Since I’m certainly no expert on modern digital servos, I called Hitec RCD and talked to their servo expert – Mike Mayberry – to get the technical information for the rest of this article. And the first thing I asked Mike was what are we getting in these higher performance, and higher cost, servos? He said we should expect higher speed and torque, along with improved gears and resolution for finer control increments, with better o-rings and a heat sink. Although the average pilot may not be able to feel these improvements, they are actually an insurance policy for improved flight performance and longevity.
I also asked Mike to give me some specific information on servos in general so we’ll know more of their internal working, which will also enable us to better understand the manufacturer’s servo specifications so we can make a better educated purchase. Here are some of the interesting points Mike had about servos.
Years ago all we had were analog servos with a deadband (or electronic slop) of about 8 milliseconds, but now we are seeing digital servos with a deadband of 1 millisecond for improved resolution. This also means an analog servo requires more control movement to develop full power when compared to a digital servo.
There is also quite a difference in servo motors. The average servo uses a 3-pole motor while a more advanced servo would use a 5-pole coreless motor. The 5 poles provide more steps for the motor to improve its accuracy, and the coreless feature means it’s lighter for improved acceleration. The bottom line here is that the better servo motor will move faster, with more torgue and greater resolution. Not a bad combination.
And now that we have the servo moving stronger and faster, we need the gears to transfer the power to the helicopter. Mike said the normal white nylon gears have been the standard in servos for years, and they do a good job for smaller 30 size helicopters. However, larger and higher performance helicopters require an improved gear set, such as the Karbonite gears offered in many Hitec servos. These Karbonite gears are 4 times stronger than the nylon gears, have no flex and absolutely no wear. These gears are certainly a great improvement over what we have seen in the past.