Shaft Coupling

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Notes

  • Coupling is the most critical aspect of mechanics, and most failure occurs at the coupling.
  • Keyways do not work [1]
  • Clamps without keyway do not work. [2]
  • Clamp couplers appear to be the best, but what is their limit?
    • We saw 3500 lb drive on 4" radius, or DIY clamps at about 14k in lb with LifeTrac v8 nut planting.

Calculations

  • Shaft Torque Rating
  • Coefficient of friction of steel is 0.2 [3]
  • Split-shaft coupling under 1000 in lb - [4]
  • 2.25" shaft coupler is $400 and 14000 in lb. [5]
  • Double chain for up to 2.5" shaft is 11k in lb [6]
  • 2" clamping shaft coupling, $300, 20k in lb [7] just on round shaft. Implication is that keyway does not help, as they keyed version is rated for the same hold.
  • 60-20 double chain holds about 15k in lb, good for LifeTrac 4-9 models [8]
  • 80-20 does 38k in lb [9]
  • 100-20 is good for 70k in lb [10]. If we use a 6000 in lb motor - we can gear down only 12 times. This means 3500 lb drive from each wheel - which we already did using the tracks in LifeTrac 8. For 4WD, we would get 14,000 lb of traction force. For larger wheel loaders, we would need to go higher strength.
    • 100-20 sprocket - only 8" diameter.
  • Rather long - 8020 is 6" long Doublechain.png. Capacity goes way up with number of teeth (why?)

Coupling Types

Fastener Types

  • Quarter Turn coupler - can be removed many times. [13]
  • Huckbolt - clamp bolt that does not loosen - [14]. See dramatic loss of clamp using bolts.

More

File:Servocouplingguide.pdf

File:Helicalcouplings.pdf

Beamcoupling.png Beamcouplingrelief.png

This report discusses attributes of different types of shaft couplings used to transfer power from the engine shaft to the hydraulic pump.

Jaw Coupling

Please note that once a coupling is selected, special attention must be paid to the shaft keys. They must fit tightly, as any slack will eventually destroy the coupling.

File:CouplingDestroyedByKey.png

The jaw coupling is composed of three pieces:

  • Two coupling halves, to connect to each of the two halves, with three piece jaws to transfer power and a spider insert to make soft connection between the two jaw halves:
JawCoupling.png

Note: Experience has shown that this type of coupling does not work well with the Power Cube, as the spider insert fails after 40 to 100 hours of operation.


Solid Coupling

The solid coupling consists of a solid steel piece that connects to each of the two shafts and has set screws to secure the coupling to both shafts.

SolidCoupling.jpg

This is the currently preferred coupling and is used in new Power Cubes.

Double Roller Chain Coupling

The double roller chain coupling is composed of three pieces:

  • Two pieces connecting to each of the two shafts
  • A chain to transfer power between the two shaft couplings
ChainCoupling.jpg

This coupling looks promising, but has yet to be tested with the Power Cube.