Quote:
Originally Posted by GeeTwo
The bull gear is the gear which handles the greatest torque in a drive train. I am most familiar with the term in relation to submarine drive trains, but I have seen it in other contexts.
See this thread. Essentially, near or beyond this limit, the sun gear is too small to engage the planetary gears. (I assumed that there are at least three; if you only have two, you can go higher). |
"You must spread some Reputation around before giving it to GeeTwo again"
I never considered that particular issue before, very neat! Seems obvious in retrospect...
Of course one could solve it by placing the gears in front or behind each other, but that seems useless when you could just stack two stages.
Quote:
Originally Posted by chadr03
If weight is your only concern larger gears can be machined thinner below the teeth and spoked to be much lighter. A gear rim will typically have significant stiffness and rating if there is at least two tooth depths of solid material below the root but beyond that most of the material is not very highly stressed. So you can get quite high ratios without significant addition of weight when compared to a solid gear.
That being said the main limitation in very large reduction single stage gearing is deflection across the pinion under load. The larger the ratio the greater the gear forces and the larger the gear forces the more deflection along the shaft. When the pinion deflects all of the loading will move toward one end of the tooth effectively reducing the face width. If there isn't significant loading then large reductions can be made with a single stage. If there is large loading deflection starts to become a real issue when you start getting much higher than the 4:1 ratios that are common in single reduction boxes.
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If I lighten the gears, then the problem becomes a lot more complex due to the need to calculate the volume of leftover material with respect to the radius of the gear needed to preserve strength. I'm really looking for a mathematical solution here, not a realistic one.
Correct me if I'm off, but shouldn't the pinion tooth load only be proportional to the mechanical power the motor is outputting and the pitch radius of the pinion, and be independent of the gear ratio?