Me vs. the HEQ5 Pro

Me vs. the Skywatcher HEQ5 Pro

The HEQ5 was ordered as a semi-portable mount for my Mewlon 210 and arrived a week later in two slightly battered boxes. Compared to my G11 (first impression ... "wow, it's well made") my first impressions were more "that's better than I expected" - my last Skywatcher product, an 80ED refractor, was a very strong performer but fit and finish was not its strong point. The HEQ5 is familiar Skywatcher cast-and-painted metal, painted plastic and cheap plastic knobs, rather than the G11's machined and polished looks. At least this time I got a manual, although it seems to be of a one-size-fits-all variety that covers details like collimation of a Newtonian reflector and how to use a Barlow as well as useful information about the polar alignment 'scope. I didn't need to use it to put the mount together, although I did check later to try and figure out what the supplied spanner and allen key were for (I didn't use either of them).

Assembly was easy. The only minor irritations on putting the mount together were a lack of safety screws for the saddle and the difficulty of adjusting the latitude north of about 40 degrees as the adjustment mechanism hits the mount head. Compared to the G11 the whole RA and DEC adjustment mechanism is rather feeble; it seems prone to backlash and very easy to break. The tripod has 1.75" upper legs with retractable 1.25" lower legs which don't look particularly stable but are probably good enough. Two 5.1kg counterweights came with the mount, which go on a rather thin-looking 0.7" counterweight shaft. This is also fairly short which is something of a limitation with a heavy OTA, although it does have the nice feature that it retracts into the body of the mount for transport. The mount, tripod and counterweights are all fairly easy to carry when fully assembled - one of my main requirements.

The mount was purchased to carry a Takahashi Mewlon 210, which it does very well. The OTA seems very stable and was easy to balance. The Mewlon dovetail can attach directly to the HEQ5 mount head, but with this setup there is no obvious way of attaching a safety screw which is something of a concern. The alternative is to use a William Optics saddle bolted to a Skywatcher dovetail (which I purchased with the mount) to attach a Takahashi saddle bolted to an ADM DUP - unfortunately this combination weighs over 4lbs and is enough to make it impossible to balance the Mewlon with the supplied weights.

The mount comes with a nice hand controller, which was clearly readable in daylight. The firmware version was 3.10 (the latest, available here, is 3.12). On power-up it goes through the usual time, date, location setup (much like my old ETX-105) before prompting to begin the alignment process. Slewing is quiet, although the motors have an odd rattle at low speed. The only glitch at first was that pressing UTILITY -> SHOW POSITION appears to hang the controller, so it looks like a firmware upgrade is in order to see if that fixes things. Some searching on Google suggests that 3.10 has some problems. Sadly the DB9 - RJ11 cable that was supposed to be with the mount didn't make it, so I'm waiting for one to turn up in the post so I can update the controller.

01/06/2007 - first 'light'

The weather broke with tradition and allowed me to use the mount on the day it arrived, and I must say that my first impressions are very positive. The hand controller is simple and easy to use, and setup is very quick - I stuck the mount on the deck pointing roughly North (I didn't bother with the polar 'scope), did a one-star align and slewed to Venus. It was a little off-centre in the finder - no surprise - so I centred it and it tracked quite happily with a 5mm eyepiece (483x in the Mewlon) and hadn't left the FOV after ten minutes. That's not a huge ask, but it's not guaranteed either and is exactly what I wanted from the mount. I'll leave the party tricks to the G11/Gemini, this one just needs to be quick and simple.

After aligning UTILITY -> SHOW POSITION appears to work fine, and there are some other nice features of the hand controller like input voltage, current temperature and a live readout of where the mount is pointing. There's none of the complexity (and power) of Gemini, but it seems a nice system.

I couldn't resist opening the mount up for a look...

06/06/2007 - computer control

A new RS232 cable arrived in the post, so I went about updating the hand controller. This was simple once I read the manual carefully; I tried to follow the instructions for "linking with a computer" (p.11), rather than the more relevant "updating the SynScan firmware" just over the page, and then wondered why I couldn't connect. After much fiddling about with different COM ports, cables and the like I read the correct instructions and it was simple. The updated firmware fixes the UTILITY -> SHOW POSITION glitch along with some other enhancements. The hand controller now shows:

Hardware 3.03
Firmware 3.12
Database 2.05

One of my projects with the mount is to collect some PE data from PEMPro, which has become something of an obsession with my Losmandy G11. I don't plan on imaging with the mount yet (and there's no way to upload a PEC curve from PEMPro to the HEQ5 Pro anyway) so it's just curiosity and some mild concern about Skywatcher QC. Getting PEMPro connected to the mount was simple. First up, a few downloads are required

Download the ASCOM platform v4.1 and reboot (important, otherwise you get errors the first time you try and run it).
Download the updated Celestron driver (note that PEMPro requires version 4.2.17, available here, rather than 4.2.15 which appears to be the latest version available from the ASCOM website) and the updated Updated Helper Component (5.0.2) required by PEMPro.
Download PEMPro (at the time of writing I used v2 beta build 29).

Once that's done, it's time to get PEMPro configured. I started the mount wizard and selected 'Other' as the mount type (the HEQ5 Pro is not explicitly listed). The HEQ5 Pro has a 135-tooth worm with an 10:38 period (see left image), then in the next step I selected 'Use ASCOM driver' and then selected 'Celestron Telescopes'. Finally click 'configure'. This gives a number of options (see right image). Scope type is 'NexStar 5i', and the track mode and serial port need to be set. The rest is, I think, optional, although I entered site information in case it was used somehow.

Once that's done the mount needs to be switched on, plugged in to the computer and the alignment procedure needs to be completed in full (if not, any attempt to connect will fail). Once that's done simply click 'connect' on the main PEMPro screen and the mount is connected. Easy!

September 2007 - update

I haven't added anything to these notes since the mount first arrived, not because it isn't being used but because I haven't really changed what I do with it: generally I just put the mount down facing roughly north, turn it on, one-star align and then goto is reasonable for visual use. With a little more care it's good.

However, i've spent enough time with it to form some impressions. The hand controller is nice and easy to use and the mount performs very well for visual use, so I'm pretty happy with it. However, stripping down the mount shows a rather less encouraging picture; Skywatcher's quality control department really didn't try too hard with my mount. Metal shavings in the DEC bearing grease are unacceptable at any price point, while the hand controller firmware still has rather too many bugs, the build of the mount isn't great and the insides are liberally coated in grease, regardless of whether or not it's on something that moves. I've stripped the mount down and improved things somewhat, but it really could use a full strip-down, clean and regrease at some point. So, in general, I think it sums up Chinese equipment; the performance and features are very good for the money, but the build quality would be unacceptable if the mount cost more than it does. Other mounts that can match the HEQ5 pro's features are much more expensive - a Losmandy GM8 with Gemini would be more than twice the price - but, equally, they would be better made and better put together. For what I paid i'm still happy (well, apart from the metal shavings...).

A few things can be improved. I'm changing the rather flimsy tripod for a wooden one made by Berlebach, and will probably replace the mount head with one from Ambermile to allow me to bolt on the Takahashi 'hockey puck' adapter for the Mewlon. I'm also contemplating replacing the sliding counterweight bar with a fixed, thicker one, but that may be more effort than it's worth.

December 2007 - update

The mount continues to do what I want for visual use, and i've yet to try imaging. The Berlebach tripod is an improvement over the standard one although it's also considerably heavier, making the mount a bit of an effort to move any distance. I've also discovered that the hand controller really doesn't like cold weather, and becomes very sluggish - the mount is also prone to occasionally locking up in the cold, forcing a restart. I'm not quite sure what triggers this, but it's rather irritating. In general I'm a bit ambivalent towards the mount; the unreliable electronics are a continuing source of frustration, but most of the time it works well for what I want from it. When I get fed up with it I have to remind myself what it cost - if i'd spent twice as much money for a GM8 then i'd probably be agonizing over having so much money tied up in a mount that doesn't get a huge amount of use...

Part of the issue is that I haven't spent a huge amount of time trying to understand and tune the mount. I spent night after night analyzing the G11 and Gemini to understand the assorted glitches and niggling problems, but this mount gets very little attention - I tend to dump it outside, power it up, and just reboot it if it hangs. I think I see a 'project' coming on...

January 2008, it's cold...

...and the mount keeps locking up. I think this is down to two things. Firstly it's extremely sensitive to voltage, so if the power supply can't maintain 12V in the cold then the mount locks. This is the cause of most of my problems, but when it's very cold the lock-ups seem to be caused by the mount electronics themselves. This is apparently a `known issue', but still rather frustrating.

February 2008, polar alignment

One thing I don't much like about this mount is polar alignment. For visual use it doesn't matter much, and the mount performs perfectly well without bothering with alignment at all. But i'm now doing some lunar imaging, and that requires some attention to alignment to avoid field rotation becoming an issue - not as much attention as long-exposure imaging, but some.

There are lots of problems here. The polar 'scope is behind a cheap plastic screw-on cover which seems very easy to cross-thread in the dark. And the polar 'scope itself seems to have been designed by someone who has never used a telescope; the markings are crude, and the illuminator is much too bright and washes out the field of view. It's not well aligned with the mount, and compares very poorly to the excellent G11 polar 'scope. Another problem is that the mount's adjustment knobs are awful (especially the altitude-adjustment knobs). They are made of cheap - and decidedly bendy - metal and two knobs are used, so you have to slacken off one and tighten the other. This makes fine adjustments very hard. I'm tempted to try replacement ones available from AstroDevelopments to see if that improves things.

If I was doing long-exposure imaging then i'd drift align, but lunar imaging is precisely the sort of area where a good polar 'scope makes getting reasonable polar alignment quick and easy (drift alignment, while easy once you have the hang of it, can't be described as quick). The G11 had a great polar 'scope and took seconds to get close. Sadly the HEQ5 doesn't, and the process is much more painful.

April 2008

I've got a new 3500mA regulated power supply from ModernAstronomy.com and it appears to be much more reliable than the old one, and managed to cope with the recent cold and snow. Hopefully the lock-ups are just caused by the power supply.

A new 3.21 firmware appeared on Skywatcher's support site, so i've upgraded to that. No immediately obvious changes, but it fixes inconsistent Double Star and Variable Star Catalogs and adds an interesting PC Direct Mode. The hand controller now shows:

Hand Controller Hardware 3.03
Hand Controller Firmware 3.21
Database 3.21
Motor Controller 1.06

June 2008, PEMPro at last

A year after I got the HEQ5, I finally got round to acquiring some PEMPro data. This used an 80ED and the Lumenera SKYnyx 2-0M (2.38"/pixel) to capture four complete worm cycles (approximately 50 minutes of data) in good seeing. The generated PEC curve doesn't look too bad:

Peak-to-peak periodic error is 23.6 arcseconds, which is pretty much what's expected for a mount in this price range. However, the RMS error is 8.55", which indicates that the curve that PEMPro generated isn't a great match to the actual data. This can be seen pretty clearly by comparing the raw data to PEMPro's periodic fit

So it looks like there's also a fair bit of non-periodic error in the mount, caused by vibration, random binding/releasing etc. The worst-case errors appear to be on the order of 1"/second or so; at image scales of 2.5"/pixel or higher (e.g. a 600mm focal length refractor) this shouldn't be too problematic to autoguide out, but would be a major limitation on higher-resolution imaging.

The dominant causes of periodic error can be seen in the power spectrum:

This is dominated by a large (7") peak at the fundamental frequency of the worm gear. These are errors that occur once each rotation of the worm, and are probably an indication of the quality (or otherwise) with which it was made. There's also a significant contribution from the second fundamental, occurring twice each worm period, from the worm gear being not quite round. No other fundamentals are visible.

So what's the conclusion? Well, the PE is much as i'd expected - not great, but, at short focal lengths, something that's easy enough to autoguide out. The first fundamental strength and the RMS errors are much higher than my old G11, and these are a reasonable indicator of the quality of machining of the mount. But, all in all, not too bad. The major problem is the fast random errors; these would present much more of a problem than the mount's periodic errors, and would be the first thing that needs addressing if I was going to use the mount for serious imaging. Quite what is causing them is something of a mystery, although I wonder if there's something trapped in the gears/worm assembly somewhere. I've already had to clear some metalwork from the mount, and wonder if there's more to find.

Looking at the raw data, there's an interesting feature between 8:00 and 10:00 of the worm period, where three of the worm cycles have the problematic fast sawtooth error, while a fourth is smooth. All of the worm cycles go through smooth patches before resuming a sawtooth motion, which makes me wonder if something is catching but occasionally working itself free. Speculation at this point...

That's all, folks

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