Building a GOTO Mount

A number of folk have commented they would like to see more build threads and also that making astronomical equipment is more interesting to some than the pretty pictures.

I am part-way through a project to convert an ordinary EQ3-2 equatorial telescope mount into a full GOTO system - one that I can hook up to my computer, align and then tell it to find various objects in the sky without having to use setting circles or 'star hopping'.

The project will be a combination of tweaking and adjusting existing parts, making small gearboxes and motor drives and the electronics to control it.

At the moment I just have a simple 'proof of concept' tracking drive. This thread will summarise that and then follow through as I make the finished GOTO system.

I may drop in a few other related accessories along the way.

Neil

I shall be gazing with interest

If ever there was a non-cost-effective of obtaining a GOTO system this has to be it ... Don't account for your time ... remember this is amateur work in the most noble sense of that word.

MichaelG.

Just to whet the appetite, this is the current right ascension drive. I've since modified it a bit. Note the use of gears scavenged from old computer printers. Also an Arc Euro 'Bristol' handle. I will take some photos of how the slightly modified version is put together.

Before reding I wondered what a GOTO mount was, better title would have been GOTO mount for telescope?

What does 'GOTO' mean in the astronomical world?

I now know its it a mount that make the telescope point to a particular place in the sky, but is the name GOTO because its 'goes' to where you tell it?

Just to add to the topics confusion, should this thread been in the 'build' section rather than related hobbies?

Ian P

Q 1&2 Yes, same as that, although 'goto' mounts track as well.

Q 3 - I don't want to wind people up further...

Neil

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Neil,

Given that the Topic is "Related Hobbies" ... I think KWIL makes a valid point

"Building a GOTO mount for the Telescope" would be an exemplary title for the thread.

MichaelG.

Edited By Michael Gilligan on 14/11/2015 22:16:41

Surely it is a 'computer controlled telescope mount'. The GOTO part is just a software feature that is optional. Other software functions might be auto tracking, or star following, or parking at the end of a viewing session.

I a sense you are right Bazyle, because once I have a box that can respond to the commands from a computer (there are a number of standards) all those functions and more become available. I still need to make the gubbins that go between motor and computer, and it's my aim to include at least a basic goto function in it so I don't need to have a computer with me.

My intention was to include the electronic part as this is an upgrade to an existing tracking setup. For a start, it requires a second motor.

My motivation is the frustration of trying to find things a few evenings ago when poor seeing made it difficult to star-hop, and my skills using the setting circles are poor. By the time I had my target centralised in the camera and the camera rotated for a decent framing, I took a test picture and it came out entirely blank.

But this also allows me to focus on other areas that may be of interest. I won't make an extended discussion of the software, for example, unless pressed to do so.

My starting point is an EQ3-2 mount fitted on an EQ5 tripod, fitted with my own gearbox for RA drive using a medium sized stepper motor. The reduction ratio is greater than normally used so the 'slew rate' is modest but the drive is smooth which matters more to me. I have a control box that allows solar, sidereal and lunar tracking rates and fast slewing at various different speeds. I also have a motor/gearbox combination for declination, but I haven't wired it up.

I plan to cover areas such as:

The choosing of gears and a gear ratio making of the simple plate-backed gearboxes. This should be of interest to anyone thinking of using a motor of any type to drive a relatively lightly loaded reduction gear train.

The use of a Polulu stepper driver board, and how to calculate the appropriate drive rates for different output speeds.

My method of designing and making printed circuit boards.

Making a case that is both robust and practical and suitable for mounting directly on the tripod.

Dismantling and regreasing the mount.

Making a practical and usable handset.

Making a stepper driven focuser.

Making a portable 'power pack' with outputs suitable for driving other accessories (such as dew heaters).

I will also looks at thing such as casing the gearboxes - this would be an ideal task for a 3-printer, I may resort to plastic card or sheet metal, or I may try producingan STL file then leaning on someone with a printer

My initial aim is to simply be able to centre a 'known object' and then enter its co-ordinates. I can then either enter a differential move or an absolute move to take me to another object. I shall make the electronic hardware so communication with a computer so I can access other functions through 'Stellarium' or a similar program. I will also include an interface to allow an 'autoguider' to be plugged in and allow more accurate tracking.

Neil

Not quite the same, but could be adapted for the job, a few years back on the Stirling Engine Forum there was quite a long thread for a tracking device for a reflector for a solar powered Stirling Engine, the method we came up with in that case consisted of a solar cell that ran a motor until the relector cast a shadow over it, then as the sun(earth) moved the motor started again. Manual reset for the next day. A computer operated system, with auto reset would be much better.

Ian S C

Neil, were you intending to make/adapt an ASCOM driver for it? Seems it should then be able to interface easily with all sorts of astronomy software, much of it free. One example here.

Ian, on a visit to Jodrell Bank, I encountered a small radio telescope attached to a chart recorder. Using the joystick, I got it to point to the Sun, and the chart pen recorded a rise in the trace. An observer said, "How did you do that?" I said, "Easy, just move the dish until the shadow cast by the central aerial mount disappears, then its pointing at the Sun"

Later, when I set up an old Sky dish to do this myself at home, I had a dish with an offset feed, so I had to invent a device to show which way the dish was pointing. A few strips of wood created a false shadow-caster, and it worked really well!

Geoff

The problem with Ascom is that despite being open source, they are too clever for their own good.

Instead of having simple set of documentation for the communications, you have to download a byzantine 'platform' and try and extricate them from different parts of it. Its a classic example of object-oriented programming - imaging trying to understand how a body works if presented with a set of jars each containing an isolated organ.

After emails asking about access to a single document explaining the standards to the Ascom team went unanswered, I gave up trying to find the wood amongst the Ascom trees. (<Can you tell I'm grumpy?>

Instead I found "iOptron® Mount RS-232 Command Language 2014" which has all the features I need and is compatible with Stellarium.

Yiour sun-finders remind me of primitive IR detecting guided missiles.

Edited By jason udall on 15/11/2015 18:31:37

Thanks Jason,

I'm already stocked up on polulus - geared down ~10:1 a modest stepper has no problems turning the handles.

As for Arduino, I'm a died in the wool AVR addict - the chips in Arduinos. I already have an ATMEGA644P20 lined up - technically obsolete and a bit smaller than the one in the Arduino Mega, but more then enough I/O, timers. PWM etc.

Edited By John W1 on 15/11/2015 20:13:57

I seem to be having a bad day so trying again.

I'm inclined to agree with you about ASCOM Neil. What it's actually doing is buried too deep. I'd wonder about iOptron in terms of their method of aligning especially in unfavourable conditions, if you go that far - it swing back and forth between 2 stars. Celestron like the scope pointing at the meridian. Meads horizontal and pointing north.

I use a spirit level and a compass. It's surprising how accurate that can be. What's wrong with Meade's protocol. It's compatible with just about everything and is in all of their scope manuals.

A couple you may not be aware of and both pretty powerful.

These nuts use x m l and are talking about thin clients but there is some use of a 'pi around. The other problem is that the insist people run bleeding edge Linux distro releases.

http://indilib.org/

This one is a mix and graphics are handled by a tablet. Lot's of reading on this link. The code is on sourceforge.

http://www.cloudynights.com/topic/385710-piastrohub-raspberrypi-for-autoguidingdslrgoto/

John

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