[TowerTalk] Mast slipping

donovanf at starpower.net donovanf at starpower.net
Sun Apr 22 22:58:06 EDT 2007


Keith,

I don't think the problem is a design flaw with the 2800, I believe it not rated for very large 3 element 40 meter full sized Yagis (including
the SteppIR MonstIR) in strong winds.

Orion 2800 rotators failed catastrophically in three different installations in my local area when used with very large antennas
(full size 3 element 40M Yagis and SteppIR MonstIRs).  In each case it
was a result of 40-50 MPH winds typical for this area.  Each failure
occured soon after installation of the rotator.

"Square feet" is an inadequate rating for rotator capacity.  Very large
antennas distribute wind loads over a large structure, and considerable
energy is stored in the flexing of very long elements in the wind. This
stored energy creates heavy torque loads that overload all but the strongest rotators.

The Orion 2800 doesn't have a problem handling large "shorty forty" and
long boom Yagis for the higher bands.  I use an Orion 2800 to turn a
5 element 20M Yagi on a 48 foot boom at 200 ft, and its been trouble
free for nearly ten years.  But I wouldn't consider putting an Orion
on my full size 3 element 40M Yagi at 200 ft, that's a job for a
prop pitch rotator, such a those that are readily available from K7NV.

73!
Frank
W3LPL


---- Original message ----
>Date: Sun, 22 Apr 2007 21:10:44 -0500
>From: "Keith Dutson" <kdutson at sbcglobal.net>  
>Subject: Re: [TowerTalk] Mast slipping  
>To: <towertalk at contesting.com>
>
>Frank,
>
>Are you saying the Orion has a basic design flaw that no amount of
>strengthening or improvement will correct?  If so, please elaborate.
>Thanks.
>
>73, Keith NM5G
>
>-----Original Message-----
>From: towertalk-bounces at contesting.com
>[mailto:towertalk-bounces at contesting.com] On Behalf Of
>donovanf at starpower.net
>Sent: Sunday, April 22, 2007 5:32 PM
>To: towertalk at contesting.com
>Subject: Re: [TowerTalk] Mast slipping
>
>Keith,
>
>I know this isn't a popular message; however...
>
>The actual experience of three different PVRCers who tried to turn full size
>3 element 40M Yagis and SteppIR MonstIR Yagis with Orion 2800 rotators is
>that the rotator was quickly destroyed by normal heavy winds.
>
>You don't want your new antenna project keeping you awake at night during
>heavy winds!  That's no fun.  
>
>My recommendation is that you sell that 2800 and purchase a rebuilt prop
>pitch from K7NV.  You will sleep well and it will not de destroyed by any
>wind.
>
>I'm not down on 2800 rotators, I have four of them and they are great for
>anything smaller than a full size 3 element 40M Yagi or a SteppIR MonstIR.
>
>73!
>Frank
>W3LPL
>
>---- Original message ----
>>Date: Sun, 22 Apr 2007 17:21:11 -0500
>>From: "Keith Dutson" <kdutson at sbcglobal.net>
>>Subject: Re: [TowerTalk] Mast slipping
>>To: <K7LXC at aol.com>, <towertalk at contesting.com>, <alwilliams at olywa.net>
>>
>>Ya'll have me wondering about my 40M tower plan.  Last fall I took 
>>delivery of two M2 40M4LLDD Yagis.  This antenna has 4 elements on a 42 
>>foot boom, but a surprisingly sparse 13 square feet windload rating.  
>>They will be mounted at 100 and 200 feet on a 190 foot Rohn 55G tower.  
>>The top antenna will be rotated by an Orion 2800 that was purchased at 
>>the same time.  The lower will be rotated by a TIC Ring.
>>
>>This tower was supposed to be going up this spring but unexpected 
>>surgery has delayed the project for a year.
>>
>>After hearing about all of the mast slipping problems I decided to take 
>>the Orion out of its box and have a look.  According to the 
>>instructions, the "positioner" has been recently improved and 
>>strengthened.  Since I do not have an older unit, I have no way of 
>>knowing what is improved or how much stronger it is.  Here are some specs:
>>
>>wind area		35 sq ft
>>start torque	4200 in lb
>>rotating torque	3200 in lb
>>braking torque	17000 in lbs
>>vert load cap	1800 lbs
>>
>>I took a photo of the mast clamp halves (see below).  Interestingly, 
>>there is a hole in each that is sized to take a 1/4 inch bolt.  This 
>>could certainly be used to pin the mast but leaves doubt about the 
>>strength to hold it.
>>
>>http://www.dutson.net/Transfer/HamRadio/Orion2800Clampds.JPG
>>
>>73, Keith NM5G
>>
>>-----Original Message-----
>>From: towertalk-bounces at contesting.com
>>[mailto:towertalk-bounces at contesting.com] On Behalf Of K7LXC at aol.com
>>Sent: Sunday, April 22, 2007 12:04 PM
>>To: towertalk at contesting.com; alwilliams at olywa.net
>>Subject: Re: [TowerTalk] Mast slipping
>>
>> 
>>In a message dated 4/22/2007 8:43:23 A.M. Pacific Daylight Time, 
>>towertalk-request at contesting.com writes:
>>
>>>  About a year ago I had a conversation with the m2 people  about 
>>> their
>>rotator
>>clamp slipping on my Monstr's mast.  What follows  is my memory of the
>>conversation:
>>
>>>  1. It is better to  have the clamp slip than to harm the rotator.
>(Note:
>>
>>the
>>wind  banging repeatedly on the gearing can weaken the gears?)
>>
>>>  2.  The specified braking torque has not been measured (or
>calculated?).
>>
>>>  3. Pinning voids the warranty.  I would  assume that using a 
>>> different
>>mfrs
>>clamp would also void the  warranty.
>>
>>>  4. They recommended a clamp bolt tightening  sequence that should be
>>followed.  Unfortunately I wasn't able to get  a firm answer on what 
>>torque to tighten the nuts to.  The sequence to  follow is:
>>
>>>  a) bolt the rotator to the mounting plate but  leave the bolt/nuts 
>>> not
>>tightened
>>b) with the bolts to holding  the rotator to the mounting plate loose, 
>>tighten the bolt/nut pair of the  clamp that is nearest the bottom.
>>c) tighten the next (middle)  bolt/nut pair of the clamp
>>d) tighten the top bolt/nut pair of the  clamp
>>e) repeat steps b,c,d several times
>>f) now lastly,  tighten the bolt/nuts of step a
>>
>>>  I did get an answer of 40  ft/lbs from the m2 person but I think 
>>> that was
>>just pulled out of the  air.
>> 
>>    Very interesting but not useful. It doesn't do  anything about the 
>>significant design flaws of the Orion mast clamp that ARE  the problems.
>>None of the above will keep the mast from slipping. 
>> 
>>Cheers,
>>Steve      K7LXC
>>TOWER TECH
>>
>>
>>
>> 
>>
>>
>>
>>************************************** See what's free at 
>>http://www.aol.com.
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