Quote:
Originally Posted by Gama
Friction drives use 2 rollers pressed firmly together or by a band.
They provide very low or no PEC.
The larger mount mobs all use this method.
You can use the worm setup to drive the smaller roller. A few images of one here http://www.observatoryscope.com/prot...operation.html
Theo |
thanks Theo for the advice.
I do know a thing or two about PE and different drive methods.
Are you sure you're not confusing PE for backlash?
Any gearbox drive train will have PE.
The final drive method turning the RA axis obviously contributes
the most 'error' to the final drive shaft.
I know drive belts (your example shows belts on both axes) would have
almost no
backlash, but the biggest PE component would be the
accuracy of the smaller pulley wheel driving the big RA pulley.
If this is dead on concentric, then the next biggest PE would be the
accuracy of the worm/wheel driving this small wheel.
You're probably correct that this whole combination has less PE
than a rather large , well machined worm/worm wheel driving a
GEM.
But it would still have some PE.
I have measured the PE in several systems over the years (using K3
Drift Explorer) and for gear trains it is usually a sine wave.
The main sine wave is repeating/cyclic fast-then-slow PE of the very
last gear in your drive train.
This is the machining errors of that gear.
Superimposed on that sinewave is a smaller cyclic sine wave which is
the next gear back in the drive train.
These are measurable and able to be zeroed out in the Bartels system.
As there is a worm involved, albeit one gear back in the drive train of
your example, it would have a measurable error and contribute PE.
Although I fully appreciate your advice, I thought it would do no harm
to attempt to machine a worm/worm gear.
Steve