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]

Actually this is for adjusting the elevation angle for microwave and millimeterwave antennas, as well as an optical transceiver. The beamwidth of the antennas is less than 1 degree and for the optical equipment, far less than 1 degree. For the optical setup I'm going to use this elevation control as a rough alignment and then micropositioner motors (with 2 um resolution) for fine adjustments. Each transceiver is about 30 lbs and on will be used at a time.

So basically this thing has to have zero backlash and tight coupling, as well as zero slippage. That for the most part rules out gears and chains, though I suppose zero-backlash gears could be used. Belts would also work I suppose

To get an idea of the size of things, the driven drum will be 6 inches in diameter and the drive capstan, 3/4 inch diameter, both made from 6061 aluminum billet. Initially it will be hand controlled, but eventually I'll add stepper motors so that I can computerize it and automatically track a received signal for best performance.


-Tony