Torque Impact of Gear Train?

[Bayview-BOOM]

Assuming an RPM-increase gear-train, if more gears are added to the gear train, without changing the step-up ratio of the total train, and without changing the desired output torque, will the first gear require more torque to turn it? Less torque? Or no change?

For example, compare:
1:64
vs
1:4:4:4

Will there be any difference in the torque required to turn the first gear? If not, will there be a reduction in the amount of torque required at the intermediate stages?

 

[3DDave]

There may be a tiny reduction in initial force with more gears as any backlash will prevent later gears from instantaneously moving, but there's also the likelihood that more gears will generate more friction and make up for that.

You will also have more mass at higher RPM in the later stages, making for more inertia to accelerate but it will likely be more compact than a single stage.

I presume this is all academic or you would have mentioned why you wanted to know.

The main effects are easy enough to calculate and will change depending on the details of the assembly. Only you can know the rotational inertia of the gears based on material and design. You may also need to look at the torque losses due to friction.

I am not sure how sequential identical stages could be configured, at least not with spur gears, without interference between the gear shafts.

 

[Bayview-BOOM]

When you say the main effects are easy to calculate, are you talking about friction?

I'm not a professional gear designer but I'm pretty sure that sequential stages can have identical ratios. That doesn't mean the gears are identical.

 

[brucesilver]

Assuming an RPM-increase gear-train, if more gears are added to the gear train, without changing the step-up ratio of the total train, and without changing the desired output torque, will the first gear require more torque to turn it? Less torque? Or no change?

For example, compare:
1:64
vs
1:4:4:4

Will there be any difference in the torque required to turn the first gear? If not, will there be a reduction in the amount of torque required at the intermediate stages?

Nah, the torque at the input stays the same if the overall ratio and output torque don’t change. You’re just spreading the same work over more stages. The intermediates might see less torque individually, but input torque doesn’t change.

 

[3DDave]

The input torque stays the same if the input torque remains the same.

The acceleration and throughput of torque changes.

There are more friction surfaces and more bearings to contribute friction with more stages.

Draw the stages and show the selected gears.

You don't need to be a professional gear designer, just have a 2nd year engineering education. If you don't have at least that you won't have much success designing a gear train.

 

[mfgenggear]

just add to the really good advice all ready given.
it really depends on many factors.
application
design of the gear box
design and type of gears ,
example helical vs spur, or bevel or size and
required output torque.
the AGMA quality of gears and surface finish.
the precision and quality of shafts, bearing and type of lubrication.
I am old and lazy. I use gear programs for
input torque and rpm, to output torque and rpm. and it matters for reliability and and number of cycles. type and material properties. hertz hardness.
I mean it's not a simple answer.
coefficient of friction of the materials.
efficiency is all or part of the equation.

 

[mfgenggear]

To my understanding a goal of 97-99% efficientcy. Which njas commented by 3Ddave
Should be correct.

 

[GregLocock]

Yup you lose about 1% in each interface, with spur gears, properly designed. Double that with helicals.

 

[dtimberlake]

With all them gears I'd expect lubrication churning etc might start to matter.

 

[3DDave]

If one wants to know more: https://apps.dtic.mil/sti/pdfs/ADA107933.pdf

Fuze Gear Train Efficiency​

Miscellaneous Citation | Accession Number: ADA107933

Abstract:​

This report describes the results of an analytical study of the point efficiencies of various types of fuze gear trains. Involute and clock-tooth profiles for two and three pass step-up gear meshes which operate in spin and nonspin environments are compared, and the differences explored. The conclusions of an investigation concerning the geometrical factors which influence the point efficiencies of multipass step-up gear trains are discussed. The analyses on which these results are based are given in detail.