Solved Differential Thrust on Spektrum DX6i

[MrKilometer]

Hi all,

I'm having some issues with setting up differential thrust on an FT Guinea Pig. I'm using a DX6i, and have one ESC going to the throttle channel, and the other to the aux channel. The mixes I'm using are as follows:

Mix 1: Throttle -> Flap
U -100%, D -100%

Mix 2: Rudder -> Flap
R 25%, L 25%

When I throttle up, the motor attached to the esc that is connected to the throttle channel works, but the other one does not. The interesting thing I noticed is that when I set the "up" percentage on mix 1 to greater than 0%, the other motor (the one connected to the aux channel) works, and adding a greater value on the mix causes the motor to spin faster (so 10% mix gives 10% throttle, etc). It's worth noting that I have gotten differential thrust to work with this transmitter and plane, and these problems started when I replaced the Flite Test 35amp ESCs with Xilo 40amp ESCs and an external BEC.

I know this is a niche issue, but any help would be appreciated. Thanks!

 

[Merv]

Mix 1: Throttle -> Flap
U -100%, D -100%

Try changing U from -100% to +100%,
On mix 2, R or L will need to be negative.

 

[Intashu]

I followed the same general mixing you'd use for talierons when using my DX6i. but that resulted in neither motor going to 100% unless i was also turning.

I eventually just bought a little dedicated taileron mixer to run twin motors, attaching it to the rudder and throttle channels allowed me the proper control I actually wanted out of them. I love my Dx6i but it just lacks some of the more complex smarter options/features newer transmitters carry these days.

as for why it isn't working, when they're both connected have you tried to follow the throttle programming for the new esc's as it's configured? maybe it's just mis-reading the signal for neutral so it doesn't want to start?

 

[MrKilometer]

Try changing U from -100% to +100%,
On mix 2, R or L will need to be negative.

I tried that, and it just sets the throttle to 100%, and it's not adjustable from that position using the throttle stick on the transmitter.

 

[MrKilometer]

I followed the same general mixing you'd use for talierons when using my DX6i. but that resulted in neither motor going to 100% unless i was also turning.

I eventually just bought a little dedicated taileron mixer to run twin motors, attaching it to the rudder and throttle channels allowed me the proper control I actually wanted out of them. I love my Dx6i but it just lacks some of the more complex smarter options/features newer transmitters carry these days.

as for why it isn't working, when they're both connected have you tried to follow the throttle programming for the new esc's as it's configured? maybe it's just mis-reading the signal for neutral so it doesn't want to start?

I followed the throttle programming for both, but I might try redoing it for good measure. I’ll play around with it a bit more, because it feels like there should be a way to get it to work with the DX6i. The mixer is a good idea, would you mind sending a picture/link of the one you used?

 

[tamuct01]

The DX6i only has 2 mixers. To properly do differential thrust you need 3. You can get a partial differential on the DX6i, by linking Aux1 to Throttle (mirroring throttle channel to the Aux1 channel) and the 2nd mix tieing Rudder to either Throttle or Aux1. You would need the 3rd mix slot to tie Rudder to the other one (Throttle or Aux1, whichever wasn't used in Mix2).

With just the 2 mixes you can make one of the motors slow down or speed up with the rudder, but not the other.

 

[MrKilometer]

Yup, I know. I had differential thrust working before, but now one motor doesn't spin up as stated above.

 

[Tench745]

You say setting up to +100 has the motor running constantly. Does it slow down as you increase throttle? If is does, you'll need to swap up and down mix values U-100 D+100.
I gave my DX6i to my brother or else I would pull it out and try the program myself.

 

[Tench745]

You say setting up to +100 has the motor running constantly. Does it slow down as you increase throttle? If is does, you'll need to swap up and down mix values U-100 D+100.
I gave my DX6i to my brother or else I would pull it out and try the program myself.

Disregard. I did a little more reading/remembering about DX6i setup. Both values should be either negative, like you have them, or positive and then reverse the channel.

 

[MrKilometer]

Well, an update:

It works! After reading all of your suggestions, and tinkering with it some more, I accidentally discovered the problem (as is so often the case). After resetting the throttle positions on both ESCs, both worked on seperate channels, but not in sync. In a test where I reset the throttle values and activated the mix while the aircraft was plugged in (maybe not advisable), I noticed the aux motor was spinning at a low, stop-start speed. Throttling up, to my suprise, caused both motors to spin! Adding an extra -6% in made it so that both motors are synced, and with mix 2 going flap-> rudder, I’m off to the races! My theory is that the ESC on the aux channel was not arming (and this is where I get speculative) because the throttle position was too high - for some reason, the ESC wasn’t playing it’s “you just plugged in the battery and I’m about to spin, dummy” tune. For those interested, the final mix is thro->flap D-106%, U -100%.

On a side note, I’m aware the DX6i can’t do “true” differential thrust, but it’s enough to taxi the airplane, which is all I really need from it. Thank you to all who helped me out!

 

[Bricks]

Did you calibrate the ESC`s may be the difference in throttle run up between the motors.