Tight wire construction; balancing a unicycle on a tight wire

There is again interest in building tight wires and riding unicycles on
them, so I’ve decided to repost in slightly edited form my most
comprehensive post on the subject dated Sat, 30 Mar 2002 15:01:20 -0600.

Appended after that additional brand new material on how to build a
tight wire! Yay!


I did research and tried unicycling on a tight rope many years ago and
may have a few ideas to offer that may not have yet been suggested.

Tips on modifying a unicycle for use on a tight wire (reposted):

The wheel should have a 1 3/4 inch or wider rim with a molded rubber
compound put in with about 1 inch wide track for the wire as I recall.
I never built such a wheel, but rather used a bare 3/4 inch rim instead
that didn’t work very well due to low friction between it and the wire.
Tom Miller probably has much greater experience in this area as well as
in all areas of tight wire walking and riding.

Unicycling on a tight wire (reposted):

>I am loath to use a balance pole as suggested a couple of times as my
>tightrope experience is all without balancing aids. I feel they detract
>from the performance unless being used for wire walking at a height,
>i.e. 20 - 30 feet or more. And if you suddenly add things like balance
>poles to an act which otherwise didn’t have one, people tend to assume
>that you are have started cheating in some way. And in a sense they are
>correct! Also I have to work in restricted space a lot of the time, and
>a 14 ft pole just wouldn’t cut it.

People (professionals) have definitely done unicycling on a tight rope
without a balance pole. Also, you could use a shorter balance pole and
could compensate for the shorter length with more weight in the balance
pole, particularly more weight at the ends. The use of the balance pole
can be thought of as a stepping stone towards riding without one by
reducing the length and/or weight of the balance pole. Several balance
poles of varying length and weight may help attain the ultimate goal of
using no balance pole at all.

Tips on building a tight wire (reposted):

You want the wire tension to be as tight as possible, but stay well
below the tension rating of all components. I’d recommend a tension of
about 1/10 the rating of the weakest component. A torque wench on the
turnbuckle, adjusted (multiplied?) by the effective lever of the
turnbuckle would help measure the actual tension. NEW[ Measure the
circumference of the threaded rod and divide by two times the distance
between adjacent threads to get the effective lever value of the
turnbuckle. ]

Professional tight rope walkers and tight rope unicyclists use a minimum
of 5/8 inch thick tight wire with 3/4 inch or 7/8 inch more common just
for added grip between the foot or wheel. The added strength of such
wide wires is not really needed, but is still useful in case of major
defects in the wire. A greater number of smaller diameter strands will
be stronger and less prone to catastrophic failure!

Be careful about turnbuckle (wire tightener) strength as these are
usually rated at about 1/10 the strength of the same thickness of wire.
In fact, you can almost ignore the wire as the component that may fail.
Usually it is the cast steel components (1/10 the wire’s strength) or
the wire support structure that will fail. I recall that a U shaped
support structure of a professional’s portable tight wire buckled when
it was tightened after numerous prior shows; it was obviously far too
weak to support the wire (actual strength/failure strength ratio not
large enough) and the repeated stress (fractures) finally did it in!

In designing a tight wire, remember to use components rated 10 times
greater than the needed strength. Be sure to identify and focus on the
weakest components. Almost more important, consider how the design
might fail and adjust it to reduce the possibility of injury or death
due to a component failing (such as a turnbuckle or U connector, etc.)
For example a loose safety (backup) cable or chain could prevent a
broken turnbuckle from becoming a lethal projectile; obviously a safety
(backup) cable or chain must absorb the “failure energy” without itself
breaking. NEW[ Note that a chain the same size in diameter as a cable
with be only 1/10 as strong as the cable. ]

Also consider safety of the rider when he falls. Obviously, a two foot
high wire will almost always be safer than a twenty foot high wire. A
safety net should be safer than no safety net. Soft grass should be
safer to land on than hard concrete. Even tar, especially in the
hottest days of summer, will be slightly softer than concrete. Finally,
don’t forget use full body armour or at least minimal protective gear.

The rest of this post is all NEW material.

More NEW tips on building a tight wire:

For anchors at the two ends of the tight wire, I used these industrial
sized 6 foot long with over a inch thick rod that had a 12 inch wide
spiral auger (12 inches long also). I’d suggest they be drilled into
the ground several feet at a 25 degree angle, the auger end pointing in
line with the wire and away from it. A 6" x 6" post dug down at least 3
feet will also make a good anchor, but the wire must be attached at
ground level, otherwise the post can break in two if the wire is secured
several inches or more above ground (Those inches become a lever and
when and if enough force is applied to the wire, the pole will break.)

For low tightwire supports, I simply used 2 large 8" x 10" x 16"
concrete blocks stacked on each end which placed the wire at about 16"
high.

> Any suggestions on where to get the spiral auger rod anchors?

I would try the Yellow Pages under wire rope or building material. I
can’t remember where I got mine.

> How did you put them in?


|Con. | ~~–,__
|Block | –,__
Ground___________||____________
–o__ ____________________
~~–,__
~~–,__ //,.
///////
"///
I put the spiral auger rod anchors into the ground at an angle of
20-30 degrees from horizontal as pictured above. The little o is the
end of the anchor that the cable or a turnbuckle can be attached to.
(The turnbuckle must be at least a few inches above the ground so the
ground doesn’t prevent turning it.)

> Can you crank them in by hand using a long rod?

Yes, a steel bar about 3 feet long can be put through the (o) eyelet of
the anchor and turned clockwise to screw the spiral auger into the
ground.

To get one of these anchors started into the ground, one may have to
start with an angle of about 70 and reduce the angle while turning till
one reached the desired 20-30 degree angle. Otherwise, simply dig a
small pit so the auger can fully engage the ground starting at the
desired 20-30 degree angle.

> Also, I would think that the tension on the wire would break the
> concrete blocks. No?

If the angle of the cable (wire) is 30 degrees, that puts half the
tension force down on the back edge of the block. I’d guess that at
20 degrees the down force would be reduced to maybe 1/3 of the wire
tension.

However, I would still recommend putting a 10" x 16" x 1 1/2" wooden
plank over the 8" x 10" x 16" concrete block to distribute the force
over a greater area of the concrete block.

> What orientation did you use them at? holes up or holes sideways?

Holes up - that is the orientation in which concrete blocks are used
for building construction.

I did try stacking the concrete blocks two high, but I would do so only
if they can be placed on a paved surface. Soft ground or grass can
give a little and that would make a two high stack unstable.

If one high is high enough, don’t use two high. If you are sure you
want two high, I would now use 3 blocks at each end. The side view of
the blocks would be:


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> Any suggestions on where to get a sufficiently strong come-along?

I would use a turnbuckle rather than a come-along. A come-along could
be used to get the cable slightly tight, but you must use a
turnbuckle for the actual cable tightening process for safety reasons.
Get the strongest rated turnbuckle you can; this will probably be the
weakest component (the cable will usually be 10 times stronger for
example). A turnbuckle has a connecting O or hook on either end (O is
stronger) that is part of a threaded rod that goes through the large
turning part:


| |
_____ | ______________________________________ | _____
| _ || |_________ | || _ |
| |_| | |
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|
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_____________________________| | ||
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|______________________________________________|

> Any suggestions on where to get sufficiently strong connecting
> hardware?

Cable eyelets (placed inside a small cable loop to protect the wire
strands), small U bolts (to attach a cable end to itself, thus forming
a small cable loop), large U connectors and bolts can be found where
ever cable is sold. Turnbuckles are also sold there. Maybe even
anchors.

In the Yellow Pages, look up wire rope.

The large U connectors are also a potentially weak component. Get the
strongest that will fit through the O’s of the turnbuckle or the cable
eyelets. Remember that any component that would be under tension anyway
close (10% or more) to the wire tension should be made as strong as
possible.


Here’s a web site with a fair amount of information on building a tight
wire:

However, I’d suggest a thicker cable than 10mm (.4 inch).

Tom Miller of The Unicycle Factory may be a good source of information
as well:

765-452-2692

The Unicycle Factory
2711 N. Apperson
Kokomo, IN 46901

Sincerely,

Ken Fuchs <kfuchs@winternet.com>