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 Project Orion (Astrophotography Tool) 
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Joined: Tue Nov 29, 2011 7:04 pm
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Post Re: Project Orion (Astrophotography Tool)
Although it's pretty slick, still more than i want to spend

Are you planning on publishing your new design here ?

Jack Ripper wrote:
thats getting a lot closer to the new design were looking at developing. but yeah, that is a LOT of money. lol.


Wed Nov 30, 2011 3:11 pm
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Post Re: Project Orion (Astrophotography Tool)
markus wrote:
Although it's pretty slick, still more than i want to spend

Are you planning on publishing your new design here ?

Jack Ripper wrote:
thats getting a lot closer to the new design were looking at developing. but yeah, that is a LOT of money. lol.


Most likely. I wanted to have this done a while ago. But it got put on the back burner, probably start looking at this again early next year

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Wed Nov 30, 2011 5:30 pm
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Post Re: Project Orion (Astrophotography Tool)
Just been reading through this thread, cool idea!

How come you went down the barndoor concept, as opposed to a rotating head like that japanese one. Or this one:

Image

It strikes me that with a good motor and gearbox, it would be a whole lot easier to build!

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Wed Dec 07, 2011 1:02 pm
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Post Re: Project Orion (Astrophotography Tool)
agour wrote:
Just been reading through this thread, cool idea!

How come you went down the barndoor concept, as opposed to a rotating head like that japanese one. Or this one:

Image

It strikes me that with a good motor and gearbox, it would be a whole lot easier to build!


the barndoor was just a simple design. small leightweight. We ran into the issue with the curved rod, and then we got derailed on building timelapse gear. We plan to get back to Project Orion here soon. hopefully sooner than later, windtertime is full of cool deep space objects to shoot :)

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Wed Dec 07, 2011 1:17 pm
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Post Re: Project Orion (Astrophotography Tool)
The only issue i see with going the gear(worm gear) root is just how accurate it has to be cut
The smaller the gear diameter the less forgiving it is to tracking errors - that's probably why all the worm gears for eq. mounts are so big and expensive

One of the advantages of the Astro Trac is, the long pivoting arms give you lots of torque and a certain degree of forgiveness on positioning errors. The more i look at it, the astro trac is just nothing more than a barn door on it's side - now i wonder where they bought that really small stepper for the arm ?

If i'm completely out in left field with this please feel free to set me straight :-)

//mjc


Wed Dec 07, 2011 2:33 pm
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Post Re: Project Orion (Astrophotography Tool)
nope, you are absolutly correct

if i had the intelligence to understand the mathematics needed behind tangent error correction, we would have done with a straight rod that was hinged on either end and basically had the same device as an astrotrac in a slightly different configuration.

the problem is the more it opens the faster the motor has to turn. the first minute or two should be spot on, but after that you will start seeing increased arc second errors then eventually arc minute errors

i like the direct drive system. our next design is basically a box with a direct geared bobble-head on it that will rotate one rpm per day. of course it would only go 180 degrees, it would last the entire night.

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Wed Dec 07, 2011 2:59 pm
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Post Re: Project Orion (Astrophotography Tool)
I know what you mean by math skills - my calculus is a bit rusty :-)

Here's a great resource page "Smart Barn Door" - even has matlab and assembler code examples
After reading it a couple of times i kind of wonder if astro trac modeled theirs after this one

http://www.keteu.org/~haunma/proj/barndoor/

//mjc

Jack Ripper wrote:
nope, you are absolutly correct

if i had the intelligence to understand the mathematics needed behind tangent error correction, we would have done with a straight rod that was hinged on either end and basically had the same device as an astrotrac in a slightly different configuration.

the problem is the more it opens the faster the motor has to turn. the first minute or two should be spot on, but after that you will start seeing increased arc second errors then eventually arc minute errors

i like the direct drive system. our next design is basically a box with a direct geared bobble-head on it that will rotate one rpm per day. of course it would only go 180 degrees, it would last the entire night.


Wed Dec 07, 2011 3:59 pm
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Post Re: Project Orion (Astrophotography Tool)
Wow... that is soooooooo beyond my math skills.

However this part x*sqrt looks kinda dirty. I think the direct geared drive is more in my ability.

Lol

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Wed Dec 07, 2011 4:52 pm
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Post Re: Project Orion (Astrophotography Tool)
does sound kind of dirty :-) sqrt is square root in case you didn't know

I read near the top of this thread i believe, that you did have a astrotrac for a short period
You didn't happen to open it up and take a look ? closeup pictures of it ?


Jack Ripper wrote:
Wow... that is soooooooo beyond my math skills.

However this part x*sqrt looks kinda dirty. I think the direct geared drive is more in my ability.

Lol


Wed Dec 07, 2011 6:33 pm
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Post Re: Project Orion (Astrophotography Tool)
markus wrote:
does sound kind of dirty :-) sqrt is square root in case you didn't know

I read near the top of this thread i believe, that you did have a astrotrac for a short period
You didn't happen to open it up and take a look ? closeup pictures of it ?


Jack Ripper wrote:
Wow... that is soooooooo beyond my math skills.

However this part x*sqrt looks kinda dirty. I think the direct geared drive is more in my ability.

Lol

I had one but it was faulty. Its just a ssmall stepper with a lead scew tied in with a microcontroller of some sort. There is not much to it. Nice construction, very light, the polar scope is junk though in my view. The rest of it though is very nice.

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Wed Dec 07, 2011 6:49 pm
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Post Re: Project Orion (Astrophotography Tool)
They must have quality control issues at the Astro factory - I've read quite a few comments like that, where the unit is faulty right out of the box

That stepper must be small - based on measurement from pictures, the motor diameter is about 0.8 inches - wouldn't think you could development much torque with something that small

The latest version looks pretty slick with all the extensive lightweighting they've done to it

Here's another style that looks similar to the Astro but doesn't suffer tangent error and it like a partial big worm gear - the Fornax - still relies on machining an accurate gear though

http://fornax2002.hu/angol_fornax10.html

//mjc

Quote:
I had one but it was faulty. Its just a ssmall stepper with a lead scew tied in with a microcontroller of some sort. There is not much to it. Nice construction, very light, the polar scope is junk though in my view. The rest of it though is very nice.


Thu Dec 08, 2011 2:43 am
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Post Re: Project Orion (Astrophotography Tool)
WOW, thats a pretty clever design. i bet like the others it costs an arm and a leg. it mentions that it is for 50mm and under. yet the images shot it with substancially larger lenses.

Thecurved rod design we already came up with and consider a failure works for 50mm and under perfectly, you can track for hours with no visable problems.

however our aim is to get it out to 800-1000mm with no visable artifacts.

I wonder if thier reccommendations for 50mm and under is due to vibrations from the stepper.

the route we plan to go uses a 2rpm dc motor from servo city and with a pair of high spec worms pulling a 2500:1 ratio, speed monitored and controlled by a microcomputer.

the only issue is the worms are expencive as hell so we are planning to mold and cast our own based off some industrial 50:1 gear sets my partner managed to get ahold of using a vaccume molding and casting process. He has used it in the past to replicate gears with great results.

however i got pulled onto project chronos, then he started building a house with a friend, and he keeps getting orders for chronos parts, so right now we are just sort of trying to get our shit together.

in the end our goal is to match the performance of any sub $1000 system with a $350 product.

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Thu Dec 08, 2011 7:12 am
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Post Re: Project Orion (Astrophotography Tool)
I thought it was a neat design too - a different spin on the barn door/ astro trac
Looks like it's still in the prototype stage - one neat thing about it is, you don't need an equatorial wedge, it's built in
I imagine with the stepper driving directly like that, that vibration is and issue, unless they're using microstepping but then battery consumption would go up i think(in order to hold position)

After seeing the toast-pro i went pricing worm gears and found the same, very expensive for even small ones - do casted gears still maintain the high accuracy required for tracking ? something i've never done but it's a great idea compared to trying to machine them accurately

I've been reading about the chronos project and it looks great - really like the rails you picked for it

//mjc


Fri Dec 09, 2011 3:04 am
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Post Re: Project Orion (Astrophotography Tool)
markus wrote:
I thought it was a neat design too - a different spin on the barn door/ astro trac
Looks like it's still in the prototype stage - one neat thing about it is, you don't need an equatorial wedge, it's built in
I imagine with the stepper driving directly like that, that vibration is and issue, unless they're using microstepping but then battery consumption would go up i think(in order to hold position)

After seeing the toast-pro i went pricing worm gears and found the same, very expensive for even small ones - do casted gears still maintain the high accuracy required for tracking ? something i've never done but it's a great idea compared to trying to machine them accurately

I've been reading about the chronos project and it looks great - really like the rails you picked for it

//mjc


the steppers wont introduct vibrations if they run at a decent speed, more than 50-60rpm. when you get to 5 rpm and under you start getting vibrations. The tracker i build got some vibrations but they were not enough to affect the image as far as i could tell as far as 200mm

yeah Chronos is probably my favorite thing right now. lol its been a LOT of fun developing the system

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Fri Dec 09, 2011 8:10 am
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Post Re: Project Orion (Astrophotography Tool)
That's good to know about vibrations and low speed limit - if you had to run at speed less than 5 rpm, does micro stepping help reduce vibrations ? did you try micro stepping with the barn door you built ?

//mjc


Quote:
the steppers wont introduct vibrations if they run at a decent speed, more than 50-60rpm. when you get to 5 rpm and under you start getting vibrations. The tracker i build got some vibrations but they were not enough to affect the image as far as i could tell as far as 200mm

yeah Chronos is probably my favorite thing right now. lol its been a LOT of fun developing the system


Sun Dec 11, 2011 5:17 am
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Post Re: Project Orion (Astrophotography Tool)
I'm using an easydriver to the stepper wich defaults tto microstepping. The vibrations feel like a hum if you touch it, they just are not enough to affect the performance of the system

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Sun Dec 11, 2011 8:08 am
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Post Re: Project Orion (Astrophotography Tool)
Thats good to know about micro stepping - is this using 1/2, 1/4, 1/8 steps ?


Mon Dec 12, 2011 3:01 am
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Post Re: Project Orion (Astrophotography Tool)
markus wrote:
Thats good to know about micro stepping - is this using 1/2, 1/4, 1/8 steps ?


ill have to check, i think it runs 1/8th step by default. microstepping in my experience is better at slowing things down than reducing vibrations. its good as long as you keep it going too, thats why i dont use it on chronos, cause when doing SMS i like to release the motor so im not constantly drawing power. cause once you drop power it will pop to the nearest full step. lol

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Mon Dec 12, 2011 7:36 am
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Post Re: Project Orion (Astrophotography Tool)
Nice project! I had an Astrotrac Travel System for the past month (just sold it) and have been very impressed by its performance. Aside from the dead-on-arrival problems etc, it seems to have a pretty good reputation. It's portability will be hard to beat.

On a related note, I built an Astrotrac-style barn door mount when I first got into astrophotography a few months ago. It used a Firgelli linear motor that could be programmed to track to a specified distance with high accuracy - the model that I had left over from a recent project had +/- 0.2 mm accuracy out of a 5 mm drive range.

http://www.firgelli.com/Uploads/L12_datasheet.pdf

On my first go, I managed to track and get round stars for 4 mins at 24 mm on my Canon 5DmkII's 6.4 um pixels without trailing (normally visible after 10 secs without tracking). It was just a matter of mounting the linear motor between two planks of wood connected by a hinge, and then working out the maths for the software to guide the motor...

Jack Ripper wrote:
if i had the intelligence to understand the mathematics needed behind tangent error correction, we would have done with a straight rod that was hinged on either end and basically had the same device as an astrotrac in a slightly different configuration.


The basic barn door design uses a constant tracking speed based on the length of the tracking arm. I believe the Astrotrac is so accurate because it
    (1) can vary the motor speed based on knowing the distance that has been tracked, in addition to the length of the tracking arm, and
    (2) has been pre-programmed at the factory to correct for tracking error due to small differences in machining (ala Periodic Error Correction on big mounts).

The maths needed for the hinged-straight-rod type of tracking is based on relatively easy trigonometry - I've drawn up a diagram and completed the derivation at the link below.

http://dl.dropbox.com/u/13644418/barndo ... ations.pdf

The gist of it is this: given the tracking arm length l0 in metres and current tracking position (i.e. distance away from the arms being "closed") lx in metres, you can calculate the future tracking position ly after z seconds have lapsed (i.e. you need to move ly - lx metres in the next z seconds) with the following formula (sin/arcsin uses radians):

Code:
ly = 2 * l0 * sin [arcsin (lx / 2 / l0) - pi * z / 86164.09]


For example, let's say your tracking arm is 0.32 metres long and at a position of 0.13 metres, i.e. the two 0.32 metre long arms are connected with a hinge at one end and separated by 0.13 metres at the other end. According to the formula, you'd need to move the tracking arm by ~ 1.36 millimetres over the next 60 seconds. If you were at position 0.05 metres, then you'd need to move the tracking arm by ~ 1.40 mm over the next 60 seconds.

If you were simply to change the motor speed according to the formula, then your tracking would become very inaccurate due to errors (such as rounding in the formula, mechanical tolerances, etc) over time. However, if you always know your tracking position and can move the motor accordingly (ala the Astrotrac or the linear motors I was referring to, above) then you simply make sure your tracking position is always equal to ly in the formula above. In this case, your errors will cancel out and you'll always be at the maximum accuracy that your machining allows.

Using this approach, your tracking accuracy will be limited primarily by
    (1) quality of machining,
    (2) accuracy of the tracking arm length measurement l0,
    (3) accuracy of the tracking position measurement lx, and
    (4) accuracy of the elapsed time measurement - anything that isn't an atomic clock is inaccurate.

Errors #2 - #4 can be corrected for in software by training the tracking device - i.e. comparing the output of the tracker against known-correct measurements, and then applying correction factors in the tracking maths. For example, by measuring against a GPS clock you may be able to figure out that your micro controller "loses" 100 seconds per day, and then applying a correction factor such as in the formula below:

Code:
tc = t0 * 86400 / (86400 - 100)


Hope this is either useful or has been an interesting thought experiment. Good luck with your project!


Sun Jan 08, 2012 6:26 am
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Post Re: Project Orion (Astrophotography Tool)
Forgot to mention a few things... if you have a straight bolt driven by a motor, you can measure the lx distance by directly sensing the distance between the two boards (e.g. Sharp Distance Sensor 2D120X that's accurate to about 0.1 mm from personal experience), or calculate the distance according to the number of motor steps that have been performed. If you're doing the latter approach, you can use a known-accurate distance sensor (e.g. laser distance sensor) to build a calibration map of "number of steps from start vs true distance" for extremely precise tracking - I think the Astrotrac does something like this. Finally, small micro controllers often don't implement floating math (or do it slowly/poorly) so you can pre-calculate the formula with the sin/arcsin values and store it as a look-up table rather than calculating in real time.


Sun Jan 08, 2012 7:43 am
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Post Re: Project Orion (Astrophotography Tool)
Hi Naskies,

Looks like you've done quite a bit of figuring and work on DIY'ing the astrotrac

I'd love to see a picture of it

One question i have is - is the accuracy of the linear actuator(0.1mm) enough for this mount ?

Regards
Markus


Sat Jan 14, 2012 6:29 am
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Post Re: Project Orion (Astrophotography Tool)
Naskies, I think my brain jut popped reading all that. lol. Im terrible with math, im going to try to take the time and figure it out though and i really appreciate such a detailed post on here.

we have a new design we plan to try, but we have been so busy with other projects that it sort of fell on the way-side, plus we have still been perfecting the vaccum molding process so we can manufacture our own gears to make things much cheaper. The design is a compact direct geared system with a double worm drive.

Markus, .1mm resolution should be pretty good, but with longer focal lengths i think thay it may exhibit some movment. I managed to track with my plexiglass tracker for about 4 minutes at 300mm,, and the result was a barbell shaped star caused by the ratcheting movement of the curved rod. However, the shape was a barbel, not zig-zag, or a string of pearls, which tells me the speed was pretty much dead on. However at 70mm i was able to get 6 minutes of tracking with no ill effects. the stars were nice little dots. The problem is 70mm is nearly worthless IMO, 24mm and under is usefull, and 300mm+ is useful.

I also would love to see a pic of Naskies DIY setup, i love seeing how other people problem-solve, and i tell you what, it is quite a challange to get things to move that slow.

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Sat Jan 14, 2012 9:11 am
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Post Re: Project Orion (Astrophotography Tool)
Hi Jack,

I too built a version of the tracker from Gary's web-site.. If you wouldn't mind posting the parts list from the improvement you're working on, I'd really appreciate. I'm looking to improve upon the original as well, but for decidedly non commercial purposes... :-) Thanks in advance for any and all info you feel comfortable sending my way.

Best regards,
Barry
Austin, TX


Sun Jan 22, 2012 9:57 am
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Post Re: Project Orion (Astrophotography Tool)
Don't know why you just don't use a 3 volt 1RPM motor,,6 volt battery for power with a 350 voltage regulator and the final voltage set with a variable pot,,that way you can get a perfect 1 RPM,,on mine I'm using a 1/4 20 rod so the math is for it,,had my polar scope stolen so am in the process of getting another,,


Sun Jan 22, 2012 10:55 pm
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Post Re: Project Orion (Astrophotography Tool)
i used a setup like that in my first design, and it was a major headache. The circuit i used was straight off of gary seroniks website. When it worked it worked great, but when i would swap from a light wide angle lens to a heavy 70-200 2.8 telephoto that extra weight would bog the motor down a little so i would have to recalibrate. Also as the battery drained i had to recalibrate. and every time i started it i had to recalibrate. It was just a big recalibrating pain in the ass. For wide angle it was pretty good, but anything much over 50mm it got really difficult.

doing it with a arduino / stepper motor eliminates the problem of recalibrating, and gives you far more control. It WILL open the same speed no matter the battery level, or if you have a flea-weight 50mm 1.8 lens or 70-2002.8 with teleconverter. plus i was having a hard time finding the proper sized small gear, so once again, with the arduino setup i could use any small gear i wanted and just adjust the speed, and no longer had to worry about load or battery levels, it just perfectly works every time.

Also going with Arduino, it was a simple matter of some light programming and an input and output jack, and i have it setup to work SMS with my timelapse rail Chronos. WHen it sees the shutter signal open it starts tracking, when the shutter closes it snaps shut to the exact same position it was in when it started. So now i can shoot SMS and track the stars and give myself an extra 10-15 seconds of expsoure time with very minimal effects on the foreground. I have not had a chance to take it to a dark zone but a trial in my backyard at 24mm at 1m on a DX sensor worked great. But the foreground was a litle fuzzy, i but 45 seconds at 12mm will give me an extra 1/2 stop worth of light and keep dot shapes stars and pull a cleaner image from the milkyway.

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Mon Jan 23, 2012 7:19 am
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Post Re: Project Orion (Astrophotography Tool)
Barryinaustin wrote:
Hi Jack,

I too built a version of the tracker from Gary's web-site.. If you wouldn't mind posting the parts list from the improvement you're working on, I'd really appreciate. I'm looking to improve upon the original as well, but for decidedly non commercial purposes... :-) Thanks in advance for any and all info you feel comfortable sending my way.

Best regards,
Barry
Austin, TX


Ill get a list of the parts going here soon when i have some time. If you are using the same dimentions from gary's site then that 1rpm is really the most critical element for final gear speed. Im using an Arduino, an Easydriver, a small protoshield for soldering points, and a small stepper motor $15.00 from sparkfun electronics. You would want a way to close it, so you need at minimum a button or switch to tell it to rewind (unless you can just disengage your gears, mine are locked into the design to try to keep them from wobbling) and maybe a 1k resistor for pullup work. A couple jumper wires and that is pretty much it.

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Mon Jan 23, 2012 7:25 am
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Post Re: Project Orion (Astrophotography Tool)
Do not know why the problems with a 3 volt 1 RPM motor,,the motor has plenty of torque,,I level my mount perfectly,,use a polar scope and set the offset from Polaris,,any deviation from both them screws things up,,put my Canon T1i on the door with a 300mm lens on,,recheck polar alignment for the weight on the door and make adjustments,,throw the switch,,wait a few seconds for vibrations to settle and open the camera shutter,,have never gotten any slow down from weight,,at about 7 min maybe just a hair off 1 RPM,,change lenses to a lighter one and nothing changes and stays at 1 RPM,,with the barn door mechanics and design you are limited time wise to error free tracking,,the mathematics in any setup,,leveling,,alignment,,add up and only add to tracking error,,just ask the guys that use the AT or Kenko SkyMemo single axis trackers,,the Barn Door has it's limits and using a 300mm lens is one of them,,anyways I like the design of your plexiglass mount and maybe think on it a bit,,have access to a lathe and milling machine,,lots of luck with your project and I'm a great DIYer myself.
Chas


Mon Jan 23, 2012 9:46 am
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Post Re: Project Orion (Astrophotography Tool)
Cool, thanks for the reply! I'll check those items out on sparkfun and keep an eye out here for any updates.

Best,
Barry J.


Mon Jan 23, 2012 10:13 am
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Post Re: Project Orion (Astrophotography Tool)
I got the design info from Sky & Telescope June 2007,,didn't like their design layout so just used my own with the 1/4 20 rod math,,same bent rod,,wanted a 1 RPM motor so called SDP-si.com and got their 3 volt 1-RPM motor,,am an electronics tech so built a power supply with variable output voltage in the 3 volt range so I could turn the 1-1 gears at 1 RPM that a 1/4 20 rod design called for,,the mathematics for polar alignment are very critical so if one part is wrong it adds to any measurement errors and adds to final error of tracking,,did my best in the building of it,,???? my polar scope offset to the NCP as best I could and it works quite well,,I do not do deep space,,just Milky Way with 20mm lens,,I like a lot of foreground in my photos as it adds other points of interest,,I'm sure you know what your doing and will figure out all that's bothering you,,just wanted to give a couple thoughts on mine,,was thinking of making a camera dolly track using the same motor for time laps,,but in my own design,,just have to think on it a little,,1-RPM geared down is pretty slow pulling a dolly,,good luck and keep me informed,,nice to see other DIYers.
Chas


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Mon Jan 23, 2012 12:09 pm
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Post Re: Project Orion (Astrophotography Tool)
Ok, so I have a question for this group... Why not use a worm gear drive like this one, http://servocity.com/html/vertical_shaf ... _gear.html
for a setup similar to the Japanese toast pro tracker??

That looks simple enough, but, being deficient at math as well, I'm having trouble decphiring exactly what speed you'd need to turn to achieve the proper tracking rate... The toast setup uses an 83.5 mm diameter platter to mount the camera on, with the camera mount slightly offset from center, I'm thinking that this should be an even simpler, more accurate method of tracking, I just need a push in the right direction on starting the calculations...

Thanks in advance for any help you can send my way!!

Barry J.
Austin, TX


Tue Jan 24, 2012 1:59 am
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Post Re: Project Orion (Astrophotography Tool)
And I think I may have found my answer...

https://github.com/selste/openDrive/wiki/Tmc428Math

I'm going to give the worm gear method a shot, and if I have any success I'll post my results here... :-)


Tue Jan 24, 2012 2:13 am
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Post Re: Project Orion (Astrophotography Tool)
Barryinaustin wrote:
Ok, so I have a question for this group... Why not use a worm gear drive like this one, http://servocity.com/html/vertical_shaf ... _gear.html
for a setup similar to the Japanese toast pro tracker??

That looks simple enough, but, being deficient at math as well, I'm having trouble decphiring exactly what speed you'd need to turn to achieve the proper tracking rate... The toast setup uses an 83.5 mm diameter platter to mount the camera on, with the camera mount slightly offset from center, I'm thinking that this should be an even simpler, more accurate method of tracking, I just need a push in the right direction on starting the calculations...

Thanks in advance for any help you can send my way!!

Barry J.
Austin, TX


one rotation per day.

that is the end goal of movement in a nutshell. or 15 degrees per hour. The next design we are planning on uses two 50:1 worms to get a 2,500:1 ratio, which at i think it was somewhere around 1.7rpm gets you to the 1 RPD speed.

For the 30:1 gear ratio you would need a very very very slow motor, one that does maybe one rotation every 48 minutes. or run that with another gear reduction.

however, im really glad you shared that link, i want to order a couple of those i already have some ideas on what to do with them. lol

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Tue Jan 24, 2012 6:59 am
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Post Re: Project Orion (Astrophotography Tool)
Cool, that makes a bit more sense to me now... Though, looking briefly at the prices on some of the precision worm gears, it's got me wondering if I should just bite the bullet and get a proper go-to scope mount with an auto-guider port... Portability, be damned!! ;)

I still really love the idea of this thing being ultra portable though, so I'll press on and see what happens.

Barry J.


Tue Jan 24, 2012 10:07 am
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Post Re: Project Orion (Astrophotography Tool)
The whole idea of DIY is to make it as simple and light as possible,,if you do a search on Google for Barn Door Tracker it'll give you more information than you can handle,,I used the formula for a 1/4 20 rod at 1 RPM and that is 11.42 in. from the center of the hinge to the center of the threaded rod,,however long you want the rod is just for tracking time,,to correct error math in lift you curve the radius of the drive bolt curve,,11.42 in.,,my motor is 3 volts at 1 RPM,,I use a 6 volt battery and the electronics to make a power supply with a 350 voltage regulator,,the output voltage resister is replaced with a pot that I can very the output voltage a bit up or down,,the gears are 1 to 1 and with the full weight of camera and lens I adjust the voltage to make it turn at 1 RPM,,that's as simple as I could have made it,,as much care as possible in building for the center to center distance of the rod and hinge,,and in having the tripod level and aligning on Polaris,,I use a polar scope to align that has an offset from Polaris to the NCP,,very few DIYers do it perfect so the point is to keep the errors as small as possible because they add up in the final tracking,,if you read up and fully understand what's going on with each part of this project you'll know what boo boos you've made by the photos you take and can correct them,,a good FREE piece of software you can download is Stellarium,,once you put in your long and lat it'll show you what's up there and where it is,,another little note for those that have never thought of night star photography,,at about 11:30 in the evening Orion is up in the south and very easy to find,,put a 50mm lens on your camera and use MF for best focus and shoot a 1 or so second shot just to get your interest up,,put a tree or house in the frame as well for added interest,,the first photo is just of Orion in the east behind some trees,,the photo of the pier is due south and am just waiting for a clear skies and a wider lens to get the pier and Orion in a single photo,,that'll be tricky.
Chas


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Wed Jan 25, 2012 1:57 pm
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Post Re: Project Orion (Astrophotography Tool)
Chas wrote:
,,very few DIYers do it perfect so the point is to keep the errors as small as possible because they add up in the final tracking,,
Chas


Thats where a CNC mill comes in handy. ;) Ill have to check on the math, but using a 10-32 rod mine sits about 7.14 (i think its been a while) from the center axis of the hinge.

Same basic idea though. I went a different route for polar alignment, i got a 100mw laser designed for a sniper rifle so i could adjust it and make sure it shot perfectly straight which that is lined up with the hinge within a 1/1000th of accuracy.. I turn it on, and it is like a straight ruler pointing into the heavens. So i point it directly at polaris (having a geared tripod head makes this sooooooo much easier) then i trace an imaginary line between Polaris and Kochab, then i move 1.5 moon widths towards Kochab from Polaris and there is your NCP

This is not the most recent image of my tracker, but this is basically it. The only difference is i mounted the Arduino and stuff to it so it is a single piece.
Image

here is a shot from my camera to the north star, the green line is actually my laser. lol. (watch out for airplanes) The only issue with the laser is that most astronomy clubs dont want you near them. But thats not a big deal for me.

Image

Two programs i reccommend for Android, Google Sky map, which is free and shows you whats around you, and then Star Chart which is not a free app but worth the price, it is far more robust in finding messier objects and such.


I diddnt realize i never put any of my results up here. i suppose it would be nice? Right now my tracker is good to about 70mm almost indefinatly with 20-30 seconds of effort to align it. Im not very happy with it, mainly because of the dreaded ratcheting effect seen here. I wanted to be able to track for 300mm for over a minute. The photo i incorrect though, that was tracking at 300mm for 4 minutes. If it were not for the ratching i would probably be outdoing Astrotrac. it is just a fundamental design flaw on the curved rod tracker, i would be curious if the ratcheting effect is lessened if i went 11.42 instead of 7.14

Image

The Orion nebula. This one was done with my old wooden tracker, its very similar to my new plexi tracker just not as precise.
Image

Pleiades
Image

Orions belt
Image

here is the milkyway
Image


here are a couple that show Stacked vs non-stacked
Image

Image

Image

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Wed Jan 25, 2012 5:16 pm
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Post Re: Project Orion (Astrophotography Tool)
here is one i got in Sedona last year around this time

Image

Another starfield during tht same trip

Image

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Wed Jan 25, 2012 5:29 pm
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Post Re: Project Orion (Astrophotography Tool)
Chas wrote:
,the Barn Door has it's limits and using a 300mm lens is one of them,,s



Why do you say that? With proper alignment and a well built machine (an none of that ratcheting effect with a curved rod) you should be able to use almost any focal length. I would say the curved rod style definatly has a limit, but if you use straight rod and are able to correct for tangent error the barn door should work with pretty much any focal length

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Wed Jan 25, 2012 5:32 pm
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Post Re: Project Orion (Astrophotography Tool)
Very very nice,,the Milky Way above the trees is outstanding,,the only difference between rod thread size is the separation between hinge and rod,,I took my measurement right from the barn door search because I wanted the weight,,and I cut a wedge out of wood for 49 degrees where I'm at so just a touch for alignment,,I check my star chart to see what angle Kochab is at and turn the Polar scope line that way and do the offset,,and yes a barn door does have limits and 300mm is stretching just a touch,,if you had the tools to make it perfect it would still have it's limits,,not so much the BD but you and your ability to align properly,,for a DIY project it's a niffy tool and when you do get it right get some crackerjack photos,,once I get on to and play with time laps a little will use the BD design and see if it works for travel while shooting,,it is smooth so it should work,,and it's nice to show photos of what your doing,,thanks,,I like that MW.
Chas


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Wed Jan 25, 2012 6:12 pm
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Post Re: Project Orion (Astrophotography Tool)
I was wondering about your alignment scope. It looked like the ones on the astrotrac, i had one of those for a week but it malfunctioned and wouldnt rewind properly, i sent it back and they were all backordered, i think thats when i dumped some extra cash for my nikon 24-70

Its always nice to see another competent DIY'er, i look forward to seeing some of your results!

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Wed Jan 25, 2012 6:32 pm
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Post Re: Project Orion (Astrophotography Tool)
Found this one on the web a while back,,not sure if it would out do the curved rod or not,,bit more work to it and have to find a way to attach the motor,,make it of CNC aluminum with edges bent 90 degrees for strength,,would be much easier for correct measurements and adjusting for correction,,good rainy winter project.
Chas


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