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Hardware Reviews

Editorial Review [13 May 2003]

DiSEqC 1.2 motors - Mini group test (Page 2 of 4)


Introduction cont. and Stab

Proper implementation however could give us options required for ergonomic but more advanced usage - move my dish to HotBird and switch monoblock to LNB B pointing offset on Astra 19.2E. While I'm watching Eurosport on Astra move my second dish with second inbuilt tuner output to PAS @ 43W and record a program from Fox Sports onto a hard drive. It's all theoretically possible, the options are present in the standards, but in practice they are still science fiction.

In the newest versions of the DiSEqC protocol with assigned version number 2.0 and above we can even optionally enquire of our "dish driver" about the state of a command. "Listen mate and I need you to answer, tell what's motor doing now? (E2 31 64)". The motor may then reply with response formed as [framing byte] and data bytes. Framing responses could be translated to

"Motor here, understood" (E4),
"Motor here, don't know who are you talking to" (E5),
"Motor here, can't hear you please repeat" (E6)
and "Motor here, don't know what you're talking about, please explain" (E7).

Possible answers (data bytes) paired with E4 are:
.7 Done moving
.6 Enabled software limits
.5 Was last seen moving west
.4 I'm still moving
.3 Reached software limit point
.2 Don't have any power
.1 Reached hardware limit
.0 Don't know where I am, don't know who I am

The responses listed above, although obligatory with the newest revision of DiSEqC standard v. 2.2 are recommended but not required to be understood by DiSEqC 1.2 equipment, so you won't see the two way communication between devices too often. It is, however, sometime in the near future of the motorized satellite market, as inevitable as everything else in modern technology.

If any of you, somehow, got through all these explanations above without falling asleep you may wonder about one more issue. If not all receivers understand and request responses from motors and not all motors send responses then how do we know if our dish on the roof stopped moving before we start fine tuning it? A very valid question. Approximately 80% of today's receivers won't have a slightest clue. Others, designed by more experienced code writers and hardware designers will try their own methods - be it measurements of the current drawn by rotor, detection of signal from LNB, pulse count or message queuing.

You would imagine that at the dawning of the 21st century, turning a mere 12kg around its axis shouldn't be much of a problem, but bear in mind that the compatibility with existing wiring also enforced the limitations. The power available for the rotor is less than 500mA to share with LNB. "By the book" DiSEqC 1.2 specifications allow 350mA for the motor, but at the same time stressing that the peak/maximum power intake should not be more than 400mA. For a better illustration, the petit motor spinning your hard drive caching this page is consuming about 350mA @ 12V. With so little to work with and so much to achieve the downsides are quite obvious - equipped with tiny, low voltage engines DiSEqC 1.2 rotors can't possibly move large or heavy dishes.

Having bad experiences with DiSEqC 1.2 motors before, one of the tests I specifically insisted on was durability. Docklands in London is a perfect spot for such an exercise, there's at least 100 miles of riverbed for the wind to gain some speed and nothing but Isle Of Dogs to stop it. You don't have to do much for this test - you just mount the whole lot on the pole outside the building and leave it on for a few days.

Click to enlarge
Some receivers, like Force Dmaster series, can estimateknow fairly well approximate time when DiSEqC rotor is going to reach required position and indicate its progress.

In the following review I stress tested the three rotors most commonly encountered in shops across Europe. :

Stab HH120.

Click to enlargeAround 1997, when Eutelsat published specifications of their extended Digital Satellite Equipment Control protocol version 1.2 (this time including a few extra commands to move a dish using definable reference positions) a fairly unknown Italian workshop, slightly macabrely self-titled Stab Italia, designed the first horizon to horizon rotor, using the new DiSEqC 1.2 protocol.

Today Stab products are used as a reference, and as the protocol itself has been slightly revised and additions made, many manufacturers actually consult Stab regarding DiSEqC 1.2 implementation. The most commonly used Stab additions include so called GotoX commands, where the presumed position of the satellite is calculated using the latitude and longitude input by the user. The GotoX implementation was later remodelled into the USALS software available free (?) to STB manufacturers.

Stab is very open to co-branding. Therefore their products are often disguised as various more and less known OEM variety and shop labels - Cryptic, HDT, Chess, Manhattan to name but few. Many may disagree but in my experience Stab clones can and do vary slightly in overall build quality and materials used. For example, when we were reviewing the Force Dmaster 1122S, due to an error in the design, the receiver had problems driving some motors. Strangely enough this bug wasn't as evident with the Stab manufactured Force Skywalker as it was with the, at first sight identical, HH100 clone we were testing the receiver with.

OEM Stab motors can often be purchased at amazingly low prices as part of generic bundles. In 2001 the French Castorama chain stores were reported to sell an FTA receiver, dish and Stab labelled rotor for 1000 French Francs, at the time being an equivalent to approx 150 Euros. Throughout the same period all British satellite stores sold HH 100 motors alone for the same, or higher, price.

Click to enlargeThe Stab HH120 is almost identical to its little brother - HH100 with the exception of a longer pole extension and slower gear stepping. Accommodating dishes of a radius up to 120 cm or 17 kilograms, the HH120, weighed by me, totalled at very close to 3.5 kg including mount. At the bottom of the main body I found two F connectors with their barrels protected from moisture by threaded collars and two matching plastic protectors for the cable and plugs. There are two small holes near the F connectors, and given their placement, I presume their main job is to drain moisture. Despite the lack of any seal, the HH120 passed my water test without any problems, no sign of corrosion, moisture or any other ingress was found inside the motor.

Upon opening the cast chassis of the HH120 I was surprised by the small amount of lubricant the manufacturer had decided to cover the gearing with. Ever since I took a peek inside one of the HH100 motors over a year ago It doesn't cease to amaze me how these tiny clockworks operate at all, considering most of the already minimal dose of brownish, thin liquid can be found splashed all over the cover around the gearbox by the fast spinning tiny 16W Taiwanese made motor.
Click to enlargeThe working mode of HH120 I examined was accompanied by a loud sandy noise of fairly high, whining pitch, which I presumed to be quite appropriate considering the level of lubrication. Timed with a stopwatch, the HH120 travelled across the horizon at a speed just slightly over 1 degree per second. In practice it means six long seconds between Astra 1 and HotBird, 14 more seconds to reach Thor and almost 1.5 minutes to travel from Pas1 at 43 degrees West to Turksat at 42degrees East. But having low gearing on the engine doesn't necessarily mean only bad things. The rule is - the bigger the dish, the harder it is to align and the smaller the error margin. Keep in mind that thanks to he fact that the motor moves in smaller steps this factor could actually help fine tune the positions. On the obstacle course the generic HH120 would not shut down when the dish movement path was obstructed by a wall, therefore we should assume there is no circuit preventing the rotor from putting the maximum pressure on its gears when the dish is driven onto a wall or against strong wind.

Click to enlargeThe HH120 comes with 49 memory slots, of which 26 are already taken by positions preprogrammed by the manufacturer. The Stab, similar to all rotors tested in this article, responded to GotoX commands and was fully compatible with USALS. No surprises there.

Overall the rotor, mounting, and add-ons provided felt sturdy - but a little on the rough and spartan side. Throughout the test the motor performed well, if a little noisily, but after two months of use with steel Triax TD 88 dish I found the transmission mechanism had slight but evident signs of wear, especially on the smallest gear.

Click here for an audio sample of Stab HH120 (mp3, 235Kb)

Quality of build 7
Performance 8 (beware of windy conditions)
Features 7
Support 5 (no replies to questions)
Value for money 5

 


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