Heq5pro Backlash Setting

[pjphilli]

Hi
I am still in the process of refining the setup of my Heq5Pro mount.
The Set Backlash feature was set at zero in the original software (Ver 3.2.2). I have now set it to the default of 10 arcmin as recommended in
the Instruction Manual. My question "Is there an optimal way of adjusting
the Set Backlash?"
Cheers Peter

[pjphilli]

Hi to Myself
Since I have had no replies from my learned IceInSpace friends on this subject perhaps I have found the ultimate silly question?
Anyway, I took advantage of the daylight Moon yesterday to do some backlash adjustments to my HEQ5PRO mount. First, I adjusted out a bit of slack in the DEC gears, the RA was Ok in this respect. Then I imaged the edge of the Moon and with the Set Backlash at zero. I found that three very brief taps of the DEC movement button were needed to reverse DEC movement and achieve one slight movement in the Moon image. I then tried 10arcmins of Set Backlash and discovered that this was obviously too much. I eventually ended up with a Set Backlash setting of 1arcmin. With this setting a very brief tap on either direction of the DEC buttons gives an immediate equal small movement of the image in the respective direction. I set the RA Set Backlash at the same amount.
Comments would still be appreciated!
Cheers

[Tandum]

I'm using PHD for guiding and it says it is adjusting for backlash in it's alignment procedure, so I've never looked at it :)

[h0ughy]

while guiding i have it st to 0 as the software is doing the work

[Kevnool]

That is a lovely choice of words

[pjphilli]

Thanks Robin,David and Kev for your replies.
I previously was using an EQ5 mount which is a good little mount for its price but it was let down by the cheap tracking motors. The backlash in these stepper motors/gearboxes was quite large. Although PHD took this into account when performing calibration, when tracking it could not advance the scope across the backlash gap faster than the sidereal rate. Hence, the PHD corrections often got lost in the large backlash gap.
When I was adjusting out the excess gear slop in my HEQ5PRO I could see that the backlash correction was in effect speeding the mount across the backlash gap at fast slewing speed. This means for instance that when PHD wants to change direction in DEC guiding it would encounter virtually no backlash delay. It remains to be seen, but I think that this would be an advantage.
Incidentally, before I made the the above adjustments I found that the backlash of the mount straight out of the box was quite small and PHD had little problem with it.
Say Kev - those skies at Broken Hill must be a skywatchers paradise!
Cheers Peter

[JohnH]

Peter,

My understanding is that you should always set 0 for RA backlash, the reason is you should not guide at more than 1x siderial (0.5 is better) so the RA gears are in constant motion or at worst stationary and therefore never unload - even when the correction is -ve.

I also set DEC to 0 in the controller and do my best to eliminate DEC corrections with accurate polar alignment. Residual DEC drift is one direction only - so I set PHD to apply corrections in the opposite direction to that (and keep the agressiveness down) and thus overshoot and DEC backlash problems are avoided....mostly.

[pjphilli]

Hi John
Thanks for you interesting comment especially regarding Set Backlash on RA. I tend to agree with what you have said and on thinking about it perhaps the backlash correction could cause problems with RA guiding where backlash normally does not come into play if you ensure that a small positive load is kept on the RA gearing. I now think that I will remove the Set Backlash from RA. As far as DEC is concerned, I too polar align carefully and I tend to find that the DEC, when it does move, tends to oscillate slightly in each direction but generally drifts off slowly in one of the directions. So I usually have PHD dec guiding set to Auto so that over a long period of multiple imaging the images stays mostly in the same position on the screen. I think that the Agressiveness setting in PHD covers both RA and DEC? - so to optimise RA guiding I usually have it set in the 50-60% region.
Cheers Peter

[Kevnool]

Well Peter most nights you can observe here except tonight with a severe weather warning for strong winds tonight ....i hope Sab,s not looking but the cloud ratio to melbourne is 1:10...sorry Sab....cheers Kev.