Some issues with my WK-M (throttle cutoff in Atti, wobble in atti)

[Sar]

Hi I hope someone can help I've been doing all sorts of searches and find similar, but not exact problems I'm experiencing.

I built a WK-M on an F450 frame. The motors are are Turnigy Air 2215Js (900kV/200W) and the ESCs are Turnigy Super Brain 40A (8kHz PWM, Gov Off, Fast Start, LVC 5.0, Insensitive Overload protection) *I ordered some plushes, but they're on a month long back-order* with an AR7000 Spektrum Receiver on a Futaba 9CHP w/Spektrum module. Battery is 3S/2200mAh. Props are GemFan 10x4.5.

The IMU is mounted dead center and aligned forward, and securely, on the top plate of the F450 with thin 3M foam (2mm?) and no physical contact with any other equipment. IMU wiring is not tensioned and does not pull on the IMU. The GPS is mounted on the medium length pole over front left bolt holes of the F450 frame and aligned forward. Motor rotation was verified against the manual multiple times. The frame has been balanced front/back/left/right.

I set up the motor enable to intelligent mode. In manual flight mode I move the sticks for intelligent start, the motors start. I fly around, I land(throttle all the way down) and the motors run until I do the intelligent stick move to stop. In Atti mode I have to do the intelligent stick move to start the motors, but I notice (on the ground fortunately) that if I pull the stick down below 10% the motors turn off by themselves(!?) This is weird as I expected intelligent mode on the motor start/stop to be the same in all modes. Is this normal?

As for the wobble. Originally I had a lot of wobble in manual mode, this cleared up once I connected the pitch and roll to the remote gain knob. The gain is at 60 percent right now, at 100% it was very wobbly, but OK I got it mostly stable in manual. When I switch to atti it's completely different and gets a substantial wobble, though it's still flyable the wobble grows in amplitude then settles back down then grows again. I'm not sure what's going on that would cause a huge difference between atti and manual mode or what specifically I should be looking at. I remounted the IMU just in case with no difference. In Atti mode I was getting two white flashes on the LED(and 1 and 2 yellow)

If anyone has some ideas on what's going on here I would appreciate hearing them. I'm scratching my head right now.

 

[robvree]

Hi Sar, welcome to MRF. Let me see what kind of wisdom I might be able to help you with.

IMU Mounting - Many people will recommend ditching the foam and using the thin 3m tape that is more like gel. It's strong, secure and also easy to remove if you have to. However I doubt this is the cause of your wobbling. Can you physically wiggle it around with your fingers?

Intelligent mode - Yup, this is how it works. If you start the motors with the stick combo but you do not raise the throttle above 10% within a few seconds they will shut down again. If you do raise the throttle above 10% they will continue to spin. If you then move the throttle below 10% again and keep it there for 5 seconds (3 seconds on older firmware) the motors will STOP. The only way to start them again is with the stick combo. If you raise the throttle raise above 10% BEFORE they stop (5 second rule), they will not stop. I'm not sure why they call it intelligent mode. Maybe something was lost in translation. In any case, you should not ever have to lower the throttle below 10% during normal flight. If you do, you have 5 seconds to raise it up again. If you keep the throttle below 10% for 5 seconds, your multi is probably going to crash anyway because it will be falling out of the sky.

Wobble - First, balance your props. Did you do that? Check them again to make sure. Next, balance your motors. Now is everything secure on your craft? We talked about the IMU. Is it REALLY secure? If everything is secure, good. Now determine your center of gravity. Search these forums and you will find a recent thread with a video that might help. Don't assume your COG is in the middle or between your center plates. You must have everything attached to your craft that you will be flying with. Many of us find that the Z axis is the hardest to figure out and the most moody when it comes to getting solid GPS hold performance. Measure the distances from the COG for your IMU and GPS using the very center (like the core of the earth) of both devices. Once you have all the measurements, REMOVE YOUR PROPS and hook up the WKM to the assistant software. Go through each tab and click the DEFAULT button if there is one. Start at the first tab and begin putting in your settings again. In the Autopilot tab, since you already say 100% for the basic gains is too much, set the pitch and roll to say 80%. Center your X2 knob on your Tx and then enable X2 control of the pitch and roll basic gains. This way center on the knob is 80%. Now turn the knob in both directions and make sure you know which direction increases and which decreases the setting. Leave everything else at 100%. Check the reset of your settings. Power down the multi. Disconnect. Put the props back on (correct way). Go outside, switch to ATTI mode. Arm motors and slowly increase throttle making sure everything is ok before take off. Take off and hover. If things are wobbling (especially if it is BAD), land. Turn the gains down a little and try again. Repeat until the wobble is gone. Don't try flying around just yet. If you are confident the basic pitch and roll gain is set correctly to be just a little below where you get a wobble, GREAT! Once again, go inside, REMOVE YOUR PROPS and hook back into the setup software. Now take a note of where your basic gains are. Select INH so they are no longer controlled via the X2 knob. Now center your X2 knob on your Tx and turn on X2 control for your ATTI gains. Go outside and hover again. This time your wobble should be gone when hovering (you are in ATTI mode right?). Now give the multi some roll to one side and let off the stick. Now go back the other way. When you let off the sticks did your multi level out quick enough for you? If it was too fast then turn down the gain. If it was slow and mushy, turn it up. My guess is you will end up with a setting that is equal to or lower than your basic gains. Once that is set you should be ready to fly around and start thinking about all the other settings to really dial it in.


Hope that helps you get you going.


Cheers!

Rob

 

[Sar]

Hi Rob,

Thanks for taking the time to write a very detailed response.

The foam tape I used for the IMU is high density, the IMU doesn't rock around noticeably by hand. I do have some thin tape that's essentially double sided cellophane tape but with a much stronger adhesive I can try.

That seems pretty odd for the intelligent mode(the diff in operation between manual and atti shutoff). I'll keep it in mind while flying then!

I balanced the COG X and Y with all of the equipment/batteries/etc on board. As near as I could tell the Z is about 1cm below the top plate. I'll redo my measurements as I was measuring from the base of the GPS case and IMU case so that could make a large difference.

The props are balanced, but I need to set something up to balance the motor rotors. I'll need to set something up for that as I can't use my magnetic balancer for that, but it shouldn't be too hard to do.

I'll spin through the calibration again as well and see if that makes a difference.

Thanks for your help, I'll post back once I get a chance to go through these.

Jon

 

[srbell]

For the intelligent mode, I simply set my idle down with a negative value about 10%. After I start the motors I flick the switch so there's no chance of the motors stopping in flight. Not like that would normally happen, but who knows...you could trip or get stung by a bee and accidentally chop the throttle. The bee thing actually happened to me while flying one of my RC jets. Flew in through a hole in my shoe, not a good outcome lol! Don't wear old shoes flying expensive rc gear : )

 

[Shoryuken]

In manual mode, the motors are directly driven via your Throt stick. The gains you are tuning are for Atti/GPS mode. If you want to tame manual mode, use EXP.
In intelligent cut off mode, motors stop when throt is 10% below for 3 seconds, AND the quad is landing on ground. That is to say, motors won't stop in the air during flight even throt below 10% for 1 minute.
Besides what Rob suggested, remember to calibrate all ESC one by one via TX and Rx.

 

[swisser]

Just to back up waht Shoryuken said, in Intelligent and Atti/GPS it will NOT stop the motors even if you go below 10% throttle when it's airborne.

 

[Sar]

srbell: Last night I had been thinking of setting up a 'throttle hold' mix on a switch to do similar, but from the other answers below this shouldn't be a problem. (I'll probably do it anyway for peace of mind and make it more similar to flying helis hehe).

Shoryuken / swisser: Thanks guys, good to know the thing isn't supposed to 'flame out' in mid-air It flys pretty good in manual mode with no expo. I've been flying helis for quite a while and could never tolerate much expo on them but I do use it on planes/FPV. I'll probably add expo when I start attaching cameras. Flying in manual felt pretty nice overall and not uncomfortable. All the ESCs are calibrated as well so I can cross that off the list.

 

[Sar]

I have some news on this, things are performing much better. I didn't re-balance the motors (still planned but I lack a really decent balancing setup that will support motor cans) but I did manage to get things performing a lot better in atti mode. I have the basic and atti gains on the radio. The basic is still set very low and the atti gains are low. My test area is limited to a 6x6 kitchen space due to it being night time and snowy out.

I double checked the prop balances on my magnetic balancer again and was even more picky about the balances. I reset the gain values, started from scratch. I made a minor adjustment to the sensor package placement (z) to account for the difference between the bottom of the sensor and the exact middle of the sensor package(I had place Z at the bottom of the IMU originally) and flew it.

But, one of the biggest changes I made was to crank down the prop adapters crazy tight. I was afraid of damaging the props when doing so but I think this made the largest difference after testing each change. They're the 'clamp' type adapters, which aren't great, but the set screw type I ordered weren't very good. Any idea where to get some really good setscrew type prop adapters? I believe there may have been some slipage (even though they originally seemed tight) that was causing a power loss.

Most importantly I'm not getting white flashes while hovering. Here's the video and, while it's still shaky, keep in mind that a 6'x6' flying area generates a lot of airflow recirculation/turbulence. My micro helis have had the same kind of instability in this room but fly great outdoors. If the weather isn't too snowy outside tomorrow I'm going to take it outside and see how it does.

 

[Tomstoy2]

I think you will find it will handle much smoothr with smaller props. 10 inch are great for performance, but 9's or 8's will allow the controller to do a better job of smoothing it out. Depends on what you want it to do, of course.

 

[Sar]

Things are going pretty good at the moment, thanks you for everyone's suggestions.

I went down to the 9" props and also added some weight (GoPro on 2 3s 2200mAh packs in parallel). My F450 weighs a LOT compared to the other quad in the video (which is on an FY91Q FC) but seems to fly okay. Even the onboard video surprised me with it's smoothness considering I just stuck the camera on the frame and haven't balanced the motors yet.

 

[Sar]

Hey folks, again I just wanted to thank you for the input. Since my last post I've machined and built my own Y-6 with the DJI-WKM controller. I got to try it today but it was windy, even so it was awesome. I was expecting a total tank but it actually flew very well for a 2:1 thrust/weight ratio. I'm planning on upgrading the motors and machining the booms plus doing some mods to the landing gear, but I'm really loving this controller. I put up a video for my blog, being such it has some 'extra' content in it, but shows a lot of the build process.

-Jon