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« on: June 01, 2010, 09:47:24 PM »
harsh
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hi all,

i ve been messing my head with the mixing issue for my new tricopter design, I have no past experiences with mixing,
so i will put my question straight, How can i mix two motors with throttel and Alieron control??

what i see is if the mixing is done between throttle and aileron channel , and the throttle is full, then is there any room for rpm control through aeliron channel??
i have one futaba 6ch programable tx and a 4ch futaba tx....

thanks for answers
Harsh
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« Reply #1 on: June 01, 2010, 10:06:39 PM »
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The mixing is same as a 120deg CCPM heli. It is unlikely that the 4ch tx has this mix, but some of the Futaba 6 ch ones do have it.
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« Reply #2 on: June 01, 2010, 10:14:46 PM »
anwar
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For tricopters, the simplest is to use a radio that supports 120 degrees CCPM mixing.  Then hookup one gyro each for each motor, and a 4th gyro for the "motor tilt" (ie rudder) servo.  You will then have to play with gain and limit settings (you can tie the gains on all 3 gyros used for the motors together, and drive them using a single channel on the receiver).
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« Reply #3 on: June 01, 2010, 10:23:55 PM »
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srry anwar, i just got 50% of what you said above,
i have a 6EXA futtaba
can you eleaborate it i dont know any thing abt ccpm ??
you see i have never been to helies before ... it would be gr8 for me and others who are in same position as i am, if you can elaborate what you just said... thanks
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« Reply #4 on: June 01, 2010, 10:42:41 PM »
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If you have the 6EXA, it should support 120 eCCPM heli mixing. 

1.  First of all, I assume your tricopter is going to look something like the one in this thread : http://www.rcindia.org/self-designed-diy-and-college-projects/tricopter/

2.  Now, 120 degree CCPM is when the radio sends signals to more than one channel to get proper movement of the swash plate in such helis (or to multiple motors, in the case of the tricopter).  So when you apply right aileron, the front left servo has to go up, the front right servo has to go down and the servo at the back does not move.  This mixing is done in the radio, and the signals are sent out on multiple channels.  When you apply up elevator (you pull the elevator stick back), both the front servos go up, and the back servo goes down (in the case of a tricopter, both the front motors increase rpm, and the back motor reduces rpm).  This is the basics of 120 degree CCPM, where 3 servos placed at 120 degrees on a circle helps tilt the swash plate.  In addition, when you increase throttle, the swash moves up, where all servos move up (or in the case of tricopters,  all motors go to higher rpm together).

3.  If you use a radio capable of such mixing, the radio will do all the mixing needed for you, so there is NO need for any on board mixing on the craft itself. Just think of the 3 ESC/motors as 3 servos that move the swash plate in a heli.

Let me know any specific areas you need further clarification on, and I will try.
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« Reply #5 on: June 02, 2010, 12:02:31 AM »
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If you have the 6EXA, it should support 120 eCCPM heli mixing. 

6EXA does not have the swash mixes. I had one and had to upgrade when I started on helis. The newer 6ch Futabas do have swash mixes.
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« Reply #6 on: June 02, 2010, 12:23:39 AM »
anwar
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You are right.  It is the 6EXHP that has swash mixes. That was my first radio Smiley

The newer 6ch Futabas do have swash mixes.
Even among the newer radios, there is some confusion.  The non2.4Ghz versions 6EXAP and 6EXHP each has only airplane and heli functionality respectively.  In fact, it is only at the 6EX level where both software is not present in Futaba radios of 6 channel or higher (it is present in all 7 channel radios and higher, so one does not have to worry much about getting an "airplane radio" versus a "heli radio").  The 6EX 2.4Ghz does have software for both though !  This difference is not something I was aware of earlier.
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« Reply #7 on: June 02, 2010, 12:33:17 AM »
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If the radio cannot provide you with mixing, your main choice now is something like this :

http://www.rcgroups.com/forums/attachment.php?attachmentid=3172310

This design has the "gyro between the mixer and ESC", so the mixer+gyro issues are contained.  Details on this thread :

http://www.rcgroups.com/forums/showthread.php?t=1218835

The top of that thread also has another design where the "mixer sites between gyro and ESC", and that causes significant issues.  With the above design, the simple/cheap mixers will work OK.

This will work great in a 6 channel setup, where you can use the last 2 channels to set the gains on the gyros remotely.
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« Reply #8 on: June 09, 2010, 11:16:47 PM »
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so summary is this i have to get a new tx, and ditch my 6exa ....
okay.. one more thing how do you set the gains of the gyro... and what this gain thing actually implies
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« Reply #9 on: June 10, 2010, 12:00:48 PM »
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Just a thought, do we also need to mix all 3 (120*) channels with throttle so that we get increase and decrease of speed motor as per throttle!!?Huh?
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« Reply #10 on: June 10, 2010, 12:20:10 PM »
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With CCPM mixing, this happens automatically as the 3 swash servos (replaced by ESCs+motors in the case of a tricopter) move together.
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« Reply #11 on: June 10, 2010, 12:27:12 PM »
anwar
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so summary is this i have to get a new tx, and ditch my 6exa ....

It is up  to you, whether you want to go with a better CCPM capable radio, OR do on-board mixing and use existing radio.  FWIK, the CCPM radio based method is pretty much a guaranteed success as there are no hardware mixers involved.

okay.. one more thing how do you set the gains of the gyro... and what this gain thing actually implies

On most of the current generation gyros, you connect the "remote gain" wire of the gyro to one of your free channels, and set the rate from the radio. Roughly speaking, gain controls the "amount" of compensation applied by the gyro to neutralize uncommanded changes in orientation.
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« Reply #12 on: June 10, 2010, 12:34:06 PM »
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hi anwar,

yes in CCPM, 3 swash servo will move according to aileron and elevator which will control movement in this case ESC+Motor. but in this case if we need to increase throttle then all motor speed should also increase to lift the tricoptor, how will we achive this!!???

Ashish
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« Reply #13 on: June 10, 2010, 12:38:59 PM »
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When we increase throttle in CCPM, all 3 servos also move up together (or down, depending on the heli model).  So what you are looking for is automatically achieved. 

Note that this is in addition to the servos working together to achieve movement for aileron control, elevator control etc. 

In short, not only the swash tilts, it also moves up and down on the main shaft.  This upward/downward movement is caused by all 3 servos working together, and when the same signal is applied to 3 ESCs+motors, they will also generate the same effect of lifting the tricopter up.
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« Reply #14 on: June 10, 2010, 12:49:39 PM »
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ooh yes!! u mean pitch of the blades, yes 3servo also move with throttle!!! missed out this point, got it!!
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« Reply #15 on: June 10, 2010, 11:12:21 PM »
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thanks anwar for the info, so for this current project which radio should satisfy my needs??
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« Reply #16 on: June 11, 2010, 12:31:06 AM »
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I think 6 Ch heli is suited for ur application, but i think since ur planning to buy new one go for 7 ch TX, i will suggest DX7!!!!
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« Reply #17 on: June 11, 2010, 02:47:56 AM »
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DX7 is a good choice, I only hate its trainer switch ! The guy who came up with that design must have never trained anyone ever in his life.

The Futaba 7channel would also work as an equally capable life long radio.

For your project requirements, any 6 channel CCPM heli capable radio should work.  But radios are things where one time investment makes sense, as long as you have decided that you are going to be in the hobby for a while. If you are taking the long road, a 7 channel is the way to go, as Ash suggested.
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