Gear Woes

[Simon G]

Ok, to start, I'm an aerospace engineer, not an ME. So gears are a new thing for me!

I'm trying to make a gear box for the chipuah (sp?) motors, but I'm banging my head against the wall, because it seems to me that I will surely shread gears with this monster of a motor.

According to my calculations, the tooth load on the pinion of the motor, at max 315 oz-in torque, tops out at 126.4 lbf. (19.688 in*lb of torque, 0.3115 pinion OD)

So at that force, according to my berg catalog, I should be shearing off the teeth of the 44T gear. That can't be right!

They give me a calculation of:

Wt (force transmitted) = (S*F*Y)/(DP)
where:
S is the max tooth stress (brass alloy 19ksi)
F is the face width (0.5" for the 44t gear)
Y is the lewis factor (0.399)
and DP is the diametral pitch, 36

Thus I get Wt of ~ 105 lbs which is < 126 lbs = BAD!

Am I being overly conservative???
What am I doing wrong???

Please help!

Thanks,
Simon