JR 770T Gyro - drift on the bench.

[malc1]

Hi

I have a JR770T gyro that shows up a slow drift when the heli is hovering and on the bench you can watch the servo wheel gradually move around in one direction.

Any ideas?

[aerocal]

While it may be an issue with the gyro this is generally due to the gyro not having a solid reference to center.If you have trim added in or if you move it when you power it up before it fully initializes.I used a 770 a little bit and didnt have an issue with it but Ive seen this on some of the cheaper gyros.While I dont think its recommended I have added some trim to get the drift to stop on the bench and then reinitiaize and it seems to settle it out.That is if you have already tried raising the gain to the point of it hunting and it doesnt help.This will only occur in HH mode.

[kevinww]

The 770 is one of the very few gyros where it is acceptable to use a bit of subtrim as it doesnt sample the centre pulse of the radio and assumes it is a certain value. If your radio is not sending what it expects you get a drift. You will need to add a bit of subtrim, not trim, to synchronize the centre point that the radio is sending at neutral stick and what the gyro is expecting.

[aerocal]

Subtrim/Trim whatever.Your just readjusting what the gyro expects to see for center.Kind of funny.I havent used one too much but like I said Ive seen it a few times on the GY401(clone) type gyro.Now that I think about it we always figured this was a clone of a G401(Futaba) gyro.Maybe they actually cloned the 770.

[malc1]

Ok thanks

I'll get the heli back on the bench and make some trim adjustments to see if I can stop it.

[Hendo67]

You didn't say what transmitter you're using, but this may apply to you. Your pot center(s) could be a little off which is why you would need to add sub trim to remove it. If you have a DX 8 with the latest firmware, you can recenter the pots. Just go to the monitor screen and look at the values at the right. At neutral stick they should be zero. Use the trims to adjust any off values to zero (while in the monitor screen and with the latest firmware) and you will be re-centering the stick pots. This is not adding trim, but actually adjusting the pot values to a zero value at a given stick (pot) location.
This only applies to the DX 8 that I know of, but may also be a feature on the 18.
Good luck!

[malc1]

I'm using a JR DSX9 (UK model) by the way.

[Hendo67]

Interesting factoid. You can hook up a DX 8 as a master in Buddy box, go to the monitor screen and see how far off your pots are when you activate the slave. Can't do anything about it, but you'll know for sure how far off you are.

We found all this out when we were having a tough time getting FBL controllers to not drift when the slave was active. We had to trim it out on non DX8 radios to eliminate the drift due to the discrepancy between the zero on the different radios. Worked fine once we figured out what was happening. All 3 axis were affected with drift.

[aerocal]

Originally Posted by Hendo67

Interesting factoid. You can hook up a DX 8 as a master in Buddy box, go to the monitor screen and see how far off your pots are when you activate the slave. Can't do anything about it, but you'll know for sure how far off you are.

We found all this out when we were having a tough time getting FBL controllers to not drift when the slave was active. We had to trim it out on non DX8 radios to eliminate the drift due to the discrepancy between the zero on the different radios. Worked fine once we figured out what was happening. All 3 axis were affected with drift.

What you are describing is associated with the Trainer system.It doesnt really have to do with "the pots being centered".Its kind of confusing to describe it in that way.The Master stays where it is setup.In the case your describing you must trim the slave to match the Master.In the case of a single radio not using Trainer system it doesnt apply.

[Hendo67]

You are correct that you will need to trim the slave to the master. What I was saying, albeit unclearly, is the the monitor function of the master can give you an idea of how far off the slave is. My JR 12X stick centers were off quite a bit compared to my DX8. Makes me wonder which one is right, but at least with the 8 I can "calibrate" it myself.
OP- sorry to hijack your topic. I was just trying to illustrate how the trim (or perceived trim with off centers) can affect a gyro.

[aerocal]

Originally Posted by Hendo67

You are correct that you will need to trim the slave to the master. What I was saying, albeit unclearly, is the the monitor function of the master can give you an idea of how far off the slave is. My JR 12X stick centers were off quite a bit compared to my DX8. Makes me wonder which one is right, but at least with the 8 I can "calibrate" it myself.
OP- sorry to hijack your topic. I was just trying to illustrate how the trim (or perceived trim with off centers) can affect a gyro.

As long as I can remember using buddy boxes there was always a bit of difference between radios.Even 2 of the same model.This was true of centering itself too.We can just see it now that we have monitors with a digital number there staring at us.It freaks alot of ppl out.OMG OMG everything should be zero.Not always true.Never has been.The accepted industry tolerance is 3% IIRC.

Yeah we did kind of hijack sort of.But we all are learning something so its all good.Carry on.