Solved Twin Motor Question...?

[BATTLEAXE]

As some may know I have gone and built the SeaDuck, scaled down to 85% for a 48" WS, and better sized to the 2212 1400kv motors. It comfortably spins an 8" prop controlled by 30a ESC's on 3s. Some of you may have seen the maiden vid i posted this past weekend, I have fixed the signal issue and the airframe of coarse, then took it up for the re-maiden tonight. It held signal more consistently so i was able diagnose other issues. First was the antenna position, found that the antenna pointed up as opposed to the side was better for signal retention. Might have something to do with how an individual holds the radio, however this is what I found to be the better option.

That being said here is my query. In setting up the ESC wiring I made the power leads from the battery in parallel, one to each motor, then disconnected and taped off the positive lead to one of the ESC's. Makes sense, you don't want to double the voltage to the receiver. Done. Now in flying tonight i found that as long as i didn't use rudder stick (left, right), the motors held consistent power through a turn. Once i applied the rudder input to get yaw control i would see and hear the inside motor start to glitch out and on, causing loss of power and straight into a tip stall. Let go of the rudder stick and then you get your consistent power back and are able to pull out or the diving spiral.

I did recently get a tip from someone, YT channel RC VIDEO REVIEWS, told me to disconnect the ground lead as well. The ESC only needs the signal from the receiver, not a ground wire. I thought about this and I couldn't see why he would be wrong. Now that I got home I did make the adjustment. I did take it out in the back yard for just some taxi testing to see if i would notice or hear any glitching, and being on the ground it wouldn't dive out of the sky. I took wide laps and it found to hold the radius and no momentary drops in power.

Have any of you heard of disconnecting both the positive and ground wires or just the positive?

This is the first time I have heard anyone mention ground wire, I have always heard just the positive wire. Mind you this is also my first twin, so I am not sure myself. I will be taking it up for another couple batts tomorrow and that will tell the story.

Does anyone know the theory behind this and the advantages or disadvantages either way... or does it even matter?

Just curious as to how this works, plus my brain will sleep once i know. Thank you

Here is a pic of the duck...

Its not this pretty anymore but it still is functional

 

[Merv]

I am far from an expert.
In my thinking you must have a signal wire and negative wire. The electrons from the signal wire must have a path back to the source. If not nothing can flow.

I don't believe the reason for disconnecting the positive wire is double voltage. I believe there are two types of BEC's, linear & switched, one type will play nice a second BEC, the other type will have problems. It's my understanding that the BEC's will fight each other, one will call for a slightly higher voltage & the other slightly lower. They will never be exactly the same.

 

[BATTLEAXE]

I am far from an expert.
In my thinking you must have a signal wire and negative wire. The electrons from the signal wire must have a path back to the source. If not nothing can flow.

I don't believe the reason for disconnecting the positive wire is double voltage. I believe there are two types of BEC's, linear & switched, one type will play nice a second BEC, the other type will have problems. It's my understanding that the BEC's will fight each other, one will call for a slightly higher voltage & the other slightly lower. They will never be exactly the same.

I did switch it and it works either way, on the taxi testing. I did not consider the linear and switching BEC options though. It should be the switching type though is what you say...

 

[JasonK]

EE here -> you need a common ground for your signal wire to work (unless your using differential signalling, which our servos and ESCs are not).

Now, that common ground might be via the battery connection to the ESC and to the reciver, IF, everything has a shared negative power rail (one thing you can avoid is something called a ground loop, which can happen if you have 2 different ground paths connecting 2 devices).

On the cutout on yaw, what is your rudder -> motor mixes? if it is 100%, you could be cutting out your inside motor.

 

[BATTLEAXE]

On the cutout on yaw, what is your rudder -> motor mixes? if it is 100%, you could be cutting out your inside motor.

Motor differential is set to 25%, nice and light for now. I would like to set it up to the rate switch so it increases as the rates go up.

I am sure if it was set to 100% differential mix i would notice a inside motor cut out. If the cruise input on the throttle is at say 60%, and the mix is at 100%, any signifigant pull on the rudder stick would completely drop the inside motor. But this would happen in a smooth fashion, run down to off, then respool coming back to center, but smoothly. This is a glitch like there is a crossed signal or something in that realm, like there is signal confusion or improper connections.

The ESC's I am using are SimonK 30amp that are meant for multrotors, which in theory should be able to smoothly handle differential at the very least. That is how quads stabilize is by using differential on 4 signals via flight controller. I feel it has something to do with the wiring.

 

[quorneng]

Battleaxe
Be careful in assuming that your issue with the rudder is caused by a problem with the way the ESCs are connected.
As you say using differential thrust is nothing odd. It may be an ESC wiring issue but I would also be looking at it being caused by something else.

The positives of 'linear' BECs can be safely joined together (although the load is very unlikely to be shared equally) however 'switching' BECs are most likely to interfere so only one must provide the power. The majority of BECs are now of the switching type so unless you are certain they are linear BECs safest to only have one red wire connected.

 

[Merv]

I did switch it and it works either way, on the taxi testing. I did not consider the linear and switching BEC options though. It should be the switching type though is what you say...

So it works with only the signal wire?

 

[BATTLEAXE]

Battleaxe
Be careful in assuming that your issue with the rudder is caused by a problem with the way the ESCs are connected.
As you say using differential thrust is nothing odd. It may be an ESC wiring issue but I would also be looking at it being caused by something else.

The positives of 'linear' BECs can be safely joined together (although the load is very unlikely to be shared equally) however 'switching' BECs are most likely to interfere so only one must provide the power. The majority of BECs are now of the switching type so unless you are certain they are linear BECs safest to only have one red wire connected.

Perfect. I think you just confirmed the fact that one red wire is all that is needed, which is what i had going from the beginning. The ting i was wondering about was the ground wire from the same ESC that has the positive disconnected. I guess it just comes down to the ESC's. Thank you sir

 

[BATTLEAXE]

So it works with only the signal wire?

Yes. It spins and on the ground taxiing it seems smooth

 

[Merv]

Yes. It spins and on the ground taxiing it seems smooth

I can't wrap my mind around how that works. I can't argue with success.

 

[BATTLEAXE]

I can't wrap my mind around how that works. I can't argue with success.

It was roughly explained to me that all was needed was the signal wire for the one ESC. All the power and grounding comes through the battery wires to the ESC. And the ground from the primary ESC receiver lead is all that is needed for the Rx.

Have you built and set up twins before? This is my first so this is why I am curious as to how this works and what to look for in trouble shooting

 

[shadeyB]

Interesting discussion, & views
I am far from having answers or knowing solutions
I have only built 2 twin motor jets, 1st one both ESC’s were wired as normal and no dramas or conflict from each other and had a wonderful time with her.
after seeing other discussions and advice on this subject my 2nd build I removed the positive wire from 1 ESC , still no issues Or conflicts and still enjoying flights with her
However the 1st time wiring it up both motors would pulse from time to time while above 1/4-1/2 throttle ,,,,, confused by this I switched the motors out thinking that was the issue and resolved the pulsing ?
As for differential thrust , not tried that yet as it’s above my pay grade at this time

Just sharing my experience on this subject

 

[Merv]

It was roughly explained to me that all was needed was the signal wire for the one ESC. All the power and grounding comes through the battery wires to the ESC. And the ground from the primary ESC receiver lead is all that is needed for the Rx.

Have you built and set up twins before? This is my first so this is why I am curious as to how this works and what to look for in trouble shooting

No, I've never built a twin.
Sounds like you are using one battery? I'm wondering if the signal wire only will work if you ran separate batteries to each ESC?

 

[BATTLEAXE]

Interesting discussion, & views
I am far from having answers or knowing solutions
I have only built 2 twin motor jets, 1st one both ESC’s were wired as normal and no dramas or conflict from each other and had a wonderful time with her.
after seeing other discussions and advice on this subject my 2nd build I removed the positive wire from 1 ESC , still no issues Or conflicts and still enjoying flights with her
However the 1st time wiring it up both motors would pulse from time to time while above 1/4-1/2 throttle ,,,,, confused by this I switched the motors out thinking that was the issue and resolved the pulsing ?
As for differential thrust , not tried that yet as it’s above my pay grade at this time

Just sharing my experience on this subject

So you hooked up the first with all wires connected and had no issues huh. I always heard that was bad for the RX. Maybe if this doesnt work i might just go and try that

 

[shadeyB]

So you hooked up the first with all wires connected and had no issues huh. I always heard that was bad for the RX. Maybe if this doesnt work i might just go and try that

Lol I’m not suggesting this
But yes on my 1st twin build I didn’t know any better, had issue with bench testing and running throttle up , motors pulsed from time to time .
I then when maiden took place the same happened at 1/4 throttle lol needless to say took her home after rough maiden and landing , switched the motors out to new ones and off she went like a rocket with no issues , interference or pulsing
Then one day the ground came ups too close and buried her head like an ostrich
By the 2nd one I had read posts on removing 1 wire ? Thought I’d give it a go and like 1st build no issues
And yes I just crashed her today lol

 

[BATTLEAXE]

Lol I’m not suggesting this
But yes on my 1st twin build I didn’t know any better, had issue with bench testing and running throttle up , motors pulsed from time to time .
I then when maiden took place the same happened at 1/4 throttle lol needless to say took her home after rough maiden and landing , switched the motors out to new ones and off she went like a rocket with no issues , interference or pulsing
Then one day the ground came ups too close and buried her head like an ostrich
By the 2nd one I had read posts on removing 1 wire ? Thought I’d give it a go and like 1st build no issues
And yes I just crashed her today lol

If i do attempt it i might toss it on a cheap Rx to see what happens... magic smoke will tell the story lol

 

[JasonK]

No, I've never built a twin.
Sounds like you are using one battery? I'm wondering if the signal wire only will work if you ran separate batteries to each ESC?

There needs to be a common ground between the receiver and the ESC, so if you have separate batteries to each ESC, your going to need a round wire somehow back to the receiver for both ESCs.

 

[BATTLEAXE]

There needs to be a common ground between the receiver and the ESC, so if you have separate batteries to each ESC, your going to need a round wire somehow back to the receiver for both ESCs.

Ok cool so i am powering both ESC's from one battery with a parallel feed. So they are both fed equally split power.

 

[JasonK]

So you power negative battery lead is your common ground.

 

[BATTLEAXE]

So you power negative battery lead is your common ground.

Correct. Thats the theory anyway