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Last update : 2015/09/21

motorized Barn door tracker for DSLR Photography



it is a small motorized equatorial platform used to photography stars, star clusters, nebulae,
and more generally for astrophotography.
this equatorial plane works on the principle of a Barn door tracker
If you take a photography of stars in night at a speed of 1/200s
or 1/50s, you'll see a few stars on your photograph.
If you make a photo with long exposure at a speed of 30 seconds or 2 minutes,
you will see hundreds of thousands of stars.
But if you make a photo without an equatorial plate or an equatorial mount,
there will be dragged on photography (as on photo22).
To photograph the sky and the stars, you must compensate the rotation of the earth.
This is why we need a system like a plank Equatorial compensate this movement.

The simple solution is to use an equatorial mount telescope, but the price is high (minimum 150 Dollards).
Make or even an equatorial board is not very complicated and will cost less than 30 Dollards + the price of the motor.
It exists on the internet, many embodiment of Equatorial board or plank Equatorial or equatorial platform.
There are also several principle tangent board, board isosceles isosceles board dual arm
board in an arc ...
I chose to make a board tangent because it is the easiest to achieve,
but the problem of the plate tangent, it is a drift in time.
I stumbled upon the excellent site of Fred http://www.astrosurf.com/fred76/planche.html
On his website he offers to make a little piece to correct the drift.
Well it works perfectly.

The principle of a plank Equatorial tangent is very simple:
Two planks of wood are connected by a hinge, the two plates is drilled to allow
spend a threaded rod. The threaded rod rotates, advances, and moves the second plate which is fixed
the reflex.
The principle is very simple, but implementation must be accurate.
I spent some time thinking about the engine, because we do not find many examples of board
Equatorial motorized and most examples I did not.

I'll explain how to make a motorized Barn door tracker.
For the impatient, the photo01 shows the equatorial plate mounted on a camera tripod.
On photo02, we see better the board and its engine.
The photo03 shows the two planks of wood attached by the hinge.
Before you read more, watch photo21 is the list of basic equipment needed to achieve
the equatorial plate. You will find all the materials in a hardware store, except the engine.
The engine I bought costs 12 Dollards in june 2010, I bought it on the website of Galileo:
http://www.galileo.cc/GALILEO-france/boutique_accessoires_list.php?rub=Moteurs
It comes complete with the hand control.
Within a year the price has risen from 10 Euros to 71 Euros. It is found on several sites of astronomy at the same price
sand is probably the importer has increased its margin (although this motor costs a few Euros in China).
I leave you the task of finding it yourself engine not too expensive (what counts is to find
an engine that runs at 1 or 2 revolutions per minute).
There is also another solution is to buy an engine for disco ball, some are 3 rpm (Just use a gear with 10 teeth
and the other with 30 teeth, or a gear with 20 teeth and the other 60 teeth, for leverage the speed
and the rotation is 1 rpm). I saw to 6 Dollards, the effort is not very important,
this type of engine should be fine.

As you have probably noticed, I also use two gears, one of 20 teeth and another 40 teeth.
I bought the gears on the website GOTRONIC: http://www.gotronic.fr in the robotics category.
The gears are wide, is to compensate for manufacturing flaws because I had a drill
and a screwdriver to make my board equatorial.

to make this board Equatorial need:
2 wooden boards (eg 30 cm x 12 cm)
1 piano hinge (it is thinner than a hinge carpentry)
1 wheel (a wheel off I will explain later why)
1 threaded rod diameter 6 mm
1 round tube of 12mm diameter
1 round tube of 10mm diameter (aluminum tube)
1 sleeve for threaded rod inside diameter 6mm and 8mm outer
1 Printed Circuit Board (to make piece for correction of tangent)

The first thing to do is fix the planks of wood with the hinge.
Be specific, the hinge must be perfectly and securely connected to the intersection of two
wooden boards (photo03 photo04 and). The two planks of wood must be able to close completely.
As you can see from the photos, I have a wooden board a bit shorter than the other,
it is because of the clamping circuit made corrective (photo09).
Now he'll have to make the hole in the threaded rod. This is the hole that requires the most precision. Try
to drill the hole on the tenth of a millimeter (do not worry it will come to correct the error by adjusting the engine).

In the list of materials, I have advised a threaded rod of 6 mm diameter threaded rod for this one-step
1 mm. The pitch is the distance between two grooves of a threaded rod.
On photo05, I give you the right distance for a threaded rod that has a pitch of 1 millimeter or thread and that is
one revolution per minute. The hole drilled is the size of the threaded rod, 6 mm in our case.
If your spindle is another thread or not (eg 1.25 mm, 2 mm), you must calculate the distance
with this formula: x = (w * N / (1.00274 * (tan (0.2524305555555)))
W is not the thread or threaded rod and N the number of minutes per round threaded rod
(Tan is the tangent 0.2524305555555, X is the result of calculating the distance).
This distance is the distance between the center of the hinge and the center of the hole you must drill.
This formula applies also in millimeters and inches for English speakers.

Now that the hole is made, we will create the system of movement of the threaded rod through the wheel (photo10, photo11).
I board a roller fairly wide (30 mm) to have good support and above all prevent the threaded rod moves.
This will also reduce engine vibration and displacement of the threaded rod.
So you have a wheel that you remove to get the rubber wheel.
If you choose a wheel as big as mine, the center hole of the wheel should be 12 millimeters.
But the sleeve to the threaded rod has an outer diameter of 8 mm.
That is why the list of materials there are two round tubes, one 10 mm and a 12 mm.
Cut the round tube 12 mm so that it enters the center hole of the wheel but not to exceed (ie 29 mm).
Cut the round tube 10 mm to 35 mm aluminum (a little longer than the round tube 12mm).
As the tube is 10mm aluminum, and aluminum is softer than steel tube 12mm, you will be able
enter into force tube 10mm in the 12mm tube with a hammer.
The tube is now 10mm more than 5-6mm tube 12mm.
From the side or exceeds 10mm tube, you'll force push the sleeve for threaded rod that has an external diameter of 8mm.
View photo14 photo15 and we see the steel tube and 12mm tube 10mm aluminum slightly exceeding (photo15).

The caster wheel in a hole of 12 mm, the steel tube was also a diameter of 12 millimeters. The wheel is
rubber material. It is our little piece of steel tube of 12 mm between the center hole of the wheel but can
turn in without forcing. It will have, making movements back and forth, expanding by 0.1 mm hole in the wheel
rubber. I have a hundred movements back and forth to enlarge the hole a little wheel.
The wheel hole must be enlarged slightly but not too much, because it does not let the 12mm round tube moves,
you just need it to run without rubbing too hard.
I also recovered the wheel, a disc or steel washer that was provided with.
This puck is used to prevent our 12mm tube out of the hole of the wheel. This puck to
diameter of 8.5 millimeters, with the drill I have enlarged to 10 millimeters. Thus our round tube is 12 mm in
the hole of the wheel, the round tube 10 mm we have entered into force over the washer (photo12 and photo15).
We now have a round tube 12 mm, who contain a round tube 10 mm, which contain our sleeve
for threaded rod 8 mm in outer diameter, and all this in the hole over the wheel with the puck.
We will now fix a gear on the sleeve for threaded rod.

If you buy the same engine as me, this engine makes a turn in 2 minutes, in our case, it is necessary that the threaded rod
make a turn in 1 minute, so that the threaded rod ahead of a millimeter per minute.
So I used two gears to increase engine speed. These two gears are also used to connect the motor
the sleeve threaded rod must turn to move the threaded rod.
Using a gear of 20 teeth and another 40 teeth, my speed I multiply by 2,
So my sleeve threaded rod will do a lap in 1 minute and then move my threaded rod of a millimeter.
You must then drill the gear teeth 20 to enlarge the hole to 8 millimeters to fix it on the sleeve
threaded rod that you have previously pressed in force in both tubes. To fix the gear teeth 20
sleeve on the threaded rod, I used glue strong as the "super glue".
Warning ! must be perpendicular to the gear sleeve threaded rod.
It is time to set the caster wheel to the board because the wheel does not rotate. The wheel is just support for
round tubes and the sleeve. I used two screws to fix the wheel in the wooden board.

On the engine I set the gear teeth 40. For the 40 tooth gear is perfectly perpendicular to the engine
I found an old piece of Meccano red (photo10). You have to find a piece that can do the same thing.
To attach the motor to the board, I used a screw diameter of 10 millimeters and 70 millimeters in length.
This hexagon bolts (photo05 and photo06) is fixed on the wooden board and is held by bolts (photo11).
I put several bolts so that the gears are aligned (photo13).

Now we will create the small Printed Circuit Board will correct the drift of our equatorial plate.
I chose a Printed Circuit Board because it is a matter very easy to cut with a knife and sanding.
The Printed Circuit Board is also a strong material (fiberglass) and a very thin layer.
As I have said on the website of Fred http://www.astrosurf.com/fred76/planche.html, there is the exact curve
that this piece should have a remedy. On his website, On his website he offers a JPG image but it is the right scale
for M6 screw pitch and the author states that everyone is to put the correct scale.
I therefore propose on this website under "Download" to download the JPG image on the right scale for
a threaded rod 6 mm in diameter with a pitch of 1 mm and one revolution per minute.
Warning! It will make this curve with the greatest accuracy if you have small drift errors over time.

To fix this piece of corrective tangent, I made a small groove in the wooden top, and the piece is
properly maintained at its base (photo07).
to lock down and that the piece can not move, I used two squares of white plastic (photo07 and photo08).

At this stage of manufacture, the engine is fixed. The assembly of the wheel,
round tubes and the sleeve is completed and attached to the board.
The play is performed corrective tangent and attached to the top shelf.
The bottom plate is shorter than the top shelf for the play corrective tangent and the two brackets
white plastic does not interfere with complete closure of our plate equatorial (photo08 and photo09).

It remains only to make a groove in our threaded rod (photo06) for the threaded rod is nested on the part corrective
tangent. This allows the threaded rod to always stay connected to the play editor, but leaving the possibility to
threaded rod to slide the piece tangent correction.
It also serves to prevent the threaded rod to rotate, as it should certainly not turn.
This is not the spindle turning, but the assembly of round tubes and the sleeve.
As we threaded rod can not rotate, forcing the threaded rod is forced to advance or retreat.
To reduce friction and blows, I put a little grease in the groove of the threaded rod.
Based on an idea of Fred, it is possible to replace the groove in the threaded rod with a small roller or ball bearing
to minimize friction.


Enjoy ! We conducted our motorized equatorial plate.

We have to fix our SLR the equatorial plate.
I used two pieces of wooden dowel that I connected and fixed with two screws (photo16).
A central screw with a wing nut allows tilting left or right patella photography.
I used a Manfrotto ball to fix my DSLR.
This ball can be rotated through 180 degrees of the SLR camera, up and down.


Pure fixed on the equatorial plate camera tripod, I used a thin piece of wood with a thin
Plexiglas plate to compensate the banks of a camera tripod (photo19).
I used a system with two screws to completely block the plate equatorial camera tripod.
A screw is secured with a bolt and between simply a hole in the equatorial plate.
The other screw through the camera tripod and is screwed into the equatorial plate via a threaded sleeve.

I hope I was clear in my explanations for the manufacture of the equatorial plate.
It's not easy to describe the stages of manufacture.

Now he is testing and use.
To use the board Equatorial like to use an equatorial mount, you have to put in a station.
The station is set to point to the axis of the hinge to the north celestial pole when you are in
the northern hemisphere and toward the south celestial pole when you're in the southern hemisphere.
Warning! Do not confuse the earth's magnetic pole and the pole of rotation of the Earth (celestial pole).
Search the Internet to understand.
I give you a link to calculate the angular difference between the magnetic pole and the pole of rotation of the earth
depending on your location: http://geomag.nrcan.gc.ca/apps/mdcal-fra.php

You must align the hinge pin piano with the pole of rotation of the earth (photo05).
The alignment must be perfect for a very long track stars.
In the northern hemisphere, the north celestial pole is right next to the pole star.
Once the station made up, you can adjust the speed of the engine if there is a slight delay or a slight
advance after a few minutes. To adjust the engine, I drilled a small hole in the hand control (photo20).
Through the small hole, I have access to the potentiometer for adjusting the speed of the engine without
removing the hand control.

You've probably noticed that I have fixed a reporter on my board equatorial.
This allows me to set my station without seeing the pole star with the help of a compass, and knowing
the angular difference between magnetic north pole and the north celestial pole.
But with this method there is always an adjustment to do to have a precise polar alignment.

I am doing some tests with my Nikon D90 and my goal of 300mm (on a Nikon D90 this is a 450mm).
I come to shoot 90 seconds without duplication of stars.
On photo22, I made a long pause of 40 seconds at 300mm with a motor speed X4 (by pressing
X4 button hand control).
This allows us to see that there is virtually no lack of monitoring and especially no vibration.
This layer allows Equatorial therefore take pictures with big telephoto without experiencing vibration.
I have not yet been able to do photography with breaks of more than 90 seconds because I live in town.
Above 90 seconds in the city, the images are orange and lose detail.

On this website under "Sky and Moon", I put some pictures as examples.
These photos were made to areas where, in the naked eye can not see any stars.
I also chose those areas close to the horizon to check the accuracy of tracking stars.
The results are very good (photography Etoile01 to Etoile03).
I had the opportunity to make some nice pictures.
You can see in the "Sky and Moon" on this website.
You will also see some pictures I made last summer with this motorized Barn door tracker.

Good production and good hunting stars, star clusters and nebulae.

Copyright 2010 ThierryD - http://rienquepourlesyeux.free.fr
Last update 17/01/2011
Reproduction prohibited

Use arrows for the direction and speed. Click on thumbnail for enlarge.