HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Sep 24, 2012, 04:44 AM
Registered User
Joined Jun 2012
2,810 Posts
Quote:
Originally Posted by nerys View Post
I am wondering if I can improve the performance of the u816 by putting lady bird propellers on it (I wish the LB props where as cheap as the u816 props :-)

has anyone tried that? are they the same physically as far as the way they attach to the shaft?
Yes you can put LB props on the U816 and yes it does improve performance slightly. If I remember correctly, it required about 4% less throttle (on the LCD) to hover and felt slightly more stable. Not a massive amount, but worth doing if only because the LB props don't fly off as easily as the U816 originals.

See my prop comparison here: http://www.rcgroups.com/forums/showt...4#post22585047

You could also try MJX X100 props and they'll probably be even better. I've not tried that yet as I'd broken a few and preferred flying the remaining ones on the MJX. But I've just got back from holiday and have 3 new sets of MJX props waiting for me and @$1.45 x 3 = $4.35 they are cheaper than the LB's.

I see I have a lot of catching up to do, but I spent some of yesterday trying to get my U816 to fly upside down, as I saw you'd asked that question while I was away and had some predictable responses from the usual suspects.

Videos to be edited and a fuller post to come, but basically, yes: props work just fine when swapped (CCW>CW, CW>CCW) to reverse airflow when motors are inverted - as you'd suggested. A bit less efficiently than a prop designed to rotate that way, but more than enough to lift the U816.
The FC isn't too happy about the new CoG though, so flying it is....a challenge.
Brandigan is offline Find More Posts by Brandigan
Last edited by Brandigan; Sep 24, 2012 at 06:25 AM. Reason: Added price of MJX X100 props
Reply With Quote  (Disabled)
Sign up now
to remove ads between posts
Old Sep 24, 2012, 05:00 AM
Registered User
OnceAFly's Avatar
Singapore, Singapore
Joined Oct 2011
847 Posts
Ya like magic said you can put all kinda icon for the model you wish! And i have a few on my tx now

Sorry for the OT and Thanks chris for the walk through video you've made! cool: You the man!
I'm so getting over on the toy quad and moved on!
OnceAFly is offline Find More Posts by OnceAFly
Reply With Quote
Old Sep 24, 2012, 06:44 AM
Registered User
Canada, ON, Ottawa
Joined Dec 2011
1,878 Posts
Quote:
Originally Posted by jesolins View Post
V,
You mean BOHICA It appears the Walkera V2 flight controller or "Receiver" as they call it is exactly the same FCB layout and components minus the $5 845 accelerometer and the connector for the firmware update. The contact lands are all still there. It would be an easy SMD work to put on the accel and then load the Walkera V1.1 firmware. Then you have the "twice the price" V1 version. Time to mod!
Cheers,
Jim
Quadrocopter and Tricopter Info Mega Link Index
I had to consult the Urban dictionary for BOHICA
FYI my comment about Walkera's apparent generosity with V.2 was said somewhat sardonically... but I guess it didn't tranlate over the web that well. hehe

I be mighty interested if you manage to "upgrade" your V.2 board with success. do keep me in the loop.
At the very least I was thinking of putting the missing update sockets onto my V.2 board when I get it, since they also provide an easy way to plug-in LEDs for power.

Thanks for the infos Magic, custom model picture/icons are a nice touch. Deviation sounds extremely versatile, I hope the Devo10 version supports many of the same features.
vpsporb is offline Find More Posts by vpsporb
Last edited by vpsporb; Sep 24, 2012 at 06:51 AM.
Reply With Quote
Old Sep 24, 2012, 07:26 AM
Registered User
Canada, ON, Ottawa
Joined Dec 2011
1,878 Posts
Quote:
Originally Posted by nerys View Post
your problem not mine

----

anyway. I have the ladybird and it IS very responsive except in throttle. I am starting to think its the devo 4 tx thats the problem.

I am going to start saving up to get a devo 8 maybe a devo 10 if the FW is ready by the time I am ready to buy (couple months so it might be :-)

it would be killer nice to have one good high quality tx to do it all with
If you don't find the throttle responsive.... you must have a firmware1.0 Ladybird. Mine takes 1/2 to 3/4 throttle stick just to Hover!
My fw1.1 Ladybird has a very responsive throttle, just a bit of left stick... and she's shooting for the skys! While indoors with a freshly charged LiPo it's disconcerting how effortlessly it lifts-off and hits the ceiling!

You may need a UP02 update kit too...
vpsporb is offline Find More Posts by vpsporb
Reply With Quote
Old Sep 24, 2012, 11:14 AM
Registered User
Joined Jun 2012
2,810 Posts
Reversed props and inverted thrust test on a U816

Quote:
Originally Posted by nerys View Post
if you REVERSE the rotation of the props (you do this "NOW" by swapping the clockwise prop to the counter clockwise arm) the unit will thrust model Z- relative.

even if the prop is 50% as efficient it has MORE than enough thrust to lift the models mass into the air since it has in excess of 200% of the power it needs to fly. The "foil" on these props is MINIMAL at best.
Your theory seemed sound enough, but as I was away, I had to wait to get back to test it out, but I'd already seen here that the U816 props weren't as curved as the LB and X100 props and gave slightly less lift, so they'd be 'less bad' than a more heavily pitched prop when running in reverse.

As you pointed out in another post: just inverting the prop makes no (or not much) difference to the thrust (if you could do it with these type of props - which you can't, as they're not like larger types and only fit one way). Just like a nut going on a bolt, it works the same both ways round, but as U816 props are something like a wingnut, we can't just invert the prop to confirm that. Although what we are going to do does confirm that in a different way.

People already know that if you put the props on wrong and mix up CW/CCW the quad won't fly, or will flip if some of the props are on correctly and some wrong. Putting them all on wrong (swap CW/CCW) would therefore make it try and push itself down rather than up. Having done that, if you then invert the motors, you've got the thrust pointing upwards again.

Just remove the tiny screws at the end of the legs, ease the motor housing off and rotate it clockwise 180 degrees. Be very careful, all but one of my legs had almost no slack in the wires and I was concerned that pulling too hard might break/unplug something somewhere. If your wires are also short (or shorter) don't do it.

Do them all clockwise, then you'll remember to do it anti-clockwise when putting them back to normal to avoid twisting/straining the wires too much.

OK, so the body/FC board isn't inverted, but that wasn't what was wanted anyway. I actually did try just inverting the motors, turning the body/FC board upside down, leaving the props as normal, but the FC immediately tried to right itself by flipping over.

Although it can lift itself with 12g to spare (instead of the 24g normally available - this is due to the props being less efficient when spinning backwards) it doesn't really want to fly very well (see video). It wants to spin on the spot really quickly, and with lots of trim on the YAW, what you see in the video is about as good as it gets.

I think the Centre of Gravity is off, with the thrust from the props being lower, and it's a bit like trying to balance a broom vertically by the handle. It 'falls over' a lot. It's a lot easier to hang a broom by the end of the handle.

Strangely, it doesn't care which way up it is when binding. As it was difficult to keep it level when resting on the props - it would rock about on the (slightly swollen) battery holder when the board/body is the right way up - so I put it on its feet with the battery on the top and it worked just as well/badly when flown - as you'll see in the video - i.e. it didn't stop it 'falling over', or spinning, but it also didn't make it flip. It was also very sensitive to the position of the battery and I spent ages moving it about and saw big changes in its behaviour, but I think the CoG problem is just too far off for it to be stable.

Conclusion: If the props were more neutrally pitched (equally happy spinning either way - more efficient when going backwards, but less when going forwards compared to currently) and the motors could be made to spin in reverse quickly enough, you could have some very interesting behaviour out of one of these little quads.

New theory: People trying to make octocopters out of two v929s could try a similar trick of motor-inverting and prop-swapping one v929 and attaching it under another one set up as normal. A few cable ties through the feet would do that fairly easily.

The props won't get in each other's way (although landing/takeoff would be tricky - you'd need to make some extra legs Edit: A Starbucks Smoothie Dome as an 'upside down' canopy under the lower battery would work, as it's taller than the props) and the upper one being able to fly normally might be able to balance out the CoG instability of the semi-inverted lower one. You'd get all the extra thrust, with none of the (well, maybe less ) problems you have with boards being far from their props, or at funny angles.

Someone might even find that the v929 is better at flying semi-inverted than the U816, as it only has 3 gyros rather than 6 (acc+gyro), but I'll leave that for someone else to discover.

Note: I'm a bit confused by the values I got from the scales in the different directions of thrust. It might be that these scales aren't as accurate at registering negative weight as they are positive, as some of the values don't quite add up, but you get the general idea for comparison purposes. 24g of extra lift available normally, but only 12g when the props are spinning backwards. Someone else can do the % of efficiency loss taking the total weight of the quad into consideration.

I wasn't too strong on the throttle in the video. I'd already tried over a hardwood floor with more room and the sound of the motors hitting the ground from three feet up on the top of the props wasn't pleasant. I may as well have hammered the props onto the top of the motors, so I decided on a softer landing for the video. Over the bed there isn't much headroom, so as soon as it veered off, I cut the throttle. Maybe, just maybe, some skilled flier can get something better out of it outside with a lot more room and some grass, but it's tipping it down here, so I didn't try it.

U816 inverted thrust and flight test (1 min 36 sec)
Brandigan is offline Find More Posts by Brandigan
Last edited by Brandigan; Sep 26, 2012 at 08:58 AM. Reason: Smoothie dome
Reply With Quote  (Disabled)
Old Sep 24, 2012, 12:20 PM
Registered User
Joined Jun 2012
2,810 Posts
Quote:
Originally Posted by dave1993 View Post
sigh... not again....

all other parameters equal the smaller the mass the LARGER the vibrations. this can be seen by comparing accelerometer graphs in the multiwii projects. almost directly proportional to size. it takes more energy to move more mass so a given prop and motor imbalance will have less effect.
I'd answered this on my iPhone while on holiday, but it didn't stick, so I'll try again.

Yes, 'sigh' indeed... as in this specific example no other parameters are equal.

The second half of this sentence is unrelated to the first half: "it takes more energy to move more mass so a given prop and motor imbalance will have less effect. "

It's a false conclusion. Like: "All cats have four legs, so all four-legged animals must be cats".

The mass of the quad is smaller but so are the props and the speed of rotation is higher. Less energy is required (smaller battery ), so less capacity for vibration. A bumblebee doesn't have 'larger' vibrations (vague use of the word 'larger' there, but I'll assume you mean amplitude) than a hummingbird. Try the free seismometer app on an iphone and rest a quad leg on it to see that peak to peak the vibrations are smaller. This translates into a sort of blurring video effect on an LB sized quad - which is almost acceptable - rather than a noticeable wobble on a v929. On my 900g X450 before I balanced the props: whacking great big wobbles that would be impossible to reproduce on even a v929 without taking a big chunk out of one of the props, or bending it badly, let alone an LB clone.

Quote:
Originally Posted by dave1993 View Post
and i think anybody who has tried videos knows the difference between big quad and little one.
Not sure what this means. Anyone who has eaten a banana knows what an orange is? But, yes, I've tried a camera on Micro, Mini and larger quads.
Brandigan is offline Find More Posts by Brandigan
Reply With Quote  (Disabled)
Old Sep 24, 2012, 12:33 PM
RC beginner
New York
Joined Oct 2008
6,054 Posts
Quote:
Originally Posted by Brandigan View Post
it doesn't really want to fly very well (see video). It wants to spin on the spot really quickly, and with lots of trim on the YAW, what you see in the video is about as good as it gets.
unfortunately i can view rcg gallery videos but not facetube so ill take your word for it that it gets off the ground. not surprised that its not controllable though considering the slim lift budget of those highly inefficient backward props.

Quote:
Originally Posted by Brandigan View Post
Someone might even find that the v929 is better at flying semi-inverted than the U816, as it only has 3 gyros rather than 6 (acc+gyro), but I'll leave that for someone else to discover.
considering the bigger props are almost an order of magnitude more efficient this version might actually turn out to be controllable. unfortunately the higher mass would work against you when reversing direction in nerys "3d quad" scenario.

Quote:
Originally Posted by Brandigan View Post
Someone else can do the % of efficiency loss taking the total weight of the quad into consideration.
ive measured thrust of five of the six different availble toy quad props now and in all cases reverse thrust was about 20-30% that of normal spin (depending on the particular model). this does not seem to jive with your 12g/24g quad measurments but this stuff is more art then science anyway. im a little surprised it lifts but not so much that its not practical for a 3d or even upside down quadt. note that s107 tail props are 100% symmetrical (no camber) and do fit the 7mm motors which would make for an interesting experiment.

sincerely,
-usual suspect #1
dave1993 is offline Find More Posts by dave1993
Reply With Quote
Old Sep 24, 2012, 12:50 PM
RC beginner
New York
Joined Oct 2008
6,054 Posts
Quote:
Originally Posted by Brandigan View Post

It's a false conclusion. Like: "All cats have four legs, so all four-legged animals must be cats".

Quote:
Originally Posted by dave1993
and i think anybody who has tried videos knows the difference between big quad and little one.

Not sure what this means. Anyone who has eaten a banana knows what an orange is?
well... considering all the cat and fruit distractions im not surprised you are a bit confused so ill put it in simpler terms... those hobbyists who put cameras on big quads have less trouble with cmos wavy lines than the guys who try this with little ones. if you dont recognise this as true then maybe spend a little more time reading posts in the multi forums and less time looking for trouble (not that i mind. lol!).

sincerely,
-keyser söze
dave1993 is offline Find More Posts by dave1993
Reply With Quote
Old Sep 24, 2012, 12:58 PM
Registered User
Joined Jun 2012
2,810 Posts
Quote:
Originally Posted by dave1993 View Post
unfortunately i can view rcg gallery videos but not facetube so ill take your word for it that it gets off the ground.

ive measured thrust of five of the six different availble toy quad props now and in all cases reverse thrust was about 20-30% that of normal spin (depending on the particular model). this does not seem to jive with your 12g/24g quad measurments but this stuff is more art then science anyway.
No need to take my word for it. Get with the 20th(!) century and watch the video. It shows the quad on the scales, zeroed, then with the quad at full throttle.
Brandigan is offline Find More Posts by Brandigan
Reply With Quote  (Disabled)
Old Sep 24, 2012, 01:09 PM
Registered User
Joined Jun 2012
2,810 Posts
Quote:
Originally Posted by dave1993 View Post
well... considering all the cat and fruit distractions im not surprised you are a bit confused so ill put it in simpler terms... those hobbyists who put cameras on big quads have less trouble with cmos wavy lines than the guys who try this with little ones. if you dont recognise this as true then maybe spend a little more time reading posts in the multi forums and less time looking for trouble (not that i mind. lol!).
Yes, I also have less trouble with CMOS vibrations, but not for the reasons you are stating. Larger quad mass = easier to damp vibrations which are at a low freqency anyway. Before I got a magnetic prop balancer for my X450 I had a hand-held one that was frankly junk, but it removed all video vibration, as what was left was damped by the weigh of the quad. v929 = less mass, but indirectly geared props, so lower vibration frequency and more balancing required. LB/U816/v939 less mass again, but now the camera is a large percentage of the overall weight, so harder for it to be vibrated, and direct drive props with different vibration harmonics that do not affect video in the same way.

The forums you mention: How many of them are putting cameras on LB sized quads, or are you simply extrapolating size/difficulty from incomplete data?
Brandigan is offline Find More Posts by Brandigan
Reply With Quote  (Disabled)
Old Sep 24, 2012, 01:12 PM
RC beginner
New York
Joined Oct 2008
6,054 Posts
Quote:
Originally Posted by Brandigan View Post
No need to take my word for it. Get with the 20th(!) century and watch the video. It shows the quad on the scales, zeroed, then with the quad at full throttle.
i will repeat that this is not possible unless you would be so kind as to upload here. resource (netbook ssd) and legal issues with adobe.

btw most of the rest of us have moved on to the 21st century. that explains a lot though.
dave1993 is offline Find More Posts by dave1993
Reply With Quote
Old Sep 24, 2012, 01:16 PM
RC beginner
New York
Joined Oct 2008
6,054 Posts
Quote:
Originally Posted by Brandigan View Post
The forums you mention: How many of them are putting cameras on LB sized quads, or are you simply extrapolating size/difficulty from incomplete data?
im guessing few dozen including myself since theyve only been out a matter of weeks compared to years for the bigger ones. anyway 90% failure even with such a small sample is convincing (at least to me). compared with 99% success on the hundreds or thousands doing it on the "real" quads. like with skitch i graciously give you permission to develop your own theories. to some it is "Suggestions of Physics" rather than "Laws".

ps have i mentioned how much i MISSED you last week.
dave1993 is offline Find More Posts by dave1993
Reply With Quote
Old Sep 24, 2012, 01:45 PM
Sir Crashalot
stonecutter's Avatar
Joined Oct 2011
2,279 Posts
The Brandi and Dave show..... Gotta love it....
stonecutter is offline Find More Posts by stonecutter
Reply With Quote
Old Sep 24, 2012, 01:46 PM
RC beginner
New York
Joined Oct 2008
6,054 Posts
Quote:
Originally Posted by Brandigan View Post
Larger quad mass = easier to damp vibrations which are at a low freqency anyway.
i KNEW youd come around! you are a very smart guy.

btw thanks for that excellent prop review. i searched and searched for it thinking it was a separate thread but jesolins finally pointed it out as a post here. it really saved my butt in that "discussion" with nerys. and several of the guys in my dquad thread were very impressed. great photos and it inspired me to pull out the thrust stand again. thanks.
dave1993 is offline Find More Posts by dave1993
Reply With Quote
Old Sep 24, 2012, 02:15 PM
Former IAF pilot. Retired
kosem's Avatar
France, IdF, Paris
Joined Apr 2012
780 Posts
Quote:
Originally Posted by stonecutter View Post
The Brandi and Dave show..... Gotta love it....

Ideal timing for a new sub-forum maybe??
kosem is online now Find More Posts by kosem
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Suggestion Personal attack Rule as it applies to Trader Talk Thread Titles porcia83 Site Suggestions / Complaints 3 Jul 27, 2012 12:58 PM
For Sale Quadcopter Parts Sale Thread mfkubak Aircraft - Electric - Multirotor (FS/W) 10 Jul 26, 2012 03:33 PM
Discussion Why are there so many heli threads in the Airplane Micro RTF forum? Bowerz Site Chat 38 Dec 15, 2009 07:43 PM
Wattage RTF Micro Flyer (thread #2) Skyshark Scratchbuilt Indoor and Micro Models 233 Sep 17, 2009 03:22 PM
Wattage RTF Micro Flyer (thread #1) Bleriot Scratchbuilt Indoor and Micro Models 384 Dec 15, 2004 03:28 PM