Odd Dec Balance - iOptron CEM 70

[Grifflin]

Hi All

I have an iOptron CEM 70 mount and while the RA balances just fine, the Dec axis balance is weird.  If the balance is way off then it behaves as you would expect when it is front or back heavy.  however, as it gets close to balance it settles at about a 35 degree angle to the West.  If I push it further West it will return to its 35 degree position as if it was back heavy but if I push it in an East direction it returns to its rest position as if it was front heavy.  If I move the scope forward or back from this point it seems to push it into an unbalanced state.

Now, I have heard about Z axis balancing and I see that iOptron have a Z axis balance counterweight which has a very short counterweight shaft which screws onto the side of the saddle (there is a screw hole on either side to accept this).  I'm not really clear what this does and if it would help me to get a 'proper' balance in Dec.

All that said, my guiding seems to be ok (0.7 - 0.9 arc sec/pix) with a SW 80ED on it but if I put a heavier scope on it and start to work the mount a bit more, is this balance weirdness going to start to hurt me?

OR....am I missing something and making a newbie mistake?

Really grateful for any thoughts or insights here please.

Neil

[Stefek]

The mount itself will deal with that , especially with relatively light scope. I have just taken 8mm threaded bar, cut it to about 20cm and screwed into the hole on DEC saddle . 

Asked my neighbor to cut me few pieces of steel with 30mm diameter with various lengths (from 5 to 50mm) and drill it and make the thread in the center. 

Now I have various weights that I can just screw closer or further and balance the scope 

(Esprit 120 or Edge HD 8 )perfectly .  I regularly have guiding RMS in 0.4-06" range.

[Grifflin]

16 hours ago, Stefek said:

The mount itself will deal with that , especially with relatively light scope. I have just taken 8mm threaded bar, cut it to about 20cm and screwed into the hole on DEC saddle . 

Asked my neighbor to cut me few pieces of steel with 30mm diameter with various lengths (from 5 to 50mm) and drill it and make the thread in the center. 

Now I have various weights that I can just screw closer or further and balance the scope 

(Esprit 120 or Edge HD 8 )perfectly .  I regularly have guiding RMS in 0.4-06" range.

Thanks Stefek

Just for clarity, are you saying that you have also had a similar issue and you have used a small counterweight on the saddle to correct it?

Neil

[Stefek]

Yes, I have Esprit 120 and with guiding scope, filterwheel, autofocuser  it is almost impossible to balance it only by moving counterweight on RA and shifting scope backward and forward , so that with disengaged RA and DEC , the scope stays in any position that you push it to.  One need so called 3D balance , adding additional counterweights on DEC and also on RA .(i also have additional weight on RA, which I made by drilling the hole in my counterweight, made thread in it , and screwed in a bar with some weight on it . That additional bar is perpendicular to main counterweight shaft. My balancing sequence is:

1.  put RA axis to horizontal position , and align the DEC axis so that scope stays horizontal. (only by moving the scope backward or forward) 

2. Keeping that  position will move counterweights so that it gets balanced along RA axis.

3. At that point I have the system balanced in horizontal position. Will move it to "home" position. I lock DEC and will move RA , if it does not stay , I rotate the counterweight with additional bar on it until RA stays wherever I put it.

4. Then I lock RA and if DEC does not stay where I push it, I would move DEC counterweight  in or out  until DEC stays whetever I put it.  After all I just check whether it all stays wherever I push with both axes disengaged. 

 

 

[Grifflin]

2 minutes ago, Stefek said:

Yes, I have Esprit 120 and with guiding scope, filterwheel, autofocuser  it is almost impossible to balance it only by moving counterweight on RA and shifting scope backward and forward , so that with disengaged RA and DEC , the scope stays in any position that you push it to.  One need so called 3D balance , adding additional counterweights on DEC and also on RA .(i also have additional weight on RA, which I made by drilling the hole in my counterweight, made thread in it , and screwed in a bar with some weight on it . That additional bar is perpendicular to main counterweight shaft. My balancing sequence is:

1.  put RA axis to horizontal position , and align the DEC axis so that scope stays horizontal. (only by moving the scope backward or forward) 

2. Keeping that  position will move counterweights so that it gets balanced along RA axis.

3. At that point I have the system balanced in horizontal position. Will move it to "home" position. I lock DEC and will move RA , if it does not stay , I rotate the counterweight with additional bar on it until RA stays wherever I put it.

4. Then I lock RA and if DEC does not stay where I push it, I would move DEC counterweight  in or out  until DEC stays whetever I put it.  After all I just check whether it all stays wherever I push with both axes disengaged. 

 

 

Got it...thank you.  😀

[jhart]

I have seen a YouTube video which claims this DEC balance problem can be solved by angling the counterweight bar slightly.  Has anyone had success with that method?

[Grifflin]

22 hours ago, jhart said:

I have seen a YouTube video which claims this DEC balance problem can be solved by angling the counterweight bar slightly.  Has anyone had success with that method?

Not seen that....have you got a link?

[jhart]

Hi,

Here is the link to the Youtube video I mentioned: https://www.youtube.com/watch?v=AnE5ikgzX7s  

 

[Grifflin]

On 01/12/2021 at 01:36, jhart said:

Hi,

Here is the link to the Youtube video I mentioned: https://www.youtube.com/watch?v=AnE5ikgzX7s  

 

Thanks Jhart....apologies for the delay in replying, only just saw your post.  Checked out the video...to be honest, my  RA balance seems to be ok so I'm loath to start messing with it just yet.  I'm sorting out something for the Dec saddle first (not done yet) to see what difference that makes.

Neil

[EarthLTD]

On 30/11/2021 at 18:36, jhart said:

Hi,

Here is the link to the Youtube video I mentioned: https://www.youtube.com/watch?v=AnE5ikgzX7s  

 

Beware this person's videos.  He gives bad advice.  There is a reason comments aren't allowed. 

[EarthLTD]

On 21/11/2021 at 13:12, Grifflin said:

Hi All

I have an iOptron CEM 70 mount and while the RA balances just fine, the Dec axis balance is weird.  If the balance is way off then it behaves as you would expect when it is front or back heavy.  however, as it gets close to balance it settles at about a 35 degree angle to the West.  If I push it further West it will return to its 35 degree position as if it was back heavy but if I push it in an East direction it returns to its rest position as if it was front heavy.  If I move the scope forward or back from this point it seems to push it into an unbalanced state.

Now, I have heard about Z axis balancing and I see that iOptron have a Z axis balance counterweight which has a very short counterweight shaft which screws onto the side of the saddle (there is a screw hole on either side to accept this).  I'm not really clear what this does and if it would help me to get a 'proper' balance in Dec.

All that said, my guiding seems to be ok (0.7 - 0.9 arc sec/pix) with a SW 80ED on it but if I put a heavier scope on it and start to work the mount a bit more, is this balance weirdness going to start to hurt me?

OR....am I missing something and making a newbie mistake?

Really grateful for any thoughts or insights here please.

Neil

The Z-axis balance on my CEM 70G was way off.  I had two issues.  My C11 has an off center balance so after I balanced RA, the DEC would go off to the side. 

The bigger problem with the RA was with the manufacture.  The Counter Weight shaft was not in a straight line with the load.  It was off by more than the small adjustment of others with youtube videos.  I don't recommend what I ended up doing for anyone else. 

I took the bolt out at the top o the CW shaft and loosened the two smaller screws holding the shaft's position on the RA axis.  I could position the CW shaft such the the imbalance was very close.  But I could see that the bolt would not return to it's hole.  The movement distance was too much for the holes to align.  I very carefully used a dremmel and made the bolt hole more of a slot.  To prevent the bolt from moving in the slot, I made a crescent shaped piece of metal in the extra space to keep the bolt from sliding out of position.

The final corrections are done with two small CW that Ioptron sells for this purpose.  One goes on the saddle for DEC.  The other was put on a 10k CW in a hole that I drilled and tapped.  I can easily put it on the left or right or anywhere in between. without changing the horizontal balance.  Now it's actually fun to balance no matter what equipment I am using.

Ron

[Same old newbie alert]

Its the 3rd axis highlighted by its fluid axis... Don't misalign the  the counterweight bar as the grubscrews is what's holding it all together.. ioptron don't recommend nor have heard of it

[Grifflin]

Thanks all.  Just as a follow up, I have not touched the RA axis but have used an M8 rod cut to about 10cm which is screwed into the Dec saddle.  Whilst not perfect, it has made a noticeable improvement to balance and, perhaps more importantly, guiding.  Still not quite right but my guiding has gone from about 0.7-0.9 RMS to about 0.5-0.7 RMS.

Neil