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About this blog

This Blog will cover the development of the scope and it's drive system.

Entries in this blog

Getting Better.

I've been slightly less than perfectly happy with the guiding, finding it hard to beat 4 arc seconds FWHM in my raw subs. So... I've made a new bracket for the RA motor out of 6mm thick 60mmx60mm aluminium angle.. and finally I've got it guiding tonight with the newly secured setup. On a 5 minute sub working at 1500mm focal length on 5.4u pixels I'm getting a FWHM of 4.01 pixels, that's 3 arc seconds FWHM. The focussing image (1 second long) was giving 3.3 pixels FWHM, so that suggests the g
rfdesigner

rfdesigner

0

Where are we?

I had a recent message about this blog, good to know I haven't been writing into thin air!.. and of course I've added nothing for too long. So.. where are we? 1. Mount functions: Slew works Guiding Works PEC kind of works.. I have a new PEC algorithum which should improve things. Park, needs adding GOTO needs adding, software written with this in mind. 2. Drive needs propper PCBs and dsPIC in the base to allow GOTO (spherical maths, needs sin/cos/tan) 3. Base unit needs boxing up. 4. Hand
rfdesigner

rfdesigner

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New House, New Camera

Well it's been a LOONG time since last posting. A house move and other family crises intervening. Finally things are settling down and I managed to get out under the stars for the first time proper at our new house. Scope is now in a semi-permnent position (scope permanent, camera, PC etc. not) So got the gear guiding again and got out my new and shiny ATIK 383L+ :D Thin cloud + full moon so I was never going to get a good shot :mad:, but at least I could get the scope aligned etc. New for th
rfdesigner

rfdesigner

3

OAGing

Well.. I've now got an OAG (SX-OAG) and after many months of delay caused by other demands and uncooperative weather, I got my first autoguided shot with the mount. I knew the DSLR and the guider were not parfocal, so I accepted the inevitably poor shot and had a crack anyway. Stacking 30 x 30 second shots with no software registration showed the movement was not discernable. Out of focus yes, but 'sharply' out of focus, not just blobs so the autoguiding is really working. Next up: C mount ext
rfdesigner

rfdesigner

1

Stumped by Metrication

Next in line is was the second axis. I added the code, debugged it, and got the slew working for it. All relatively simple as it was a cut a paste from the RA axis but without needing to make it track, same error feedback but it keep calculating the same position, sounds a waste but once GOTO and corrections for misalignment and atomspheric effects on position get added it will be changing continuously. anyway.. added the circuitry, tested, added the motor drive chip and motor and bingo.. w
rfdesigner

rfdesigner

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East a bit..

Well after much hair pulling head bashing and general frustration I've finally got my hand controller communicating with the motor driver. So you choose 'slew mode' and press the east button, and the motor starts slewing east, let go and it immedaitely resumes its normal tracking, press west and it turns to the west. Might seem simple but it's been anything but. Two completly seperate chunks of code in two seperate PICs. The first PIC scanning a keypad for finger presses, interpreting modes dou
rfdesigner

rfdesigner

5

359 or 360 teeth.. just how do you count them

On the face of it easy, but in practice less so. In my case my drive system has been slightly lagging the stars and I'm trying to work out exactly where the error lies. It looks like the error is around 2% so worm wheels on their own don't account for it, but it could be part of the problem I thought it might be that the worm wheels got swapped when the mount was refurbished, in which case the mount would be running a tad slow. So how do you count 360 teeth?.. and trust your answer when you'r
rfdesigner

rfdesigner

1

Ouch!

Nothing much technical to report from Saturdays imaging session.. alignment is going to have to get better, but that's all. Lots of imaging: M42, M1, something as yet to be identified which was supposed to be M81 but wasn't , M82, M51. However with the counterweight all black it's not terribly visable.... Not terribly visable as in: bang ouch! :mad:, cut knee through jeans... why do voices carry so much at night? What was perhaps more impressive was that the scope never lost track!..:D 1
rfdesigner

rfdesigner

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Improved Tracking

Well I finally managed to get back outside after what seems like a month of bad weather, poor sleep due to my youngest teething, car problems and colds & bugs. The drive system has been adapted with a new shaft coupler.. I'm very pleased with this... all much tighter better algned etc. Testing: So of course it was a full moon. very very thin cloud and all planets too low, too dim or just not visible.. so where to point.. ah yes M42. Well after a bit of aligning I stopped the stars drif
rfdesigner

rfdesigner

0

Improved Tracking

Well I finally managed to get back outside after what seems like a month of bad weather, poor sleep due to my youngest teething, car problems and colds & bugs. The drive system has been adapted with a new shaft coupler.. I'm very pleased with this... all much tighter better algned etc. Testing: So of course it was a full moon. very very thin cloud and all planets too low, too dim or just not visible.. so where to point.. ah yes M42. Well after a bit of aligning I stopped the stars drif
rfdesigner

rfdesigner

2

Latest Bug Fix

Got the tracking correct, finally. What was it?.. a miscalculation.. no. mis-specced/counted motor/worm.. no. straight lack of understanding.. no. pure and simple foul up.. that'll be it. The software has a sin lookup table for generating the microstepping, it used to use a 128 sample 1/4 sine ramp to generate it, but I found that a 150 sample 1/4 sine ramp improved theoretical performance. I had changed the lookup table without error, then forgot to change the software that turns that
rfdesigner

rfdesigner

0

Hacking the tube

This is more of a note to myself The focusser was in the origional position (far too close to the primary mirror) so I cut a new hole for the focusser 55mm closer to the top of the tube. After collimating images are quite a bit better. No more vingetting at 0.001 degrees off axis. Seeing was only ~2 arc seconds, Trapesium stars looked about 1:4 size to seperation.. but at low altitude. Straight up was ok still need to get collimation bang on, not 100% happy right now, although a focoult meas
rfdesigner

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Starting things off

A quick potted history is probably due. The scope is a Fullerscope MKIV mount with a 12" newt on it. I bought it about 11 years ago knowing it need pulling apart and rebuilding, but the price was low, the mount solid and the optics were good.. The bits that were rubbish I could change. The Newt has now been modified with a window so I no longer have diffraction spikes and tube currents are better suppressed. It does however make it rather heavy... I can just about lift it, portable is not
rfdesigner

rfdesigner

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