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Let's get rid of the BL on the HEQ5 mount! A very simple way to do it.


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Hi to all.

The most popular mounts - even those that are included in  the small-medium range group, do drive the axes rotation  via worm wheel coupling . 
This one are plagued by the drawback that I have always considered very unpleasant: the mechanical play  is not properly controlled and it can’t be always limited within acceptable tolerance limits.

The adjustment of  Back Lash (BL) is entrusted to two screws (more often they are grains) usually positioned at 180 ° from each other. However - as we all know, even a wheel very slight eccentric creates
an inconstancy of contact with the worm: when the play is adjusted for an initial position of the axis, it is not in other positions. 
In other words, there are positions where the worm rotates with adequate friction, others in which the same friction can increase significantly, and still others where it is so reduced to the point 
that it causes excessive play. 
So, the tuning screws are  sometimes  too tight and sometimes too loose … mission impossible to find the right compromise! 

This behavior is already annoying in manual movement because  the task of pointing at an object  in a steady way  is not feasible because it ever  'jumps'. 
In photography it's even worse. 
Not only does an unavoidable backlash often  appears in Dec – and it is very badly correctable also by the autoguider software, but- and it is dirty worse, the tracking in RA does not perform evenly 
and smoothly.  The typical ‘micro’ irregularities in  star images is what we see in our shots. 

Many high range mounts adopt different methods to contain lashes, and the best ones adopt mechanical systems with which that error is reduced to zero. 

With this long introduction, I will tell you what very simple modification I thought of making on my HEQ5.

Please, stay tuned 🙂

Beppe

 

Edited by benzomobile
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Hi to all. The most popular mounts - even those that are included in  the small-medium range group, do drive the axes rotation  via worm wheel coupling .  This one are plagued by the drawback t

Just three preliminary notices:  - I take no responsibility in case of damage to your mount. I recommend these procedures to those who have a minimum of familiarity with the manipulation of mecha

Hi Kathleen. In reality the backlash due to the small gears  before the worm gear coupling is not so significant. On the other hand, the complicated combination of eccentricity and irregular

Posted Images

Posted (edited)

IMG_20210101_162958.thumb.jpg.039328b2cc102f88e358fc318cc1c847.jpg  IMG_20201025_151137.thumb.jpg.17dc9a4e380bb8446afba10acddcaff8.jpg                         IMG_20201025_151114.thumb.jpg.70f167de603a273b428eb694ee4aee89.jpg          

  IMG_20201025_151157.thumb.jpg.158d2351fce904b9717e691b2f7e072b.jpgIMG_20201025_151213.thumb.jpg.e248297ed0f4c19be8d452965f82b2f8.jpg

Just three preliminary notices: 

- I take no responsibility in case of damage to your mount. I recommend these procedures to those who have a minimum of familiarity with the manipulation of mechanical parts. 
- About mount taking apart procedure, please refer to https://www.astro-baby.com/heq5-rebuild/heq5-m1.htm  
- These mods are pretty identical for both axes, except for particular details that - in case, I will indicate .

Worm holders modification

Disassemble the holder, remove the full worm  assembly and get rid of the tuning grub

To apply each additional piece, I invite you to use the bi-component epoxy resin you see in the photo above left. 
Once cured, this adhesive acquires very high hardness and durability, provided that you mix the two components in equal quantities to obtain an optimal bond. I use a small digital scale to do it.

Get two pieces of aluminum profile (see pic above middle).
- a flat one 15mm wide and 1.5mm thick, and
- a square section one with a side of 15 mm.
A length of 20 cm is pretty enough for both of two.

Cut two pieces of the flat bar so that they can rest stacked on top each other at the base of the space between the two holes of the holder. 

Their corners will have to be filed so that the piece can be inserted inside the space without leaving gaps,  after which you can glue the piece in the correct position (pic above right).

Cut the square bar in order to obtain two cubes of 15 mm. File their edges and vertices to ensure that three sides of the cubes can come into close contact with the seats at the two ends of the holder.                                                 

Sets well with epoxy (pic below left)

Remove the small bronze cube that act as  stop of the adjustment grub and place them, with a small amount of grease on the space between the two aluminum cubes.                                                                                                                                                     

You have to  make sure that the bronze cube will enter without significant play; it  will be able to slide smoothly into the predisposed seat (pic below right).
If there is too much play, put adequate shim between the cubes and the holder.  Put in epoxy.


If everything is fine (please do double check 😉 ) let the resin cure itself.  Just in less than 5 hours the adhesion will start to be  dirty strong.   Remove the bronze cube (it was only there to calibrate the gap).

Until next time for next step ... 

Beppe

 

 

 

 



   

Edited by benzomobile
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I sense that at some point - a spring will be introduced to the assembly or maybe permanent magnet?

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2 minutes ago, vlaiv said:

I sense that at some point - a spring will be introduced to the assembly or maybe permanent magnet?

Just a ... tiny spring 😉 

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Posted (edited)

                                                                                                                                                                                                                

IMG_20201027_152315.thumb.jpg.54ab2120c57c7d7d2605f9d4758b6569.jpg        IMG_20201027_154351.thumb.jpg.2ce691a2efc2e557067a1006bcab207b.jpg      IMG_20200816_161027.thumb.jpg.9acf32ac7557fd85b0a202dc0fc5dcb1.jpg

 

Are we all here for now? If the answer is yes, then we can move on. Now comes the most critical stage of the whole process ... 

Reinstall the worm on its holder and  carefully reassemble the axle.  Remove the motor gear. 
Tighten securely the three M5 holder bolts making sure that the worm can rotate smoothly and playlessy (use your thumb and index finger on the gear) (pic at side)

Insert a sharp tip one M4 threading tap into the threaded hole on the middle of the convex part of the holder (obviously you have already pulled away the grub) (pic above left)
Tighten the tap so as to leave a good centering mark on to wall of bearing housing of Dec axis or on to small plate at the base of RA axle base collar.  Both have the height of about 8mm.

Now mount a 3.2mm bit on your drill and - entering the threaded hole, make a pilot hole about of 2-3mm deep inside the mark you have made before.  This operation can be done freehandly (pic above right).

 

IMG_20201030_152303.thumb.jpg.15c050827598c82dbad90549d8cca778.jpg

 

 

Once this is done, you'll again have to disassemble the holder and remove the worm. 

Using a bench drill, enlarge the threaded hole in the holder with a 4.2mm drill bit. 

(See pic at side)

 

 

 

 

 

 

Take the block axle out and place it firmly on the base of the bench drill to carefully drill with a 4mm bit through the bearing housing, until  the Dec  bearing outer cage. Please, be gentle and careful not to damage it! (pic below left ... don't mind the grease), or to cross the whole small plate next RA axle base collar  (pics below middle and  right).

IMG_20200815_181958.thumb.jpg.13122647e5de6f6ed300e370aab32bf6.jpg                     IMG_20201027_155300.thumb.jpg.63c95d34abd744c5f1cb78f6eebf64f5.jpg                 IMG_20201216_140038.thumb.jpg.15323b731abc246242bea0cae162084d.jpg  


If you've made it safely this far, congratulations, ninety percent of the 'hard' work is done!

Until next time ...
 

 

Edited by benzomobile
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7 hours ago, cuivenion said:

Some of the images aren't showing.

Please, take it easy, you'll  see everything  you need  when you reach the end of this story  😉

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Thanks Beppe. That explains it. My mount has the Rowan belt modification on both axis so don’t see any.

Good luck.

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18 minutes ago, TerryMcK said:

Thanks Beppe. That explains it. My mount has the Rowan belt modification on both axis so don’t see any.

Good luck.

Even with belt mod - there is a chance of backlash.

If worm gear is not sufficiently round it won't have good contact with worm in one part of the cycle. When is the case - depending on where worm adjustment is made along the worm gear circumference - two things can happen:

- you can have proper meshing on one part of circle and backlash on the other or

- proper mashing on one part and binding on the other

Binding is usually first seen and worm adjusted to avoid it - but that leaves some of the backlash.

This happens as worm is static against worm gear and can be fixed if it is made floating instead. Floating worm needs some sort of tension to keep it pressed against worm gear - and that is where spring or magnets come into the picture.

It is called spring (or magnetic) loaded worm gear and newer mount designs have it, like - iOptron mounts and little AzGTI by skywatcher.

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1 hour ago, TerryMcK said:

Thanks Beppe. That explains it. My mount has the Rowan belt modification on both axis so don’t see any.

Good luck.

Hello Terry,

I was expecting this observation  🙂  HEQ5 - the so-called Heavy-Duty black one,  had an archaic motorization, the so-called Synta, which I modified in my own way. This is another story I'd like to tell you in the future ...

I thank you

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49 minutes ago, vlaiv said:

Even with belt mod - there is a chance of backlash.

If worm gear is not sufficiently round it won't have good contact with worm in one part of the cycle. When is the case - depending on where worm adjustment is made along the worm gear circumference - two things can happen:

- you can have proper meshing on one part of circle and backlash on the other or

- proper mashing on one part and binding on the other

Binding is usually first seen and worm adjusted to avoid it - but that leaves some of the backlash.

This happens as worm is static against worm gear and can be fixed if it is made floating instead. Floating worm needs some sort of tension to keep it pressed against worm gear - and that is where spring or magnets come into the picture.

It is called spring (or magnetic) loaded worm gear and newer mount designs have it, like - iOptron mounts and little AzGTI by skywatcher.

Thank you my friend,

It is just as you describe. What I have come up with is actually a coupling where the worm is floating.  I had the very lucky intuition that this could be accomplished with a very simple modification.

In particular, as you will see, what is needed is a small elicoidal spring that acts by compression. Its pressure force  is very critical ...I tried 3-4 different types of worms.
What I understand very clearly is that its compression has to be really light. In fact, it must not be too weak to make the mechanism ineffective, but not too strong to increase excessively the friction with the gear.

Please, follow me until the end 😉 

 

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13 minutes ago, benzomobile said:

Please, follow me until the end 😉 

Will certainly do. I'm really interested to see the whole modification and how you managed to make it all.

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Just now, cuivenion said:

Don't think they do it for the HEQ5 though unfortunately, so I'll be watching this thread with interest.

No I was just going to post the same, also it doesn't come cheap for the NEQ6 at £300 including postage.

Steve

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1 minute ago, benzomobile said:

And neither do I.  Perfect!

In fact, I thought a sort of similar mod could also have been applied to EQ6 mount, nd, perhaps to other types of mount

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Posted (edited)

Here I am again  🙂

Important: after each drilling operation, remember to clean the workpieces thoroughly of all metal debris!

Well, at this point we are moving on.
The following material must be obtained (this is the total needed for the two axles):

- two pieces of approximately 20-30mm cutted off from a brass - or stainless steel - rod with a diameter of 4mm ; 
- four 4mm center hole, about 10mm OD x 6mm thick drill bits limit rings with their grub locking screws  (pic below left)
- two helical compression springs with a wire thickness of 0.7mm, 10mm in length and 6mm outside diameter (see pic middle below )

 

IMG_20210101_171704.thumb.jpg.34de0e050f7fe48d8293cfcbdd2bfc6d.jpg

                  Spring.JPG.7e927503b556e356b1575b3b5de5f1af.JPG                             IMG_20210101_154520.thumb.jpg.b5c7766d94a4b63a32555f709b916694.jpg  

Using a piece of medium-fine sandpaper, peel away the paint all around the 4.2mm hole drilled in the holder until the bare metal underneath is exposed (pic above right) .

Place the whole mount block above the table - remove the counterweight shaft, otherwise you will have difficulty working - RA bar facing upwards, and apply the worm assembly (holder + worm). 
Lubricate the 4mm rod sliding path, the worm, the gear and the surface on wich the worm assembly rest, using a dry spray lubricant (IMHO, MoS2 one is the best choice, but PTFE one is fine too). 
Insert the small rod and the spring on it internally, as shown in the images below.

IMG_20201216_160835.thumb.jpg.8a77002b20d21262f34094e803828e91.jpg

            IMG_20201216_151943.thumb.jpg.a23f60994b037f69988ca6da74dbf65c.jpgIMG_20201216_161117.thumb.jpg.437a92582f3ea58a62f573c95080d07b.jpg

 

 

IMG_20201219_120756.thumb.jpg.162bd3f07d6a02184e90e0d785d31e69.jpg

 

 

 

                                                    

 

 

 

 

 

 

Make sure that the worm assembly slides well on the underlying surface and that the spring is working properly (see clip)

Now carefully  slip in - DON'T FORCE - the gear (may some tilt will be necessary to do it) and ONLY AFTER you can insert the three M5 bolts, screwing them in without tighten them, but leaving them loose 
(important thing). You will see that the proper match between the worm and the gear will be established automatically  (see pics below).

IMG_20201216_161442.thumb.jpg.9db5a4007a394a797f92e6a79649b515.jpg

                                                                                               IMG_20201219_122258.thumb.jpg.69c4d3c1d1e451a293b7bfdbabc01c55.jpg

 

The tuning operation ... on next time

 

Edited by benzomobile
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Many thanks for this thread, its interesting and the video is useful in explaining the final proposed operation.
I'd have thought the first step in removing the backlash would still have been to do a belt mod, are you going
to do one as well to the mount as there is still a source for backlash between the gears between the motor
and worm ?

Kathleen  

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You can still get backlash from the worm and the main gear. If the main gear isn’t perfectly round it will bind at some points and be too slack at others.

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49 minutes ago, cuivenion said:

You can still get backlash from the worm and the main gear. If the main gear isn’t perfectly round it will bind at some points and be too slack at others.

Are we talking the large gear that meshes with the worm here or the main gears that drive the worm that the Rowan Belt mod replaces ?

If the gear that meshes with the worm then I think the idea id this modification is to remove the back lsh that cannot be removed by changing the overall mesh as you say because out of round of the gear (or even just general manufacturing errors) causes binding at least once per rev (maybe more times per rev if more errors than just runout or roundness.

So without this modification you can improve tracking no end by removing the overall backlash between this gear and worm by adjusting the position of the gear to the worm.
But because of the errors in the machining of both worm and gear this can only remove backlash on certain parts of the meshing as you say it will tend to bind at at least one point in a revolution of the gear, unless it was made perfectly round and with no runout of the pivot wrt the gear cutting.

And the removal of backlash anyway is no easy task as the adjustment required is very fine and the difference to optimum backlash removal and binding is only a few degrees of the very small grub screw (from memory - a while since I tuned mine in).

But this modification should make both the overall removal of backlash and also stop it binding as the weak(ish) spring should take up any slack to prevent backlash and will allow some small movement to prevent binding (so the spring is always under some amount of compression).

 

If you are talking the main gears that the belt mod replaces then it needs the belt mod to remove that backlash.
Doing both mods (in theory) will remove almost all the backlash (I think anyway if I have understood it properly) .

Steve

 

Edited by teoria_del_big_bang
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