Home Racing World

I'm lost as usual and need some help in the pinion selection. One thing I understand is the ratio aspect, but when looking at slot gears there pinions were marked 5.5mm, 6.0 mm, 6.5 mm and 6.75 mm. Now this is where I start to stumble. I read Slot. it's explanation and something about the outside diameter? Can someone simply explain just what the numbers mean and the benefit of one over another.
Another area of question, what's the benefit of the material a pinion is made from, plastic, brass or aluminum.
One final question. Are all the inside diameters the same or maybe what I should ask, how universal are pinions, which brings a question in a similar area. Are motor shaft OD's the same across manufacturers. :oops:
Thanks

The 5.5, 6.0, 6.5 and 6.75mm dimensions refer to the outside diameter of the pinion, measured from one end of a tooth to the end of the opposite tooth.

There are two motor shaft diameters. 2.0mm is the most used diameter and most short and long-can motors use 2.0mm motor shafts. When you get into the slimline motors, they usually have a 1.5mm motor shaft. There are now more 1.5mm pinions on the market but 2.0mm is the standard size of the center hole. There are some sleeves that you can buy to put onto a 1.5mm motor shaft to make it 2.0mm and you then have more choice when choosing a pinion.

5.5mm pinions are usually made for inline applications. When you go into sidewinder applications, things get a little more complicated. The standard is 6.5mm but it all depends on the distance between the rear axle and the motor shaft. Even Slot.it has had different distances in their cars and motor pods. Usually, if you're using a 18mm spur gear, you'll need a 6.5mm pinion. A 19mm spur gear will require a 5.5mm pinion. But there are exceptions to this rule, depends on which motor pod you're using.

You can see the valid combinations in a reference chart we've made, that you can download here (look for the notes at right):
slotitgearratiochart.pdf

Then, for anglewinder applications, you need to use a 6.5mm pinion, unless you're using a long hub anglewinder gear from Slot.it (this one requires special 6.75mm pinions). Again, some people like to play around those parts to get a different gear mesh that they prefer but you have the general idea here.

If you want to ensure long service from your gear set you would never want to run metal against plastic (either pinion to spur/contrate gear or visa versa). The metal gear would always wear the plastic component away.

General, for normal use, plastic gear sets are most often used by the slot car makers for the following reasons:-

1. Cost effectiveness of the injection-molding process.
2. Elimination of machining operations.
3. Low density: lightweight, low inertia.
4. Uniformity of parts.
5. Capability to absorb shock and vibration as a result of elastic compliance.
6. Ability to operate with minimum or no lubrication, due to inherent lubricity.
7. Relatively low coefficient of friction.
8. Corrosion-resistance; elimination of plating, or protective coatings.
9. Quietness of operation.
10. Tolerances often less critical than for metal gears, due in part to their greater resilience.

Having said that, most slot car makers have trouble matching the gear sets. Important mini-engineering criteria are often not adhered to like:-
The Arc
The base Circle
The Chordal addendum
The Diametral Pitch
The Flank
The Module
The Pitch Point and the Profile Shift.

It's complicated.

Jules

... and to add to the confusion. Scalextric often has a splined motor shaft, can a brass gear be pressed on that?

Not without sanding the splines. Use fine grit wet-sanding paper.

While we are on the topic of pinions, it has come to my attention that the majority of inline pinions are 5.5 mm.
whether on a 1.5 mm or 2 mm shaft , the pinion diam seems to be 5.5.
Is there anyone aware of a manufacturer who make a larger diameter in linen pinion, than 5.5 mm in the 8tooth and 9tooth range of 48 pitch.
It seems a slightly larger diameter pinion would turn the crown faster.
Any thought or direction would be appreciated.
Bob

You can use larger diameter if you trim the motor shaft and shim your rear axle to prevent side to side free-play and to center. But the same ratio, is not going to change much, at least no change I noticed. I guess it's up to you and the series you run in if this is worth it to do.

But with the motor shaft resting inside the crown, this dictates how large a diameter pinion you can use. So 5.5 MM is the standard size.

You can put a brass pinion gear on a splined motor shaft if you use a good quality gear press, I do it all of the time. With Slot.it motor pods there are 18mm and 19mm versions. A 6.5mm pinion is the thing to use with either pod. If you were to use a 19mm spur gear with an 18mm pod you would have to use a 5.5mm pinion. The sum of the diameters has to be 24.5 for the gears to mesh properly. With plastic crown gears a brass pinion will wear out long before the crown gear does.

I have a good gear press. But forcing a brass pinion over the splines can sometimes distort the pinion.

Agree with Harry

I always sand or file the splines down. It is an easier fit, no risk of gear distortion and no fear of bending the armature shaft.
A touch of loctite or a quick solder job does the trick very nicely.
Bob