Originally Posted by jameschen072

In Chinese, quadcopters are called 四軸 which literally means 4 axles...and since they usually translate directly from Chinese, this gets translated as "4 axis" sometimes...

Eureka! I finally understand, thanks!

Originally Posted by TFMeouch

... To make matters worse, one of the blades that come with the mini pet was already loose before I even started flying it. I ended up using all my spare black blades.

Take some CA glue on a cocktail stick, wipe most of it off then poke it in the hole in the prop and wipe it around a bit. You only want the slightest smear of glue in there. Let it dry and it should be a tighter fit on the prop shaft.

I think not all have 3 gyros+3 accelerometer, i.e. 6 axis.

6 axis -

Walkera Ladybird V1
UDI U816
Mini Pet
SH-6043

3 axis -

Walkera Ladybird V2
WLToys V929
my hybrid LB/U816/V929 board

unknown -

WLToys V939

Originally Posted by e_lm_70

Thanks ... this explain all.

I guess all these micro Quad, must have the famous 6 axis : 3 gyros + 3 accelerometer .. I don't think a 9cm quad can be advertised as "toy rc" without the autolevel function ...

So ... I guess all these micro quad must be on similar league ... only difference it is how they may have implement the control on the micro quad

I also notice that the 4 motor and not exactly 90deg ... there must be some reason for have the motor pointing a bit in the inside ... making the 4 propeller not completely flat but with air flow from outside to the center of the quad ... maybe it optimize the turbulence

Tchuss

e_lm_70

Originally Posted by jpconard

unknown - WLToys V939

since v939 controller board is so much cheaper than v929 one we can assume no accel. in fact you can get a v939 pcb for less than an accel chip from digikey. anyway "we doe neeeed no steeenkin' accelerometer".

Originally Posted by jpconard

I think not all have 3 gyros+3 accelerometer, i.e. 6 axis.

6 axis -

Walkera Ladybird V1
UDI U816
Mini Pet
SH-6043

3 axis -

Walkera Ladybird V2
WLToys V929
my hybrid LB/U816/V929 board

unknown -

WLToys V939

Somebody stated that putting a V929 board on a MiniPet (or something else) ... he got better result

Ladybird v2 ... actually it is just a speculation that has only 3 gyros and no accelerometer ... maybe they just remove 2 gyros ... and 1 accelerometer ... at the end I think all is need is a accelerometer for X-Y ... and a gyro around Z axis ...

Tchuss

e_lm_70

Originally Posted by dave1993

since v939 controller board is so much cheaper than v929 one we can assume no accel. in fact you can get a v939 pcb for less than an accel chip from digikey. anyway "we doe neeeed no steeenkin' accelerometer".

I think an accelerometer chip cost no more then 1$ if order in quantity B2B

Tchuss

e_lm_70

ps: On ebay I can get an accelerometer board, for less then 5$ shipped ... http://www.ebay.com/itm/Arduino-MMA7...-/180943870262

Originally Posted by dave1993

since v939 controller board is so much cheaper than v929 one we can assume no accel. in fact you can get a v939 pcb for less than an accel chip from digikey. anyway "we doe neeeed no steeenkin' accelerometer".

What's the difference with and with out ?

I ask honestly, as V929 doesn't have it, yet it hovers and flies goooood

A gyro senses rotational movement, an accelerometer senses lateral and vertical movement. There is no such thing as a quad with only accelerometers, it simply wouldn't fly. The gyros are used to keep the quad on the same plane with itself.

Originally Posted by skitchen8

The gyros are used to keep the quad on the same plane with itself.

So, the basic minimum setup like we have in our V929's is

- 3 axis gyro (X,Y,Z) ?

Originally Posted by skitchen8

A gyro senses rotational movement, an accelerometer senses lateral and vertical movement. There is no such thing as a quad with only accelerometers, it simply wouldn't fly. The gyros are used to keep the quad on the same plane with itself.

Who told you that ?

A gyro sense a rotation ... so it is used for stabilize that it is not rotating ... but the gyro know only if it is rotating ... it has no idea if has rotare 90deg or 120deg or 10deg ... it just a sensor that say ... I'm rotating right now at X deg per seconds ...

An accelerometer ... can know if the sensor is 90deg or 20deg, or whatever degrees ... it just need to send the X and Y acceleration ... if these are both 0 ... then it is flat ... if X is 9.8g ... and Y=0 ... then the sensor is perpendicular to the horrizon, in the X axis .. etc

So ... why not ... a pure quad based on accelerometer is possible

But 1 gyro is needed ... the one around the Z axis ... else there is no Yaw control-stabilization possible

Tchuss

e_lm_70

ps: Using the mem- effect ... so story the gyro reading ... also called head holding in the helicopter gyro ... it is in theory possible to assume in which orientation is the sensor ... it also require that at start up the sensor is on flat position ... but .... the mem effect will accumulate some error over the time ... and it is very sensible from vibrations ... so .... this holding is not really working fine ... if not for hold a position for few seconds with some error accepted ...

^^ that's true for helicopters (one Z-axis gyro)

But for quad's i believe we need (3-axis) ?

Otherwise how would board know that it's level when applying throttle to engines ?

Originally Posted by e_lm_70

So ... why not ... a pure quad based on accelerometer is possible

maybe possible but not practical. ive flown the tricopter below w/o gyro or accel. again, possible but not practical.

Originally Posted by shafter

^^ that's true for helicopters (one Z-axis gyro)

But for quad's i believe we need (3-axis) ?

Otherwise how would board know that it's level when applying throttle to engines ?

Using Accelerometer on X and Y

Actually I think it is even more accurate then not using gyro.

Tchuss

e_lm_70

Originally Posted by dave1993

maybe possible but not practical. ive flown the tricopter below w/o gyro or accel. again, possible but not practical.

Yes ... you must be a talented RC pilot

I also know of people flying helicopter without gyro ... actually some cheap toy don't have it

Yes, if everything is tuned perfectly, or it is mega stable ... a human input can compensate the absence of electronic support.

Still ... gyro in the quad and tricopter are used for historical reasons ... since pioneers did use mixer and gyros ... and no control board. ... so accelerometer has been appeared later on the control board ...

Anyhow ... it is possible that as we speak there are already chip with 3 gyro and 3 accelerometer integrated in a single chip with i2c interface that push automatically all the 6 value in one shot .. making more easy the programming stuffs ... at the end this chip got common since from the time they have been added on a mobile phone, thats why they are so cheap now.

Tchuss

e_lm_70

This test flight indoors shows the v939 looks a lot easier to hover than my U816.

9imod.com-wltoys mini ladybird V939 test flight (2 min 40 sec)

Harder to tell on this one, but the pirouettes look clean, at least:

WLtoys V939 (1 min 29 sec)