Fred,
Great progress , looking good
Yes, one design fault with NexDome is they use 4 external nylon wheels to guide the shutter opening ( they should have weatherproof hoods or shrouds but it’s all $$$ )
Mines been up for 16months now and although they use UV stabilised plastic , I can envisage replacing them within a year or two.
The Dome itself is UV stabilised ABS and is guaranteed for 15 years ( still looks brand new )
Looks like your not to far off finishing it ( probably more satisfying building your own Obs from scratch)
I started with flexible garden edging, but found after a while it was too stiff and binding/dragging on the overlap I'd built in to the base ring.
Changed it to thin, flexible concrete jointing stuff, ("insertion rubber"?) which is working fine.
On my old 2m dome I used the tar-backed roof flashing, which could be flared out at the bottom as necessary. (I think that's what you used on your joints?)
Neville. This pic is what im doing, pretty rough and not accurately to scale. The PVC angle and bar used are pretty thin and flexible, but stiffen up when bent with a heat gun. I used a rubber strip to pack out the dome ring diameter, I made the ring too small, it should have overhung the base ring, but most of this build design was on the fly as I went.
I cant really use rubber on anything that shows externally. Bunnings only has black, this whole thing needs to be white (to match house,daughters order). I tried to paint black rubber white, too flexible, didnt go well.
I haven't shown flashing tape on the pic, it and sealant will be applied where required.
I could have just made one large skirt over everything, but im trying to get the interface between the base and dome to look as slim and non-clunky as possible.
I thought about flared Buyte flashing tape, its used on the segment joins and the slot cover, but it does look a bit loosy goosy, I thought id try a bit harder on the base.
A bit of a techy update.
The structure is finished and in the rain, no detection of leaks so far.
3D printed rack and pinions fitted and tested with motors.
I used 4 motor/gearbox/gears around the dome rack in parallel to spread the load because they were cheap and I had them. Very strong.
Spring loaded door hinges from bunnings worked a treat to mount the motors, covers dodgy alignments to keep gear/pinions nicely meshing.
The 2 motor drives (Pololu MAX14870 $28) are remarkably small but easily handle the small load allowing smooth accel/decel and current limiting.
The plan to use an ultrasonic proximity detector (Sensortechnik UPR-A 1500 CP TVPA 24 C $80 on ebay, more elsewhere) instead of fancy software to calculate dome rotation, on test works better than expected. Its a proper industrial sensor with a built in teach function and tracks the dome slot very well.
The dome top has no electrical connection at all with the base (no nasty slip ring). It will communicate with the base via a wireless link and the slot cover will be powered by a battery, charged by a small solar panel on the top.
Ive decided to build/program the dome control electronics myself using Picaxe 28X2, RF transceivers and custom PCBs instead of a PC or PLC, more fun, way cheaper.
Hi Fred,
Great project and an excellent build.
Could you please elaborate on:
"The plan to use an ultrasonic proximity detector (Sensortechnik UPR-A 1500 CP TVPA 24 C $80 on ebay, more elsewhere) instead of fancy software to calculate dome rotation."
Will you attach the sensor to the scope? If so, I can see how this would work perfectly for an Alt-Az mount, but GEM mounts can place the scope at odd angles resulting in even stranger dome slot positions for the scope to view through. I'm eager to see how you overcome this.
Jason. Yes the sensor will go on the scope and it is EQ mounted.
Except for near meridian the tracking is simple, its a small refractor and the slot is big enough to view through just with the sensor tracking the slot edge.
I got a bit worried near the meridian when the sensor started detecting the top edge of the slot, what a mess i thought, but thats fine!, the dome just keeps rotating longer on this detection until this edge also disappears and the slot eventually flips right round!.
I do have some doubts about every orientation, i suspect (unless I can code this situation in, the dome motors have built in encoders) meridian flip and switching from north to south the dome will need to be set manually at the start, but since this is in my backyard and i tend to only image one object a night anyway, im fine with this. I manually operate flip on my remote rig too, its just easier, so im used to it.
Ill have a sensitive wifi video cam (baby monitor, can see in near dark, although i might turn a light on for this) in the dome so i can do all this remotely from inside.
Ingenious approaches and skills Fred, nice work and good to hear you have no leaks, after a minor seal improvement, in one section of my entry door, neither does my 3M Scopedome, phew!
Hi Fred,
I wonder what will happen when the scope is on such an angle that the sensor detects the slot top and side simultaneously - could the system become ‘stuck’? This may be a very rare situation… anyhow, I hope your sensor works well as it will eliminate the laborious setup measurements needed for traditional dome slaving.
Quote:
Originally Posted by Bassnut
I got a bit worried near the meridian when the sensor started detecting the top edge of the slot, what a mess i thought, but thats fine!, the dome just keeps rotating longer on this detection until this edge also disappears and the slot eventually flips right round!.
Last edited by AstroApprentice; 26-08-2022 at 08:25 PM.
Thanks Mike. Im told every dome leaks at some time. I cant wait.
Jason. The sensor has a simple on/off output, it detects anything in its view. Simultaneous edges doesnt matter, will just cause rotation regardless.
Actually, I think this will make handling mount flips easy. On a flip it will just keep rotating untill the slot is clear.
A small update.
I designed and built a PCB for dome and shutter control.
It has a motor controller and radio transceiver on it. Given the dome top has no electrical connection with the base, radio control was required for the top.
Ill have 2 of these with different software. The base controller will drive rotation and the top shutter operation. You don't need all this really, but you know, i did this because I could, and it was interesting to do. The transceivers act as wired RS232 devices so I can do anything I want, like monitor battery voltage, shutter microswitches and any problem that might ensue on the top remotely. Base rotation and shutter motors are fully accel/decel/speed controlled too (not your crude relay hammering), so less stress on motors/gearboxes. I made the PCB a bit universal so I can turn lights on or make an alarm ect, its got lots in/outputs.
Yes well, dated perhaps, im using the PICAXE version(Basic, a totally integrated and stable environment). I have found what you can do with a micro is more important than how flash it is. One line of code can do what an arduino needs many lines for, and faster. It allows fast and intuative coding. Also i must admit, im used to it, in my comfort zone. The Arduino ADI is powerfull to be sure, ive used it, but PICAXE kills it for fast reliable results for simple machine control. And you can just buy the PICAXE PIC chip for use with a custom PCB.
I wouldn't say dated, I'd say old school (with reverence). I'm not at all implying you should have used arduino, in fact I'm more anti-arduino because you don't learn how to do thigs properly, kinda like getting a chauffer and thinking you've learned to drive. PIC's and HC0x were my faves in the day depending on the task. I've scoured too many datasheets to remember. Arduino makes it super easy in both supply (OMG quantity lead times of the past!) and coding if you can suffer it's limitations or just want to use it and don't care about the why & how stuff. I mean you can also easily sidestep the "arduino processing" stuff and use it properly and enjoy the swathes of hardware targeted at the environment. I use ESP32's or STM32's mostly, again coz they've made it too easy not because I can't otherwise.
Anyway, the result looks A1 you should be proud.
Update. So ive cranked up the automation design a bit and made/coded a wireless remote control box for it (no PC or wifi needed), the box is repurposed from an earlier timelapse project. Its old school, switches and buttons, no menus to surf through.
It continuously monitors conditions like weather and shutter status. If shutter to base comms is lost, or rain ensues whilst still open for some reason, and a few other operational failures, then an alarm goes off. Its a convenient device to have next to my bed (with display off) and alarm only when the situation is dire whilst imaging.
Its proving very useful for installing/diagnosing the dome drive system. It has manual and auto drive options (with limit switches) and OBS light dimmer functions. So i dont have to be in the OBs to test it comprehensively.
Ive been testing dome rotation automation using a Velleman board and Lesvedome ASCOM driver, as an interface to my motor controllers. ive lost a bit of confidence in the proximity sensor idea by itself, and given the ASCOM driver and interface board were so cheap (Maxim DL has scope position parameters built in) I gave it a shot.
And ASCOM control allows other scheduled/weather functions too (via DL maxim). I find ASCOM generally flaky though, I might revert.
Anyways, progress is slow, but I have the time and the weather will be **** for a few months yet. Ill be well prepared when it gets better.
haha thanks Alex. Not so good with the mechanicals though, but I can overcome deficiencies with electronics and coding. inefficient, but if it works it aint cheating I recon.
