20 replies to this topic

[JimR]

So, if I were to take the plunge and start using piano wire instead of .063" brass rod for the frame rails, what size piano wire? :?

[yomama]

Probably a dumb question, but where is piano wire sold? Is that the darker-colored rod at the hobby shops?

[Cheater]

Todd, piano wire is often called music wire. Any decent hobby shop should have it in stock, especially those selling R/C airplanes and equipment.

[TSR]

K&S is the main supplier of "piano" wire and just about every hobby shop on the planet carries their line as well as all the brass stuff.

[Slotgeezer]

. . . For frame rails, I'd try .055 or .063.

I'll second that motion! :mrgreen: . . . Two rails of .055" for mucho "flex", two rails of .063" for minimal "flex", and one of each for "medium flex", depending of course on length of rails.

[gascarnut]

I built a frame for one of the East coast racers with one .055 and one .047 rail each side - he says it is a jet.

I guess it's a case of try it and see . . .

[GT40]

You can also use single rails of 0.078 steel.

I have built a couple of chassis using square brass tube of 0.13 to 0.15 inch depth for main rails. These are quite sturdy and have absorbed numerous wall shots by my 9-year-old son. They don't have much flex to them, though. They are very easy to solder, and very easy to attach things to.

[KenMiles]

Hi Jim, Racers.

I'm finding that although piano wire is superior in strength to brass/bronze, its properties are not always desirable. The common opinion expressed about brass/bronze is that once it's bent, it doesn't return. I believe this notion to be misleading. I'm not an engineer, but I am certain that just as steel has elastic limits and yield points, so do alloys of brass and bronze. In other words, structural metal will bend and return to its original shape until its yield point has been exceeded.

As applied to scratchbuilt scale slot car chassis, brass and bronze still have a place. The spring properties of piano wire tend to load up and snap back, which on some tracks is okay but problematic on other tracks. I was recently told by a veteran chassis builder that at one point, 1/16" diameter copper plated welding rod (softer steel) was tried for chassis rods. The goal was to find a material without quite as much spring as piano wire.

You'll have to experiment with differing combinations of rods. Currently, I'm settled on employing sheet brass in a torsion design copied from JK's early Scorpion. I really like the handling properties of brass, which I can report brass chassis do NOT permanently deform from the forces generated by going through turns. The chassis is evidently not stressed beyond its yield point in ordinary slot car use. Crashing, however, will deform a brass chassis. The goal is handling. When your chassis is working, the risk of crashing is greatly reduced.

Eventually, I am certain some formula including both piano wire and brass/bronze will emerge. But this is the fun of chassis building - you have to experiment to find out.

:mrgreen: 8)

[TSR]

Indeed spring steel in plate or wire form has "resonance" properties that may actually work against it in certain conditions. Brass is more inert and does not transmit the same kind of frequencies as steel, and indeed it DOES matter.

[Tex]

This is the nature of building the better mousetrap. Just as one is declared to be the worldbeater, another comes along, of different materials and design, and beats it. Vive' la difference!

[Hworth08]

1/16" diameter copper plated welding rod (softer steel) was tried for chassis rods. The goal was to find a material without quite as much spring

At our local track we used the 16" steel welding rod quite a bit in 1967, til the angle-winders came in. Only Tiger Milk, no glue, which required a chassis with good side and foward bite. Using stock 26D and 16D Ball Bearing motors weight was a concern so good use of the frame material was important.

The steel welding rod is about a third of the way between bronze rod and piano and "survived" pretty well. It's also about $10 a pound tube like bronze rod. We used to sand the copper plating off, it will crack and release in a crash. The steel rod doesn't solder as well as piano wire and will require liquid flux.

Don't say if it helped or not but we tried quite a bit of 1/16" brass tubing stuffed with either .025" or .032" piano wire. Brass tubing is the best material we have for absorbing harmonic vibrations.

Hard to say what really works, these little frames seem to each have a life of its own so much.

Probably the dumbest thing we tried was to epoxy the frame together thinking maybe the heat from soldering would effect the hardness of the brass. We were trying!

[Pappy]

Hard to say what really works, these little frames seem to each have a life of its own so much.

I think there's too many variables to say any one method is better than the other. Track conditions, track surface, track layout, motor used, gearing, body, tires, weight distribution. Build it and keep working with it until it handles. When I was a kid I didn't understand this. I'd build a chassis and if it didn't handle I'd scavenge parts off of it and build another.

[Cheater]

Butch, as you know, you can build several stamped steel chassis exactly the same, gear 'em the same, even use the same motor, and they'll all handle differently. There are a lot of variables we don't understand and we can't control . . .

But there are some guidelines that have been helpful to me.

1) Reducing "long" weight will almost always help handling, with "long" weight being weight a greater distance from the guide pivot than "short" weight.

2) Reducing "high" weight will almost always help handling, with "high" weight being weight above the bottom of the chassis.

3) Less chassis movement generally handles better than more.

4) Chassis alignments are a critical part of the handling equation.

5) Chassis beam stiffness is a significant factor in traction generation.

[Tex]

Here's my two cents. So far I'm running with these thoughts.

If the track is high speed and the car and body will develop their own traction through downforce, I like heavy piano wire main rails. The car needs to snap out of the turn, not just drive thru it.

If the track is slower with tight turns, the chassis must develop the traction. In this case I use two rails of bronze rod for the main rails. Real flexy.

The drawback is that you have to keep this bronze age car off the walls. The car goes deep into the turn and then drives around it quickly and smoothly. The slower track car must turn right and left on its own with very little help from the downforce being generated. Flex in the frame is needed. The high speed track car must be stiffer to take advantage of the downforce being generated. My bronze cars won't exit turns on a high speed track as fast as my piano wire cars. My piano wire cars don't make enough bite to be fast through the turns on a slow, tight track.

(Tex scribbles furiously in his little note pad.)

[Pappy]

(Tex scribbles furiously in his little note pad.)

Three month's later, Tex realizes he can't read his own writing :shock:

[Pappy]

4) Chassis alignments are a critical part of the handling equation.

Henceforth "Magna Jiggy".

[Hworth08]

I'm still a kid, just older now, but when I built a bad car I usually sold or traded it. Even the bad scratchbuilts would usually run circles around the factory kits or RTR cars. Some of RTRs were way over-powered back then, now they're way over-priced for me!