
10112008, 10:04 PM

#1

Tech Champion
Join Date: Sep 2008
Location: Deerfield, WI
Posts: 5,582

Spur and Pinion Math
I just want to see if this holds water.
P = Pitch
Diameter of the Spur = D, Number of teeth on the Spur = N.
diameter of the Pinion = d, Number of teeth on the pinion = n.
D = N/P for the working diameter of the Spur
d = n/P for the working diameter of the Pinion
Radius = D/2 or d/2 for Spur and pinion
My internal ratio for my car is 2.0588.
FDR = (Spur/Pinion) * 2.0588
If the distance between my spur gear center and the center of my motor shaft is 1.125 inches, I need a pinion and spur that the combined working radii are equal to 1.125 inches +/ the extra 1/8 inch my motor can still be adjusted. I calculate the the radius of the Spur, the radius of the pinion and add them together. My final number should end up between 1 and 1.25 inches. In my case I also had to end up with an FDR of 3.4 to match my 17.5 brushless.
so...
((93/64)/2) + ((56/64)/2)) = 1.164" which is between 1 and 1.25 inches.
and
(93/56) x 2.0588 = 3.419 FDR
Seem reasonable?
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John Higgins former student of The Ian Ruggles Negative Reinforcement Driving School. The "Team Principal".



10112008, 10:07 PM

#2

Super Moderator
Join Date: Sep 2003
Location: Semper Fi
Posts: 27,202

Quote:
Originally Posted by liljohn1064
I just want to see if this holds water.
P = Pitch
Diameter of the Spur = D, Number of teeth on the Spur = N.
diameter of the Pinion = d, Number of teeth on the pinion = n.
D = N/P for the working diameter of the Spur
d = n/P for the working diameter of the Pinion
Radius = D/2 or d/2 for Spur and pinion
My internal ratio for my car is 2.0588.
FDR = (Spur/Pinion) * 2.0588
If the distance between my spur gear center and the center of my motor shaft is 1.125 inches, I need a pinion and spur that the combined working radii are equal to 1.125 inches +/ the extra 1/8 inch my motor can still be adjusted. I calculate the the radius of the Spur, the radius of the pinion and add them together. My final number should end up between 1 and 1.25 inches. In my case I also had to end up with an FDR of 3.4 to match my 17.5 brushless.
so...
((93/64)/2) + ((56/64)/2)) = 1.164" which is between 1 and 1.25 inches.
and
(93/56) x 2.0588 = 3.419 FDR
Seem reasonable?

for the E4 you need a total teeth count (pinion and pur) for 64 pitch between 137 to 140 to have a good mesh , so you will need a 88 spur and a 52 pinion to be in the 3.4 fdr range
for 48 pitch you need a total teeth counf of 105 teeth.



10112008, 10:29 PM

#3

Tech Champion
Join Date: Sep 2008
Location: Deerfield, WI
Posts: 5,582

Quote:
Originally Posted by Marcos.J
for the E4 you need a total teeth count (pinion and pur) for 64 pitch between 137 to 140 to have a good mesh , so you will need a 88 spur and a 52 pinion to be in the 3.4 fdr range
for 48 pitch you need a total teeth count of 105 teeth.

Thanks! I do need to research the mesh count. The only thing I stumbled across tonight was that 48 pitch gears need at least 17 teeth on the pinion to make effective contact. I'm pretty careful when adjusting backlash, just didn't know I could over do it with teeth.
__________________
John Higgins former student of The Ian Ruggles Negative Reinforcement Driving School. The "Team Principal".



10122008, 05:26 AM

#4

Tech Master
Join Date: Jul 2007
Location: Mooresville, NC
Posts: 1,187

Quote:
Originally Posted by liljohn1064
I just want to see if this holds water.
P = Pitch
Diameter of the Spur = D, Number of teeth on the Spur = N.
diameter of the Pinion = d, Number of teeth on the pinion = n.
D = N/P for the working diameter of the Spur
d = n/P for the working diameter of the Pinion
Radius = D/2 or d/2 for Spur and pinion
My internal ratio for my car is 2.0588.
FDR = (Spur/Pinion) * 2.0588
If the distance between my spur gear center and the center of my motor shaft is 1.125 inches, I need a pinion and spur that the combined working radii are equal to 1.125 inches +/ the extra 1/8 inch my motor can still be adjusted. I calculate the the radius of the Spur, the radius of the pinion and add them together. My final number should end up between 1 and 1.25 inches. In my case I also had to end up with an FDR of 3.4 to match my 17.5 brushless.
so...
((93/64)/2) + ((56/64)/2)) = 1.164" which is between 1 and 1.25 inches.
and
(93/56) x 2.0588 = 3.419 FDR
Seem reasonable?

Try: http://www.rcracing.com/Gear_Ratio_Program_1100.cfm



10122008, 07:44 AM

#5

Tech Champion
Join Date: Sep 2008
Location: Deerfield, WI
Posts: 5,582

Quote:
Originally Posted by lidebt2

I was using that to find and chart my initial ratios. That is one nice program. The only thing it didn't have was the gear radius. I bought the right spurs and pinions to get my ratios, but ended up short distance wise. The spur and pinion almost made contact. Finding the pinions I need is going to be the hard part.
__________________
John Higgins former student of The Ian Ruggles Negative Reinforcement Driving School. The "Team Principal".



10122008, 09:35 AM

#6

Tech Elite
Join Date: Jul 2008
Location: Sonoma County
Posts: 2,018

The only time I really need to use math is when I need to find my FDR. I gear by motor temperature. If I hit in the range of 160170F then I'm geared right where I want to be.
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10122008, 06:24 PM

#7

Tech Regular
Join Date: Aug 2008
Location: RVA
Posts: 455

48P there are 48 teeth per inch, straight line not diameter or radius.
64P = 64 teeth per 1 inch.
Tim



10132008, 07:37 AM

#8

Tech Champion
Join Date: Sep 2008
Location: Deerfield, WI
Posts: 5,582

Quote:
Originally Posted by got2bqik
48P there are 48 teeth per inch, straight line not diameter or radius.
64P = 64 teeth per 1 inch.
Tim

Wrong.
http://www.robotgames.net/Resources/Gears/gears.htm
Diametral Pitch
Diametral Pitch (or just "Pitch") P = Number of teeth / Pitch Diameter.
The Pitch Diameter Circle goes to approximately half way up the height of the teeth.
Common (diametral) pitches are 12 (big teeth), 24, 32, 48, 64 (fine teeth).
Knowing the pitch diameter is very useful. To figure out how far apart the shafts of two gears should be, add the pitch radius of the first gear with the pitch radius of the second gear.
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John Higgins former student of The Ian Ruggles Negative Reinforcement Driving School. The "Team Principal".



11012008, 11:22 AM

#9

Tech Regular
Join Date: May 2007
Posts: 365

just look at the chart.. it has almost every rc car model you need
http://spreadsheets.google.com/pub?k...jA7nLsQ7N2eRfg
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11012008, 12:17 PM

#10

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