SharpSky ASCOM compliant digital focuser project

[dtrewren (Dave)]

Hi Allan,

Excellent, very pleased to hear you got everything up and running ! Also thanks for the positive feedback, very much appreciated.

Yes soldering does take a little bit of practice. One of the main reasons for designing the PCB with through plated holes was to make the soldering easier as the holes are effectively tinned through the board. The downside of this is that it makes (in my opinion) it much more difficult to get a component out of the board once soldered in. Solder pumps and de-solder braid are less effective if the hole is through plated.

Horses for courses I suppose.

Good job & clear skies,

Dave

[wasyoungonce (Brendan)]

Easiest method to de-solder on a double sided PCBs.....cut the component off and just de-solder the left over legs.

Works a treat for ICs/resistors/capacitors etc but not so good for SMD's...you tend to twist the legs which can tear the pads off.

For this get some "Chipquick"....adds a low melt point to the solder joints. You can bridge the legs of an IC with this (form a blob) and get the legs * pads hot (well relatively hot but not hot enough to damage pads) at once and just lift up the IC. Works a treat.

If your not into "chipquick" you can get good hot air SMD de-solder stations cheaply from fleaby from $50.

Of course...junk any removed component, never re-use them.

With soldering....clean..clean and clean again. Clean your iron tip every joint and multi core solder (with a spray solvent). I did write a doc on this (to put on IIS) but didn't(don't) have a method to macro record of some action videos.

Anwyway...FWIW.

[dtrewren (Dave)]

All very good advice

I definitely favour the method of chopping off the legs of leaded components and then remove the legs individually. As Brendan says the component is best binned anyway so the priority is to preserve the PCB and cause as little damage as possible.

The 'Chipquick' is an interesting product, that's new to me ! In the past when removing SM devices I have used a heat gun and found this very effective.

Luckily, I have a secret weapon if all else fails ..... it's called a 'Rachel'. She's a contractor at work employed to perform board modifications and fix boards. The boards are ten+ layers with features I can barely see - if she can't fix it .... it goes in the bin

[peter_4059 (Peter)]

I've been thinking about changing to a stepper system for a few weeks now and after looking into this I've decided to give it a try. Ordered a kit today and can't wait to get hold of it.

Dave is doing a great job developing an excellent product and offering it to astronomers at a very reasonable price. Thanks!

[dtrewren (Dave)]

Hi Guys,

Just a note for anyone that might be using/interested in the SharpSky client software.

I have made a couple of modifications :

1)
To make it clear where the focuser has last moved to any 'Go' button pressed is highlighted in ..... well a Coral colour in sympathy with antipodean reefs (suggested by Peter, the feature not the colour)

2)
I have added an emergency HALT button. Whenever the focuser is 'moving' the HALT button will stop movement immediately. Current absolute position when halted is preserved.

Latest V1.5 version is live on the website :
www.dt-space.co.uk/SharpSkyClient

The client is ASCOM compliant and will therefore work with any such focuser including the ASCOM focuser simulator.

I have tested the client post modifications, but if any problems are found please let me know.

Cheers & clear skies,

Dave

[allan gould]

New software works well Dave. Many thanks for that

[dtrewren (Dave)]

Cheers Allan - thanks for the feedback

Clear skies, Dave

[allan gould]

Originally Posted by dtrewren

Cheers Allan - thanks for the feedback

Clear skies, Dave

I forgot to note that I did not have the problem that Brendan did with the Moonlight stepper. It purred like a kitten with no motor chatter and thus did not have to alter the step period.m

[dtrewren (Dave)]

Hi Allan,

Excellent new s on the MoonLite stepper. I can't remember if Brendan bought an actual MoonLite stepper or sourced the same motor as they used (Brendan ?).

I essentially found the step period using a simple empirical method, ie just reduced the period until the motor became unhappy and started missing steps and then added 10% to the value. That came out to ~35ms for the motor supplied with the kit.

Those MoonLite Hurst motors are very nice and they are always a pin compatible upgrade option if you have some spare cash.

Does the MoonLite motor have a mechanical clutch which can release the drive ?

Clear skies,

Dave

[allan gould]

Yes, Moonlight have now incorporated a slip clutch into their attachment to the focuser. So now it's easy to do a rough manual focus, tighten the clutch and then focus critically. Love it with your controller but I'll have to get the temp compensation working when I can set up the components.

[dtrewren (Dave)]

Hi Allan,

That's a real nice feature having a clutch The temperature compensation shouldn't be hard to set up. One obvious thing to point out and it can cause a bit of head scratching is to make sure the compensation is running in the correct direction.

So as the scope cools it contracts so the focuser should wind out to compensate and keep you in focus. If you think it's running in reverse there is a switch on the SharpSky driver window under 'Temperature compensation' called 'Direction reverse'. Once checked this reverses the direction of only the temperature compensation.

Easiest way to check is set a really big 'steps/degree' value say 100 and then cool the sensor with something .... a bag of frozen peas and check the focuser moves in the correct direction.

Cheers & clear skies,

Dave

[allan gould]

Ah! The old frozen peas trick - will do. Thanks for the tips Dave

[dtrewren (Dave)]

Hi Guys,

While you chaps are pushing up the Zzzz or hopefully imaging I decided to make a little video.

I have had a few questions regarding temperature compensation so decided to make a short video just showing the SharpSky temperature compensation actually operating in practice and upload the result of the logged data. I hope is clarifies the operation a little

Video : http://www.youtube.com/watch?v=b-7uyLQSZ4o

The file logged during the demo :
http://www.dt-space.co.uk/SharpSky/s...ky_templog.txt

Any questions or comments please fire away.

Clear skies,

Dave

[wasyoungonce (Brendan)]

Thanks Dave. But what I want to know.....Wot does the Mrs dtrewren think of you using her peas?

[dtrewren (Dave)]

Your not going to believe me Brendan but those are actually my own private bag of peas I bought specifically for temperature testing - the normal family peas have a habit of being eaten just when I need them most

[allan gould]

David
You are costing me a fortune!!! After building your controller for the stepper I'm going to have to replace the DC motor on my 10" RC with a stepper motor and that will entail a new back plate. Sigh, just more money but I love your controller so much that that it's necessary.

[dtrewren (Dave)]

sorry about that .... but you are buying the best in terms of motors assuming you go for another MoonLite ?

[wasyoungonce (Brendan)]

Actually the DIY install ML steppers are quite cheap, you get a Hurst geared stepper inside and a fully milled housing with motor clutch system.

Hurst motor alone is ~$95usd.

Beauty of all this is that if you want you can change your hurst motor for better step accuracy ...lets say if using a shorter FL scope (Smaller CFZ) of lets say F4.0.

[peter_4059 (Peter)]

My kit was waiting for me when I arrived home this afternoon. Very nicely organised into a number of labeled plastic bags making identification of the parts a breeze (thanks Dave).

I've soldered all the parts onto the PCB and powered it up this evening and get the "heatbeat" light so all looks good at this stage. I now need to make up the leads, drill the various boxes and put it all together.

I'm hoping it will work with a longer (3m) DB9 cable between the controller and the stepper so I can keep the power and USB connections in my box of gadgets beneath the tripod.

[troypiggo (Troy)]

Wow. That was quick.