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May 24, 2008, 10:40 AM
Power Wheels Guru
UNGN's Avatar
Mini-HowTo

Dual ESC's for Differential thrust rudder control


I'm working on an Estes 747 real radio conversion and want to control the EDF's on each wing with two 15 amp ESC's and plugged into throttle and rudder using a Spektrum Dx7/AR6100 to mix them.

My question is can I just plug in the two ESC's into my AR6100 as-is or do I have to disable one of the BEC's?

See below for Differential Thrust mini how to
Last edited by UNGN; Jun 29, 2008 at 12:43 AM. Reason: Changed from question to How To
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May 24, 2008, 03:08 PM
Registered User
vintage1's Avatar
Mmm. depends a bit on the BEC.

It's probably safest to knock up a little distribution board and feed half the servos and the receiver from one BEC and half from the other.
May 24, 2008, 04:43 PM
Registered User
i haven't had problems placing 2 speed controllers through a mixer well not with the BEC's but it probably best to disable one of the BEC's and route the red wire from the speed controller to where the mixer's red wire goes which should bypass the mixer.

do your speed controllers have an arming sequence like the Xtras where you have to raise the throttle to full then minimum then neutral?
May 30, 2008, 09:23 PM
Power Wheels Guru
UNGN's Avatar
I think I have a 3 mix program on my DX7 that will work for now.

Basically, I have one ESC plugged into the the throttle and one plugged into the gear slot.

One Mix slaves the "Gear" to the throttle at 100% with a - 100% offset. This mix runs the two ESCs in parrallel with the throttle.

The other two mixes slave the Throttle and Gear to the Rudder stick that speed up and slow down the motors for turning. I'm going to start out with 10%+ and 10%- as the max differential between motors to start and adjust based of flight characteristics.

The only downside to this set-up is the ESC's seem to have slightly different low voltage cut-off's. It probably won't result in a pinwheeling flat spin because the other side will cut out soon enough, but I'm training my 9 year old test pilot to put the throttles to zero if it performs an uncommanded yaw.
Jun 29, 2008, 12:36 AM
Power Wheels Guru
UNGN's Avatar

Differential Thrust TX programming for DX7


Here are my DX7 screen shots for dual ESC differential Thrust.

Right now we have it set up for +10% / -10% for each ESC at full rudder deflection.

The right side ESC is plugged into the Rudder slot on the receiver, the left side ESC is plugged into the Throttle slot.

I initially had the right side plugged into an auxillary channel, because it would start out at zero, instead of in the middle, like the rudder servo does, and it is easier to mix.

The aux channel was mixed to the throttle 100% and both of these were mixed to the rudder for 3 mixes.

I really wanted to use the aux channel for other things, so I thought about it and mixed the rudder with itself for a 4th Mix. Because one of the first three mixes was a rudder mix, I combined the two rudder mixes, so I'm back to 3 mixes using the rudder and Throttle slots on the receiver, which is ideal.

If none of this makes sense, see the screen shots for more detail.

The plus/minus 10% differential appears to be a good starting point, but I will experiment with different twin aircraft to see what works best.

First Mix:



Second Mix:



Third Mix:
Last edited by UNGN; Jun 29, 2008 at 10:04 AM.
Jun 29, 2008, 12:55 PM
Power Wheels Guru
UNGN's Avatar
Just got back from the maiden flight with my 747. Plus/minus 10% isn't enough to overcome the huge tail and long fuselage.

It definitely has an effect and turns the aircraft, but I want to kick the nose around more, and 10% aint gonna do it.

I'll double it to 20% and see how that goes.

10% was a great starting point, however, for a plane with ailerons.

Now that I think about it, I guess I could have put in 2 10% mixes and added or subtracted them with a switch.
Jun 29, 2008, 01:06 PM
my karma ranover my dogma
galaxiex's Avatar
I used 30% on this plane but it is MUCH smaller, and I used a V-Tail mixer for the throttle control, thrust differential.
I just could not figure out how to do the mix in the radio. (DX6)

Your post on how you did your mix has given me some ideas on how to mix mine, I will go back and try some things...
Jun 29, 2008, 04:47 PM
Power Wheels Guru
UNGN's Avatar
Quote:
Originally Posted by galaxiex
I used 30% on this plane but it is MUCH smaller, and I used a V-Tail mixer for the throttle control, thrust differential.
I just could not figure out how to do the mix in the radio. (DX6)

Your post on how you did your mix has given me some ideas on how to mix mine, I will go back and try some things...

Every gram counts, so a transmitter mix should allow removal of the mixer.

If you don't have ailerons, definitely have as much as possible rudder mix, then take out some if its too sensitive in yaw.

Like an Aero Ace, you want to have zero throttle turning capability. 10% doesn't really give that.

Today when the 747 was heading for trees, I was giving it full rudder and it was turning flat, but not fast enough, so I leaned it over with the ailerons and gave it full up elevator and it turned right around. You don't want to be in that situation without ailerons.

I'm going to try to put flaps and retracts on my 20" 737, so I needed to free up the extra channels on my receiver and can't spare the couple grams for a mixer board.
Jun 29, 2008, 05:40 PM
my karma ranover my dogma
galaxiex's Avatar
Quote:
Originally Posted by UNGN
Every gram counts, so a transmitter mix should allow removal of the mixer.

If you don't have ailerons, definitely have as much as possible rudder mix, then take out some if its too sensitive in yaw.

Like an Aero Ace, you want to have zero throttle turning capability. 10% doesn't really give that.

Today when the 747 was heading for trees, I was giving it full rudder and it was turning flat, but not fast enough, so I leaned it over with the ailerons and gave it full up elevator and it turned right around. You don't want to be in that situation without ailerons.

I'm going to try to put flaps and retracts on my 20" 737, so I needed to free up the extra channels on my receiver and can't spare the couple grams for a mixer board.
I agree, every gram counts.
No ailerons on mine but with any turn input it banks quite well, probably due to the dihedral.
Then I can yank it around with the elevator if necessary.
The way mine is setup with the mixer, it has zero throttle turning and reasonable sensitivity at part throttle.
At full throttle it is much more sensitive to yaw input but not uncontrollable.

Again, grams count, but this little P-38 managed to fly this vid cam, e-DVR 5in1, approx 1 oz.

Retracts on that 737 would be cool, kinda small plane for retracts tho..
What will you use for gear? The small GWS units?

Mini P-38 rc airplane onboard vid camera (3 min 18 sec)(3 min 18 sec)

Mini P-38 airplane camera test # 2 (1 min 12 sec)(1 min 12 sec)
Last edited by galaxiex; Jun 29, 2008 at 08:52 PM.
Jun 29, 2008, 06:04 PM
Power Wheels Guru
UNGN's Avatar
Those are great videos.

We want to get an edvr for this kind of stuff. We could put a couple on the 747 and it would never know they were there.

Do you have counter rotating props? I would think the prop torque could help in banking the plane, because it appears to bank very nicely.
Jun 29, 2008, 08:51 PM
my karma ranover my dogma
galaxiex's Avatar
Thanks!

Yes they are counter rotating,
hmmm never thought of that,
that the CR props might be what makes it bank so well.
Jun 29, 2008, 09:52 PM
Power Wheels Guru
UNGN's Avatar
I think that is why our Star Scream F-22 banks so sweetly, with the torque from the outside motor lifting the outside of the wing and forcing the inside down.
Jun 30, 2008, 11:54 PM
Power Wheels Guru
UNGN's Avatar
I redid the mix on my JAL 747 to give 25% differential instead of 10%.

due to the 125% max mix limit, 25% is the most that can be done with a DX7 using this particular 3 mix method. I could probably add 2 more mixes to provide additional differential.

I've also added a 4th mix to eliminate the nose down tendency that some differential thrust 2 channel planes have built into them when the power is cut (power = nose up, cut power = nose down)

Now, Power = down elevator, cut power = up elevator. This should reduce the nose ins that the original plane is famous for.
Last edited by UNGN; Jul 01, 2008 at 09:05 AM.
Jul 15, 2008, 02:49 PM
add lightness
PositivelyJoe's Avatar
dang nab it!
I want to do the diff. thrust rudder control on my E-flite P-38, but I have a DX6i which only has 2 mixes.
any ideas?
Jul 15, 2008, 04:22 PM
my karma ranover my dogma
galaxiex's Avatar
Quote:
Originally Posted by Zagi400flyerMN
dang nab it!
I want to do the diff. thrust rudder control on my E-flite P-38, but I have a DX6i which only has 2 mixes.
any ideas?
Sure!

Use a V-Tail mixer like here...

https://www.rcgroups.com/forums/showthread.php?t=796909


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