Author Topic: Star-tracker  (Read 378 times)

Chris Smale

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Star-tracker
« on: December 30, 2017, 03:34:10 PM »
Busy building me a star-tracker. That's why I needed that worm/wormwheel-set I posted earlier.
The geared stepper has 1:100 ratio, the (self-made)worm/wheel another 1:157. That should be enough to slow things down.
Worm and wheel are pushed against each other with a controlled spring.
There's an adjustable green laser on board serving as 'Polaris pointer'.
There are 3 large and 2 smaller ball-bearings.
The unit measures 160x75x55mm(about 6x3x2 inches)
At the top of the smooth rod (on the right side) comes a small platform.
There are 3 large and 2 smaller printed parts.

A DC-version of this star-tracker will also be made.

The electronics for this tracker will be designed and made by Guy, our electronics guru.
PCB not yet in the drawing






salonpeli

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Re: Star-tracker
« Reply #1 on: December 31, 2017, 08:08:00 AM »
I like the spring loaded worm idea.

Don


grateganir

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Re: Star-tracker
« Reply #2 on: December 31, 2017, 03:53:19 PM »
Hi,
This is what I'v got so far.
Works perfectly, not tested under stars yet. Still, one weak point has to be removed.

In the last pictures there's a 'dummy cover' on top, just to look inside while it's running. The real cover is on the right.










colzefuli

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Re: Star-tracker
« Reply #3 on: January 08, 2018, 02:25:08 AM »
Chris,
I really like the work you are doing and all the attention to details. Congradulations.

However, there is one thing I don't understand: what is the purpose of the shaft that sticks out right next to the motor? Would a camera not normaly be attached to the worm gear driven shaft only?

Paul Woodrow

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Re: Star-tracker
« Reply #4 on: January 10, 2018, 03:34:08 AM »
Pierre,

The wormwheel's axis is supported by two ball bearings. One ball-bearing sits at the bottom of the box and the other is pressed into the cover. On top of that axis(outside the unit) rests a large ball-head to support a camera or whatever small device.

Thanks for the comment.

adtalhalyg

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Re: Star-tracker
« Reply #5 on: January 15, 2018, 11:08:57 AM »
Quote
Pierre,

The wormwheel's axis is supported by two ball bearings. One ball-bearing sits at the bottom of the box and the other is pressed into the cover. On top of that axis(outside the unit) rests a large ball-head to support a camera or whatever small device.

Chris,
I understand the drive shaft part that's connected to the worm gear. My question is about the other shaft that we see right next to the motor housing. It doesn't even stick out of the box cover when the cover is closed (next to the small mirror used for the laser pointer). I'm wondering what that shaft is for. Thanks.

halubicom

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Re: Star-tracker
« Reply #6 on: January 20, 2018, 10:02:40 PM »
Misunderstood, sorry Pierre....

Stepperaxis and worm should stay perfectly aligned and at the same time, to make good contact, the worm is springloaded against it's wormwheel. The only way to do this by making a rotating unit, see third picture in post #3, and that's why the ball-bearing on that shaft you mentioned. So doing possible irregularities in worm or wormwheel are eliminated. Not tracking errors of coarse just eccentric irregularities of worm and/or wormwheel.
There are also two (small) ball bearings at each end of the worm. The worm is pushed against it's wormwheel and at the same time that worm should rotates very smooth of coarse.
That worm's spring is visible in the drawing, not in the pictures.

I did another 12hour run, there's only a minor tracking error. Have to test during a nighttime-session to find out about periodical errors in the system. Fingers crossed....

acbrawexel

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Re: Star-tracker
« Reply #7 on: January 21, 2018, 02:46:12 AM »
Quote
Misunderstood, sorry Pierre....

Stepperaxis and worm should stay perfectly aligned and at the same time, to make good contact, the worm is springloaded against it's wormwheel. The only way to do this by making a rotating unit, see third picture in post #3, and that's why the ball-bearing on that shaft you mentioned. So doing possible irregularities in worm or wormwheel are eliminated. Not tracking errors of coarse just eccentric irregularities of worm and/or wormwheel.
There are also two (small) ball bearings at each end of the worm. The worm is pushed against it's wormwheel and at the same time that worm should rotates very smooth of coarse.
That worm's spring is visible in the drawing, not in the pictures.

I did another 12hour run, there's only a minor tracking error. Have to test during a nighttime-session to find out about periodical errors in the system. Fingers crossed....

Another way and eliminate friction irregularities (all friction really)of the ball bearing pivotis to compliantly mount the worm assembly. BUMP see fig 2.Also does double duty of spring loading the worm assembly against the worm.

Don

Mike Meckler

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Re: Star-tracker
« Reply #8 on: January 21, 2018, 04:54:05 AM »
Quote
Misunderstood, sorry Pierre....

Stepperaxis and worm should stay perfectly aligned and at the same time, to make good contact, the worm is springloaded against it's wormwheel. The only way to do this by making a rotating unit, see third picture in post #3, and that's why the ball-bearing on that shaft you mentioned. So doing possible irregularities in worm or wormwheel are eliminated. Not tracking errors of coarse just eccentric irregularities of worm and/or wormwheel.
There are also two (small) ball bearings at each end of the worm. The worm is pushed against it's wormwheel and at the same time that worm should rotates very smooth of coarse.
That worm's spring is visible in the drawing, not in the pictures.

I did another 12hour run, there's only a minor tracking error. Have to test during a nighttime-session to find out about periodical errors in the system. Fingers crossed....

Chris, thank you for the explanation. I should have understood that by myself. Very well thought out the way you rotate the entire motor housing to ensure constant contact between worm and gear.

grateganir

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Re: Star-tracker
« Reply #9 on: January 23, 2018, 06:11:08 AM »
Quote
Misunderstood, sorry Pierre....

Stepperaxis and worm should stay perfectly aligned and at the same time, to make good contact, the worm is springloaded against it's wormwheel. The only way to do this by making a rotating unit, see third picture in post #3, and that's why the ball-bearing on that shaft you mentioned. So doing possible irregularities in worm or wormwheel are eliminated. Not tracking errors of coarse just eccentric irregularities of worm and/or wormwheel.
There are also two (small) ball bearings at each end of the worm. The worm is pushed against it's wormwheel and at the same time that worm should rotates very smooth of coarse.
That worm's spring is visible in the drawing, not in the pictures.

I did another 12hour run, there's only a minor tracking error. Have to test during a nighttime-session to find out about periodical errors in the system. Fingers crossed....

The pivoting worm only compensates for backlash and as said not tracking errors. Adding an encoder on the wormcould allow software to change the drive rate and compensation of eccentricities due to periodic runnout of worm / worm wheel.

Don

quiterhardpho

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Re: Star-tracker
« Reply #10 on: January 25, 2018, 02:04:25 PM »
Hi,

Busy assembling V3, had to redo the stepper-holder as it was to weak.

At the same time I made myself a holder for powerpacks. I normally use these powerpacks for my cordless (Makita)drills. Two of them in series gives me 14.4V. One fully charged set of batteries gives the tracker a workingtime of about 5 hours.
The contacts I made from SS chopsticks.








Fred Lafever

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Re: Star-tracker
« Reply #11 on: January 25, 2018, 06:28:05 PM »
Now THAT is what a 3D printer is for.

Todd Vann

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Re: Star-tracker
« Reply #12 on: January 25, 2018, 11:40:26 PM »
All is ready, tomorrow first shots, need to move to 'Digital Photography forum' now.

Wedge is printed for 51° latitude.
The small hex-bolt(lower-right) is to adjust tension between worm and wormwheel(there's a spring underneath).


aiyahoke43

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Re: Star-tracker
« Reply #13 on: July 05, 2018, 11:42:26 AM »
"Busy building me a star-tracker. That's why I needed that worm/wormwheel-set I posted earlier.
The geared stepper has 1:100 ratio, the (self-made)worm/wheel another 1:157. That should be enough to slow things down.
Worm and wheel are pushed against each other with a controlled spring.
There's an adjustable green laser on board serving as 'Polaris pointer'.
There are 3 large and 2 smaller ball-bearings.
The unit measures 160x75x55mm(about 6x3x2 inches)
At the top of the smooth rod (on the right side) comes a small platform.
There are 3 large and 2 smaller printed parts"

I am agree what you said. Thanks for your sharing.