HEQ5 gear problem

[zhgutas]

Hiya all.

Been playing with my new (for me) HEQ5 (NON-goto) at home, getting re-accustomed with equatorial stuff, remembering PA and sorts, and noticed that widely mentioned weird sound on slower speeds (2x and 8x). While 16X buzzes like a bee, switching to 2X or 8X has that rattling noise. None of it is present while tracking though.

So I took the plastic motor cover off and found this:

1. After pressing any of the RA or DEC buttons, there is a sound of motor running, then only after a half a second or so (depending on a speed) you can start to see the gear turning, and only after 0.2mm or so the second gear engages and starts turning. If the button for the same direction is pressed the second time, only the first part happens (buzz, but no motion at all), as the gears already touch each other.ViewVideo: turn up the sound!

2. With both axis locked tight, there is almost no play in DEC, but some ir RA (no more than several mm either side though), and moving RA causes it's gears to move consequently.

3. It is possible to move all gears by a fraction of a turn each way with fingers very easily, which does not seam to move the remainder of a gear system (i.e. any axis). View My Video

This would not be such a big deal if I wasn't planning on experimenting with autoguiding. because if I understand correctly, this "looseness" could cause autoguider errors.

I tried to include the links with the video, to better explain what I meant. Sorry for quality (nokia..) and shaky hands I advice to turn up the sound too, to see the timing better.

Would appreciate any help from all you clever people

Cheers

Marius

[moocher]

There are tutorials on the web for backlash adjustment. If your guiding say via Maxim it lets you input a figure to compensate for it....most other programs won`t.

I had to adjust my old HEQ5 in both RA and DEC afer i did it guided like a dream.....

Alan:)

[Astro_Baby]

Its backlash that your seeing I think. It can be tuned out to some extenet by adjusting the worm mesh/engagement.

Theres a guide here to adjusting the worm engagement. I assume by the way its a Syntrek mount.

HEQ5 - Worm Adjustment

If you mess with the worm engagement allow LOTS of time because it can be a long slow process.

[roundycat]

Backlash is NOT a problem for guiding, provided you don't have yards of it. Just be careful how you balance the scope.

Dennis

[zhgutas]

I assume by the way its a Syntrek mount.

.

Nope.. It's an oldie HEQ5 with simple oldie gears I've had a look at your guide before AB. Well, all of them, really:) very detailed and useful!

I know one of the things is gear engagement (where first starts to spin, and only then the second one). I think I would be able to tune that with your and couple other guides. I'm more worried about the "hesitation" of the first gear to start moving after the button is pressed and the movement "buzz" starts, but no obvious movement happens... Could this be something internal to the motor itself?

P.S. in your tutorial you it says "check that the motor gears can easily move the axis by manually turning them by hand or using the mounts motors". I'm not able to move the gears manually, except for that small amount of "play". Though the motors DO seam to work OK, this is the first HEQ5 I've had a proper chance to lay my hands on, so all the "smoothness" etc. is very relative, as I have never known what "smooth" actually looks like..

Dennis, I am worried about an imaginary situation like this:

All up and running, imaging cam is doing its imaging, guider guides, RA goes a bit slow, guider software kicks in and boosts RA speed. All good! However, if (when!) there's some deviation in DEC, lets say, I would guess it should take some more time for that to be "fixed" due to the backlash.. Though it's just my speculation, I'm absolutely new to guiding, and pretty new to imaging too so I may as well be wrong here. I hope I'm wrong! That would save me so much hassle!

Cheers

Marius

[Glider]

I guide using PHD. After calibrating in each axis it says it goes through a final stage of backlash zeroing.

I've never given any thought to what this meant but it seems to work!

I also balance the OTA slightly heavy.

[Astro_Baby]

Hmmm - with the standard mount the motors on mine were dead silent. SO much so that when I first had it I became convinced they werent running at all

With the standard mount the worm engement can be a bit tighter because the motors are more torquey and the speed is limited to x16 sidereal.

On a Syntr4ek with x300+ sidereal and stepper motors which lack the same torque the worm engagement has to be a bit looser or the mount just binds up.

I wonder if the slowness of your motors to react might just indicate the overall slow running speed of the motors.

[zhgutas]

With the standard mount the worm engement can be a bit tighter because the motors are more torquey and the speed is limited to x16 sidereal.

Sounds logical, but I would have thought there shouldn't be a delay in turning the second gear if the engagement was tight, i.e. there would not be any free travel between the gear "teeth"..

Anyways, as I said, assume this could be improved by moving the gears closer, but what about the "hesitation" for the first gear to start moving? Could it be an internal imperfection, and thus, probably not fixable then? Tough hoping Dennis and Glider are right, I should be OK with this.. ten again, I sometimes DO get that annoying "need to fix it" type of feeling )

Marius

[Astro_Baby]

ten again, I sometimes DO get that annoying "need to fix it" type of feeling

How well I know that feeling. The last one has resulted in weeks of work. It all started with deciding to clean a mirror - its led on to a complete strip down,, repaint and rebuild for an entire telescope.

[zhgutas]

How well I know that feeling. The last one has resulted in weeks of work. It all started with deciding to clean a mirror - its led on to a complete strip down,, repaint and rebuild for an entire telescope.

Exactly That's why I'm usually scared to start something, as I know it will almost certainly evolve into something way more massive than planned

Marius

[roundycat]

Marius, my comment about backlash not really being a problem depended on two things, 1-that you don't have yards of it and 2-that you balance carefully. Everyone seems to take for granted that in RA you balance 'against' the gears so the gears never come out of mesh. In Dec it is a bit more difficult as it is almost impossible to balance against the gears if they change direction and they will when imaging near the zenith.

Some deliberately misalign the mount so it only ever corrects Dec in one direction, a bit like RA. Just figure out what direction that is and disable corrections in the other direction.

I use a different method when near the zenith and the scope tends to hang like a slack pendulum. I use a shock cord or weight and string around a pulley so as to pull the camera end of the scope to one side. This permanently biases the mount in one direction so you can treat Dec as RA as far as balance is concerned.

Be very cautious about playing with the gear backlash as you need to test it all round the worm gear, the whole 360 degrees. The worm might be good but it doesn't mean to say the gear will be. If you turn a piece of metal in a lathe and then reverse it in the chuck and turn the new bit down to the same diameter you almost always find some eccentricity. If that exists in the worm gear (or the worm come to that) it will be tight in one place. If you adjust there, as you should, then it will be loose elsewhere. You can't win that one. A bit of backlash means your gears will never jam, a tight spot could mean a burnt out motor.

Dennis

[zhgutas]

Cheers Dennis, as I said, this being my first HEQ5 therefore having no benchmark for stuff like this makes it difficult for me to understand objectively what should look like what. I'm basically just gathering info now, not going into any excessive "modding" (breaking ) 'cause I haven't started guiding yet, and probably won't for another month or so, and I only then will I see whether or not I need to do any adjustments, or I can live with it.

Thanks for all your comments guys, by the way

Marius