Trouble with Sail Servos
Having trouble with Sail Servo. Damon had a problem with his sail servo on Sunday. The gears stripped on it, they are plastic, and he has to buy another. The reason, I think, is that the mainsheet tension was too tight. The servo was not allowed full swing as the sail was in all the way. In the sheeted position the servo could still have swung about a half inch more. He was letting a kid sail his boat who did not understand that when the sail is in it does not have to be pulled in constantly, but the adjustments were too tight anyway. The servo is capable of pulling about 138 inches of torque, according to the liturature, which is more than the gears in it will take, apparently. Make sure that the sheets are not tight like guitar strings when the sail is all the way in.
How will he have to replace the servo? I told him that a nice replacement is the HiTec 645 MG sail servo, for about $40 (read further before buying). It will drop right into the mount when he takes the old one out. He will have to cut the wire and install a plug to the receiver. The best thing to do with the sail arm is to use the new white plastic round piece that comes with the servo and shave down the sides so it will fit into the old sail arm. Then glue it in, West Systems Epoxy works well as John McBrearty found out. Rough everything up with course sandpaper to make sure you get good contact.
I just did some research and found some other servos that would be appropriate for the task.
|HobbyPeople||Servo City||Tower Hobbies|
|HS-5625MG||109oz at 4.8vlt||1.57"x0.78"x1.45"||2.18oz.||<$55||<$50|
|Cirrus 704MG||181oz/195oz||1.6 x .78 x .61"||1.73 oz||$30|
|Cirrus 750MG||127oz/149oz||1.6 x .78 x .61"||1.93 oz||<$25|
|Cirrus DS751MG||149oz at 4.8vlt||1.6 x .78 x .48"||1.93 oz||<$25|
|Cirrus 701||126oz/144oz||1.6 x .78 x .61"||<$20|
The Hitec 645MG is the recommended replacement for the sail servo if it goes bad. As you can see by the chart is about 107oz/inch torque for $40. For $70 you can increase the Torque by about 40% with the 985MG. For $115, and why would we spend that much, you can increase the torque 2.5 times with the 5955TG. Another alternative is to get the Cirrus 704 MG, which is okay, not as good as Hitec I am sure (cheaper right?). But for $30 on the internet (32.99 in the store) you can get 181 oz/inch of torque. I looked at it in the store and it looks like it should just drop in to the same place. When mine goes bad I will try out the Cirrus as I think it is the best buy.