Hi Roy, I like your want for the answers! I have an eagle tree, great bit of kit, but, you are relying on the given info regarding the battery to be correct. As an example, I have an internal resistance meter, I fly planes, so rely on accurate lipo battery info. The "c" rating, and milliamps on most chinese battery stuff is grossly over egged! as are esc ratings and so on. I wouldnt get too hooked on these stats. If the batt is losing a cell, throw it and get another, its not worth the hassle. Overlay that graph with volts, this should correspond to the amp spikes, and if you have a gps then also overlay speed, faster is more amps is quicker volts drop for enjoyment 😲 check out my amp draw on my Huntsman! Paul
Hmmm! Looking closer at your chart, and the average current quoted at the bottom, it seems your 'rough calculation' could also account for much of the difference! You used 2.55 amps, the chart says 2.04A average. delta is 0.51 A or 20%. Looked at that way the situation gets worse! To get any closer to the real consumption you would need to integrate the whole curve! Rather you than me Gungadin! Cheers Doug 😎
Absolutely correct Sir Dave! There are statistics, lies and damned lies! Test gear calibration was a professional pain in the ... for me for many years. All comments re ambient temperature, internal resistance absolutely spot on👍 Goes back to my comment in the debate you mentioned, pay a bit more for the batteries and you'll get more out of 'em. But unfortunately 'what goes in does not (always) come out' 🤔 The capacities printed on the jacket should always be taken with the proverbial pinch! They are only an indication of perfect performance in 'this the most perfect of all possible worlds'! I remember matched cells too, much more expensive, and not critical for scale ships. Cheers Doug 😎
Hi Roy I can understand your conundrum. My work at one time involved gathering and presenting statistics. The difficult part was knowing what answer was expected. There are statistics and dammed lies and at the end of the day they are at best an indication, but should be taken with a pinch of salt. To try and shed some light: What charger were you using and was it calibrated and if so who by? Same goes for the recorder. Did you measure the temperature when charging and discharging. Looking at your chart I not sure I quite agree with your consumption calculation as the 2.55 amps was at best for no more than 40 mins. Batteries will waste energy in the form of heat and this explains why more energy is required to charge to the retained capacity. We did discuss the battery internal resistance earlier and this can have a real effect on the capacity and the batteries ability to deliver. Assuming your measuring equipment is correct then I believe the differences are likely to be due to temperature variations caused by the internal resistance. If when you charge your pack one cell is noticeably warmer than the rest of the pack it has a higher internal resistance. At one time you used to be able to buy race packs which had been formed from individual cells that had been matched. Cost a lot more but if you were racing with the pack they gave you the edge. Cheers Dave
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, The 600s strike me as very high revving for direct drives in such a twin set up. The the alternative would be the #1793 600 Speed. Remember Fred it has only a 3.17mm output shaft. Weight difference is not dramatically less, 15g. (250-235) Power is only 2/3 (60W) so it will probably 'potter'. Current draw at max . eff. is 1A less (>10%). So I don't see that the 700 needs a significantly bigger / heavier battery - don't have to put the pedal to the metal ALL the time 😉Anyway; Fred already has the 700s, 6316s! 👍 Whatever you do Fred enjoy it not regret it. 😉 Cheers Doug 😎
Hi Fred, I take it you have the 91W version (#6316) see pic for specs. It has a 42mm dia. case and a 5mm shaft. So I would try 2x 35 to 40mm max. props. Shafts: 5mm, if you can, find one with needle roller bearings, try Raboesch (the most expensive of course! But very good and robust.) if you are going for 'all out speed'! Zoom zoom 😉 http://raboeschmodels.com/index.php/en/ If not ball bearings, last resort sintered phosphor bronze bushes. Fit an oiler if the tube doesn't come with one. Will you use a 7.2, 9.6 or 12V battery (or a LiPo somewhere in between!)? Good luck and happy sailing, Doug 😎
Hi Doug Micro and mini servos are great until they break then they are a bin job. That Hitek has a broken drive to the internal pot. I have looked inside and could hardly see the components let alone repair. Had two go on my RG65 yacht. Early bad design of the rudder shaft which rusts and causes the servo to overheat, mine actually melted and the motor was welded. Now replaced with a standard size servo, plenty of room and not really a weight problem as I use a LiOn 6v battery and switch mode supply. 6V burns out the micro servos, as happened with my first servo in the RG65. If it has a 6pin plug it probably is an early Bonner servo. Doubt it will work with modern kit. Might be a collectors item so you could try flebay Good to hear you can upgrade the Flysky/Turnigy sets to 10 channel. Does it support s-bus as this will allow even more channels? Dave
After a slight pause (6 months since last post 😱) have finally found some time between family and work commitments to push things forward a bit. A bit short on workspace at the moment as garage and office is chocca (Hi Dad - when we move house can you look after some stuff for us...?) so have spent some time practicing battery charging, and setting all the electrics and basic R/C controls up on a little test rig. The blue support for the prop drive shaft is a bit of a clip-on folder binder strip I stole. The shaft is held perfectly. I'll keep this in reserve as a possible means of mounting things in the hull, when the time comes. I have a 2000mAh Nimh battery powering a 10A Deans marine ESC. The receiver is a Devolution Devo RX1002, the servo an Align DS520 (both salvaged from my foray in to the lunacy that is R/C helicopters). The motor is a Deans marine KYTE. Just messing with the white metal prop for now, will obviously use the nice shiny brass one I bought on the proper build.
Hi Chris They are all based on 550 motors made by Mabuchi or Johnson. They were GP motors available in different configurations for specific purposes. You can look on data tables to find the exact specs if the motors still have visible markings. The Graupner is designed to run on 8.4volts but the motors can be wound to run on different voltages. I suspect the one with the fan is taken from an electric drill. They used to be popular with the fly boys pre brushless so they are available in large quantities at cheap prices. I suggest you run them with an ammeter connected to a 8.4 (approx) battery and see what current they draw. High current would be good for a fast runaround for 10 mins or so, low current will have more tork and be suitable for a scale cabin cruiser/tug etc. If you have two that draw roughly the same current at the same volts they might be suitable in a twin prop, provided they both rotate at the same speed. Dave
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 Dave, The vessel in question was my Damen 4207, which has featured in an earlier blog. The installation of the LI-PO battery transformed the model, which now floats above the waterline and performs well. I am still trying to get a video and, once the new ESCs are fitted, will try again.In the meantime here is a picture of her underway.
Glad to hear you have solved your problem. Overrunning any system will result in some interesting issues and you are fortunate that yours shut down or failed open circuit otherwise all the electronics could have cooked. If you are getting a separate on-board power source the best option is to go for a switched mode supply, most will give you lots of amps without the heat problems of an ESC and are designed to work with higher battery voltages. You must disconnect any +ve power lead from any ESC to your rx. If your ESC has an on/off switch do make sure it is switched on, preferable before you power up the switched mode unit. Be good to see some pics or on water video Dave
Oh, sorry, i misread the original post. Even if both bec's had been connected, i dont think the situation would be any different. With one esc failing, i have noticed that its a crapshoot, as to what happens next, as i have had times when one has caused the other to fail, and also where the working one has continued at the same speed it was going (but in circles). The other option is to use a desperate battery for the 3rd, and disconnect bother the reds on the esc's. I reckon RHBakers occurrence was one of pure chance personally, as I cannot think of a logical reason for it happening. Best wishes Dave W 😊
Only if you put a blocking diode (rated for the BEC max current) in the positive (red) BEC lines to stop the BECs feeding back into each other. Otherwise you may damage one or both of the ESCs. Not quite sure how the RX would react but I think it would be OK (may depend on the manufacturer /type) and you would have the double current capacity available for servos and functions. Test it on the bench first !! Generally speaking you are right, and this is a problem I might be facing shortly with my twin screw destroyer Hotspur and quad screw cruiser Belfast! The more elegant way of course is to fit a Fail Safe switch which connects either the other ESC supply or a separate battery if the primary source fails. Such switch modules are available (at least here in Germany!) for a few quid. Cheaper than a damaged or wrecked boat! BTW: was the RX still doing anything? Rudder control? Not quite sure why the stbd ESC shut down if the fault was in the port unit! Cheers Doug 😎 PS That's one of the reasons I prefer a separate RX batt when space and weight allow!