Replies to This Discussion

Permalink Reply by Michael Pursifull on August 1, 2012 at 12:39am

Why do you want to send the position data over telemetry twice a second? 

How would having that information at the GCS/Mission Planner help improve your position hold?

Permalink Reply by Michael Pursifull on August 1, 2012 at 12:42am

See Configuration/Planner/Telemetry Rates - Position. This is where you would usually adjust how often the position data is sent to your ground control station/APM Mission Planner.

But changing that does nothing to improve your position hold mode. Position hold, like all of the flight modes, are handled by the APM, not by the ground control software...

Permalink Reply by Michael Pursifull on August 1, 2012 at 1:23am

hertz

Are you attempting to export the position of one APM and feed it to another for "follow me"? I believe the ctrl-g option to export position data is fixed at 2Hz. The default position rate is 3Hz, if I recall correctly, already faster than you are trying to set it for....

Permalink Reply by Michael Pursifull on August 1, 2012 at 10:54am

Follow me is implemented, in the APM, as "GUIDED" mode. A single position is fed to the APM, and it navigates to that position. It is not a "Position Hold Update", it is a "go here" message. 

At least, I think that is how it works, I haven't looked at it myself, and that is from memory, from reading others' posts.

Permalink Reply by Gustav Kuhn on August 1, 2012 at 11:38am

In Mission Planner, "Flight Planner" window, press Ctrl F, that brings you to an advanced menu.

It is self explanatory, other than altitude.

Maybe that is set up by "Default Altitude" ?

Permalink Reply by Michael Pursifull on August 1, 2012 at 1:26am

bear in mind that the actual "Follow me" new position instructions will have their own latency, as will processing the "new" command to navigate to the new position. That is a separate issue from the question of how frequently just plain old simple position hold is having its position updated.

Permalink Reply by Michael Pursifull on August 1, 2012 at 1:28am

add to that the radio telemetry link latency itself.... which in the case of a busy Xbee link can sometimes be on the order of a couple of seconds...

Permalink Reply by Michael Pursifull on August 1, 2012 at 1:15am

What is your position hold doing now? What would you like for it to do? What GPS do you have?

1) you can change the rate of reported position from telemetry inside APM Planner-> Configuration/Planner/Telemetry Rates - "Position".

2) the APM *is* checking/updating its position while in position_hold, at about 10 times a second (but it might be getting new GPS data less often, at 5 times a second, for example.)

Permalink Reply by Michael Pursifull on August 1, 2012 at 2:39am

I had never looked at it before, but I took a peek at the code. If I am reading it correctly, the APM Mission Planner's mainloop updates the pan/tilt at 10Hz, and there is a comment that notes that the default position update from telemetry is 3Hz. 

But why would you care, Monroe, you just point your antenna straight up anyways, right? ;-)

Permalink Reply by Michael Pursifull on August 1, 2012 at 3:03am

ah. Well, I'd be more concerned about the one way latency of the GPS, APM, telemetry link, Planner processing loops and back out to the tracker servos, than I would the 3Hz updates. Jon's Challinger is doing some outstanding work which will apply to address GPS latency, which can be more than a second in some cases, and dead reconning between GPS reports. You may want to talk to him about it.  Other than that, avoiding retransmits on Xbee, if used, would help, too.  I believe the 3DR radio has a smaller tendency to accumulate latency, but you'll want to read over the setting recommendations and figure out what reduces the retransmits and ecc if you find they are adding delay. It's really only a significant problem at close distances, since your arc is probably sweeping huge portions of the sky at any significant distance. 

Permalink Reply by Michael Pursifull on August 1, 2012 at 3:08am

I wonder if you can get the stability you want for zoomed optics out of a typical tracker setup..... I'd think you need some very pretty gear to not have motion/vibration fussing. And a gyro would introduce a bit of its own latency, wouldn't it? Anyway, sounds like fun, I'd love to see photos when you start building. 

I've been thinking of doing some rocktoon stuff myself, just for the learning/fun of it, and have been thinking about a rocket-mounted APM, and hacking up some code for it. Let me know if you're still looking for someone to toy around with custom code for it, I'm thinking in the same direction, and I might be able to help here and there.

Permalink Reply by Michael Pursifull on August 1, 2012 at 10:39am

Thanks for the list add. I'm a big fan of HiL. I've been looking for an excuse, besides the known reasons, to start using FG also (mainly have been using X-Plane) 

Are you building the tracker from an APM? It would reduce the parts needed for 3rd parties to build one, but add significantly to the per unit cost, I guess. Anyway, please let me know if I can help with that, too. I can, at the very least, offer a regional (before you go wider) test point for lower altitude tests. I am regularly at 75075 and 75554, so that gives you two remote test points, both of which are close enough for lower altitude tracking tests.

73

kg4sen

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