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I have an Aerokits Fast Patrol Boat, what scale 20mm deck gun did you buy is it 1/24? Also I was thinking of powering mine with a Graupner 700BB Turbo motor and Nicad battery packs or Lipo batteries. My hull doesn't have spray rails, should I fit some? Sorry for all the questions but I'm returning to powered model boats after a long absence! Thank you for any help received.
Hi MB, Attached are two extracts from the official USN Bureau of Ship plans for an MTB. Kindly sent to me by the colleague I bought the PT Boat from. Also a pic of the forward (starboard!) gun tub on a model, showing what can be done these days with some photo etch upgrades😉 Not mine I'm afraid🤔 I get the impression that the Aerokits version is somewhat stylised. Have fun, cheers Doug 😎 BTW: If you don't want to tackle LiPos just yet you could use Hi Power NiMH. LiPos do involve some investment when you first start using them: Lithium safe charger, relatively expensive battery packs and LiPo safe ESC. The latter can be preset to stop if the LipO is discharged to it's lowest safe voltage, i.e. 3.2V per cell. Below that the LiPo cells will most likely (99.9%) be irreparably damaged.😡 Cheers Doug 😎
Evenin' Dave, "Interesting stats especially the stall current. This would rate the motor at 280 Watts with your 7.2v battery" 😲 If the battery pack was 7.2 volts nominal and was 'healthy' then according to Allen's measurements it was down to an average of about 0.98V per cell. Also not so healthy for a NiMH. 5.91/5=1.182 volts per cell. A healthy voltage for NiMH 😊 Indicates a shorted cell if it was a 7.2 pack, and the healthy cells could still deliver 40A for a short while. If the boat needs ballast anyway I would go for the useful ballast of a 6V SLA. Which is what I intend to use in my Danish cutter with the Taycol Target. Such boats don't need the short term, high current that NiMH and LiPos can deliver. G'night All, Cheers Doug 😎
I think you might need pointing in a direction, so I had a quick look on Hobbyking, and this motor is the sort of thing you can use, although this particular one would need you to swop the shaft around, this is just a guide, other s will no doubt add comment, its the right size, 5mm shaft, right kv and watts. https://hobbyking.com/en_us/turnigy-g15-brushless-outrunner-... brushless esc https://hobbyking.com/en_us/hobbyking-90a-boat-esc-4a-sbec.h... you don't need the high amp capability, but its reversing, programmable, water cooled, and has an sbec, so the main battery power this 5 mm shaft, move your motor to the centre section meaning weight distribution is more central, and you can now use a shorter shaft, and get a couple off plastic "x" props, I would say 40 to 45mm will be the one. This will give a good speed, and you can power on 3 cells or 4 cells lipo, get higher c rating (40c or more) and higher mah so you have fuel in the tank available https://hobbyking.com/en_us/turnigy-battery-3000mah-4s-40c-l... This is just a guide, a starting point, as I feel you are unsure where to start, others with more knowledge will come in regarding this, having experience with lipo, brushless, 3 foot ply boats, and esc's, depending on budget, this would be the sort of thing I would be getting.
Has anyone had experience of the M sonic microprocessor digital Eco Marine ESC. I had one given to me recently. But I have no details of rating, amps ,voltage etc. Any idea who makes them or how I can test without damage to motor or receiver or ESC. It has a Tamya battery connector also there was a totally dead 7.2 battery pack with it, but as the bag of bits it came in was a variety of junk and stuff from a neighbours loft it may have come from anything. Cheers Colin.
Hi Steve Stick your motor on a temp ramp holder and connect up to the ESC. Get a selection of different sized props and pitches and fit one to the motor. Connect the battery via a Wattmeter and run the motor at full whack. Record the results Amps and watts. If either are above the motor or ESC ratings the prop is too big or too coarse pitch... Try with different props until you find one that is within ratings spec This is a very rough and ready method and the load will reduce when the model is in motion so will always be within spec. Once you have the size and pitch it really is a question of trying slightly different sizes and pitches to get the best for your model. Take great care when testing with air props, modern brushless motors pack a big punch and at full whack any contact with the blade is to be avoided. Dave
Hi Alex They will be connected in series with the positive connected to the negative. I suggest you carefully cut off the heat shrink covering, taking care not to cut into the cells. You can then check each cells voltage. The nominal is 1.2v rising to 1.4v when charged. Any around 1v or less will never hold a charge so mark them with a marker pen. Hopefully it will be one of the end cells that has failed. On your type of pack the bottom of the battery (negative) will be in a metal case attached to the top (positive) of the next cell. I use a flat blade screwdriver to separate the cells (they are spot welded) and sometimes you can get the case off the bottom of the dud cell, leaving it attached to the positive of the next cell. I suggest you then charge the remaining good cells to see if they all take a full charge. If they are OK you can get a new cell or just make a lower voltage pack. I use a piece of stranded wire to repair the joint. You will need a 40+watt iron and some solder paste, and may need to scratch the battery case and pin for the solder to take. If you were careful with removing the heat shrink you can use it to cover the pack with a bit of electrical tape to make good. Please ask if you need any guidance with the process. I have been doing this for many years and may not have explained in enough detail if it's new to you. Do remember if the battery is charged it can short in its unwrapped state so do make sure you bench is uncluttered and kept clear of any metal objects. Good luck
Hi J. Your motors are nominal voltage 7.2v. Try a single 7.2v 3300 NimH pack, quality from Component Shop. It will be short running time, powering 2 motors but will give you an idea of performance, then you could buy a second, 1 for each motor, if this did not work out or you want more performance then go for brushless motors, still with the 2 battery packs. I would try the single pack first, suck it and see, develop it from there without breaking the bank!!!! Cant see any ESC, have you got 1 or 2? if 1 use a 'Y' lead to connect the second battery. Mark
HI JJ. Your question about a safety bag, Damaged / overcharged lipo's can catch fire, think of the Boeing scandal that grounded the fleet last year. Charging in a safety bag is advised the bag is fire retardant material, which will contain any problem. Your remarks about the boat not coming onto the plane is down to the weight of the battery, my fireboat started with 7.2v NimH packs 1 for each motor, Graupner 700bb's, good cruise but not quick, but short run time, 10mins. I have re-wired to allow 3s lipo's, but not had chance to test it yet, but should go like stink. With a fast hull, weight is important, 4 x lipo packs, 1kg, half the weight and possibly 6 times the power delivery. In your first post you mention 600 motors on 6volts, they are probably rated at 8.4volts, same as my 700's hence the lack of performance, also the battery, at 12ah it should last about 30mins, was it fully charged??? and is it showing at least 6volts, ie not got a duff cell??? Canabus, in his post described an ideal set up with brushless motors, 1600 watts is just over 2 hp, 750 per horsepower so you can see the difference in performance with different motors and battery set up's
I know this will sound very basic to experienced members, but my question is; If I want to use an "MTroniks" Viper Marine ESC, which is rated at 12 volts, and a similarly rated brushed motor, how can I easily get 12 volts out of two 7.2 NiMh battery packs? As you can surmise, my electronics expertise is zero. Brian Hill.
[Score: 7/10] 30"/1600g 80' Elco PT Boat Single Propellor (2 Blade X Type 40mm) Direct Drive to a Turnigy Typhoon 500 Heli (2 Blade X Type) Powered by LiPoly (7.4v) 5Amp/h Batteries Controlled Through Turnigy Marine 60 Amp (60Amps) ESC - Comments: A scratch-built stand-off model based on Model Boats free plan (design by GG). Material mainly balsa wood (hull) and plastic (styrene) on superstructure. Propulsion unit differs from the original design. This is a second set up, not really tested yet. Original set up was Speed 700 Turbo, 12 V NiMh battery pack 4100 mAh, it was 500 g overweight. The only "special feature" are working position lights. It was a pleasure to built and it is pleasure to sail her.
Hi Richard, as an extra to Dave M. the battery packs are different sizes, 5000mah and 3300mah, if both batteries are connected together they will cause problems with power balance, as said the cooling slots are covered. You said the motor was cooking, have you tried it since? maybe it was the ESC that cut out through the overloading with the prop to big. PS what size prop is fitted? The 540 in the 4th pic may not be big enough, a 600 size or even an 850 would give a lot more torque and probably more speed, you can back off the throttle but a small motor will always struggle, and will probably be run at near full power a lot of the time. Hope this helps Mark
Mention was made earlier of the two sets of red and black wires being for separate batteries. The manual says "Do not under any circumstances connect a separate battery pack to each pair of red and black wires - it may seem logical but you will very probably do fatal damage to the P94" I would agree with the previous post from NPJ "slow down and read the manual" There's a lot in there. Hope your tug installation goes well