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Editorial Review [13 May 2003]
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DiSEqC 1.2 motors - Mini group test (Page 2 of 4)
Introduction cont. and Stab
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.
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
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).
answers (data bytes) paired with E4 are:
Enabled software limits
Was last seen moving west
I'm still moving
Reached software limit point
Don't have any power
Reached hardware limit
Don't know where I am, don't know who I am
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
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.
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.
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.
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
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
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.
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.
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.
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.
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.
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.
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.
here for an audio sample of Stab HH120 (mp3, 235Kb)
|Quality of build
||8 (beware of windy conditions)
||5 (no replies to questions)
|Value for money
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