saac

Vlaiv I don't think it is as indeterminable as it may appear. Treating it as a simple adiabatic expansion will get you pretty close to the value in practice - nozzle considerations accepting (choking, throat velocity).  Nor is your target of -50 Celsius overly ambitious; for example a common CO2 fire extinguisher (55 bar , 3 litres) will easily get down to that range.  Discharge a CO2 fire extinguisher through a close fibre cloth and you will be able to collect lumps of dry ice at -78 Celsius - the horn of the extinguisher will itself drop by as much as 50 Celsius if the extinguisher is fully discharged. 

Out of interest what is your plan, are you looking to build the setup yourself - interesting project, good luck with it. 

Jim 

For a 1st approximation I would tend to treat it as a reversible adiabatic expansion  so T2/T1 = (p2/p1) ^ (Ƴ-1)/ Ƴ .      Ƴ  (adiabatic heat capacity ratio) for air is approximately 1.4. 

T2 = (278) * (1/200) ^0.286

T2 = 61 K,   but air freezes at around  58K

200 atmo is too high!   In practice you would also need to allow for the efficiency of the nozzle used to throttle the gas so the final expanded temperature would be a little higher. 

Jim 

I can't remember exactly Lousie just that it was all very reasonable. I've bought lenses and a beam splitter for an interferometer project and also a set of lenses to build a Rochester cloaking optical train.  From what I recall there was no import duty as such or if there was it was pretty insignificant.  The benefit of course is compared to the likes of Edmund Optics and similar Surplus Shed prices are way cheaper. It's just a matter of them having what you need.  I'd highly recommend them though.

Jim 

49 minutes ago, Kev M said:

Would an  eyepiece not do for the 30mm ?

 

Failing that.... https://www.surplusshed.com/

 

 

 

 

x2 for surplus shed. I use them fairly regularly, very reliable, they may have what you want and if not ask and they may be able to find it. Standard USA postal service but not too long a wait.   They had some cracking 5 inch objective lenses a wee while back , would make a nice project.  

Jim 

Just now, Dave Lloyd said:

Have you been spying on me? 

Secret handshake time Dave , we are in the same club  

Jim 

On 14/05/2019 at 13:24, Vondragonnoggin said:

 

what I’ve seen though, and it’s natural to want to do this, is that members that just grab on to EAA camera or EAA NV, get pretty excited about seeing things they never thought possible previously without getting huge telescopes or requiring the darkest skies and they want to “shout it from the rooftops” to others or be able to suggest it as an alternative to “get a bigger scope and drive to darker skies” and traditional method astronomy practitioners see it as “bragging”.

It doesn’t matter if the same behavior happens when they themselves upgrade to larger scopes or dominate the Deep Sky forums because they have giant dobs. That of course is not “bragging”. It’s a double standard that persists to this day on most forums. 

Without being disrespectful and I mean that sincerely but this type of stuff just makes me cringe  - I really cannot get excited about people getting emotional or defensive about their particular way of doing something. Likewise whether we should have dedicated forums or not or call it visual or assisted or whatever - for crying out loud it's a hobby. You do it because you enjoy doing it -  If somebody swears by standing buck naked with their head in a tea pot , left foot in a bowl of custard, whistling Dixie and observing through the spout afocal good for them. Do what works for you and don't feel the need to put a badge on it - life is way to short for that  folks.

For what it is worth I'd use  NV  at the drop of a hat if I could afford it , I also do visual and astrophotography have dabbled in spectroscopy and naked eye and I have on occasion (many) just stood and marvelled at the impenetrable blanket of grey cloud. Never once did I feel like putting a name to it, I did it for fun and because I wanted to. 

Jim 

9 hours ago, Chriske said:

Is there a specialist Hubble space telescope out there...??? I have a few questions about Hubble.
This is were I have most of the info from.

Zoomed in on the back of Hubble I see a few(4) vent-holes. Why are there vent holes at the back..in space..?

A few more questions yet to come, thanks..!

Chris would one on those Haynes Manuals be useful, I believe there is one on the Hubble.

Haynes Manual - Hubble

Jim 

19 minutes ago, ejp1684 said:

Hi Jim.

I posted about my experiences with Lowspec earlier in the year here. I've done quite a bit since (weather permitting!) and a couple of nights ago obtained some nice spectra in Cygnus. I've been using a 150pds so far but I now have a 200pds on order which I hope will give even better results.

In short, I would recommend it as a project. It took me quite a few hours to complete, especially filing down the moving parts which hold the grating so it rotates smoothly, but well worth it.

Eric.

Thanks Eric I think I'll definitely try it out. I've played around with the Star Analyser and managed to produce a decent looking spectra of Vega using rspec. I stopped short of getting my head round correcting for instrument response but I've always wanted to go back and pick it up again. The Lowspec looks like a very neat little unit - thanks for the link to your write up, following that now. 

Jim 

1 minute ago, ejp1684 said:

Referring to an earlier post about Prusa i3 printers, I bought one from ebay about three years ago, and it's still going strong. I also use dirt cheap PLA, again from ebay, for about £10 or £12, and they have performed as well as a £33 one from rigid.ink. In my experience 3D printing is as much an art as a science; it took me many hours to work out all the settings to produce quality prints good enough for my purposes. And by that I mean successfully printing all the parts for the Lowspec spectrograph, including all the screw threads where necessary, which surprised me.

Eric.

Eric, can I ask how has the Lowspec spectrograph performed for you, would you recommend it as a project?

Jim 

1 hour ago, teoria_del_big_bang said:

Yes that was good filament, but was expensive. I did not know they were not selling it anymore 😞 

Steve

I certainly saw a lot of positive recommendations for as well Steve  but pricey compared to others. That said I'd be tempted to try an expensive brand against the likes of Creality own brand which has performed well for me so far . Christmas is coming so I'm drawing up a list now  - a reel of plastics , oh how days have changed  

Jim  

16 minutes ago, PeterW said:

People are starting to make rocket nozzles with 3D printing. The latest machines make material with better properties than wrought, but there are still concerns about the cost effective validation of parts that are hindering uptake. Some lower temperature turbine blades and blade repairs are being undertaken already. All users need to assess the properties they need and the risk and implications of failure. Many people are happy with cast material which can have many more internal defects....  the technology continues to rapidly evolve, so what wasn’t possible a few years back is now easy to achieve.... interesting times.

 

PEter

Indeed Peter but not with PLA  

Just out of interest additive layer or even sintering technology would have to progress beyond imagination to meet the performance of Rolls Royce single crystal blade technology.  But as you say some very interesting things are happening in the world of industrial 3D printing particularly in aerospace where a range of components are now 3D printed (both metal and non metal) .  The method of manufacture, cold pressing, forging, casting, fabrication etc has always had an influence on the mechanical properties of material (advantageous and undesired) , it's an area of engineering science well known to design engineers. 3D printing is no different. 

JIm 

25 minutes ago, Gina said:

I'm getting a feeling of déjà vu here -  I think I have already said that I've found PLA eminently suitable for a number of applications.  I've used it plenty in astro projects, for instance.

To be honest Gina I think the world of 3D printing and its wide range of filament materials opens up an aspect of engineering design to many whom it may otherwise never really have been a consideration.  We both come from engineering backgrounds so these considerations are well understood but I guess the assortment of filaments can be confusing to many.  Like any hobby/interest there abounds misconceptions and "urban legends" - the 1 cubic meter  pier foundation syndrome comes to mind   

With specific respect to PLA I think it is a good all rounder:  inexpensive, good printing performance , no toxic fumes emitted.  It is a good general purpose filament and where it does lack a particular property then other filaments can be chosen with printer capability also in mind. The Ender 3 and 5 models are PLA and ABS capable but at the moment, certainly  for my needs, I can't see a need to use ABS yet and certainly not without some form of enclosure and fume extraction.  Ill be printing PLA for some time to come before I start on my 3D printed cold fusion reactor  

 Jim 

9 hours ago, gian said:

PLA mechanical qualities are too poor for prodicing parts that will see real world use. 

 

 

I'll disagree with you on that one gian. The brackets I have printed in PLA do indeed have the mechanical and aesthetic properties for their intended application (adjustable bed for K40 laser engraver). Likewise the PLA printed assembly to hold the beam combiner will also function without difficulty.  My Polemaster camera when not mounted for polar alignment functions as an electronic finder held in place by a PLA printed adaptor  and has functioned perfectly well over the past 2 years.   I certainly wouldn't look to use PLA for a third stage RB199 turbine blade nor a wing box on an Airbus, but neither would I use mild steel, aluminium or carbon composite . However, PLA certainly does have "real world " application.  In common with any other engineering/manufacturing project material selection is part of the design consideration - 3D printing is not exempt from that consideration. To say however that PLA is not suitable for real world applications perhaps calls for a broader definition of "real world"  - my uses to date are certainly real world and PLA has satisfied the design brief very well. 

Jim 

I must admit I like the Ender's magnetic bed it gives excellent adherence without further preparation and it makes removal of the print a doddle. Having looked at the brackets I made for the K40 laser bed I can't see that I will have any problem with PLA for the majority of my practical applications (not really into toys and models); currently printing out a beam combiner again with PLA and so far all is well. 

Jim 

1 hour ago, Thalestris24 said:

Yes, yes I did all that. I didn't realise I had to keep doing it every time... Probably moving the printer didn't help. Anyway, after dinner I levelled again and also went back to the Creality-supplied PLA again and that's working fine, so the Sunlu PLA+ seems to need a lot of tweaking... I think I'll order another reel of ordinary black PLA. Any recommendations of affordable brands?

Louise 

Experiment with the gap Louise, position it so that there is a real noticeable drag on the paper.  You will know if it is set right as soon as the printer lays down the first few lines of the raft/brim bed.  I had a similar problem as you described when I did my second print - it just wouldn't adhere to the bed. I reset the level this time lowering the gap and it worked fine.   For filament I've been impressed by the Creality supplied sample so I'm going to stick with that at the moment £17 or thereabout from Amazon.

Jim 

Jim 

2 hours ago, Gina said:

 

The nozzle should be something like 0.2mm above the bed.

I'll have to leave it to someone using the sort of controller you have, I'm afraid, Louise.  You need the bed level and the nozzle about the thickness of a piece of paper above the bed.

Lousie as Gina said your bed is too far from the nozzle. I would start by going through the bed levelling procedure again. Send the printer to its home position, disengage the stepper motors, then place a slip of paper between the nozzle and bed. Adjust the height until you can feel a noticeable drag on the paper - it should still be able to slide out though. repeat for each corner and again if necessary. Don't overthink it , and if you end up with the gap being smaller than it should be then (show in the deposition of the filament) it will at least adhere to the bed - you can fine tune it later.  You should be able to alter and save the temperature profiles here. 

Jim 

The Reddit forum looks like a good source of info Lousie , it's not something I've used much. It looks like as you say a known problem then. I hope you can get it sorted. 

Jim 

55 minutes ago, Thalestris24 said:

I'll try reseating the ribbon cable connectors tomorrow. I don't want to have to send it back... I noticed when I was doing the assembly that moving the gantry up and down caused the screen to flash!  That suggests that it was generating inductive voltages which could have caused some damage You'd think they would have incorporated measures to prevent that... 

Louise

I noticed the same thing on mine Louise, I m guessing a strategically placed diode would have sorted that out.  That said, I don't think it's causing any problems mine has worked flawlessly, I really can't fault it.  I can upload a video showing how the encoder and screen on mine behaves if that would be of any use for comparison. 

Jim 

1 hour ago, Thalestris24 said:

Oh well, the T2 connector came out ok It fits nice and tight, and feels solid, but it's hard to tell how durable it might be. I suppose the good thing is that one can just print out another one! 

 

I'll try to print out a few other components tomorrow, and using the black Sunlu filament I bought.

Louise

That's looking really good Lousie you will be pleased with that. It's very satisfying especially when its something that you are going to make use of. I haven't noticed the problem you reported with the encoder not responding. Having said that if I am at the top of the menu and turn it the wrong direction (anti clockwise) it does nothing  - I half expected that it would scroll from the end of the menu upward if you know what I mean.  When Im in a mid part of the menu it will operate fine in either direction.  Happy printing  

Jim 

I would caution against looking to do astrophotography at the outset, certainly not for a whole class experience. To be honest sitting waiting for multiple exposures to be taken and then processing will be tedious for pupils and they will quickly lose interest. However that is definetly something to work up to in teh future. The best option I would suggest is either visual, certainly for the moon, solar observing, supported by some form of video capture if you want to view real time images in the classroom.  Astrophotography is a bit of  steep learning curve which brings in a whole set of additional requirements and where it is something you can work towards as a growth project I would not recommend it for a class activity. That said, astrophotography is perhaps something that a smaller group of more dedicated and patient group of pupils such as an astro club could engage in.   

As a secondary school teacher myself (Physics) I have offered both whole class and astronomy group activities in school and by far the most successful has been the visual experience.  I have used a video setup for solar observation including our last partial solar eclipse and will be looking to do similar for the transit of Mercury in Nov. The advice offered by Pete above regarding seeking help from a local Astro club is definitely something you should consider.  For what it is worth there is a lot in a project like this for a school to benefit from with respect to cross curricular engagement;  you could engage pupils who are interested in design and manufacture, electronics, programming, art and their associated departments.  Definitely worth pursuing.  

Take a look at the ATIK Infinity , search it out on YouTube to better understand its capability, If it is within budget something then like this would be excellent for remote viewing (whole class or small group). I would also try negotiating a supply deal with a retailer for single supply, most are willing to offer some for of "educational discount" especially for a whole set up.  

Jim 

ATIK Infinity - Video Astronomy

11 hours ago, GoodOleJim said:

 

Indeed. The mount is pretty ideal here. I'm gathering information still on our preferences for viewing, though I'd like to focus mainly on lunar and planetary viewing. 

Really we just need something we can control remotely! I've bookmarked all of your suggestions.

Right. Real time astronomy is what we're striving for. Our budget is pretty wide open right now, but don't want to spend above our needs. 

Based on our needs, we'll need the mount, telescope, and camera capable of real time viewing.

Based on what you have said above then I would go for the Skywatcher AZEQ6-GT (room for growth)  and an 8 inch reflector something like the Bresser-Messier NT 203 or a SkyWatcher  200p (the one in the link is bundled with an EQ5 mount which whilst a budget mount will still allow it to be controlled remotely - this will save some money for you).   Usually refactors are favoured for planetary use but I'd suggest that your pupils would be delighted to see the Andromeda Galaxy some of the globular clusters and nebula so a reflector would  be a good choice. As far as software is concerned to allow remote operation you are in lucky as most of it is free and excellent at what it does.  For controlling the telescope download and take a look at EqMod and Stellarium or Cartes du Ciel.

Jim

Eq Mod Youtube

DemoCartes du Ciel

Stellarium

Skywatcher Explorer 200P

 Bresser-Messier NT 203

SkyWatcher AZEQ6-GT

3d printed pizza  

Jim 

1 hour ago, Dr_Ju_ju said:

You may well be an eager beaver, but don't rush anything, slow & sure is the best way......

No need to be over cautious it simply works and works well - Creality get's my thumbs up. If problems arise as surely they will they will be investigated and overcome; but so far, it's on its 8th print and storming through with excellent results.  I'm quite pleased now that I have the combination of the laser cutter and 3 D printer they  complement each other very well. 

* Manual adjustable bed for Co2 Laser (K40) by dgferrete, Published on April 2019, www.thingiverse.com/thing:3595259

Jim 

Sorry , double post !

Jim

Yes, frequent tea refills was in my instructions too.  Good luck with putting it together. 

Jim