Let's separate "need" and "want" shall we? Does Josh need 7s? Probably not. Does Josh want 7s? Well, I know the answer.... Andy.
So after some more flights yesterday (MAN I love the longer battery life!!!!) I do have some vibration problems coming through the gimbal... I need to go through and re-check everything for propor balance. I may also need to remove the zip-tie mod for the vibration dampeners that I was using previously. I have another idea to try and help smooth it out without using the zipties. I also need to adjust the throttle curve on my MX20... Josh
Interesting to read that you may need to remove the cable-tie O-ring modification, Josh. What's leading you to that conclusion? Andy.
How hard the jitter is. Its not the smooth jitter like it was before. It seems the zip tie is making worse now.
Hey Guys, Thought I would give a little update on how everything is going. I have made a few adjustments to the PWM Converter. One specifically was adjusting the PWM refresh rate from the PWM converter to the ESCs to 500Hz. I know this is higher then the ESCs can handle but it smoothed out the flight characteristics by a decent amount. It made a noticeable difference in how it flew. I still have some off vibrations coming from either the props or the motors.. but it did get a little better from where it was before. If I fly with the radian turned off the footage isn't smooth like it should be when it's off. However this is an issue I had even before I did the upgrade so I don't think it's upgrade related... possibly just a prop/motor balance issue. Here are a few videos of the copter in flight so you can see how stable it is! BTW, with 2 8000mAh 5s batteries I am getting around 18 1/2 min of flying time before the low voltage warning shows up. This is with a 5DMKII mounted. I have the remaining items for my first RED EPIC flight test arriving tomorrow. Im hoping to have a flight with one this weekend or early next week. SloMo: Normal: Things left to do still: Adjust the GPS and Alt. Hold so it all works correctly. Currently if I flip the AH switch the copter shoots up... thinking it's just a throttle neutral point issue... Thats what im hoping anyway. Josh
Josh: Can you verify whether you have Vario altitude control selected -- if so, then you shouldn't need to worry about throttle neutral settings. Andy
Hey Andy, Here is some sample footage. The first is with Radian on. This is a 5DMKII with 50mm lens. Here is with Radian off. Also 50mm on 5DMKII Where are these vibrations coming from???? Any thoughts would be great. Josh
A quote from a previous conversation with Andy: Here are my answers: 1. Yes there isn't much of a difference... 2. Yes... do you think this is from motors/props? I am re-balancing props right now... a few were off... I've balanced then 3 different times now and they seem to change every time. What would the odds be of the balancer being off? If the shaft is off balance slightly how much will that affect the prop balance? 3. Yes. The majority of the jitters are in the tilt. Any help would be great. I spent a couple hours working with the PID settings and it didn't really seem to help. It did a little but not enough to fix the issue. Maybe im doing that wrong? Thanks everyone! Josh
That just means that the Radians and servos are not implicated. So that's one thing less to worry about! The dynamic balance is a product of the motor and the prop -- even the angle of the prop with respect to the motor casing is likely to make a difference, I suspect. (Edit: By that I mean the orientation of the propeller in the horizontal plane with respect to the motor casing -- if the prop is slightly out of balance and the motor casing is slightly out of balance and that heavy blade ends up above the heavy side of the casing then the whole assembly will shake more.) Furthermore, as I mentioned in an email (but will reproduce here for the benefit of forum members) my working theory is that the gimbal can only cause low frequency vibrations below about 5 hertz because it's like a pendulum and it just doesn't want to shake faster than it's "natural" resonance. Therefore, if the vibration is faster than 5Hz, it's probably coming from the motors/propellers.... However, the motors and propellers can also produce low frequencies -- if one motor is vibrating at 1,000 Hz and other is vibrating at 1030 Hz, if the vibrations combine (coming down the booms into the hub, say), then the result is that you get a "beat frequency" of the difference between the two other frequencies -- namely 30 Hz --- the same holds true if the difference between the two motors is only 5 Hz! We can see that the motors are changing speed so I wonder whether what you're seeing is indeed the result of a beat frequency? (Edit: On watching the video again, the vibrations are not constant -- they seem episodic, and that would suggest again that beat frequencies might be the cause.) That seems faintly relevant, but I'm not quite sure to what....at least we know that it's not gimbal rotational vibration caused by lateral deflection of the vibration isolators...at least I don't think it is. Will changing the PID values really produce such high frequency vibrations? They look to me (just eyeballing them) to be around 30-40 Hz, but I will immediately defer to Anyone Who Knows This Stuff. Sorry I can't be of more specific help....let's see if anyone else has some ideas. Andy.
Thank you for the information Andy. Like I mentioned earlier... I have gone through and re-balanced all the props... there were 3 that were pretty out of balance. Not sure how or why since they all balanced correctly last time.... I'll be flying again tomorrow and hoping that it will look better. On the PID front, do you have any good information on how the tuning is supposed to work? Just curious! Also thinking about trying out my old APC 14x4.7's on the copter to see if it's any smoother. Josh
Hi Josh: Let me know what you find. Did you see the thread on using a iPhone to balance the motors? If balancing the props doesn't fix the issue, then you might want to check this thread. Hey, and it gives you an excuse to get an iPhone if you need an excuse. I've not seen the situation where balanced props go out of balance....well, other than when I "adjust" the prop by shock-stopping it on a tree. As for the PID tuning, I'm afraid my only source would be Mrs. Google. There seem to be quite a few relevant hits for: mikrokopter pid tuningThis one stands out as containing good info, though: https://sites.google.com/site/mikrokoptertool/advanced-setup Andy.
Ok so I re-read through EVERYTHING again and I think I may know what is going on... I hope anyway. I am going to play around with the ACC/GYRO - comp setting. I have it set on the default 32 and will try playing with that and see if it will smooth out the "Vibrations" that the ACC and gyro's are seeing. I am hoping this will smooth out this odd movement... I half remember having a similar issue on my old setup and after playing with that number it helped... but I don't remember for sure. I might have time to test today... if so I will report back. Josh
Josh I seem to remember a post from Tabb about different props. Think I saw you changed to Graupner e-props. If I remember correctly Tabb said something like the APC SF props were smoother in his experience (para phrase). That might make sense as they are more flexible and would absorb/disipate vibrations better than the more rigid carbon fibre. Wood props are probably in between the two. Same thing happens in real helicopters based on the time of hub, something flexible like and elastomeric hub vs a rigid hub. Benefit of a rigid hub has been that you can more likely fly a loop with a rigid hub .
Josh: Just a thought: Do you have any wires resting against the Flight Control Board that might be transmitting vibration into the board. The FC board should be mounted on vibration isolation standoffs and there should be no motor wires resting against it. That's something I've got to fix on my C8 as when I braided the wires it had the effect of shortening them so that's not much spare wire to guide the pig-tail wires from the Power Distribution Board away from the Flight Control Board and I've got quite a few wires in hard contact with the underside of the FC board. Andy.
Josh, Are you using 6S or 5S? I was talking to Lothar from MK.de and he gave me suggestion how to make the FC ME 2.1run on 6S batteries. Bill