Which flexible coupling is better?

[onemilimeter]

I wish to measure the vibration of a motor which is connected (via flexible coupling) to a DC generator as load. I found two types of flexible coupling as shown in attached image. Which one is better for this application (to minimize the vibration due to mis-alignment)?

Thanks

 

[waross]

Bob M3, Google zero-backlash gears.

Bill
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"Why not the best?"
Jimmy Carter

 

[onemilimeter]

Thanks waross for your suggestion to google "zero-backlash gears".

 

[sreid]

I think Back-Lash and Torsional Rigidity have been adequately explained by others. The zero back lash and torsional rigidity of the Zero-Max "Flex Disk" coupling should be obvious by looking at a picture of one.

Clamp style hubs are generally prefered. Set screws mar the shaft and tend to loosen even if two are used at 90 degrees.