Positive or Negative Differential Thrust

[Theuglycamel]

Hello All,
I've been playing with my first throttle mix and to honest will probably only build twins from now on. I'm a week away from good enough weather to maiden (Guinea Pig) and in my boredom I've figured two ways to mix. One gives me positive thrust on the outboard engine with rudder input. My other reduces thrust from the inboard engine. Problem with the first is lack of differential at full throttle, and the second is less action taxing. I'm assuming I could mix the mixes and get the best of both worlds, and I dug into the PhoenixRC model to see if I could tell how it's configured. In the sim, giving right rudder at idle (0 i should say) spins up the left engine (positive mix). With this mix I shouldn't have any thrust left at full throttle to give differential (can't add to 100%). But in the sim, it also applies negative mix to the inboard engine. I know I shouldn't be comparing to a sim, and I'm not trying to make my cheap ass radio do anything even close to this (need 2 more mixes as I can figure). I'm just curious if anyone WITH a sweet TX could explain how you'd accomplish this with your rig. Or, perhaps just somebody to call me a numbskull and lol that I don't know how... Either or would be greatly appreciated!

 

[DamoRC]

In not an expert on mixes and my radio (Dx6i) can't do a proper diff thrust, but the goal is to be able to control both together - left rudder increases the speed on the right motor and decreases the speed on the left motor (and vice-versa for right rudder). What kind of radio do you have?

 

[Theuglycamel]

I'm running a flysky isx right now. Only 3 mixes, so I know it's not gonna happen with this rig. Right now I'm running negatives since it makes more sense to me to keep control at full throttle. I think if I had one more mix I could simply flip this for the other engine. Thanks for the reply!

 

[tamuct01]

I've been running differential thrust on my Guinea Pig for a while (Taranis radio), and I use a max of +/- 50% throttle tied to the rudder input. This means that at 50% throttle and the rudder hard over one motor is at 100% and the other stopped. You are correct that at above mid-throttle the one motor can't exceed 100%, but it's just something that I've gotten used to. Also, my GP is running on 4S and is way overpowered anyway, so I don't fly at full throttle often. The choice of mix setup is really up to you and your preferences. As you have discovered, there are tradeoffs in each setup.

 

[Arcfyre]

I have a positive mix on my sea duck and it works very well, especially for water taxiing where very little power is required for making turns or picking up speed. A negative mix would be more fiddly in this situation I think.

 

[Theuglycamel]

I agree completely Arcfyre, and to be honest I'll probably set a Mode so I can switch over to positive any time I'm on the ground. I'll play with this tonight and see how I like it. I've been watching a few vids on how fellers are accomplishing this with $1000 rigs but I'm still wrapping my head around it. This may actually steer me in the direction of what TX I want to buy next. Thanks for the input!

 

[Chappie66]

Something below that should get you in the ball park.
The pos and neg mix values, in Mix 2 and Mix 3, if memory serves, control how much the rudder will affect the throttle
The pos and neg mix polarity depends on which ESC is in the primary throttle channel.
I played with it on my FS-I6X...or something close, dang memory. But I now use a Taranis. Will break out the old standby tonight (fingers crossed) and experiment.

Mix 1
Mix is On
Master Ch3
Slave Ch5 (or where you plugged 2nd esc into)
Pos. Mix 100%
Neg. Mix 100% (this makes the 2nd esc mimic the 1st)
Offset 0%

Mix 2
Mix is On
Master Ch 4
Slave Ch 3
Pos. Mix -30% (may need to change polarity depending on which ESC is main)
Neg. Mix -30% (may need to change polarity depending on which ESC is main)
Offset 0%


Mix 3
Mix is On
Master Ch4
Slave Ch5 (or where you plugged 2nd esc into)
Pos. Mix 30%
Neg. Mix 30%
Offset 0%

 

[Theuglycamel]

Chappie66, I think you may have solved my numbskullishess... My mixes are Identical to your description EXCEPT I never tried running the POS and NEG mix together on the same Mix. I assumed (of course) that I would need a separate mix for Pos and another for Neg. I don't know why but I had it in my mind they would cancel each other out. Maybe I should have written my mixes down THEN looked at them. I can see now that mix 2 is applying 30 pos to engine one while at the same time Mix 3 is applying neg (reduced thrust by 30%) to my secondary engine. I never even tested using both on the same mix. I was hoping this was going to be super complicated and would require an upgrade... lol.
Sometimes you just can't see the forest for all the trees... Thanks again everyone!

 

[Chappie66]

Chappie66, I think you may have solved my numbskullishess... My mixes are Identical to your description EXCEPT I never tried running the POS and NEG mix together on the same Mix. I assumed (of course) that I would need a separate mix for Pos and another for Neg. I don't know why but I had it in my mind they would cancel each other out. Maybe I should have written my mixes down THEN looked at them. I can see now that mix 2 is applying 30 pos to engine one while at the same time Mix 3 is applying neg (reduced thrust by 30%) to my secondary engine. I never even tested using both on the same mix. I was hoping this was going to be super complicated and would require an upgrade... lol.
Sometimes you just can't see the forest for all the trees... Thanks again everyone!

Let us all know if it works...I will probably still do the experiment. I am a slave to my desire to tinker.

P.S. Upgrades are never a bad thing....why I moved to OpentTX and now might try ER9X on it, just because

 

[Theuglycamel]

I feel ya there, Only reason I was concerned at all about this, is because I got bored and it was bugging me. Shoot, it took me 3 days to decide if I liked the props counter-rotating inboard or outboard. And I still haven't decided completely on that one lol. I'm assuming you like the Taranis, have you or anyone you know had experience with Futaba? I've been a fan since buying my first AM in 1994, and I've been eyeballing the 10JA for a LONG time.
Sometimes it almost feels like cheating when programing a TX now days. It was so much fun setting brakes and dual throws by beep code... lol.

 

[Theuglycamel]

Hot dog that did it, The top end differential is hard to notice but it's definitely there! Now I do apologize Or being so quick to cast away my FS. I've had nothing but range to complain about, and I can't see too well anyhow... Thanks again! I'd still love to hear if anyone has a different way off mixing throttle. Just for conversations sake.

 

[kilroy07]

Here's how I have my Kraken and SeaDuck (FlySky I6X)

 

[Chappie66]

I feel ya there, Only reason I was concerned at all about this, is because I got bored and it was bugging me. Shoot, it took me 3 days to decide if I liked the props counter-rotating inboard or outboard. And I still haven't decided completely on that one lol. I'm assuming you like the Taranis, have you or anyone you know had experience with Futaba? I've been a fan since buying my first AM in 1994, and I've been eyeballing the 10JA for a LONG time.
Sometimes it almost feels like cheating when programing a TX now days. It was so much fun setting brakes and dual throws by beep code... lol.

Yea I admit I do love the Taranis. The Companion GUI allows me to program almost everything without touching the radio, except to upload the settings.
Most of the folks I fly with are Spektrum, JR, and a couple of us OpenTX folks.

If you want more authority in the differential, modify values in Mix 2 and Mix 3. I set them low to give a more graceful yaw authority, but at 100% I am sure a flat spin would be ridiculous, somewhere in the magnitude of the Bushwacker video I would presume.

 

[Keno]

Like to add one thing to this make sure you do a "Throttle range setting procedure". Aligning your tx stick to your speed controls. Not doing this contributed to an accident. as in, nothing happened and all of sudden something happen and then something ate my hand. And agree with Taranis and the X10S comments.

 

[pressalltheknobs]

Hot dog that did it, The top end differential is hard to notice but it's definitely there! Now I do apologize Or being so quick to cast away my FS. I've had nothing but range to complain about, and I can't see too well anyhow... Thanks again! I'd still love to hear if anyone has a different way off mixing throttle. Just for conversations sake.

On the i6 (probably the i6X is the same) you can set rates on the rudder (CH4) and use that to control the amount of Thr differential on switch. Probably works best where your plane doesn't have an actual rudder control surface.

 

[Theuglycamel]

I'm almost satisfied with my dual rates now. I'm looking at 45% rudder mix on low rates and 80% on high. Won't really be able to tell how I like it till she's in the air. Looks like this Sunday may be my day for testing. Pressalltheknobs, I meant to look at your setup on my TX last night and got caught up on painting. I'll for sure see if I can link rates to my two throttle channels tonight.
This is definitely the largest platform I've had in my fleet so far, and I've noticed peculiar effect... MODS MODS MODS lol. I've never had a plane that could take every servo that you shove in it. I've already scrapped my ia6b for an ia10b. I'm not one to post "Dreams" so I'll keep my ideas to myself until I actually get some things built, and until my camera and FPV goggles gets here from Amazon. Thanks again everyone for all the input! Friendliest forum I've been on in a LONG time!

 

[kilroy07]

On the i6 (probably the i6X is the same) you can set rates on the rudder (CH4) and use that to control the amount of Thr differential on switch.

Oh, good idea (I hadn't thought about doing that!) I'm still a little hesitant about diff thrust in flight... For taxing on the ground it's GREAT!!
Maybe at lower rates I would be a bit more comfortable using it more aggressively.

This is definitely the largest platform I've had in my fleet so far, and I've noticed peculiar effect... MODS MODS MODS lol. I've never had a plane that could take every servo that you shove in it.

Wait until you build a Kraken... It doesn't even notice all the crazy things I've slapped on it! (It didn't appreciate when I modded her into a pusher though...)

Thanks again everyone for all the input! Friendliest forum I've been on in a LONG time!

Yea, it's kind of what we are known for... Welcome to the family!!

 

[Theuglycamel]

Hello again, I'm finally wrapping up the last bits on the Guinea "Goose". I started a new thread over on Swappables & FT just to display a bit. Got a few knick knacks I'll add over there later this weekend. I'm shooting for this Sunday to get her in the air. If she comes back in one piece she'll earn another few stripes and a name badge. Planning on an egg drop at Easter for the kiddos. So no more Guinea Pig, she's now the Golden Goose.

Thanks for all the help on the Diff question. I'm programmed now at 30% with low rates and 70% on high. I'll let ya'll know how she handles and try to get a decent video. (it'll be the second flight, I'm superstitious about maidens lol). Ya'll keep rockin!

Excuse the mess...

 

[Theuglycamel]

Ok, I posted this vid in my newbie thread and my Golden Goose thread. But I wanted to let everyone know how the diff thrust worked out. I was running high rates, no expo, and 50% diff in this video. I can definitely see where the thrust adds a whole new component to flight. I was able to pull some wicked flick turns and roll-outs by flight #4. Got 6 total last night before dark caught me, and that was after my Oak Tree durability test as well. I will say that I'll be moving to 100% diff. I was surprised how controllable the rudder actually was with diff added in. My only complaints were nose gear durability, (especially jumping cow patties) and how low the tail wants to hang while banking (almost 80% rudder to keep her level). I'll get the nose gear worked out tonight and I think bumping the diff thrust up will help with the tail sag. Then I can get started on this cargo hatch... It'll be raining Easter Eggs before the month is out!

InShot_20190312_084731265.mp4

• Theuglycamel
• Mar 12, 2019
• ft guinea pig maiden flight