Gentlemen, many thanks for all the feedback. To respond to Dave's questions first: the charger I have been using is an MRC Super Brain 989, and the recorder is an Eagletree Micropower E-logger V2; both are off-the-shelf items and not calibrated. I know there can be some discrepancy between the two, but surely not enough to explain the numbers? I cannot check the temperature of the battery. That will be affected by another variable - charge and discharge current, will it not? As Dave and Doug have pointed out, I made a very, very rough, simple, conservative calculation of mAh looking at the chart. I did not try to be mathematically precise. It was a number for me to explain my question of whether the apparent charge and discharge efficiencies made sense and could they be explained. I have learnt a lot from this exchange and, since I have already acquired 3 battery chargers over the years, I am reluctant to invest in another one only to measure battery impedance. Question is now, does future potential use of such a charger make better financial sense than simply throwing away the questionable batteries and replacing them. Decisions, decisions. One final question, what charge and discharge efficiencies would you expect from a new battery past its "running-in" duration? I am aware that mAh capacities are not based on any recognised standard, but I have been led to believe that the stated capacities of Panasonic and Venom batteries are more reliable than most. Thanks again, Roy
Doug, Regarding your comment, "Avoid using double jointed couplings, they waste power and create wear and noise". Can you please explain this in more detail? I have heard this comment before, but my experience has been quite the opposite. No noise, no wear (yet) and no noticeable loss of power, presumably evidenced by the couplings getting hot. Roy
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
My preferred logo paper is the white waterproof adhesive-backed vinyl made by Papilio for inkjet printers. http://www.papilio.com/inkjet%20waterproof%20adhesive%20film... You may find a supplier in the UK - which is where I presume you are. A UV-resistant spray is all that is recommended. Its adhesive is far superior to that on waterslide transfer paper. Roy
Regarding Doug's suggestion of putting a diode in the red wire from two ESC's, the forward voltage drop in the diode will reduce the voltage at the receiver by 0.6 volt less than the BEC puts out. Is this going to affect the operation of the receiver and everything connected to it? Does the BEC voltage vary depending on the load on the ESC, or is it stable enough? Roy
For someone on a budget, the described methods of recovering a battery may be worth a try. On the other hand, if I have spent a year or two building a scale model, it's not worth risking it for the cost of a battery. Roy
Gentlemen, after charging the packs at 100mA for 24 hours, I stripped off the heat shrink from one pack for testing. Unloaded, 4 cells in the pack showed 1.40 volts on my multimeter, with one cell showing 1.37V - near as dammit to 7V for the pack. With a load applied, the current started at 0.95A, dropping to 0.9A when the voltage fell to 1.15. The one cell was consistently the lowest, but never more than ~30mV. From this test I calculated that the capacity used was 2250mAh. Not the rated capacity of 2550mAh, but almost there. During these tests I discovered that the recording meter that I had been relying on for the previous testing was giving inconsistent readings, a fact I only discovered when I started using my multimeter. This possibly resulted in my considering the battery discharged in previous tests, when it was not. Roy
Dave, I've tested one battery pack as you suggest. With a load of 0.95A the voltage drops immediately from 6.75V to 6.2V, and in just under 4 minutes drops to 6V. I presume this meets your diagnosis that (at least) one cell has failed. You are correct in presuming that my charger is indicating the 1200mAh capacity. I have been charging at 0.8A, which is the lowest current setting on that charger. I now have both packs charging on 100mA, which is the closest I can get to the recommendations from Doug and sidley70, but this charger does not indicate mAh. Roy
I have a related but different question. I have 2 battery packs each comprising 5 new AA NiMH batteries of 2550mAh capacity of a well-regarded and long-established manufacturer. They are not charging up to their rated capacity. I have put them through 6 or 7 charge/discharge cycles and the maximum charge they will take is 1200mAh. The packs will charge to full voltage, around 6.8V, and I discharge them down to 6V. More than one cell must be defective for it to be only half capacity, and how likely is that. Are there any other techniques that might restore the capacity, or are they forever stuck at 1200mAh? Roy
Dave, one of the advantages of epoxy that should not be discounted is that it is almost completely odourless. THat is an especial advantage in places where the winter is long, cold and snowy, and painting and epoxy-ing has to be done indoors. Roy
Maybe you can answer a question about these tugs for me. The plan I have shows large washports in the bulwarks. On all the pictures I have seen it is very difficult to make them out. So my question is, where these tugs built without them, or did they have hinged covers which were tight fitting, or some other arrangement? Too late to make changes to my model, so this is simply out of curiosity.
I have been puzzled by conflicting statements on the web, some stating that adding resin and fibreglass will strengthen wooden construction, and others stating that it will not. For my own understanding I did some tests, which others may find interesting. These are not by any means scientific, and meant only as a guide for me in model construction. The results show that coating balsa with resin and fibreglass cloth does strengthen it. For those who want to see more detail, these are the results. Three separate strips of balsa, each 18" long by 1.5" wide were cut from a single sheet 36" long by 3" wide, 3/32" (2.4mm) thick. Each strip was placed on top of two supports 10" apart. A load was applied in increments to the centre of the span. After testing each strip in its uncoated condition, each one was coated with Deluxe Materials Eze-Kote resin, according to the maker's instructions, and a layer of fibreglass cloth applied on each side. The cloth was a piece I had spare so I don't know what weight it was, but I estimate between 1 and 1.5 oz per sq yd. After coating each strip was tested again. The results are shown in the chart. The lower the deflection when loaded, the stronger the strip. Although all strips were cut from one sheet, strip 3 was clearly stiffer and stronger than the other two in its uncoated state. It benefited least from the addition of the fibreglass. Strips 1 and 2 showed a significant increase in strength.
Now here's a question for the experts. I have two identical waterjets for fitting into a model; same size and same rotation for forward motion. Will I see the same effect as if I had two open water props which were the same? Roy
Inwards or outwards - should the props be turning to meet together above the shaft or below it? Also from Wikipedia "Contra-rotating is where parts of a mechanism rotate in opposite directions about a common axis, usually to minimise the effect of torque. Contra-rotating propellers should not be confused with counter-rotating propellers, a term which describes non-coaxial propellers on separate shafts; one turning clockwise and the other counter-clockwise." Torpedoes are a marine example of contra-rotating props. Roy
I should clarify my comment about 'no sanding' since it's not all 'plain sailing'. The first coat goes on easily and did not, and should not, require any sanding. For the second and subsequent coats, the fibreglass is essentially smooth and does not hold the resin in place so well. So these coats will be fine on a horizontal surface, but on a slope the resin will tend to run, and overlap on a hard edge. If you can ensure that you don't apply too much resin it's fine, but if you get runs, you'll have to sand.
Having now completed fibreglassing a hull using the method shown in the video mentioned earlier, I can say that this has been, by far, the most satisfactory fibreglassing I have attempted. A smooth hard finish with no bubbles, no ripples, and no sanding. So for anyone who has been struggling using the technique of undiluted resin and credit card spreaders, I can thoroughly recommend the video'd method. Roy
I have read on this forum and others that fibreglass has no strength and am puzzled by these comments. Fibreglass is commonly used for building the hulls of full-size boats, including lifeboats, which implies that it has considerable strength. Admittedly, their hull walls are much thicker than on a model boat, but the strength is there. I have seen a fellow model boater take a hull made of balsa, which had been coated with fibreglass and bang it on the edge of a table, with no damage. As we all know, you can poke a finger through untreated balsa. Finally, some data is provided on wikipedia that fibreglass impregnated with polyester resin has a tensile strength of 8000 pounds per square inch. So some clarification of the 'no strength' comments would be appreciated. Roy
Some can do fibreglassing as easily as shelling peas. I have fibreglassed 3 models so far and have yet to master the technique. I've spent far too much time sanding the results to make them smooth. For my next project I plan to follow the guidance shown here:https://www.youtube.com/watch?v=ujk-wBQDUSk. He talks about 'denatured alchohol' which, in the rest of the English-speaking world is referred to as methylated spirits.
I was able to test the new paddle wheels on the water today and they have proved to be the solution to the old wheels digging in. She no longer develops a list when under way. The other advantage is that there's no longer a big wave from the paddles, and it's possible to get up to a realistic maximum speed. Hope to have some video to post in the near future.
Screw holes for holding the support beam in position were marked in the sponson supports and drilled. At this point the assembly could be installed permanently. - Removed the nut and washer from the centre of the master rod and attached the support beam to it; replaced and tightened the lock washer and nut. - Slid the wheel onto the shaft until the locating holes for the support beam lined up with the screw holes in the sponson supports and fitted the screws. - Final check of rotation on the shaft.(see video) - Tightened the wheel drive collar onto the paddle shaft. This was a 3/16” collar drilled for a short length of 1/16” brass rod, which was soldered in and then bent to fit into one of the drive holes near the centre of the inner side wheel. The video shows the motion for the starboard wheel. It has been operated under radio control, but even at its lowest speed it goes too fast unloaded to see the motion clearly. All that is required now is some liquid water to try it out and learn whether the objective has been achieved.
I will be interested to learn how your electronic solution to speed control and steering works. I have not run my model at full speed because the paddle wheel throws up quite a wave behind it and would throw a lot of water onto the aft deck. I typically operate the paddles independently to try and minimise the list, and use the rudder for steering. Roy
A beam was needed to support the pivot for the feathering mechanism. It was made to straddle the gap between the two sponson supports. There’s even less information available about this than there was for the feathering mechanism. My second attempt was the best solution and comprised the following parts. - Two 3/8” lengths of ¼” brass angle; with a clearance hole drilled in the top flange near one end, to suit the small sheet metal screws I had on hand - A length of 1/8” x ¼” rectangular brass tube to span the gap between the sponsons. - Approx 2” length of ¼” x 0.030” thick brass strip - A ½” length of ½” wide by 0.030”thick brass strip - A 7mm length of 3/16” brass tube as a bushing for the pivot. The rectangular tube was cut to length to fit across the sponson supports and inside the paddle boxes. The two pieces of ¼” angle were soldered at right angles under the ends of the 1/8” x ¼” tube. The paddle wheel and the beam were placed in position. The paddle wheel was set up while stationary to position the paddles so that one was on bottom dead centre and vertical. The axial position of the pivot point centre was marked on the beam, and the distance below the edge of the beam measured. The top edge of the ½” square strip was intended to be flush with the top of the beam, and a 3/16” hole was drilled through the former at the pivot point centre. This was soldered to the ¼” wide brass strip, and then the 3/16” tube soldered into the hole. The drill press was used to set it at right angles to the strip for soldering. The strip was joggled, to ensure the rotating paddles cleared the support beam, and with the 3/16” tube on the side nearest the hull. The brass strip was clamped to the support beam, with the complete assembly in place, and the pivot position adjusted to give the optimum motion of the mechanism. The brass strip was soldered to the support beam, and then removed and painted.
The paddles were cut from 0.050” styrene, the attachment points for the support arms drilled, and the support arms fitted and glued in with epoxy. The paddles and the side wheel assembly were painted black, with small pieces of masking tape over the pivot holes in the paddle support arms, where the pivot tubes were glued to them, and painted over later. When it came to assembling the parts, the sequence was as follows: - Fastened one end of the links to the inside face of the master rod (looks like a banjo); using #2-56 UNC bolts with the bolt heads on the outside face, a 4.5mm length of 1/8” brass tube as a bushing, and two #4 washers, and a #2-56 nyloc nut. - Inserted a #4-40 UNC bolt and washer in the centre of the master rod from the inside, secured it with a 5/32” brass tube bushing, lock washer and nut - Fastened the outer end of the links to the paddle arms, with the links on the outside of the paddle arms, with the bolt heads on the inside face, otherwise same as inner end of the links. The next step is to make the support for the pivot of the feathering mechanism.