Auto Guiding Sky Tracker

Have made a sky tracker before. The function is quite OK.

But I'm frustrated by the polar alignment. To get accurate polar alignment, it is very time consuming.

That is why I build a new one with auto guiding capability. With this new sky tracker,

the set up time can be reduced to below 10 minutes.

It is not the normal auto guiding sky tracker that guides only the west-east direction.

It guides both the east-west and north-south directions.

On the other hand, it is not the traditional equatorial or Alt-Az mount.

It is in fact a normal sky tracker on the top of a seesaw.

Anyway, it still can be used as a normal sky tracker that does not have auto guiding capability.

That is no computer or guiding scope is required if you want to reduce the loading of my backpack :)

The key materials are two 1:100 harmonic geared NEMA17 steppermotors,

three camera quick release adapters, some aluminum bars,.......

No additional gear, timing belt or else are required.

It makes the fabrication works very simple.

Precise workmanship is not required basically.

A bench drill and some fitter's tools will be OK.

Of course, a bench milling machine and lathe will help a lot.

The dimensions are not critical.

Just make sure the angle of the seesaw matches with the latitude of your location will be OK.

On the top, it is the normal sky tracker that control the west-east direction.

And on the bottom, it is the seesaw that controls the north-south direction.

Nearby the bearing on the side of the seesaw, there is a screw.

It is used to limit the movement of the seesaw.

It is used when auto guiding is not used.

That is the normal sky tracking mode.

On the other hand, under the seesaw, there is a mini turn table.

It is used for polar alignment by drift method.

The whole mechanism is mounted on the camera tripod by using a camera quick release adapter.

That is it can be taken down from the camera tripod quickly and easily.

Not full 360 degrees of the west-east motor will be used.

Only the region in red will be used.

The aim is to reduce the length of the moment arm, and thus reduce the torque being applied to the motor.

On the other hand, in this region, the weight of the camera will help to reduce the effect of the gear's backlash.

It can be split into two portions, so that they can be put into the backpack easily.

Owing to the design limitation, some sky trackers get difficulty in pointing the camera to the zenith.

And it is not easy to maintain the balance of the system.

A L-bracket and a tilting platform have been built to resolve these problems.

The L-bracket lets the camera mounted right over the motors.

Thus reduces the torque being applied on the motors.

More stable and less electricity consumption.

The tilting platform let the camera point to the zenith easily.

The L-bracket can also be mounted in opposite direction.

It helps the camera to point to the low latitude southward sky.

This tilting platform can be rotated in 360 degrees.

It helps the camera pointing to low latitude sky in whatever directions easily.

On the left hand side, it is the polar scope.

To make sure it is parallel with the motor axis,

a aluminum tube with a hole the same size as the polar scope is turned by a lathe.

And both this tube and the motor are fixed on the same aluminum plate perpendicularly.

So the parallelism of the scope and the motor axis can be guaranteed.

A nylon stopper is put on the camera quick release plate.

It helps to avoid the camera from moving.

It is very essential for long exposure time photo taking.

I used a old 50mm lens as the guide scope.

And used a cheap electronic eye piece as the guide cam.

A rear lens cap and a 3D printed adapter are used to put the lens and eye piece together.

A very old palm size computer that runs XP is used.

And a free software "GuideMaster" has been installed

-- to receive the image signals from the guide cam through a USB cable.

-- to process the image signals and then generate the sky tracker control signals.

Software download : http://guidemaster.software.informer.com/

The sky tracker control signals need to be converted into the signals that can be understood by the sky tracker controller.

Thus a "signal converter" has been built.

For the detail, please refer to :

https://github.com/kevinferrare/arduino-st4

Sky Tracker Controller.

This is in fact an Arduino based controller for panorama and timelapse photo taking.

I modified the circuitry and program to include the sky tracking function.

BTW, this controller can control the sky tracker to perform the normal star tracking without the guide cam and computer.

The internal batteries of the computer and the sky tracker controller can last for about 3 hours.

External power supply is also available, just to make sure you can enjoy the whole night without worry :)

A 10000mAH power bank for the computer.

A 12V battery pack for the sky tracker controller.

Of course, polar alignment is still required.

But the time consuming drift method is not a must now.

The set up time has been reduced to under 10 minutes.

And for wide angle lens, the normal sky tracker mode is OK.

That is no need to use the computer, guide scope and guide cam.

Less weight :)