Looking for an external mixer...

[Xnaron]

I am wondering if anyone here has come across an external mixer that can be used in a coaxial helicopter (two rotors one on top of the other rotating in opposite directions)

I am looking for an external mixer as defined below.

Inputs:
- rudder and throttle

Outputs:
- top rotor motor output
- bottom rotor output

Mix Function:
While rudder is neutral both top and bottom rotors would be running at the same speed. When rudder is moved left or right the bottom and top rotors would increase and decrease speeds to turn the craft left or right.

The gyro would be in-line between the receiver rudder output and the rudder input on the mixer.

Does a mixer like this exist off the shelf or would it have to be built?

Thanks,
Brendin

[Miami Mike]

Assuming that each of your rotors is operated by its own separate motor and ESC, then it seems to me that an ordinary elevon mixer ought to do what you want.

http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXELT4&P=7

[Xnaron]

I new there had to be a simple answer for this. Thanks very much Mike you pointed me in the right direction.

Brendin

[alexcmag]

A V-tail mixer will work, but is not the better choice because they usually are 50% mixer, if used with motor-rudder control, will to this:

- At low throttle, will send 25% power to both motors
- At low throttle, left rudder, will send 0% power to one motor, 50% to other
- At low throttle, right rudder, will send 50% power to one motor, 0% to other
- At mid throttle, will send 50% power to both motores
- At mid throttle, left rudder, will send 25% power to one motor, 75% to other
...
- At full throttle, will send 75% power for both motors
- At full throttle, left rudder, will send 50% power to one motor, 100% to other
...
And so on...

So depending on how much power your motors are, your heli can never have a good climb (motors will never go over 75%) or will never land again (motors will never go below 25% power).

If you have a computer radio with programable mixings, you can mix channel 3 to 4 and 4 to 3 (I suggest 100% 3 to 4 and 50% 4 to 3 as start, so your motors will turn off when throttle low and will go full power with throttle up).

Or... If you have a PIC programmer or a friend that can program a PIC microcontroller, I can send you the source code for a mixer, the circuit is very simple, just 2 servo extensions and 1 PIC12F629 8 pin microcontroller.

[Xnaron]

A V-tail mixer will work, but is not the better choice because they usually are 50% mixer, if used with motor-rudder control, will to this:

- At low throttle, will send 25% power to both motors
- At low throttle, left rudder, will send 0% power to one motor, 50% to other
- At low throttle, right rudder, will send 50% power to one motor, 0% to other
- At mid throttle, will send 50% power to both motores
- At mid throttle, left rudder, will send 25% power to one motor, 75% to other
...
- At full throttle, will send 75% power for both motors
- At full throttle, left rudder, will send 50% power to one motor, 100% to other
...
And so on...

So depending on how much power your motors are, your heli can never have a good climb (motors will never go over 75%) or will never land again (motors will never go below 25% power).


Does this also apply to an elevon mixer?

[Miami Mike]

As far as I know, v-tail mixers and elevon mixers are the same thing. The only differences are which receiver channels you plug the leads into and which servos you connect to the outputs.

[Xnaron]

Thanks... If I can find an elevon mixer that has a gain pot for aileron and elevator I should be fine. I couldn't find any tech details on the slinger elevon mixer. From the picture it looks like it might possibly have a gain pot but can't tell.

Brendin

[red-panda]

I'm using GWS mixers on a twin (side by side) rotor heli, in this case mixing throttle and roll, with a gyro on roll, with a second mixer handling yaw and fore/aft cyclic, and have had no problem with limited travel on any axis. What I have noticed is an occassional tendency for the mixer to start up in "confused" mode which results in very strange outputs when any stick is moved from its nominal neutral. The cure for this is simply to cycle power.

chris

[alexcmag]

I'm using GWS mixers on a twin (side by side) rotor heli, in this case mixing throttle and roll, with a gyro on roll, with a second mixer handling yaw and fore/aft cyclic, and have had no problem with limited travel on any axis. What I have noticed is an occassional tendency for the mixer to start up in "confused" mode which results in very strange outputs when any stick is moved from its nominal neutral. The cure for this is simply to cycle power.

chris

Probably GWS mixers have auto setting on neutral/max/min of each input.

[Zlatko]

Hi All,

Have a look at DigiMix-II
http://www.firmtronics.com/rc-products/digimix-ii.php
A bit more expencive than GWS but have a lot more capability.

http://www.californiasailplanes.com/digimix.html

Cheers

[vtolman]

The VEE-TAIL OMNI mixer does all you want, it flies my counter rotating VTOL airplane with gyro between the reciever and mixer. The mixer controls the ESC to speed up and slow down both motors.

[Xnaron]

I looked at that one...I am going to try the mixer sold by www.tufflight.com . This is the digimax mixer 2 as linked above. Joe at Tufflight is top notch. He is the first vendor I have ever dealt with to refund an overcharge in shipping.

If the digimax II mixer doesn't work I'll try the omni mixer...thanks for the post. Have you done any forward flight? Transitions: hover->forward flight and back? Any video?

Thanks,
Brendin

[Xnaron]

This is what I am thinking about using the mixers for...

[thanhTran]

Looks great Brendin. I think it will work. Can't wait til you fly it :). Thanks very much for sharing

thanh

[Zlatko]

Brendin !!!!

Thats exactly what I tried to do :)
I used IPS-A motors/gearbox with 10x4.5 contra props from ToddsModels.
http://www.toddsmodels.com/Props/propsother.htm
First I used 3 GWS mixers with 3 GWS PG-03 gyros, but the V-tail mixers were not too good ( not enough resolution/steps ). Then went with 3 digimix-2 but discovered that it would self oscilate ..... ( I guess the gyros, but it could be because of so much cascading .... not too sure ).
I gave up on that as I didn't have too much time to play and in the mean time got the X-UFO :) ... much cheaper.
http://www.hobbypeople.net/gallery/106560.asp

http://www.rcgroups.com/forums/showthread.php?t=366513

Cheers