Stub Mandrel

Here's a quick hit with the 'Astra Image Stick':

These actions include effective noise reduction:

https://www.prodigitalsoftware.com/Astronomy_Tools_For_Full_Version.html

For the very best in noise reduction (and sharpening), look at:

https://www.astraimage.com/

Missed it by 27 minutes. Watched the actual launch on replay, they seemed to struggle to light the blue touch paper! Talk about straight to animation... that looked a bit dodgy to me.

2 hours ago, Thalestris24 said:

Without an inductor wouldn't it be an effective initial short circuit? Anyway, hopefully the buck converter will do what I want.

Louise 

Only very briefly, the secret will be to match the capacitor to the load and the PWM frequency.

Less briefly:

40W @ 12V is about 3.6R. Power - V^2/R therefore R=V^2/P.

The  PWM frequency of the typical cheap eBay modules is 13KHz.

One cycle of power 1/13,000 = 0.00008 seconds.

To get smoothing the time constant RC should be >> than the supply period, 1 millisecond should be fine.

so if 0.001 = 3.6 * C, C= 0.001/3.6 = 0.00027 F = 270uF.

The energy in initially charging the capacitor (lets assume the power supply's internal resistance is negligible and it charges within one PWM on cycle) is 1/2*C*V^2

1/2 * 0.00027 * 12^2 = 0.039 joules, but this charging is typically at 50% efficiency so roughly enough to raise the temperature of a1/50 of a gram of water by one degree centigrade.

This might make a neat little blue spark, but it's nowhere near enough energy to fry your PWM module.

Science, don'tcha love it?

?

I did think a choke might help, but to be honest a capacitor should work fine. Once it is charged (a few cycles) the current through the PWM should be no greater than without it.

The Wanhao D7 looks almost affordable...

What is rarely understood is that the heatsink has to dump the heat removed from the camera PLUS the heat used to power the peltier.

A peltier is 10-15% efficient, I think in our rather peculiar setups we need to assume 10%.

In which case a 40W peltier running would provide 44W of cooling and have to dump 44 watts into the surrounding air. Think how warm a 40W bulb gets or even a 10W LED lamp, that's a surprising amount of heat.

If you don't get that all out the heatsink the peltier will warm, not cool, the cold finger.

This is why (a) fan cooled heatsinks are essential and (b) why an underpowered peltier can work better (if the heatsinking is ineffective).

As for PWM and Peltiers, why not try fitting fit a decent sized capacitor across the peltier?

3 hours ago, mikey2000 said:

QHY5R-IIc is that it's a bit too low resolution to decently guide a 1000mm scope through a 180mm finderscope.  

If its any help I guide a 1200mm scope with a 280mm guidescope and a ZWO ASI120MC

5 hours ago, Thalestris24 said:

He doesn't do setpoint cooling but claims to get sub-zero temperatures at 30 deg C ambient. He also manages a ~1.8mm thick plate. Not sure if he had any probs with condensation.

I have a very similar loop of nichrome to the one he shows.

Thickness of the plate is virtually irrelevant with copper.

I did some calculations as I was sceptical and the limts are teh thermal bond between copper and sensor and copper and peltier.

You may be losing some cooling if you have a thermistor between copper and sensor, you need them, to be a close as possible.

Neil

No expansion joints?

Hmm! I don't think the 450-D records actual sensor temperature. Imaging at -2.5C with the peltier flat out the Exif reads 2C.

I get ice on the outer part of the finger at room temperature, obviously that may not all get to the sensor even wit the insulation on, but until I sussed the heater element I suffered persistent icing up of the sensor.

Here's an image from 20 past midnight on 10 August 2017, during the period when I was getting mine sorted out.

Camera temperature in the Exif is 8C. The night-time minimum temperature that night was 6C, probably a couple of hours later.

To get that level of ice on the sensor glass (which is separated from the sensor by a decent air gap) suggests cooling well below zero. It is ice not dew as I looked at the sensor and sawice on it.

M96 and M95 from last night. A bit pedestrian with such small targets. I should have centred higher up, and got M105 and friends in shot as well...

And can you imagine the distress of a metre-print failing at 95%...

You get house-built steam engines, why not a house built 3D printer? Fill a whole room with one (may be difficult to get prints out the door...

1 hour ago, reezeh said:

That might be an idea. The hardest part would probably be making sure you get all of the slots aligned if you're building one like this, otherwise it's just a wider single piece about 15-20cm wide - but I think I see problems there with routing that too. And I'm no DIYer.

The secret with routing is always to use a jig or a guide of some sort.

As  man with two routers I really ought to make myself one. But router dust and scopes don't go together well. Perhaps in the summer when I can do it outside.

It's not exactly a detailed set of settings, it would good to have a lot more info.

Impressive though, I haven't tried far beyond 50mm, never thought of trying longer.

And if you get fed up with astronomy, you can use it as a holiday let for the Cloud Appreciation Society. Roll back the roof and enjoy the view... ?

Ah, slightly confused then realised that despite the part description in the first picture, it's wifi not bluetooth.

The module I have is bluetooth, so ideal for my laptop as it will just work as a serial port.

I've got plans to do this -I have the module.

Rather than a big buck converter, I'll use a 3.3V regulator chip which will be smaller.

52 minutes ago, tekkydave said:

Nice, but £199 according to https://www.mintronics.co.uk/webshop

Yes, but it is an outright purchase that allows commercial use.

This is Alibre Atom3D. You can fully define everything parametrically if you want:

12 hours ago, Gina said:

Well, I've been writing code for well over 50 years but still prefer WYSIWYG!  ie. graphical.

I can claim 41 if my mate's ZX80 counts... ?

I'm using Alibre Atom3D which is the hobbyist version but is great fun (and quick) to use.

Wow that looks like hair-shirt CAD to me.

Why would anyone not want to use a graphic interface? (speaking as a parametric CAD user).