Arduino Focus control and Cloud sensor

[Reggie]

If the chips are within their rated temperatures then they're not getting to hot if you're that worried about heat, add some heatsinks to the top of the chip to help get rid of it. I'm personally more worried about the amount of power drain there will be more than the heat dissapation.

[ncjunk]

In the sgl code we use the easydriver pin to cut the power after 20sec so then people can decide to remove the power or not. I dont on mine and the stepper does get warm but i've been to lazy to add a wire to the power off pin.

[Euan]

Here is a word of caution for anyone building the focuser....

I noticed since last summer that my V-Curves weren't always 100% repeatable, and my focusing was OK on one target but my focus offsets never seem to work right

I've just taken it all in the house, pointed it in the sky and tracked with callipers the return point after going all the way in and out. Here is the result:

Now, I have got a fairly chunky imaging train, so this may not apply to everyone but make sure you test this properly!

I'm using the motor many have used in this thread, here: http://www.coolcomponents.co.uk/catalog/oscthumb.php?src=/images/09238-1.jpg&w=600&h=600&f=jpg&q=95&zc=1&hash=d3dc27a93f6ed9bc3c848aae426ec174

Now this only uses 0.33A of the max 0.75A I can get from the EasyDriver, so I've just bought one of these to try instead, which pulls 0.5A. Will post up the results once it's swapped.

http://proto-pic.co.uk/stepper-motor-bipolar-200-steps-rev-35x28mm-10v-500ma/

[ncjunk]

Euan,

i would have thought the problem would be more likely a mechanical slippage issue somewhere and not the motor. Unless the motor isnt set up correctly.

Why do you think the problem is the stepper?

have you eliminated all other possibilities?

i must check mine sometime but it seems to work well enough so i havent bothered. but a steppers pretty precise so should provide repeatability regardless of type and no error. hence my doubt.

is there a way you can try your motor on its own and see if the number of degrees it rotates each time are the same?

sorry but i doubt its a motor problem..

[ncjunk]

btw. i have pretty good repeatability or sufficient for requirements using the same motor i just set an initial position of the draw tube and marked it and checked it came back. the only problems i had were when it wasnt screwed down tight enough causing slippage or when the frequency i was driving the stepper at was too high causing incorrect stepping (affects the torque)

[OzDave]

I was checking exactly this sort of thing the other day too. Without any load on the focuser draw tube, the draw tube moves in and out repeatably 100% every time.

When I loaded up my imaging train on the draw tube, with the focuser sitting on my desk, I found that the draw tube tension wasn't right and this caused the motor to not be able to move the draw tube repeatably. However, it wasn't the fault of the motor - it was turning just fine but the draw tube was just slipping a bit due to the load. This same problem would have occurred moving the draw tube manually with the adjustment knob too except maybe I wouldn't notice it in the dark and just keep moving it till I got focus.

After I adjusted the tension screws I got better performance and repeatability.

For reference, I also have the Mercury Motor from CoolComponents, although I have it attached to my Moonlite in place of the 8:1 slow motion knob and then with an additional 3:1 gearing via some timing pulleys. This gives me plenty of torque to move the draw tube, provided the tensioning is set correctly for the load it has to carry.

Hope this helps,

David

[ncjunk]

The holding torque in the motor that you have the problem with is greater than the new one your buying. I would suggest it would be better to get the existing working.

see the comments earlier in the thread 2 days ago? for the delay settings that work.

from ozdave! the previous post...who managed to check what i was too lazy too... but my value of 800 on 800 off turned out close enough

hope you get it working euan.

[OzDave]

I've not seen that many images of how people got their focuser together mechanically, so in case anyone is interested, this is the current state of my focuser and how I have approached the mechanical aspects of the project. In the image below, the focuser is attached to a Moonlite CR2 with a bracket that I manufactured myself from a sheet of 1.5mm aluminium.

The timing pulleys and belt were custom ordered from HPC Gears in the UK. The large pulley is a 40 tooth MXL pitch with a 3/8 inch custom bore to fit the shaft of the Moonlite. The small pulley is a 15 tooth MXL pitch with 5mm custom bore.

I cut the bracket using a hacksaw from a sheet of aluminium (45mm wide in the image). I bent it by hand in a vice and drilled the various holes using a hand drill (not electric) for extra precision.

The bracket is attached to the focuser using the tension screws. Normally these grub screws are recessed inside the focuser and are a 1/2 inch long. I ordered replacement grub screws online, 1 inch in length so that they can both tension the focuser and provide an attachment point for the motor bracket. Presently the bracket is simply attached using simple washers and nuts, but I intend to replace those with sprung washers as the nuts have a tendency to come undone with the slightest adjustment of the tension bolts.

Still to be done is to cut the bracket to size properly once I have boxed up the electronics that will get mounted on the bracket.

Regards,

David

[Euan]

i would have thought the problem would be more likely a mechanical slippage issue somewhere and not the motor. Unless the motor isnt set up correctly.

Why do you think the problem is the stepper?

have you eliminated all other possibilities?

I stand corrected. When I started to tighten up the grip on the Feathertouch, I found a source of slippage with how two parts of the stepper shaft were connected!

..back to the drawing board

At least I know how to test it now

[Euan]

I now have a really dodgy looking shaft coupler that wobbles, but at least it's more stable. It's went from 0.3-0.5mm drop per 10000 steps, down to about 0.15 or thereabouts

I reckon this should be good enough, this is the worse case with the scope pointed straight up. Thanks guys!

EDIT: Got a better suited coupler on order, I reckon the wobble is actually contributing to the difference. Will see if I can get this lower

[yesyes]

I've not seen that many images of how people got their focuser together mechanically....

In case you haven't seen mine, here are "a few" images... Very similar approach to what you're doing.

http://www.yesyes.info/index.php/diy/motor-focuser/

[ncjunk]

You guys and your profesional looking focusers! I bent a scrap bit of thin metal around and attached it using the four existing crayford screws. It kind of floats about abit but works....as long as you don´t touch it.

[Mr TamiyaCowboy]

my focuser is an old plastic skywatcher thing, rack an pinion.

the idea i had was to use a servo gearbox to drive, either a pully system or direct drive a pinion gear on the rack and doing away with manual focusing.

i will be mostly using the scope and focuser for imaging and not viewing.

[OzDave]

In case you haven't seen mine, here are "a few" images... Very similar approach to what you're doing.

http://www.yesyes.info/index.php/diy/motor-focuser/

That looks pretty neat Chris! Your brackets look much better than mine. I don't really have the tools for decent metalwork. With your large pulley, do you have any issues with the belt slipping off? My pulleys are both flanged but the belt seems to move from side to side between the flanges randomly. Probably to do with the alignment of the pulleys I guess.

I like that power box you've made. Is the supply inside something you salvaged, or is it available for building up projects like this?

Do you ever get power glitches resetting your kit in the middle of an imaging run?

I've been thinking of making some kind of power box, but was worried about glitching and brown outs. Current plan is to build something around a battery rather than a supply, but had looked at the idea of a supply backed by an old UPS.

David

Sent from my iPad using Tapatalk

[yesyes]

That looks pretty neat Chris! Your brackets look much better than mine. I don't really have the tools for decent metalwork. With your large pulley, do you have any issues with the belt slipping off? My pulleys are both flanged but the belt seems to move from side to side between the flanges randomly. Probably to do with the alignment of the pulleys I guess.

I like that power box you've made. Is the supply inside something you salvaged, or is it available for building up projects like this?

Do you ever get power glitches resetting your kit in the middle of an imaging run?

I've been thinking of making some kind of power box, but was worried about glitching and brown outs. Current plan is to build something around a battery rather than a supply, but had looked at the idea of a supply backed by an old UPS.

David

I don't really have proper tools for metal working either. I've only used a cordless drill/screw driver, a Dremel clone and a tiny vice.

The belt is not slipping off the larger pulley. I see it moving left and right a bit but it always stays away from the edge. The flange on the smaller pulley is keeping it more or less in position. I've tried to make the 2 shafts as parallel as I could by bending the bracket holding the stepper a bit.

Regarding the power box, the PSU I used is this one:

http://www.ebay.co.uk/itm/12V-20A-240W-Switch-Power-Supply-Driver-For-LED-Strip-light-Display-220V-110V-/320777680321?pt=UK_Mobile_Phones_Communication_Radio_Parts_Accessories&hash=item4aafd6f5c1

To be honest, I haven't been using it much. I'm busy doing so much DIY stuff for astronomy that I don't actually get around to doing any astronomy... I'm building all this stuff in preparation of having an observatory at some point. Only need to buy a house first... ;-)

I did use the power box maybe 4 or 5 times so far and did not have any power supply issues.

Hope that helps..

[Euan]

My setup is working now. It was the motor after all. No amount of adjustment on the focuser would let it hold it's position, the lowest I got it was 0.3mm per 10000 steps.

The new motor holds it without any slip. Result!

Once I get it back outside in the new obs, with the upgraded (again) EQ6, I will be able to get some V-curves. Still a few months away.

[ncjunk]

My setup is working now. It was the motor after all. No amount of adjustment on the focuser would let it hold it's position, the lowest I got it was 0.3mm per 10000 steps.

The new motor holds it without any slip. Result!

Once I get it back outside in the new obs, with the upgraded (again) EQ6, I will be able to get some V-curves. Still a few months away.

I'd love to know why its doing it as electrically speaking it shouldnt slip if the hold torque is sufficient (and i thought it had greater holding torque than your new one)

is the 0.3 a constant slip in one direction?

[Euan]

I'd love to know why its doing it

I'm not sure, but as soon as I had changed it, it worked. I changed the PSU as well to suit the new stepper from 12v 500ma to 10v 1.2A.

Here are the spec differences, I just thought higher current load = higher pulling power? Slightly different units they must be copied from the manufacturers spec

Old one

Rated Voltage : 12V

Rated Current : 0.33A

Holding Torque : 2.3kg*cm

New one

Voltage rating: 10V

Current rating: 500 mA per coil

Holding torque: 1000 g-cm (14 oz-in)

[Euan]

Actually, is the old one pulling max 0.33A per coil? That would have left me slightly short of current when using the 12v 500ma PSU.

The new 1.2A supply has more than enough juice for that one

[yesyes]

Actually, is the old one pulling max 0.33A per coil? That would have left me slightly short of current when using the 12v 500ma PSU.

The new 1.2A supply has more than enough juice for that one

That is most likely why it didn't work properly. It is the current per coil.

[Euan]

That is most likely why it didn't work properly. It is the current per coil.

Now that I'm home I've just checked and it was actually a 800mA supply, so this should have worked then?

[Starflyer]

Hi all,

After my initial failure (see here) I've had a chance to play now and have managed to get the motor moving at least. I had a tinker and change the following setting;

volatile int SPEED = 500

The motor is energised as soon as it's turned on. When pressing in or out in the app the motor LEDs go out and the motor doesn't move, subsequent presses make the LEDs flash on very briefly and the motor still doesn't move. The power to the motor is cut after the first press, so this works as intended.

volatile int SPEED = 100

When pressing the in / out buttons the motor motor doesn't quite do 360 degrees at 200 steps, but at 2000 the error is about the same. When moving it runs at a fixed speed, quite fast, changing it in the app has no effect on the speed. Again the power to the motor is cut after the first press.

volatile int SPEED = 200

Motor runs more slowly but starts with a jolt, it takes 4700 steps to do 1 rotation.

I hope some of this gives you a hint of what's wrong

Cheers,

Ian

[ncjunk]

Speed in your case is RPM and not the delay that we use for the easydriver board. I am just looking through the Library as I cant remember how the halfstepper works.

Can you try a few more speeds 100, 50, 25 and confirm the steps per revolution for each.

How have you got it mechanically set up? You have a 200 step stepper so the configuration we have with half stepping should be 400 per revolution.

ThankS

Neil C

[Starflyer]

Hi Neil,

Mechanically it's still on the bench with a flag attached to the motor. Here's what I have in the sketch for the steps per revolution, let me know what to try here;

AF_Stepper motor(200, 2);

int motorSteps = 400;

At Speed = 25 I get slightly less than a full revolution in 200 steps out but a full revolution inwards, it takes around 3 seconds.

At Speed = 50 I get slightly less than a full revolution in 200 steps out but a full revolution inwards, it takes around 2 seconds.

At Speed = 100 I get slightly less than a full revolution in 200 steps out but a full revolution inwards, it takes just over a second.

All help muchly appreciated,

Ian

[ncjunk]

which Arduino code did you try that with?