Building and Using Astrometry.Net on MacOS

Why Astrometry.net on MacOS? because Macs are built to take bullets and have long battery life. Unfortunately building almost anything on MacOS is ten times as hard as doing it on Linux. There are some (old) instructions for building Astrometry.net on MacOS here. However they are dated 2012. The instructions for Homebrew work fine on Yosemite with python 2.7:


However, there are some missing steps:
With the above conditions met, Astrometry works fine.

Takahashi EM-1S RA Drive Analysis

I had a look at the innards of the Takahashi EM-1S RA drive, because I wanted to see how hard it would be to convert it to center-positive. Quick answer: it's hard.

Here is the outside of the EM-1S RA drive panel. It is obvious that there is no way to switch from northern to southern hemisphere tracking:


Inside, we see a Sanryusha P43G stepper motor with 24 pulses per revolution and a 1:500 gearbox. This is the same motor in my EM-11 Temma2 Jr. and presumably many other Takahashi mounts.


The circuit is fairly simple but full of obsolete components.


We see the following IC's:
  • IC1: OKI M5562, Google is not very helpful, but most likely this is a clock generator IC
  • IC2: Toshiba TC4013BP, dual D-type flip flop, probably the logic generator for the stepping waveform
  • IC3: TDG2004, my immediate guess was this is a variant of the ULN2004 stepper motor driver
Supposedly, there is a switch on the board to enable southern hemisphere tracking, but there is no such switch here. It's fairly apparent that in order to make this mount useful in the southern hemisphere, the wires from the motor to the ULN2004 will have to be switched around - a highly annoying chore.

With some tracing, we can determine that the topmost two wires from the motor are the commons (the motor is a 6-wire unipolar with split center tap) and the other four wires are the four phases.

Therefore, it should be possible to reverse the direction of rotation by swapping the four wires that go to pins 13, 14, 15, and 16 of the TDG2004.


Repairing Astro-Physics GTO Hand Pad Cable

The cable on my Astro-Physics GTO hand pad cable (AP part number E0190CABLE-E) had deteriorated over time. The rubber insulation had peeled and cracked, exposing the shielding and conductors underneath.

I repaired it temporarily using black duct tape but the tape left a sticky residue and was pretty ugly. Astro-Physics wants $75 (plus shipping) for a replacement cable. Good to know I can buy the part, but I wanted to save some money.

While at Popular Bookstore last night, I saw a kiosk with a strange Play-Doh like adhesive, Sugru. A video was playing, touting various wonderful features. The adhesive was quite expensive (S$ 19.90 for eight tiny single-use packets) but I figured it was worth a try.

This adhesive can also be purchased on Amazon, for $19.58 - so the price at Popular was actually lower.

And.. 12 hours later.  The adhesive has hardened into a somewhat-flexible silicone rubber which feels pretty tough (the red material around the handpad cable at the bottom-left of the photo below). I would say this is a qualified success!


A Tale of Two Taks

I recently was able to buy a used Takahashi EM-1S from Yahoo Japan Auctions. Generally, Japanese sellers don't ship out of Japan, but From Japan made the process much easier. There's not much in the way of buyer protection, however. More on this later.


I already own a nice Takahashi EM-11 Temma 2 Jr. which I've reviewed in the past (the mount on the right in the above photo). It is supposed to be my travel mount (for when I travel to the Canary Islands.. someday..) but ironically I am not too keen on traveling with it because it is rather expensive and would be subject to the slings and arrows of outrageous fortune in the checked baggage.

Incidentally the EM-1 (the mount on the left) has a Canon 300mm f/4 L telephoto lens on it, and the Kenko Lens2Scope adapter, which is a 10mm eyepiece (of narrow field.. I estimate 40 degrees) and erecting 45-degree prism. The Lens2Scope is useful because when traveling, you can use the camera lens as both a small telescope and for astrophotography.

But I digress.

I got the EM-1S for the unheard-of price (by Takahashi standards..) of around $550. Based on the serial number it is a 1991 model, about fifteen years older than my 2006 EM-11 and making it 26 years old. It did not come with a counterweight shaft or weights, but I thought that was fine since I have an extra counterweight shaft and weights.

And that is where the good news ends. It arrived with a bent RA worm shaft. I tried to straighten the shaft on the RA clutch knob with a pair of pliers.. and the shaft snapped clean off. I was able to successfully straighten (more or less..) the RA worm shaft with a block of wood and some judicious whacks with a hammer. The shaft isn't perfectly straight but the worst of the RA spur gear wobbling has been taken out. I hope I didn't damage the worm with that Lizzie Borden activity..

The EM-1S has a tangent arm in declination, not a full worm. Oops! and it's quite hard to turn. I cleaned and re-lubed it but the DEC slow motion still binds a bit and does not feel smooth. Also, it seems to not have ball bearings, but rather sleeve bearings (like the Vixen Super Polaris and Great Polaris of similar vintage).

The worst bit is - my particular EM-1S is missing its famous Takahashi polar scope. Which is quite annoying. I do not know if I will get any satisfaction from the Yahoo Japan seller, since they stated that "only the parts shown in the photos are included" - and the photos showed the mount with its manhole polar scope cover screwed on, and no evidence of a polar scope.

In any case: the manhole covers on both the EM-1S and EM-11 fit each other. I suspect the EM-11 polar scope would fit as well but I don't want to remove it and potentially ruin the alignment. They both have the 35mm dual bolts on the top (I was able to use the Berlebach dovetail clamp from the EM-11 on the EM-1S). The tripod bases are also compatible. Even more impressive, both mounts use the same Sanryusha P43G stepper motor with 24 pulses per revolution and a 1:500 gear reduction.

I hear that the current small Takahashi mounts still use this model of motor. They must have a massive warehouse full of these motors somewhere.

The EM-1S does seem to have a larger-diameter RA worm wheel and is a bit lighter than the EM-11. It is powered by a rather large center-negative 6V battery pack, I will check if I can power it from a USB power bank.

Overall I am a bit underwhelmed. The old Tak isn't at the quality level of the new one, although admittedly it is better-built than Vixen mounts of the same age. And the lack of a polar scope peeves me - although luckily most of the time I won't actually be using the polar scope since I'm at a low latitude. I will try to see if getting a Takahashi polar scope is not out of the question cost-wise; if cost is prohibitive I will probably find someone to machine an adapter so I can use the cheap CG-4 or CG-5 polar scope in the EM-1S.

Was buying the EM-1S worth it? I will give a qualified yes.  P2Z, P2, and Space Boy mounts on Yahoo Japan (the mount I really wanted) sell for high prices (95000 JPY or $900 if you're lucky, but more typically up to $1500). I wanted a cheap Tak mount with setting circles for travel and got one.  Hopefully the periodic error is low (-er than my Vixen Super Polaris) because that was my goal.