I'm very sorry to have missed the safety warning, but my mind was on another point entirely. I did include the fuse...However I would like to say that back charging between batteries is a norm. Every E bike does so. And I have never seen mention of extra boards between parallel cells for those. The 18650 cell is most common, with a minimum of 6 cells in common, parallel. The only real essential is to start with balanced voltages. There are YouTube videos of how this is done, with the real aim of getting the viewer to buy the kit.
I did exactly the same and suggested buying a pack ready made, which will parallel 2 cells as I mention, and have three in series, with a balance connector for charging. Most people lack the skills and confidence to start building their own battery packs. And carelessness with lithium cells will cause fires, if not explosions.
Don't mess with them unless you know what you are doing.

The build blog is up and going but comments, replies and likes are absent. I'm wondering if there is any real interest.

I didn't dare to say that. Has rank got privileges?

It does bring certain advantages with it Petty Officer😉
😎

Going back to battery life....not having one myself I did a little web research.
Salient facts
1. Many folk don't know exactly what sort of battery they have. Don't assume that you have got it right. Check.
2. Gel batteries are safest in confined environments and funny angles.
3. You don't get any benefit for free, there is always a tradeoff.
4. Gel batteries are the poorest battery technology for fast discharge. Eg a battery rated 7Ah discharged at 7A should last 1 hour? Wrong. Reckon on about 35 minutes at best.
5. Gel batteries need careful and proper charging. If your charger is the wrong type or has a sensing or timer fault you will get reduced battery charge, faster sulphation etc all resulting in shorter run time, end result eventually a dead battery.
6. As suggested earlier, if you have a constant voltage charger, 13.6V is the next best simple charger. That is a very slow charge technique; wait until the charge current has been stable and very low for 12 hours minimum, but then you can leave it trickling for a long time.
7. If you want 7Ah equivalent performance to a gel battery you will get very near using a 12V 3 cell LiPo rated 4.4Ah. Do not trust any cell claiming more than 3Ah or so such as Chinese claiming 9900mAh . I can buy six Sony VCT4 cells 3x 2x2.2Ah =13.2V 4.4Ah for 18 pounds, but doubtless one can buy a battery pack. At 7A Lithium will be very happy. The Fleet Admiral would correctly insist on a 15A or less fuse. Due to the superior discharge characteristics the Lithium will give rather better performance overall, finishing at 9.3V or so. Gel ratings reckon on full discharge at 9.2, but voltage dips sensed by an ESC may trip you out earlier. Its the end point that really matters in giving those last few minutes.

Without knowing the ESC number I can't answer that!
But there are 2 major possibilities.
1. A crossover reversing switch. That eliminates 3 out of 4 switching elements and can reduce losses. Relay would be rated near or above ESC rating. If above 20A it would be big. Can incorporate a resistor so as to allow less power in reverse.
2. A device to ensure all is well before enabling the Switching devices to start up.
Could be in the main power line and double up as an On switch. Again, fairly big, but smaller than in first option because it only needs one contact.
Other possibilities exist but need a mind more perverted than mine...

Gentlemen, you illustrate exactly why I built my own first ESC (ignorance and mistrust of purchased products,) and partly why I then continued with my Tug dual ESC blog. Advert over...but in a few blogs time I will be covering H bridges, which are present in every ESC and may, I repeat may, be a real source of some of your problems.
With no disrespect intended, you don't really know what, if anything, is wrong.
I can say that battery specifications and tests can be horribly misleading. In particular, battery voltage cannot be interpreted with a DVM. In my testing I have seen battery voltage, on NiMh at 7.2V nominal, dip and recover by over 500mV in a single 3msecond cycle while drawing only 3A. That is more than enough to trigger under voltage trips rather earlier than expected, and I'm sure that other technologies or poorer state of charge would give even worse figures. Figures given by marketing men are totally worthless, and I understand that Chinese batteries can be only 10℅ of what is promised.
Going back to H bridges, several aspects of the design are critical. In particular, if the design allows even momentary "shoot through" - google that- you will get poor runtime at best and early under voltage tripping as a certainty. Higher voltages make that a higher possibility, again depending on any short cuts in the design. The ESC numbers you mention only seem to have options for up to 9 cells, which means absolute max running at start of around 12.6V and rapidly decaying on a few seconds to 12.2 and below.?? But your 12V batteries will start at 14.4 and should not be run below 8V, so a 5V drop out is extremely low, the battery is over discharged by then. If you could select the 9 cell option, and if I was designing the ESC I'd be putting dropout at around 7.5V and hope for recovery to 9V to allow a limp home mode.
What is there to do?
Testing battery discharge time at a load nearly equal to the motor load is a first step only. A stack of light bulbs is easy and convenient, although a purist will argue. That will confirm that the battery is basically good or bad. You just time how long it takes for volts to drop below 1.1V/cell NiMhl (1.5 for lead acid, 3.3V for lithium) but do NOT flatten the battery much more than this or you may wreck it, especially lithiums.
5 mins after you start this test, take the light off measure the battery volts, put the light back and see how much the battery drops. That is a crude measure of battery internal impedance. You can repeat that test at any time during the discharge cycle. High battery impedance will always result in problems. For NiCd and NiMh battery holders with springs are an absolute no go because they will double the battery impedance. Strong clips may be OK for a small motor. So connections are critical. Soldering some materials needs care because you may get a poor joint even if mechanically it seems strong. Gold plating is a well known culprit. It starts OK and vibrates off.
The gold standard is the oscilloscope. You just set the boat going and look at the power supply. (Light motor loads can be misleading so pushing against the side of a tank is best)
All is revealed by this test, if you know how to interpret what you see.
In time, I'll be putting some pictures on my blog when I cover H bridges, and how to sleep at night.

Agree with this. I did try and pick up the motor servo but it does not exist. I had the official circuit diagram too. Hence this build, having to start again from the motor outputs.

I did put up a block diagram originally on the Electronize forum, but will repeat it on the build blog shortly, tidied up with comments. So I made a decision to deal with the inputs first as I intended the blog to teach a little electronics, as requested by 2 followers. This is a problem with threads, early comments, questions and answers get forgotten.

I could have just derived a circuit to recreate the motor servo signal from the motor signals, then bought bits to do the job. However, this boat version has a huge dead band and minimum motor speed is just under 25%, which is not really slow.

I think using the motor outputs makes this design relevant to all of these tugs and variants, as the interfaces are common to all.

If I commercialised it as a kit of a built PCB with connectors for most of the hook up, the parts cost in 100 quantities would be about 10 pounds including PCB. On normal commercial markups that would be nearly 100 retail or much less than 30 if made and sold from China....Bionic Bill has a working FM radio costing just a pound or so.
Not too bad but as you say, not really commercial. On the other hand it has only cost me much less than 20 pounds including replacing 2 blown up bridges that used badly chosen components.
I worked in precision and expensive design high end electronics for 40 years. Still learning to try and keep it simple....

Before getting into the logic of what we do with the inputs there are two sections to clear up; this is the first. I restrict myself to three main parts at once, as far as interfacing is concerned.

So far, we only have a limited rudder signal , RUDFLT.
This just represents the input pulse length with an analogue signal.
We need to reproduce a similar signal to that inside a rudder servo, where a potentiometer is moved by the rudder servo rotation. However, we need to turn this into two signals, direction and deviation.
The circuit attached has a lower set of Voltage against rudder pulse length diagrams to illustrate what is going on.

I mentioned ratiometric techniques earlier; this circuit uses that technique. B/2 can be thought of as a local ground, so we can have plus and minus around that.

Although RUDFLT has been referred to our battery voltage, B, we still need to amplify and further filter this. The reason for the exact numbers will be explained later, but for now,

rudders centred = 1.5msec input pulse

has to give us B/2. This needs a precise gain, set by R25 and R257. These are actually made up of two or three standard resistors so as to achieve the values.

The gain is quite low, around 2.858, which is near enough to the theoretical value calculated next.

The "perfect" input voltage at the 1.5msec point is B*1.5/8.6
We want B/2, so the required gain is (B/2)/(B*1.5/8.6).
The B drops out so the required gain is 8.6/(2*1.5) =2.866
Nothing is perfect, especially the input limiter previously described, and in practice I had to make a very small adjustment. That is the same as adjusting the rudder position on a controller.

Worse is to come.... When the input signal varies away from the centre B/2 we have to extract the deviation, which is the difference between RUDAMP and B/2 in either direction. We have to add a rectifier. Its actually a standard circuit. The trick is in U2 where we amplify any input less than B/2 by 2; when more than B/2 the amplifier just stops where it is at the point considered. ( I tell the truth in principle, R258 and its friend at 6.8K should really be 10K. But reducing both alters nothing, and enables the amplifier to behave better at low battery voltages). So the actual voltage o/p of this stage is less than indicated in the sketches, but the matching 6.8K puts the correct current into the summing next stage, and that is what matters.

When we add together and invert RUDAMP and D46/R253, the required output is calculated as shown. So this starts near zero, goes up to B/2 and then back down to zero.

Rudder direction is extracted from RUDAMP; when greater than B/2, direction is right rudder, when less than B/2, it's left rudder. I'll show the comparator that does this later, which is the fourth Triangle shape of this bit of the circuit. In practice, there is always a deadband where rudder is central, just as throttle also has deadband and is zero. A nice consequence of this is that actually none of this circuit need be very precise and we can use cheap amplifiers.

It looks a lot of bits, but can actually be one quad amplifier, an LM324 costing about 40pence. I actually use LM328 duals, just to make a bit of space.
Many servos also still use one chip, plus a potentiometer. I can't buy those chips for less than about £6 for 5 of them. And they have quite a few bits round them too.

Next we'll look at the PulseWidthModulator circuit that interfaces this analogue to the digital logic. That logic uses all the inputs that we have extracted from the raw signals of the Tug, which actually gets us near to actually driving the motors.

I googled boat ship dual rudder alignment.
Got:- The importance of tuning your Rudders from power and motor yacht.com(no spaces)
As per my first query the article mentions toe in and toe out, plus Ackerman steering, now mainly obsolete and replaced by a computer.
What I have seems to be toe out and the article generally recommends a little toe in.

I'm sorry but its not possible to show the servo under the deck.
One servo directly drives one rudder via a metal link. The other rudder is directly slaved to the first via a horizontal plastic bar that shares the servo movement. So both rudder tillers move the same way, same amount.
But viewed from the rear of the boat, the rudders are splayed out by about 10 degrees.
They don't point the same way. If right is straight, the left rudder will turn the boat counterclockwise to port. I guess to go straight ahead, both rudders try to gently turn the boat in opposite directions.
If now the boat happens to twist a little, without any rudder change, the arrangement would tend to correct the twist.
Eg both rudders slightly splayed out. Boat twists to starboard at front. The right rudder is now straight to the motion and the left rudder more strongly opposes it. So the boat self corrects. But if both rudders were straight it would self correct anyhow.
In reverse, things of course work opposite and the situation is unstable. Which is maybe why in reverse it has always been extremely poor and tends to whiz off to one side

Thanks for that. I can add that if one rudder is straight, then the "misalignment " is such that that the other rudder is turned out. So if R rudder is straight the boat will tend to turn to port.

As a Newby I don't know what to expect with 2 rudders on my Southampton Tug. I can see that they are not parallel. But there is no adjustment for this. The bar that sets both rudder positions is prefabricated to a given length. Now I know that when a car's steering is turned the inner wheel turns more than the outer.
Is the non parallel setting trying to achieve something similar? Or is it just wrong?
If rudders should do the same as a car, with the inner rudder turning slightly more, is there ever a mechanism fitted to do this? I remember my Airfix slot cars had such an arrangement, called Ackerman steering.
Advice or comments positively welcomed

😋Tried the Tug on the pond today. I had fairly windy conditions. Results on the dual ESC generally pleasing. Going forward, as expected, slow turning much better, turns going fast about the same.
Backwards gave best results at medium speeds. This is because a fast motor cannot be made to go faster still and a slow motor is not reversed in that mode; the design precluded that. I still have a list on the boat ( my fault due to being too aggressive with battery position) and going backwards this seems to have an effect as one side being deeper than the other has more water resistance at the stern.
With no throttle and using rudder only to control both motors in opposite sense the Tug generally turns on the spot. It moves maybe half a length as the turn starts and then turns almost on the spot, though large wind gusts slowed things down a little. That deckhouse is huge!
So although this mod does not give 100% motor vector control the improvement to manoeuverability is very significant, allowing decent control of the boat with the original controller. As with all manual control one soon learns the actions which work well.
I previously mentioned the rear hatch. I was a bit discombobulated when at full rudder I saw the hatch lift in the middle.... I had not removed enough of the servo rotor arm. But I had brought my cutters and that soon got sorted.

Attached is the start of the circuitry and description. It was a WORD document, then RTF, then plain text but the website would not accept any of these. So I extracted the picture and just cut and pasted into here. PDF here we come? If anything is not clear, ask me or Google the phrase that is not understood. even my PAINT picture seemed to have problems and was originally reported as an invalid file, though that has altered even as I type. You can see it on a Windows computer at least by clicking and selecting one of the options such as Background image. I have now tried an Android tablet and clicking away managed to view the diagram.

Now that the boat has floated, I'm properly starting this design blog. I'm intending to describe the dual ESC and mixer with the aim of teaching some relevant electronics as we go.

The first thing in any design is to define what we are going to do, Then consider what sources we have to manipulate in order to achieve the objective.
In this case we have a Tug that manoeuvres worse than a slug. Windage is a disaster with little keel and a high non central superstructure.

The obvious thing to do is to fit a rudder mixer so rudder operation also changes the speed of the motors to help out, especially in reverse, or even stopped. These are commercially available, but this version of the boat cannot use such commercial gear because the required motor signal is not available. All we have is the present motor drive signal direct on the motors and the servo signal to the rudder, which is conventional. We could scrap everything and start again, but…..

The requirements are:-
When stopped, rudder only will turn the boat by sending the motors in opposite directions, with no throttle applied.
When going backwards, if the rudder is deflected more than about 25% the motors will change speed (be modulated) so as to help create a turn.
When going forward slowly, large rudder signal will change motor speed significantly. However, at full speed, even full rudder will not change the motors much, if at all, because the boat might tip over. In fact, full rudder at full speed can only slow one motor, because full speed cannot be exceeded.
With less than 25% rudder, with throttle applied the boat responds to rudder only.
With throttle applied, no motor may be reversed nor may more than full speed be demanded.

So now let's look at the inputs required.
We need to know Throttle setting (speed) and direction, forward or back. That is not too bad. The motor on this boat version is driven by an H bridge with a forward signal and a backward signal. The repetition period is 8.6 msec and the mark/space ratio determines the speed. So we have to blend these two to get speed and record which of the two is active so as to obtain a forward and back direction signal. If neither is present then speed must be zero and we can derive a Stopped signal.
We also need Rudder deflection and direction. The servo signal containing this information for the rudders is nearly conventional.
A short pulse is repeated every 8.6msec. 1.05msec is full left rudder and 1.95 msec is full right rudder. 1.5 msec is straight. There are several methods of extracting this; I chose a simple filtering and gain method as being a low component count.

The other thing to consider is the battery. These have a distressing habit of having a changing voltage as they discharge. One can work at just less than a minimum voltage, using a voltage regulator. Or take the more aggressive approach and do a design that uses every bit of battery voltage available. I choose the latter because it has less component requirements. This is called a ratiometric technique; all circuit design is done using ratios of the battery voltage at that instant. With one exception we don't generally worry about volts absolutely, at any point we have a proportion of the battery voltage.

So let's look at the input circuit FIG1 that gets these signals for us. It’s actually quite simple. The picture is attached to this post. I hope its readable.

Abbreviations.
Below, for instance SPeeD would be written SPD. I interpret once only, but abbreviations like this usually go in groups of 3 characters.
If you see, for instance, B/3 that means 1/3 or 33% of Battery Voltage
All inputs are changed (limited) to be either zeros or full battery volts. So voltages beforehand do not matter. Protection resistors also make it difficult for a mistake to blow up the existing PCB.
WHITE and YELLOW are the wires presently going to the motors. These are removed and go to this circuit. There is no need to go into the deckhouse PCB.
I just describe the WHITE forward channel. As we have disconnected the normal load, I feel better giving the old circuit a little load, that’s R1. D1, R3 and C1 form a fast attack, slow decay filter; a short pulse will easily keep this charged enough until the next one arrives.
Going down and left, Q1 is an ORed inverter. WHITE OR YELLOW will turn on Q1 so SPeeDPulseWidthModulation is the signal that digitally represents speed in either direction.
R8C3 are used later to tell another circuit about SPeeD in ForWarD only.
U1,2 and 5 are Schmitt trigger inverters. These are funny beasts, but handy. If the input reaches 2B/3 the output goes to zero. It will stay there until the input drops to B/3, when it will go Hi, to full 100% of B. So it gets rid of noise without using lots of filters.
The RUDDER servo signal is extracted by breaking into the white servo wire and grabbing the signal from that. Its generally at only 2.5-3V or so, quite low. Q2 doesn’t care. Anything above 1V causes a LOW on its output, R10, and hence a HI on U5. So there we have the 1.05 to 1.95 msec pulse at a known rate, representing rudder position, now “slaved” as a proportion of our B voltage. With a bit of filtering, we are ready to go.
Finally, AND gate U4 detects that both FWD and BCK are STOPPED. All required signals are present and correct.
It wasn’t that bad was it?

Worth a go on the hatch to predistort it. Because it clamps very hard onto the gasket at each end I suppose a bow is natural. Maybe a less dense or thinner gasket would be better.
I have a stash of 1 mm O ring material that might be more elegant. The gap I can see is at least 1mm in the middle so it was never watertight.

Something similar was recommended to me in an earlier post. Costing about 35 pounds plus postage, but is only the rudder to throttle mixer and not the drives as far as I can see. A lot of plugs coming out of it. Again no good for this latest Tug version.
If you are doing a complete refit I would consider the option to just fit 2 ESC devices and get full motor control useful in reverse and spot turns, with rudder mainly used only for going forward. You might need three thumbs, but if you have a suitable controller it saves the cost of a mixer ehich is just something else to fit in and go wrong...As a Newby I have not closely examined the vast range of possible controllers.

Well some of that gave me a good clue re the hatch. I really wanted a battery opposite the servo to help correct the list I had seen.
I also suspect that if you balance a weight in one corner with a weight diagonally opposite it might result in a corkscrew type motion - certainly seen on this tug where it wobbled rather a lot.
So I turned the hatch round. Mine has a tag that fits into a small slot in the deck, and the horrible catch. I made a matching slot for the tag then had to just take a little bit off the other end. The seal was never perfect as the hatch bows up a bit in the middle. The catch now slightly fouls the rotor arm on the servo, but not the one in use so a quick snip sorted that out. Thanks for the hint.

Not about the build....Just to confirm that I double checked re video; definitely uploaded an mp4 file and that is not what I subsequently downloaded. As suggested, once I tracked it down on the tablet, I had to change the extension back to mp4 before I could view it. So something in the loop is altering the file extension. I do hope its not my tablet....

Yes, sorry. A vertical dipole as now suggested makes a lot of sense, being 2 x 1/4 waves sort of stuck together. And if vertical would be omnidirectional. Unusual but perfectly possible.
The use of coax may also be a sort of balun as well?

I think the educational bit will start when I have learned a little more....

Yes I found the download on the tablet and it was mpeg4. So you are 100% correct. But I also found the original that I uploaded and that is mp4.!!?? How did it change... To use the download I also had to rename it and it was fine.

I agree that the manouverability is not what I hoped; but a higher drive level will improve things. I have not yet looked at the dual ESC mixer you mention. It must be a clever bit of kit and I will look it up. I am curious about how it can work unless you replace the Tug receiver and then rewire the lights section of the PCB? The sticking point in this job has been that there is no standard output for receiver servo output for throttle. That means that to insert a standard rudder mixer into the throttle control lines is impossible. I have used the 2 original motor control signals as a substitute for the missing signal, but it is nothing like the servo timing. Thanks for the battery and hatch info. My 3x2 is 2400 mAH and that should be enough for me. I have C cells and plan to fit those in time I conclude I need more weight.

The video stored on my lousy tablet is MP4. I can't see what arrived on the site. And when I try to look at it on the site, then same lousy tablet will only offer to open it with a word processor.....I will have to start using my main computer....

Well I had a short video showing the Tug wiggling its bottom in the bath. The bath is smaller than the Tug so it could not do a circle.
But although I got it to less than 5MByte it looks like the site won't accept the video. Sorry. Can anyone tell me what to do?
More seriously, it was able to wiggle port and starboard while I used no throttle, just rudder.
However, it did move forward slowly as well, which I guess is because its more efficient going forward than back. No problem, one just gives a twitch back on the throttle, but that does require momentarily reversing the rudder.
I think it would be easier to drive if right rudder on the controller always asked for a clockwise turn rather than the theoretically correct opposite rudder in reverse.
But it is at least all on one controller.
I am not too happy about the fairly low maximum prop speed chosen under rudder control only and will adjust this up. Presently, the max speed trying to turn on the spot is about 45% of full speed, and I think more like 60% would be better
More seriously and completely unrelated, why does one boat use two different hatch locking systems? The front hatch is a compact joy, very flat.
The rear hatch has a complex slide mechanism that sticks down a long way. Its also slightly offset so as to miss the rudder servo. My new battery location at the rear only just works for a flat 6x1 battery, and I think it might be fouling the hatch thus lifting it off the seal.
The 3x2 version will need to be rotated or moved forward a bit.
This is why we do testing, most of these things will be quick to adjust.
The real fix is to do what I always intended, and use 2 lithium cells that are AA size. I have 4 on order but the Chinese Mail appears to have hired a slow snail. I may have to shift the battery location forward a little.

Re aerial length. A single whip antenna can be brought to resonance when it is only a 1/4 wavelength PR about 3.5 cm at 2.4 GHz. The next best would normally be 3/4 wavelength.
Any length can be made to work with tuning.
But its a bit like a tuning fork.
One end is fixed and the other end gets hit and goes to and fro. And that, in nature, happens at multiples of 1,3,5 etc of quarter wavelengths

Folk don't seem to understand this problem.
You would never connect a 2 cell battery directly in parallel with a 3 cell battery. At best one would charge the other and at worst there would be a fire.
You can regard any one ESC like a battery. So joining the two output red wires is the same as joining two batteries.
You would not expect any problem because the two ESCs nominally give the same voltage.
But the electronics inside can try too hard to have their own way.
For example one ESC might be giving 4.99V and the other 5.01V.
On their own either is legal and OK.
But put them together and one tries to push the voltage up and the other tries to pull it down.
Neither is happy because neither can win.
Worse, if there is some clever software in there or any circuitry that senses an error, the only safe thing for the ESC to do is to shut down and maybe try again. There is a lot of potential to damage the included H bridge (google that term} and if the power supplies are not right the risk of severe damage is too high.

On this tug everything goes round the deckhouse because it always seems to get in the way.
I have added a few cm to its wires to ease things a bit.
The replacement pair of H bridges has been constructed, fitted ( or to be honest, squeezed in) and seems to work. So I am back to where I was 2 days ago with a working boat waiting for a bath test before refitting the deck.
Another blog has been talking about RFI problems.
According to my scope I have one too, but its not me. I observed one mode of operation where there seemed to be a little imbalance in the extremes of speed.
This was rapidly discovered to be an error in the first op amp of the circuit.
This has a huge amount of 100MHz on its pins and I reckon that is causing the error.
Unlikely to be the opamp as that is a cheap device capable of just 1MHz.
Perversely, even if I turn off all power supplies its still there! If I remove the opamp its still picking up
So I guess its due to the fact I live very near to a major transmitter and any bit of metal picks up signal of the FM band 88 to 108 MHz.

I did a lot of RFI work. The whip antenna was always tuned to resonance using an aerial tuning unit. But it remained unidirectional, which is what we want.
The crude equivalent is a loading coil at the bottom of the aerial. You see similar on the roof of some older cars, a sort of spring that can double as an aerial support. For us, the value of that would be fixed at manufacture so no need to worry about it.
The point of tuning the aerial to resonate at the required frequency is that wanted signal increases and interference then gets rejected by the aerial circuit, so the rubbish does not get in by that route. Which is ideal. But as remarked earlier, gremlins creep in by any gap, just like a rat...

We have a UK warning of "Don't try this at home". I always prefer to learn from the mistakes of others. But in everything where you part invent, cut and shape bits, it's amazing how you measure three time, cut once and curse when it doesn't fit.! We learn, get up and plod on....accepting that when it goes wrong its usually from a direction we never expected.

And re the aerial as a flagstaff. In some parts of the UK, radio amateurs needed planning permission for their aerials. But not for a flagstaff....