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(Original Article by Tim McCarty, edited by Bill Pickl)
"$50!" the man barks. "Sorry that's the going price for sail winch servos," the hobby store salesman replies. "Gosh darn it. Well I gotta have rotating cannon….. mumble… mumble… darn things are so big to.. mumble… mumble… and I don't need all that torque either."
Sail Winch servos a love/hate item of our hobby. With this servo and a modified radio transmitter you can proportionally aim your cannons with the knob on your radio so you don't need to look at the ship to see where the cannons are. A very nice feature but it comes at price. So if your budget minded is there an alternative? The answer is yes if you are willing to give up proportional rotation so you get rotate clockwise or counterclockwise and will need to look at your boat to stop the cannon where you want them.
One inexpensive alternative is using a standard cheap-o servo modified to work as a sail winch that turns continuously in either direction. It'll only cost you about $11 plus a quarter for a pair of resistors. What follows are servo modification instructions. Please note this is a common mod used by R/C modelers and robot builders. Many robot websites include similar articles to this one if you need more info.
Remove the four long case screws and take the servo apart. Stack those gears least you forget where they go! Once apart it should look like figure xx.
Look at figure xx. See that thing with the brass end and the three tiny legs. That's a potentiometer, commonly called a pot, and that's gotta go. Just snip those pot legs near the top leaving the legs attached so you have something to solder the mod to.
In figure xx only the legs are left. Off to the side are two resistors we plan solder to those legs. Use either 2.2K or 3.3 K ohms resistors from Radio Shack. The actual total is supposed to be 5K ohms to match the original pot, bit it's not that critical. Ya might want to trim the long resistor wires a bit.
Now twist the wires on one end of the resistors together and solder the wound end to the center leg on the board. Solder the other end of each resistor to one of the other two legs. Only one per leg. You should now have something that looks like figure xx. Electronically you are telling the radio the servo has reached its center position. So it stops when the stick is centered and moves if you move the stick of center.
Note the gear in the photo. If you look closely you'll see it has a little plastic nub that limits the gear from rotating more that 60 degrees. Well we can't have that! Grind that nub off with a dremel or melt it with a soldering iron or use whatever destructive means you want.
Reassemble the servo and make your own sail winch drum by taking a 5/8" diameter wood dowel rod and drilling a ¼" hole down the middle. Cut off a 3/8" thick slice and screw this to a standard round servo wheel. Glue on a
(Continued on page 9)
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