1. It should steer the car (I hope that one was obvious!)
2. It should have low friction in the slot (good idea)
3. It should not get hung-up on irregularities in the slot (of course)

This is all very well and good, but I also heard some other things that might not be so obvious to some racers.

Like lead wires, for instance. Lead wires, of course, carry the current from the braids to the motor. But they also serve another very important purpose: They act as springs that make the guide flag spring back to the center when the car is picked up - or they should! Why, you ask? Because the track marshal can’t get your car back on the track if the guide flag is not straight, that’s why! (I know you NEVER come off the track, but if you did, this would be important!) We often see marshals try two or three times to get the car back in the slot only to have to reach under it and reposition the guide flag first. You could have turned a lap in that much time! It also pays to make sure that the guide flag does not stick when forced to the extremes in a wreck. It should always spring back to the center, unless you like the idea of the marshal hanging on to it for a while.

What about guide flag pivot tightness? This is a matter of hot debate when you ask racers about it. Some like it flopping all over the place, and some like it so tight you wonder how the car gets around the turn. Why would more guide turning friction be better? Well, the friction required to turn the guide flag could be adding a stabilizing effect that keeps the car from swinging out on corners and loosing control. This could really be factor is very lightweight cars. I would argue that this is a poor way to stabilize the car, though, because the friction against the slot must be very high when this is going on! I prefer the flag to turn freely, but not loosely. I even oil the pivot to make it move smoothly.

About rear axle tightness, and gear mesh, someone once said, "Move it from side to side with your fingers. You should be able to feel it, but not see it. If you can see it move, it’s too loose. If you can’t feel it move, it’s too tight." I like that method for guide flag pivots, too.

Remember my first article about center of gravity? Apply this to the guide flag and you might start thinking about the height at which the guide hits the slot, the front-to-back point at which the slot applies sideways energy to the chassis via the guide flag. There’s a lot of serious physics going on in those corners! Look closely at the wear pattern on the flag itself. There is much to be learned here. In a future article, well lookinto this more deeply.

Okay, now about braids. The guide flag is more than just the flag, it’s also the braid holder and guide, and nothing is more important that keeping the braids on the track - nothing! I am often amazed at how little attention some racers pay to their braids. Not just the braids themselves, but the way that the braids wear, which indicates the pattern of their contact with the track braid. A lot of racers spend hours looking for mechanical problems when the real problem is electrical contact! I would suggest that the guide flag plays several important roles with regard to the braids and braid-to-track contact. These are:

1. The guide determines the angle at which the braid rides on the track. If the angle is too low, the front edge of the braid wears out quickly and small track braid bumps and rough spots slow the car down, or even make it flip out of the slot. If the angle is too high, you’re leaping over bumps.
2. The guide height (how far below the chassis it hangs) determines if the braids can remain in contact with the track braid through variations in braid depth, around corners, and through the rough spots. If the guide flag is holding the braid up, then contact is not what it should be. Be sure that the braids are free to apply all the pressure of the cars weight and air forces against the track braid and that nothing serves to lift the braid and weaken the contact. Use washers between the chasis and the braid to experement with lower guide positions and see what the effect is.
3. The leading edge shape of the guide determines if it rides up on corners and lifts the braid off the track. Run the car around a corner with your hand and try to feel the contact between the guide and slot. Is it smooth and uniform?

If you want to learn more about your guide flag, put nice new braids on the car and run it for a little while, and then take a good long look at the braids. Be scientific and install the braids neatly and with precision. You might be interested in what you see in the wear patterns! Change the guide flag angle or height, and repeat the test to see the results.

I have also helped many a racer who had a car that ran fine until a sharp turn, or until the tires broke loose, and then it jumped like a jackrabbit out of the slot. A closer look revealed what many old timers know to look for right away: The braid shorts against the chassis when the guide turns sharply enough. The car is in the turn and, all of the sudden, full brakes! No wonder it takes off! (By the way, this is a good argument for making sure that the cars chassis is NOT in contact with either lead wire or motor brush bracket. I’ve seen cars crash because the chassis hits a high spot on the braid and shorts out. Use an ohmmeter or voltmeter to make sure the chassis is not connected to either braid!)

Okay, now I will proceed to tell you what I think about guide flags. See if you agree with these hard-learned methods:

First, I feel that the guide should cause the braid to slide along the track with the leading edge slightly higher than the bulk of the braid. This will allow it to "ski" over bumps and roughness easier. However, there should not be too much angle or the braid will try to "jump" over bumps. ("Getting air" is good for skateboarders, not slot racers!) If the leading edge of the braid shows all the wear, bend the chassis slightly to raise the attack angle a little. If all the wear is toward the back ends of the braid, try the reverse. The idea is to get the most copper in contact - in all conditions.

By the way, resist the temptation to put the car on a tech block and stare at the guide and braids. Nothing could be more inaccurate! The car is altogether different in action on the track than on the block. Run real braids on a real track and look at the wear. This is where the information is!

I have seen photographic evidence (high speed video, actually) that the braid contact moves toward the rear of the braid (the free end) as the car lifts up. This is why many racers use a sharp pointed tool to fray the ends of new braids into frazzle. As the car tries to lift up, the frazzles are like little springs that expand toward the track and maintain contact with it. The braid should be flexible and fluid so that it can roll with the punches. I like to splay out the last 1/8" or so of new braids before I install them for this reason. They don’t look as neat, but they work better!

Another interesting fact that I learned from an engineer who designs big relay contacts: When the contact between two flat pieces of metal starts to break, the arcing heats the air between them to very high temperatures in a very short time. The air expands and drives the surfaces away from each other! This is why big high-power relays have cut marks across their contact faces to vent the heated air away. This would suggest that nice, flat tightly woven braids are not as good as somewhat loosely woven ones that allow tiny pockets of air to escape. Another argument for fraying the ends a bit!

At the risk of upsetting the old timers who do this without thinking, I would also like to mention a method for making the braids lay down nicely on the guide flag. Hold the car belly-up, and nose up, between both hands. Place your thumbs on the braids on either side of the guide flag, pressing the braids away from you and down against the guide. Now, slide your thumbs away from you such that the braids are pushed toward the front of the car. This causes the fold in the leading edge of the braid to be tightened. When you remove your thumbs, the braids will lay down nicely. Until you discover this, it’s almost impossible to make the darned things lay down!

About braid juice and similar chemicals, I’ve heard a zillion arguments! I like to use a little braid juice because it appears to clean the surfaces of oils and glue and makes the contact better. But I’ve also found that the juice itself burns and makes a reside of its own if you use too much. I did a little test and put a "popular brand" in a tin plate and cooked it on the stove. After a while, I had a black gooey residue. After painting some of this residue on a metal surface I found that it makes a pretty good insulator! Burned braid juice is BAD! Remember that next time you go to splash a bunch on those braids. If you run the same braids for a long time, as in slower classes, hold back on the juice. If you run a braid-eating monster that consumes more copper than you local public utility company, you might get away with a little more because it won’t be around that long. One racer said he puts a drop of braid juice on a rag and wipes it across the braid surfaces, using it as a cleaner but leaving very little on the braids themselves.