Gps setup question

[Luvmyhelis]

Okay. We are working with a highly modified fpv 700 stretched 600 Logo. Sk720b with Gps2 module. Head speed is 1700 with Edge 693s. Gps is setup to position hold and return to home. Gps gain at 22. Control rates are 250 as we moved them up due to the Logo doing the toilet bowl routine during gps activation. And guessed the previous 180 control rates may not have been enough for the Skookum to react? Now the heli starts pitch pumping pretty aggressively when gps is activated? We tried lowering the gps head hold gains down to 17 but no change really. And am now lowering the control rates down to about 220.

Here is the last gps log, just wondering which way we need to go to 'tune' out the pitch pumping?

Any pointers in the mean time? Thanks guys!

[Xrayted]

Although it seems like it, its not your collective misbehaving Randy, It's the elevator.

Look at the log image and see the blue is collective and stays rock steady where you have position hold activated, but the green elevator is spiking up and down rocking the heli back and forth where you were turning position hold on and off between 55 and 74 seconds according the the event log

Georgi commented on this same thing recently from another member having similar issue with low hold gain, and it once again seemed to point to low control rates. The model is trying to get a response and overcompensates at first when low control rates are used, but will eventually settle in.

Raise them up to 280-300 and see if the behavior changes, but be careful and ready to bail out to manual just in case. Large toilet bowl effect circles when activating GPS was a compass calibration issue back when the GPS was first released and some guys were reporting it. Not using magnetic canopy mounts are you? I wonder if any of the on board FPV equipment is causing compass issues since this model is not the typical build?

[georgi UK]

=] Additionally Randy, and not helping matters, this heli is setup way too aggressively in both cyclic banks for bell gains, bearing in mind the GPS is also using these settings it's a mixed bag to work with.

Reset and lock E40/A48 to calm things down. Ideally setup a bail-out bank and tune that firstly using 100/120 % SL gain. inverted or upright recovery to observe transitions, looking for determined and smooth but not jerky recoveries as a baseline. This is the GPS core unplugged.

I don't get the gov gain setting either, although the heli seems happy??!

[Luvmyhelis]

Ahhh, info! This sure beats searching in the dark with zero idea where to move the values! Thanks so very much for the time and effort. This really helps.

And Tony, good thoughts on the interference issues.
It was a wiring nightmare, with the owner constantly evolving the equipment on top of things. Each time I see the heli it has something new in place. Which doesn't simplify the process. So in the background I am aware other issues may be influencing our gps process. We spent days just grounding and separating circuits just to get the gov working right. And countless hours spent talking to the only other real successful fpv heli guy around, who just happens to be part of our club. He is flying Skookum, but without gps.

But getting these gps values right certainly are a good starting point. And now I know why we saw the quick elevator dip the instant gps was activated, then the pumping action.

So, up the control rates even farther, 280 or above, take down the elev aileron to 40/48 using one of the two available banks with SL above 100%. Then be quick on the sticks and turn it off if things are still dicey. Got it!

How does our gps gain value look? At 22 should we move it at all?

[Xrayted]

Yikes, I missed those crazy high Bell gains! 96 and 100 is much too high and way out of proportion with the control rates. The control rates and Bell gains must be set together in the proper ratio.

I see the "self tune Bell gains" is still activated, so that is what likely jacked those bell gains up there while you were using those low 180 control rates. High self tuned bell gains are indication that the control rates are too low for what is being asked of the model, so it keeps self tuning them up trying to get the response it wants but cant get.

Turn off the self tuning and lock them down to an appropriate level. On big, heavier models I like control rates in the 280-300 range with Bell gains in the 60-70 range, so about a 4.5 ratio of control rate to Bell gain, but there isnt anything scientific in those values other than feel in flight, and my GPS seems to work well with them too. The factory 3D pre-sets are at a 5:1 ratio as well as Georgis recommendations assuming you stay down at the lower 250 control rate value.

My GPS hold gain has always worked well in the 20-30 range

[Luvmyhelis]

Gotta tell you guys both thank you! Mikes heli flew in gps mode like it is supposed to. We are testing with higher tail rates tomorrow to get that part sorted also. But it held in very gusty winds in position hold within roughly a foot small box of movement.

Mike wanted me to let you know his deeply felt appreciation for the help he received on this thread. Honestly, I don't think in the years now I have know him, I haven't seen him this happy or jacked. You guys nailed it!

During the tuning procedure I did notice the bell gains increased as we increased the cyclic rates, which may explain part of why those bell values were so high when we tested it with the previously higher than 180/200 rates we had moved up to 250. As I didn't quite understand we were robbing the Sk of its own control of the heli in gps.
I now get it!

[georgi UK]

=] Saying hi to Mike, not sure where the settings finally ended up, I was trying to remote tune the on-board gear package also. Randy is eyes on and knows what to look for.,,,,,,,

[Luvmyhelis]

I just got a phone call, and now have yet another gps equipped heli to setup from another heli guy from the neighboring state. This time a 700 Lama Scaler. Should be fun......

[georgi UK]

Originally Posted by Luvmyhelis

I just got a phone call, and now have yet another gps equipped heli to setup from another heli guy from the neighboring state. This time a 700 Lama Scaler. Should be fun......

=] You gotta post pics for that bro!

[Luvmyhelis]

I will here shortly post up pics of both I hope. Anyways. We flew the Logo yesterday. Hit Pos hold in a hover, it held perfectly. However in the next instance during a slow bank, he hit it again and the pitch pump was back again. So, raise the rates again even further?

GPS Test 7-24-16 (6 min 15 sec)

Dangit, the skl file is too big. Can we compress zip here and post?

[Xrayted]

Randy, if I understand your post correctly you guys are hitting position hold while the heli is still in flight motion?? That is not the purpose nor the proper method of using of PH if true. You should already be in stationary hover when activating PH, and as you stated it works fine this way.

GPS cannot stop a heli in its tracks while in flight, so I would fully expect there to be an unpredictable and possibly violent result as the heli tries desperately to hold a GPS position that was referenced when activated, yet isnt possible at all to achieve with its inertia already taking it well past that point.

Deck rescue or rescue now has a + pitch component to it first which will stop much of the forward momentum of the heli before placing it in hold at the end of the rescue, and even then you may still get a little wide swinging or bounce depending on what the heli was doing and how fast it was moving when the rescue occurred beofre it completely settles in. Less FFF typically = a smoother rescue, stop and hold.

You dont have this upward momentum advantage if you simply slam the brakes on using PH while in normal forward flight, so you need to slow or stop the heli first on your own beofre activating PH

[georgi UK]

=] Please email me the log Randy, is that head running CCW?

[Luvmyhelis]

Originally Posted by Xrayted

Randy, if I understand your post correctly you guys are hitting position hold while the heli is still in flight motion?? That is not the purpose nor the proper method of using of PH if true. You should already be in stationary hover when activating PH, and as you stated it works fine this way.

GPS cannot stop a heli in its tracks while in flight, so I would fully expect there to be an unpredictable and possibly violent result as the heli tries desperately to hold a GPS position that was referenced when activated, yet isnt possible at all to achieve with its inertia already taking it well past that point.

Deck rescue or rescue now has a + pitch component to it first which will stop much of the forward momentum of the heli before placing it in hold at the end of the rescue, and even then you may still get a little wide swinging or bounce depending on what the heli was doing and how fast it was moving when the rescue occurred beofre it completely settles in. Less FFF typically = a smoother rescue, stop and hold.

You dont have this upward momentum advantage if you simply slam the brakes on using PH while in normal forward flight, so you need to slow or stop the heli first on your own beofre activating PH

Ahhh, understood, and thanks!

Originally Posted by georgi UK

=] Please email me the log Randy, is that head running CCW?

Nope, the head rotation is CW. Log sent....

[georgi UK]

=] Awaiting your reply for the log,,,,,, and as Xrayted is explaining, when PH is triggered the GPS has it's primary target. Which gets ugly in fff, so the trick is to toggle the PH again to erase it's memory and give it a fresh one which will then be more realistic,,,,,,,

[georgi UK]

=] Take 2 ,,,,,,, Randy I think while Mike is testing things out, get him to temp. position the go-pro to include the Super Brights status,,,,,,,