to get right to the point, my GY401 has gone wacky; with gyro, servo kicks all over the place, without it is smooth...now for the details:
i built my bergen gasser about 5 months ago. after one gallon of fuel, everything was going just great. then i started to get a tail rotor glitch. when i would start up for the weekend, the tail would kick or wag (depending on your personal vocabulary). because i am a scholar of runryder, i researched and i thought it to be a tuning problem...afterall, if your tail is kicking, the engine is rich!!!. in fact, this was reinforced because what i did was fly for a few minutes and it went away....what i figured was that the plug was a bit "fouled" because of priming or temperature changes (coincidentally this problem occured with winter's onset). so i flew with the tail kicking all over for a few minutes, then it cleared up. this happened for 3 or 4 tanks over the course of 3 or 4 different flying days. now, as time went on and i did more experimentation with video cameras and such, it got worse. it got so bad that the tail went completely nose in from a tail-in hover.
i simply couldn't shake it. i leaned the damn thing till it wouldn't lift off the ground. i then tried the standard settings and tried flying for a while to see if it would "clean up". well sh**%. didn't work. so i did more reading and saw that people were having problems in the past with the GY401.
i talked with chris (bergen...of course) for quite a few private messages. he had some great ideas. first off, check your mechanism for binding. mine is really smooth, smooth as a baby's bottom. then i tried all the tuning changes, rich, lean, even tried the damn setting that gave a perfect hover for the first gallon.... and THAT didn't work! chris had a very great idea, check the voltage. did this happen on a new charge and then as the battery voltage dropped a bit, it worked?
the GY401 is rated for 6V operation, and i chose the S9254 because the S9253 doesn't have any torque. at $100 a servo, this is a tough lesson to learn all by itself. as we all know, futaba recommends 4.8V nominal for the digital servos.
i am using 6V batteries, but before you go wild and accuse me of over-voltage, i have diode-isolated my dual battery pack system and i have a second diode on the tail rotor servo just to reduce voltage for the digital 9254. (diodes always have a voltage drop in them). almost fully charged, i have 5.5V going to my gyro (and the entire system) and since i have a second .7Vff diode going to the tail rotor servo, it is seeing about 4.8 volts.
so i had time today to try some things. i took it to the field and started it up. at idle, the servo was kicking all over. it moved like no tommorow. i put it on the ground and tried all engine RPM's and rotor speeds. the damn thing was very erratic all the time, i thought it was going to break the boom...it was rotating the servo arm about 20 degrees at random.
i went home.
i was desperate so i put in a trusty S9202 on the tail rotor an bypassed the GY401. now when i ran it, the servo was very very smooth. this poses two questions, was it the S9254 digital or the GY401? easy question to answer. i plugged the S9202 that operated smoothly from 0 to 1700 RPM headspeed into the GY401. now when i ran the engine up, the servo was going crazy!
so, apparently the GY401 has a problem. i am not sure if i have had any sort of voltage spike, if perhaps my sparkplug resistor has lost it's resistance or if something else has occured. i do know that i have seen elsewhere that the GY401 apparently had a bad batch and i wonder if i had one? maybe digital servos just don't work with the gas engines that well? naw, i know that isn't the case becuase everything used to work....
the real puzzling thing is that i started out with a perfect flying machine. everything was real smooth and over the course of 2 gallons of fuel (not starting until after 1 whole gallon), it started wagging all over the place, the tail is kicking like a donkey! i never changed anything except that i have mounted video equipment, etc. and of course i removed that stuff for the sake of the the scientific method. it didn't make any difference.
so my GY401 and my servo are going to futaba for a checkup. i will update the post when the stuff comes back and i re-install them. it is kicking now and it never did before with the exact same equipment so after service, this should be a good experiment for the whole tail wagging problem.
fly like ya live!