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The DIY homemade German equatorial (GEM) telescope mount.

An introduction to my telescope mount

Here at the Curdridge Observatory we like improve our astrophotography with a practical DIY approach. We feel that spending hundreds of pounds on a commercial telescope mount suitable for decent astrophotography is a dull and uninteresting route to take. Instead we decided to make our own DIY telescope mount. Whilst there is little merit in recommending this irrational approach to others, it does have the benefit of being far more fun than going out and buying the same EQ6 that everybody else owns.

My guide for writing Arduino telescope controllers

early picture of telescope mount diagram of telescope mount oct 2012 of telescope mount


A Gallery Of Telescope Mount Photos

Only members of the mirror-making brigade (and they are even more potty than me) will fully appreciate the large satisfaction you get from doing astrophotography with a homemade telescope mount. Imaging with commercial mounts gives lots of fun and pleasure, but you are always measuring yourself against others with similar equipment. When you construct your own DIY telescope mount, the pleasure you take from each of your images increases by many magnitudes. As a bonus there are no standards to live up to, thus a much greater sense of freedom. If things breakdown, you are the best person to fix them. There are no suppliers or hand-washing telescope salesmen to grapple with, just your self and your tool box.

On the downside, everybody will know you are completely mad. There is a depressing number of modern astrophotographers who look upon DIY and custom modifications as a bit odd and think everything should just work out of the box like a washing machine. These people tend to buy lots of equipment, complain loudly when it doesn't work and produce mediocre results at best. We don't like these people much.

Making any sort of telescope mount is a major undertaking. Making a GEM telescope mount suitable for GOTO and astrophotography and near-unattended operation is extremely daunting. The project was started some years ago with no particular target date in mind. Sometimes I worked intensely on the DIY telescope mount project, and sometimes the project laid untouched for months and months. Finally this summer I have got the homemade GEM mount installed in my observatory and in service.

DIY telescope mount design

The design of the homemade DIY GEM mount is simple in the extreme. Keeping things simple is usually the best. I don't tend to design much in advance on bits of paper. I take a general idea and try my best to foresee problems and improvise accordingly. The design is also dictated by the tools I have. I own a 7x12 mini lathe and a micro-mill, so I'm not going to be making 24 inch worm wheels.

My DIY observatory telescope mount has one key advantage over most commercial amateur telescope mounts. The majority of telescope mounts you can buy are designed with a certain element of portability in mind. This is always going to mean a compromise. My mount is going to be put in my observatory and then never moved for years. Therefore I do not have to design in much portability. As it turned out, the finished thing weights 30-35kg. Undo six bolts and it comes into two halves. Easy to move if you really wanted to.

Some general remarks about the design.

The point here is to make as many of the parts as possible. However, in many cases I had to buy things that I could not make easily, such as the ball bearings and shaft steel. In other cases buying something like a 10mm bronze bushing for 70p is far more sensible than trying to make one. Nuts, bolts, studding and washers are all purchased.

Things I remember buying

I have not kept track of the costs over the years, but I estimate around £350-£500 in parts. The figure for metal stock is very vague as I have a number of sources! Of course, this isn't counting the tools I already own or acquired since starting. If you wanted to do this yourself, you'd need a small lathe, £400, a small mill, £300, and tooling (as much as you like, at least £250+). But making stuff is a hobby so you can argue how much you count those costs. That said, you'd have to be balmy to try.

The point is I never set out to save money. I already had the mill and the lathe, so I've probably not spent much more or less a member of the normal herd buying an normal mount. Whether I've got anything better or worse is impossible to answer. I might not have a better mount, but I have a heck of a lot more personal satisfaction. A rough summary of costs is found here

Things that I particularly remember making/doing

One final thing that is impossible to measure. Time. God alone knows how many hours I've spent either working or thinking on this project. Easily exceeding 1000 hours. You'd be amazed at how you can work solidly in the workshop for a day, and still end up with one tiny part of the whole machine.

Does the homemade telescope mount work?

Please check out the recent images recent images page which shows the images I've taken using this mount.

The all up test I did over the weekend of Easter 2011 proved that there was nothing fundamentally wrong. Various tracking tests show periodic errors of about 20 arc seconds however, one should read much into those figures. The true test of a mount is whether it can take the full load of scope and camera, point at a target and gather 6 hours of 20 minute exposures with round stars on that target over the course of cold winter evening. Such a test is a little way off, but we are certainly hoping to get there!

The current status as of June 4th 2011. I've installed the telescope mount in my observatory and wired up all the cameras and electrics. Just night I was able to have my first session of drift alignment. I got it down to the order of 1 arc second per minute drift in both west and South, and then I got bored. I tried an autoguided image. As it was getting quite late and I was very tired, all we ended up with was one single 30 minute sub frame of the Pelican region. There are numerous faults with the image - terrible focus for one! Click on the thumbnail below - as you can see there is a bit of wobble in the DEC guiding which needs looking at. Strong wind didn't help either! However, on the bright side, I've never done a 30 minute exposure before.

Camera: Artemis 285 (Sony ICX285). Optics: 8 inch F5 Newtonian with Coma Corrector.. Not calibration and only a quick stretch to process. Astrodon 6nm Ha Filter

What is the load capacity of my homemade mount?

I didn't design for a particular load capacity I was just aiming for "very strong". Let's look at the Losmandy product range. The Losmandy GM8 is rated at 30lb equipment. The GM11 is 60lb equipment and the Titan is 100lb. My current imaging rig weights around 30lb and the mount carried this without any sign of a struggle. On the other hand, I'm not sure about putting 100lb of equipment on it. The most popular amateur mount at the moment is the EQ6. I've not seen published equipment load limits for this mount, but I've heard people suggest an upper limit of 55-60lb for an EQ6. My best guess is something in the EQ6 - GM11 category, i.e. 50-75lb load capacity. Mind you I don't have anything that heavy to put on it, so for now the point is a little moot.

One aspect that helps with load capacity is the offset join between the end of the RA axis and the DEC base plate. This means that one of the DEC bearings, the dec worm wheel and clutch, the worm gear and the motor and all the metalwork that holds it all act as a counterweight. Hence my 30lb imaging rig is counterbalanced by 1 modest weight. That counterweight shaft is 20mm stainless steel and can easily take the 3 such weights I own I tested that! I have never understood commercial mount designs where they put the DEC worm on the "telescope side" of the pivot point - it just means you need more counterweights.

High focal length Imaging

I currently image at a focal length of 1000mm and this gives me an image scale of 1.33 arc seconds per pixel. The mount appears to cope with this. One day I hope to do higher resolution imaging, I don't have the scope just yet.

By the way, I should point out I'm not an engineer by trade, I'm a computer programmer. I've no formal training or work experience in metalwork. It is all just a hobby, but as Garfield once said "It is amazing what one can achieve when one doesn't know what one can't do."

Much credit due to these pages from which I gained a great deal of inspiration in the early stages. Link

Arduino Control

This year I have added my homemade Arduino GOTO telescope control system and got rid of the hopeless Meade system.

Here follows a few links to pages on my blog where I've discussed the mount.
Main homemade German equatorial GEM telescope mount project Category page
Homemade GEM telescope mount slew video
Picking up the telescope mount project
Mount slewing video take 2
First test of putting the big telescope on the DIY mount
All up test of telescope mount project
Painting the telescope mount