So, after the successes of this week, my new set is:
Today I only managed ten reps of 50m before failing and then had a further fail before swimming out the rest of the set. I can live with that. Again, the 25s are still quite hard to keep on the pace and I’m failing out around the ten reps mark.
Work is getting in the way of swimming a bit at the moment, so I ended up missing out on Tuesday. I decided I’d have another go at the same set despite completing it on Monday, just to prove that it wasn’t a flash in the pan. And indeed I did manage to complete it again. Very pleased, but this means that the rest interval must come down again for next time.
A new set this week, though very similar to my old one. In fact the only change I’m making is to reduce the rest interval for the 50m swims to 25s.
And to my surprise I still made it all the way through the 18 reps of 50m. Very pleased with that. Still struggling to follow that with the full 18 reps at 25m however. Around ten seems to be the most I can manage for the time being.
I have now finished bench-testing my third dew controller (had to wait for another humidity sensor to arrive as the one I had appears to have been faulty). So, I think it’s time to start looking at Robert’s focuser controller.
The Sourceforge site with all the details is a bit overwhelming at first because there are a number of different designs: myFP2E, the wifi version which has actually moved to a separate project on Sourceforge; myFP2N with a touch-screen display; myFP2M which is a ready-made controller with various options and the standard DIY version which also has a number of hardware options. There being no big friendly “Start here to build your own focuser” button, the documentation here is probably the place to start.
I have a number of OTAs that I’d like to be able to fit a controller to, varying from my Photoline 72 which is about f/4.75 when fitted with a focal reducer, to my C9.25 and PST at f/10 or even my 127 Mak at almost f/12. Obviously the size of the critical focus zone at f/4.75 is only marginally larger than a gnat’s whisker. In order that I might hang on to what remains of my sanity I think it makes sense to keep the hardware the same, which probably makes something like the Nema17 with a 27:1 gearbox the obvious choice. Whilst I might get away with the 5:1 gearbox on some of the OTAs, there’s no real cost advantage to using the lower reduction ratio gearbox and I think I’d probably still end up needing micro-stepping for the faster OTAs.
I did consider not using a gearbox and using timing gears and a belt drive instead, but I’m not sure that really gains me anything other than potentially being able to hang the motor under the focuser on ‘fracs and newts rather than have it poking out of the side.
So, for the moment at least, my plan is to use the Nema17 with 27:1 gearbox from OMC across the board, which means I’ll be using the DRV8825_HW203 driver and need the appropriate circuit design.
On the electronics side, unlike the dew controllers I intend to build these on strip board. I do actually have one circuit board for a revision of the controller that is a couple of revisions behind, but I’m thinking I may save that for a combined travel dew/focuser controller box. Circuit diagrams and layouts are available in the STRIPBOARDS directory, but it’s not immediately obvious which are the relevant reading. I started with “BOARD OPTION DRV8825 HW203.pdf”, which I think is the main document covering most of the DRV8825 builds. I’m not actually too worried about displays, temperature compensation and suchlike as the focuser will be remotely operated and software will take care of refocusing properly, but having a set of buttons to adjust the focus manually would be good. The documentation for the buttons (in the OPTIONS directory) says that pressing both buttons together resets the focuser position to zero and beeps to confirm that it is done. I was wondering what the buzzer was for…
The main build document doesn’t cover exactly which options I want, and in fact suggests that the strip board layouts may be out of date when compared with the “everything” design, so one of the first jobs would seem to be to compare the various circuits, work out what does what and remove the bits I don’t need or add the bits I do and see how that affects the strip board design. I think “Stripboard DRV8825-HW203 FULL” is not that far off, though I don’t need the firmware programming switch or the temperature sensor. Some of the other designs appear to have a 1N5408 diode and a 100uF electrolytic capacitor across the supply and ground that I’m not fully sure I understand the reasons for yet. Hopefully I can work that out in time.
And another repeat of the set I’ve been swimming for the last few weeks.
The pool was busy again today and I wasn’t really enjoying the choppy water, but despite that I managed to complete the 50m set without a failure and manage ten reps of the 25m set, though neither was quite as fast as yesterday.
Still, that means the rest interval gets reduced next week, which should be interesting.
Apparently so-named because it lays square eggs. But perhaps it just lays these. An average “large” size egg (the pale cream one, obviously) alongside for comparison.
I had a stack of hive brood chambers containing old comb that I was going to melt down. It must have been bumped by a deer or something like that, which left room for some hornets to get in and build a nest. And what a nest it was!
I found these the other day, so I thought I’d just add them out of interest…
First, the remote control for the telescope room LEDs. I keep meaning to 3d print a little holder for this to fix to the wall, or perhaps even the inside of the door.
And second, the HDMI switcher. This also has a remote, though it uses a battery size (button cell) that I wasn’t familiar with. It seems to work well enough though.
It has four HDMI ports, plus a USB port to go with each. Plugging a keyboard and mouse into a 2-port hub that goes into that USB port means I effectively have a KVM for each of the pier-top machines.
Another repeat of the same set. Busy pool again, too. I failed only on rep 16 of the 50m set, but wasn’t unhappy as my times are really starting to get back to where they were now — I had a small number of 46s reps and quite a few in the 47s.
The 25m set was a touch slower than Tuesday, but still not too bad and I’m happy enough with it.
Now my dew heater controllers are finished I need to get some more heater straps. Whilst casting about for suppliers I came across W&W Astro who I’d not heard of before. Their straps appear to be film-based and what comments I could find (particularly from people I know of) seemed pretty good, so I’ve taken the plunge.
This 50cm strap intended for my 127 Mak arrived earlier this week:
It does appear well-made and has an elasticated velcro fixing for holding the strap in position.
I look forward to seeing how it performs. The Mak is a bit of a challenge as it seems to dew up at the slightest hint of moisture in the air.
