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    7

















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    Tug Dual ESC Electronics
    by SeamanCook ๐Ÿ‡ฌ๐Ÿ‡ง ( Petty Officer 1st Class)
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    ๐Ÿ“ On the water
    21 hours ago by SeamanCook ( Petty Officer 1st Class)
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    ๐Ÿ˜‹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.
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    ๐Ÿ“ The real blog starts
    2 days ago by SeamanCook ( Petty Officer 1st Class)
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    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, butโ€ฆ..

    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. Itโ€™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, thatโ€™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 doesnโ€™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 โ€œslavedโ€ 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 wasnโ€™t that bad was it?
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    ๐Ÿ“ File problems
    2 days ago by SeamanCook ( Petty Officer 1st Class)
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    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....
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    ๐Ÿ’ฌ Re: File problems
    2 days ago by RNinMunich ( Fleet Admiral)
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    It's not SC.
    It's quirk of the site๐Ÿค”
    Stephen will have to have a look at that, or maybe it's something he did deliberately for some reason, or the Provider server does??
    ๐Ÿ˜Ž
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    ๐Ÿ’ฌ Re: File problems
    2 days ago by Martin555 ( Fleet Admiral)
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    I had to take the "g" from the mpg4 before i could view the video.
    I am wondering if it is an Apple thing, as i use a Apple MacBook Air computer.

    Martin555.
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    ๐Ÿ“ Not quite in circles
    3 days ago by SeamanCook ( Petty Officer 1st Class)
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    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.
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    ๐Ÿ’ฌ Re: Not quite in circles
    3 days ago by robbob ( Commodore)
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    Hi SeamanCook.
    For your video, try changing the file extension from .mpg4 to .mp4
    It will make the file more compatible with most media players.
    Rob.
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    ๐Ÿ’ฌ Re: Not quite in circles
    3 days ago by RNinMunich ( Fleet Admiral)
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    "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?"
    For a clever 'lad' SC you seem to have little curiosity or perseverance๐Ÿ˜ฎ
    Herewith the instructions (as posted several times already!)
    IF the vid appears at all; as Media File (as yours does) or even Invalid File, it will usually still work. Click on the file icon as usual.
    When the large version of the icon appears click on the download arrow; miniscule blue box at top left. Your device system should then offer you the choice to Open with Win Media Player or whatever player is the prime choice on your device.
    Click OK and the video runs.
    Your motors/gearbox seem to make even more of a hell of a racket than mine!?๐Ÿ™‰
    I quieted down the gearbox on mine considerably by running it slowly while squirting in judicious dollops of Teflon based prop shaft grease.

    Apropos the rear hatch latch (๐Ÿ˜ฎ):
    In my Southampton upgrade I'm fitting a decent size NiMh battery between the prop shafts.
    Something like 4800mAh instead of the original green 800mAh dog poo AA cells (well known from garden solar lights which crap out after a couple of cloudy rainy days๐Ÿ˜ ).
    That stupid latch sticks down so far that it gets in the way.
    So I'm cutting it out, fitting a sill all round the hatch aperture and will use neodymium magnets to hold the hatch down๐Ÿ˜‰
    BTW I also discovered that a 6 or 7 C size cell NiMh flat pack WILL fit between the shafts if you turn the hatch round, fit a new lip for the latch at the front end and cut away the old latch under the deck at the aft end.๐Ÿ˜‰
    Bon chance with your controller tweaking mon ami๐Ÿคž๐Ÿ‘
    I plan to use the Action/Component Shop Dual ESC/Rudder mixer to do what you are trying.
    All operated from the right stick on the TX. One thumb operation - Economy of effort and a hand free for the special functions, such as the Bierkrug or wine glass๐Ÿ˜
    (I sail from the Biergarten at the edge of our lake๐Ÿ˜Š Prost allseits!)
    No 'throttle twitching' or 'momentary rudder reversing' required.๐Ÿ˜Š
    Cheers, Doug ๐Ÿ˜Ž
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    ๐Ÿ’ฌ Re: Not quite in circles
    3 days ago by RNinMunich ( Fleet Admiral)
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    "the Tug wiggling its bottom .."
    In current street parlance I believe that that is known as 'Twerking'๐Ÿ˜ฎ
    Just when you've think you've seen most everything, in almost 69 years and 40 of 'em spent trundling round the world to almost any country with a coastline and a passable navy, along comes a 'Twerking tug'!!!
    Ye Gods and little fishes๐Ÿ™„
    ๐Ÿ˜Ž
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    ๐Ÿ’ฌ Re: Not quite in circles
    3 days ago by RNinMunich ( Fleet Admiral)
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    Hi Rob,
    "For your video, try changing the file extension from .mpg4 to .mp4"
    Vid worked fine 'as is' for me on my Win10 PC, as described above.
    Vid is short and NOISY! ๐Ÿ™‰ (may be the 'bathroom effect').
    All in all I had the impression that my bog standard early version Southampton, 40Mhz radio and no frills, is more manoeuvrable!
    Cheers, Doug ๐Ÿ˜Ž
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    ๐Ÿ’ฌ Re: Not quite in circles
    2 days ago by SeamanCook ( Petty Officer 1st Class)
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    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....
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    ๐Ÿ’ฌ Re: Not quite in circles
    2 days ago by SeamanCook ( Petty Officer 1st Class)
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    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.
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    ๐Ÿ’ฌ Re: Not quite in circles
    2 days ago by SeamanCook ( Petty Officer 1st Class)
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    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.
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    ๐Ÿ’ฌ Re: Not quite in circles
    2 days ago by RNinMunich ( Fleet Admiral)
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    Hi SC,
    I appreciate that what you are trying to do is very different from my plan.
    But then so is your tug, at least as far as the electronics are concerned.
    Mine is a very old 40MHz version with no lights or other frills.
    So a complete refit is necessary.
    I looked at the combo RX/ESC/Rudder PCB and concluded that there was no point wasting time trying to mod it. I want to update it to 2.4GHz anyway, as I have a stock of RXs for my Spektrum DX6 and Turnigy i6 clone, German rebrand!
    Then I ran across the P94 twin ESC/rudder mixer from Action/Component shop. Ideal for the job.
    https://www.componentshop.co.uk/p94l-dual-esc-and-mixer-2-x-...
    I've added lights to the mast and cabin roof already, next are cabin and deck lights, individual circuits to be switched by a 4 function RC switch. A second 2 way switch will be used for smoker and Honk honk ho~nker sound๐Ÿ˜‰ All good fun!๐Ÿ˜
    Good luck with your endeavour, watching with interest๐Ÿค“
    Cheers, Doug ๐Ÿ˜Ž
    https://www.componentshop.co.uk/p94l-dual-esc-and-mixer-2-x-10-amp.html
    ๐Ÿ”—
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    ๐Ÿ’ฌ Re: Not quite in circles
    2 days ago by robbob ( Commodore)
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    I downloaded your file onto my Kindle Fire HD tablet and it tried to open it in a document reader too. This is despite having various media players installed including VLC player. Changing the file extension to .mp4 makes the file more recognisable to media player software. Not sure why if you uploaded a .mp4 it should then become a .mpg4 when downloaded......very odd.
    I will be uploading a short video myself soon as part of a build blog update so I'll see what happens then.
    Rob.
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    ๐Ÿ’ฌ Re: Not quite in circles
    2 days ago by RNinMunich ( Fleet Admiral)
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    A Win 10 PC immediately offers the current Media Player, which works.๐Ÿ‘
    I'll have to find, dust off and charge my Kindle Fire and see what that makes of it๐Ÿ˜‰
    Only normally use the Kindle as an E-book reader, and then mostly when on holiday - which there ain't been much of this mucked up yearโ„๏ธโ„๏ธโ„๏ธ๐Ÿ˜
    Doug ๐Ÿ˜Ž
    BTW: on a PC when you click on the little blue Download box the PC tells you the file name and type and suggests the most suitable player it can find on the PC to play it. Also offers a choice of looking for a suitable alternative if you prefer.
    Guess that this is where the deficiencies of many tablet operating systems comes into play๐Ÿค”
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    ๐Ÿ’ฌ Re: Not quite in circles
    2 days ago by robbob ( Commodore)
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    Hi Doug.
    My Win 10 PC also plays the file immediately and it was downloaded as a .mpg4 file
    SeamanCook said he uploaded a .mp4 file

    So if the file extension is being altered within the site from .mp4 to .mpg4 then something fishy is going on....perhaps Stephen (FireBoat) should investigate ?
    Rob.
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    ๐Ÿ’ฌ Re: Not quite in circles
    2 days ago by RNinMunich ( Fleet Admiral)
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    Agreed Rob๐Ÿ‘
    I've also noticed that the icon often appears as 'Invalid File', usually with MOV files and similar.
    Looking forward to your vid.
    Cheers, Doug ๐Ÿ˜Ž
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    ๐Ÿ’ฌ Re: Not quite in circles
    2 days ago by SeamanCook ( Petty Officer 1st Class)
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    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.
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    ๐Ÿ’ฌ Re: Not quite in circles
    2 days ago by SeamanCook ( Petty Officer 1st Class)
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    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.
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    ๐Ÿ’ฌ Re: Not quite in circles
    2 days ago by RNinMunich ( Fleet Admiral)
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    Odd that!
    My ancient Southampton has never had a list at all!
    So I'm fitting the new battery between the shafts to keep the lateral balance.
    As low as I can get it without fouling the cheapo gearbox, and well away from the rudder servo.
    Had considered rebuilding that, but not before everything else is modded and running๐Ÿ˜
    My hatch is still perfectly flat and seals well onto the foam gasket.
    Try gently warming it (hair dryer? Heat gun on LOW?) and putting it under suitable weights.
    SLA batteries are good for that sort of thing. I've even used a car battery in extreme cases!
    Good luck๐Ÿคž
    Doug
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    ๐Ÿ’ฌ Re: Not quite in circles
    2 days ago by SeamanCook ( Petty Officer 1st Class)
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    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.
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    ๐Ÿ’ฌ Re: Not quite in circles
    2 days ago by RNinMunich ( Fleet Admiral)
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    "You might need three thumbs,"
    That is preeecisely why I DO NOT want to go that way.
    I've never been a fan of tank steering, especially in boat/ship.
    Why waste channels, and thumbs๐Ÿ˜‰, when there are more elegant ways?
    Check out the four operating modes in the pdf I posted.
    As I'm going to shift the battery aft I've got bags of space forward, where the original gubbins tray was fitted. Removing or reshaping that opens up loads of possibilities๐Ÿ˜Š
    ๐Ÿ˜Ž
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    ๐Ÿ“ Going in cicles round the (deckhouse)
    4 days ago by SeamanCook ( Petty Officer 1st Class)
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    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.
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    ๐Ÿ’ฌ Re: Going in cicles round the (deckhouse)
    2 days ago by RNinMunich ( Fleet Admiral)
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    "I live very near to a major transmitter and any bit of metal picks up signal of the FM band "
    Sounds like you need to build a Faraday cage around your test bench SC๐Ÿค”
    Chicken wire is a (not very pretty but) reasonably effective and cheap way to do it.
    How do I know?
    Had a similar problem in the late seventies, testing tiny portable radios near Staines, with the radio systems of Heathrow Airport not far away! Not to mention the Police HQ just down the road and various seemingly badly maintained Taxi Service radios!
    Good luck๐Ÿคž
    Doug ๐Ÿ˜Ž
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    ๐Ÿ“ No apparent reason for fail
    5 days ago by SeamanCook ( Petty Officer 1st Class)
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    Well I said in a recent post that in my experience more damage was caused by testing than the testers fixed in the first place. My "no apparent reason" for a fail was possibly the testing itself. After the damage was removed, on initial retest I put my high impedance scope probe onto a power supply pin and saw a flash. Impossible! But true. Now scope probes regularly go open circuit in their wire. But in over forty years I have never ever had one go short circuit.
    There a first time for everything. So testing probably shorted a wire out and the rest becomes history. But probably a good thing as I was mistrustful of the circuit anyway. Fix underway.
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    ๐Ÿ’ฌ Re: No apparent reason for fail
    4 days ago by RNinMunich ( Fleet Admiral)
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    A most curious 'educational series' SC!
    Under the title of 'Don't try this because...' perhaps?
    Doug ๐Ÿ˜Ž
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    ๐Ÿ’ฌ Re: No apparent reason for fail
    4 days ago by SeamanCook ( Petty Officer 1st Class)
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    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.
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    ๐Ÿ’ฌ Re: No apparent reason for fail
    4 days ago by Newby7 ( Sub-Lieutenant)
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    The unfortunate part is you didn't get a picture with the flash.
    Rick
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    ๐Ÿ’ฌ Re: No apparent reason for fail
    2 days ago by SeamanCook ( Petty Officer 1st Class)
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    I think the educational bit will start when I have learned a little more....
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    ๐Ÿ“ Output stages
    6 days ago by SeamanCook ( Petty Officer 1st Class)
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    As I said, I was not happy with the parts I bought for the output stage and sure enough for no apparent reason one device has developed a slight fault just as I got the deck back on. Unusually, not complete destruction. But typical of a small over voltage spike. At a 12V rating these devices were marginal on my normal design rules so I pay the price and scrap them.
    So that output stage is coming out and getting replaced. I need a few days to buy in the proper bits but a temporary set of a silly big size will go in tomorrow. That's another thing down to experience....
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    ๐Ÿ“ In the boat
    6 days ago by SeamanCook ( Petty Officer 1st Class)
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    A couple of photos here showing the bits in the boat. The circuit board could be half the size or less on a proper PCB but a first hand built prototype needs spare space.

    The next visit is to the bath or a pond. I think everything is going the right way but my mechanical and spacial ability is zilch.

    Still considering how to present this build as an educational series and whether to throw away and replace the output stages as I am not 100% happy with the devices used. And I have used the spares....
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    ๐Ÿ“ Obeying the Fleet Admiral
    7 days ago by SeamanCook ( Petty Officer 1st Class)
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    You must always have a fuse he said. But I wanted a switch. So I made a pair of wires with a connector that would normally be joined by a switch. But I fit a fuse into the connector and the fuse acts as the switch. Job done sir.
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    ๐Ÿ“ Progress with installation and H bridge as a smoker.
    7 days ago by SeamanCook ( Petty Officer 1st Class)
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    Nothing goes to plan. The photos will follow. I installed the board; it ran for a while, and when I applied the power for the third time, I got the dreaded grey smoke. That sort of thing is a nightmare because one does not know why the fault happened. It was working and I didn't touch anything sir.
    You have to guess, unless you are certain of having made a mistake. I don't believe in failures due to bad luck. So I made some improvements which I will detail later, and also added a switch so as to turn things on with all inputs active and set. I learned a few things about low current H bridges.
    Simple Sailor reminded me earlier about logic level MOSFETs. I was tempted and I fell. But it turns out that all the usual precautions on H bridges are required. You don't really save anything, because logic chips do not have enough Oomph to drive the FETs at a reasonable speed. You really have to add a buffer amplifier. And most switching circuits have a tendency to self destruction which must be resisted. I discerned a design rule to share.
    If designing an H bridge with only one drive point on each side, the sum of the Vgs of the top and bottom FET when conducting the nominal load current must be less than the rail voltage. That is generally true for logic level FETs with single battery cell devices, but for 2 cells, or anything above 5V or so, a single point drive of an H bridge with logic level devices is liable to have problems, grey smoke being one of them. You should really use the old, bigger higher Vgs rated devices. Especially when you're a modeller rather than a speed merchant.
    You have to drive the top and bottom transistors of one 'leg" of an H bridge so that there is a "dead band" when both are nominally off, or at least nearly off. This goes against nature and what FETs want to do, which is to both stay on together in an embrace to destruction. Normally, that means a driver chip is required but I am far too mean for those and found a workaround. I think a 3 cell 12V device would certainly need a driver chip, which all add their own problems, especially as many do not handle flat out full speed. At a future point I will cover H bridges and their foibles and differences. At no time may any transistor gate be uncontrolled, especially at turn on. The normal ESC is a bargain....
    Surprisingly, I rethought my ideas on old fashioned Bipolar devices, and provided the current is no more than 5A they probably work out cheaper and simpler than MOSFETs especially at higher voltages. And low voltages below 2V is possible, where a MOSFET will star to struggle. They can be made more tolerant of abuse and the driving of them is actually quite easy.
    Anyway, after a few hours soldering and retest....
    Success! At least until it goes in the water. I added some LEDs which tell me if a prop is going forward or back, and the brightness indicates the speed. The circuit seems to be behaving properly; all functions work. Whether its all in the right direction only a trip to some water will tell. And to some extent, its a matter of preference or even practicalities.
    I examined the Tug electronics and it's a little more non standard than I expected.
    The rudder servo pulse is 1to 2 msec, but occurs at a rate of about 8.6 msec, over twice as fast as usual. Servos don't care about this but I do; cue some value changes to readjust gain.
    The motor throttle pulses also come at every 8.6 msec. Full speed is seen, but the minimum starts at 2 msec or just under 1/4 speed. I feel that is excessive for a Tug. In time I will add an adjustment for that. When throttle is stopped and I move the rudders, as designed the motors turn in opposite directions for a spot turn. I can make the motors turn very slowly indeed, albeit in air. So it looks like the 2 msec they have used corresponds to a maximum servo pulse.
    Provided it works OK in the water I will start to document the circuit in sections and use each section to illustrate the use of common and inexpensive electronic parts.
    This has ended at a slightly higher cost than originally envisaged, but still very light for the functionality. It's the bits at the edges that cost.... I have realised from other blogs that every expert among us accumulates numbers of small tools, methods and knick knacks that help us to practise our expertise. When you come to help someone else get started, the real cost suddenly stares you in the eye. What is cheap and easy for me turns into something expensive for another to duplicate because of such start up costs.
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