Q. What servo should I use for my, car, boat, plane, helicopter, etc.?
A. One of the most frequently asked questions is "What servo should I use for.....". While there have been many magazine articles that attempted to provide a general rule of thumb to answer these questions, we offer you the following information.
There are two factors that go into the design of a servo, Speed and Torque. In many cases, Hitec will create one servo geared for speed while sacrificing some torque, then create its twin, which is geared for torque at the sacrifice of speed. Our 525/545, 625/645, 925/945 servo products are perfect examples.
If you are not sure which servos to use go with high torque.
When in doubt ask your peers about servo application questions. Look at what others are using in comparable applications. Usually the kit manufacturer will suggest a servo of a certain physical size and torque value specification in the aircraft, car or boat plans, it's wise to follow their guidelines.
Even though micro servos like the HS-81 may offer 38oz/in of torque, they are not appropriate for larger powered aircraft due to the flight loads placed on the control surfaces. Smaller servos have thinner gears that are inherently more fragile than those of "standard" sized servos.