Equatorial Platform for the North

Intro: Equatorial Platform for the North

In this Instructable, I will show you how I designed an equatorial platform for my telescope. But first, what is an equatorial platform?

This device will let you observe an object for several minutes or take photos of the night sky without having to worry about star trails. Technically, it rotates at the same speed as the earth but in the opposite direction. You can now take long exposure images of your favourite constellations, nebulae and galaxies.

Most platform on the internet are designed for mid latitude observers. However, living above 60 degrees latitude, I needed to design my own platform. This is how I built it.

STEP 1: Design

Since I am living in the north, Polaris sits quite high in the sky. This fact lead me to a triangular design with a polar axis in the south and 2 curved sections toward the north.

The drawings above shows 3 circles on the top of the platform. These are the position of my telescope feet. This is optional but it helps to secure your instrument in place.

The second drawing shows an upside down V shape. the top corner of this shape is where the polar axis is located. A threaded rod serving as the axis will be fixed at this location.

The base of the platform is similar to the top but extends further toward the north to accommodate bearings and a motor.

Please note that this design is one out of many. If you want to learn how to create your own or if you want to modify it, I invite you to take a look at Reiner Vogel's page and his detailed instructions.

STEP 2: Parts

The parts are displayed on the pictures above. Here's a list of material:

- 1/2 inch birch plywood for the base, the top and the curved segments.
- 1/4 inch plywood for the circles (optional). They will hold your instrument in place (telescope, tripod).
- 5/16" threaded rod which will serve as the polar axis.
- 10 skate bearings (polar axis and circular segments rollers)
- 3/4" threaded rod to serve as a worm screw
- 72 teeth cog
- 4 rpm DC motor
- 3 hockey pucks
- Screws and small pieces of wood

STEP 3: Cut the Top and Base

To begin with, we'll cut the top and base of the platform in a triangular shape. You can use the SVG file attached. The scale is 1:1. By rotating the part, it can be cut on a laser cutter with a 20x32 bed (2 layers of 1/4 in plywood). It can also be cut by hand but make sure to keep the original size (21" tall for the top board without the vertical segments attached).

The overall shape doesn't really matter. You just need to make sure you keep the position of the polar axis (see diagram) and the length, position and inclination of the 2 straight sides.

For the base, you can have the same shape but make the north side longer and extend the south side a little.

STEP 4: The Polar Axis

We can start by assembling the polar axis. To do this, screw the threaded rod into a piece of wood and cut the other end of the wood at 30 degrees. You can then glue it under the top part of the platform, making sure that the axis of the rod goes through the polar axis (top corner of the triangle in the diagram).

STEP 5: The Vertical Segments

We will now install the vertical segments onto the top part of the platform. Place the board upside down (polar axis up) and screw the segments into the sides of the board making sure the boards make a right angle. Pre-drilling the holes will help.

STEP 6: Make the Bearings

These bearing will allow your platform to move smoothly. One of them is powered by a DC motor. The other one consists of 4 bearings mounted onto a 5/16" screw.

The powered one has the bearings mounted into its support (thick plywood). Around the threaded rod is a tube (plastic or metal) covered by a rubbery material. The final diameter should be about 1/2".

STEP 7: Motorise It

In order to function properly, the motorised bearing rod should extend a few inches to the north side. On that rod, we'll put a system of worm and gear. This will create a strong but smooth circular motion.

I used a 3/4" threaded rod to make the screw. The cog has 72 teeth and the DC motor turns at 4 rpm.

You can use a stepper motor or a DC motor. I chose a DC motor because I already had one and I could adjust the speed easily by simply changing the voltage with a variable resistor.

STEP 8: Assembly

You can now place the top part of the platform onto its base. The vertical segments should be on their bearings.

You will notice that the threaded rod for the polar axis has no support yet. We will add it now.

First, level the base of the platform and make the top and base parallel. They should both be horizontal. Now measure the distance needed for the support of the polar axis. You can then cut this support in a piece of wood and cut the bottom side at a 30 degrees angle. Drill a hole all the way through. You can now slide the polar axis inside.

To ease movements a little, the polar axis support can have one or more skate bearings inside. I have 2 on my platform.

STEP 9: Add Feet

Your platform is almost complete. But there's one more thing we need to add. In order to cancel vibrations from the ground, and to make is more stable, we'll add 3 rubber feet. A good and cheap option is to screw 3 hockey pucks.

STEP 10: How to Use It

It is fairly easy to use as long as you can see Polaris. Place the platform flat on the ground and turn the pointed side (polar axis) to the south. The side with the bearings should be facing north. If you are below latitude 60, you will have to raise the south side. If you are above it, you will need to raise the north side (2 rubber feet).

When you are fairly confident with your alignment, push the moving board (the top) to the west (left if you're looking at Polaris) and place your instrument on top of the platform.

You can now start the motor and look through the eyepiece or camera. The stars probably won't stay centred on your first try. You will need to adjust the speed of your motor while keeping your eye in the eyepiece.

Once the speed is set, your instrument should stay aligned on the objects you're aiming at.

The platform will run for about 60 to 90 minutes. Indeed, the vertical segments will reach their end after a while. You will have to push it back to its original position (west) and re-align your instrument.

STEP 11: Results

You can now observe and take photos of galaxies, nebulae and planets at high magnification.

The more precise your alignment, the longer you can keep the objects centred in the eyepiece or on the sensor of your camera.

My platform lets me take up to 15 seconds exposure with a 1000 mm focal length. This is enough for common deep sky objects since you can stack multiple photos to get the same result as a single longer exposure.

Comments

[SuperNova7]

Hi, very nice design of your platform, I would like to try the construction for my latitude 45° north. I wanted to know if it is possible to have the dimensions of the two platforms (upper and lower) for an 8" dobsonian thanks

[GarrasP]

Just change the angles of thu pivot points to your lattitude. Youll have to recalculate the shape of the 45 degree sectors though. Its easy. You imagine a right angle over the platform , extending from the north star, through the pivot point and into the ground. This forms the opposite side. The adjacent side from the drive roller to the intersection of the opposite side will give you the radius of the circle length you need to set your compass to. If you dont have one big enough, you measure the radius which is the same as the adjacent side (around 52 cm or so) of the imaginare triangle. So you put your radius arm (any scrap piece of wood), measure said radius and loosely nail it to the table to put your pencil at the end of the arm and trace your circle using the swinging arm. This gives you your correct sector shapes.

[pixelsaurus]

Love the design but how did you calculate the shape of the sectors?

[ThomasJ1]

Short answer: by hand :)

I actually used this page to understand the geometry involved in equatorial platforms: http://www.reinervogel.net/index_e.html?/Plattform...

He also has a PDF with all the dimensions that you can use to build your own if you don't feel like doing the maths.

[GarrasP]

Nov 2023. Now, looking at the sector bottom edge, i see its 90 degrees compared to 90 degrees vertical. Does the sector create torque drag as the weight of the telescope change in relation to the center of gravity of the platform as it changes over time which results in its ability to be steady for only 15 seconds at a time? Ive seen another example where the builder sanded the bottom of the sector at 120 degrees using your 60 degrees lat as the example.

[SimonH]

Hi, thank you for these it's a great help and I was really stuck on the curved segments but as it happens you live at the same latitude as me. My only question is how do I print the sdf file soi can use the segment print out to trace onto my wood. Thank you again.

[ThomasJ1]

Hi Simon, you could just print it on multiple sheets and tape them together if they are too large.

[SimonH]

Hi I tried but when I open sdf in web browser then print it only shows 2 pages of A4 with parts missing and looks way smaller than it should . Do you have the segment part in pdf or jpg format? I'm really unfamiliar with the sdf format .sorry

[ThomasJ1]

I don't know what .sdf is but if you have Inkscape on your computer, you can open the SVG file and print from there.

[SimonH]

Great sorry yes my mistake I was tired I meant .SVG and thank you I'll install inkscapr and go from there. Thanks again and brilliant tutorial

[ju1234]

This is an old thread but I am hoping I will get a reply from ThomasJ1. Few questions:

1. The design of the "Polar axis": is there a reason for cutting and positioning the wood at 30 degrees? Is it based on latitude of your location? Would the angle be different for a different location?
2. Is the height of front polar axis (the space between upper and lower board) same as the height of the back (vertical segments)? Is the platform (top board) level/horizontal?
3. You mention "below 60 degrees raise the south side and above 60 raise north side (2 pucks)". I thought the curve of the vertical segment is cut to the specific latitude and the device will be accurate only in that latitude. So for 50 degree as well as 30 degrees, all you do is raise the south side by a fixed height. Same amount no matter where you are? The fact that platform will no longer be level does not matter?

Thank you for your help.

[ThomasJ1]

The 30 degree angle is because I live a latitude 60. (90 - 60 = 30). It doesn't have to be too precise. You can shim the south or north end to align the axis with polaris.

The height of front and back should be about the same. If the top is not horizontal, the telescope may fall over at some point.

The curve is specific to the platform, not to the latitude. I could have made a 45 degree platform with a conventional vertical segment but I would have to raise the south side so much that the telescope would be quite off balance.

The vertical segments only depend on the distance from the platform axis. However, in my case, the axis is 60 degrees from horizontal. Some may have 40 or 20, hence the different vertical segments for each platform.

[ju1234]

Thomas, thank you very much. Your design is so much easier than most others. So, I have decided to switch to this design. Please, if you can help me with few practical considerations.

3/4" threaded rod you used as the worm: I assume it is 10 threads per inch? Instead of buying the 3 foot rod, pretty expensive, I am planning to just use a section of 3/4" bolt. Will that work? Your photo showing the motor assembly: it appears that you have used a threaded tube or some thing? Or did you drill a hole in the rod? I see an Allen screw in that rod. If tube, source please? I suppose I could use the standard plumbing 3/4" pipe. But I don't think they thread it more than just an inch or so at the end. How long a segment is needed as a worm gear? Motors usually have only about 5mm shaft. How to couple it to the 3/4" tube or rod? I did not find any on line.

The 72 teeth cog: source? If 3D print, can you please provide the STL file. The gears teeth have to mate the worm. So this must be a specific cog that you used? More info about this will be appreciated.

I like the idea of fixing the motor stand with butterfly nuts, perfect.

I downloaded the design. It shows picture of both the north bearing and the upper platform. However when I go to print, it shows only one page with the bearings only.

Thank you.

[ThomasJ1]

Yes, I am using a 3/4" threaded rod but a bolt will work the same way. Just drill a hole on each end. One is for the motor which gets attached with a small allen key, the other hole is for a pin to keep the worm gear centred.

The gear is from here: https://www.sdp-si.com/products/Gears/Spur-Gears-72-Pitch.php They also have worm gears if you don't want to make your own.

I'll check at home where the rest of the design is.

[Malkaris]

Very nice, I'm moving to a place where I should be able to see more sky at night. I'm actually looking into ways to photograph satellites (the artificial kind) but I think I'd need a platform more aggressive than this. I'd still like to build it myself, do you have any advice?

[ThomasJ1]

Hi,

It depends what you are trying to achieve. If you want close-ups of the ISS for example, you'll need a telescope, a robust mount and a fairly high slew speed.
Another thing to note is that satellites are not following the ecliptic, (except the geosynchronous ones of course), so you don't really need an equatorial platform for this task.
I would go with an Alt-azimuthal mount (can be handmade) with high speed stepper motors.

Then you'll need to use an arduino or raspberry pi or a computer to control the mount. A bit like this: https://www.instructables.com/id/Star-Track-Arduino-Powered-Star-Pointer-and-Tracke/

I hope it help a bit.

[Carpenter Guy]

Although I don't have a telescope, this is very cool! Those pictures make it worth it :-)

[LarryK4]

About 3 years ago, I decided to make one of those CNC router things to help me make a Eq. Platform. After all that time I've built 4 or 5 CNC routers (each bigger-more powerful-faster-etc.) and now that I've built a machine that's big enough to actually cut this, here you supply wonderfully simplistic build than I was envisioning. I'm not sure if I should be sad or happy, BUT the two things I KNOW that I must do is to start building your wonderful design and give you my heartfelt vote. Well done!

[ThomasJ1]

Thank you Larry, I wish you good luck with the build and don't hesitate to post comments or send me a message if you have any questions.

[deluges]

The pictures are beautiful, you got my space vote :)