The M6 flange nut was pressed into the larger gear and I drilled a hole in the bottom board of the barn door to match the OD of the flange nut which locates the gear into position and keeps it engaged with the smaller drive gear.
I also used a control knob (think its called a potentiometer) to fine tune the speed as I found that the 2rpm motor from china wasn't very accurate, might have something to do with my voltage supply??
Russ, did you drill the larger gear out to accept the nut and the smaller gear to take the 6mm shaft?
Did you just put the potentiometer in series with the motor or did you use a voltage regulator? Without a regulator the speed would not be constant.
Russ, did you drill the larger gear out to accept the nut and the smaller gear to take the 6mm shaft?
Did you just put the potentiometer in series with the motor or did you use a voltage regulator? Without a regulator the speed would not be constant.
Steve
Hi Steve,
I drilled the large gear so as the hex of the nut was a tight press fit, I also used a strong adhesive to hold it in place.
I purchased a 12v DC motor speed controller & a 12v DC 2RPM motor off eBay. The gears were from Jaycar. I got the M6 brass rod from work and bent it to get a curved radius.
The last photo was taken with my barn door on 23rd July with my 6D & canon 50mm f1.4 lens @ f3.2 ISO 3200. Approx 30 exposures ranging from 10 to 60 seconds.
The last photo was taken with my barn door on 23rd July with my 6D & canon 50mm f1.4 lens @ f3.2 ISO 3200. Approx 30 exposures ranging from 10 to 60 seconds.
I purchased a 12v DC motor speed controller & a 12v DC 2RPM motor off eBay. The gears were from Jaycar. I got the M6 brass rod from work and bent it to get a curved radius.
Russ,
What battery did you use? Do you find you have to recalibrate motor speed every time you use it?
What battery did you use? Do you find you have to recalibrate motor speed every time you use it?
TIA
Steve
At the moment I am using my car jump starter. I like to re-calibrate it each time anyway. I might order a speed controller with an LCD speed display soon.
Maybe a stupid question, bear in mind I am a newbie.
All I have read re barn doors is they need to be aligned with a ref point, north or south celestial pole. As we don't have a definite sky ref to do this, how do we do it?
Elevation seems to be easy, just use a protractor with a pointer set up on the barn door. Aiming south is a little more difficult. I have seen some suggest a compass and correct for magentic deviation, but any ferrous metal in the barn door would affect the compass. If the rod and hinges are brass, maybe no problem. However, the motor will have a magnetic field, as will the wires going to it. Hence I guess the need for a ref point in the sky. Am I on the right track here?
At the moment I am using my car jump starter. I like to re-calibrate it each time anyway. I might order a speed controller with an LCD speed display soon.
Steve_C,
I use a 2nd hand, 4 X telescopic sight from the local gun shop.
It's attached via a (slide scope in), Aluminium bracket, adjacent to the brass hinges & is very accurate once set up.
Using a SCP finder chart, it's relatively easy to find it.
Might take a little while to "fine-tune-it-in" but it works well.
For the elevation/latitude, I had 2 hardwood wedges made up.
One "large variety" under the bottom plate on the tripod & a smaller one for the camera ball mount.
Piccies are in Post #25 on the 2nd page of this thread.
Maybe a stupid question, bear in mind I am a newbie.
All I have read re barn doors is they need to be aligned with a ref point, north or south celestial pole. As we don't have a definite sky ref to do this, how do we do it?
Elevation seems to be easy, just use a protractor with a pointer set up on the barn door. Aiming south is a little more difficult. I have seen some suggest a compass and correct for magentic deviation, but any ferrous metal in the barn door would affect the compass. If the rod and hinges are brass, maybe no problem. However, the motor will have a magnetic field, as will the wires going to it. Hence I guess the need for a ref point in the sky. Am I on the right track here?
I have used Google Earth/ map to work out true south in relation to the orientation of a fence line. Measure the angle between south and the fence lay it out with a string line and point the hinge in that direction. Helpful for ball park alignment and if you can't see the SCP. In that case I drift align my double arm drive
I live in a Nth Western Sydney suburb, so to get to a dark sky loacation takes me at least an hour. Nearest reasonable would be Bowen mountain, is anyone here a member of NSW Astronomical Society?
Location: '34 South' Young Hilltops LGA, Australia
Posts: 1,482
Quote:
Originally Posted by Steve_C
How accurate does the curved rod need to be? I have bent it as close as I can to the correct radius for an M6 rod, 9".
How accurate does the measurement from the hinge to the rod need to be? within 1mm, .5, 2?
steve
Hi Steve,
A 1mm error in the radius, that is where the radius error results in a 1mm greater radius than the ideal radius will result in a drive rate error of 4 arc sec per minute. This is not significant for short exposures on wide angle lenses. Up to 2 min exposures up to 100mm lenses. Accurate polar alignment will present a bigger problem than this error.
Steve_C,
I use a 2nd hand, 4 X telescopic sight from the local gun shop.
It's attached via a (slide scope in), Aluminium bracket, adjacent to the brass hinges & is very accurate once set up.
I can pick up a rifle scope from Ebay pretty cheap. Not sure if they are customs restricted though. How did you attach yours? They seem to have a wedge shaped mount.
A few years ago I picked this up on Gumtree here in Melbourne for $25.00
It was made in 1988 by ST Astro in Beaumont Texas USA and came with original letters between the ST Astro and the purchaser (no email back then, only snail mail), instructions and transfer receipt.
He paid $155 USD back in 1988.
It doesn't have a curved rod, but a circular cutout in the top and bottom arm, which changes angles as the arms separate. It has a tube to assist in the alignment, but is not really of any benefit here in the southern hemisphere. It runs on 12v (1 x 9v and 2 1.5v AA batteries). I have used it a few times, but have never really got it aligned well enough to prevent star trails. Anyway, I just thought I would post as an alternative to the curved rod.
Thanks
Andrew
Steve...
The Telescopic sight fits into 2 machined < grooves in the barrel.
But, it will fit very neatly over a "T" bracket.
I made an Aluminium "T" bracket. (The Al. "T" bar that I had, was offset, as you can see.)
Screwed that on the top board, adjacent to the brass hinges.
I gave up on visual alignment and developed a drift align procedure. It is fairly straight forward.
As usual, align with TS and set latitude. With the camera pointed in the direction of the area to be imaged, with the live view screen horizontal, take a 10 second image. If the stars are round increase to 20 or 30 seconds and more until drift is evident. Corrections are made in alt and az until drift is eliminated/negligible. You only need to correct up to your maximum exposure time for the night.
This method also corrects for refraction error. Not just for the big boys toys. It works very well once mastered.
