Here's a conundrum that I'd like your thoughts on. I recorded some data on one of my boats now running on a couple of the battery packs that were cycled as discussed earlier. They are 6V 5000mAh NiMH packs which, after their final charge, showed they received 5500mAh according to my charger. For the subsequent run I fitted a recorder which showed the current consumption, as on the attached chart; typically 2.55A, with a maximum of 2.9A. A rough consumption calculation based on the chart, of 2.55A for 70 minutes, is a little less than 3000mAh. When I recharged them after the run, the charger showed they'd taken 3850mAh. Why the difference between the 3000mAh consumption, and the replacement charge of 3850mAh? The charge and discharge efficiencies are obviously less than 100%, but this data suggests that the two combined are only 78%. So, for example, if the two efficiences are equal (89%), if the charger states a charged value of 5000mAh, the battery has only accepted 4450mAh (=5000*89/100). When delivering the power, it can only put out 3960mAh.(=4450*89/100). Or in other words, only 78% of a battery's stated capacity is usable. Or is there a different explanation? Roy
Hi Dave, Yep, agree, to a certain extent. I have also had surprising results with 385 / 400 sizes; for instance with my 110cm heavy and cramped submarine. On the surface it outruns most boy racers 😁 Not exactly scale but all good fun. A little down angle on the forward planes and it throws up a beautiful handlebar moustache of water 😊 Not too much angle at speed or it sticks it's tail in the air 😲 No, the main question was that Fred already has the 700s so I simply suggested a decent match, 5mm shaft and so on. If he wants to spend on more motors fine. the the 3mm shaft would surely save weight, mostly through the smaller tube. Don't know the rest of the detail of the boat; beam, draft, safe waterline etc, but I would have thought a 3 footer would have a reasonable carrying capacity, like my 3 and 4 foot warships. Most of those run on multiple Speed 600s. And there I have the usual warship high length to beam ratio and associated stability problems! Like I said; he pays his money and takes his choice. Personally I would give it a whirl with the 700s since they are in the box! Maybe though with a 3 or 4mm shaft and appropriate coupling so he can adapt later if he wants to. Would still think a pair of 35 props would do the trick. Whatever, have fun Fred. Look forward to the Sea trials Report! (Wrote, read and commented enough of 'em in my old job!) Cheers Doug 😎 Oh no! Yet another thunderstorm just started, my terrace is already swamped 🤔
Hi Tooley, Since you are now a member - Welcome aboard👍 - post in the Forum (e.g. Boat Specific or Build Blog) not in the Guestbook, we can't answer there 🤔 Re advice: 'quick' 😉 trip to Swansea Maritime Museum to take some measurements and check details?? Good luck with the build, nice subject👍, and above all Have Fun! Cheers Doug 😎
Hi Chris, no you don't need 70A wire! 😊 That might be horribly thick and stiff for a scale boat. You need wire the same size as probably on both your motor and battery. Same the 'standard' wiring in cars. Available I suppose at Halfords and any car diy shop. WHAT YOU DO NEED IS A 15 OR 20 Amp FUSE TO PROTECT THE WIRING IF THE MOTOR STALLS (PROP GETS BLOCKED) 😡 If your ESC has a BEC supply for the RX put the fuse in the positive motor lead, probably red or yellow. If not, i.e. you have a separate battery supply, put the fuse in the positive lead from drive battery to ESC. Then at least the RX will still work and maybe you can see from shore if it still responds; e.g. by switching on lights or some other visible function. With twin or more props fusing the motor wire itself can sometimes help get the boat home on a remaining engine. Somewhere in the Electrical stuff blog is a long discussion on the subject! Have a look here https://model-boats.com/forum/electrical-related/28332 "What type of wire?" Happy sailing 👍 Cheers Doug 😎 PS: Almost forgot, if you have a brushless motor you have no choice but to put the fuse in the positive wire from battery to ESC! Brushless ain't got no positive!
Hi rolfman Your quadcopters use forward only escs. I suspect the problem with model boat escs is the reverse. I don't have the circuit diagrams for ESCs so its difficult to be certain what causes the problem. I do know some escs with bec and switches work without being switched on if connected to a signal and power supply but subsequently fail usually with the full forward either on or off. Not all escs exhibit this which is why I asked what esc was being used. Trillium You are correct and is another reason I advised against this suggestion. dave
Hi Doug I use a charger that measures the internal resistance of my batteries. Damaged cells exhibit high internal resistance and cannot be recovered to their full capacity. I agree you can flash the cells and they will recover the voltage but will not take or deliver the current. As a result they will quickly discharge under load and prevent the whole pack from delivering its full capacity. I sail model boats on a large lake and recovering a model due to battery failure is difficult, so I don't risk using sub standard batteries. I have not used wet Lead acid batteries for many years but I agree the Epsom salts trick did work on such batteries. I agree flashing is highly dangerous with any battery as there is a high risk of explosion. Great care should be taken and, unless you are competent, should not be attempted. Take care Dave
Hi Dave, Ta 👍 After thinking back to the fun (and pong!) of laminating my destroyer hull I came to similar conclusions 😉 Won't have to mess about with acetone either, not so easy to buy in quantity here. Little bottles of nail varnish remover are expensive 🤔 I don't need to add strength. Just want to clean up and seal the old girl prior to painting the inside with Hammerite and subsequently fitting the new brushless and electronics. Got curious after reading all that about sealing with resin! Cheers Doug 😎
Hi Chris, As usual the EU has had it's say on the subject:- "The European Union agreed in February 2013 to the mutual procedures for the complete denaturing of alcohol: Per hectolitre (100 L) of absolute ethanol: 3 litres of isopropyl alcohol, 3 litres of methyl ethyl ketone and 1 gram denatonium benzoate. " The MEK should help the solvent properties 👍 Purple resin would look quite nice, different, ! 😉 But I don't see the colouring agent (methyl violet, AKA gentian violet) in this mix. Optional extra! Cheers Doug 😎
Thanks Doug, your concerns are well founded, I have had previous experience of the stuff, so will be letting the experts do it for me In a lab. Yes it is a banned substance but some specialized labs can use it, and I still had a contact in such a place. Don't tell the wife about the old Queen. Colin.
Hi Dave, Exactly, If it ain't broke - don't fix it! 👍😉 Will get some experience of current kit on my Sea Scout upgrade - A Quantum leap from Taycol to Brushless 🤔 Weather same here, ca 30°C 😎 with intermittent thunderstorms expected from tomorrow 😡 Cheers Doug 😎 PS The sub outruns many 'speed' boats, long and thin with plenty of Oomph! 😁
Hi Doug Progress especially with anything electronic moves at lightening speed and our PCs are almost obsolete as soon as we buy them. I suspect your sub like many of mine has kit sourced from an earlier period and I can well remember all kinds of suppression aids we used to have to use especially with our cars to suppress the interference from the ignition! I suspect it is only the modern high frequency ESCs that will have a problem, earlier kit used discrete chips that used much lower frequencies for the pulses. The original chips used became unavailable so manufacturers had to adapt to what was available. If your sub works OK I would leave well alone. Eric's problem could well be motor related but could also be from a faulty servo, my suggestion to unplug the rudder servo would eliminate this from the equation, but I am awaiting a response Sun's back but thunderstorms promised for tonight! Happy days Dave
Hi Dave, I guess you're right! I obviously have more catching up to do than I thought 🤔 Re your question - if you mean my sub it has no interference problem; RX is in the bow, motors and suppression boards in the stern as in my pics. Two big 4AH 'lumps of lead' in between! I simply wondered if Eric's problem was due to interference from a cheap motor in the outboard. I have taken a couple of these apart (from inflatable boats) and the motors are pretty basic with little or no suppression. But if he's using a hi freq. ESC then chokes are probably not the solution. I that case I might go back to a simpler ESC myself! Cheers Doug 😎