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Old Aug 23, 2012, 11:02 AM
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Originally Posted by e_lm_70 View Post
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 ...
Okay I'll correct my statement: quads as we are used to need gyros. One without them wouldn't be any fun to fly. You can easily measure angles with a gyro, it reads out rate of roll. Take rate of roll and multiply by time and you get angle. Maybe it would be possible to fly one with only accelerometers, but it wouldn't be as easy as one with only gyros, and also more expensive.

All this talk had me looking at some 9 DoF chips out there and making me want to build my own FC. My winter project might just be reinventing the wheel for no good reason
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Old Aug 23, 2012, 11:14 AM
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Originally Posted by skitchen8 View Post
Okay I'll correct my statement: quads as we are used to need gyros. One without them wouldn't be any fun to fly. You can easily measure angles with a gyro, it reads out rate of roll. Take rate of roll and multiply by time and you get angle. Maybe it would be possible to fly one with only accelerometers, but it wouldn't be as easy as one with only gyros, and also more expensive.

All this talk had me looking at some 9 DoF chips out there and making me want to build my own FC. My winter project might just be reinventing the wheel for no good reason
Wrong .... a gyro can estimate an angle ... only making an integration of all the sensed values ... that means it estimate a angle making an error ... and it also need to know the initial angle position.

A gyro sensor does measure only a radial speed

Tchuss

e_lm_70

ps: Actually you did write down something almost correct: Take rate of roll and multiply by time and you get angle. ... problem is that the rate of roll can change in any moment ... so ... for get an accurate reading a gyro sensor need to be read as often as possible ... so you have lot of sensed value to be multiplied by little time ... still ... you have an error in this operation ...
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Old Aug 23, 2012, 11:27 AM
Quads Helis Planes Cars
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On page 1 it says rotor diam of the MJX X100 is 6 cm. which is smaller then the Ladybird
Is that correct because GLB has it at 14.5 cm.
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Old Aug 23, 2012, 11:37 AM
It flies!!! ... so who cares ?
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Originally Posted by Nerm View Post
On page 1 it says rotor diam of the MJX X100 is 6 cm. which is smaller then the Ladybird
Is that correct because GLB has it at 14.5 cm.
I would make a wild guess (.) and say the 6cm is the actual physical diameter of ONE single rotor blade, while 14.5cm is the distance between the outer ends of TWO rotor blades once they are installed on the craft.
(with 4 rotors, there can NOT be a REAL diameter anyway ... [as the whole thing is much more of a square!!!])
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Old Aug 23, 2012, 11:45 AM
Quads Helis Planes Cars
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Originally Posted by erdnuckel2 View Post
I would make a wild guess (.) and say the 6cm is the actual physical diameter of ONE single rotor blade, while 14.5cm is the distance between the outer ends of TWO rotor blades once they are installed on the craft.
(with 4 rotors, there can NOT be a REAL diameter anyway ... [as the whole thing is much more of a square!!!])
That's my guess as well as that's the size of the Ladybird's blades.

So at 14.5 cm it's still larger that the Ladybird. That's good as I'm looking for something to fill the gap between Ladybird and MQX sizewise.
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Old Aug 23, 2012, 11:55 AM
It flies!!! ... so who cares ?
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Originally Posted by Nerm View Post
That's my guess as well as that's the size of the Ladybird's blades.

So at 14.5 cm it's still larger that the Ladybird. That's good as I'm looking for something to fill the gap between Ladybird and MQX sizewise.
Well, in a few days you will be able to see it in pictures on my blog ...
The package is listed as being in KEARNY NJ right now, so it can only be a few more days before I get it delivered (if the USPS doesnt mess anything up, which they are unfortunately incredibly talented for ...)

To be honest, the only "real" reason I ordered it, was because I wanted to try the TX as it looks like it may for once not be the POS kind of TX all the other toy clones have ... (even though I am trying to fly most of my crafts with either my 9X or the Devo10 now, if I HAVE to absolutely get a new TX because they use a proprietary protocol just so you are forced to buy their daing TX, then I want it at least to be one that gets as close to FULL SIZE as possible ... I hate this childsize toy tx crap!!! .)
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Old Aug 23, 2012, 11:58 AM
Flying mostly micro's
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I have a MJX X100 on the way, I think it's finally here in the states and I'm very excited for it to get here and try it out! it has both gyros & accelerometers (they call it 6 axis) which I believe is 3 gyros & 3 accelerometers but I'm not positive. Anyhow it's supposed to be a great flying micro quad and supposedly one of the best as far as the clones go. Time will tell! Hurry up postal service!
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Old Aug 23, 2012, 12:19 PM
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Originally Posted by e_lm_70 View Post
Wrong .... a gyro can estimate an angle ... only making an integration of all the sensed values ... that means it estimate a angle making an error ... and it also need to know the initial angle position.

A gyro sensor does measure only a radial speed

Tchuss

e_lm_70

ps: Actually you did write down something almost correct: Take rate of roll and multiply by time and you get angle. ... problem is that the rate of roll can change in any moment ... so ... for get an accurate reading a gyro sensor need to be read as often as possible ... so you have lot of sensed value to be multiplied by little time ... still ... you have an error in this operation ...
If you have a clock cycle speed that can keep up with the resolution of the gyro you can actually do these calculations with very little error. My example using seconds was to clarify the concept, obviously measuring in seconds introduces a huge error rate.

Look at a video of a v929 doing flips and tell me how inaccurate angle measurements are with a gyro only... in order to self level after a flip with only a gyro it has to do these angle calculations to know when it should flatten back out, and when coming out of it it overshoots and then comes back, if the accumulated error was as high as you make it out to be you would never be able to do a FC controlled flip, and especially never do more than one yet I have done it myself.

Clearly I have no idea what I'm talking about though, and the experience that me and other v929 owners have had is all being made up because gyros are incapable of making these measurements.
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Old Aug 23, 2012, 12:42 PM
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Clearly I have no idea what I'm talking about though, and the experience that me and other v929 owners have had is all being made up because gyros are incapable of making these measurements.
well... one other thing is clear... nobuddy can accuse skitch of being sarcastic.
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Old Aug 23, 2012, 12:46 PM
Quads Helis Planes Cars
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Originally Posted by erdnuckel2 View Post

To be honest, the only "real" reason I ordered it, was because I wanted to try the TX as it looks like it may for once not be the POS kind of TX all the other toy clones have
I have one on the way as well and the looks of the bigger TX was a selling point for me as well because I just can't fly as good on those small tx with their overly stiff springs on the rudder control. The tx on the TREX100 is like that.
Even when I had a Solopro I found the tx that came with it awkward but then bought the larger Nine Eagles tx and was able to fly like a champ.

I'm hoping this one will be good.
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Old Aug 23, 2012, 12:47 PM
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Originally Posted by erdnuckel2 View Post
(with 4 rotors, there can NOT be a REAL diameter anyway ... [as the whole thing is much more of a square!!!])
It can be a Diameter if measured diagonally, as is usually the case with bigger quads. If you want to see what the largest blades you can fit to your quad, you also have the Top Diameter.

Although I'm seeing most sellers of these smaller quads showing a square drawn through the prop centres, as shown on this diagram.

Be handy if that was on JamesChen's 'list of comparison criteria for reviews' that he mentioned, so we can make proper comparisons.

To start the ball rolling - U816: Diameter = 12cm, Front width = 8.5cm
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Old Aug 23, 2012, 12:52 PM
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shaft to shaft is the most common term for "real" quads which is shown in that 1st pic. for a tri its hub to shaft (radius). because prop diameter can vary depending on desired pitch and current draw.
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Old Aug 23, 2012, 12:52 PM
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I blame my coworkers lol I work with a bunch of truck drivers and it seems that when you get a CDL there is a bare minimum of sarcasm required to pass the test

I don't mean to offend anyone, I apologize.
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Old Aug 23, 2012, 12:55 PM
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Originally Posted by skitchen8 View Post
...

Clearly I have no idea what I'm talking about though, and the experience that me and other v929 owners have had is all being made up because gyros are incapable of making these measurements.
I could not agree more

Anyhow ...wow it can keep accuracy for half a second and for 360deg ... with a tolerance of +/- 1% ... wow

An accelerometer is accurate for ever

Anyhow .. gyro measure radial speed ... not angles ... yes you can make a trick ... but you get errors, more vibrations and more errors

Go figure why no board with gyro only offer autolevel feature

Tchuss

E_lm_70
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Old Aug 23, 2012, 01:02 PM
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All you need to know and more...

http://en.wikipedia.org/wiki/Gyroscope
http://en.wikipedia.org/wiki/Accelerometer
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