Sunday, April 9, 2017

Project - Mast support for heavy masts


For my portable endeavors I have built an aluminum push up mast and I have bought various fiberglass poles from Spiderbeam. I actually started out with a 10m pole from Spieth. That was rather thin, so I went for the 12m HD version from Spiderbeam.
To get my inverted v's for the low bands up higher I then bought the 18m version and recently I went even further and got myself the tallest pole they sell - 26m.  

Heavy masts present a challenge when working /P. I can manage to set up the 18m pole in the open field on my own but it is quite a bit of work and it would be a really daunting task with the aluminum mast and the 26m pole.

When I built the aluminum mast I went looking for a proper mast support that I could use with my car. Typically this would mean a drive-on support. The ones I found on the internet however were too light for my sturdy (and heavy) mast.

Not having any welding tools available to me at the time (I now have an arc welding machine), I decided to build something myself out of wood. After some experimentation I went for a design where I attach the support to the wheel using lashing strap, instead of driving on the support.

If you are reading this to try something yourself, keep in mind this design only works if you have spoke rims on your car.

I never got around to write something about this support, even though I got questions about the design. After buying the 26m pole I had to build a new support - for a much larger diameter mast - so I decided to take some pictures in the process.

The end result looks something like this (showing my first version):

The tried and trusted version from different angles - note the rubber pads that go between the support and the car tire:

I constructed the old one for my aluminum mast that has a diameter of [--- mm]. It can also hold the 18m Spiderbeam fiberglass pole. Conveniently the tall vertical wooden beams are the same width as the bottom segment of the mast. This means that the only spacing that is critical when you build it, is the spacing between the two vertical wooden beams.

Now for the 26m I built the same support but I could not find wooden beams of the desired width, so I used the nearest (smaller) width and added planks to end up with the correct width - as you can see in the picture below.


Wooden parts cut to desired lengths 
Now that the vertical beams are of the correct width, the only spacing you have to worry about is the one between the two vertical wooden beams. I used the bottom segment of the Spiderbeam pole to define the space, as shown below.



The length of the horizontal wooden beams is not critical. They define the space between the car tire and the mast / pole. I use [--- mm] to leave enough room for my shoes - so that I can use the support to position myself higher when I push out the mast segments.

The height of the upper horizontal beam is critical in the sense that you need to make sure it stays within the height of the car tire (more about that later).

Once all the horizontal beams have been added the support looks something like this:


What is left, is adding the frame that you can tie to your car rim. I use 44x44mm wooden beam for this frame. The height and width for this last rectangular frame have already been defined by the structure you have created so far. It is therefore important that the upper horizontal beam I referred to earlier, is positioned at a height that puts the top of the frame we are now going to add right against the rubber of your car tire.





When I completed this stage I took two more steps: a piece of (ply)wood on the bottom of the support - this keeps the mast / pole from getting stuck in the ground (e.g. in case of a muddy underground). And I add pieces of rubber that go between the car tire and the wooden frame (refer to the pictures above of the old version).

Now you have the lower support for your mast. This might be enough to keep your mast straight up. In my case I added a second support on the roof of the car. This helps keep the heavier masts (like my aluminum mast and the 26m Spiderbeam pole) straight up without guying. 

This roof support is nothing magical. It is simply a wooden beam (44x44mm) that is longer than the width of your car + the distance to the mast. At one end I add two pieces of wood at a distance that equals the width of the mast. Through these pieces of wood I put a threaded rod (M8). This rod is positioned at such a distance that it keeps the mast in place. I use some pvc pipe to keep the keep the sharpish threads from damaging my mast / pole. This roof support looks like this:



I use lashing strap to attach the support to a roof rack on my car.  

5 comments:

  1. Hallo Lars, prachtig die constructie die jij gemaakt hebt. Ik heb diepe bewondering voor je energie en je enthousiasme. Was het niet gemakkelijker en mogelijk goedkoper geweest om een stalen klem/voet te gebruiken die je onder je achterwiel zet?
    Ik heb er een van staal voor nog geen 4 tientjes gekocht via MP en voldoet uitstekend. Als je die een keer wil uitproberen dan geen probleem.
    73 Hans, PE1BVQ

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    1. Hallo Hans, een metalen drive-on voet zit zeker nog in de planning. Ik heb inmiddels een lasapparaat. Ik wil er eigenlijk 1 maken met kantelconstructie voor de mast.
      De bestaande versies drive-on supports die ik kon vinden waren niet stevig genoeg voor mijn zware mast en / of niet de juiste maat. Welke mastdiameter kan jouw support ondersteunen? Heb je een weblink?
      73, Lars.

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  3. Hoi Lars, Bedankt voor de duidelijke beschrijving. Ik heb nu zelf iets gemaakt met een ca. 1.70m PVC buis + tuien, waarin ik een mast kan plaatsen. Moet je wel grond hebben waarin je relatief makkelijk maar toch stevig piketten/haringen in kan steken.

    Groeten,

    Enno, PF5X

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