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Good cheap competition tower

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illini

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I'm interested in trying my hand at NAR competition. Don't expect or even want to be a BTC, but hope to at least be competitive when and where I do compete (i.e., I'd like to avoid total humiliation :)). So...I'm researching building or buying some GSE for competition. Specifically, been looking for ideas on building a tower, pistons, and combinations thereof. I have the following minimum requirements:
  • Ability to accommdate a variety of model sizes (e.g., 13mm, 18mm, 24mm, eggloft)
  • Ability to integrate tower with a piston
In addition, I'd like to meet the following "soft" requirements:
  • Low cost
  • Configurable to a variety of lengths (e.g., short tower for small models w/o piston, longer tower for models with piston)
  • Configurable as tower only, piston only, or tower with piston
  • Small footprint for transportation and storage
  • Did I mention low cost?
Unfortunately, the only commercial towers I've found are designed for HPR and are expensive. Also, most of the plans I've come across are for towers that are large and bulky, configurable in model diameter but not in length, relatively costly to build, and often require more tools than normal people have. In my opinion, most of the towers I've seen look impressive, but are over-engineered.

I recently came across the following idea by George Gassaway that appears to be close to what I want:

https://www.spacemodeling.org/gcg/omnipad_tower/omnipad_tower.txt
https://www.spacemodeling.org/gcg/omnipad_tower/omnipad_tower.jpg
https://www.spacemodeling.org/gcg/omnipad_tower/tower_assembly.jpg
https://www.spacemodeling.org/gcg/omnipad_tower/tower_ring.jpg

The basic idea is to make your main rails from rigid fiberglass tubing commonly used for kite spars, with smaller diameter tubes acting as connectors to form any length you want. These are attached with tape to a cylinder of fixed size (build one cylinder for each diameter you need) with epoxy fillets to guide their placement. A piston may or may not be included by installing the piston tube through the core of the cylinder. The tower is lightweight, rigid, and doesn't appear to require a massive (but impressive looking!) structure to support it. The greatest expense appears to be the fiberglass tubing which runs about $5 for a 54" piece, buy 6 of these and 1of smaller diameter for connectors and for $35 you're almost there.

Anyone have any thoughts on this? Seen one in action? Built one? See any pitfalls? Got any better suggestions?
 

Micromeister

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My Tower has served my well for many years. It's mostly PVC with aluminum channel rails fitted with teflon rod runners. completely adjustable for any size model for micro-maxx to BT-101 as long as the fin set stays within 9.5" OD. 36" wooden legs allow alt-azmith adjustments and a self containted piston mount will accept any of my metal head zero volumn pistons. another add-on cluster relay attachment give the tower 2xmmx to 6C cluster altitude capability. I haven't kept up with the dollars invested but the original parts and 10" dia PVC rings ran about 45.00 buck, adding the teflon rods, piston mount and relay may have added another $30.00.
best of all it fold up and fits easily in a trunk or in my van. Heres the standard Lift off pic but maybe you'll be able to pick out the tower:)
 

illini

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Hmmm...you've got me thinking of using the best of both worlds by using modular 1/2" fiberglass tubing for rails with adjustable-diameter support structure like yours. Then I would have electrically insulated, variable length rails and not have to fashion a new cylinder for every new model size. Probably the place to start is to pick up some fiberglass tubing and make sure I really can build straight rails from 2 or more pieces with connectors. Then I can better evaluate requirements for the support structure.
 

Micromeister

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You are probably right about using the Fibreglass rods. I visited McMaster-Carr's web site this morning only to find the 3/8" x 1/2" x .050 alum channels I purchased for my tower are no longer available:( I didn't mention my tower has 6 rails to accommodate 3 and 4 fin models..Actually I've use it with 6 fin models as well:)
as far as anti-short, the rails are designed to set a little about the lower 10"dia pvc ring with an adjuctable wire spanning two rail connection arms, this is used as a "fin stop" which puts the motor(s) and igniters below the aluminum rails, really convienent for hooking up 6 C clusters:D
If you start with 1/2" dia fibreglass tube rails i'm sure you could attach 1/4" or 3/16" dia teflon or graphite rods to the facing edge to reduce contact area and friction. 1/2" tube should be pleanty large enough to drill for 6/32" or 4/40" machine screws and wing nuts for swing arm adjustments.

I found a slightly better photo of the tower. it's another cluster launch but at least this one doesn't have the tower cloaked by smoke:) you can also see the "range box relay" cluster ignition box add-on attached to the lower ring on the left in this photo.

Somewhere in the stacks I have a close up of the connecting arms and 3/8" alum tube support stiffeners that hold the 10" rings apart.. If i run across it i'll post that one later. it would also show the piston drop down mount.
 

illini

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Good pics. Thanks. Getting good ideas. I see you're keen on the idea of using a low friction material like graphite for the interior of the rails. What do you think of using 1.3mm graphite rod like this as the interior surface of 1/2" fiberglass rails like this? How would you attach the graphite rod...epoxy?
 

wyldbill

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MM,

On another note, can you detail the way that the rails are mounted/adjusted/positioned? Can't really tell from your photos. Is there any mechanism to move them as a "set" or only individually?

thanks,
-bill
 

Micromeister

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Yeap!
the graphite, boron or Teflon rod as a facing material is the way to go.
I went with solid teflon rod from McMaster-Carr Adheard to the aluminium channel face with 3m 468-mp .010" carrierless D/F structural acrylic VHB tape and 3 tiny #2 x 3/8" sheet metal screws on each rail. Care had to be taken not to drill all the way through the center and top screw locations. these things are slick as snake snot and clean up with a little fantastic cleaner and a paper towel.

Each rail is attached to the 3" x 10" pvc ring with 3/8" x .25" x 4" aluminum up/down bars. both ends are rounded with a 6/32 x 3/4" round head machine screw, lock washer, flat washer, Hex nuts on the Ring/Channel connections and Wing nuts at the bar/rail connections. All hardware and fasteners used on this project are stainless steel.
Each of the 6 rails are adjusted individually by loosening a wing nut, usually one is enough to allow the arms to be raised or lowred into position around the model body.

Zero adjustment of the individual rails is accomplished by using spacer washers under the Ring/Channel connection. Once finished I haven't had to readjust the rails during the entire time i've used the tower.
Dang I'm gonna have to pull her out of the shed this evening and take some better photos...Could be a day or so but I'll up load some detail pics soon.
 

Micromeister

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Didn't take as long as I thought it would:) the pic page below had to be really reduced in res and size to get it under 100k so I suck large letters A-M in the lower right of ech photo, Let me know which pics you'd like to see in a larger format.
 

illini

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Howsabout B, D, G and L for starters? Thanks a bunch!
 

illini

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Great pics. Thanks! That's a beaut. The wheels are turnin'...
 

Micromeister

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One more observation from the last two competition years.

Since Apogee (who used to make a very nice alumimum rail tower which I think may still be available througth BMS) discontinued the 10.5mm competition motors and many of the long delay 13 and 18mm bp motors for estes have gone the same way. I have notice a number of BTC's using "enclosed tower launchers" these are not "closed breach Launchers" which I still believe are illegal for competition. but reduce the wind disturbance factor as the model climbs the tower. Most I've seen are 4" dia and 6 to 10 feet long. some with bottom caps others without. the internal rails are usually 1/2" round aluminum tube, with draw springs on 1/4-20 machine screws through the sides of the pvc tube and adjusted from outside with wing nuts. Some are fitted with piston adaptors in the bottom "cap". These are really BTC items with a max model dia to support the Pratt or Apogee Egg capsules, but mainly used for P/D and S/D models. Wish I had thought to take a photo of one but alas I did not:(
 

wyldbill

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Thanks MM! Truly worth Nx1K words. Can we have A and M as well please?

Much appreciated,
-bill
 
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