Summary: Takeoff from a foam pad on top of dry grass/lumpy lawn alleviated instabilities experienced when taking off from the dry grass/lumpy lawn. No gain changes made to the 3DR ArduCopter code, using the "factory" settings for Stabilizer and Acrobatic modes.
Started basic flight testing of a ready-to-fly 3DR ArduCopter-B with APM 2.0, in cross-configuration, under R/C control at first (and a ground station with XBee or 3DR radio telemetry with an EEE PC laptop as the ground station to follow in the near future.) The drone's designation is PeeDee 2.
(PeeDee 1 is another story, an earlier ready-to-fly arducopter from Udrones that's now sitting in the metaphorical hanger. The APM board does not command all four motors, the multiplexer chip appears to be failed and in need of replacement. PeeDee 1 is scavenged for parts as needed.)
Installed a 7 channel Futuba R617FS receiver. It's hard to secure under the cap of the stack-up plates above the APM 2.0 module because of the connectors to the APM 2.0 inputs connect normal/perpendicular to the receiver. Cramming it all under the topmost stack-up plate bends and stresses the connectors - an invitation to future trouble. The receiver is therefore stuck and held in-place between the topmost stack plates with double-stick tape, and with receiver antennae routed out of the stack ninety degrees to each other to help hold the receiver in place. May move to velcro to hold the receiver to the stack plate in the near future. (The receiver is visible in the photo.)
PeeDee 2 ground testing took a couple of calendar days. Used the Arducopter Wiki as the ground test plan:
1. Calibrated radio channels with LIPO disconnected.
2. Automatic ESC calibration
3. Motor direction and connections check with CLI mode and Motor command. Watched the paper labels on the motors to gauge the direction of motor rotation.
4. Re-leveled sensors and adjusted magnetic declination before Sensor checking. Used the Configuration page in APM Mission Planner 1.2.10 with mavlink 1.0.
5. Sensor checking - used APM Mission Planner 1.2.10 with mavlink 1.0, watched Flight Data page graphics update when PeeDee 2 pitched, rolled and yawed by hand. Also, lateral, vertical and longitudinal displacements, looked at the raw data on the screen. All ok. (did re-level PeeDee 2 using the Configuration page before sensor checking.)
6. Finally, attached the props, careful to check prop type with motor location in the cross configuration.
Initial ground test on dry grass (Seattle area rain free for 40+ days.) After GPS lock indication (blue light on top), ran engines up to point where PeeDee 2 started to lift off, but not lifting off, then throttle back down. Props stayed on. Did this several times to look for any vibrations of unusual activity. Ran engines up, and close to takeoff point, pitched the drone up and down, one pair of legs in contact with ground while other pair lifted (front/back). The rolled the drone left and right, one pair of legs making contact with ground while other pair lifted (left/right). Looked ok to try a takeoff, but winds picked up to 5 mph with gusts up to 8 mph. Waited for gusts to die down before every takeoff attempt.
Takeoffs in stabilizer mode immediately rolled to one or the other side with the drone crashing bottom up. One prop broke. Replaced the broken prop. Again, on the next takeoff, PeeDee 2 immediately rolled over and crashed. A prop popped off, put it back on. Tried one more time to take off. The prop that previously popped off now broke apart into three pieces on engine run-up. Didn't see the crack in it when putting it back on. (Lesson learned - now check all props for cracks, and check props for tightness, after every landing.)
Local hobby store carries 10 by 4.7 props, secured new props and replaced all four. Followed the troubleshooting guidance in the wiki,
"Arducopter tilts/flips over or wobbles crazily when I try to take off."
Discovered a configuration error - had the drone set to plus configuration when it's in the cross-configuration. Fixed the configuration on the Configuration page on Mission Planner with mavlink connection to PeeDee 2.
Repeated the ground test plan - run engines up to liftoff, check pitch, roll, and it all passed. Prepared to take off in acrobatic mode. On every takeoff in acrobatic mode, one or two of the drone's legs appeared to get stuck in the grass and the drone tumbled over. Tried several takeoffs in Stabilizer mode, and again, one or two legs appeared to get stuck in the grass, and the drone would flip or tumble.
Went to a local fabric store and bought a 0.5 meter by 0.5 meter by 2 cm thick piece of foam pad. Put the pad on top of the grass, and Pee Dee 2 on top of the foam pad.
Presto! PeeDee 2 took off reasonably well off the foam pad, every time, in acrobatic or stabilizer mode. When lifting off in acrobatic mode, switched as soon as possible to stabilizer mode. Finally settled on takeoff in stabilizer mode, off the foam launch pad. It's very stable in pitch, roll as it takes off that way.
The throttle response is interesting, though. It takes "extra" throttle to leap up off the foam launch pad, but once above the pad, throttle needs to be reduced in order to keep below two meters above the pad. Otherwise, the throttle required to "break free" from the launch pad is enough to send the drone up a good two meters quickly (a pop up.) This looks like a ground effect interaction with the foam pad.
Takeoff from the foam pad rather than from dry grass on lumpy lawns did alleviate the instabilities at takeoff. No gain changes made, PeeDee 2 is using the "factory" settings for stabilizer and acrobatic modes.