thanks. my stock v939 will be sorry that I read this. So can you confirm that motors and boards are all compatible b/n v939, udi u816, mjx x100, walkera LB, sh 6047?

Good observations, Dave!

DIY is the implementation of the Mother of all... Need.

rc

Maybe something usefull for using our TX
http://www.hobbyking.com/hobbyking/s...mpatible_.html

They should sell the board and the tx maybe under another name. At the end of the manual there are listed as spares

Has anyone tested where the low voltage cutoff is on the V939 boards?

I just tested mine and it seems to be around 3.15V (under load). The cell pops right back up to 3.7V under no load but wow, that LVC seems kind of low.

Although it could be reducing the throttle (ie. the force landing) before that, I'm not sure. It's hard to test on the bench.

I always fly with timer and haven't had any problems with 7:00 Min and 300mah LiPo
At 7:00 I mostly get 3.65V - 3.75V which is healthy for my LiPos

You might be surprised at what the load voltage is though.

I'm not saying it's a horrible thing. It is what it is. Some (most?) of these little cells can't deliver much current (despite their rating) and the voltage drops quick under load.

I have around 50 flights on each of my 300 mAh Turnigy nano-tech's, flying all the way to shutdown and they show no sign of deterioration (in flight time or otherwise). I was just surprised at how low it's actually cutting off because it seemed OK due to the end voltage (unloaded) being 3.7V or so.

Originally Posted by Cid156

Maybe something usefull for using our TX
http://www.hobbyking.com/hobbyking/s...mpatible_.html

They should sell the board and the tx maybe under another name. At the end of the manual there are listed as spares

that is very interesting. id give my left arm to get one of those modules. unfortunately with that shipping theyre charging an arm AND a leg.

im almost willing to do it though just to see what protocol is used.

Looks identical to the HiSKY module (FBL100, V922, etc). Notice everything is in the same place, even the labels are the same F/J/W, etc.

Of course that doesn't mean it is but it seems likely.

they say ht8/v922 protocol is not flysky compatible. i suppose we wont know for sure until somebody tries it but thats a bad sign. oh well... it would have been nice to buy a flysky module with cool looking quad thrown in for free.

So, it was bad motor(s). For my quad, I got 2 CW and 2 CCW from banggood. Two with red/blue wires are OK, but those with black/white wires, were funky right from beginning. They turned a little stiffer when prop flung with finger, but otherwise seem OK too. In bad crash I broken one badly and replaced it with hubsan motor a friend gave me. Vibrations are almost gone, remainings must be caused by other bad motor. Now quad flies really good, finally!

Just got my v939 board and replaced the ladybird board with it on my Hquad. I use my turnigy 9x with it. First impression is that it's quite stable, however once I give stick inputs, the quad will start drifting around and it's very hard to keep it still. also with the ladybird board if you let go of the stick it will stabilize right away, whereas with 939 board the quad will keep moving unless you give opposite stick input, is that normal? also what's setting on 9x do you use for this quad?

Originally Posted by Richard_s

So, it was bad motor(s).... Now quad flies really good, finally!

Glad to hear your problem is fixed now, R !

Mine arrived with 1 motor doa. I got two flites of 4 or 5 seconds... all the rest amounted to nothing more than flipping over as I applied power and tried and tried and tried to adjust the trim...

BG says NO warranty... all are pre-tested, and it's a toy.
I guess that's the risk on a cheap item.

Now I've determined it's not the board.
It's either the wires, or connections inside the motor, or motor.
I switched plugs around on the board and only that motor would not run, when plugged into a different location.

Now it's Chinese New Year, so it will be a while before I can even buy a new part.
rc

Originally Posted by boycoldface

Just got my v939 board and replaced the ladybird board with it on my Hquad. I use my turnigy 9x with it. First impression is that it's quite stable, however once I give stick inputs, the quad will start drifting around and it's very hard to keep it still. also with the ladybird board if you let go of the stick it will stabilize right away, whereas with 939 board the quad will keep moving unless you give opposite stick input, is that normal? also what's setting on 9x do you use for this quad?

You're noticing the difference between the 6-axis stabilization on the Ladybird versus the 3-axis of the V939. If you ever want to do acrobatics on a "real" multirotor or heli then you will have to learn 3-axis flying anyway so think of it as a good safe way to practice that.

I use a 9x also but no special settings other than I set the aileron and elevator rates to something like 75% so it won't auto-flip.

Hi, that's great to know. I thought my board was defective or sth. Yeah I have a real quad too but I was under the impression that all these micro quad are stable like the ladybird. obviously not. I'm still learning to fly my real quad so learning to fly 939 is definitely helpful. the ladybird is way too easy to fly haha.

thanks for the info

Originally Posted by LittleMo

Has anyone tested where the low voltage cutoff is on the V939 boards?

I just tested mine and it seems to be around 3.15V (under load). The cell pops right back up to 3.7V under no load but wow, that LVC seems kind of low.

Although it could be reducing the throttle (ie. the force landing) before that, I'm not sure. It's hard to test on the bench.

I ran some quick tests a while back and came to the rough conclusion that the LVC was around the 3.00V level. My guess is that the control board monitors voltage and will 'take note' as soon as it dips under 3.00V. It will then permit you to continue to fly for as long as the battery holds enough voltage to keep the props spinning, however once you cut the throttle the board will prevent you from throttling up again.

This allows you to safely land, but it also prevents you from over discharging the batteries. Unless you do what I did once, continue to fly the quad with it's two front legs skating along a smooth floor. You can continue to do this for a surprising amount of time and can probably over discharge you battery in the process.

The LVC sounds low but you need to know how much the voltage dips on these little packs under high load. Do not believe the ridiculous C-ratings, especially the nano-tech ones which are outrageous. These packs struggle to hold 5A (16C) constant let alone the claimed 13A (45C)!

As you noted, if you check the battery voltage after the first 'throttle cut' is normally around the 3.6-3.67V mark. This end value will vary depending on the IR of the battery and how hard you were flying it when the voltage dropped below 3.00V.

ie) If you were doing high speed full throttle runs with hard banked turns then you'll dip below the cutoff voltage much earlier than if you a just hovering around in your living room. Or if you have an old battery with high IR then you will find the voltage can quickly crash below the cutoff value under a high load maneuver.