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View Full Version : When is a high torque servo neccessary?



jingalls007
04-14-2011, 03:46 PM
.. servos don't seem to get to much attention on the forums but I am currently servo shopping and wanted to get a few ideas on good, reliable servos. thx

Fluid
04-14-2011, 04:58 PM
The bottom line is you need a servo which will have enough power to maintain your steering input under all conditions. For RTRs like the SV27 and UL-1 a standard servo with at least 40 oz-in of torque on 4.8 volts is adequate. Heavier, faster boats need more torque IME, and I usually don't use servos with less than 100 oz-in on P and Q boats. And then I will usually run 6 volts (a 5-cell receiver pack) which increases the servo's torque by ~25%. On big, heavy 10S boats I run a quater-scale sized servo with a minimum of 150 oz-in of torque at 4.8 volts. You can buy smaller servos with the same power, but the larger ones are cheaper and because the parts are bigger they are less prone to break.

I prefer a digital servo especially on SAW boats because these servos have strong centering power to hold the boat on a straight line at very high speeds. I had directional stability issues with standard servos - no problems after the switch to digitals.

What happens if you don't have "enough servo" in your boat? I've seen several instances where the boat's handling was poor, the turning radius wide, and the boat would hook in turns. This was all due to inadequate servo power, changing to a stronger servo solved the problems. I believe that a lot of the handling problems boaters experience are due to weak servos, or inadequate voltage to the servo....

This latter is a hidden problem which few boaters even think about. On a big fast boat the high torque servo will pull a lot of amps (relatively that is). The wire on most radio switch harnesses is very small gauge and it will have a voltage drop at 3-5 amps drawn by powerful servos. That means you servo is not putting out the power you paid for. Use switch harnesses with heavy gauge wire and minimize the length. Lots of gas boaters found that their boats steering was improved by using thich wire.

This servo is very popular for fast 4S and 6S race boats:
http://www.servocity.com/html/hs-645mg_ultra_torque.html

.

ron1950
04-14-2011, 05:16 PM
thanks fluid ...i didnt ask the question but i needed the link to the hitech servos....

jingalls007
04-14-2011, 06:05 PM
Jay, you ALWAYS educate me, I can't thank you enough =)