A Low Cost RA Stepper for Small Telescopes

[AstroTux]

regards polar alignment, you shouldn't need Polaris to do it if you have clear south & east views. If you've got these, then you can try Drift Alignment. it's a bit more hassle, but worth the effort for good subs!

Once I thought I'd give this a try, but the only views I get from my back garden are South, Up and North in Winter !! Unfortunately living in a terraced street where the local council have decided to put a conservation order on all the trees in the area just means that I am gradually being swallowed by an urban woodland. Trees to the East of me, houses to the West of me, here I am stuck in the middle with you .

[Gina]

+1 for drift alignment

[c3po]

I'm not much better of Alan, i have only north views...but no polar scope (as I'm sure you can appreciate having the same scope). Views to East and West are over neighbours fences, and to the south is my house, so drift alignment is a pain too!

[Leo.A]

I have a polar scope in my EQ3 Pro GOTO mount and it's absolutely useless in Australia. I can't find Polaris no matter how I strain my eyes....(I know, I'm never going to find it).

I'm keen to get started with this project and tidied up my Celestron Astromaster 130 mount last night. All I have to do now is fix the stupid plastic leg adjuster lock, it's cracked. A hose clamp (and strong glue) should help as a temp measure.

My Skywatcher EQ3 pro mount had the declination zero point in the wrong place and nowhere near the correct free play on the 2 worm gear drives for RA and Dec motors (I had drift, worm skipping across top of RA gear). I pulled it all apart too and set the gearing up properly, greased it all and zeroed the setting circle. With that so far out, I know why my 3 star alignment always fails (read something about cone error on SGL and decided to check everything).

All I have to do is mow the 1/4 acre block and I can play (after I rake too) Every 5 days, cut the grass.......ARGHHHH, it grows so quick in Spring and summer.

[AstroTux]

I have a polar scope in my EQ3 Pro GOTO mount and it's absolutely useless in Australia. I can't find Polaris no matter how I strain my eyes....

:icon_salut: Leo.A, you nearly had me there.........

[AstroTux]

All I have to do is mow the 1/4 acre block and I can play (after I rake too) Every 5 days, cut the grass.......ARGHHHH, it grows so quick in Spring and summer.

Do you get any nasty critters in the grass out there? I had an uncle who lived in Melbourne and the stories he had of funnelwebs, black widows, etc., used to make me run a mile......

[Merlin66]

Astrotux,

No funnel web's in Melbourne, they live up in Sydney!

We have the redbacks down here.....

[AstroTux]

No funnel web's in Melbourne, they live up in Sydney!

We have the redbacks down here.....

Maybe that was it. I have to admit to a very strong dislike of spiders so I probably didn't listen too well ! Spiders and crabs are the only creatures that I seem to have a morbid fear of ( I even got used to the enormous 'roaches in the Middle East ), so I don't think I would last two minutes in Australia.

You guys are obviously a lot braver than I am !!

[AstroTux]

In the ol' days I used a single stepper driver chip (1020?) with a R-C controlled 555 chip timer for the pulses. This gave a compact drive pcb for say a 1 rpm output. Ideal for barndoor mounts etc.

This there still a similar driver chip available today??

Having looked through all my back catalogue of stuff, I now think you are probably refering to the SAA1042. This was the stepper motor driver of choice for some time as it just took a train of pulses. These are still available, but at rediculously inflated prices compared to what they used to be.

I found this site had an interesting dual axxis stepper motor driver buillt using these http://www.atmsite.o...tep/dastep.html . If you need some I still think I have a few laying around in my lab that I can let you have.

[AstroTux]

I thought I would post an 'improved' version of the code for this project in case anyone wishes to try it.

This version ( V1.10 ) adds the capability to use the UP and DOWN buttons to slew the RA axis by a small increase in speed either forwards or backwards. It has proved extremely useful when trying to centre an object using a webcam as it does not lead to the 'bounce' that I have experienced when trying to centre an object by adjusting the RA clutch of the mount by hand.

The UP and DOWN buttons are still used to control either the focuser or to adjust the tracking rate and this feature has been added as a third option. The user can select which option they require through the main menu. If this option is selected, the user can then adjust the slew rate by a small amount in the next menu screen. The slew rate value simply multiplies the tracking rate in use e.g. a slew rate of 2 would mean that the RA axis would move at twice the normal rate when the UP or DOWN button is pushed for a brief period of time.

The user's value for this slew rate parameter is stored if they wish to save their settings, and is recalled if they use their saved settings on startup.

The changes to the code are evident in the forever loop in the main() function, the choices in the menu() function, the startUpChoice() function and the parameters passed to the calcRate() function.

The attached file simply contains the new main.c file ( main_V_1_10.c ) as all the other files ( lcd.c, lcd.h and StepperMotor.h ) remain unchanged. To use this simply include this file in your build code instead of the original main.c.

Wishing you luck if you wish to try it :grin: .............................................

main_V_1_10.zip

[c3po]

how you doing with the re-design of the new unit Alan? Hopefully the week or so in Snowdonia has refreshed you adequately?

[AstroTux]

how you doing with the re-design of the new unit Alan? Hopefully the week or so in Snowdonia has refreshed you adequately?

Yep!! And I didn't fall off anything nasty. I did see some great stars though http://stargazerslou...ind-a-dark-sky/ !!!!!

The unit is nearly ready, I am just waiting for the LCDs to pop though my letterbox and everything should be all systems go...... :grin:

[c3po]

Yep!! And I didn't fall off anything nasty. I did see some great stars though http://stargazerslou...ind-a-dark-sky/ !!!!!

The unit is nearly ready, I am just waiting for the LCDs to pop though my letterbox and everything should be all systems go...... :grin:

woohoo! I'm starting to get really frustrated trying to polar align with my eq130, and 8x20 finder-scope i've bought & bolted on to help really hasn't. Although it has a x-hair but isn't illuminated and its really difficult aligning it with the scope centre of view, even in daylight!

one thing I've been wondering, did you attempt to remove any backlash from the scope's RA axis? mine has plenty, i'd hazard to guess that it's in excess of a few degrees...

[AstroTux]

I'm starting to get really frustrated trying to polar align with my eq130, and 8x20 finder-scope i've bought & bolted on to help really hasn't.

One thing I have noticed with these scopes is that the setting circles are completely naff!!

I use a green laser pointer to help with locating objects ( as I am a backyard man really and so cannot get into trouble with other astronomers - yet!!!! ). By using this to align on a tall straight object object at some distance ( a telegraph pole is great ) with the OTA of the 'scope at the side of the mount I can be assured that the mount is pointing directly at the object. If I then align again with the OTA on top of the mount this time I find that 88° on the DEC setting circle is really my 90° point. This has caused a lot of problems when trying to polar align, but it seems sorted now.

I don't tend to get much backlash in the RA axis, but I have found that if you do not tighten it sufficiently then it will move quite freely.

[ringz]

The Vixen way of illuminating the cross hairs of the polar aligning scope on my DX mount is to mount a 3mm red LED centrally in the objective of the polar scope and power it with battery and potentiometer for brightness control. It works very well.

[Merlin66]

Guys,

I'm still interested in finding an SAA1042 chip, if anyone can help!

(I have a double arm barnyard mount with the ol' stepper - just lost the driver box......)

[AstroTux]

Not sure if you got it, but I sent you a PM. I don't have any SAA1042s but do have some SAA1027s that do a very similar job and you can have gratis. The difference seems to be that the SAA1042 is a driver for bipolar stepper motors ( and may have a built-in H-bridge output stage ) whilst the SAA1027 is a bipolar stepper motor driver. Huh !!

Having read between the lines it would appear that the SAA1027 uses bipolar technology rather than FETs to achieve its purpose in life, and is designed for unipolar stepper motors. You would have thought that the person responsible for writing the datasheet would have been aware of the word bipolar and its meaning in StepperMotorLand :grin: !! Instead they just added to the confusion..........

You could always try http://www.ebay.co.u...=item1c277227a5 if you need the SAA1042.

Hope this helps,

[Merlin66]

Thanks for that.

I'll go with the eBay option.

[c3po]

not wanting to rush you along or anything but....how you doing with the builds Al?

[AstroTux]

Just thought some of you may be interested in the new hardware V1.20 I have produced for this project.

Here are a couple of photos:-

As can be seen the LCD is piggybacked onto the main unit. The connection holes are for power in, the keypad and the focuser and RA stepper motors. You can also see that either, or both stepper motors can be tied to the unregulated or the regulated voltage lines by a wire jumper.

The 1/4 watt resistor visible next to the LCD simply provides the bias that adjusts the contrast on the LCD, and can be changed should the contrast need to be increased/decreased.

I still have enough components to do a couple more of these boards should any of you want one. Some of you have expressed an interest and I have replied to you all using PM, but it appears that you have not read my replies. Please check your PMs :grin: .

[ismangil]

Mine has arrived!

Alan kindly added headers for the solder challenged...

Haven't had a chance yet to play with it.

[Leo.A]

I'm lucky, the worst I got are funnelwebs, tiger snakes, king brown snakes and copper head snakes. I have moved away from the base of a mountain (between it and a creek) to a more populated region in my town and don't have the snake problems now, thankfully.

Snakes are protected in Aus but my garden spade says otherwise!

[Leo.A]

I use a green laser pointer to help with locating objects ( as I am a backyard man really and so cannot get into trouble with other astronomers - yet!!!! ). By using this to align on a tall straight object object at some distance ( a telegraph pole is great ) with the OTA of the 'scope at the side of the mount I can be assured that the mount is pointing directly at the object.

Unfortunately, green lasers are illegal in Aus but I believe as a member of an astronomical society I'm permitted by law to possess one. I recently purchased a 3mW green laser (gun sight) from Ebay but even with the stated protection of supposedly being permitted to own one, I'm too afraid to use it.

I have a MacDonalds close to where I live and I'm sure the moment I point my laser towards the heavens some visiting/passing city dweller is going to call the police under the assumption I'm trying to kill the occupants of non existant planes over my region.

The only commercial air traffic near my region is way too high for me to do anything other than maybe leave a 1mm spot on the undercarriage. Unfortunately, with all the hype about people trying to bring down planes, the cops will turn up and I can't be bothered arguing the point with law enforcement officers who won't even know the laws relating to permitted use (local cops are ......)

I saw a webpage with supposed pictures from a laser on a windscreen of a plane (simulator actually). The pics were taken at F2 for 1/6 second. If I took a picture of the moon at that setting it would be a big bright ball too.........ID10T ERROR!

[JamesF]

Unfortunately, green lasers are illegal in Aus but I believe as a member of an astronomical society I'm permitted by law to possess one. I recently purchased a 3mW green laser (gun sight) from Ebay but even with the stated protection of supposedly being permitted to own one, I'm too afraid to use it.

On the assumption that the law does indeed allow you to possess and use one I'd be tempted to write to the head of the local police force informing them that you understand that in general their use is illegal, but that you will be using the laser from time to time, that you are a member of such and such astronomical society and area therefore permitted to use one by whatever law, that you understand the issues relating to their use, tell them what model it is and that it meets the applicable regulations and that they are welcome to visit and confirm that it does so if they'd like to arrange a convenient time, or to contact you if they have any concerns, before, say, a month hence, when you plan to start using it.

If they don't respond then should anyone official or otherwise come knocking on the door you can say quite honestly that the police are aware that you're using it, that you've asked at a senior level if they had any issue with you doing so and that they have not raised any concerns.

It's one thing the local plod turning up and arguing the toss over the law, but quite another when you tell them that someone higher up their food chain is aware of it already and hasn't considered it a problem.

James

[AstroTux]

Unfortunately, green lasers are illegal in Aus but I believe as a member of an astronomical society I'm permitted by law to possess one. I recently purchased a 3mW green laser (gun sight) from Ebay but even with the stated protection of supposedly being permitted to own one, I'm too afraid to use it.

In the UK the majority of green lasers are limited to 1mW and state a range of about 4Km ( approx 13,000ft ) and are sold as being useful to astronomers for pointing out objects in the night sky, and for mountain rescue applications. I take the view that as most of the air traffic in my vicintiy is at around 35,000ft I cannot do any damage. I deliberately don't point them anywhere near aircraft coming into and out of Heathrow and as I live nowhere near Ben Nevis I cannot use them to signal the rescue helicopters that always seem to be in its vicinity :grin: !!