Tower: Overview and Winch

The tower is constructed from schedule 40 steel 2.875" OD tube.  It is 36' tall.  It is made from a 15' piece coupled with an extruded aluminum coupler.  Guy wires support it at the 15' and 30' level.  A rotary thrust bearing sits at the top for the generator.  Steel plates make up the base which also holds a 15' tube for the lever arm.  This is called the Gin pole.  1/4" steel cable serves as the guy wires.  The Gin Pole is actuated through a coupler to a chain connected to the winch cable.  The pictures below show the tower ready for lifting.  The next set of pictures shows the winch setup.

The winch can move 2500lbs.  I welded a platform out of 3/16" steel angle iron to give the winch arm plenty of clearance from the ground.  The platform is bolted to a concrete pad using 4 1/2" anchor bolts.  The concrete pad is 10-12" in diameter and 3' deep.  I used 6 pieces of rebar, 4000psi fiber reenforced concrete to reducing cracking, and 18" long 1/2" J-anchor bolts.

Now for some physics.  The concrete can withstand 4000psi in compression.  Conservatively, it can take 5% of this for shear forces.  0.05 x 4000 = 200psi.  Now the surface area of the anchor bolts is pi*D*L, which is
3.14*0.5*(17" of submerged bolt) = 26.7
Now, multiply by the number of bolts = 4*26.7 = 107sq inches
The shear force the four bolts can hold in the concrete is 107 sq in * 200lbs/sq in = 21,400 lbs.

This seems like a lot.  The bolts will give before the concrete lets them go.  In other words, the winch is not moving anywhere.

What forces will the winch see?  The tube weighs under 6lbs/ft and is 36' long.  The generator, blades and tail probably weigh close to 60lbs.

Tube: 6lbs/ft * 36ft = 216lbs. Center of gravity at 18'. Momement = 216*18 = 3888ft-lbs
Generator moment: 60lbs * 36ft = 2160 ft-lbs
Total moment = 6048 ft-lbs

The maximum force will be when the tower is at zero degrees and the gin pole is at 90 degrees.  The 15' gin pole needs a moment equal to the tower-generator moment:
15' * X = 6048
X = 403lbs

The winch cable pivots 20' from the tower pivot and connects to the top of the 15' pole, making an angle of 37 degrees.  Using basic trig:
403/F = cos(37)
F = 504 lbs

So, my winch will easily handle 504lbs of tension on the cable.


The anchor is made from 1/4" angle iron and welded into a T shape. The base is about 3.5' wide. The anchor is sprayed with Rustoleum. The hole is more than 1/2" from


The guy anchor is to the left and is close to a 50deg angle with the ground. The pulley anchor is close to vertical. The cable running through it is connected to the winch. The pulley has a minimum breaking strength of 7500lbs and can accommodate a 1/2" cable. If I use 25% safety factor I can have 1875lbs of pull on the chain which is rated for 2000lbs. I got the pulley from CMI Gear.