WOT: mechanical engineering question Options

[TonyAKAVW]

I'm building a "roto-lok" system http://www.roto-lok.com/tech/technology.html

for the rotation of an antenna for amateur (ham) radio purposes.

I'm trying to find an equation that relates the radius of a pulley/drum to the total friction. Basically I want to make sure that I put sufficient turns of wire around the drive shaft so that it does not slip. I've been searching on the web and I can't even really find equations relating tension to friction, etc.

Any advice on where to look?

-Tony

[TonyAKAVW]

Well, lets say there is one turn on the large drum, with some resulting friction. The capstan must at the least be able to provde this same friction, or else the cable will slip on the capstan. I plan on increasing the friction by adding more turns of cable to the capstan. What I want to know is how to calculate the number of turns for the capstan given that the coefficients of friction are the same, but the radii are different. I think that the weight that I'm turning doesn't factor in to finding this out.

Now if I find that I need to have two turns on the large drum, then I would have to double the turns on the capstan. I'm planing on using as many seperate strands as I can to make the coupling as stiff as possible, but that is in part at least constrained by the number of turns I need on the capstan to prevent slippage since the capstan is not extremely wide.

For the bearings, I'm using needle bearings on precision gound hardened shafts, so I don't think their friction will be a dominant force here????

-Tony