Gyro problem when first powered

[john_moore007]

I have been having a problem with the gyro on my trex-450 sport to the point that I actually replaced the Logictech 2100T with a GP780 gyro to try and resolve the issue with no success.

Basically the problem I am having is that I when I power the heli for the first flight the gyro does not seem to calibrate correctly which results in massive tail drift. Unplugging and reconnecting seems to cure the problem and the gyro holds without drifting.

I spent some time messing with the heli last night and noticed that on first power-on the tail was driven to its limits one way so I decided to rebind the receiver (spektrum DX6i and AR6110e).

I have not had chance to test things yet but is it possible that on first power-up the gyro was calibrating to the rudder fail-safe position? I always have the TX powered before powering-up the heli.

Anybody seen this before?

[soggybongo]

Remove the link from the rudder servo arm. Turn on the radio. At this time adjust the ATV on both sides of the rudder to 100% and the ATV on the aux channel to 60% on each side. Make sure you don't have anything else modifying the travel, such as AFR or dual rates. That's just for you guys with fancy radios. Move the rudder stick full left then hold the link over the servo arm and choose a hole that will allow full travel without binding. Check to make sure it doesn't bind to the right either. Ideally, you'll have the same travel both ways, although most models allow for more travel to the right. Adjust the position of the arm on the servo and the control rod length so you get full travel both ways without binding at 100% ATV.In your transmitter, zero out any subtrim, tail rotor compensation, or any other tail rotor mixes. Check to see that the tail rotor pitch does not change in any flight mode, unless a tail rotor command is given. Do this by moving the cyclic and collective throughout their range, being careful not to move the rudder stick to the side. Turn the radio off.Switch on the transmitter then the receiver. Be careful not to move the model. Watch the rudder servo. After a few seconds it will twitch. That means the gyro has initialized. Now move the rudder stick to one side and let go. If the arm returns to center and stops, you are in normal mode. If it drifts slowly to the other end of it's range, or stays put, it's in heading hold. If it's not in heading hold, put it in heading hold mode using the gear switch. If it drifts away from where you put it, use subtrim (or trim tabs, if you don't have subtrim) to stop the drift. When you're finished, the rudder servo should stay pretty much where you put it. In higher end radios that have trim rates, you should be able to get it very still.Now check to make sure the gyro is operating in the right direction. On the bench, move the model so the nose swings to the left. The control rod should move forward, toward the front of the model. Once again this is assuming a clockwise rotation of the main rotors while looking at it from above. If not, switch the "reverse" switch on the gyro sensor.Go ahead and lift the model into a hover and switch to heading hold mode. Do your final trim to keep the nose from turning. Turn the model into the wind and switch to normal mode. Careful here, the model will probably begin to yaw. Get some help if you aren't comfortable with nose in. Make a mental note of which way it turns. If it turns left, shorten the tail rotor control rod. Repeat if necessary. That's it. You're ready to fly...backwards, sideways or upside down...even straight ahead.Fine tune the gain using ATV. In heading hold, the gain should be set as high as possible without wagging. Bump up the ATV on the aux channel until you notice a little wag, then back off a little.

hope this helps

[pchristy]

I've had a problem that may be related with a CSM gyro I use on my Morley Bell 47. On the initial switch-on, the servo "centers" 45 degrees off 50% of the time. Switching the receiver off and on again without switching the Tx off usually results in it centering correctly.

I think its caused by the gyro trying to calibrate before the receiver has "locked" to the transmitter. Switching the receiver off and on again makes the gyro recalibrate, but the receiver locks up more quickly after a short power reset.

I suspect this only happens with Spektrum based systems, but as I'm the only one I know who has suffered from it, I haven't been able to compare notes - until now?

[p4ddy]

I was getting the same before xmas on my logo & my 450. The logo was using a CSM720 at the time so i switched it out & put the GP750 back in but it continued. The same happened with the 450 using a GY401 so i assumed my TX had developed a fault. I sent it (DX7) to Horizon for a check but no fault was found. Strangely enough when my TX was returned the gyro issue on all my heli's had vanished??.

[john_moore007]

Sounds like exactly what I have seen. I checked a few minutes ago and I no longer get the tail driving to its limits on first power-on, so I think that the gyros must have been calibrating from the fail safe setting before the receiver connects to the tx.

Just confirmed in the manual that the failsafe positions on the dx6i are set when binding.

Sent from HTC Desire using Tapatalk

[pchristy]

Sounds like its a more common issue than I'd thought!

I don't know about the DX6 - I'm using a DSX-9 - but I thought that, when in heli mode, only the throttle fail-safes. This actually makes a lot of sense in a heli, BTW!

However, I have never checked to see what the Spektrum receiver puts out before it finishes binding. I suspect it puts out nothing at all, because I *think* that it doesn't have any non-volatile memory on board, and has to grab the fail-safe info from the transmitted signal once its bound.

If that is the case, the gyro will be trying to calibrate against - er, nothing! Which might explain some of the odd results we've been getting!

P4ddy - it could be that they found nothing wrong with your system, but maybe upgraded the firmware, or tweaked it whilst they had it. If this led to it binding more quickly, it would have reduced the problem, maybe to zero?

[cjcj1949]

The rudder bind value should be set to neutral and be the same on the tx. You can check the bind value by switching the rx on before the tx. This does need to be done once a week or after any setup changes. Safety systems must be checked or that can be faulty when you try to use them.