Differential Thrust Setup on a Spektrum DX9

by FliteTest | August 21, 2018 | (4) Posted in How To

Here's how you set up differential thrust on a DX9. You can also use this tutorial for a Spektrum DX6

Differential thrust is extremely useful to have on all sorts of multi-engined aircraft. It can help with your yaw, it can get you into cool maneuvers like flat spins, and it can also allow you to steer around whilst taxiing. Many modern radios have the ability to program differential thrust, so here's how you do it on the Spektrum DX9

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1. Motor and ESC Setup

You're (rather obviously) going to need at least two motors to do differential thrust with. Link the motors with a battery 'Y' harness to power them both from one battery.

2. Reciever Pins

Insert one ESC lead into your throttle channel and one ESC lead into your Aux channel.

3. Transmitter Defaults

When looking at your transmitter monitoring, you should see that increasing the throttle will only power the throttle channel. This needs to be changed so that moving the throttle moves the Aux 1 channel too.

4. Pairing the motors (no differential)

Go into 'System Setup', scroll down the list and click 'Channel Assign'

To pair the motors together (without any differential thrust), just assign Aux 1 > Throttle. This will make the throttle control the Aux 1 port on your receiver in parallel to your throttle channel. This means that both motors will spool up equally. However, ignore this step if you want to programme differential thrust.

5. Pairing the motors (with differential)

From the Channel Assign menu, you'll want to click the 'Next' button at the bottom of the screen to get you to the 'Channel Input Config' page. 

Assign Aux 1 > Thr. This will allow you to programme mixes around your two throttles. 

6. Programming your first mix

You'll need two different mixes to make this work. First, go back to the main 'Function List' menu and then select Mixing

Choose P-Mix 1 and Assign Rud > Aux. Next, change the right-hand number to +100. You can increase or decrease this number to adjust the sensitivity of the differential thrust. A higher number makes the effect more extreme.

7. Programming your second mix

Choose P-Mix 2 and assign Rud > Thro

This time, change the left-hand number to -100. With that, you're almost finished. 

8. Check your stick movements

Make sure that a right input on the rudder powers up the left motor and vice-versa. If this is not the case, you'll have to swap the two ESC leads plugged into your receiver around. This will ensure that the rudder inputs steer the aircraft in the right direction. If you need to tune the sensitivity of the rudder, you can simply adjust those numbers (currently set at 100) in the mixing menu. You can also play around with the expo of your rudder and set up dual rates.

9. Have fun!

With that, you should have successfully setup differential thrust on your Spektrum DX9 transmitter. Go out to the field, get your plane into the air and have a blast! If you have any questions, or need clarification on anything, write a comment below. 

Article by James Whomsley

Editor of FliteTest.com

Contact: james@flitetest.com

YouTube Channel: www.youtube.com/projectairaviation


CrazyFastFlying on January 17, 2019
How do I setup Differential Thrust on a Walkera devo7?
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Timson on October 26, 2018
I did that before reading the article. My problem was at first that I assigned a switch to the Aux because I thought I had to. That doesn’t work. I then put the source of the Aux to N/A and used three mixers. One to have the Aux connected with the throttle, one to mix it with the rudder and one to mix the rudder and the throttle as shown in the article.
Also I put a three position switch. Mode 1 is Air: Everything works like a normal four channel plane, mode two is landing, flaps up and mode three is water: differential thrust on the engines for swimming.
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jtuttle11 on August 21, 2018
I like this way, gotta try it on my DX-8
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bobr on March 22, 2020
I used this setup on a iX-12, no problem it worked fine, BUT.... I have used a throttle kill switch forever, which now does not kill both motors. Anyone any ideas on how to have both??
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bob@rcmodel.com on January 15, 2020
Trouble setting up diff thrust on my Dx9. If I am following this right, on rx port assmts position 6(aux 1) won't show Aux 1;allows any other option. When I go on to channel input configuration Aux 1 shows as N/A.
When I go into the mix menu P-mix 1 won't display aux 1 as an option (shows 2&3 OK)

i have read thru the dx-9 manual and this article repeatedly and can't find what I am doing wrong. Help!
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iowaopie on May 6, 2020
how do i assign a switch to turn it on and off so it does not mess with my other planes

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Differential Thrust Setup on a Spektrum DX9