by
Daniel J. Dyke
WARNING: The following fix should be done at your own risk. If you want a guarantee then I guarantee this will not work and will damage your car. If it does work and you want your car damaged then hit the thing with a five pound sledge hammer.
This may seem stupid to many, but there are people who need help figuring gear ratios, what they mean, and how to change them. It is also their first course in becoming a slotcar geek and a major lesson on spending money without getting a single slotcar. It assumes the person really wants to be a geek. Slotcar geeks do not buy pocket protectors but they do buy cool things like Dremel tools and all their glorious attachments and accesories like a drill press stand.
Here are the tools you want to buy to do this project. Not all are necessary, but you do want to be a geek and be able to talk with the rest of the boys as equals don't you?
1. HammerFIGURING THE RATIO
2. Allen Wrench to fit SlotIt wheels
3. Dremel Tool (the one with a ton of tips and wheels, gizmoes, and thingamabobs).
4. Drill Press Attachment for a Dremel Tool
5. A set of titanium drill bits in 1/64" increments.
6. A first aid kit.
7. Engine breakin greese - go to Pep Boys for this.
8. Light Lubricating oil.
9. Anvil: I am trying to get you into the fulness off the hobby. You need a small anvil!
THE RULE OF THE TOOL
Open your slotcar and count the the number of teeth on each gear. Take the number of teeth on the big gear and divide by the number of teeth on the little gear (the pinion). The resulting number is the ratio. If the big gear has 27 teeth and the little gear has 9 then the result is 3. This is called a 3:1 ratio. Many SCX cars come with this ratio.
DECIPHERING THE RATIO
The higher the first number is the greater the acceleration and braking power, but it comes at the cost of top speed.
The lower the number is the more top speed you have, but it takes longer to brake and accelerate.
When do you need to change your gear ratio? The following situations call for a change:
1) If you have a real long straight, fast curves, and your car stops accelerating about half way down the straight then you might want to change ratios.
2) If your car seems sluggish around most of the course and never stops accelerating then you need to change the ratio.
3) If your car is winning on the straight, but losing a lot of distance on the the tight part of the course then you need to change.
A change is good ONLY if the overall lap times improve. (You don't have a laptimer! Call Mr. Bugs). Usually the right ratio is a compromise between accelerating off the corner and top speed on the straight.
NEVERS
1. Never go for ultimate topspeed, if the car is sluggish or stalls coming out of a turn.CHANGING THE RATIO
2. Never use replacement gears that are not compatible. The easiest way to tell is to turn the wheels by hand and if they don't turn smoothly, get help. The safest way is to buy all new gears from SlotIt.
There are five ways to deal with this problem.
1. A NEW MOTOR: Leave the ratio the same, but get a motor with more rpms or more torque.Say you want faster acceleration and less top speed and your car currently has a 3:1 ratio. The little gear has 9 teeth and the big one has 27. What do you do? The following are step by step instructions for each of the above listed options.
2. A BIG GEAR CHANGE: Change the big gear to one with more or less teeth.
3. A LITTLE GEAR CHANGE: Change the little gear/pinion but this is more expensive as you need a gear puller.
4. Change the diameter of the wheel-tire combination.
5. Do a combination of the above.
A NEW MOTOR
If you decide to go with a new motorthen you have two options depending on what your car is needs.
1. If the car needs more top speed, buy a compatible motor for your particular car such as a SlotIt, MRRC, TSRF, or JK Falcon. How do you know if it is compatible? Ask the seller or go to the discussion boards.
2. If the car needs more torque, SlotIt sells some with a stronger torque curves, but with less RPMs. My favorite motor of this type is the PMTR 1500 Hot Rod motor from Professor Motor, but can be purchased from other vendors. HRW sells a green one that is supposedly the same motor. I have not checked this point out, but have been told it was true.
The big gear is referred to as the crown or contrate gear, but only if the engine is an inline engine. It is called a spur gear on a sidewinder/anglewinder.
SlotIt replacement gears are the easiest to find since most dealers carry them. Since you will be dissembling the rear axle anyway, you should consider replacing the whole rear axle assembly. SlotIt sells these as a kit which includes precision turned wheels, axles, bearings, and gears. Since you are advancing to the stage of being a major slot car geek, here is a free piece of advice, (well actually it is all free), buy one of every size of gear SlotIt makes. It will make your dealer happy and you will have an arsenal of parts to use in testing. SlotIt makes pinion packs for both sidewinder and inline motors that contain every size of pinion for the particular configuration. Remember to buy the SlotIt Allen Wrench as they are not available at 99.99% of the hardware stores in this country. Now that you have made your million dollar purchase, here is the step by step.
1. Remove the body from the chassis. There should
be 1-5 screws on the bottom that need removed. Watch for things like
exhausts that protrude through the chassis. Do what is necessary
to keep from breaking them.
2. Snap out the rear axle assembly by gently lifting
on the wheel and pressing down on the chassis until one end pops out. Do
the same to the other end.
3. If you are replacing the whole assembly then do it now.
If you only want to change the gear the remove the whole axle assembly.
a. To remove the wheels firmly grab both the wheels (one in each hand) and twist in opposite directions. At least one should come off. If one wheel sticks, grab the axle with pliers in a place that does not touch where the bearing will rub when the axle is in the car as a burr can cause the thing either to turn poorly or not turn at all. Once you have grabbed the axle, turn the wheel until it lets go.b. To remove the gear from the axle you need to make an axle removal stand. This should not be used with SlotIt products. Remember you are becoming a geek and want to do this right. It is two pieces of 2x4 with a piece of 5/8" (use what you have as long as it is substantial) plywood nailed across the 2x4s to make a little table. How long should the 2x4s be. Does it stand up? Long enough! Drill a 3/32" or 7/64" hole through the top of the wood. Use a drill press for this as you want the axle perpendicular. Don't have a drill press? Go to work or church and ask around for a carpenter.
Put the axle in the hole with the teeth of the gear facing up, if you are removing a gear for an inline axle. If you are removing a sidewinder then put the short end of the axle up. Tap the tip of the axle with a hammer. I said tap you fool not smash. If it does not move then tap harder until it does. Still not move get a bigger hammer and smash the thing as no proper slotcar ever had a gear that was tight on the axle. If they were we would have nothing to complain about. Bent the axle? Go get a new one at the sacred slotcar store or get a piece of 3/32" piano wire at a model train store and cut a piece to fit with the Dremel Tool. Don't have a Dremel Tool? Hey, I am making you into a geek, go to Home Depot or Wally Mart and get one with a cutoff wheel and while you are at it get the drill press attachment and a set of titanium drill bits.
d. To replace the gear tap the axle down in the hole until it touches the wood. Position it over the hole on the gear changing table and tap it int position. If you tap it too far turn it over and tap the other way. If the axle is loose go to a hardware store and get permanent Loctite. Back the gear away from where it is supposed to be and put a drop of the Loctite on the axle and move the gear into place. How long does it take to dry? I don't know because I go to bed. I always to overkill on waiting.
CHANGING THE LITTLE GEAR
The little gear is the pinion. If you put one on with less teeth then you will get more power and less speed. If you put one on with more teeth then you will get more speed, but less power. On sidewinder cars you have to get matching gears. Again the SlotIt gears are the best.
1. Buy a gear puller, read the instructions. There are several gear pullers on the market and I have used three of them.
a. Ninco has one that is both a puller and press, but the metal is soft and the tip of the screws that push the shaft from the gear or the gear on to the shaft are easily rounded off and eventually will become unusable.2. Buy a SlotIt pack of pinions (Part #s: SIPIMX [inline] or SIPSMX [sidewinder]).b. Champion makes a nice steel puller which is my favoite so far. The disadvantage is that it does not have a gear press like the Ninco. It is sold by www.fantasyworldhobbies.com.
c. Northwest Shortline makes the biggest gear puller, but it is not recommended for taking pinions off motors which it will do sometimes if there is plenty of space between the gear and the motor, but it is great for pulling stuck aluminum wheels.
3. Measure how much of the motor shaft is sticking out beyond the pinion then remove the old pinion following the instructions included with the puller you bought.
4. Put on a new pinion that either increases or decreases the number of teeth. How is this done? You have two options; a hammer or a gear press. I use a claw hammer because a heavier hammer seems to work easier because I have to supply less energy.
a. Get a ushaped piece of metal and drill a hole in it slightly larger than the shaft of the motor.5. Put your motor back in and see if your car is faster or slower. If it makes no change in the laptimes then try it again. If the times improve keep changing the gear until they go the other way. Use the ratio that was best overall.
b. Place the pinion on the piece of metal and then put the shaft of the motor in the hole as far as it will go then tap the other end of the motor with the hammer until the pinion starts to slide on. The problem is that the pinion will only go on until the end of the gear and the end of the pinion are flush.
c. Position the motor shaft over the hole in the metal until it is right above the hole. The hole must be smaller than the outer diameter of the pinion and just a little larger than the motor shaft.
d. Tap (gently) the motor shaft with a hammer until the pinion slides down to the place where the original pinion was positioned. If it goes on too far use the pinion puller to move it the other way. You must work slowly.
CHANGING THE DIAMETER OF THE WHEEL-TIRE COMBINATION
This is done for fine tuning purposes. If you get too agressive with it then the car looks stupid. Simply stated using a smaller tire is like using a smaller pinion. It gives more power and less speed. Using a larger tire gives more speed and less power. Instead of searching for a smaller tire just sand the old ones down a little. I know a guy who chemically shrinks his tires for a box stock class at a track with short straights. The tires look stock but they are about 5% smaller. Too bad you can't sand tires to make them larger! When I get time I will make a graphic of how this works.
COMBINATIONS
You can mix and match the above techniques for certain effects.
For example an eight toothe pinion and a 24 tooth pinion allows you to
use really small rear wheels. It does not change the ratio over a
9/27 combo, but it is physically smaller. This is what I had to do
for my Fiat Abarth which has dinky rear tires. A 8/32 combo
with a really large tire might act like a 9/32 with a smaller tire.
It becomes one of those variable things that a person has to get used to
with time.
LINKS
How Stuff Works:
General Concepts
How
Stuff Works: Types of Gears
Toy Craft
Gears
and Gear Trains
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