T-Rex Alt-Azimuth Mount
The following is a product of my constructive lunch hours at work. I love to give back when I can because reviews have always helped me very much before a purchase of any equipment. I hope you guys that are considering the T-Rex will find it helpful. And although the mount is still in its honeymoon period, there have been a few quirks with mine that may shed light into the future of this fine mount. I’ll try to make this as informative and as detailed as I can.
Every amateur astronomer needs an altitude-azimuth mount. There are times when it’s cloudy and taking all of our heavy equipment out for a mere couple of hours just isn’t feasible. Other times, we may have to get up for work the next morning, and a grab and go setup becomes invaluable. Personally, I either run out to my balcony which conveniently faces the ecliptic, or travel 50 miles out to Long Island. In either case, I do not mind carrying the bulk of my equipment which collectively weighs about 120 pounds, (160 total,) but I have to be able to squeeze at least four hours out of the session. A normal observing run for me is eight hours, because I only get out once or twice a month due to conditions, and the fact that I work the PM tour. Also, an alt-az mount makes a great platform for observing terrestrial wonders that are too high or so far away that we could not otherwise enjoy them.
A few months ago, after the purchase of a Takahashi refractor, I got this brilliant idea to install an old Vixen Porta II mount on a Meade standard field tripod, the one that supports the LX-200 series. I drilled three holes for the mount on the top platform, bolted it in, and drilled into the casting of the Porta, screwing an old photo tripod handle into it. The spreader rods also needed to be shortened because the footprint was just too wide for the balcony. After the modification, the tripod was able to get much closer to the railing, hence the scope was able to get closer to the zenith. (Yes, I have an overhead balcony.) I then added the Vixen flex cables and was set. Even though the tripod was overkill for the Baby Q, I felt it was necessary because while most times a good quality photo tripod would have sufficed, there were always those nights with the sneaky rogue winds that would try to bully the equipment into toppling over. The Meade is 20 pounds, and made a great foundation that I grew to have much confidence in. However, a problem did eventually manifest itself, and that was that it was getting extremely annoying to find things off the sky chart. Yes, grab and go is fun, but what happens when those clouds that were supposed to linger begin to hop along in differing headings? Then a serious observing session beyond g&g commences. And all you have are cables in your hands and a sky that without a computer, seems endless in all directions- although it is great fun to aim an instrument anywhere and just search for whatever. Finally, we could all do without those headaches and eye fatigue that creep in after panning and searching for something in those ever-widening concentric squares.
So I decided to get an alt-az mount with digital setting circles. After much research and playing with different mounts at NEAF, and bothering club members at various fields, I settled on the T-Rex, sold in America by Deep Space Products. I selected the Rex for its looks and obvious capabilities, but a good portion of my decision rested on the fact that it accepts these nice long slow motion cables, as I am not into nudging. To me, if I can’t have the heads of the cables resting in the palms of my hands while my hands are on my lap and my head is in the eyepiece(s), I’m not happy. Kind of like when my friends say to me, Why don’t you get yourself a house on Long Island with a big backyard so you can have your own observatory? And I reply, Because if I can’t throw my backpack on and walk to work, I’m not happy. Some things, as Dr. Phil would say, are dealbreakers.
My experience with Ed Thomas of said company was really pleasant. Since I ordered the white version, it took just about under a month for the unit to get to me in the east. Ed was responsive to e-mails and went out of his way to keep me posted on delivery. I wish I had additional business to conduct with him.
The T-Rex comes very well packed and shipped. In fact, every, and I do mean every, piece and bolt is drowned in plastic or bubble wrap. When I removed the head from the box, even though I already knew how much it weighed, I was surprised at how heavy and solid it was. Now, you’re probably thinking, Is heavy a good thing? Yes, to me it is. I will be using this mount mainly for my cherished Baby Q, which, as we all know, is a very valuable instrument, along with the oculars, and I do not want to worry about the solidity of their mounting. Actually, I was so impressed with the Rex that I felt compelled to purchase the Celestron Edge HD 11” and its carrying case just so I could have another scope to use with the mount – more toward the upper end of its capacity. Off topic for a second as they say in the forums- this scope rocks big time. It is definitely the best SCT I have ever owned- probably because of its off-axis performance. The beautiful ivory tube doesn’t hurt either.
The mount comes in a very sturdy carrying bag that has a reinforced pad on the bottom to accept the weight of the heavy body. It has a separate bag for the spreader, and even a padded piece to keep in between the tripod legs so they do not rub together. Believe it or not, the case receives the entire assembled unit, which is a great plus. You just pull it out, stand it up, and fish out the computer which lives in a dedicated pouch of its own on the side of the bag. The entire thing weighs 40 pounds, minus the scope itself.
When you really look at the details of this mount, they are rather impressive. The clutch levers are adjustable by pulling them up and letting them go. This keeps them out of the way of any moving parts, including you. When you place the mount in the case for transport, you must remove the clutch levers (they’re actually called clamp handles) because they are made of plastic and will surely break when the heavy mount shifts in the case. Nice bolts are included to cover the holes and you should use these to seal the openings from contaminants as these are critical greased surfaces that should be kept clean. Additionally, the flex cables are not removed with inconvenient hex bolts. They are attached to adapters which you can Locktite and firm up permanently, like the tripod bolt, then turn the toothed heads on the ends of the cables themselves with your fingers to release for transport. The computer tray slides on to and off of a more permanent post which I myself have Locktited onto the mount. (I fly RC helicopters which is why I use so much Locktite.) Simple but ingenious.
At the field:
I placed the Baby Q in the included ADM dual dovetail saddle (which you may turn and remount at an angle more to your liking) and clamped it down. As you can see in the pictures, I drilled two holes in a Celestron dovetail, worked a little Dremel magic and mounted the Tak clamshell on it. I obviously wanted the freedom to slide the scope back and forth, and change OTAs without removing the mounting plate. Despite what any manufacturer claims, we all know that any mechanical design will function better if it is balanced correctly. Whenever a company boasts that you don’t have to rebalance when you change eyepieces… well, that may be true, but performance will inevitably suffer when you have to tighten the clutch or similar design to compensate. I will later find that both OTAs will fall out of dynamic balance when the scopes are near the zenith because the 21mm Ethos and the Televue binos with 24mm Panoptics are just too heavy not to cause an off-axis dilemma. It’s also a bit more complicated than adding an additional weight somewhere just to adjust the static balance. I will have to order two dimensional weight sets and mount them on opposing sides of the problem because of where the imbalance originates. A couple of pounds should do- to remove the stiction (static friction) in the extreme altitude movement. It is important to clarify that this occurs only through the altitude slow motion control. As we all know, a perfectly balanced instrument should stay put wherever you leave it.
I also notice that if the OTA, especially a big one, is not balanced, you can feel the force from the scope being lifted from the zenith to almost horizontal transmitting to the worm gear, especially if there is play. Eventually, the two mating surfaces are going to sustain damage from the constant friction of rubbing together. The point is, balance, balance, balance. The outdoor pictures were taken the night that the equipment was not balanced yet, because I wanted to get familiar with my new scope and mount. However, so I would not harm the new gears, I did take the precaution of lifting the scopes with my fingers when I sensed there was stiction coming on.
If you find yourself with a scope that is just barely out of balance, you can cheat a bit and, as in my case with the 85, push it forward and find a balance point between 45 degrees and the zenith instead of the horizon (90 degrees) and straight up. This will allow balance to hold farther toward the coveted zenith, where the best views are found. This works well and is doable since who needs good balance in that void unless you’re doing terrestrial work. Keep in mind this trick does not work with the HD 11 because only half the dovetail ultimately ends up in the ADM clamp which of course utilizes only half the surface area which of course makes me nervous, which of course would make me feel downright stupid if the $3,000+ HD 11 fell off and rolled away.
I will include the specifics with pictures on attaching a Losmandy rail with its 2D counterweight system because the Celestron Edge HD 11 is becoming a popular instrument these days due to their reported quality. There is a good chance you will consider this scope for your T-Rex, so here is a description of what you are in for:
The fix for the HD 11 turned out to be a real unexpected headache. I am used to Meade optical tube assemblies that have screws in the castings for accessories that just screw out, and you can replace them with the longer screws that came with said accessory, to secure say, a Losmandy balance rail. The HD 11, I discovered to my horror, has a screw with a nut which turns with it as you attempt to remove it. And where do you think that nut is? What the logic to this is I’ll never know, because opening up the instrument and revealing the primary and secondary mirrors to contaminants and fingerprints as well as messing around with the corrector’s axial tilt all just to secure a small bolt is just weird. I don’t know why they would make this so. Then to top it off, they have these two collets that protrude from either side of the outer casting that hold the corrector cover in place. But they also prevent the removal of the retaining ring- and maybe the corrector itself. Now I had to worry about the perfect collimation the scope had. They claim the assembly is laser aligned, but does that go for the removal of the entire corrector or just the fastar unit? Only a night out and an exacting star test will tell, and I’ll let you know how that went by the end of this review.
Well, I did not have the nerve to open the system because the scope is new and I just do not want to contaminate the interior or risk misaligning things related to collimation. And besides, those screws are offset from where the Losmandy had to go anyway. I installed double-sided tape on the rail and pressed it into the two castings and added the weight for trial. The two dimensional counterbalance was perfect, but now… was I to drill into the castings to mount the rail? Can you picture the shavings being sprinkled all over the interior like some freaky metallic rain? That would have been worse than simply removing the corrector! So after much thought, I cut the ends off the Losmandy rail and mounted one on the end of the front casting OUTSIDE the corrector (LOL, I love getting away with stuff like this) and installed the weight and sat there to see what would happen. Well, the balance was perfect with the weight screwed all the way out with the binos, and when I need to use the Ethos, all I have to do is twirl the weight up to the base of the bolt since the Ethos is not as heavy as the binos. All worked out perfectly, and I did the same to the FSQ-85 with the other end of the chopped rail. Icing on the cake was that I did not have to cover the beautiful Edge HD sticker with the long rail. Coolness. -Please check out the pictures of everything repaired as far as backlash (we’ll get to this) and balance- this, about a week after that night out. I have subsequently been out with the equipment and all works perfectly, I can report. I was also very pleasantly surprised that the HD 11 was very stable on my balcony, with a 18mph wind whipping out of the northwest. I would have thought that the larger profile scope would cause steadiness problems in the eyepiece, but all observations were nicely still. Vibration pads used.
Slow motion control “boxes”.
First let me say that it is important to not only turn the adjustment screws clockwise/counterclockwise quite a few times in the following project, but to understand what each one does. If you just sit and stare at their locations for a few minutes, you should get a good idea of the functions of each.
I found it necessary after the first night out to remove the rectangular plate and adjust the ten screws around the worm in order to achieve a perfect mesh on the declination axis. I discovered through trial and error that the best way to execute this “operation” is to first make certain the shafts are secure by merely checking the inner set screws, then leaving that adjustment alone unless you feel it necessary to go back to it. The reason I left it was because the worm turned perfectly inside the shafts, so I thought it best to leave well enough alone. The large brass screw I felt was best to loosen first because I didn’t want the mesh of the gears so rigid when I would adjust them. If I tightened the four hex bolts to close up the project, what happens to the worm if it’s not lined up- but can’t give anywhere? I then loosened the small hex screws designed to push the box away from the mount, and placed the blade of a flathead screwdriver down flush against the hole where they exit. I continued to lightly back them off and then turned the wrench with two fingers so they would come out and rest against the blade. Now they were all perfectly even. I then removed the screwdriver and turned the screws one half of a turn, from the 12 o’clock position to the 6 o’clock position, watching the end of the wrench closely. Now they were even and protruding out of the bottom of the box the exact same amount so there was no tilt in the assembly, hence an awkwardness in the mesh. (Grease can only cure so much untrueness.) I bolted the box back on and found that the distance was perfect, and the mesh was right on the money. -This step was already tackled many times before finding the exact amount to turn the wrench. Like bad takes in a movie, I did not hit it the first- or the twentieth time. In fact, when I began, the backlash was so pronounced that when I lifted the scope down from the zenith, the handle could be felt moving through its play and contacting the shallow ridges inside the horizontal barrel of the mount. BTW, I was happy to have the perfectly meshed and precise right ascension axis, as it gave me an accurate goal to shoot for. Without it, I would never have known how perfect would feel with a well-meshed gearing. I kept going back to it to use it as an example. The process took me about three hours, because it’s such an exercise in trial and error. I suggest that once you get the correct mesh, you must remove the box, check it, compare it with the better axis, then replace it. Don’t forget to lightly snug up the brass end bolt so there is no play in the sideways worm travel in the box. Also very important is to tighten the four outer hex bolts very well in altitude, as the gears inside this box bear the load of the OTA. If you are unbalanced, well, you get the ugly picture. -So is my adjustment really as good as the factory could have gotten it, or does it just feel that way? I can’t see inside, so I’ll never know. Hopefully, it won’t bind or develop play over time because I did not hit the sweet spot.
I have also discovered play in both axes with regard to locking the clamps down. When I do, there is a 1mm amount of nothing that allows the instrument to feel sloppy. Through the eyepiece, the entire FOV will seesaw. I am in the process of finding a fix and by the end of this review, should be able to report that all is well. (I like to keep things in real time for dramatic effect.) –To understand what I am referring to, if I were to line up the two marks on the barrel and tighten the clamp down, I could still shift the scope where the marks would move away from each other about 1mm. The same goes for right ascension. Obviously, nothing should move at all when the clamps are secured. I have a feeling I have to revisit those boxes.
The complete version of the T-Rex comes with absolutely everything you will need, especially the Sky Commander XP4 Flash computer, which will guide your push-to efforts around the sky. It comes with a couple of coiled cords (attached to each other in a Y configuration) which are labeled RA and DEC. They both can be inserted neatly into their respective jacks, via phone-type plugs. Back to guiding your push-to efforts- My FSQ-85 and 21mm Ethos have the desired object in the field of view all of the time, which is really cool. (Note how I meticulously align in a coming paragraph.) The option of a third star alignment for narrower field optics would be nice, where the computer could build a more stable “table” in the sky. With the HD 11, the computer does not perform as well. In fairness, there are other variables at work when the instrument starts to get bigger. Curiosity had me test how fast I had to twirl or tilt the mount to outrun the alignment and I am able to report that you really have to move your scope unnaturally fast to do this, or inadvertently bump it fairly hard. The night I took the outdoor pictures was a seven-hour observing session. By the end of the night, the Sky Commander still performed exactly the same as when I did the alignment so many hours prior.
The fast track setting is not necessary, but I use it just the same since I have to bring my large Kendrick astro power pack for dew prevention anyway. It also runs the heater inside the Sky Commander itself to keep the display happy in colder weather. Lastly, it allows one to keep the backlight illumination of the display on HIGH, because the MEDIUM is a bit low. During that long session, the display was on high continuously and gave no hint of trouble. You also don’t need to be concerned with using the STANDBY mode with that kind of power availability. If you use the fast track setting with a 9volt, you will find the battery runs down very fast. There is a nifty battery meter in the menu to keep track of power, and I did this deliberately (for this review- I’m not normally that suspicious) to find if the manual was exaggerating the fact that this power drain would occur. The manufacturer was spot on, as the battery quickly ran itself down in fast track mode, indeed seemingly drawing an extra 50-100 mA. If you decide to use the external power option, you may remove the 9v battery from the compartment. Please note that I have found the mount to be just as accurate with a 9V and no fast track, but more sensitive to the speed at which you move it, losing alignment easier.
The computer assumes that the mount and scope maintain axes that are always orthogonal, or perpendicular to each other, due to the dedicated celestial coordinate system. Simply put, the computer calculates (thinks) that way. The reason I mention this is so if you have a problem with the mount keeping its alignment, you may feel the need to rule out the technical issues first before assuming it is the operator turning or tilting the head too fast. Another aspect would be to question whether or not the encoders are representing the precise angular position of your declination and right ascension axes. Rest assured it is obvious to me that the mount’s orthogonality is not an issue, as it is always solidly perpendicular, and the encoders are all installed correctly with regard to orientation and rigidity.
As for alignment, I have found that leveling the tripod (the head has a bubble built in) and using a reticle eyepiece puts you on the right track for accuracy. If you don’t, there is a REALIGN feature (kind of like Meade’s high precision pointing) that can keep things pretty close to the desired object. Having said this, it is difficult to know if you have landed on your dim object, as the accuracy, as mentioned, is not that fine with longer focal length instruments, which is probably what you would be using to find the dim fuzzies. You will have to make a couple of concentric circles from where you landed all zeroed out. BTW, I used the 9mm reticle and the 3000mm focal length of the HD for alignment. That’s as pinpoint as you can get.
Note: I am used to the electronic elegance of my extremely accurate LX-200, and still was very impressed with the Sky Commander’s performance.
The first thing that is necessary to do when you receive the T-Rex is run through the setup menu and make certain everything is set for this mount, so that all components will work happily together. The setting choice for the T-Rex mount (don’t forget these two components, the mount and the computer, are separate from each other, and were not specifically designed to work together.) itself will be DOBSONIAN, the hemisphere NORTH, (or SOUTH), RA direction NORMAL, DEC direction NORMAL, RA and DEC encoder resolution 4096, FAST TRACK we covered, Sidereal Clock ON, RS 232 Baud Rate 9600, and Si Tech Mode OFF. Very simple.
The main operating menu has cool features including:
-Search and ID
-Limit search magnitude
-Realign on object
The installed catalogs are (I have assisted on the unusual ones):
-NDS (Named Deep Sky)
-NST (Named Star)
-ARP (Arp peculiar galaxies)
-HIC (Hickson galaxy clusters)
-S (Special Objects)
I won’t go into details on the working of the main menu because like me, you may enjoy discovering everything for yourself without being prepared ahead of time. Trust me when I tell you that it is fun and easy. In closing this category, I highly recommend the use of an external battery.
-Extremely attractive. You’ll read other alt-azimuth mounts described as beautiful. You haven’t seen beautiful until you see the T-Rex in white.
-Nice feeling of pride in ownership.
-Very well and robustly constructed. Yet at the same time, designed with the user in mind.
-Very sturdy with stock GMT-128 tripod.
-Comes with a choice of high quality knurled metal handles, or long flex cables. They are all an absolute dream to use. Other mounts have you reaching up for the slow motion controls, if they have them at all. This gets old very quickly, as you learn how heavy your arms are. Even the Rex’s shorter metal handles sit where they can easily be utilized in most observing positions- by the user facilitating the use of his elbow for support along the torso or thigh.
-Very smooth with no backlash whatsoever, once you tweak the adjustments. Of course it should be noted that you may have better luck than I did in this area. Your T-Rex may come perfect from the factory.
-The slow motion gearing is easily accessible through plates with standard hex bolts. Want to throw a bit of grease in the mix? Go ahead. It is a very user friendly system.
-No counterweights to deal with at all. Great!
-4096 step optical encoders are nicely and securely installed, safely inside the body of the mount, isolated from moisture, dirt and impact. They are direct-coupled for a 1:1 gear ratio.
-Clamp handles are fun and easy to use.
-Because there is no tracking, the mount is dead quiet on the quietest of dead quiet nights.
-Even with the HD 11, there is absolutely no feeling that you need any counterweight on the other side as the mount turns without effort in azimuth.
-Computer is fun and easy to use. Standby feature is cool. Won’t lose alignment while conserving battery power.
-You are able to push the scope around and continue the movement with the slow motion cables without having to stop to lock and unlock the clutches.
-Excellent payload capacity. Assembly does not flinch with the Edge HD 11, even with the additional few pounds of (scope) counterweight and gear.
-Heavy. This is a good thing for me. I like knowing that my valuable scopes are secure. At 50, 6’, 190 pounds, (and a runner) this weight does not cross that threshold into being bothersome. Obviously, YMMV. In any case, I think the price point and weight are more geared for the serious and advanced observer.
-Steady as a rock even in windy conditions.
-Accessories available such as a custom pier and extra long slow motion cables to accommodate very long refractors. Also easily obtainable are different tripods, bases and adapter plates.
-The designer of the mount is easily accessible in case you have problems and need advice.
-Nearly $3,000 complete. If you have inexpensive equipment or you are simply a casual observer, you probably won’t want to deal with this aspect.
-Heavy. Again, if you have inexpensive equipment or you are simply a casual observer, you probably won’t want to deal with this aspect.
-On my particular unit, there was backlash in the declination axis, and play in both axes after being locked into position. A less patient person may damage the gears when attempting this repair. It doesn’t take much. For that kind of money, things should arrive in perfect condition.
-Although well-intentioned, the declination slow motion control handle should not be the same handle that lifts the load of the OTA, as the mesh of the gears absorb some of this force. This is evident as you try to turn the handle while you are raising an out-of-balance load. The handle won’t turn. Another fixed handle below perhaps?
It is my opinion that the T-Rex is the best altitude-azimuth mount on the market today, largely because of its slow motion capabilities and the choice of long or short handles. Having claimed this, one should also keep in mind that it is a geared mount. Speaking for myself, I will keep on top of things as far as lubrication goes, especially since I am now intimately familiar with the inner workings. As for the play in the gearing after the mount is locked down in both axes, I contacted Barry Gooley, the designer of the Rex, and president of Kokusai Kohki, the company that makes the unit, which is a brick and mortar store in Japan. He promptly returned my e-mail with very specific instructions on how to take care of this problem. He also indicated his door was open in case I still could not find a solution. He basically walked me through the procedure I had already completed, so I felt that maybe I should go back and tighten things up a bit. If you recall, the RA axis that appeared perfectly meshed actually wasn’t. I found the same problem in the other axis that I thought I repaired, but it too was still a bit loose despite feeling perfect. I learned that even though the backlash is seemingly removed under normal slow motion controlling, when you lock the axes down, they can still have play. So now both are kind of firmed up a little too much I feel (felt), but all play is gone. As long as it does not bind or grind, I’m happy. I tested it by distributing the existing grease, and going completely around on both axes. Tension is even and smooth, albeit just a bit snug to turn. As long as that minute see-sawing is gone, I’m fine with it.
The T-Rex is great to have on hand as a primary mount, or supplemental equipment to compliment others that may have different qualities. I suspect it can handle weight as far up as a C-14, although don’t quote me on that, as I probably wouldn’t go farther than an 11 myself - (If I had a 14 I am quite sure I would try it.) Does this capacity warrant the heavy price tag? I say yes. Because it’s not just the capacity. When you use this mount, it’s mount nirvana. The thing is so smooth and such a joy to swing around using the clamps; tighten a little… then a lot… then not at all. Swing, swing… I admit that I didn’t expect to be working on my new toy so soon. However, I happen to be an avid tinkerer, and it actually gave me a thrill to open it up and play with the guts of the mount. Quite a difference from my cheapo that I used for quite a while and I thought I was happy with. But when you look at the picture of the Meade field tripod with the Vixen Porta II, you can see that there is no way to use any other type of instrument, whereas the Rex will carry many, many more. So I am happy with my decision. Also, when I am in the wind at the field, or in New Hampshire or similar scanning the rocky cliffs for interesting objects, it will be quite a luxury using this mount as opposed to some inexpensive unit that I always feel the need to have one hand on. I will always feel comfortable and secure that the FSQ-85 and the huge Edge HD 11 and their very valuable diagonals and oculars are sitting on a foundation that has no chance (notice I did not say virtually no chance) of tipping over or malfunctioning on either of its two axes. As an experiment, I placed the fully loaded HD 11 in the most awkward position possible when I was last out. That’s the gap where there are no tripod legs to leverage it. I tried to push it over with moderate force. Of course, I could have pushed it right over, but this was just a strong wind simulation, or maybe even a deer bumping it. The assembly stood its ground. That’s a good feeling. No, that’s a great feeling. And keep in mind that the HD 11’s C of G extends outward pretty far, so its listed weight in relation to the Rex’s capacity is actually conservative since it is far from the center axis. You could probably get away with a much heavier refractor for this reason, since the weight would be tucked in.
The biggest question you have to ask yourself as a person in the market for a grab and go setup is, Am I justified in buying a mount that is heavier than what I need to grab and go? After all, the whole point of g&g is so you can grab and go. This mount does not really qualify for that because of its weight. Even getting it into and out of the bag can be a bit of a hassle. (I cradle the main cylinder with my right hand and hook my left arm under the three legs. It gets easier with practice.)
As mentioned, the security of our instruments should be a priority. In use, the T-Rex is like having a big strong caring person watching out for your equipment while you go get a different eyepiece. Someone you can trust to walk away from.
Good luck on your decision and clear skies!
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