Thank you Thomas. Yes that was the system that I was thinking about.. I will have to search around for more information on it and when it was in production.
Back to the jitters.
Today a parcel arrived at my door that had a few servos in it.. First to get a look at was the Corona DS-939MG Digital Servo. Opening up the case showed a board that looked reasonable as to the soldering. The cable clamping system seemed to work in a sort of way. Overall the electronics side and how the board was located and wired up, was a lot better than the Towerpro MG90S servos. What was rather strange was the fact that Corona has used a resin/plastic gear as the first gear wheel from the motor pinion gear, unlike Towerpro that have an all metal gear train.
Next on the list was the Corona CS-929MG. This was virtually the same as the DS-939MG apart from the servo electronics board. This had the same chip (KC2462) as the Towerpro MG90S servos. So I was starting to get a little concerned as to how this servo would perform with regards to any jitter. I found a solder joint on one motor tag to be lacking somewhat in solder. There was a very small bit there that looked like it would fall apart with time/vibration, so a quick touch up with some solder was needed. The gear arrangement was the same as the DS-939MG.
Both servos were tested on the bench with a variable power supply between 4.8 and 6 Volts. The DS-939MG passed the rudder stick flick test without any problems at all voltages.. Nice!
The CS-929MG wasn't as good, as that did show some tendency to jittering at all voltages used. Certainly it wasn't as bad as the MG90S's but it was there. Further checks were done and it was found that under a slight damping load, that it worked fairly well. So In am happy to use this servo in most situations. The DS-939MG Digital servo would be my servo of choice of course.
I do wonder if Towerpro have tightened up the deadband so much that the servo will hunt all the time, or if they have cut down the component count, that included any capacitor or resistor that helped the servo avoid this problem. Up until now I cannot find much information on the KC2462 to see what is in the circuitry that could explain what is going on.. In mentioning Towerpro I am assuming that what I have is rip off cheapo copies of the real things, as my past experience (two years back when I bought the last good batch) of Towerpro servos was a positive one.
