Hi
I bought the board to prevent battery cross charge and discharge as I saw it advertised on the companies website. In all honesty I had not thought about it before. I remember my brother telling me that on the vessel he was chief engineer on that precautions had to be taken by a distribution panel which managed the power produced by two generators to prevent one pushing power into the other via the distribution board when they were both running i.e. One generator producing more power than the other.

Regards
Kevi

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.

Hi Kevin,
Very pleased to see that you installed the protection board to block possible 'Back charging' between the batteries👍👍👍 A very sensible precaution.
Was very disappointed and dismayed to note that SC did not mention this when he wrote of using Lithium cells in series/parallel connection🤔
Well worth the money to prevent possible loss of the boat - or much worse if the brown stuff hits the fan on bench testing!💥🔥🤕😭
Cheers, Doug 😎

I quite agree Rick. I'm sure that's the case.
Even some of us experienced in electronics are somewhat bemused by SC'c unstructured and disjointed style. And irritated by some of his sweeping generalisations.🤔
He still seems to be low on this particular learning curve himself and reporting more failure than success at the moment.
Although there is also much to be learned from "Don't try this because ..." reports.
I also believe that many are disappointed cos they thought they were going to learn how to build a simple ESC. They're not! ☹️
This rather complex circuitry is intended to provide a rudder/motor mixer function for twin screw RTR models (such as the HobbyKing Southampton/Richardson tugs) which use a single proprietary combination RX/ESC/rudder control circuit board.
(Later models now also include some electronic switches for lights and smoker on the same board. My oldie doesn't😭 Not to worry I'm upgrading it from 40MHz to 2.4 Gigs anyway.)

As far as I can decipher, in essence what SC is trying to do is to tap the control outputs to the motors and rudder, and use them to recreate the input signals from the RX which created those outputs in the first place!!🤕
Then apply those to his own circuit which splits the original single ESC control output into two. These he will then apply to the two motors in a mix ratio governed by the rudder commands.
Probably a rather limited market so to speak

SC:
I think you'd be better off continuing your experiments in private, documenting everything as you go. In a Word document and with close up photographs of each construction step and simple explanations of the functions of each new circuit stage and new components as introduced and why it is there.
Then when you have it up and running you can edit and tidy up your Word doc and post it chapter-wise as a cohesive structured 'How to' that will be easier for novices to follow.
This would also give you time to tidy up the breadboard experimental layouts to make a more compact easily reproducible layout.
Word documents can be posted on this site no problem. Converting to pdf is even better.
Here endeth the 999th Epistle to the Wise!
Cheers all, Doug 😎

I think as Martin posted you're above most of us with the subject line. Make it easier for me to get what your trying say.
For me when I read the post and have to look up what your talking about I stop reading.
Maybe others are the same way.
Rick

Hi Seamancook,

Your knowledge on electronics is way above a lot of us who were hoping to learn a little about how to make a few things work using some electrical components.

Electronics theory only tends to make things confusing when a simple “add this to that and it will do this” is what I and many others need to know as the majority of the time it will be a one-off thing to just get something to work and will probably not be used to make another one for years.

Perhaps the subject you have chosen on your log is too complicated for us beginners.
Maybe we need to start with some simple circuits that can be easily understood and used on our model boats.

Martin555.

Hi,
Been busy doing necessary chores. Also been replacing power distribution system for a HMAFV Halifax. Was running on a 12v gel cell, now converted to two 12v sticks of NiMh. I have removed a hunter systems distribution panel and replaced with an Action Electronics power distribution for two buhler motors via two Electronize ESCs. Also using BEC on system as well as power to the loud horn! As I am using two battery packs I have taken the precaution of installing a voltage protection unit to stop one battery charging/discharging into the other, again Action Electronics. Now all working just needs sea trial.
Now the electronize unit which started the debate. I decided to connect it up before removing the mossfet. Low and behold discovered that there's was a loose connection to a blade fuse unit. Removed and ran well on the bench. I still had a secondary fuse to the battery.
Got to the lake last Sunday. And while conducting a test before launch discovered that the relays worked but I only had full ahead or full astern available to me, with no neutral. Will replacing the mossfets cure this or is this a symptom of something else. In the meantime I have purchased a soldering pump and an Electronize esc in kit form as New from e bay.

Regards
Kevin

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

The more you write here or in a blog I will be reading to see if I can learn more on electronics .Rick

This forum started with a specific problem on Electronize controllers and kind of got diverted. Kevin, did you fix it??
Julio, just keep an eye on Build blogs where I will be recording and sharing the Southampton tug upgrade and maybe extend it to more general electronics on a How it works basis. I want to photograph the install process and maybe some of the test waveforms as well. This is the first time I've done this so its a case of learn as I go. I'm watching the Arduino thread with interest as this is processor equivalent of what I do.

Hello SeamanCook:
This topic is exciting ...
I don't know what to do: do I stay here and follow this post from "Electronize speed controllers" or do I go to the post you want to open about the Southampton Tug?
What doubts do I have !! ... please help me !!
Julio😭😭

I intend to start a build blog for my Southampton Tug ESC upgrade, which is progressing well.
So this will be my last entry here regarding this project.
I realised that I had not included anything for low battery detect. However, no info was available regarding anything already on the provided PCB.
So I took the tug to my local pond in Norwich UK and sailed it in windy conditions until the battery went flat.
As a Newby I found this an informative experience.
The deckhouse acts as a wonderful windsail and even in forward, steering was a bit chancy.
The tug seems to lean to port, even though the battery is well to starboard.
The tyres need to be above the waterline and drain holes may be an idea...
The motor ESC mod specs for the upgrade look about right, and the chosen compromises look sensible.
When the battery went flattish, the existing controller detected this and the boat entered a "burp" mode. Demanding any throttle resulted in a couple of seconds on and a couple of seconds off. That was very sensible indeed. It meant the boat could be returned to shore and it was obvious that something had to be done.
My scratch build dual ESC has been tested and looks good to go.
So its time to take the deck off.

I caught the allergy from my Uncle.....Seriously, one can buy any common simple ESC, as thenFlet Admiral pointed out to me . I built my first ESC as a learning exercise. However, the new device I am making now for the Southampton Tug simply cannot be bought. The reason is that the Tug does not make the Servo output for the motors available. It's deeply buried in a bit of plastic called a microprocessor. So if one wants separate motor control there are three practical options, as a purchased mixer cannot work.
1. Fiddle with the various switched devices, free up one line and use that to operate a switching relay to reverse one motor. That gives turning on the spot.
2. Partly gut the unit. Fit a supplementary receiver and 2 ESC devices. You end up with 2 controllers to handle and a big bill. See the YouTube video on that option. If you throw away all the fitted electronics and rewire you could get back to one controller.
3. DIY. My approach will give me decent and adjustable motor control in forward and reverse to aid turning and also turning on the spot. Parts cost about a fiver. And if it goes wrong, I can fix it. But I will still only be using the original controller and I do not even have to touch the installed PCB.
That's a nice simple affordable operating option. I am taking photos as I go and as this is a popular boat there may even be demand for a PCB so others can copy the work.
You pays your money and takes your choice as to how you spend your time and cash.

I'm not allergic to spending money.Spending it is easy finding it is the harder part.
Rick

I have uploaded information for an ESC for a brushed motor on my NAXOS build blog. I would be happy to move or have it moved by moderator to an ESC blog if it deserves a place within that blog.

Thanks, I needed to look at this end of this when he starts to reassemble. He's doing similar to me but spending real money. I'm allergic to that sort of thing.
I've been asked to post photos of my progress. Apologies for quality. I've started the scratch build and have put this on a copy of the block diagram. If anyone wants a higher quality copy that can be done.

Hi,
From what i can remember the Southampton's deck is a push fit and has a Vaseline seal.
After all screws have been removed just gently pull apart.

It would be nice if you could show us photos as you go along.

I don't know if this will help.



Martin555.

Oh, an extra detail I'd like to check. Comments welcome. It seems that its usual that if a boat is turning clockwise with R rudder applied, and it is then reversed but the Captain still wants a clockwise turn to continue, the rudder is reversed. In practice, a 2 motor system can do all the work and rudder has only a small effect but in the interests of realism.....I have found that windage on the Tug has much more effect than the rudder can correct in reverse. That is one reason for doing this mod.
Checking my design it works out that to be realistic needs less bits in my design as I actually save parts needed for this reversal of the rudder.

I've partially dismantled the Tug. The main PCB is in the deckhouse. Classic Chinese; some brilliant and a few very bad bits, especially on the main motor drive controller output with reject soldering. No wonder blowups and burnouts have been reported. 30A input wiring with no fuse, but 3A wiring to the motor.....
Its no problem at all to pick up the signals I need for the double ESC mod proposed, in fact I am tempted to remove the badly soldered bits ( which my mod makes redundant) and use the remnants that are left instead of my planned first stage.
Getting the hull separated from the deck is not so easy. I have found there are 14 screws, with some buried under davits etc. Does anyone know if the deck is glued or sealed to the hull? Is there anything I have to cut along the join line? Where to pull, shove or twist? Any hints or tips appreciated. The skill is not in the hammer, its knowing what to hit and where....

I do enjoy reading the posts but must say I don't understand most of it please keep posting as I may see the light and something may rub off on me LOL.
Rick

Following tips from Simple Sailor I have ordered some MOSfets for the Tug mod. As it is a small current ( until things go wrong) it looks like tiny devices will do. In past life I was working at 3500V and 4000A pulses so this to me is tiny, a challenge at the other end.
Design now getting rationalised to reduce component count a little, and help to set up and test with minimum test gear.
I am winding myself up to disassemble the Tug, just in case they have encapsulated the electronics to make things waterproof and therefore hard to get at the pickoff points I need.
Construction of hand wired prototype starts next week.

I know absolutely nothing about electronics but i am interested to see this.
I have a second hand Southampton tug that had a burnt out PCB, so i replaced it with a normal ESC and receiver also changed the battery and it works fine.


Martin555.

Hi Seaman Cook. It is a bit of a mine field when looking at specs. It would be good if you set up an Electronics blog, I would certainly follow it. Just to let you know that the account I have with RS has no min order value and most of the bits I get are one or two off but it depends on their pack size. They have a credit/debit card payment option and I have ordered as little as £2.95 for some capacitors which were carriage paid and next day. I agree the low Vgs (th) is usually for low current level. As mentioned I have my IRL MOSFET running at 3Vdc with a 1 Amp current draw but I am using it as a switch and driving the gate with 3 V from a reed switch. I will be posting the project at some point on the site.

I designed the Southampton Tug mod this afternoon. Assuming that you have a boat with a single speed control and 2 props, reverse manouvering is likely to be poor. Such is the case with the Tug. the wind is dominant in reverse. As I said earlier, a You Tube video documents an equivalent. This new proposal is much cheaper as it uses no RTR bought in equipment.
If enough folk are interested, want to play, and it is not possible to buy an equivalent, I will do a PCB when the prototype is proven. Such PCB will occupy about 4 square inches if done in larger surface mount components that can be handled, or 8 square inches if done with legged components which are getting harder to buy.
No change is made to the tug PCB so you can always go back. This mod bypasses the existing final drive components, but picks up its drive signals- 2 wires onto big points on the existing PCB.
It also picks up the rudder signal from the normal servo connector.
I add several extra operating modes.
Nothing ever happens compared with normal until the rudder is operated to about half deflection or more. So normal operation is the same, except top speed will go up a little as the present drive components are adequate only.
In forward, if rudder is sent hard over, the motors will change speed a little; one faster, one slower. this is mainly meant to help with steering while slow ahead. A "play" location will enable the degree of motor change to be adjusted with forward speed.
In reverse, the amount of motor difference will be much increased, thus allowing controlled curved reverses; the throttle control will still determine the speed.
If stopped with no forward or reverse throttle applied, just operating the rudder will operate both motors in opposite directions; the model should turn on the spot.
The big advantages are:
No controller changes required for the extra functionality. No jiggling with 2 speed controls and rudder,
All present functions retained. Right rudder = clockwise turn in any direction of movement.

Dirt cheap- I reckon on about £5 for the basic bits including 2 new drive modules for the motors, which are not very powerful. A PCB would be extra as opposed to a scratchbuild, but it would save hours and errors.


I reckon this will be applicable to other models with the same issue. I do note that mixers can be purchased that will do this job for a conventional system, so applicability may be limited. But with this system there is - joy- no software to crash.
Does anyone want to play too?

No need to apologise at all I think your knowledge can help all of us and I welcome a build blog on ESCs.

Regards
Kevin

Sorry Kevin, I hope I didn't hit a nerve....I intend to start a build blog for those who want to fiddle about with simple electronics. With luck, someone may turn up who can program...
I lived on electronics like ESCs for years but the power and voltages were a tad higher than these. To effectively share the designs at sensible cost means PCBs and surface mount these days. The setup costs are considerable and you would still get nowhere near the Chinese costs because they buy in thousands, not ones and twos. But if enough folk want to copy a decent or unique design something could be done. I have PCB software and can get them made at reasonable prices. Watch for the Southampton Tug mod coming up. I'm keen on this one. It will add a lot at dirt cheap prices and easy to make too.

Sounds to me like your skills are marketable. Have you thought of setting up a little cottage industry for ESCs you could even offer a bespoke service. Would it be possible to supply parts and instructions as a kit even!!!

Regards
Kevin

I started years ago with a broken down boat in the river..... I am looking at these logic level FETs and so far have to say my Chinese ESC version has made good device choices...but already one is no longer made. I find at using some logic level devices contravenes my design rules, which are that the device must be rated at least 1.5x any level I can see or know about.
An evaluated choice for one logic level device threw up the wobbly that absolute maximum Vgs was 8v. No good for a 6 cell battery or 2 cell lithium. The sort of thing that gives random blowups..... RS and Farnell are known to me but I didn't think they would run individual accounts. And yes. I love to fiddle too. But not with processors. The forums have too many broken ESC devices where folk are trying to replace a PIC. Why do they blow up when spikes are around?

I agree with Fleet. It's not worth making an ESC as they are so cheap but the fun for me is in the design and making. I have been an electronics engineer for over 40 years and still love messing around. Always something new around the corner and never to old to learn. I buy my stuff from RS Components which in my younger days was called Radio Spares also have an account with CPC who I find better for spare parts. Since retiring I have started to get into the Arduino which is what steered me in the direction of the logic level MOSFET.

The Fleet Admiral has already pointed out that ESCs are cheap so why bother? As a newbie I made mine not knowing what I could buy. But the learning has put me on track for a big and cheap mod to my new Southampton tug.
I have problems buying these logic level FETs as I use CPC whose range of 160 devices is slanted to higher voltages. Any supplier suggestions for hobbyists?
I looked at a couple of spec sheets and find that Vgs of 1.5 V usually is the threshold point but to get into decent current levels of 10A or more you need 4.5V. So the truth for models as opposed to speedboats is somewhere inbetween. CPC have some useful devices but nothing like as good as the devices from China. I looked up the data sheet and you get a brownie point because, lo, your L appeared in the full number.

Hi. Not sure about the China versions as I am using a Fairchild MOSFET and it has a a Vgs of 1-2 volts. I have also tried an IR IRLML2502PBF-1. These are surface mount 7A devices and have a Vgs of 0.6-1.2 V. They are a pain in the B... to solder on as they are surface mount but very cheap. Nice for a compact motor controller. I was using them with 3 Vdc drone motors. I like your ESC design. I was looking at repairing an Electronize unit but found that the PIC chip had blow and although I could replace it I couldn't find the software on any forums so gave up. However now that the contact details are on this site I might take a fresh look at it.

A useful steer. May depend a little on manufacturer and definition of logic level by the marketeer.. I would hope anything that is well on at 4.5V would do fornus.
I'm currently looking at a Chinese basic ESC. The Ns are IR8726. No heatsink. No L suffix. The Ps s are similar. The IR device is 0.008ohms at 4.5v Vgs. Did I miss a decimal point there?
Its rated 20 A, but they have fitted 22AWG wire rated at 7A. Ho hum....
Generally MOSfets are like taps; up to a limit on the control more juice flows.
But if they are easy to turn on you can pay with a small leak unless you turn it firmly off.
In general bipolar devices will be a very poor choice except for very small motors using less than 1.5A.
As an extra, if paying more for a better MOSfet means you can avoid a heatsink then that is a good tradeoff. A package you can solder to the board will outperform because the board can act as a heatsink and normally the unused reversing devices will also help get rid of any heat.

Hi. Just a little update to this and I am sure everyone already knows this. If you find a MOSFET with the letter "L" in it's numbering it will be a logic level MOSFET and will work down to almost 1.5 Vdc. I am using them in a 3 Vdc motor circuit and when driven on their resistance is around 0.058 Ohms. They don't even get warm. IRL540A. I had tried the IRF530 and it wouldn't switch on. When I did drive it from about 5 Vdc it got warm as it wouldn't turn fully on. Anyway the IRL version solved the problem.

Oh I spent nothing. All bits from my stock which limited choices.
I reckon the bits could be bought for about 8 pounds.

I tested it between 10 and 6 volts. For the boat it was destined to be fitted in I use 7 NiMh cells because it has a small prop, and is not too fast. So 9.8 V at start and I count full discharge at 6.5V on load when one cell dies rapidly. The components are rated 15V.
The H bridge fitted is over the top really. It would easily do 20A or more but a silly heatsink as fitted has the advantage of making the 4 MOSfets rigid and a short term total overload would be survived; with the S/C protection fitted its nearly bombproof.
Its a learning exercise!
If I wanted low volt capability I would use bipolar transistors.
It took me two days part time to build, but that included a lot of thinking time. It is on veroboard but second time round is faster.
The mechanics such as heatsink drill and isolation are always fiddly. However after a first proto is going one always thinks of simplifications. And omissions.
This is a data latched design. There is no demand ripple, its one of 16 speed choices.
Literally one good command pulse will set it going. For ever!
Idiot here did not put in a watchdog circuit so that the boat will stop if RF is lost. I've had no probs but I intend to be safe not sorry.
Hope that answers the main questions. I am going to draw things up neatly so copies possible in time.

Hi
Proof of your excellent knowledge and application. How would you rate your esc i.e. What max voltage and Amps could it manage ? How much do you reckon you spent and rough build time?
Regards
Kevin

Success! Sailed the boat today and worked great with excellent speed control for slow manoeuvering in each direction.
Re getting the circuit working, because it is designed in distinct blocks any basic errors were fairly easy to see. The bits at the edges were the hardest. There is not much feedback; all required timing information is available on the input pulse and the counter outputs, just needing a little decoding. Unlike software, I can see several things happening at once. Software can only change one operation at a time and debugging exceeds my skill levels.,
1 Suppression. The CMOS devices used are cheap and cheerful with high noise immunity. Total new cost about £3.
I have a really horrible spare motor which sparks abominably. It managed to screw things up somewhat, so a little rewiring to improve grounding helped fix that. But why take chances? I added a proper RFI filter to the motor wires in the real thing, home made of course.
2. The clock has to be reasonably stable but easily adjustable in frequency to get the zero speed point. Getting that right took a little time, but now it moves only 0.3% over a 6 to 10 V supply range, which is OK for this application. The basic design was good but I was fooled by an incorrect application note, which used components much bigger than were really possible. I got extra clock pulses as a result, until I spotted what was happening and fixed it. That was the single biggest time waster.
I think this is why most ESC devices give you a 5 V output. It costs nothing extra. They have to generate this for their own internals so they have no stability problems and 9V would blow many processor ICs. But they will work on a different principle of "measure the timing" and then decide what to do.
This design directly derives the timing and PWM from the incoming pulse.
3. This ESC has no voltage stabiliser because it doesn't need one, which means that driving the output MOS stage needs no level shifters, which often will not pass DC.
But adding a 5V regulator for the receiver would not be an issue.

The only problemette found on sailing was that I had removed the old control gear and fitted the new ESC on the other side of the boat. We are not talking about much weight here relative to the boat size.
It developed a district lean to the right or starboard if you insist. I shifted the receiver battery 50 mm to port - only about 70 grammes - and that improved things a lot

Hi SC,

Clever circuit design 👍 I bet it was a pig to get it working the first time.

Graham93

You've reached the Age of 60. You know everything. The trouble is remembering it.
Getting back to homebrew ESC. I was asked for a few details.
Here is a picture of the device on final test before it went in the boat. It sails today...I hope it is visible, I am non IT literate.
On the KISS principle I avoided clever ICs which usually have gremlins. The ESC counts 0 to 15 over the 1 to 2 msec interval of the receiver output, and stops when the pulse ends. So speed and direction are 0to 6 reverse with 0 f.astest. 7 is reverse but stopped. 8 to 15 are forward.
So I have just 7 reverse and 8 forward speeds which is enough for me.
The speeds are stored as a mark space ratio in a shift register, which then recirculates the data at the clock speed of nominally 16kHz. The motor sees a waveform that repeats at 2 kHz.
Zero speed point is adjustable and if the count detected is minus or more than 15 the motor does full speed. The H bridge is short circuit protected and to keep the Fleet Admiral happy there is a backup fuse. It works over a range of 6 to 10 volts.
Oh, it also includes a basic servo test circuit. Without a transmitter you can set the speed and just go.

Hi Kevin.
Here,here.
I have a saying that I tell the Grandchildren.....
“Daddy knows lots of valuable things,BUT..Grandad knows everything”
Regards
Bill👍🤔

Hey keep talking about the young folk - I'm 61 this year. You never stop learning the principle that you never stop learning. People with age have an irreplaceable set of skills that they have learned and honed. Their greatest assets are wisdom, skill, knowledge and learnt experience.

Kevin

" Making my own is a learning exercise ...."
Back then it was a financial necessity SC!🤔
Nevertheless, it's good to see some younger folks these days following in our footsteps with the same kind of 'What if?' curiosity👍
More power to your soldering iron!
Cheers,
Doug 😎
Attached pics of one of my first attempts at an ESC, using the technology of the time some 35 years ago, adapted as as winch / crane driver for my destroyer.😎
Basic principles are still the same as back then, regardless of what frequency (27, 35, 40 Meg or 2.4Gig) or hopping protocol is used to in transmission:-
PWM/PPM decoder --> analogue/pulsed voltage output to servo / ESC.

Hi Kevin,
"I may have a go at removing and ordering a new one to solder in."
While you're at it order five!
You will probably need to replace all 4 in the ESC, they seldom go individually kaputt, and a fifth as reserve will not cost the earth😉
Depending on the design you may need two each of two types, check the type numbers printed on them😉
Cheers, Doug 😎

I'm sorry for the 2 reasons, my brain gets as tangled as the wires. And yes, Every battery I fit has a fuse connected because I started out with the wrong sort of connector and mistakes can happen. I'm sorting that out.
I have a bad record of broken down helpless boats. The first time I ever took out my original model, my daughter nearly died laughing when the propshaft came loose in the middle of the river...
But yes I accept that a modern ESC is a good buy - until it breaks. I have even ordered one for the tug - see later. Making my own is a learning exercise and I will use it to replace the servo controlled resistive speed setting device in that original boat, that I have just returned to service after a small gap of thirty years...
I happen to have a vast stock of electronic bits so the cost to me is zero.
And if I get the connectors wrong I will be able to fix it provided the fire is not too intense.
I know little about PICs and Arduinos except that the startup time and effort is large and the equipment looks cheap but is actually rather pricey. I hate staring at a bit of encapsulated expensive gear that will not work, cannot be disassembled and I can't fix. We Asperger's sufferers are a funny bunch and want to be in control.
The home made ESC is turning a small motor now and next will be to put it in the boat.
I do have a fire extinguisher in my workshop in case the fuse fails. Safety First.
The tug is the next project. I want to use speed and reverse control on the props to improve turning capability in reverse but using the original controller. Does anyone have a mixer circuit that does not use a microprocessor or do I need to design my own?😁

Hi Sc,
"What fun! One eason (sic) for a over current electronic protection is two fold."
Hmm! A two fold one 'eason'!
"A fuse will prevent a fire after the H bridge has overheated and blown up."
Hmm2!
The object of choosing the right fuse (or circuit breaker) in the first place is to prevent the 'H bridge' from overheating and blowing up. A quick blow fuse of suitable rating will accomplish that task very well. As you intimate, essentially a fuse is there (in domestic appliances at least) to prevent a fire in the power wiring, contrary to popular belief.
But for us boat modellers; insertion of a fuse below the max current rating of the motor and/or ESC (whichever is the lowest) also protects the motor and the ESC.
Have fun building your circuit though😊
I have built ESCs in the past, first using bipolar power transistors SN 3055s and a relay and then Darlingtons, and later FETs, N channel of course😉 due to the lower internal resisitance, but nowadays it's just not worth the time and effort. ESCs are much cheaper and versatile now than 30 - 40 years ago and I prefer now to invest the time in research of the original ship and the effort in the recreation as a scale model.

" Usually the ESC just cuts out and you are floating helplessly downstream. That is one reason I have just bought a tug.... "
When I purchase an ESC I look closely at the specs; max volts and amps OK, but then also I look at the Low volts function. I look for one that limits the motor current but does not stop dead!
Most of my ships are multi-screw anyway (with two exceptions), so with a bit of luck if one screw is jammed I can get home on the other, or in some case one or two of the remaining shafts.
With modern 2.4Gig sets with back channel telemetry you can also monitor the drive battery voltage on the TX.
Unfortunately not applicable to my 40Meg sets for submarines, but for such applications there are other Monitor and Fail Safe circuits available.
Please don't let me dampen your enthusiasm for re-inventing a wheel though.
Each to his own👍 Will be interesting to see your circuit design in a blog here.
Good luck🤞
Cheers, Doug 😎
PS. for unforeseen emergencies I also have a Southampton tug (and a large towel🙄) on hand😊
PPS I have recently tested a selection of ESCs for operation in a mini model using a central power supply of a single 3./V LiPo cell. The Graupner Micro Speed 4 performs very well. In fact down to 2.0V.

Kevin, going back to H bridges. I have just managed to obtain a circuit for the Southampton tug from the very friendly manufacturer. Their H bridge uses the older bipolar transistor, not the MOSFET. The difference is total, but from our point of view, the MOSFET needs less bits to energise it, but the bipolar will work at lower voltage, whereas a MOSFET starts to struggle below about 6V. So those package numbers are important. They will tell you what is fitted.
Testing the devices? Look carefully first. Any bulges or cracks and its a goner.
For MOSFETs you need a multimeter.
Put pins towards you with the metal downwards.
LHS pin should be very high resistance to both other pins, testing in turn. The reading should be on a Mohm range. It might start low and then rapidly get bigger. That is good.
Join the LH and RH pin with a link.
Select the diode function on the multimeter.
Test in both directions between centre and the linked pins.
One direction should show open circuit and the other a value, often around 500.
If you get a low reading that is similar in both directions the device is blown.

What fun! One eason for a over current electronic protection is two fold. A fuse will prevent a fire after the H bridge has overheated and blown up. Electronic protection can be fast enough to stop that happening. You now have a chance to reverse out of the stall situation. Only a chance....
The other reason is battery protection. Some now use lithium batteries but even NiMh can come to a full stop. Its not too hard to reduce the electronic current limit as the battery voltage approaches the end. So it cuts in during normal running and annoyingly the speed drops. That tells you to bring the boat back into port. Now. Usually the ESC just cuts out and you are floating helplessly downstream. That is one reason I have just bought a tug....

Hi SC,
"On my device I am adding a current limit/ cut out so a stalled motor or stuck propeller does not cause blowups. "
I use a similar device, it's called a fuse! 😉😁
I agree with Kevin, a blog of your ESC build would be of great interest and help to many members I'm sure👍
Cheers, Doug

Thinking about your skills have you considered a build blog on this site to advise on building own speed controller with do's and donts with maybe some photos. I notice some article in the Model Boat Magazine were people were starting to use arduino as part of their model control systems.

Regards
Kevin

Many thanks for your advice on this. You clearly know your stuff and must be quite accomplished. I have researched the 'H' bridge and understand the function. Interestingly and before really good electronic speed controllers were available I have seen pictures and diagrammes of H bridge set ups utilizing sets of micro switches operated by a cam on a servo. Thanks again will follow your advice. PS ordered a solder pump over the weekend having seen one in use on UTube.

Regards
Kevin