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My New Pulsar 2.1m Obsy - Finished :-)


Jkulin

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Looking really good, brings back memories from last year when my second hand Pulsar Dome went up. 
Just a tip on the painting, my wife wanted a green dome but In my haste to do the job I attempted to paint the dome section in between showers with the result that the paint did not exactly dry to a high gloss, so will need to be redone later this summer.

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On 28/06/2020 at 09:30, tomato said:

Looking really good, brings back memories from last year when my second hand Pulsar Dome went up. 
Just a tip on the painting, my wife wanted a green dome but In my haste to do the job I attempted to paint the dome section in between showers with the result that the paint did not exactly dry to a high gloss, so will need to be redone later this summer.

Thanks yep I will only do it when it is forecast to be bone dry but not red hot, Skipper has been advising me and he's a real pro.

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@tooth_dr Thanks Adam for pointing @Xsubmariner my way, hopefully now that I have double checked all the measurements Martin might be able to advise.

I have posted a copy of the spread sheet with my dimensions on for the 120EC, can anyone comment or advise if they think my dims are correct? I believe this is a 2.1m dome rather than the 2.2m: -

image.thumb.png.8d47e1de96f3772e80ee675e03c34de8.png

I truly would appreciate anyone's thoughts before I start to play with the software, for some apparent reason which is unlike me, I am apprehensive to get it wrong?

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Hi John ..  I believe the reference point (RA centre on the Mesu diagram) for the offsets is the intersection of the RA and Dec axes..  which for your mount looks to me as the point between the two RA bearings..  rather than where it looks to me that you have it (just below the dovetail clamp) you need vertical and horizontal offset of this point from the centre of your pier ( to add to your pier Offset measurements) ..and the GEM offset which is the distance from the reference point to the centre line of your scope ..  

HTH And that I’ve understood your diagram ..  looking on my phone

Dave

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46 minutes ago, Laurin Dave said:

Hi John ..  I believe the reference point (RA centre on the Mesu diagram) for the offsets is the intersection of the RA and Dec axes..  which for your mount looks to me as the point between the two RA bearings..  rather than where it looks to me that you have it (just below the dovetail clamp) you need vertical and horizontal offset of this point from the centre of your pier ( to add to your pier Offset measurements) ..and the GEM offset which is the distance from the reference point to the centre line of your scope ..  

HTH And that I’ve understood your diagram ..  looking on my phone

Dave

Hi Dave, thanks for your help, I'm probably being stupid, but looking in the manual the RA Axis is what I think I have used: -

image.png.6677c49ecee262f39650ab7d0534a36a.png

So I have just been out to remeasure and amend the measurements on the image, have I got it totally wrong?

image.thumb.png.2137f6a0e94487385a1f4641eb28ab21.png

Apologies for being a pain?

Edited by Jkulin
Corrected Spreadsheet
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Hi John

I'm not sure... I'm a bit weary and its a bit late for spreadsheets I'm afraid...     but I believe the measurements you need are those in blue on the attached diagram ie the d, h and t equivalent on the Mesu picture

Dave

579456662_JKulinMount.thumb.jpg.64a551b3eb5e87f7f3ae1eb21947ddb8.jpg

 

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Thanks Dave, much appreciate you help, when you feel refreshed can you advise where to take the d measurement from and where does the a end and the t begin, sorry about all the questions?

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Hi John,

Sorry for the slow response, been busy building a very large retaining wall. Dave’s representation of the Mesu Mount points above is correct with my experience. I used the same spreadsheet to get initial settings, but in application had to adjust the GEM offset value to get the best scope-dome slot fit in my Dome.

My values are only representative of my mount centre line position giving N/S, E/W and U/D offsets and the Gem offset value to the centre line of your scope. 

There is no risk to your equipment other than the scope not aligning with your dome slot. I used Ascom POTH to set AZ&EL goto commands for the scope and mount to check the alignment initially. Let me know if you have further questions.

 Martin

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Thanks Martin for the reply, much appreciated.

I have never used the POTH facility, so am a bit green about how to interface that, can you brief me a bit please?

Steve worked with a developer to create an Ascom driver based on an Arduino unit, Steve really did a cool job on it, but I'm just struggling to convert the parameters out, so any thoughts about how I can integrate the POTH into SGP would be most appreciated?

Many Thanks.

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7 hours ago, Jkulin said:

Thanks Dave, much appreciate you help, when you feel refreshed can you advise where to take the d measurement from and where does the a end and the t begin, sorry about all the questions?

Morning John, D is the distance from the centre of your pier to a vertical line dropping from the point of intersection of the RA and Dec axes ..  looks like it’s pretty small if not zero .. On your diagram of the CEM A plus T is the GEM offset which is the ( on the Mesu diagram T alone is the GEM offset) distance from the intersection point of the axes to the mid point of your scope.. 

Dave

 

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The offset (d) moves slightly when you adjust the altitude setting on the 120 but this movement will be pretty small. Dave's suggested RA position is the one that I would also suggest for this mount BUT as mentioned previously, on a friend's mount this didn't work correctly BUT there could have been other issues in play. This would be a good start point for you.

With regard to POTH, it is very easy to use and has been a saviour for many people in the past who have had issues with controlling software as it just works  - if you need any help with the POTH settings once you reach that stage, just shout!

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Right so as I had an hour or so to have a play, I thought I'd check that all the mechanics work as there is no point setting everything up unless it will work.

So first thing with some trepidation I told the dome to raise the shutter, with screaming and stuttering half way up I knew something was wrong, it turns out the new wooden stop that I had fitted was fouling the cable ties that was holding the Cat5 cable in place after I repaired it from having to cut it to separate the roof, once that was sorted it would raise and lower manually, so time to try the motor...not a good idea as I had wound the cable incorrectly and it had come out of its guide, I may have to look at a smoother more efficient way to raise the shutter but at least now it is working and shutting off correctly.

So now comes to check the rotation, I wasn't worried about how it did it as long as it was smooth, first job was to tell it to find zero, yep the new zero position was working and cutting the motor properly, so the next job was to tell it to rotate to the North, this is where I had run out of time, but not before I had come across another problem that I haven't got my head around yet, see the video below: -

So it runs along nicely but snags in this particular spot and will not get itself out of the mire, I can't see anywhere that is is catching or that the aluminium rail is not lined up smoothly, I can't see any wear to the belt, so am really at a loss, I've asked Steve for his thoughts, but would welcome anyone else's ideas.

So until I have worked this out then, there really is no point of moving forward, I have ordered just in case 10m of replacement timing belt, in case the issue is down to wear or poor alignment on my behalf, but as it is fitted with EvoStik impact adhesive it might be a pain to remove.

So some positive news and some head banging non-progress, I have got to get to the bottom of this first.

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Hi John,

It looks to me like your dome or sidewalls are not quite circular which is causing the drive motor to to skip. Can you disengage the motor and try rotating the dome by hand to check for tight spots.

While my dome drive mechanism is different I have a couple of tight spots that were overcome by increasing tension on the drive wheels. 

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48 minutes ago, Xsubmariner said:

Hi John,

It looks to me like your dome or sidewalls are not quite circular which is causing the drive motor to to skip. Can you disengage the motor and try rotating the dome by hand to check for tight spots.

While my dome drive mechanism is different I have a couple of tight spots that were overcome by increasing tension on the drive wheels. 

Thanks Martin, she rotates really freely when the motor is disengaged, that was the first thing I checked when we lifted the lid on, Steve hinted that perhaps that I needed to increase the tension, so I'll have a look if I can tomorrow.

Thanks for the input.

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Hi John, 
At the risk of stating what you have no doubt concluded yourself in that given it runs ok around the rest of the circumference, there must be something different at that location which Is causing it to jump. If it is not a tight spot on the free rotation is it possible there is a flat spot in the wall moulding such that the engagement tension is being lost?

@Tomatobro was a bit wary of the torque that could be transmitted by the timing belt arrangement so he went for a steel rack and pinion arrangement mounted in the vertical plane when designing it from scratch to motorise my Mk1 Pulsar Dome.

One other observation: your dome is fair zipping around compared to the speed that mine runs at. That is perhaps contributing to the risk of a belt tooth jump?

 

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Very best of luck with POTH and dome-synching.  I have never got it to work, with the dome just going to random positions     that are nowhere near where the scope is pointing (and yes, I have triple-checked my input dimensions). Every time I used it, something also happened to the dome position in the native Pulsar software (even though it wasn’t open) which meant I had to recalibrate the dome in the Pulsar software to get it to home/park in the right place.  It also permanently messed up the link between my mount and the PC, so that I had to unplug the mount EQdir lead and plug it back in again to get the computer to recognise it every time I started up. 
I gave POTH up as a bad job, deciding that imaging time and life is too short to waste on it.  I just set the dome tracking rate in the pulsar software instead and keep a periodic eye on it.  With a bit of care I can usually get 2-3 hours before I have to give the dome a nudge, depending on object elevation.

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17 hours ago, Jkulin said:

Thanks Martin, she rotates really freely when the motor is disengaged, that was the first thing I checked when we lifted the lid on, Steve hinted that perhaps that I needed to increase the tension, so I'll have a look if I can tomorrow.

Thanks for the input.

Hi John,

Just checked your video footage, and you need to increase the pressure of the gear onto the drive belt. It is amazing how much it flexes. Looking really great though.....Nearly there 👍

Steve

 

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Well problem solved with regards to the jumping...you know when the obvious is staring you in the face but it isn’t obvious? Well I had a spare couple of hours today and was determined to get to the bottom of it🥴

The sticking was not sticking in that place that I thought, I released the motor drive and slewed it by hand, listening all the way round and it transpired that it was this...3302D834-A3BE-4FAE-BEB2-9D35F0FCB507.jpeg.5c50042983c29328c686d3b4c81d4704.jpeg

At about 150 degrees opposite although I couldn’t see it, I could hear it, there’s a few of these bolts in place for safety to stop the dome lifting in high winds and it was catching on the rim, removed the bolt and all is well...happy days.

Quick call to Steve admitting my failure to diagnose the fault first time round and then Steve kindly went through a few checks to make sure that the home position was working correctly.

So hopefully I can now progress with getting the offset figures calculated and checked.

Thanks for everyone’s input but none of you can take into account my own stupidity.

The reason why it didn’t stick when I put the roof on was because I didn’t fit the securing bolts until I knew everything was running smoothly.

I have ordered a new cam belt that I will fit at the weekend, otherwise it will become one of those jobs that you planned to do but never got round to🙄

So let the headaches begin.

 

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Brilliant, your dome build has come on very well, even after a few hiccups. I'm still only at the wall stage, lol. Weather disruption stops play, lol. Can I ask what drive you have for the dome? I've an older type pulsar 2.7m and would like to add a drive to the dome. Not bothered about the shutter. 

IMG_20200625_114549.jpg

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