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Array Solutions
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Rotator Comparisons
Prosistel "Big Boy Rotators" have become the benchmark rotating system for Military,
Commercial, and Amateur Radio Large Antennas.
They are used world wide by military, governments, shipboard severe marine
by the Navy and oil rig companies. They are in use in Kuwait, UAE, Morocco,
Iraq, in high heat, and blowing sand environments as well as Artic zones, and
on board Navy ships. The reason is simple, reliable operation. But it
wasn't simple to engineer and manufacture these rotators. Prosistel has
evolved them over the years to what they are today.
Why risk your installation to a messy break down. twisted and broken wires,
and hours of work to fix the damage and replace a cheaper rotator?
How should one compare a rotator when there are so many to chose from?
Let's start with specifications and what they mean.
ABOUT ROTATOR SPECIFICATIONS:
There are many factors that affect the ability of a rotator to turn or hold (brake)
an antenna or array, in the short term as well as over the anticipated life expectancy
of the rotator itself. These factors are both internal and external. Internal
considerations are related to the design and construction of the rotator, including the
housing, type of gear, type and size of motor and brake mechanism and associated control
system, and the bearings, especially those that take the vertical and the lateral loads
imparted by the antenna mast. External factors are related to the size and configuration
of the antenna system to be rotated, whether or not the rotator is mounted inside of the
tower with an external thrust bearing, the wind load (commonly expressed in square feet
[sq. ft.] or square meters of effective surface area) along the mast, and the weight of the rotating
system.
Most manufacturers simply state that their rotator will handle an antenna of a certain
number of square feet. This is where magic and guesswork take over from physics and
engineering. Knowing the surface area (sq. ft.) is not enough. Assuming that the wind
load measurement is accurate, you would need to know the wind speed at which the rating
has been established. Is it 50 mph or 80 mph, steady state or gusts, from which (or
changing) direction? Does it make a difference if the elements or boom are long and thin
or short and thick? Does it matter if the antenna is six inches or ten feet above the
rotator or thrust bearing? Does it matter if there is one antenna on a five-foot mast or
three antennas on a twenty-foot mast? Does it make a difference if it is below freezing
and there is an inch of ice coating the whole business? Yes it does!
How can you decide which rotator you need for your application? Lets take a look at the
engineering specification terminology used to specify rotators and eliminate the
guesswork. These terms relate to the torque or turning force available to get the system
moving from rest, keep it turning, bring it to a stop and hold it in place. These
specifications are as follows:
STARTING TORQUE - maximum turning force that the rotator is
able to produce as it comes up to speed from a dead stop. The greater the starting
torque and rotating torque the less time it takes for large arrays and stacks to come up
to full rotational speed.
ROTATING TORQUE - turning force available to overcome
friction and the effects of wind.
BRAKING TORQUE - amount of torque the rotator can resist
that is induced by winds or other loads trying to rotate the antenna system from it's
braked position.
VERY SIMPLY - The larger the numbers, the more the rotator can handle and the longer it
will last.
Torque ratings and practice - most
manufacturers do not actually measure the torque of their rotators. The
industry has gone to just calculating these figures instead. This was
started way back in the industry and has been perpetuated by marketing
and in reality some ruthless manufacturers. This way they can advertise
the torque specs as being much higher then they really are. Torque
is reduced by friction in the bearings, gears, and worm gears if used.
A worm gear can have as much as 50% torque loss due to friction.
Prosistel actually measures the torque delivered to a torque wrench.
Prosistel rotator testing in at over 4,000 in-lbs
Clamps - The clamp has evolved over the
years be sure your rotator clamp will not crack under tightening or
shock. The Yeasu clamps are notorious for fracturing and cracking in
half. They just don't learn. The Prosistel clamp has evolved to be the
strongest clamp you can find.
Gears and output shafts and bearings are
the weak points of most rotators, the Prosistel website has many
examples of competitive rotators gears and shafts as well as pictures of
the Prosistel sized gears.
  
The size of the gears and output shaft is one of the best indictors
of strength and long reliable operation of any rotator, the pictures
above show three sized output gears compared to a AA battery, the top of
a PST gear box removed to show the size of the bearing, which is a real
industrial bearing, and Worm gear. The output shafts are huge as
you can see. Compare to this unit from a Yeasu rotator.
We can easily see the difference in the gears. These are some pretty
small and narrow gears.
Motors are rated in power they can
deliver, usually in Watts. You can see that the Prosistel uses THE
largest DC motors of any rotator manufacture. These motors have
much higher wattage ratings then any of the rotators that try to
compete. Basically the higher the wattage motor (which weigh more too)
the less gear reduction you need to deliver torque to the load. And less
gear reduction means less friction loss and more of the torque getting
to the output shaft.
Warranty - Prosistel has 2 years and no
limits on if you PIN the mast to the rotator. Other manufacturers
disallow pinning of their rotators as a violation of their warranty.
Now we can see why most manufacturers like to use a formula instead
of measuring their product.
Now, compare the starting, rotating and braking torque specifications of "BIG BOY
Rotators" to any other rotator on the "comparison chart" and you will be amazed. Also,
take a good look at the weight differences, brake types, size of motors used.
Please visit this site for these numbers - we apologize for the
metric challenged among us, including myself but we will have Prosistel
put a SAE chart up soon.
Rotator
Comparison chart < click here then click on English and the
Rotator Comparison Chart Link on the left.
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The prosistel rotator systems meet CE and FCC part 15 Class
B requirements to market in the US and Canada
Make sure the rotator you buy meets FCC Class B or your
buying an illegally marketted rotator.
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