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Old 10-11-2008, 10:04 PM   #1
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Default 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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Old 10-11-2008, 10:07 PM   #2
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Quote:
Originally Posted by liljohn1064 View Post
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.
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Old 10-11-2008, 10:29 PM   #3
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Originally Posted by Marcos.J View Post
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.
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Old 10-12-2008, 05:26 AM   #4
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Quote:
Originally Posted by liljohn1064 View Post
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
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Old 10-12-2008, 07:44 AM   #5
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Originally Posted by lidebt2 View Post
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.
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Old 10-12-2008, 09:35 AM   #6
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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 160-170F then I'm geared right where I want to be.
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Old 10-12-2008, 06:24 PM   #7
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48P there are 48 teeth per inch, straight line not diameter or radius.
64P = 64 teeth per 1 inch.
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Old 10-13-2008, 07:37 AM   #8
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Originally Posted by got2bqik View Post
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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Old 11-01-2008, 11:22 AM   #9
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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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Old 11-01-2008, 12:17 PM   #10
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http://www.rctech.net/forum/electric...alculator.html
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