I've purchased a few inexpensive replacement servos from HobbyKing for testing. They are a mix of digital, analog, metal gear, and nylon gear.
These apparently came from the same factory, as they are all 'exact fit' replacements with the Art-Tech AS-100 servos that came with my Diamond 2500. The only exception is that they come with wiring that’s too short for use on the main wing without wiring modifications.
Here’s a photo showing (left to right) the HK-15178B (digital), HKSCM9-6 (digital), HK15178 (analog), and the Art-Tech AS-100 (analog)….
Taking them apart to see the gears or replace the wiring cables requires a special #000 screwdriver (Philips, PH000). In this photo, you can see the plastic and brass/steel gears.
The plastic gears look interchangeable, but the metal gears look to have different ratios. The HK15178 (analog) has what looks like it could have carbon-composite output gears, but I’m not sure that’s what they are.
I have a Turnigy Servo Tester and also a digital watt meter, so I was able to make some electrical tests. Here’s the test results…
I've updated the above table with some additional servos that I tested. Here's a photo showing the Henge MD933 next to the Art-Tech AS-100. The Henge servos are slightly taller, but the same width and thickness.
I installed four of the Henge MD933 on the main wing, and two of the Henge MD922 for the Elevator and Rudder. These are the same as what HobbyKing.com sells as HK-933MG and HK-922MG. I found that the Henge can be purchased from China on eBay for about the same price with shipping as buying from HobbyKing.com.
I also upgraded all servo wiring to AWG-26. To fit the Henge servos, removed the mounting tabs by nibbling them off with a box cutter. I also widened the wing servo slot. I will provide details of these mods and the installation in a future post.