Replies to This Discussion

DeveloperPermalink Reply by R_Lefebvre on March 23, 2012 at 2:19pm

I think you could use transmitter trim, if you only fly in stab mode.  But as soon as you go to Loiter mode, it will think you want to move.  

Actually, it may not even work well in stab mode, because I believe there is deadband built in to those controls as well, so you would have to move the trim a lot to get an effect.

The auto-trim is now pretty easy, so it's hard to make a case for using radio trims.

You might want to try some P-terms.  I'm going to put it back in and see if it's still OK.  I definitely noticed the heli was more twitchy when I took it out.  It might be that you want P for flying missions or aerial photography.  But then turn it down for sport flying.

I think the flybar is actually a mechanical PD controller.  The output (cyclic blade pitch) is proportional to the error (the angular difference between the rotor disk and flybar disk) and it dampens rotor disk movement because it resists change.  

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DeveloperPermalink Reply by R_Lefebvre on April 3, 2012 at 3:54pm

Ben, what is your Pitch and Roll Stab I value?

I think that the 10 deg roll angle you are seeing in MP might indicate you have "leans".  How is your APM mounted?  I assume that you see this 10 deg error when the heli is in the air, or on the ground with the rotor turning?

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DeveloperPermalink Reply by R_Lefebvre on April 4, 2012 at 4:37am

Ok first, set those I terms to zero.  That was part of my discovery.  I think what's happening is that some vibrations are sort of weakly aliasing on the gyros.  They aren't strong enough to cause a big error on the P term, but the randomness causes a "random walk" effect on the I-term buildup.  That's just my guess.

Second, using the mounting plate does not guarantee no vibration problems, because it first assumes our heli is relatively vibe free.  If your heli shakes a lot, you'll have problems.  So make sure things are reasonably balanced.  And what is concrete tape?

Third, it's possible what you are seeing in the HUD is simply the fact that your heli is NOT level in the air while you're doing the inflight leveling.  Helis don't fly level.  They always have one skid low.  It's natural.  So then if you set your heli on a flat table, it will appear to be off-level.  Because what the arming proceedure did is trick the APM into thinking that this tilted attitude is "level".  So now when it is sitting flat, it thinks it is off-level.

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Permalink Reply by Ravi on March 25, 2012 at 3:23am

hi malcom. i just hovered my align 450 few inches above ground in stabilize  mode. hovered really stable. but the tail is getting over correction. i am using external gyro futaba401 and have enabled external gyro in mission planner. what should be the gain value for extarnal gyro? the gyro is over correcting. i can see this by rotating the heli about yaw axis. i have connected gyro gain connector to channel 6 out of APM. i know i am wrong somewhere in yaw connfiguration.

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DeveloperPermalink Reply by Randy on March 25, 2012 at 5:07am

Ravi,

     You can actually tune the external gyro through the APM.

     On the APMissionPlanner's configuration screen set the CH6 drop down to CH6_HELI_EXTERNAL_GYRO and then set the Min and Max fields just below to 1 and 2.

     Another option is just to attach your receiver's channel 6 straight to the gyro's gain channel and tune it that way..then reconnect your receiver's channel 6 to the apm's channel 6 and then enter the cli menu.  There's a "test", "radio" option that will display the direct values being red from the radio.

     Not sure if that's all clear but these are the two methods I've used.

-Randy

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Permalink Reply by Christoph on March 25, 2012 at 1:54pm

To free up a channel on the RX, it thought CH6 can be used to send a steady value out as gyro gain. So I attach the gyro gain in cable of my gyro with CH6 out of the APM, enable external gyro and enter a gain in MP, right?

Can I then still use in parallel CH6 for tuning? I am not talking about gyro tuning, but tuning options lie tuning PID values? If not, how can I then feed a fixed signal to my gyro gain and use at the same time tuning options for PIDs?

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DeveloperPermalink Reply by Randy on March 25, 2012 at 4:39pm

Christoph,
Yes, the way you've connected it up is correct. Also you'll find that in the same way you've been able to tune other parameters you (and Ravi）can tune the external gyro．

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Permalink Reply by Christoph on March 26, 2012 at 1:41pm

Randy: Ok, I can send a fixed gain value to my gyro by entering following paramters:

External gyro = 1

gyro gain = value

Will this work independently from setting CH6 option? If I set CH6 option for Loiter P tuning, will APM Ch6 OUT still send the Gain = value as output signal? Or will it start sending strange values out? Does anybody know or do I need to test it?

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Permalink Reply by Christoph on March 26, 2012 at 2:13pm

Sorry, correcting my statement. It is CH7 out of the APM sending the gain value out.

It is correctly in the wiki, so I made a mistake before. So CH6 PID tuning and freeing up a channel on the RX is possible at the same time, when working with a fixed gyro gain value.

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Permalink Reply by Ravi on March 25, 2012 at 6:33am

hi randy, thanks heavens someone is there to give expert advice. i think i am the only one in this part of the world to be using APM for traditional heli. in futaba 7C channel 6 is always assigned to collective when Tx is in heli mode. so i will use the Mission planner configuration to set gyro gain min and max values. this was my first ever hovering using APM. i was surprised how stable the heli was in horizontal plane (roll & pitch). yes i am using a flybarless head from tarrot bought from www.infinity-hobby.com. very good quality stuff for electric helis. so i will try the settings tomorrow. good night randy.

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DeveloperPermalink Reply by R_Lefebvre on March 25, 2012 at 7:09pm

Had somewhat lousy weather this weekend, so I spent most of it in the shop. I decided to try something new with the tail control.  I found the stock linkage is a bit sloppy and has lots of friction.  So, I decided to do something radical, inspired by the pros.  I'm putting the tail servo at the back, controlling the tail slider directly.

So, here's what I came up with, mostly using a few stock parts, some nice metal ball ends I got from Hobby King, and one machined servo mount.  I've also decided to go without any tail fins, to help hold a yaw setting, and also I really like the idea of the tail blade protecting skid hoop.

I just have to figure out the best way to attach that hoop at the back.

The key to making this work is the anti-rotation linkage which holds the pitch slider from rotating around.

A keen eye will also notice that I modified the tail "gearbox" to make room for the rudder pushrod.  Surprisingly, it doesn't upset the balance too badly.  I guess the lack of tail fins helps.  I'm also drastically lightening up on my APM installation.  I probably won't use the aluminum box I made, and the large subframe is gone.  It's now all mounted on a radio plate just a big bigger than the stock one.  After testing it, I can't seem much advantage to the aluminum box.  I still have it, and will still play around with it I'm sure.

And here's a top view:

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DeveloperPermalink Reply by R_Lefebvre on March 25, 2012 at 7:18pm

I also assembled a new APM I got because the old one is getting... old.

I just wanted to show how I hooked up Port K for use with the LED's.  It took some finagling, but I used some of the pins from a 3-row right-angle pin header and reconfigured them.  They pass through the holes in the Oilpan and plug down into the female header on the APM board.  It takes a keen eye to see exactly what I did here:

And here's a picture of the breakout board I made a while ago.  The main purpose of this is high voltage servo power distribution.  It also houses the darlington chip to power the LED's.

And the backside, just to give some idea of what I did.

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