Sunday, August 31, 2014

Flight #4

At neighborhood rec field. Winds 15mph with higher gusting (so "windy"). Just my weekly flight (nothing really special). I stopped flying at 8 minutes before LowVoltageAlarm kicked in.

Before going to the field, I downloaded my log files to laptop for later analyzing. I also added a sticker to the outside of the Nova with my contact info (in case of fly-away or lost after crash).

During a RTL (final descent), quad was at 3 feet altitude when a strong gust of wind hit. I think the "Ground Effect" had started and wasn't helping. The Nova started rocking a lot and it was trying to compensate and level itself. It touched down (fairly soft but tilted) but still flipped over upside down (I think a prop got caught on a vine). No damage.

Because of this event, I think the quad needs more response at FlightController level (when it's in control of itself). As my piloting skills and confidence level with this aircraft have progressed ... I am also ready for a bit more control or "higher rates" for fighting the wind or general maneuvers.

I changed ANGLE_MAX - this determines the maximum "tilt" that the FC will command the Nova. I changed it from the factory setting of 2200 (22 degrees) to 3000 (30 degrees) to give the Nova a bit more response-ability when flying in the wind.

Saturday, August 23, 2014

Flight #3 - Another good flight

Third flight and third new flying site. Today we are at the park in a secluded field. Only non-ideal attribute is there is a power-wire hanging-down in about 2/3 of it (but easily avoided). Winds were 12-18mph. Flew my little v262 quad to warm-up and then let my brother fly the rest of v262 battery (he's a new RC pilot).

Flew some simple patterns and used Loiter-Mode. Loiter was holding good and re-positioning after wind-gusts. All good there. Noticed I can also Pitch, Roll and/or Yaw in Loiter and it then holds at final position ... nice.

Tested RTL Mode for the first time. Worked fine and landed better than me (without tipping over). This is even more amazing to me than Loiter. Tried it a couple of times with success. Noticed you can even switch directly from Loiter to RTL with no problems.

Only had one problem. Incidentally, this was really the first time I've seen the Nova do something un-expected. However, it was the very end of flight/battery and the LowVoltageAlarm was activated (for about a minute already) so I'm going to chalk-it-up to a low battery for now.

This is the event:

Loiter Mode - Good and Holding (fairly high)
Nova activates LVA - Light Flashing and Beeping
Switched on RTL - In hind-sight not smart of me
Gaining a little altitude and moving above RTL point
Reaches position and starts to descend (but slowly as usual in RTL)
Taking a while to descend and fighting wind
About a minute now in LVA - Beeping is getting faster (a bad sign)
About 20 ft off of ground
Suddenly, Nova rolls (banks) off fast in aft-port direction
Couldn't tell if it was flying-off or just trying to crash
I switched to Stabilize (manual) and made an emergency landing on edge of field
No damage. A little too exciting. Battery reads 10.4 volts.

Another good day. Lesson learned is ... when Nova's LVA engages (I think it's at 10.6volts) land immediately ... you are running on LiPo fumes. Also, probably not a good time to purposely engage RTL.

I have pics (so yes, it DID HAPPEN :-) but they are still on my brother's phone.

Sunday, August 10, 2014

Flight #2 - AutoTrim done

I did the AutoTrim procedure. This way, the quad's FC (FlightController) can benefit from Trims also (not just RC operator with "trimed" TX).

Removed Trims applied at radio (during the first flight) and put everything back at 0 or neutral. I recommend you be directly behind the quad, facing the wind. Actually, there should be no wind.

No problem getting into AutoTrim calibration Mode (just hold stick a while longer than required for Arming). If it doesn't work in Loiter Mode, try Stabilize. Red (and tiny yellow) lights will dual-strobe-flash when you enter mode. Only catch is that you have to take-off (with a likely out-of-trim quad) and hold a nice hover for the next 20 seconds. Lights will stop flashing signaling the end of the test period. Land the Nova and disarm to save new generated AutoTrim settings. It's only my second flight, so it took a couple of tries, but I got it done. Takes off and flies much better now (even in a little wind).

Summary: With AutoTrim the roll and pitch trim are captured as you fly in a stable hover.

1. Find a wind free environment with sufficient space to fly your copter without crashing into something. Be sure radio trims are reset to zero or neutral.

2. On Mode-2 transmitter, hold throttle stick down and right for 15 seconds or until you see the small red and yellow leds (behind Arming lens) strobe-flash in a cyclic pattern. Action is like Arming except holding longer.

3. In Stabilize mode, fly your copter for about 25 seconds in a stable hover. IIRC, red/yellow leds stop flashing in flight.

4. Land and put your throttle to zero and wait for a few seconds (the trims are being saved to eeprom). Nova will dis-arm itself.

5. Take off again in Stabilize mode and check if your copter is flying level now. If not repeat steps.

Also, I got to try Loiter Mode for the first time. Worked fine. One of the coolest things I've ever seen one of my RC models do over the years. While Loitering, I quickly took this pic with my iPhone (I know, pretty blurry).

If you are having trouble arming quad, here is a summary: If you have GPS-3D Lock (rear green led is On-steady), AND hdop <= 2.0 ... you can (and should) Arm in Loiter switch mode. Then, switch to Stabilize Mode and take-off. Otherwise, you can just Arm in Stabilize Mode ... but don't expect RTL (pilot invoked or emergency) to work during that flight. Also, don't switch to and try to use any GPS dependent modes like Loiter during that flight.

It was getting dark, but was fairly easy to see whole quad (actual direction orientation ... not so much). Good flight and got in some good practice. Pretty boring flying, but I'm getting more confident with it.

AutoTrim Notes:
While flying normally, you can trim on radio sticks if you must (temporarily to keep from crashing). But to do a proper Auto-Trim, they should be neutralized or centered first. Also, remember that Trimming due to wind forces is counter-productive because you might be pointing in a different direction later in flight. Instead, that's why we have Loiter mode.

If you enable Auto-Trim and do it poorly, the next time you take-off, quad will be out-of-trim. You can either do it again until you get it right. Or, you can use Mission Planner to reset the Trim-Defaults with the following parameters:

Auto-Trim is often required because quad's CoG is slightly off, but I think there might be other reasons. Good pilots have been know to accomplish an AutoTrim procedure in their garages (because no-wind is important), but you will have to get it pretty high to avoid the "ground effect". Also remember that concrete and shelves are hard and cars scratch easy (you have been warned) :-)

More Parameters

Checked some more parameters (suggested in Nova forums). All the parameters are at MissionPlanner/Config-Tuning/Full Parameter List/ . After you change some, click the Write button and wait 10 seconds (to save them to FC internal memory). You can also click Save button to save them to a computer file. I usually do this before and after changing parameters. So that I can have them all in one place, here are some others (some changed after 4th flight). This list has basically become what I am currently running on Nova quad in 2014  Feb 2015.

ANGLE_MAX = 3000 (default 2200)
- This determines the maximum "tilt" that the FC will command the Nova. I changed it to 3000 (30 degrees) to give the Nova a bit more response-ability when flying in the wind. Works in manual flight-modes like Stabilize and also modes like Loiter. Some pilots set it even higher (like 3500).

LAND_SPEED = 30 (default 50)
- Slows the landing speed for RTL and Land. It's suppose to help with tip-overs on auto-landings.

LOG_BITMASK = 830 (Default)

LOG_BITMASK = 958 (Default + IMU [vibrations])

LOG_BITMASK = 26622 (Almost all. A full diagnostic set used in trouble-shooting)

PILOT_VELZ_MAX = 250 (default 250)
- The maximum vertical velocity the pilot may request in cm/s

RTL_ALT = 2000 (default 1500)
- On RTL, quad will climb to this altitude (2000 = 20 meters or about 60 feet) before heading home. I think this should be high enough to miss any trees and houses (for now).

THR_MID = 575 (default 500)
[Now with Mobius camera, stock vibration-dampened camera-mount, 915Mhz Telemetry radio.
AuW with 2700mah battery is 1002g]
- Used between manual-control and other Flight Mode transitions. Not noticing any major altitude changes when switching between Stabilize and Loiter mode. But for the quad at it's stock weight (no attachments or payload) 500 was good then.

WP_YAW_BEHAVIOR = 1 (default 0)
- This determines which way the craft points when flying a mission in auto mode (or RTL). The factory setting of 0 doesn't yaw (turn) the craft when moving from waypoint to waypoint. 1 is so that it points the front of the craft in the direction of the next waypoint. 2 is the same as 1 except not even for RTL.

Others that should already be set correctly by default (in default Nova param file), but you might want to double-check anyway:

Extended Tuning Parameters from Feb 2015 (AC 3.1.2)
PIDs should still be same as stock Nova defaults

Saturday, August 9, 2014

ESC Calibration

Apparently, on the PnF model ... the ESCs are not calibrated at factory. This might be because a radio is not installed until owner receives it. I figure, better safe than sorry ... so I researched it.

Just a reminder that the steps in this blog are presented in the proper chronological order. For instance ... the radio system (and other sensors) should already be properly calibrated in MissionPlanner before attempting this. Likewise, parameters like THR_MAX,1000 should already be set. However, PC should not be connected for this procedure.

Procedure seems to work, but the tones and led flashing are a little different than the posted "all at once" YouTube video (I think since he had full-APM Flight-Controller). If you look closely behind the Red Arming-Light Lens on the Nova, you will see there is actually 2 tiny leds behind it (a red one, and a yellow one). When they both flash (I call it a strobe effect) it indicates you have entered a calibration-mode ... one that you initiated with TX and quad (as opposed to one from MissionPlanner). In this case it's the ESC (All-at-Once) Calibration Mode,

Also, he is using Mode-1 radio, while most of us here in the USA are flying Mode-2 (throttle on left). As the video shows, you enter this mode by holding the (Mode-2) Throttle (left stick) down and to the right ... like you are Arming, but much longer.

Nova ESC Calibration Summary (with FrSky radio set):
  1. Start with Nova's props removed and lipo battery disconnected.
  2. Turn on TX and move throttle to Full.
  3. Switch to Stabilize Mode on TX.
  4. Connect Nova main lipo battery
  5. Red/yellow leds behind Arming lens will strobe-flash
  6. Unplug Nova lipo, wait 3 secs, then plug back in (leave TX Throttle on Full)
  7. Nova's red/yellow leds behind Arming lens should again be strobe-flashing
  8. Fairly quickly (within 1.5 secs) move Throttle stick to OFF (or bottom of throw)
  9. Nova will beep 3 times (2 short, 1 long) signally this step is complete (with v1.0 ESCs)
    1. With v1.6 ESCs, you might get an extra 4 beeps in the beginning, but not with v1.0 ESC IIRC.
  10. You should now test throttle and get an even response from all 4 motors.
  11. Unplug main lipo battery, wait a few seconds, and then reconnect it.
  12. Now arm the motors (with right rudder/low throttle for 4 secs). 
  13. All your motors should spin if given a little throttle.
  14. Your ESC's are now calibrated. No further action is required.
I can't think of a good reason to have motors spin on arming (and several good reasons NOT to), so I then went to:
MissionPlanner / Config & Tuning / Standard Parameters / ...
and set the parameter "MOT_SPIN_ARMED" to "Do Not Spin".
The parameter had a null or empty value at first. Strangely, I had to set it and write it several times before it took effect. Anyway, it works properly now (even after power on/off cycle). A related parameter is THR_MIN, but I left it unmodified.

Motor Test is not required for successful ESC calibration, but it certainly would not hurt to do it. They should all spin and sound about the same. I test motors from MissionPlanner/Terminal (type "test", then "motors"). It will start at Motor#1 [M1] (aka Fore-Starboard Motor) but instead of following the true X4 diagonal-like M# pattern, it will instead ... proceed Clockwise around quad (so it's M1, M4, M2, M3).

When I power up my Nova with LiPo battery, mine always plays (a kinda musical) series of tones or beeps ... short-short-short-(pause)-long. This is with four stock v1.0 ESCs and the 3S-LiPo.
Stock-white Radio Note 1: I don't have one (or have ever held one), but according to forum posts, the ESC calibration with "stock white radio set" is a little different due to the way the TX & RX Bind together on power-cycle. Some say to use a temporary 5v power source (likely a battery) to keep on-board RX powered-up during entire procedure. Or, you can try this way-1 (direct-link) or this way-2 . Finally, Mr.Jagger in forums says this version #3 is best. Be sure to find one that actually works and "settings take".

Stock-white Radio Note 2: True APM Modes and comparable (Nova-CX20 Mode): Stabilize (Manual), Loiter (Stable), Simple (Direction Locked), Altitude Hold (Altitude Hold), RTL (Return To Home). In my docs, I always use the true APM flight-mode-names.

Stock-white Radio Note 3 (using confusing Mode-names from Nova/CX20 Owner's Manual): If you are having trouble Arming quad, here is a summary: If you have GPS-3D Lock (solid green light) AND hdop <= 2.0, you can (and should) Arm in Stable switch mode. Then, switch to Manual mode and take-off. Otherwise, you can just Arm in Manual mode ... but don't expect RTH (pilot invoked or emergency) to work during that flight. Also, don't switch to and try to use any GPS dependent modes like Stable during that flight.

Saturday, August 2, 2014

Flight #1 - Maiden Flight

I flew the maiden flight on my Nova today. Just a reminder ... at this point my quadcopter-flight experience is very limited. I have never flown anything this big and heavy. Winds were 12mph.

It went pretty good. Got about 9 minutes on 2200mah LiPo. Practiced hovering, landings, and simple pattern flight. Landing soft without tipping over is harder than it looks. It also landed hard once (on one skid), bounced-up, and flipped over (sure wish my prop-guards would have arrived by now).

I had GPS lock so I arm-ed in Loiter Mode but took-off and flew in Stabilize Mode. In all the excitement, didn't even get to try Loiter (or any other modes) for normal flight.

I learned if you want to take-off in wind ... punch the throttle a bit and do it (don't baby it). Take-off into the wind (at least at first). To hold a decent hover (without constant adjustments) I had to apply a bit of trim at the TX (not exactly proper procedure for APM-FC, but I didn't know at the time). Also, when lowering throttle to reduce altitude, do it very slowly. Nova really picks-up speed on descent (and ground is hard :-)

Called it a good day. Only a few scrapes ... but props, landing gear, and rest of quad looks fine. Nice outcome of weeks of planning and plotting. I like it.