| |
G8MNY > TECH 26.11.11 09:41l 308 Lines 15048 Bytes #999 (0) @ WW
BID : 18149_GB7CIP
Read: GUEST
Subj: A Light 17m /P mast design.
Path: IZ3LSV<ED1ZAC<GB7CIP
Sent: 111126/0013Z @:GB7CIP.#32.GBR.EU #:18149 [Caterham] $:18149_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (Updated Aug 06)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
Here is a VERY light weight mast system 18kg (40lbs) I designed & built years
ago, & I have use it most of my for /P. It is much lighter than anything else
of its size. It is very stringy so I called it "STRING WONDER MAST".
PURPOSE OF THE DESIGN
1/ To support an aerial @ 17m (54ft).
2/ Erection possible in cluttered sites.
3/ With modest aerial, One person could operate mast.
4/ Uses manual or Bottom rotor.
POLES
It has 4 section of thin (2-3mm) aluminium tube starting with pole 1 a 3.6m 63m
(12ft 2.5"), then 2 a 4.8m 50mm (16ft 2"), then 3 a 4.8m 43mm (16ft 1.75") &
finally pole 4 a 4.8m 37mm (16ft 1.5"). Finding sources of suitable tube
stockests can be difficult!
GUYING SYSTEM
AERIAL
.'³³`. 4 GUY PLATES GUY & STRING BOBINS
. ³³4 . ÚÄÄÄÄÄÄÄÄÄÄ¿ ____________________
. .'ô`. . ³ o __ o ³ ³ H O L D ³
. . ³³3 . . ³ / \ ³ `\. ./'
. . ³³ . . ³ ³ ³ ³ ³ WaterProof ³
. . .'ô`. . . ³ \__/ ³ ³ GUY WINDER ³
. . . ³³2 . . . ³ o o ³ ./' 1 per Plate `\.
. . . ³³ . . . ÀÄÄÄÄÄÄÄÄÄÄÙ ³____________________³
.. . .'ô`. . .. ----- 10 to 30cm -----
.. . . ³³1 . . .. Largest 1 for top guy set
. . ³³ . .
This uses 4x 10cm (4") square metal plates with central holes to closely match
the poles as all by the top one sit on the larger lower pole. The corners are
drilled to take the 3mm guy nylon strings & all metal smoothed off to not cut
guys.
The 4 sets of guys are 1.6x longer than the height they are used on to ensure a
safe shallow guying angle (45ø) can be used to give the least added down force.
I colour coded them with dye per level & each level is wound on flat winder
with the "HOLD" side marked so that each twist of 4 guys is unwound next time.
The top set needs the largest bobbin! The top 2 sets can be removed for
transport.
IMPROVED TOP GUY SYSTEM
To stop the guys wrapping around the rotating pole that can happen with the top
guys, the guy plate has 2 x 60cm (2ft) coat hanger wires threaded through the
holes as well to make a large spreader, the wires have loops bent the end to
capture the guys strings.
Aerial
³ ³ 1 turn of Coax
PLATE ³ ³ ____
============ coat hanger ./' __ `\. Washer ./\.___
./. ÃÄÄÄÄ´' .\. spreader ./ ./' `\. \. Tab`\/' `\._Screw
./ . ³Clip³ . \. wire ³ ³ ³ ³ ³ ³ ³Up
o/ .³ ³. \o ³ ³ ³ ³ ³ ³_³Clip
. ³. .³ . guy `\ `\.__./' /' ./\.___./'
. ³ .. ³ .Nylon `\.____./' `\/'
Aerial Coax Tab
Support Strings
Hanging from this plate is also 2 strings (free ends of 2 of the guys) 60cm
(2ft) long from opposite corners to take the hanging coax weight.
The top plate sits on a washer that sits on a Jubilee clip with 2 flat strip
folded around it to proved a flat surface tabs for the washer to sit on. The
clip is firmly tightened on the top pole below the aerial.
PULL UP MAST SYSTEM
1.5" \°°4 ³ Smaller Pole ³ Guy
Pole °o \ =======³_____ ______³======= Plate
°° Pole ³ ³ o / \ o ³ ³
Pulley °° Holes ³ ³ ³³\/³³ ³ ³ Pulley bolted
Wheel \_ °° / LOCKING ³ ³o[³³||³³]o³ ³ between 2x
|0À°oÄ¿ PIN ³ ³__³³||³³__³ ³ right angles
| ³ °°³ÃÄ. ³ ÀÄ||ÄÙ ³ pop riveted On.
Strong | ³ °°³ : ³ || ³ Inside rivets
Nylon\ | ³ °°³ : ³ || ³ hammered flat.
cords | _ ³ ³ : Release ³ Strong Nylon ³
| |0|³ ³³ : Cords
| | ³|³ 3 ³³ : LOCKING CATCH
| | ³|³ ³³ : ³ Inner Tubes Have³ /Pin
| | ³À³__|^Ä¿ : ³ Locating V ===Þ) <--Screw & Tag
thicker| | ³ ³ÃÄ. : ³Top pole has hole³ÚÄÄÄÄ. Release
rope | | _ ³ 2" ³ : : ³ ³³____/ Leaver
| | |0|³ Tube ³³ : : ³ ³ Ý :
| | |³|³ 2 ³³ : : ³ ³Þ SPRINGS
| | |³|³ ³³ : : ³_________________³Ý__ :
| | |³À³_____|^Ä¿ : : ³ JUBILEE CLIP ³0) :
| | |³ Notch ³ÃÄ. : : ³--------------------' : Release
| | |³ ³ : : : ³ ³Ý : Cord
| | |³ 2.5" ³ : : : ³ ³Ý :
| | |³ Pole 1 ³ : : : ³ ³
PULL UP ROPES
These are thicker ropes where you hold them (e.g. 6-10mm) & for poles 3 & 4 are
joined to strong thinner nylon cord (3mm 80kg) that can go over the 2cm dia
pulley & between the poles. The top corners of the aluminium right angle
supporting the pulley is bent over to capture the cord so it can't foul off the
pulley.
On the outer pole I put a rope tie off cleat made from a bent flat strip of
thick metal clamped with a large jubilee clip to the pole.
The ropes are attached to the bottom of the poles by a hole drill in the pole
end. Like the guy plates, these holes are cleaned up to stop chaffing.
The top rope is attached to the bottom of thinnest pole through a diagonal
hole made through it. This insures when the pull up rope is tight the pole is
in the right location for the locking pin to engage.
LOCKING CATCHES
The location of these automatic locking pins determines the amount of pole
overlap. I set the positions to give about 60cm of overlap.
On the top pin system a hole is made in the inter tube. The locking system is
mounted 2cm (1") down on the next tube, so that it clears the guy plate, & a
slot just the width of the pin is cut in the 2nd bigger tube.
Pole
smooth load Ú¿ tag for
rounded ,Ä.__.ÄÄ´³/ wire
nose ³ pin ³³]
`ÄÄÄÄÄÄÄ´³ Screw
small hole ÚÄÁÁÄÄÄÄÄÄÄÄÄÄ. hole for
for wire ³ø crank o ³release
bearing ÀÄÂÂÄÄÄÄÄÄÄÄÄÄ' string
³³flat
³³springs
³³
ÄÄÄÄÄÄÄÁÁÂÄÄÄ.
Jubilee Clip ³(/)³
ÄÄÄÄÄÄÂÂÁÄÄÄ'
³³
ÀÙ
The catches uses a shaped steel locking pin (filed threaded pillars) to support
each of the 3 inner sections. The shape has a curved top to ensure the pin
can't release under load. These are attached with 4mm (2BA) steel screws with a
tag to the flat springs which can be made from several old large hacksaw blades
& other flat spring taped together.
The whole locking system is held to the pole with a suitable jubilee clip
around the springs once the outer pole pin hole has been made.
To facilitate unlocking a flat steel strip 1.2 wider than the pin inner pole
engagement length is placed between the spring just under the pin. This is bent
around the spring to form a square flat U with the top the U making the crank
leaver for the release string. A bearing for the crank is formed with 2 small
holes though it just by the bends behind springs & nearest the pin. A sturdy
wire threaded though & attached to the tag completes this bearing.
Warning:- A failure in the release mechanism @ 3m, 7.2m, 11.4m above you, MAY
mean the loss of the mast when it comes to take it down! So make sure you are
happy with it's operation when you make it & each time you use it.
LOCKING LOCATIONS
The bottom of poles 2 & 3 are cut at an angle & a V notch to take the locking
pin. This is opposite the pull up rope tie off hole point. The angle & notch
ensure the pole do not rotate when locked, & easily find the home position when
engaging. As there is quite bit of room between pole 1 & pole 2 spacers are
pope riveted on either side of the thick pull up rope on pole 2 to reduce the
play & keep the bottom of the pole firmly against the catch.
POLES 2 & 3 Lift Rope T O P P O L E
hole ||
³ Pin Locating ³ ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄ ÄÄÄÄÄÄÄÄÄÄ ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
³ Notch ³ ³ Washer @ | | Room for³
³ /\ ³ ³ & knot | | Aerial ³
³ ³ ³ ³ ³ | | ³
³ _.-' `-._ ³ ³ Tallest locking | | Shortest ³
³.-' () `-.³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ ÄÄÄÄÄÄÄÄÄÄÄÄ ÄÄ ÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ -----60cm------- hole Hole
Lift Rope Hole
The top pole has a locating hole for the locking catch pin to find. This must
be located accurately so that under pull up load it will locate OK. Other holes
can be also be made higher up that pole to enable lower mast height to be used
if it is too windy to do the final lift. In that case the upper guys can be
tied off shorter to improve stability.
LUBRICATION
As aluminium to aluminium mechanics is not hard warring or low friction,
suitable lubrication is need. For the underside of the guy plates & top washer
I use a heavy grease that will not wash away. For the tubes & pulleys, I use
new engine oil, it is easy to apply with each tube pulled out one at a time.
ROTATOR
I use a 12V rotator with a padded out shaft that the mast sit on & a bolt hole.
It is only low torque & easily stalled rotator, so if anything fouls up it does
no damage & keeps it's direction meter in sync! Its made from scrap army kit.
Captured _ Padded
Nut Hole>³.³ 2" shaft
Water_\ __³_³__
Trap / ³ ³ Geared
³ ³ Down DC
³_______³ Motor & Pot
Base sits on foam sheet
I also use a mains one with over sized clamps that go outside the pole &
rotator, again clamp is done just enough to allow normal levels of torque only.
2.5" ³ ³
Mast ³ ³_
³ ³³
_³_ /_³_
Large==³()³=³³=)³
Clamp ÀÂÄÙ ³ÀÄÂÙ
³ / ³ Mains
ÚÄÁÄÁÄÄÄÄÁÄ¿ Rotator
_³ ³_
Wooden <______________>
Base ____³__________³____
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
Corners Pegged down if needed.
SETTING UP
A wooden A frame supports the mast while the guys, ropes & release cords are
sorted & laid out before the mast is erected.
1 2 3 \ 4 /
Rope tie off ÚÄÄ¿ __ÚÄ_ÚÄ____ `ÚÄ¿'
____ ¿Ú ______......ÄÄÄÄÄij """""\_³(_³(___() ³(³
/ / \____......ÄÄÄÄ-""""""______......ÄÄÄÄÄij_""""""XÀÄÙÀÄÙ ,ÀÄÙ.
³ ³ (_____......ÄÄÄÄÄ"""""" / \ / \
\__\_/ /' A `\
Rotator /' frame `\
Steel stakes or pegs (8 off painted anything but GREEN) are slightly larger
than large tent pegs are used (e.g. 30cm x 2cm x 2cm) with sharpened points.
Use with the open V side towards the mast & hammed right in @ 45ø angle, to
tie off the guys in 2 concentric squares.
\ P L A N /
Open part of V
faces mast ./\ \ / Inner
`. ./ __\ Brightly coloured Stake Pegs
Tie Guys`. ./,/' /' Steel Steak Peg 0
at ground `./,/ /' MAST
level /. /' Use Clove Hitch / \
Knots ! Outer
/ \ Stakes
ERECTING
Always start with no aerial or coax load, but allow enough mast space for it &
the coax loop before clamping up the top guy clip.
If the centre location is not to important you can erect the mast singlehanded.
Put 2 pegs in @ 90ø for the lower guys & tie them off (I always use the safe &
quick clove hitch for ties) swing the mast vertical & lean it almost vertical
into the 2 guys. Then put out & loosely tie off the next lower 2 guys. Put the
mast vertical & adjust ties & pegs for a proper square. If not single handed
get 1-4 slaves with different names to put in the 4 pegs.
Then pull the 2nd pole out until it's catch locks. Then put out the 4 guys for
that level to the same pegs. Repeat for guy levels 3 & 4 with a bigger peg
square.
When all is well & vertical, lower the mast leaving all guys in place. This
MUST BE DONE IN REVERSE ORDER so that the mast is supported as comes down.
Pull on the heighest pull up ropes to take the load of each catches before
attempting to release the heighest catch. When all telescoping is done just
lift & move the base away keeping the top about were it was. Put mast back on A
frame. Run out all the spare guy strings towards their respective pegs to keep
the tangle around the mast to a minium. Attach aerial & coax, coax weight to be
carried on the top guy plate.
Re-erect the mast, you may find minor guy adjustment is needed to keep the mast
vertical (straight is more important) now it is under load.
IN USE
Because this is a light weight mast, erection & de-erection is ONLY POSSABLE IN
NO TO LIGHT WINDS, wait for lulls (evening or morning). However once up, the
mast has survived strong winds (>50MPH) if the relevant guys are adjusted to
keep the mast straight. Vertical is not so important!
In public demos etc. I do not let the public in the guying area, which is
bigger than the drop zone. But one advantage of it is that it can be put in
between marquees etc. where other masts would need a huge erection area. If
tying guys to ladder racks on cars vans etc. make sure owners do not drive
away!!!
If the mast should collapse in a storm etc, in my experience it will fold &
kink one of the middle tubes lowering the aerials VERY slowly (work hardening
absorbing most of the energy) without the aerials or anything of the ground
being damaged.
Aerial used on it (one at a time) are:-
Length Weight Type
6.6M (22ft) 5.0kg 17el 2M by Tonna, (but often stripped down to 11 element)
3.0M (7ft) 2.0kg 8el 2M Quad Homemade 2 thin boom type,
6.2M (20ft) 4.0kg 27el 70cm QLY by G3JVL,
4.0M (13ft) 4.7kg 88el 70cms Multibeam by JBeam,
2.1M (7ft) 1.5kg 24el 70cms beam,
5.0M (18ft) 2.0kg 55el 23cms by Tonna.
And with some of the above plus a /M Colinear whip & a halyard for HF wires.
Coax used is the lightweight low loss POPE H100.
Why Don't U send an interesting bul?
73 de John G8MNY @ GB7CIP
Read previous mail | Read next mail
| |
