is how do you deal with this significant problem of the motor being too high up? The topical answer, it turns out, is dead simple.  Bolt everything together (wheels, axle, bushings, gears, bracket and motor) and simply let the front end of the motor angle downwards so it is at 1/16" clearance, same as the chassis, and build around that. It's a concession, admittedly, but it's all you get.
 
The math BTW, goes like this: (tire diameter - motor height) / 2 = track clearance. Rearranging for stipulated track clearance you get: (track clearance * 2) + motor height = tire diameter.  For a track clearance of 1/16", that would yield a .770" tire diameter.
 
Hope that helps!

[grooverunner]

See I knew Steve would gave a us the answer and the reasoning behind it. 

 

I had deduced in my think that it must of started out with the 1'' to 1-1/8'' dia tires, but didn't know they tipped the front of the motor down to 1/16'' clearance.

 

Thank you, Steve.

[Bill from NH]

I knew there was a reason for me not using Russkit brackets.  Not to confuse things, I let the front of motors angle down as Steve says above, JK made 3/4" and 1" wide hypoid motor brackets where the center line of the axle was above that of the motor's armature. These would decrease the angle of motors hanging down at the front and lower the bracket. The downside is these brackets aren't true vintage, but JK brackets are nice. Angled pinions provide a good gear mesh with hypoid brackets.

[tjallen]

Thanks, Steve, lots for me to think about, as usual!

 

In a quick look, I have 10+ vintage chassis or partial chassis with the Russkit bracket, or similar. I will have to look very closely to see if they are angled.

 

I see that is the natural answer from the builder's perspective - let it dangle from the axle, prop up the end at 1/16, and solder it as it sits. Some of my examples should angle downward. Many of mine are all bent up, and my eyes aren't what they were, so I've got the magnifying glass out!

 

Jimmy

[don.siegel]

Good discussion... I discovered this when I was making my first scratchbuilt chassis in '66-67, and referred to Mike Morrissey's article in the April '66 issue of Car Model: he very clearly explains how to angle the Russkit 23 motor down at the front... I think those were still 1" tires (Graupners/German spongies of course), and not yet the 15/16" in the first R&C road race series.  

 

Of course, the Midwest guys with their 1/32 pan chassis, and all other scratchbuilders with inline cars were already doing this, and had been for many years... check out the Bob Emott chassis raced by Howie Ursaner. 

 

The trend to smaller tires also indirectly explains the anglewinder - the only way to get a sidewinder motor to fit with these smaller tires was to set it an an angle! 

 

MDC and other companies made hypoid brackets, which shouldn't be too hard to find... a number of years, ago, Italian ace, the late Bruno Novarese, won one of the Bordo vintage races with an MDC hypoid chassis (maybe under a Cobra, can't remember). It handled beautifully, even tho slower than other cars, but he told me it was a bear to set up correctly! 

 

Don 

[Steve Okeefe]

Don,

 

To help illustrate your description, here's a photo of an MDC hypoid bracket:

 

 

This one (as indicated on the header card) is for an SP600, which is Revell's version of an early Mabuchi 36D, technically known as an FT-36.

 

MDC did also have a hypoid bracket for the 16D size Mabuchi; it was part number 115:

 

 

Some modern brackets intended for use in Retro cars also have a hypoid offset, although not as much as the MDC brackets had.  Retro racers have discovered (as Bill has already mentioned) that they can still get a fairly smooth mesh with standard modern plastic crown gears in a hypoid setup by using an angled pinion gear.

[Ramcatlarry]

The angled pinion helps, but run the motor slowly with the gears meshing and 'carefully heat' the crown with a lighter to reform the crown teeth to the silent running mode - really - take the heat away when they stop making noise and keep the motor running until the assembly cools down. No noise, no friction, good mesh... but not as good as an aligned pinion.

[tjallen]

I'm working on some new ideas re: this chassis:
 
 



 
 
The top one is a static model (does not roll.) The bottom one might in theory work, but Shapeways cannot print something this size in brass. You could get it in stainless steel or nylon for sensible prices. I wouldn't expect it to work really well, but???

[Cheater]

Jimmy,

Curious as to what software you used to create the above two images?

[tjallen]

I'm working at TinkerCAD. This was fun exercise, first time I used any CAD program. I've sent it to Shapeways, and have ordered my first sample [in plastic] today. I'll show y'all when it arrives.

[tjallen]

The chassis had to be soldered together, just like the old days - well, almost! Virtual brass rods soldered with virtual solder!

[Bill from NH]

Jim, I know very little about 3D printing. Why is the chassis too large for Shapeways to print in brass, yet would be okay to print in stainless steel or nylon? is it some mechanical limitation or does printing brass just take more memory to do?

 

Your CAD drawings would be a relatively easy chassis to build with conventional brass rod & solder on a chassis jig.

[tjallen]

Different materials are outsourced to different vendors on Shapeways. The brass vendors are limited to 89mm x 89mm (about 3.5 inches square.) I'm not sure why the limit. I think brass and some other metals are actually cast from a 3D printed wax model, by the ancient lost-wax process.

 

I tried to copy Steve's drawing as exactly as possible, plus looked very closely at the picture in the magazine.   I'm sure lots of people have built this very chassis on their workbench.  I'm working on a few others, too, to be revealed as I complete them.

[tjallen]

My 3D printed replica of the Warmack Chassis is back from Shapeways. This plastic model is built in homage to Bryan Warmack's classic jaildoor chassis.

 

 

I plan to post other views in slotblog's Computer assisted design forum.

[Champion 507]

Jim, that's just plain COOL!