Aug 30, 2011, 11:30 PM
Registered User
UK
Joined Jul 2007
2,678 Posts
Quote:
 Originally Posted by zadaw The Empire Strikes Back!
Wait for the next episode - attack of the clones

Regards David
Aug 30, 2011, 11:47 PM
Registered User
Joined Aug 2009
5,507 Posts
Quote:
 Originally Posted by fryfrog Okay, I give up. What the hell is a 6 axis gyro? A 3 axis gyro stabilizes left/right (aileron), forward/backward (elevator) and rotation (rudder). What do these extra three stabilize? The only thing I can think of would be up/down (pitch). Or are they just oriented in such a way that they make the normal 3 axis more stable (perhaps by being diagonal?)? I just can't think of what the extra 3 axis do. Edit: The internet seems to imply that a 6 axis system is more likely to be 3 gyros and 3 accelerometers, which means it could counteract unintentional rotation *and* linear movement. The name is deceptive.
I think the internet search gave the right idea: accelerometer is able to detect linear forces, and gyro is able to detect rotational forces.

I recently got an Iphone4, and it also has a 3 axis accelerometer, and 3 axis gyro. I downloaded an application that displays their outputs. Although I still don't know how the accelerometers produce their outputs, I am now able to predict how their output signals change with movement and position as follows:

The 3 axis (linear) accelerometer has three outputs: X, Y, and Z (left/right, forward/backward, up/down). When the 3 axis accelerometer is not moving, their outputs can be used to determine which direction is DOWN (towards the Earth's Center due to Force of Gravity). So no matter which angle the 3 axis accelerometer is oriented, the DOWN direction can be determined by looking at its output signals. I suppose a "fictitious" example would be like having a ball partially filled with water inside, and "weight" sensors all around the ball being able to detect the location of the weight/position of the water - no matter which angle the ball was oriented, because of the Earth's Force of Gravity forcing the water to concentrate in the DOWN direction, and the sensors ability to indicate the location of the water, the sensors would be able to locate the DOWN direction.

Also, the 3 axis accelerometer detects changes in speed. Back to the example of the "fictitious" Ball with water and "weight sensors, if the ball had a change in movement, the "inertia" (weight drag) of the water would tend make the water "move" (actually resist movement) in the opposite direction, the sensors in the ball would sense the "extra" weight/force, and provide an indication of which direction and how strong the change in movement is. An interesting side note is if the 3 axis accelerometer is (accelerating) in free fall under the Earth's Force of Gravity, it no longer outputs the DOWN direction (i.e. in the Ball with the water example, during free fall, the water doesn't exert a downward force on the ball, since the ball is moving just as fast DOWN as the water is!).

The 3 Gyros measure angular rotation (AIL/roll, EL/pitch, and RUD/yaw). If the 3 Gyros are stationary, then all 3 outputs are zero (plus noise). Their outputs only change when their axis are rotated. I can hold the Iphone in my hand while sitting in a swivel chair, spin the chair around, and the 3 axis accelerometer doesn't detect much; however the 3 Gyro will produce an output signal in the direction of axis rotation, and proportional to the rate of spin.

I'm not a mathematician (chemist, or physicist?), but it appears we live in a "6 degrees of freedom" world, because things (especially tiny things) can move in the 3 linear directions as well as at the same time independently rotate about the 3 axis!

I think the \$150 Iphone 4 may have more "blind" navigation capability built in with its 3 axis linear accelerometer, 3 axis gyro, magnetometer (electronic compass), and GPS, than the ICBM's had in the early part of the Cold War!

Doesn't look like we need human navigators anymore! (only remote programmers in chairs)

Last edited by i812; Aug 31, 2011 at 02:18 AM.
 Aug 31, 2011, 12:06 AM Registered User Australia, VIC, Melbourne Joined Feb 2010 2,363 Posts The above is pretty much correct, a 6 axis IMU (inertial measurement unit) incorporates 3 gyros and 3 accelerometers. This is the minimum required to define an objects position in space, relative to the start location. It is also the minimum required to tell if a heli is level (well actually you dont need the vertical acceleration axis, or the rotation about that axis - which is used for the tail gyro). So the addition of the accelerometers is to provide a coax-style auto-levelling system. However such a system will render the heli (unless you disable the auto-level part) incapable of any aerobatics, it will fight you harder the more you tilt it and most of them will prevent a flip to inverted, leaving you stranded somewhere around vertical. They also fly like a coax, so you need to maintain forward cyclic in order to maintain forward attitude (and so prevent a slow down in FF). I have a SK720 with this feature and while it is brilliant for saving the heli and precision hovering it makes it much harder to actually fly around for me since it feels really weird having to hold cyclic input like a coax. This feature will be of very limited use if you cannot enable/disable it in flight so you can use it if you lose control of the heli but not when flying normally.
Aug 31, 2011, 02:55 AM
Registered User
Joined Jan 2011
338 Posts
New video by Alishanmao:

 Flying a 3D helicopter inside my car (4 min 15 sec)
Aug 31, 2011, 03:31 AM
Sopwith Camel's Cousin
Between my tx and crashed aircraft
Joined Mar 2006
3,863 Posts
Quote:
 Originally Posted by i812 I think the internet search gave the right idea: accelerometer is able to detect linear forces, and gyro is able to detect rotational forces. I recently got an Iphone4, and it also has a 3 axis accelerometer, and 3 axis gyro. I downloaded an application that displays their outputs. Although I still don't know how the accelerometers produce their outputs, ...
As I remember it, accelerometers are often (piezoelectric) crystals that produce electricity when subject to a force (or in other words, when accelerated).
A familar form of the accelerometers for RC heli fliers are the old rate gyros, which measured the acceleration (typically of the nose or tail) as a heli yawed.
These rate gyros/accelerometers were also the basis of many (early?) head holding gyros: basically do a double integration of the acceleration measurements to arrive at what angle the tail is at relative to the starting position.
Aug 31, 2011, 05:51 AM
Sopwith Camel's Cousin
Between my tx and crashed aircraft
Joined Mar 2006
3,863 Posts
Quote:
 Originally Posted by helicopcat New video by Alishanmao: ...
Minor trivia: you and "Alishanmao" partially share a name:
Looking up in a Chinese-English dictionary:
"mao" - a common possible translation is "cat"
"shan" - common translation is "mountain"
"shan mao" - translation is "Lynx"

This matches the little picture of a cat-like creature that Alishanmao has in some of the videos.
 Aug 31, 2011, 09:51 AM Registered User Madison WI Joined Jan 2009 599 Posts So this heli can be operated in "coax" mode, where a 3-axis accelerometer is used in the control system along with the 3-axis gyro. Then as a novice advances, the coax mode is disabled and the pilot advances to hovering and flying a CP heli. After that he or she moves on to inverted hovering and 3D moves. Throughout these stages, crashes occur but there's no downtime for repairs. In addition to the major impact this can have on the micro heli market, the crash-ability factor might radically diminish the need for a sim. Wow!
 Aug 31, 2011, 09:56 AM QuAd FaNaTiC Canada Joined Aug 2009 23,251 Posts I think I might want one of these BUT would be worried about parts availability and customer service in case something is defective.
 Aug 31, 2011, 11:07 AM Registered User Joined Jun 2011 15 Posts Man this little heli looks very promising, just might be my first step into 6ch 3D.
Aug 31, 2011, 11:16 AM
Registered User
United States, NY, New York
Joined Jul 2011
23 Posts
Quote:
 Originally Posted by jcil_rkg Man this little heli looks very promising, just might be my first step into 6ch 3D.
gonna take a while for it to get to market with spares and all. why not go with a proven 6ch mcpx which is just as stable & durable if not more durable, has parts available everywhere, and can be found for as low as \$199 with transmitter?
Aug 31, 2011, 12:42 PM
Pontiac my other Obsession
USA, FL, Apopka
Joined Jul 2010
719 Posts
Quote:
 Originally Posted by jazzjohn So this heli can be operated in "coax" mode, where a 3-axis accelerometer is used in the control system along with the 3-axis gyro. Then as a novice advances, the coax mode is disabled and the pilot advances to hovering and flying a CP heli. After that he or she moves on to inverted hovering and 3D moves. Throughout these stages, crashes occur but there's no downtime for repairs. In addition to the major impact this can have on the micro heli market, the crash-ability factor might radically diminish the need for a sim. Wow!
Well said, and +1

My first post regards the little wonder was "Put me on the list... I want one"
I still do... after a discouraging recent Nine Eagles purchase (NE Solo Pro 328) I am less inclined to try their 100 sized 3D introduction and Wakera's flybarless helis just getting better every day.
I do not see this as a new Walkera micro, rather as the culmination of the micro CP up to this point.
Aug 31, 2011, 01:08 PM
Sopwith Camel's Cousin
Between my tx and crashed aircraft
Joined Mar 2006
3,863 Posts
Quote:
 Originally Posted by lovemyhelis gonna take a while for it to get to market with spares and all. why not go with a proven 6ch mcpx which is just as stable & durable if not more durable, has parts available everywhere, and can be found for as low as \$199 with transmitter?
One thing about the transmitter with that \$199 package: no expo, variable rates, mixes and other things that help make a heli easier to fly.
Not sure what is in the Tx with this RTF package (have not read the entire thread), but the upcoming Nine Eagles micro RTF CPs will/do have some/all of these features in their Tx.
 Aug 31, 2011, 01:23 PM Hong Kong Joined Jan 2010 6,533 Posts I am very unhappy about the MCPx about the tail blowout issues. I got it to learn 3D but more than half the moves result in a crash. The stock DX4e that came with it is part of the problem. To match the capability of the Genius CP, I will need to pay \$150 extra for a DX6i. Moreover, I am losing MCPx parts in crashes. I have lost 3 bearings already plus a number of linkages. It seems that the Genius CP can stay in one piece in a crash. I also want a heli that I can fly over a concrete floor without sustaining damage but I cannot do this with the MCPx. Besides the much vaunted HH warranty and service does not apply to where i live.
Aug 31, 2011, 01:27 PM
RC Helis: My Healthy Obsession
The OC, California
Joined Feb 2007
3,159 Posts
Quote:
 Originally Posted by flying-llama One thing about the transmitter with that \$199 package: no expo, variable rates, mixes and other things that help make a heli easier to fly. Not sure what is in the Tx with this RTF package (have not read the entire thread), but the upcoming Nine Eagles micro RTF CPs will/do have some/all of these features in their Tx.
The Devo 6 this heli came with is 100% programmable. It is also color touch screen (kind of cool). That RTF Tx for the MCP is useless. I tried to do what I could with it for my buddy's heli and he just ended up buying a DX6i so he could actually fly it well. So really, the RTF is not such a good deal IMO. You still end up spending \$300 for a combo that allows the MCP to fly like she should. It looks like this heli RTF is going to be around \$239 or so with a fully programmable Tx with a 12 model memory. .

I also just converted it to brushless using just the 4#3B tail conv/esc and a spare C05 with the stock pinion. Now it has great climbout and the tail holds better. Very inexpensive and simple conversion for sure. I'm starting to like this heli a little more everyday. LOL.
 Aug 31, 2011, 01:52 PM Sopwith Camel's Cousin Between my tx and crashed aircraft Joined Mar 2006 3,863 Posts One question about this heli. Does it have "regular rotary" servos, like other Walkeras? Or does it have linear servos (and if so, are the pots linear, like Eflite, or rotary, like Nine Eagles)?