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hy would some one like to explain the different combo,s, and why. take a 3-1 ratio, the standard is 9-27. going to extremes, what about 7-21 or 11-33 there must be a difference and i,d like to know. a euro sport runs 6-1 6-36 why. john
 
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a 2:1 ratio gives more top speed and less brakes a 3:1 tattoo gives more acceleration and more brakes the lower the ratio the more speed just do some simple maths hope this helps by
 

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hi, John
I believe what you're asking is what about the same ratio but different tooth counts. More than anything I believe that is based on the tooth size (and therefore stress/loading as well as ease of machining with a
quality profile). Having established a tooth size, then the number of teeth determines the spacing of the two gears, as well as ground clearance. Obviously an 11 tooth pinion is a larger diameter than a 7 tooth with
the same tooth size, etc. There are other issues such as flywheel effect if you go to extremes on size. Does this address your real point, or do you have something else in mind?

with best regards,
John
 

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The differance in the size of the gear can be crucial - too big can foul the chassis or reduce ground clearance - in anglewinders and sidewinders the right spacing to get the gears to mesh correctly (this is particularly a problem where the motor position cannot be changed.)
Some combinations mesh better than others, but this is an issue with particular makes and types rather than just number of teeth.
There is a slight tendency for more teeth to mesh better, but this is quite insignificant compared with getting the ratio right.

The right ratio is the one that makes the car go best in the conditions. For example on tracks with predominately long straights it can be better to gear for more top speed than on tracks with shorter straights where low speed acceleration matters.

Euro sport cars run better with gear ratios of 6:1 or 7:1 (Wing cars have fairly similar motors but usually run less extreme ratios because they need higher top speed.)
There are various reasons given (torque characteristics, gyroscopic couples, the motors rev so high that's what you need to reach full revs before the end of the straight etc.) Difficult to say how much a part each of these contribute to making the cars go better, most competitors main interest is that it does make the cars go better.
Incidentally, these ratios can usually produce more brakes than is wanted, so a controller with adjustable brakes is normally used.
 

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One petunia in a field of onions
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I don't really think that's the question Mr Cahill, sorry.

Let's try it this way. Given a ratio of 3:1 why is it that a 27t contrate and 9t pinion is a preferable way of achieving it to another match, say 30t contrate and a 10t pinion. Both give the same effective gearing ratio. In fact, given that the pairings achieve the same ratio will there be any observable or measurable difference, assuming that both pairings are matched in pitch.

Now, an answer on a really simple first principle (logic based?) says that the motor will have to work harder to turn the larger pairing than the smaller, and therefore more work will be wasted in noise or heat rather than propulsion.

So, then what if the same ratio is used with smaller numbers of teeth (but still matched in pitch) and use a hypothetical 21t contrate matched with a 7t pinion? Repeat, hypothetical exercise. Should there not be less work required to force the rotation of the smaller gears and be less output wasted?

Is there an engineer in the house?

Embs
 

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You called?


Several things going on here:

stress level and material properties - contact pressures, loads

sliding friction

error robustness

First point, it is not just about the number of teeth. If you use a different gear modulus then you can have the same diameter contrate with different number of teeth. Just look at some of the early brass gears, fine pitch without large diameter.

The error robusness is the bit that really determines the size of teeth that should be used. Misalignment and tolerances of build need larger teeth. A small inaccuracy should not lead to the gears disengaging and jumping teeth.

Too large teeth gives a pinion with too few teeth, you don't really want less than 8, the involute profile is compromised and you end up with more of a sliding action as the teeth engage and rotate, so friction gets higher and transmission losses increase, noise, heat, wear all the cost to you of speed and power.

Plastic teeth need a reasonable cross section to resist the high torques of modern motors. This can be achieved by increasing the depth of the tooth, but again that can lead to more rubbing. Look at the gears on the AutoArt cars, same pitch but really thin. Put a NSR motor in one of those cars and the gears are going to fail really quickly...

So 9:27 gives decent size plastic teeth, allows for reasonable mismatch, gears are not too large and the tranmission efficiency is good.
 

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A not expert take. Are all pinions the same diameter? I think so, 5.5 for in line. Tooth count and mesh aside

11:33 requires a larger spur gear so torque is multiplied. 8:24 is the same but the torque to the axle is reduced.

So wouldn't 8:24 give less tendency to break away under acceleration?

Now this all goes out the window on a Fly truck with 8:27 as the tyres are bigger so torque at the contact patch is reduced.

I suppose the same goes for angle winder with 6.5mm but my head hurts.
 

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QUOTE (Abarth Mike @ 24 Apr 2012, 10:33) <{POST_SNAPBACK}>11:33 requires a larger spur gear so torque is multiplied. 8:24 is the same but the torque to the axle is reduced.

No, torque multiplication is simply a product of the gear ratio (excluding losses) not to do with gear sizes
 

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Its true that 27/9 = 3 as well as 30/10 = 3 as well as 33/11 = 3. However that is the average mechanical advantage. The instantaneous mechanical advantage is a little more complicated and is basically the advantage with a sinusoidal wave superimposed over it. This sinusiodal ripple becomes smaller and smaller the larger the gear set. So 33/11 will be smoother that 24/8, that is the deviation from the average mechanical advantage of 3 will be less per revolution. Google something like non linear gears or some such similar thing.

cheers
rick1776
 

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QUOTE (Abarth Mike @ 24 Apr 2012, 09:33) <{POST_SNAPBACK}>Are all pinions the same diameter? In many makes they are not.
There are a few makes that do have a common size pinion with different numbers of teeth.
Usually the pinions that are near the correct pitch for the spur / crown mesh better than those where the tooth form has been compromised to get the "wrong" number of teeth on the pinion.

QUOTE (RikoRocket @ 24 Apr 2012, 09:13) <{POST_SNAPBACK}>Plastic teeth need a reasonable cross section to resist the high torques of modern motors. This can be achieved by increasing the depth of the tooth, but again that can lead to more rubbing. Look at the gears on the AutoArt cars, same pitch but really thin. Put a NSR motor in one of those cars and the gears are going to fail really quickly... Yes that is a good point but it doesn't seem to apply to all slot cars. The much more powerful cars generally use the 80 pitch gears which have considerably smaller teeth, they use a steel pinion and usually a plastic spur. These cars run ball races in the motor and axle, so there is no slop in the bearings - I think that's important with small teeth.
 

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currently, the major mfr's use consistent sized pinions; the same dia. pinion for the same configuration; IL = 5.5, SW = 6.5.

typically, more teeth=more work.
 

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Stoner opened the thread by asking questions about two very different sorts of slot car.

1 The sort of car for which 3:1 is about the right ratio

2 Euro sport where 6:1 is about the right ratio

As the motor power and gear ratio of these two sorts of slot car is very different, nobody should be surprised that the gears normally used are different.

The 5.5 and 6.5mm pinion diameter standard from companies such as Slot it are widely used in cars where 3:1 is about the right ratio, and completely unsuitable for Euro sport
 

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Generally speaking even if both ratios are say 3:1 a lower toothed pinion will have better braking so 30:10 will have better braking than 33:11 but on the other hand they will both have the same top end.

One reason for having the higher pinion would be to reduce the braking and there fore reduce chatter. You could also go the other way and say lower pinion will give you better breaking and therefore stop quickest .
 

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Lee Green
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Yes rick that maybe but on a slot track the top speed so long as its the same ratios are generally speaking going to be virtually the same whereas the difference between a 9 and 11 tooth pinion braking is a big difference
 

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27:9 seems to be the basic setup for 1/32 inline cars but what is it with sidewinder and anglewinder cars is it 36:12? - I think Ninco run a 34:12 and I think some of NC-2 cars have 33:11?
Then with the 1/24 cars we use 44:11 or 38:10

So there are obviously factors at play such as wheel size that require one to expend some brain power to understand it all

so far I have worked out that on my track a 27:10 is about 3/10 quicker than the same car with a 27:9 ratio so I will race that setup


DM
 

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Flange are you saying that 27/9 = 3 will have better braking than 33/11 = 3 ?? I have to disagree with you on that, sorry. Or are you saying 27/9 will give more braking than 27/11 ?? In that case yes. Mechanical advantage is mechanical advantage. Its not changed since Leonardo da Vinci invented the pulley system.

OK had a think about it and yes the 33/11 will possibly have less chatter under brakes as the +/- deviation from a mechanical advantge of 3 will be less. The 27/9 will possible lock up as the +/- deviation from a mechanical advantage of 3 will be greater. Without sitting down to do the calculations it may go as high as 3.05 and down to 2.95 as the gears rotate for the 27/9 set and the 33/11 set may be 3.02 down to 2.98. These are just guesses as Id have to sit down and do som trig maths to work it out.

cheers
rick1776
 

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Lee Green
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Life's not all just maths , this is from experience of the way cars go
 

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QUOTE (Flange @ 24 Apr 2012, 17:29) <{POST_SNAPBACK}>Generally speaking even if both ratios are say 3:1 a lower toothed pinion will have better braking so 30:10 will have better braking than 33:11 but on the other hand they will both have the same top end.
Please tell us all which makes of gear you have experienced that with.
 
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