Well, I'd like to think that this isn't so much about a collision of egos but more as both of us trying to learn something from the other. I have only been around BF.net for a while but from what I've seen from Danno's posts he's got pleanty of knowledge to offer. But one thing I've learned over the years is that the more I know the more I realize I don't know. I've learned a lot from others over the years and been shown wrong on many an occasion. If I do have an ego it was tipped off the shelf and smashed on the floor years back...

In any event I certainly hope that Danno is taking this all in a friendly manner and a spirit of learning. I know I am.

If I do seem "preachy" in all this it's only because I enjoy some good natured discussions and flexing my grey cell trying to show why something is the way it is in a way that others can better understand. Trust me, I had to test my own thinking before posting my earlier stuff. But it's all based on my old high school and first year university physics and my intrest in other mechanical hobbies that I've persued over the years.

Now getting back to the spokes thing. The "forces" doesn't originate at the spoke nipples. As you've said the spokes are under tension and actually the spokes are just a conductor of the forces. When the hub applies torque the spokes politely conduct the forces to the rim where the resistance to our motion is located. Being a simple conductor of the force this means that any increase in tension in the spoke is conducted equally and instantly to the spoke nipple and whatever happens at the head of the spoke shows up at the nipple and vice versa. Getting back to the examples the nipples are the equivalent to the screw eye in the wall above the arm pivot.

The arrows on the vector diagrams are just to indicate the direction of the forces resiting the original force. If there's no accelleration then "proper ettiquete" for vector diagrams says that all the arrows are supposed to fight each other such that the center point of all the vectors ends up with a net 0 force. Sort of like if you had three ropes tied together at the center and spaced out with three kids pulling on them from random angles. If the knot in the middle isn't moving and you do a vector diagram it would be three lines radiating from a common point with the arrows at the ends pointed out. All the components of these vectors would resolve to zero net accellerative force on the knot as far as motion goes for this example. The neat thing about vector analysis using diagrams drawn to scale is that it provides a very graphic view of all the forces involved. It's a lot closer to "real life" than using trigonometry calculations to figure out the alterations in loading for stuff like this. But both methods are equally as valid.

I may have a simple way for you to set up this experiment. If you use some thread a stick and a bucket you can do the whole thing and see the results. If you tie the thread to the handle of the bucket and fill it with enough weight so that the thread breaks when you try to lift it. Then remove enough weight that the thread can lift the bucket without breaking consistently. Then set up the vertical pivoting arm. You'll want to use a single pivot or guy threads to avoid sideways movement or make it a T shape with the top of the T against the fixed wall. Now pass the thread from the bucket handle a couple of turns around the end of the arm and lift the bucket up with your upper thread vertical so the arm is parallel to the floor. Start moving the upper part of the thread over to simulate the angle shown in my wall crane diagram. I think you'll find that the thread breaks at around 30 degrees from vertical. Take more weight out so the bucket is about 1/2 the weight of the breaking strength and do the test again with fresh thread. If you're holding the thread in your hand for this second one you should easily be able to feel the buildup in tension as it'll go from the light bucket only weight when the upper thread is vertical to double or more as the angle lays over closer to horizontal. When you do this you should find that if you're pretty close to the 1/2 breaking strength load for weight that the thread will now break when you lay the upper thread over to 60 degrees from vertical. The sin (or cos) of 60 being .5 so the loading increase from this specific angle is double the vertical load.

If you happen to have a digital diet scale handy place it vertically under the wall end of the beam and watch how the compressive forces in the beam build up when you tip the thread from vertical. A padding of something like two or three layers of duct tape stuck to the face of the scale pan should produce a non skid surface for the T to sit against for this.

Howzzat?