Basic understanding, which motors have to run faster

[olfried]

Hi,
we tried our first fligth with our DIY-Quadcopter. We made 2,5 meters but not for very long.
The Copter flipped and fall down. Nothing was broken because we have nice snow here in bavaria:-)
I tried to figure out what's wrong and unmounted the props at the desk and had a closer look at the config tool.

But as this is our first post, let me introduce ourselfs first. We are:
- Me (44 years, computer science professional)
- son (6 years, 1st grade, currently learning to solder ) and
- daughter (8 years, 4th grade, design hero).
We are having a lot of fun with RC-planes, Raspberry, Arduino, sewing machines, our piano and now try to get this Multiwii to fly.
Our Webpage is under: http://olaf-ramge.blogspot.de/

As our budget is not very high due to a lot of other projects we ordered only cheap china components and i am not shure if
the hardware is the problem.
- The motors are turnigy D2826/10 with 1400KV. I read somewhere that the kv should be low so maybe this is the problem.
- The sensor is a GY_521 but it seems to work. When i move the copter the pitch, roll and yawl moves quiet soft and fast.
The whole thing is a little heavy, mainly because of the heavy motors, but it is 900grams which is hopefully not the problem.

But what i figured out is the following:

When i roll the copter to the right i would expect, that the both right motors turn faster. But this doesn't seem to happen.
As you can see on the screenshot the front left and the right back motor turns more than the other. Why is this so?
I don't know if we do something basic wrong but maybe you have the time to help us a little bit to find out what's
wrong.

Does it make sense to bost the config.h or is it common to have it somewhere on the board?
Should i post it?

Thanks for your advise and espeacally thanks to Alex.

Olaf

[Alexinparis]

When i roll the copter to the right i would expect, that the both right motors turn faster. But this doesn't seem to happen.
As you can see on the screenshot the front left and the right back motor turns more than the other. Why is this so?
I don't know if we do something basic wrong but maybe you have the time to help us a little bit to find out what's
wrong.

Hi,

It's not as simple.
http://www.multiwii.com/faq#The_motor_o ... l_RC_input
It's directly tied to PID controller. If you try to null I term, you will see what you expect but the stabilization would be worse.

[olfried]

Ok, Thanks.
I tried and the behaviour of our copter is indeed like the one described on the page. Except for Mag, because
wo don't have it yet.
So the reason for the difiiculty is probably the PID-setting (and our cluelessness, of course:-)
Are there any recomendations for absolute beginners just to bring the thing in the air without flipping?
Thx and have a nice weekend
Olaf

When i roll the copter to the right i would expect, that the both right motors turn faster. But this doesn't seem to happen.
As you can see on the screenshot the front left and the right back motor turns more than the other. Why is this so?
I don't know if we do something basic wrong but maybe you have the time to help us a little bit to find out what's
wrong.

Hi,

It's not as simple.
http://www.multiwii.com/faq#The_motor_o ... l_RC_input
It's directly tied to PID controller. If you try to null I term, you will see what you expect but the stabilization would be worse.

[Alexinparis]

Hi,

The default PID should be ok to fly any multirotor.
If there is a sudden flip, it is something else. Maybe a wrong ESC-motor couple, or a bad minthrottle setting.

[olfried]

It is not a sudden flip because i am not in the air yet:-)

It is more a problem during lift off like with the behaviour of
these guys' copter: http://www.youtube.com/watch?v=45VSUoCl6Hs&feature=plcp
They found out that the orientation of the Gyro was wrong which is not my problem.

It's probably also not a problem with the minthrottle, the motors turn very smooth thank to
simonk.

But i found out something different:
I use Propellers of 8/4.5 togehter with 1400kv motors.
Maybe this is the problem. Could it help to try other propeller?

Olaf

Hi,

The default PID should be ok to fly any multirotor.
If there is a sudden flip, it is something else. Maybe a wrong ESC-motor couple, or a bad minthrottle setting.

[doppler]

No I don't think you have a problem with props and motor selection, I run a few of my quads with 8" 4.5 props with 1450kv motors and they don't flip unless I make them. When things are setup right you can even put in mis-matched equpiment i.e. I was testing 8" x 6" props, i put one on my quad with the rest 8" x 4.5, flew fine.

Now for your problem, I think it is one of three things

1) Your remote isn't sending 1500 middle signal for Roll and Pitch, thus you flip when you give it throttle. It needs to be fairly way off to flip a quad on takeoff however.
2) Your motors aren't in the right places, or spinning the right way, double and triple check, I know everyone says they are right... I was one of those.... 9 times out of 10 that was my problem... I think we just get too caught up in the moment.
3) Your flight controller isn't gyro/acc aligned. I know you say it is, but go here (I'm sorry I can't find the page anymore, it documented what you should see exactly when you change the orientation on both ACC and GYRO so you can configure your IMU properly, sorry). and do the tests to make sure it really is.... I know unless you're using Horizon or Angle that the ACC should play no role in the copter's alignment, I found this not so true or maybe I took the red pill instead of the blue... You could also try disabling the ACC for your copter (comment out the ACC define) and go gyro only and see if it's better behaved...

Keep us up to date on your efforts, looking forward to your successful flight!

Andrew

[olfried]

Many thanks for your help.
Of course it is something stupid. And it will hurt, when i find it:-)
I tried to find out if my ACC is correct and that led me to one question:
How can i know that i am in Acro mode?
I have only a four channel RC and wnated to start in Acro mode but i am not really sure, if i am maybe in, what was it called, stable mode?
I cannot find any paramter in config.h
How can i check?

And another question:
In the config.h there is written:
//#define MINTHROTTLE 1120 // for Super Simple ESCs 10A
//#define MINTHROTTLE 1064 // special ESC (simonk)
//#define MINTHROTTLE 1050 // for brushed ESCs like ladybird
///#define MINTHROTTLE 1150 // (*) (**)
#define MINTHROTTLE 1150

The thing is, i have a super Simple ESC from Hobbyking and i patched it with simonk. What should i take now?
1120 as said for super Simple or 1064 as written for simnk?
And another thing i don't understand. Why does the MINTHROTTLE value depend on the ESC and not on the motor?
Is an electronic problem that it starts only at a ceartain level?

thanks for your patience
Olaf

No I don't think you have a problem with props and motor selection, I run a few of my quads with 8" 4.5 props with 1450kv motors and they don't flip unless I make them. When things are setup right you can even put in mis-matched equpiment i.e. I was testing 8" x 6" props, i put one on my quad with the rest 8" x 4.5, flew fine.

Now for your problem, I think it is one of three things

1) Your remote isn't sending 1500 middle signal for Roll and Pitch, thus you flip when you give it throttle. It needs to be fairly way off to flip a quad on takeoff however.
2) Your motors aren't in the right places, or spinning the right way, double and triple check, I know everyone says they are right... I was one of those.... 9 times out of 10 that was my problem... I think we just get too caught up in the moment.
3) Your flight controller isn't gyro/acc aligned. I know you say it is, but go here (I'm sorry I can't find the page anymore, it documented what you should see exactly when you change the orientation on both ACC and GYRO so you can configure your IMU properly, sorry). and do the tests to make sure it really is.... I know unless you're using Horizon or Angle that the ACC should play no role in the copter's alignment, I found this not so true or maybe I took the red pill instead of the blue... You could also try disabling the ACC for your copter (comment out the ACC define) and go gyro only and see if it's better behaved...

Keep us up to date on your efforts, looking forward to your successful flight!

Andrew

[olfried]

Ok, i found it. I can check it in the Gui and need to activate it with a fifth channel, right.

Many thanks for your help.
Of course it is something stupid. And it will hurt, when i find it:-)
I tried to find out if my ACC is correct and that led me to one question:
How can i know that i am in Acro mode?
I have only a four channel RC and wnated to start in Acro mode but i am not really sure, if i am maybe in, what was it called, stable mode?
I cannot find any paramter in config.h
How can i check?

And another question:
In the config.h there is written:
//#define MINTHROTTLE 1120 // for Super Simple ESCs 10A
//#define MINTHROTTLE 1064 // special ESC (simonk)
//#define MINTHROTTLE 1050 // for brushed ESCs like ladybird
///#define MINTHROTTLE 1150 // (*) (**)
#define MINTHROTTLE 1150

The thing is, i have a super Simple ESC from Hobbyking and i patched it with simonk. What should i take now?
1120 as said for super Simple or 1064 as written for simnk?
And another thing i don't understand. Why does the MINTHROTTLE value depend on the ESC and not on the motor?
Is an electronic problem that it starts only at a ceartain level?

thanks for your patience
Olaf

No I don't think you have a problem with props and motor selection, I run a few of my quads with 8" 4.5 props with 1450kv motors and they don't flip unless I make them. When things are setup right you can even put in mis-matched equpiment i.e. I was testing 8" x 6" props, i put one on my quad with the rest 8" x 4.5, flew fine.

Now for your problem, I think it is one of three things

1) Your remote isn't sending 1500 middle signal for Roll and Pitch, thus you flip when you give it throttle. It needs to be fairly way off to flip a quad on takeoff however.
2) Your motors aren't in the right places, or spinning the right way, double and triple check, I know everyone says they are right... I was one of those.... 9 times out of 10 that was my problem... I think we just get too caught up in the moment.
3) Your flight controller isn't gyro/acc aligned. I know you say it is, but go here (I'm sorry I can't find the page anymore, it documented what you should see exactly when you change the orientation on both ACC and GYRO so you can configure your IMU properly, sorry). and do the tests to make sure it really is.... I know unless you're using Horizon or Angle that the ACC should play no role in the copter's alignment, I found this not so true or maybe I took the red pill instead of the blue... You could also try disabling the ACC for your copter (comment out the ACC define) and go gyro only and see if it's better behaved...

Keep us up to date on your efforts, looking forward to your successful flight!

Andrew

[Noctaro]

hi,
for acromode nothing needs to be checked. If you have not assigned any other modes to your aux channels, you are in acro, its the standart mode.

Btw. wiki now contains the sensor direction for each sensor to check if axis are working the required way -> http://www.multiwii.com/wiki/index.php? ... figuration
Have a look at sensor calibration for the sensor you want to check.

MINTHROTTLE is depending to your ESC because, as far as i know, each ESC brand has its own PWM spinpoint.
Set minthrottle to the point where your props run smooth but dont create any mentionable lift, i did this by trial and error. My current setting for example:

Code: Select all

#define MINTHROTTLE 1180

Hope this helps a bit.

Greetz Noc

[olfried]

Wow! I made it. I flew. Fast. Very fast. And i made a Flip. Unintentionally! Haha!
But it was really hard to control. Espeacially thrust was sensitive like hell.
I flew some courves and far away and came back and then... crashed in the ground:-(
But the ground was very soft and i only need to make a new frame, because it is not a "X" anymore.
But it was self made anyway. No matter:-)

As i only have a four channel Controller, is it possible to start in level mode without switching aux?
In config.h somewhere? Gui? Or should i wait until Santa brings the six channel RC?

Olaf

[sismeiro]

As i only have a four channel Controller, is it possible to start in level mode without switching aux?
In config.h somewhere? Gui? Or should i wait until Santa brings the six channel RC?

Hi,

In the AUX1 GUI configuration select all boxes for the level. That's it.

Regards,
Luis Sismeiro

[olfried]

I think, i know what happened and why our maiden fly was so hard.
We were in Angle/Level/Stable/Whatever-Mode when we tried to make our first flight.
And due to zero-knowledge we didn't regonize it...
I have no idea how this could happen but now we switched it back to ARM-Mode.
We built a new frame today and we will try again tomorrow morning.

Have a nice Weekend and let me close with a cite from from Wilbour Wright:
"We could hardly wait to get up in the morning."

Good night
Olaf