Hi Guys,
If you remove the guide pin from any chassis and sit the chassis on a table, should the front tires touch the table top? In other words, should the pickup shoes springs compress just with the weight of the chassis?
Reason I ask is I have an Aurora SuperMag (actually, a lot of them). The springs are very strong - strong enough so that without the magnetic attraction of the traction magnets, the front tires do not touch the ground. It is only when the traction magnets are directly over the rails is there enough downforce to pull the front of the chassis all the way down. As you rotate the chassis off the rails, you can actually see the front of the chassis rise. Eventually, it gets to the point where the guide pin is barely still in the slot.
Sit the chassis on a table and the springs don't compress at all.

Thanks...Joe

The tires should touch the track. If they don't, the springs are too strong. Try crushing them between your fingers........That should help.

With M/Ts if there is no magnetic downforce, the tires don't touch.

I would say that if this chassis has seperate traction magnets, you probably don't want the fronts to touch. There will be alot of downforce with these magnets. don't be alarmed.

Crushing the spring will not give you eaqual pressure on the shoes. Try makinf the rear hump smaller this will increase the pressure. Make sure the shoes still move smothly. then make sure the front of the shoe sits flat on the rails. If your shoes build up carbon(black spots then the pressure is to soft. If you car deslots on exceleration then they are to stiff. Try for a happy medium. Good Luck.

Hi guys,

Any chance of a diagram or a picture describing the "make the rear hump smaller" thingy? I'm new to this hobby and have an x-traction car that's jumping around madly on the track, even deslotting on straithways when hitting the gas. I figured this operation just might solve the handling issue (and save me from buying a new car) but I can't figure out what to do precisely to the pickup shoe. Also, if making it "smaller" increases pressure, I guess I need to make it "bigger" in order to soften the pressure and keep the car from jumping off?

Thanks in advance guys, your forum is an precious source of information for small clubs like ours where we don't have "pros" to give us tips!

Huhuhuhuh, he said "rear hump"....

I am curious about this as well actually, not something I've ever heard of.

CafeFroid, this car you're having trouble with......Is it a Flamerthrower XT? If it is, then the problem with those is the leaf-spring used on that set. It's very stiff (too stiff) and what you need to do is:

Take off the pickup shoe, put a downward bend halfway up the leaf spring (a trial & error process to find perfect tension). When properly adjusted these cars run much better.

If you car has the regular shoe/spring setup, you're problem may be untrue out-of-round rims:

Take the body off the chassis and remove the tires. Slowly spin the tires and watch them to see if they 'wobble'........If they do, those are bad rims. also check the axle to see if they're crooked. Replace any bad rims/axles, and that should smooth out you car.

Nah, no flamethrower here. It is a standard Auto-World X-traction (Red Plymouth GTX).

I took a look at the rims and axles and everything seem to be round and straight.

One thing I noticed though is that the front axle has a lot of space for mouvement up and down and one of the tire seem to be able to touch the body of the car.

I tried once to shave an old set of front tires to make them a bit smaller and keep them from touching the body but the car was still jumping around so I figured it was not the way to solve the issue and went back to standard tires.

The car seems to behave a bit more normally when I restrain the mouvement of the pick-up shoes (i.e. the poor man's version of the shrink wrap technique with a tiny piece of electrical tape) but it still jumps more around than the other cars at our track so I had great hopes in that pressure relieving technique slotcarcrz explained

If I'm not mistaken the rear hump referred to is the shoe hook?

By widening the hook or opening it up it pressure is relieved.

By closing the hook or pulling the tip closer to the heel, pressure is increased.

I generally use this adjustment as a fine tune. Based first on a proper contact patch. Much of it depends on the amount of stutter in play. For a huge stutter I generally remove half coil increments and retest. If it's close, then I apply the diagonal "spring crush technique" or the shoe hook trick to weed out the final bit.

Providing the stutter is minor (coil mods NOT required) I go straight to the fine tune tricks. HOWEVER, as dlw points out no amount of shoe tuning will correct lumpy rims and tires. So it's important to first establish that you are rolling smoothly. Assume nothing. I gut the chassis except wheels and tires and gently roll the chassis across a small chunk of glass. By using your index finger in the motor pit and gently rolling the chassis you can feel or see the slightest wobbles and lumps. Once a smooth roll is established then the guts are reloaded and some shoetuning can begin.

The shoe suspension is designed to to compensate for variations in rail height and still provide good current flow. They cant be expected to compensate for deformed wheels and tires too. The whole enchilada is based on the idea that the hanger hook, pivot is reasonably stable so that the shoe can travel up and down in its front hanger. It is assumed that the contact patch raises and lowers with rail height, so the shoe suspension compensates. Random oscilations of 1 or more weird tires upset shoe tracking via vibration and varying the parallelism of the rail and shoe contact patch.

For an extreme example, and assuming that the contact patch is correctly adjusted: as the front tire rotates off it's lump and the back tire is on its lump the shoe contact patch is toe heavy. Following the rotation around the front tire will be on it's lump and the rear tire will be off its lump thus making the shoe patch heel heavy. So now that you have that snapshot in your mind, multiply that rocking horse effect times wheel RPM and you can visualize a "heel toe" chatter effect on the contact patch. Not condusive to stable current flow! The shoe cant do its job if both ends are moving around randomly. As the shoe travels on the vertical axis the pivot point must be reasonably stable to maintain proper rail contact. If the chassis is also oscillating on the vertical axis because of weird tires, THEN so is the pivot point.

So now picture both sides of the chassis doing the Watusi, AKA tossing in some angular or twisting forces from the side to side cuz a car has four tires and it's little wonder current flow and handling become and issue. Ya cant have the pickup shoe dancing on both ends let alone both shoes! The rocking horse effect is always there to some degree as evidenced by a proper hourglass burn on your shoe contact. A little wider on the ends where the suspension comensates for minute rail height changes. The trouble starts when we excede the designs ability to compensate. The idea is to minumize the heel toe effect. The starting point for this is straight alxes, and round wheels and tires.

Stutter due to overspringing and wheel hop are two different deals. In general over sprung will stutter on launch and smooth out as speed increases. Tire oscilation is more constant through the speed range.
When the two effects are combined it can be very frustrating for the novice. So again like DLW sez, make sure you are rolling true before you waste a bunch of time shoe tuning a tire problem and then have to go back and have to retune the shoes after you've figured out that it was a wheel/tire/axle problem all along.

One thing I noticed though is that the front axle has a lot of space for mouvement up and down and one of the tire seem to be able to touch the body of the car.



Big front axel holes made my AutoWorld Ford GT hop like a jackrabbit as it allowed the front tires to touch the body. Switching to o-ring style front tires fixed that.

#5 o-rings that are available at any hardware store make a great replacement for the JL/AW tires. One per hub as a replacement for the narrow tire fronts, two per hub for the wider setup. But make sure the hubs are actually round first.

Gary
AKA LeeRoy98
www.marioncountyraceway.com

Thanks guys. I'll stop by the nearest hardware store to pick up some o-rings and make sure the rubbing problem is entirely corrected before fiddling any more with the pickup shoes tension.

Thanks for the great tips, this one's bookmarked for sure!

A little update about my car in case anyone else experience the same issue.

I found some o-rings at the store (although here in Quebec, there was no such thing as "#5", some 1/4 of an inch ones did the trick.)

The car ran very well with them and there were absolutely no body rubs.

Our house-rules only allow for AW original parts so I spent a while griding my original front tires up to the point where they were about the same size as the o-ring and now the car runs to 1 or 2 tenths of the leaders.

The only issue left is a tendency for the car to run on two wheels or fall on the side sometimes which I attribute to the GTX body sitting much higher on the chassis than the Firebirds and Torino I compete with so I ordered a Firebird body to put the final touch on the beast ;-)

Have a nice holiday guys!

One other thing to look at is restricting the pickup shoe travel. There are a number of options, HOWorld has a nice tutorial. I have posted my personal version on my website at www.marioncountyraceway.com under the Speed Tips link. Other options include bending the top of the pickups, masking tape, shrink tubing, etc. But find one that is easy for you and use it, it will definitely help the car!

Gary
AKA LeeRoy98
www.marioncountyraceway.com

Thanks Gary,

I had been trying to restrict the travel with some piece of tape but it was pretty awkward and unstable. The rubber band trick works like a charm, although I was a bit surprised at how small the piece I cut had to be for it not to touch the chassis or the wheels.

Now I just need to get back at the track and see how it performs! (And convince them to allow this in our rules ;-) )