Hello Greg,
The result are very unusual for an reducer of this size.
With a 14 size PE can be around +/-15 at the best for an hole reducer and up to +/- 40
With a 17 the regular value is +/- 20
With a 20 it is around 10
With a 32 below 10.
I tested the fourth on real mounts. They are accurate in a repetitive way.
Even using second hand reducer, My "old" Crux 320 with its 32 reducer is around +/- 5 without PEC correction and guide at 0.3/0.2 total rms on stable sky with PEC enable with more than 40kg OTA load.
So the rule : the bigger the better.
The PE depends greatly of the accuracy of to position of the wave generator. 0.1mm variation in longitudinal position can create a larger PE. There is a sweet spot.
Lateral error introduce a dissymmetric shape in the PE graph a part of the sinusoid is lower than the other part. At the extreme, it is flat. That's call dedoidal moves. That can destroy the reducer.
That means if we put a geared motor reducer before, we take the risk to have a play in longitudinal that will enable the wave generator to move its longitudinal position upon the model of the harmonic reducer.
With right rotation, the wave generator will pull on the motor reducer axis and will go deeper, With right rotation, it will push and it will go back.
If the axis of the motor reducer has a small tilt play or if the motor attachment is a bit tilted, this will degrade the wave of the PE upon the load or sky position.
After one year of such process a reducer can have its native PE to go from +/- 20 to +/- 80.
I did this observation on several 14 reducer models.
Last, small geared motor reducer have usually a huge backlash (>1°), and upon the load and position on the sky this backlash will produce unwanted spike and peak into the guiding that can be huge.
Several mount maker solved this issues with belt. Other by using an other harmonic reducer instead of the geared reducer and a new one by linking the motor shaft directly to the reducer.
Of course adding an encoder at the end enable to hide all the trouble but this do not solve all the degradation in the long terms due to bad alignment of the wave generator.
That's why hollow shaft reducer are the best for us. Everything is under bearing and at the best position for years. Two drawbacks : they are heavier and there is no way to adjust anything.
That's the kind of model you choose ;-)
Only Zwo seems to understood that's. And they decided to test all there reducer. That's the only way to avoid putting a bad adjusted one in a mount.
Several (All ?) other did not and client have various trouble from time to time (peak in guiding, slip, irregular PE).
So in your case with this hollow 20 reducer, I am afraid you have no way to make any adjustment.
According to me such PE might indicate a product with a wrong wave generator longitudinal position, or a really bad / cheap product ? Last option would be a second hand reducer but yours is new.
On the model I tested, new Laifual hollow reducer 14 had a PE around +/-20.
I can give you the contact I have by pm
By the way say hello to Dan for me next time you see him ;-)
Cyrille
