Legion Of Andromeda

2 hours ago, vlaiv said:

You should calibrate at DEC close to zero (ecliptic varies with season and swings between -23 and +23 degrees DEC).

This is because relative RA motion is affected by declination. If you image for example Polaris (northern star) - it will make a circle on your sensor around north celestial pole - and although it moves at same RA sidereal rate as all the other stars - it only covers very small number of pixels per hour. This is extreme example how DEC affects projection of RA onto pixels.

For highest calibration precision - you should therefore calibrate where motion of the star is greatest in number of pixels - to achieve good precision.

When you guide at high DEC - opposite thing happens if you don't have precise enough guide system.

If you have guide system that is only precise down to 0.06px and you have 4"/px resolution (rounded up). Then relative RA motion will be affected by cosine of DEC.

Say that you are imaging at dec 60° - cos(60°) is 1/2. To get actual error PHD2 needs to account for this 1/2 factor and 0.06px error becomes 0.25" and corrected by 1/2 factor now becomes 0.5". Your guide system has 0.5" error with every exposure that simply has nothing to do with seeing, mount tracking - anything - just precision of guider setup.

That is what I meant by high DEC and issue with guider precision. This might be issue that you are having regardless of what the actual cause of poor guiding is. If you've found that you have some meshing issues with gears - yes, correct that first and later look how much difference the longer focal length makes to guide performance (maybe you'll be able to guide at 0.5" RMS instead of 0.8" RMS when you fix everything).

 

sorry thats my poor terminolgy, i meant the equatorial. ....after sorting out the meshing. it started badly see pic below, but i'm currently getting 0.9 in poor seeing looking east and i havent recalibrated with the lowered the guiding rate yet because there are clouds due south now

1 hour ago, vlaiv said:

I think that here in lies the problem.

You are guiding at 3.87"/px

Centroid precision is about 1/16th of pixel or about 0.0625px - you simply can't get more precise measurement than that. That is ~0.24".

Guide assistant is calculating that to be your max drift rate as it gets that value each second it measures (it can't get better precision).

By the way 0.23"/s is rather high drift rate.

Imagine you have 15" P2P periodic error (as claimed by iOptron -/+ 7"). Worm period is 400s. This means that it takes 200s to go 15" so we have 15"/200s = 0.075"/s

Even if drift rate is twice that at 0.15" - 0.23" is still quite a bit higher than that - and that is your best result from guide assistant. Also notice that RA P2P is reported to be 8" in worst case and often less.

I think that you are limited by your guide system rather than mount.

You could try following:

1. Calibrate guider at DEC 0 regardless of where you guide (even at DEC 75°)

2. Use slower guide correction speed than x0.5 sidereal - if you can - set it to say x0.25 or x0.2 (not sure what mount supports)

3. Attach guide camera to main scope and run a guide session that way (don't forget to change FL in PHD2) - to see if additional resolution helps

4. Use 3-4s guide exposures rather than 1s or 1.5s

See if that changes things.

sorry, i meant 75 degree altitude, (50 degs in dec) so the scope is nearly vertical for m51 and 101, when i calibrate its usually towards the ecliptic / meridian, ...where do i change the guide correction speed?.... i will swap the camera over.... ive tried longer exposure times to no avail

However , since i made this post , i checked the belts which were both tight, but the gear meshing was loose...now waiting for some clear skies to test

righto, i recently purchased a second hand Ioptron CEM40 mount, it works fine as a standalone mount but has never used in conjunction with the ascom platform.

I have experience with ascom in conjunction with ATP and more recently, NINA for connectiing my cameras, focuser and my previous Skywatcher mount

However, i hit a brick wall with the cem40. i have a feeling that i need to update the firmware on the mount and the handset,,before setting up the drivers in ascom?

any guidance on best practice, cables, additional drivers, pitfalls to avoid, matching software to hardware would be appreciated.

The official source of help is a little inconsistant in detail and reliability, so i could do with comments from those that have been down this road and come out the other side

Thanks in advance

2 hours ago, david_taurus83 said:

When you go to the guider tab in NINA, have you reselected PHD2?

PHD version is 2.6.9 dev3 (with multistar guiding)

2 hours ago, david_taurus83 said:

When you go to the guider tab in NINA, have you reselected PHD2?

Under ; Equipment ~ Guider i have PHD2 selected, the others are synchronised PHD2 (experimental), Direct Guider and Lacerta... maybe i should try the experimental option

Also,; Options ~Equipment ~ Guider settings. this all looks normal to me with the correct filepath and server port being 4400

i recently migrated from APT to NINA and it's mostly fine except how it relates to phd2.

The first two times i fired up NINA it launched phd2 guiding in the first instance, before i had a chance to set up anything else, the trouble with that, is that it grabbed my main camera and allocated it to guiding, not my 120mm

So, I switched something off in NINA (cant remember what) which allowed me to install my main camera, focuser and mount...which means i then have to start and run phd manually afterwards, but NINA can't start and stop phd in relation to meridian flips, sequencing, slewing and probably some other stuff.

So, how do i get NINA to control phd automatically? am i missing a magic button?

hi there, i have been using PHD2 and APT for nearly 2 years now . i currently have a WO GT81 / ZWO OSC scope on a Skywatcher EQ5 goto mount with a 50mm WO guidescope / ZWO 120mm camera..... All running and guiding very well for a long time with a surprisingly flat histogram for a cheap gear-driven mount via ASCOM on my win10 laptop. However, i recently set up the same softwares and the same PHD2 settings on my PC from inside the house and connected to my rig hub via an active USB cable with no major issues...for a few sessions until last night....

The guiding was very jagged...not drifting off completely, just all over the place.. i restarted EVERYTHING, many times. polar alignment, star alignment, goto was spot-on! plate solving was working etc. So i am going to share my settings to get some feed back to check for any major over-sights or suggestion for improvements. BTW one thing i do remember is that my main scope and guide scope are close but not totally in-line...how important is this?... also, could a flakey serial to usb cable between the handset and the hub affect the commands?.. sorry about no screen shots from the session.

Prior to installing the Arduino, i took a couple of single, unstacked test shots last night using my old D7000 with a 50mm lens, one at 2 mins , the other at 3 mins. Now i have rewired it for the Arduino i can house the electronics in a far smaller box and after that i need to figure out some kind of alt sub-base rather than tilting the top part of my mount

54 minutes ago, theropod said:

Most stepper motor drivers can be set to direction without the need to use up a processor output pin. If the driver needs to see positive voltage on a direction pin it’s easy enough to supply it via a DIP switch. The same is true if it expects to see ground. My Easy Driver defaults to one direction without input, and reversing the motor leads controls direction. I still provide that direction pin 5v positive from the Arduino. My design is manual reversing, but adding one output pin and enabling the function in the Arduino sketch is super easy. See my post about my home made alt/az mount. Steppers are super easy.

ETA: link to alt/az project.

 

how does this and the sketch you provided earlier apply to my aforementioned setup?. I assumed you had a nema17 hooked up to a Tb6600 (optimised for current and resolution) and an UNO?, plus, your sketch makes no mention of pul, dir and ena which is why i haven't touched it yet. I now have it all running perfectly and quietly in a smaller box than before on a very basic code.

8 hours ago, sloz1664 said:

I will base my barn door tracker on this arduino design Barn Door Tracker

Steve

thats an interesting approach to overcoming the tangent error of a straight rod, as long as your coding reflects the maths involved with a rod moving at an increased rate of accelleration to keep the door rotating at a constant rate. The easy driver is nice and compact but i prefer the TB6600 for quick and sturdy connections... adding a reverse switch would be handy for me

20 hours ago, theropod said:

After checking the specs for an Uno the sketch will work exactly the same as if running on a Nano. The onboard LED is tied to D13 for both Arduinos. Try loading my sketch on to your Uno, hook it up to your drive and see what happens. You can load new sketches on an Arduino thousands of times, so if you don’t like the way it works it’s simple enough to ditch it.

The use of the millis function provides much more precise timing than using the delay function. When the delay function is called the Arduino comes to a complete halt. Nothing happens at all until the designated end of the delay. With millis the Arduino only has to keep track of how much time has elapsed. Only folding in a Real Time Clock would increase the accuracy of these timed events, and maybe incorporating an encoder to use interrupt events as precise feedback. Both of this things would add a great deal of complexity to the software/hardware, and with complexity comes headaches. Not that these things can’t be done, indeed I’ve dreamed of just such a barn door tracker. What I have now works flawlessly, and consistently.

I think someone ought to make these commercially available, and include the features I cite above. If someone could come up with a way to mount these things on any good tripod, be accurate over 10 minutes and have a really good built-in polar scope I’m sure they would sell. Heck, kits would be great for families!

ok, I disassembled the old circuit with the variable / manual pulse controller and reassembled with my UNO connected to dir/2 and pul/3 pins and their grounds of course, but no ena? as per most of the sketches and the simplest one not only moved in the right direction but i easily changed the delays from 1000 to 1180 to get the rpm needed for round stars, in this case 0.97 rpm. Apart form your sketch bearing no resemblance to the others, and assuming 13 is pul, i couldn't see any reference to a dir pin. The tb6600 microstep driver has ena, dir and pul

10 hours ago, theropod said:

Is there something about the code I posted over in the other thread that troubles you?  If your driver accepts a simple pulse stream (which it does) that code will work perfectly. One numeric value in one line of code, which I made clear in the comments, is all that’s needed to adjust the speed to suit your needs. The numerical value doesn’t have to be a whole number either as decimal fractions work just fine. Frankly I find it odd you would start another thread when your answer has already been provided, and ALL the programming done from a working example. Is there something I’m missing here?

This current post is very different and more specific to my needs and my way of doing research is to collate various sources, including your own, which will all differ in terms of schematics, level of detail, alternative hardware, external links etc ..from which i will form an informed plan with confidence. Most of which has so far referred to the UNO with sketches varying in functionality ...whereas you did say your sketch was intended for the NANO which is probably not an issue, but the concept of using millis is certainly worth investigation.... I have the UNO and 6 sketches including your own but i'm still waiting for the connectors.... early days...the only thing i have done so far is to play with the pin13 LED...I'l let you know how i get on though.

Ok, i have a fairly accurate stepper motor driven barn door tracker. consisting of a NEMA17 stepper motor, a tb6600 driver and a variable pulse generator. I wish to replace the pulse generator with an Arduino uno but i need some guidance and pointers to a schematic and a sketch that works for this setup and only needing to change the speed in the code .

the previous post for the finished project here..

thanks in advance

i completely disassembled, gave it a lick of paint and reassembled today

Here she is..... Attention! the images do not correspond directly to the paragraphs, i just put them in to break up the text.

-

Essentially, it's 2 x birch ply slabs, a control box, hinges, counterweight, mounting plate, tripod ball head, red dot finder, stepper motor, curved threaded brass driver rod

.

The door and base were going to be in solid oak as i wanted high mass to supress any motor vibrations, but went with 18mm birch ply as it was far easier to machine. I chose stainless steel ball bearing hinges for their smoothness and zero play tolerance, placed as far apart as poss but made sure they were dead inline with each other. i also recessed the hinges into the birch to ensure the inside faces lined up with the hinge pivot point. I then drilled a pilot hole through both boards that was 183mm from the hinge axis and on a centre line for the curved brass rod to pass through. ..The maths is as follows; based on M5 bar giving 0.8mm travel per thread / rotation / 1 minute... therefore 60 mins is 15 degrees of earth rotation and gives 48mm of travel, (15 x 24 = 360 degrees) so; 48mm x 24 = 1152mm circumference / Pi = 366mm diameter = 183mm radius....or if you have no control over the rpms, adjust the values accordingly; faster = larger radius, slower=smaller

.

It made perfect sense to go with a curved threaded brass rod to ensure a constant rate of rotation and no tangent error. M5 bar gave me sufficient strength but still able to be bent by hand around circular objects of decreasing in size until i got it to retain its diameter when laid over a template. Please note that one should only use the best 30cm from the middle of a 50cm rod. i secured one end to the door using SS wing nuts and washers, the hole needs to be more than 5mm as the rod not only curves through but is angled back so that the working part of the rod starts at a tangent to the inside face of the door and ends up passing through the corresponding hole in the base without to much resistance

.

I used an existing small Skywatcher dovetail mounting plate which thankfully has a 1/4"-20 threaded hole in the centre to screw onto the top of my existing camera mount, the ballhead is removed and fixed to the door for the camera of course. The mounting plate was offset so the curved rod didn't clash with the tripod pole. The position of the ball head needs to be near the hinge to lessen the weight on the threaded drive nut/rod, but not so close that weight of camera goes past the centre of balance and then pulls on the drive, or worse, the whole assembly flips over and does some serious damage if it goes past that point.

.

I partially recessed a donated 19mm bearing in the baseboard centred over the drive gear hole. i used a 19mm flat bit for the recess and opened up the hole on the underside to 10mm so that the centre of the bearing could rotate freely and allow the rod to pass without any hindrance. i temporarily added one of the wing nuts to the bottom end of the rod to keep it from flapping around too much whilst i did other things

.

The gears are at a 1 - 4 ratio. The motor spindle turns a 16 tooth spur gear 4 times for one rotation of the 64 tooth spur gear. The general sizing is in good proportion to the overall kit. In this case i used module1 plastic gears from RS components; 64 teeth with a pitch diameter of 64mm / 8mm bore in conjunction with a 16T/16dia/ 5mm bore... I also bought a spare set of 72 /18 as a back up. I used an M5 insert or 'T' nut fixed to the big gear- not inside the bore as one would think, but inverted so that the threaded shaft of the 'T' nut sits snugly down into the centre of the bearing. I removed the spikes with an angle grinder so that the flange was flat and smooth which i then superglued to the underside of the big gear...getting it central was quite tricky though. I then installed the big gear onto the curved rod most of the way up and it spun pretty well on the bearing and then made finer tweaks to the rod so it stopped touching the bearing but since the gear was very close to the baseboard , i added a small spacing washer which not only lifted it up but got the gear level with the baseboard - which is very important as you want both of the gears to be in line and level with each other. I was tempted to place two insert nuts back-to-back but they would form a straight bore over a curved rod, plus there was a high chance of the two threads binding.

.

I then installed the NEMA 17 stepper motor. First I transposed the motor dimensions onto the baseboard, I drilled a 25mm clearance hole for the 16T gear, fitted the 16T gear onto the 'D' profile driveshaft but i had to install a small grub screw into the gear hub to hold it in place. i then drilled 4x 4mm countersunk holes for the 25mm machine screws to hold it in place. Its best to slightly oversize these holes if you need to twist it around so the gears mesh nicely. also, if the motor is too low then you can easily raise it up by removing a layer or two of ply from underneath - rather than shifting the gear to the end of the shaft.

.

Electrics; I fitted an existing decent sized project box to the underside of the baseboard at the hinge end, this contained the speed controller and the stepper motor driver. The input is 12v dc, the 4 motor wires come out of one corner to the motor, i also have a broken + wire from the power socket that goes to a long-armed microswitch, the power is automatically cut when the drive rod gets to certain point for, i hope, obvious reasons. I used an old padlock key clamped between two wing nuts to hit the kill-switch... I'm not going to get into the stepper motor stuff here as it's pretty complex and there are a ton of fantastic tutorials on youtube.

.

I added a steel counterweight to the other side of the motor...it was needed!.... The ball-head camera mount is attached to a slotted steel plate (butchered from a radiator bracket) with a corresponding 1/4"-20T thumbscrew underneath that sits over a 32mm dia hole in the door, circa 75mm up from the hinge axis

.

It's very important that the axis of the red dot finder is parallel to the hinge axis. My method was to make a drawing of the section thru the kit that had both axes set out, i then stuck this to a wall 10m away, i used a small laser level against both the x and y axis of the hinge to project that axis onto the drawing in the other room and moved the drawing around until it was correct. i then turned on the red dot finder and adjusted it until the dot lined up with its own position on the section drawing.

.

I taped over the dials on the red dot finder once i was happy with their position. The proof of the pudding is once you have polar-aligned the tracker, you swing the door between its two furthest points and the red dot shouldn't move relative to the North Celestial Pole.

.

Speed is of the essence. Mark one of the teeth on the big gear and a corresponding line on the baseboard and using a stopwatch, get as close as you can to 60 seconds for one rotation by altering the dial. then take it outside and set it up, point your camera at something towards the east as this part of the sky moves the fastest relative to us, get your lens focused as best you can, set an exposure of 30 seconds without the motor running and zoom in on the resulting photo and make a note of the trail length, then repeat with the unit turned on...if you're lucky, you will have round stars this time. if not, make tiny adjustments until you do. In my case i ended up with it running slightly slower at 62 seconds on one rotation.

.

I set my tracker up so that it will do 3 hours / 45 degrees rotation. Any more than that and it will be past it's centre of balance. One could start with the base board angled down from the hinges at 30 degrees to avoid this problem at the end of a long session but i struggled enough with my cheap tripod angling back at 52 degress as it is.

i use a basic 1 amp wall transformer at home and a car battery out in the field

.

The dial controller i have used is a bit of a faff, somewhat hit-and-miss. i might upgrade to Arduino Uno for more precise control when i find the time. but the test results, so far, are very encouraging

.

I might dismantle and add a lick of paint next weekend.

All of the materials / components came to £110. I already had a tripod, small dovetail plate, project box, birch ply, bearing and steel counterweight,

.

Project completed!. I tested it last night and got perfectly rounds stars at 3 minutes duration, with 62 seconds per revolution. I managed to get the red dot finder parallel to the hinge axis.... I will post a full run down from first principles to fine tuning at a later date.

well, my project is coming along nicely 2 boards hinged with high tolerance hinges, M5 threaded rod bent to a smooth curve and passing through a hole without a hitch

I'm just about to start building a barn door tracker. My maths is good, my craft and engineering skills are very good but the idea of coding an Arduino brings me out in a cold sweat. I am sold on the concept of a stepper motor but need to control it as simply as possible with pre-assembled components..i really don't want to [removed word] about with breadboards, PCBs and soldering. so i am considering purchasing the following items to save a lot of time and stress.

MOTOR;  https://www.amazon.co.uk/XCSOURCE-4-Wire-Stepper-Printer-TE225/dp/B011NRMXYO/ref=sr_1_7?crid=277K22PDOS9AJ&dchild=1&keywords=stepper+motor&qid=1590313684&sprefix=stepper+%2Caps%2C139&sr=8-7

POWER SOURCE...maybe a battery pack? not sure yet.. i'm out in the field so it needs to be portable. any suggestions appreciated.

DRIVER ;  https://www.amazon.co.uk/TopDirect-Upgraded-TB6600-Controller-Segments/dp/B0711J1K66/ref=sr_1_12?crid=19QUZNXJ01S5M&dchild=1&keywords=stepper+motor+driver&qid=1590313835&sprefix=stepper+motor+d%2Caps%2C143&sr=8-12 

CONTROLLER.   https://www.amazon.co.uk/FTVOGUE-Controller-Generator-Adjustable-Regulation/dp/B07NVN2128/ref=sr_1_53?crid=188XP341U1163&dchild=1&keywords=stepper+motor+driver&qid=1590313302&sprefix=stepper+motor+driver%2Caps%2C137&sr=8-53

Once i get this all up and running, i might be tempted to get into more precise control via an Arduino, especially if the the above kit is too clunky. But the level of tracking accuracy at this stage is probably not a issue. My current thoughts on the engineering will be that the bottom block of the door has to have some mass to supress general vibrations, vibration damping motor mounts, i will be using high quality stainless steel, ball bearing door hinges. Adding an adjustable alt/ az sub-base for finer polar alignment. Any pointers on keeping things metric would be helpful, pretty much all the guidance out there is in imperial units....

Results are in! Some of this will confirm any previous replies..

Using a W.O. gt81 with a ZWO 1600 mc pro-cooled and a cheapo £50 2" optical 2x Barlow..............

Ok, i have a W.O. G.T.81 and a colour ZWO CMOS, used mostly with field flattener and sometimes with a focal reducer / flattener.

I recently imaged the moon, ( i was bored / curious) but it came out very well but i was only using 20% of my sensor area, so i wondered about using a barlow...

Can i use my existing optical 2"  2x Barlow in the imaging train?... and if so, where does it go ?... into the focus tube or nearer the sensor?...or half-way maybe?

I'm taking the flattener out of the equation for simplicity.....

Is there an optimal back-focus between the barlow and the sensor, then a simple matter of moving the two items away from the objective lens until sharp? like with a FF or FR?

Ive tried today with various permutations and the images are very out-of-focus... roughly how much am i to expect to come out? 5, 10, or even 30 cm?

TIA.

Hi there, it didn't take me long to tire of manual focusing via various ATP focussing tools. My most likely and affordable electronic focuser to this end would be the ZWO EAF but there doesn't appear to be anywhere to connect the bracket to the underside of the existing focusing assembly, the only two holes are the tensioner grub screw hole and the focus lock, which i assume will be redundant / free once the EAF is in place. Any suggestions from experience appreciated.

BTW, for some strange reason i get a better focus simply using the APT magnifier tool than using the Batinov Aid in conjunction with my Batinov mask, which is well out.

9 hours ago, Stub Mandrel said:

AV mode works fine with a scope.

Have the histogram peak at about 25%.

I always rotate the scope and take flats at about eight different orientations to even out any unintended gradients. Variously I use a plain painted wall in diffuse light, a card in the garden or a light panel with a sheet of A4 paper over it.

For very long focal lengths the sky works better, but still rotate.

 

just to confirm that you are suggesting rotating the scope in relation to the light source and not the camera in relation to the scope?

thats very kind of you thanks. i've just found an old laptop that i will use for my flats.. the t-shirt method is too variable

11 hours ago, wimvb said:

Flats contain a bias signal as well as dark current. The dark current is generally negligible, but the bias is not. Before you combine the flat frames into a master flat, you need to subtract the bias from them. When you calibrate the light frames, you also first need to subtract the bias as well as the dark signal. The stacking software takes care of this, as long as you provide the calibration files/masters.

Many thanks but i'm not sure what you mean by this, ive not been doing AP for very long so bear with me. how do i carry out the above procedures in DSS... literally step by step please.. or post a link to useful guide / video