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Member postings for Mike Davidson

Here is a list of all the postings Mike Davidson has made in our forums. Click on a thread name to jump to the thread.

Thread: Power supply
31/12/2010 22:58:50
If you go down the MEerKat, you will see loads of servo's capable of driving a relay via a microswitch, shimples. Mike Davidson........Plymouth
Thread: crystals
26/12/2010 15:54:09
Hi Kevin, crystals aremost important as the home office has laid down accuracy figures that all radio control sets must conform tothe transmitter crystal set s the frequency that is radiated into the ether by your transmitter, and the receiver crystal tunes your receiver exactly to matcgh the transmitterthe two crystals make an exactly matched pairwithout which your radio would not workeach crystal would work in a radio of a different frequency, but the output would be very low indeed and the receiver would belooking for a very different frequency,so it too would not workThe frequencies not milligrammes but MegaHertzwere laid down by the AmericanFederal Communications Commission (Fccand were interlaced with the CB radio frequencies at exactly 10 KiloHertz apartso one could operate without being interfered with by an adjacent transmitterand if you care to look it up, the 27MHz channels are seen as gaps in the AM CB channelsand as far as I know there are two or three channels where CB and models were allocated identical frequenciesI think that the black channel was allocated to a CB channel and hospital paging systems accounting for the number of aero modellers claiming that a CB user caused a model to crash, it certainly did for me when I was giving a demonstration to disabled children in their theraputic swimming pooland I had sailed along one wall to give one section of kids to get a close viewand I was heading towards the other side to do a lengthfor the other kidswhen the boat dug her stern right in and accelerated flat out in a hard turn to starboard, sadly it collided with the tiled concrete wall knocking one propellor right off, the other engine took over propulsion and I brought her to a halt and steered her towards me so I could recoverethe wreckagewhich was not funny. I knew that there was nothing wrong with the boat so I switched off the batteriesand lifted the boat out of the water and on to her stand where she would be safeI looked out of a window, and saw a ford capri with a six foot long CB antemnna clamped to its roof parked outsideI went utside to speak to the driver and asked him what power he was using. it turned out he was using a 1000 watt linear amplifier andI warned him that he was breaking the law on several counts, but it turned out that propagation effects meant that a4 watt legal CB could reach the eastern seaboard of USA easily so lots of CB'ers were talking to Americansand loving every minute of itso I contacted the chairman of the CB club and asked if I could speak to the attendees of their next meetingat which I explained the things they could do legally without crashing radio controlled aircraft of boats, and I did the same at the model club of which I was chairman. After that, things ran a little more smoothly.I have just realised one thing you said in your post was somewhat incorrect,which wasthat you reversed your crystals if another person was using the same colour frequencythis would mean that your transmitter would send at a frequency 455Kilohertz lower than his and your receiver would produce an intermediate frequency455Kilohertz above, and not 455 below the transmitted frequencyas it should to match the settings of the tuned circuits withinthe combination could have worked I guess, but not nearly as well as if the crystals had been fitted to the correct units. I think the best way to eliminate interference is to use the peg system where an antenna would be mounted o the controller's table with a load of coloured pegswhich you could take if you wanted to use that coloured frequencyWhat I did was to buy a nearly complete set of crystals so I could always fit a different pair of crystals to my rig and sail off into the sunset, no worriesIf you would like me to send you my paper which I wrote explainig how radio control works, send me your e-mail address, and I will send it to you as an attachment.Mike Davidson
Thread: battery charge.
07/10/2010 15:21:46
Colin, it seems to me that something occurred to  make too much current flow through the battery cells. If the cells were hot enoughto stretch the shrinkwrapcovers,the same amount of energy must have been flowing around the charger. It is possible that there was a thermal fuse was fitted to the charger. In my mind, I feel there should have been a resistor to limit the amount of current drawn from the devicebut as has been said by a previous correspondent, there seems to be a lamentable lack of regulation with the plastic encapsulated devices that have a set of plug pins to fit a 13 amp socket  .  I would suggest opening the unit to search for damage or failure, and unless you find an open circuit thermal fuse, be prepared to throw the unit in a suitable binand see if you can buy a purpose built charging unitthat is designed to charge 9.6 volts, and, READ THE INSTRUCTIONS.....   Mike Davidson in Plymouth
Thread: speed controller
26/05/2010 18:00:35
Pardon me being a bit blunt and to the point, but it does not matter a jot what boat your speed controller is going in, and a bit less what motor you intend driving with it The speed controller is just a way of telling the motor how fast you want it to goby a cheeky little bit of electronics, the speed controller is also jolly useful because when you plug it into channel 2 of your radio receiver, ittransfers power from your main battery to the receiver and, from there to all the other servo's, very useful Some clever design engineer incorporated a reverse facility into his design. A word of caution to end, just be a little bit canny that you don't try to put too much power out to the motor as this power has to be regulated by a couple or transistors in the ESC itselfandmaybe, just maybe, they could cook in the event of the propellor getting snagged. If you have an ammeter, measure the current being drawn by the motor at max chat and ask the ESC maker if that is O.K.       THen, you go into the boat's length and beam,, this only causes drag as the propellor tries to push the boat through the water making the motor's job just that little bit harder, you can help by making the hull all nice and smooth and shiny and not having too many bits and bobs in the water.
p.s. when I said plug your ESC into your radio channel 2 output, it was because there is a convention among radio control system makers, that always the speed servo should be powered by channel 2 to avoid ambiguity...Mike Davidson ...Plymouth
Thread: Back Charging of Batteries
16/05/2010 16:23:42
If you have two batteries wired in parallel, and oneis at a lower state of charge, then the lower charged battery will tend to take powerfrom the other.If you look carefully at the orientation of the cells within the lower charged battery, then, they will have a positivecharge on the negative end and a negative charge on their positive end, and it has been known for thewhole battery to retain a chargeof reverse polarity which may well cause grief in the electronics of your receiver or electronic speed control. The only safeguard against either of these is to install a diode in series withthe battery under charge or electronics you wish to protect. I never run batteries in parallel, but I buy higher capacity cells if I can afford them. When I first started, I bought Cyclone cells which had a massive capacityand were capable of giving enormous power
Thread: Motor high pitch noise
19/02/2010 18:47:19
Hi there, it's me again, Mike Davidson from Plymouth, I have been giving your problem a lot of thought, and I have a vague ideathat I know what is wrong, that is that there is a slight error in the setting up of the ESC I suggest you look at the mtronics website and download the setting up of the ESCand the throttle control I suggest you print off the procedure and go through it precisely with a friend who can readthe instructions while you carry out the actions. The clue you gave me was that the motor did not react straight away, but you needed to push the throttle more forward before the motor reacted. This points to a threshhold in the ESC program not beiNG SET RIGHT, and that you had to override the setting before the controller saw the slow ahead demand properlyIonly vaguely remember the setting up of my controller from the past, and the electronics was very stubborn and did not want to remember the setting points correctly, Have a go, and let me know how you get on. best of luck, mike davidson.
Thread: Using Fibreglass
14/01/2010 16:33:29
Hi RobertI was given some really good advice by a company selling fibreglass and resin with all the stuff that goes with it, and they gave me a brilliant method Which was to coat the plug with cantstik waxand to buff iy up to an immaculate shine, having done that, apply another layer of wax and buff that up to a brilliant shine. Repeat this action up to twelve times when you will have a deep deep shine to which, nothing can stick, hence the title Cantstik, it works like a dream for me
Thread: Thinning epoxy resin
11/01/2010 18:02:56
Hi Jeremy, I cast model submarines out of casting resin,and the suppliers provided me with a gallon of acetone to wipe resin away from surfaces liable to be damaged I don't think it is a solvent that I could use to thin resin, but it helps to clean resin offTo make resin a little thinner, I use10 % hardner rather than 8 % , but if you do that, get your skates onbecause it setslightning quickand generates quite a bit of heat in the curing process. just a few % too much, and you would end up with amber resinSometimes for a final coat, I use clear casting resin or Gel coatby brushing it on like paint and when it has set, Igive it a nice gentle rub down with 800 grade wet and drybut sometimes, I can get some 1600 gradewhich is magicon top of that keyed surface, I can use a spray can of car paint, but if you yry that, don't get any on your acetate windowswhatever you do     practice masking techniques
Thread: help needed installing a water pump!!
03/01/2010 13:10:13
John Does your pump transmitter have a channel on the receiver which is just a switch? the alternative is a servo operating a slide switch to apply volts across your pump motor. your biggest problem as I see it is getting sufficient power from six volts to produce a jet of water, my approach would be to create an accumulator which would be full of air which is unlike water, compressable, so as your pump put water into the accumulator,it would displace air which would generate pressure withinand give some force to push the water through your pipework and nozzleenough to form a jet, and have enough power in reserve to keep it goingfrom the "compressed"air. If your receiver has a switched power output or an electronic speed control, that is the way to power your pump motor, but in a previous model of mine, I ues a servo output to operate a micro switchdriving a relay switch for the power, that worked as a reversing switch for an Arun Lifeboat............................................. Mike Davidson in Plymouth
Thread: Batteries
13/12/2009 21:40:33
I have found the magazine, it was Elektor of Feb 1993and I have the circuit diagram and printed circuit board information for my magic battery charger.
Thread: Enamel Paints
11/12/2009 20:11:23
Hi there, it is not usual for me to be so late in a topic, but last week, I was in an art shop as another hobby of mine is picture paintingTo my surprise, I saw on the shelf a bottle of clear varnish, it was Daler Rowney Artist's clear picture  varnishdesigned to be applied over oil paintings. The instructions say do not apply until the paint is at least six months oldas I guess the white spirit carrier will act as a thinner for the art paintswhich will probably smudge. It looks lovely and clear, and I guess, it will not hurt Humbrol enamels. My intention is to use it as a fixer for the nameplate etcetera for my model of a Tamar class lifeboat, photo's will be goingon my profile soon.............Mike    Davidson in Plymouth
as a postscript, I guess you will be pretty safe if you spray the varnish onto a surface and quickly get it horizontal so the liquid will not run, you should be O.K...................................m.d.
Thread: Batteries
26/11/2009 17:28:46
just a quick look at the real basics of batteriesThe basic building block of your power source is a cellback in the formative years of Faraday and Leclanche experimenters discovered that if you dunk two different metals into a bowl of acid, an electrical energy source appears, you can do this too if you cut twoslots in a lemon, and then stick a 10 pence coin in one and a two pence coin in the other you will find that you have built an accumulator, not at all powerful, but nonetheless an electrical generatorthis basic unit is known as a celland it is only when several cells are joined together that you get a batteryIf you go back to your lemon powered radio, the lemon's acid will change as the electricity is used up, and the power output will dropHere, we see the effect of the capacity of the cell. No matter what chemicals are present in a battery or cell, you will see it's capacitythis is known to enginerers as the Ampere / Hour ratingIf you look at the cells I use, they are one point two volts at 300 milliamp/ hours, now if several of those cells are connected together in a battery, the voltage risesas each cell is added, so if I have ten of those cells in a battery, it would be tw1lve volts at the same capacity as the individual cells or 300 milliamp hours. I will spare a moment or two to go into the characteristics of different types of cells. The most common is the lead / acid cellwhich has two kinds of lead in a bath of sulphuric acid, this is most common ehere an application draws lots of amps for a long timeas the cell discharges, the specific gravity of the acid can be read with an hydrometeras the cell discharges, the battery strength goes downin a steady declineand the internal resistance of the cell goes down. The cells I use are Nickel metal Hydride and they have a totally different characteristic as the electrolytewill hold up well under loadthe cell voltage stays high for much more of the cycleand drops suddenly at the end. modellers who use ni-cads or NiMh batteries will have the same characteristics, the battery produces good results for a long time, and then stops quite suddenly. There are other sorts of cells available which have totally different characteristicsthey are the ordinary torch batteries on shop counters most of those are zinc carbonwhich is a zinc pot full of sal-volatele with a carbon rod stuck down the middle. better than those as Duracell will never stop telling you are the so calledalkeline cells higher power and longer lasting with a slight advantage of being leakproof. UNLESS they say different, none of the over the counter batterys or cells are r  NOT  Re-chargeable, and therefore give an inferior value for money, but they do give one point five volts per cell, so you will not need so many to achieve your required voltage, so, you pays your money and takes you choice. All the time, it MUST be noted that virtually all cells contain TOXIC materials like lead / cadmium and must be disposed of responsibly. Don't whatever you do, chuck used cells on a fire
finally, back to the good old lead acid cell, as I said before, these are two kinds of lead in a sulphuric acid bathremember that this is acid and it will eat your boat for dinner,and if it finds metal like a prop shaft of a very expensive motorcase, it will eat it. Only glass fibre resin is able to resist the acidand stay keeping the water out. There is one plus to lead acid, and that is that they give you two volts per celland surprise, I went round the tourist bit at Chatham dockyard and there they have a decommissioned submarine Ocelot which was an educationher battery was 340 volts, and that's what they put across the motor, it is theonly way the power can be developed to drive a ship of that size, so there is no substitute for power. The submarines used Diesel electric power when they were on the surface meaning that they ran the diesel to drive a generator which charged the batteries and drove the propellor motor, so, everything on the whole boat was driven by electricity, a bit like your model really, and mine
17/11/2009 16:54:24
I am at pains not to offend, but you have to agree, that both Ashley and I have said categoically DO NOT (R) NOT USE A CAR BATTERY CHARGERAS YOU WILL BE putting yourself and others in DANGER.  I feel it would be better if we all were subject to health and safety legislation, and had to wear proper personal protective clothing, this would bring home the danger surrounding charging batteriesand the poisonous and corrosive materials within that could jump out and bite your leg given half a chance. I go back to what I said about Ashley and I advising not To usE car chargeRS, and just read all the  in ths thread o see how ma people have said blithely thaT THEY usE a car charger and it does a brilliant job here I go again , trying hard not to offend, but do you not agree that those contributions are encouraging people with little or no knowledge to go straight ahead and do exactly the wrong thing, and are those people going to put their hand in their pocket ro recompese people for wrecked gear as a consequence of doing that wrong thing?????????????   I doubt it very much.
There may be a modeller in Ireland reading this who willconfirm what I am about to say, but this guy had a problem with his boat, and I got involved trying to diagnose the problem from afar by correspondence, but to no avail, so this guy packed all his radio gear up in a giant jiffy bag and sent it to me, A couple of weeks later, I sent all his gear back to him working, I had extracted the duff bit and replaced it, but this story has a sad ending, the boat was sent out to sea, and sank out of reach from the shore, Soanother tip, build in positive buoyancy if you are going to send your precious model on mission impossible, and keep your batteries dry,I am still working on getting the magic battery charger kit for modellers to build. I can say that because I built one for myself, and it is really magicAsk Ashley what he says........................Mike Davidson.......................................
Thread: subs'
15/11/2009 22:05:37
Having worked on real submarines, I can tell you that they use very low frequencies to communicate with submarineswhere VHF waves go dead straight in line of sight, and the VLF waves tend to curve down towards the earth. I have not even attempted to communicate with a submerged model yet, but we could follow the big boys and use a buoyant wire aerialtowed behind. The only way to tell one is there is if you see a line of seagulls drifting along sideways at fifteen knots. I suppose you could use a very thin whip antenna poking up out of the water surface, but as I said , I have never done it so I cannot say.
Thread: Batteries
15/11/2009 15:37:08
Well then 60 Watt, I had a young friend  paralysed at birth who had an electric wheelchair given to him by the rotarians where he lived, The wheelchair proved a bit of a problem because he and his family kept forgetting to plug it in.  I took it on as a project to get it going reliably,and that proved to be a problem. Because the makers saw it being placed in the back of an astate car, they fitted SLA batteries so no acid would spill out and corrode any metal it came into contact withI contacted the MaKERS OF THE BATTERIESwho very kindly sent me a circuit diagram of a specialist intelligent battery chargerthat delivered a charging current low enough to limit the production of hydrogen gas in the charging processbut, an additional component bothered me a bit, it was a temperature sensor to detect heat risesindicating an erronious charge rate, I don't know about the batteries, but the charger certainly got hot, and another time my own son got one of the radio controlled dune buggies powered by a 7.2 volt Tamiya pack. I've still got that pack here, but it is no good as it is banana shaped where the batteries within got so hot they melted the plasticencapsulation. He won't tell me what he did, but I bet he put it across my home made car battery charger. I deliberately did not mend it to teach him a lesson of what not to do. Keep it safe.........................Mike Davidson in Plymouth
13/11/2009 15:50:51
Well, I am dumbfoundedafter all the experienced modellers saying that on no account should you use a car battery charger to charge the smaller less robust model batteries,here you are blythely saying that you do just that. I am wondering if all your family have a full compliment of working eyesafter the almost certain battery explosions that have taken place as the amount of hydrogen gas generated by the chemical changes in the electrolyte of a sealed battery, none of the ones I have have vents to allow gas to escape. If you remember, I told you that the best charge rate is one tenth of the rated ampere / hour capacity of the battery which in the case of a 12-7 battery is seven ampere hours giving an ideal charge rate for a completely discharged battery of 700 milli amp /hourswhich is one seventh of the capability of your car battery charger, which works out as seven times too much, and if by any chance you think so little of your own life and the others around you you smoke, the chances are that you could easily ignite the cloud of hydrogen gas around the charging pointwhich is concentrated into explosive proportions, your house would go down well on November the fifth, so, I should take advice from a professionaland heed that advice, it could save you more than money, but you do have to listen to the advice you are given and stick to it. I CAN OFFER YOU NO BETTER ADVICE..................................................Mike Davidson
11/11/2009 20:05:06
To all modellers who are in the dark over which batteries to buy and how to charge them .    I have discovered a website where good batteries are available, if you wish to visit this site, put Yuasa Batteries into your search engine, and then from the menu select industrial automotiveand motorcyclethen, have a look at the range of batteries available, I saw a prtticularly interesting 12 volt 7 amp hour gell cell as soon as the page opened. From that page there is a link to a site called battery shop who quote a terriffic supply service for whatever batteries or cells you need.
 ALSO, I am in correspondence with a company that published a battery charger that is the bees knees I have asked if I can make these at cost for modellersIt will solve loads of problems if I can do that without infringing copyright, That will be possible if they waive royalties like I have asked them to do.In the meantime, I will continue trying to work out a way round it.
Thread: full speed boat turn in righthand circle
06/11/2009 20:19:52

Leslie, could your boat have a defect where one prop turns one way and the other turns the other way ?This would cause the boat to slow right down and turn in a circle. Run the boat open and see if you can see which way each of the props are turning. In the fault condition, is one motor not turning at all ?, This could cause the boat to turn in a large circle. Put it in the bath and have a look. If you have a volt meter, look at the voltage supplied to each motor,, Message me and let me know how you get on, I'm dying to know.............................Mike in Plymouth52 years with the Royal Navy.
Thread: Batteries explained
04/11/2009 17:55:15
Looking into a supply problem, I stumbled across a very interesting website, it is the Yuasa battery company, you must have seen their product all over the placeThey go quite deeply into battery construction and  some of  the advantages and disadvantages that go with them.   later on in the site they go into charrging  and how to go about it safelyI recommend all modellers to read it and inwardly digest all the good words there. I am sure it will drasticly reduce the number of heart rending stories of models being lostand ESC's glowing in the dark. DO remember that the information refers to yuasa batteries only, and not the lithium polymer batteries in some of the latest helicopters.   When you read it, think "How does this apply to me"?. Avoid fast charging unless the leaflet that came with the batteries says you can. IMpatience can be very expensive
Thread: Battery charging question and other questions from beginner!
12/10/2009 17:39:02
Did you explain your requirements to the salesperson ? It is quite important to get it rightas the gel cells are easily damagedand are quite unforgivingI've got 3 in my cupboard that I put on charge regularly to try to revive them no luck yet. I got them from brokendown fire alarms so they are probably used to being trickle chargedI got caught by this environmental rule for throwing batteries away ! I have to take them to the tip re-cycling centre
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