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Gearing short-cut


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#1 Ecurie Martini

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Posted 05 December 2017 - 01:25 AM

This may be self-evident and/or well known.  It is something that popped out of some gear selection computations that I did and thought I would pass it on:

 

A useful shortcut when choosing sidewinder gear ratios:

 

If you have a sidewinder set up with a fixed motor shaft to axle distance, are using standard pitch gears ( 48, 64, 72 etc) and want to change ratios, any combination of pinion and spur with the same total number of teeth will work e.g. 14:45 > 12:47 > 18:41 etc. 

 

I don't know if this will work with the compromise pitch/diameter gears used by Slot It and other RTR manufacturers.

 

EM


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Alan Schwartz




#2 Pablo

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Posted 05 December 2017 - 02:59 PM

Does it work with anglewinders also?


Paul Wolcott

#3 Ecurie Martini

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Posted 05 December 2017 - 04:41 PM

That's an interesting question.  I don't have a ready answer but I'll make a couple of suggestions. (i.e. what follows is, at best, slightly informed guesses)

 

There are 3 kinds of anglewinder gear setups with which I am familiar - the original straight pinion/straight spur bang them together at the corners, angled pinion/straight spur and straight pinion/angled spur.  In the first case I think it will work.  Although my guess is that it will work for #2 and #3, I'm not sure how to go about calculating the effective pitch diameter of an angled gear.

 

There is, however, a little "wiggle room"  Because the gears meet at an angle, an optimum mesh point can be selected by sliding one or the other to this point on the shaft or axle.

 

EM


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#4 Pablo

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Posted 05 December 2017 - 04:59 PM

I think you're right, and I think it will work if my memory is correct :scratch_one-s_head:


Paul Wolcott

#5 James Wendel

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Posted 05 December 2017 - 05:51 PM

Yes, it always works, because Math.   :D    C=(pi)*D.  Circumference is directly proportional to diameter. 

 

If you change the circumference of two circles (or two gears) by the same amount, then the diameters will also change by the same amount, regardless of the size of the circles.  The teeth are the same or they would not mesh.  Increase or decrease does not matter.  The absolute value of the change will be the same.

 

Disclaimer: this is true in the "perfect world" of math.  Real world manufacturing imperfections could cause some variation.


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#6 Bazzie

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Posted 06 December 2017 - 03:15 AM

Angle winders are usually easy though within reason. I usually just move the spacers/washers from one side to the other to take up slop. That way you can easily make small adjustments which often makes a world of difference


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#7 Pablo

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Posted 08 December 2017 - 07:17 PM

Alan, your info helped me with my Montague replica build.

I was waffling between 8/42 and 7/38.

 

8/42 is 5.25 and tooth count is 50.

7/38 is 5.43 and tooth count is 45.

 

This tells me the 8/42 combo will make the motor sit at a less acute angle, since the total tooth count is significantly higher.

Not rocket science, but it did give me an easy way to make the correct decision.

 

Plus, my friend Bill tells me they didn't have 7T 64P pinions in 1973 :)


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