Slide 1
Meshing teeth connect the gears’ rotations
Meshing gears transmit rotation through their teeth. Their tooth counts determine the relationship between rotational speeds in a simple gear pair.
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The teeth must have compatible geometry to mesh smoothly. Equal spacing along the pitch circles ensures that one gear does not demand a different contact speed from its partner.
Slide 2
Twice as many teeth means half the speed in this pair
A gear with twice as many teeth turns half as fast when driven by a smaller gear. External gears turn in opposite directions.
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A 20-tooth gear driving a 60-tooth gear gives an ideal output speed one third of the input. An idler can reverse direction again without changing that overall tooth-count ratio.
Slide 3
More turning effect comes at the cost of speed
Torque is the turning effect of a force. An ideal reduction gear increases output torque while reducing speed. It does not increase the mechanical power supplied to the system.
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Power equals torque times angular speed. Real gearboxes deliver less output power because contact friction, lubricant motion and other losses convert some input into heat.
Slide 4
Successive stages multiply the ratios
A compound gear train combines successive ratios. Gears sharing a rigid shaft rotate together, linking one stage to the next.
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Two reductions of three to one produce a total reduction of nine to one. Adding stages can achieve compact ratios, but also introduces more bearings, alignment requirements and efficiency losses.
Slide 5
Clearance allows movement but delays reversal
Small tooth clearance allows assembly and lubrication but creates backlash. Reversing direction may take up that clearance before the output responds.
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Precision positioning systems may preload gears or measure the final output directly. Removing every clearance without considering heat and manufacturing variation can instead make a mechanism bind.
Sources
- Basics of Mechanical Design
MIT Center for Bits and Atoms
- Simple Machines
OpenStax