MK FPV Heavy-lift X8 using standard ESC's and Futaba TX/RX

Mactadpole

Mactadpole

Member
Bartman said:
Shawn
Regarding the hot motors and ESC's.....a coax arrangement should have props with a slightly higher pitch on the lower motors as they are operating in the wash of the upper props. This has the effect of lowering the angle at which they are flying through the air which is basically lowering their pitch. If you're using 12x3.8 on the tops then the bottoms should be at least 12x5 or even 12x6, it's a trial and error thing.
WIth the props you're using you may actually be making the lift equivalent of a 5 or 6 rotor craft instead of a heavy 8.
Are you flying at the high end of the throttle curve just to hover? I've got at least what you're carrying on my standard Okto 2 and it hovers around 65%.
Click to expand...

Hi Bart,

I have the lower motors running about 10% faster than the top which I thought alleviated the need to run different pitch. I guess I should look into this more. I seem to have plenty of power as it hovers around 45-50% throttle. I am going to go ahead and put the 13" props on and see what happens. I have enough 13" to outfit all 8 motors with 13x6.5 props and also have some 13x4 that I could try on the top.

If I could just get rid of the oscillation/wobble it would be perfect!

Thanks,

Shawn
 

Bartman

Bartman

Welcome to MultiRotorForums.com!!
Shawn
A 3.8 pitch prop on the bottom is going to be reduced to virtually no pitch by the oncoming/swirling air from the top prop. Making the prop spin a bit faster will only help if the prop has any efficiency left in it to make more thrust but it will be a small gain against the greater amount you are losing with the coax arrangement.
Try a higher pitch prop on the bottom and you might be surprised. It's possible the lower props aren't making much of a contribution to stability since they're already maxed out just hovering
 

Mactadpole

Mactadpole

Member
So I tried messing with Gyro-D by lowering it to 8 and then 6. The copter flew much better and I could not detect the wobble at 6, but the copter felt a little less responsive than I like. So I finally balanced all the APC13x6.5 props and put them on. A HUGE IMPROVEMENT! It is a bit windy but I did not detect the wobble at all and it just overall felt better. I had Gyro-D at 8 and I turned up P quit a bit and lowered I a little. Can't wait for no wind and camera mounted to really see how its flying. But I have definitely taken a step in the right direction.

@Bartman - At some point I think I will try putting some APC13x4 props on top and see what happens. For now, I'm going to get it tuned with all APC13x6.5 and get in some good flights so I can get some EagleTree data logged for comparison.

Shawn
 


M

Michael64

Member
Hey Aerhead thats is just amazing video and one hell of a good pilot to boot, just an awsome video and well but together.

Michael64
 

S

Stacky

Member
Shawn, glad to hear things are going well with the build!. Where are you getting your APC props from? Thanks
 


Mactadpole

Mactadpole

Member
Well I am still trying to tune the X8 but it is getting better. I am now flying apc13x4 props on top and 13x6.5 on bottom, both at the same speed. I received my Xbee setup today from quadcopters.us and hooked them up with no problem. Until, I went to permanently mount the onboard Xbee and unplugged it to add mounting tape. I guess when I plugged it back in the connector was upside down and caused it to reset when power was applied. I spent hours trying to figure out what happened. I'll spare you the details but if you think this has happened to you contact me and I'll tell you how to troubleshoot and fix. Very excited its working again, going to make tweaking much easier.

Getting up at 5:30am to go flying in no wind! I hope!

Shawn
 

Mactadpole

Mactadpole

Member
Well I never achieved love with tuning. I am also still having troubles with my Xbee setup, the copter side Xbee keeps reseting itself for some reason. I have to hook it up to the copter and write the saved settings from the computer side Xbee to it and then it starts working again. I have sent three emails starting last Sunday to support@quadcopter.us and no response. After it happened again today I sent Sarah at quadcopter.us an email (she helped with the some question and the sale) since I have here direct address and she has always responded. Frustrating customer service. Hopefully they are on holiday or something is up with their support address.

After many flights last weekend I decided there was no hope to get rid of the twitch/wobble and that it must be something with motors or esc's. I decided to go ahead and order now motors and esc's, ugh. I did this because I had read about some folks having issues with RCTimer esc's and a "tick" they had. Also, while most folks have been happy with Pulso motors, I have read about several people having bearing issues and other miscellaneous issues. I ordered ExceedRC 30A volcano esc's and Avroto short shaft motors. More $$$, but I have to get this thing flying properly. I always do a pre-flight check to make sure props are tight and give the motors a spin to make sure I don't hear or see anything weird. I had started noticing a bit of bearing noise from some of the motors. Well, during the tear down and rebuild last night and today I test each motor and esc combo as I removed it by hooking them directly up to the rx and spinning them up and carefully spun them by hand. Results - I found two motors that had bearing noise and one motor that did not spin as freely as the others. Actually, it had about twice the friction of the other motors. On that same motor/esc combo the esc would not initialize properly a couple times. Even after re-programming. Needless to say I am very disappointed in the Pulso motors. I was surprised by the one esc too. I have never had a problem with RCTimer esc's. I hooked that bad one up to a good motor and it did the same thing.

A little bit ago I got the last of the new motors and esc's hooked up and took it for a quick little test flight using the MK default beginner settings. It flew much better but I did hear a whistle type sound and some of the motors were clicking at lower rpm. Pretty sure the clicking is because I programmed the esc's to medium timing. I had to program the RCTimer esc's to high to get the motors to stop clicking. I'm not sure what to think of the faint whistling. Is it just the Avotro motors and their fin style cooling shape on the bell? We'll see after I reprogram the esc's tomorrow to high and take it for a flight again.

Also, I decided to go back to APC13x6.5 props top and bottom and spin the bottom 10% faster for now. I believe I noticed a bit of a flapping noise on fast ascents with the APC13x4 props on top. Finally, I have decided to start balancing the hubs of the props too. It is amazing how badly out of balance some of them are. Those of you who balance hubs, do you use the little piece of fuzzy velcro on the light side of the hub and CA till its balanced with the multi-rotor setup? I saw a video somewhere about balancing prop hubs and that is how they did it. That is what I have begun doing. Got the top props all balanced so far. Some of them sure did need a lot of CA!

Hopefully we will have low winds tomorrow and I can fly to confirm the wobble/twitch is gone.

Please keep your fingers crossed for me. :)

Shawn
 
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O

ovdt

Member
Mactadpole, thanks for sharing your findings. I'm following your topic very closely.

One note about the motors: If one of them spins harder than the others (I assume you're controoling it by your hand, not without power), the problem source can be with magnetism. My suggestion would be to power it to see if it works flawlessy with power.

I had similar problem with MK 3638 motors but after powering it, the problem has gone.
 


D

Docair

New Member
I have been balancing my APC 14x4.7 and they have been a real experience for sure. These will go on my X8 and everyone I have gone through so far have had one edge that has been heavy. I have watched video on hub balancing (probably same one with the velcro etc.) and was experimenting with that route. I found the hubs on the 14x4.7 are very minimal compared to the blade thickness so I bagged the hub balancing and shifted to "edge" balancing. These would all fall to one edge when held vertically (even though balanced horizontally), just like a heavy hub side. I sand the heavy leading and trailing edge pair, and for some I had to remove quite a bit of material using 100 grit followed by 220 to smooth. I only do this on the underside of the blade. This takes some time to figure it out, but results in a truly balanced prop. I also remove all the factory edge flashings all the way around the props with 220 and light on the touch. I have tried to find more info on balancing slowflyers with small hubs and wide blades buy no luck, so I came up with my own method and it works well for me.
 

Droider

Droider

Drone Enthusiast
Think I must have had my eyes shut to this post.. cont beleive I anit seen it..

If awards are to be given to builds this has to be the winner as far as detail and perseverance goes..

Shawn

I see you are feeding 7.4v to your servo motors. I thought they were rated at max 6 volts.. how the working?

Dave
 

Droider

Droider

Drone Enthusiast
Motor and prop balancing.

I get them as close as I possibly can with tape. then check the individual motors using the MKtool motor test and an iPhone on the are or camera mount. I use Vibration app. I can record and save the readings so you can check each motor prop combo till they are all good.. You can test just the motor first. I have found my AXI's pretty good and not bothered trying to better them.

Dave

Edit. by using the motor test you can start the motors very slowley and take them right through there range and with out the props on you can here the noisy bearing no mither.. Just remember not to run your motors to long with out the props on.
 
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Droider

Droider

Drone Enthusiast
Another think with coaxial's.. You got to make sure the props are dead parrallel to each other and the ground. It can take some doing but its worth the time to ensure they are spot on.

Dave
 

Mactadpole

Mactadpole

Member
Docair said:
I have been balancing my APC 14x4.7 and they have been a real experience for sure. These will go on my X8 and everyone I have gone through so far have had one edge that has been heavy. I have watched video on hub balancing (probably same one with the velcro etc.) and was experimenting with that route. I found the hubs on the 14x4.7 are very minimal compared to the blade thickness so I bagged the hub balancing and shifted to "edge" balancing. These would all fall to one edge when held vertically (even though balanced horizontally), just like a heavy hub side. I sand the heavy leading and trailing edge pair, and for some I had to remove quite a bit of material using 100 grit followed by 220 to smooth. I only do this on the underside of the blade. This takes some time to figure it out, but results in a truly balanced prop. I also remove all the factory edge flashings all the way around the props with 220 and light on the touch. I have tried to find more info on balancing slowflyers with small hubs and wide blades buy no luck, so I came up with my own method and it works well for me.
Click to expand...

How are they flying for you? It just seems so big. Do they have the same sort of small hubs that the 12x3.8 have?

Shawn
 

Mactadpole

Mactadpole

Member
Droider said:
Think I must have had my eyes shut to this post.. cont beleive I anit seen it..

If awards are to be given to builds this has to be the winner as far as detail and perseverance goes..

Shawn

I see you are feeding 7.4v to your servo motors. I thought they were rated at max 6 volts.. how the working?

Dave
Click to expand...

thanks man, still banging my head against it. IT WILL FLY HOW I WANT! Waiting on some new anti-vib motor mounts from Sergey and ordering a new okto dristribution ring with 8 BL's.

I know another guy who's pushing 7.4v to these and getting really great results. He has had them at that for a while and no problems. It definitely made a difference with the HFP board but I never turned it back down when I switched over to the MK board because I really haven't had an opportunity to put it to use.

Shawn
 



D

Docair

New Member
Mactadpole said:
How are they flying for you? It just seems so big. Do they have the same sort of small hubs that the 12x3.8 have?

Shawn
Click to expand...

On my first test flight as an X4 they flew REALLY nice. On the current frame I felt they flew much better that the 12x3.8 I also tried. I just finished wiring up the other 4 motors and need to reconfigure the fc before the next test. The frame is big, 42.5" mtm (diagonal), and the 12x3.8 props look really small on the frame. The hubs are very small just like the 12x3.8, they are just a bigger version basically.

John

(aka ArltTech in HFP forum) There is a test video in the large props forum there with 14x4.7
 

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