wobblewing

Thanks Malcolm. The drivers for that little gadget from FLO may just be the ticket! (sorry for the late reply!)

Yes, that's exactly my point... Just looking for something simple that is 'pre-done' but has enough documentation so I know which serial commands they send out, so I can make my mount respond to those commands. Then it's easy.. I shouldn't really need to develop a driver at all. Maybe those documents you've posted tell me these commands... I'll check those out - many thanks for those... Where did you get them from? My platform already takes out the sidereal rotation.. my intention is to say calibrate its position in RA/DEC in APT and then just do the final bit of positional trimming (and later, guiding) just using simple pulse commands similar to ST4 (e.g. back a bit, up a bit etc). In essence, ST4 is all that is required, but I'd like to have a little more control through APT or EQMOD etc. I also see that someone has done something with an arduino as a serial to ST4 adapter.. The guy wrote a driver for it.. maybe I could use this: https://hackaday.io/project/4386-arduino-st4-telescope-control Cheers Andy

I'll have a look at that, Thanks Malcom. I'm not much of a Software developer, so was hoping to grab something that I could find on github somewhere and then write the mount end code to match the commands in the driver! 🙂

HI... So, nearly a year on and I'm working on an upgrade for full guiding capability... Anyone know any generically available ASCOM serial driver? I have started a thread here: Thanks! Andy PS.. also added a neat polar alignment tool red dot finder at the designed latitude.

Hi all, Further to my DIY EQ platform (thread here ).... I've got some experience using this now and have managed some reasonably decent tracked DSO images with the 150p dobsonian. I'm now working on a few mods. Namely an addition of a Declination trim adjustment by tipping the 'scope, but also a serial interface so I can potentially add guiding to the mix. Since I can create full serial control via a COM port profile over USB (easy with a micro:bit), what I'd like is a generic ASCOM driver which squirts pulse positioning string out to the serial port, thereby allowing the EQ platform to be controlled by software such as APT. Does anyone know if such a driver exists. Of course, it may be possible just to grab a skywatcher (or any) driver, but it would be easier if a very basic one has already been written with the serial commands documented (since commercial drivers will not be documented). All it needs is something like RA+, RA-, DEC+, DEC- control over serial.. Anyone know of one? I've done a bit of searching, but get lost in ASCOM documentation without it leading me to a useful generic and basic serial driver.... Thanks! Andy

How did you get on with this? I recently bought an ASI224MC and did a bit of Jupitering last night with the 150p and a 2x barlow sitting on my homebrew EQ platform (https://www.youtube.com/watch?v=fGdvxtIfSmU). However, then I tried to get a wider field of view (I realise this isn't a speciality for the 224!) by fitting 0.5x reducer.. I found that I couldn't get focus even with adjusting the truss rods (camera needs to be closer in).. Will have another play with it - was getting late and cold outside!) Thoughts? Maybe this is not practical which would be a shame as that's what I bought the reducer for 🙂

I have a set of BST starguiders. They're all fine on the Heritage 150p.

I created a longer timelapse and it appears that I can see: - PA alignment error (will do better next time). Noted the other more accurate technique. - a small amount of non-linearity as it approaches the centre of the sweep and the 'turnbucke' (ball joint thingy) goes horizontal - you get a tiny amount of speed drop requiring less than a millisecond of 'per step' adjustment. I'll approximate it into a number of linear portions of the sweep. - more significant I think is that the step signal of the micro:bit appears to jitter due to using micro python (interpreted code), it's not locked at exact 48ms per step as implied in the code - I can see this happening on an oscilloscope. Maybe I should re-compile it in C, if I can figure out how to do it on the micro:bit. Perhaps I should've used a RPi pico. In any case it's not really necessary other than for interest, as I don't have the photography gear to increase exposure beyond 10 seconds at the moment.

I'm running another timelapse video over the whole sweep, so it might help characterise the non-linearity (maybe)

A single 8 second sub, ISO 500. Looks kind of promising for an afocal effort. Will DSS this lot. My talent probably runs out here 😄

Well, clear night tonight finally - albeit with a full moon! So, testing the tracking out.. here's a hyperlapse video.. bear in mind this is ~22mins squash into 22seconds! I can juuuuust notice the non-linearity, which equates to about one third to a half millisecond timing on a step.. Will fiddle with the code, but it's not really necessary as it exceeds the exposure length I can do with my phone up against the lens. Not quite sure what the up and down is all about I think my PA needs work... But the hyperlapse really amplifies it... in real time it doesn't seem like it moves at all.

I just realised I put this in the wrong thread - I've copied this post over to there, but cannot seem to delete it from here! Sorry. Well, clear night tonight finally - albeit with a full moon! So, testing the tracking out.. here's a hyperlapse video.. bear in mind this is ~22mins squash into 22seconds! I can juuuuust notice the non-linearity, which equates to about one third to a half millisecond timing on a step.. Will fiddle with the code, but it's not really necessary as it exceeds the exposure length I can do with my phone up against the lens. Not quite sue what the up and down is all about 🙂 I think my PA needs work... But the hyperlapse really amplifies it... in real time it doesn't seem like it moves at all.

I would be quite up for making my own 12in dob. I'd build it onto a scaled up version of the platform above.. but the mirrors seem to be as expensive as buying a complete telescope, so not sure if it's worth it!

One of the difficulties i have is that i cannot easily see polaris from my observation spot. My garden is south facing but just around the other side of my house is a street lamp which causes some interference. So I sit the 'scope out the way off the street lamp by hiding behind the house, but then i cannot see polaris! I waited for solar noon, projected the sun's position onto the ground with a broomstick and then put a small mark on my patio to line the platform against!

I'm struggling to get spot on Polaris alignment throughout the whole travel, but this is because of me 🙂 and I'm getting used to it! I'm thinking about making a little gadget that clips onto the back to help with alignment (or maybe something that clamps the OTA into a fixed spot for alignment with the red dot finder). That said, rough alignment seems to work perfectly for visual.

It is definitely moving in Z and Y, whilst being pushed along X (the ball joint)... but I think it's such a small amount that it's insignificant. We will see 🙂 I might have a go at some geometry calculations to see how much it is.

A few CAD images from Fusion 360... Ok, so I used white PLA instead of black 🙂 Latitude 52deg. Adjustable levelling feet give probably +/-4deg ish. Total movement ~125mm giving 82minutes of travel.

1) actually I tried 3DP rollers to start with, but found them a bit lumpy due to the FDM layering. I switched them to skateboard bearings (had a set in my spares box!) and it made it run much smoother... I also put an open bearing in the South pivot point as I found 3DP friction bearing a bit 'sticky', although the torque of the drive mostly overcame it... By using bearings the movement is very smooth indeed. I printed the sectors to get the FDM layering along the axis of movement and then sanded it to get a very smooth surface to roll on... It's super slick and smooth. I had more of an issue with stepper smoothness at first and had to use the 32 microstep/step option (DRV8825 driver). If using the basic 1.8deg step size, you could see the stepping affecting the image being too 'notchy' and the vibration got through the mechanism. Simply increasing the step resolution fixed that (now 6400 steps per rev). 2). Maybe, I only use it out in my garden on the patio and it shouldn't get too dirty. 3) Sorry not quite sure what you mean there. 4) Yes I realise that, but I did it anyway when I was playing around with the idea, so I stuck with it! BTW, the ~10sec rewind is by hand (not driven backwards). The code is written such that when it gets to the end then the driver is disabled... So I just spin it back by hand (faster than driving it!), reset the counter and then press 'go'.

Right now I've only got about 90mins use playing around with it.. Since my dob is only little with a FL of 750mm, I tried a 3.2mm BST EP looking at a star (thus x234 - approaching the practical limit of the scope) and it was holding in the centre of view really well as far as I could tell... the problem is it was quite windy and getting knocked around a bit - so more time will tell! Also, only Mars is available at the moment and it's getting very small... so not much more useful than a star in terms of seeing how well it tracks. In theory I'm sure there is some non=linearity to deal with, but as you can see in the video the pushrod is fairly straight and level across its sweep. the small amount of non-linearity doesn't appear to be noticeable, but maybe I'll find it at some point.... It certain has very precise control, so should be easy to do in the software if needed. I certainly couldn't notice anything in practice.

Interesting thought... I only intended to make it as a one-off for my own use! It was very cheap on materials, but I spent quite a lot of time on it... I need to get a bit of experience on it first... I'm a newbie in terms of astronomy, so I don't really know what to gauge it against.. Also, I'm only doing afocal photography using my phone with a 3D printed 'phone to eyepiece' adapter, so I'm not sure if my photography setup is capable enough to really characterise how good the platform is... My engineering nouse suggests it's reasonable, but I may find foibles as I gain experience with it... I have a few improvement ideas, such as an add-on Polaris alignment 'sight'

To close this thread: I finally finished it! I ended up having to pay £2.30 for a stepper motor driver PCB (not Free 🙂 ). Other than that, it's from the parts bin and made from an old shelf. All 3d printed included the ball joints. Driven by a stepper motor and worm gear pushing/pulling the platform (way more torque than needed, but this can be turned down on the driver PCB)... BBC micro:bit coded in Python... Powered by a 2S or 3S Lipo.... It actually works really well and I've got the accuracy spot on! I had no issue at all with the potential error induced from pushing the platform following a circle profile by using a linear leadscrew. As you can see the motion is as good as linear through its entire travel, so a fixed speed across it (without varying speed across its travel according to position) worked out fine. I was going to replace the brass leadscrew 'nuts' with a split nut design so it's fast to reset.. but I found that it only took about 10seconds to spin be back by hand - so I didn't bother. There are no limit stops with microswitches, I basically reset it to the start position and press a button to reset a counter.. once it reaches the count limit it stops and flashes the screen to indicate a reset is required (although it's pretty obvious of course!)

I had no issue at all with the error induced from pushing the platform following a circle profile by using a linear leadscrew. As you can see the motion is as good as linear through its entire travel, so a fixed speed across it (without varying across its travel according to position) worked out fine. I was going to replace the brass leadscrew 'nuts' with a split nut design so it's fast to reset.. but I found that it only took about 10seconds to spin it back by hand - so I didn't bother. There are no limit stops with microswitches, I basically reset it to the start position and press a button to reset a counter.. once it reaches the count limit at the end of travel it stops and flashes the screen to indicate a reset is required (although it's pretty obvious of course!)

Ah yes, my version here is not very big. It's mainly designed to be used on a small Skywatcher Heritage 150p .. there is plenty of 'margin' on the CofG.. I think now I've done it, it could be used for bigger dobs without much modification.

Well... Here's mine.. I finally finished it! I ended up having to pay £2.30 for a stepper motor driver PCB. Other than that, it's from the parts bin and made from an old shelf. All 3d printed included the ball joints. Driven by a stepper motor and worm gear pushing/pulling the platform (way more torque than needed, but this can be turned down on the driver PCB)... BBC micro:bit coded in Python... Powered by a 2S or 3S Lipo. It actually works really well and I've got the accuracy spot on!

I already have a (paper) printer so no need to buy anything -free 😉 you can see where I'm going with this now! Haha