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Thanks Doug, always appreciate your thoughts. The relays are in a NO mode, so only operate when selected. On the bench works fine. Perhaps you do not have the same modulation issue as you are using 1000Kv and I am 2200. My motors respond rapidly, particularly around the fwd/rev position, so am always trying to accurately centre the lever. The motors I choose have integral cooling jackets and are nicely made. If they had been available in a lower rating would have probably used that. Good luck with the PT boat, looking forward to hearing what you decide with the powertrain. Good luck with the "C" check oug. Best wishes R
Finally the new brass propellers arrived, delayed about a month in one of Canada's regular postal disruptions. After minor modifications to the boss profile (the brass are more streamlined and thus longer than nylon) to give clearance with the rudder leading edges, they were easily installed. Could now refit the electrical equipment previously removed to get access to the shaft couplings. Inevitably took the opportunity to make “improvements”, so then could not get anything to work! After much frustration determined the problem was not from my improvements, but from the cheap and nasty slide switches provided with ESCs. These must have got damp during the test runs and corroded internally. Suggest when using these switches they be consigned to the garbage and replaced with proper toggle ones. Had decided to use the centre brushed motor/propeller for manoeuvring and low speed operation and then the outer brushless for high speed. Brushless ESCs do not modulate smoothly and motor operation is erratic. This was particularly evident when going from forward to reverse and vice versa. Using a lever control Tx, it was also easy to inadvertently operate the brushless control along with the brushed making the model response unpredictable. After some thinking, decided to insert a small relay into each of the white signal wires for the brushless motor ESCs. These relays would be controlled by a RC switch operated by another channel on the Rx. Hoping this way the brushless motors could be switched on and off whenever desired. The two relays would retain the ESCs as separate circuits and avoid any interference between them. The idea worked, can now operate the brushed motor confidently knowing the brushless will not be inadvertently triggered. This means low speed manoeuvers can be gently undertaken using the modulation and control ability of the brushless motors and, by selecting the auxiliary control, can add the high speed capability of the brushless. Am also hoping that when the Li-Pos trigger the low voltage cut-outs in the ESCs, this will retain a “get-home” facility on the brushed motor as that ESC operates independently. Much to look forward to when next on the water.
Used a small 6 - 12 volt pump bought from E Bay. Have used windscreen washer pumps before, but they are relatively heavy and bulky. This was quite compact and light and were closer to my weight restriction.
The pump was installed to give positive water flow even when stationary. Felt this would ensure cooling under most conditions. The plumbing is quite torturous and suspected there might be a significant head drop in the circuit. With the wisdom of hindsight, probably overkill; the water scoop between propellers may prove adequate.
Think a bilge keel should be the first step. My next suggestion would be to add some of the ballast to a removable fin keel, bolted to the underside of the hull. This will increase the righting moment, but not the weight. This can be seen if you examine U Tube videos of cruise ships and liners. They have so much superstructure they are inherently unstable. Have built several freighters and always fit captive nuts into the keel or underside. These are intended for trunnion display mounts, but have always been prepared to bolt a keel on if needed. The nuts can easily be sealed when sailing.
The weather has quickly turned colder, giving an excuse to get back to this model. Stripped out much of the interior and the prop. shafts to replace the nylon propellers with brass. These items all needed removing for painting, so decided to paint the hull before reassembly and then moving onto the superstructure. Fortunately, examining similar naval vessels and several U Tube videos, confirmed the hull as light grey, the deck a darker one of the 50 shades of grey and the lower hull below the waterline black. Used thin Tamiya masking tape to define clean colour separations, followed by regular tape, masked the hull into colour sections and sprayed using “rattle” cans. After the colours applied a light overall Matt coat to subdue any shine. The results are satisfactory. Will now reassemble and move onto building the superstructure and the other fittings. Prior to the season closing decided to experiment with my new Flysky Tx/Rx package, shortly to be fitted to this model. This Tx has a servo limiting function, which was hoping could also be used to restrict ESC output. Would like to make the full speed motor response correspond to full Tx control position. Currently can over power the model; which lifts the stern, causing it to come off the plane and then dig the bow in. Was thinking that if full throttle could be set at around 90% forward control movement and 40% sternwards the model would retain adequate performance, but without being overpowered or very sensitive to control lever movement. As the Brave was not available, tried the idea on my Daman Stan 4207 model. This is brushed motor powered and a good performer. Obviously the settings for the Brave will be different, but at least could try to see if the idea would work – it did! This Tx function is easy to use and adjustments can be made whilst the model is on the water. Once the ideal settings are achieved they can be programmed and then retained in the Tx. Will try this on the Brave when back on the water next Spring.
Although have modeling experience, all my earlier vessels used brushed motors. This was my first brushless. The model is now running well, but thought, for the benefit of others considering this transition to summarize my experiences. Must stress the performance of a brushless motor is incredible when compared to a similar sized brushed; for a vessel such as this they are almost obligatory. They are worth the trouble! Had been advised that the best powertrain installation for a 37” Brave Borderer is either a single or twin screws, not three. This was good advice! Much heartache could have been avoided with a single screw installation. Unfortunately, that is not the correct layout for a scale builder. Tried three major powertrain iterations, with several variations within each group. All motors are 28mm O/D : 1) The original installation used 3 x 4600kV inrunner motors with 30 A ESCs. Had bought these items used. The motors were too fast and had little torque. The ESCs also did not have adequate capacity. The result was erratic performance, a high fuse failure rate and the eventual failure of an ESC and motor Picture #1. 2) First upgrade was to 2 x 2400kV inrunner motors, using 50A capacity ESCs. The centre shaft was fitted with a brushed motor. This combination did work, although suffered greatly from motor “squeal” and “stutter”. Eventually a motor burnt out and failed. Picture #2 3) Upgrade two: retained the 50 A ESCs, with 2 x 2600 kV outrunner motors, again with the brushed inner shaft motor. Reprogrammed the ESCs to soft start parameters. Much better, performance and reliability can now be considered acceptable. The squeal and stutter are largely corrected It has justified the challenges of getting here. Picture #3 Have tried both 2 and 3S Li-Po batteries, suggest use the minimum voltage needed to achieve the desired performance. Higher voltages translate into faster response and performance, but with less control modulation. The model can be easily overpowered. In summary, from my experience. For a marine application; chose low (under 2000kV) kV rating motors with an outrunner layout wherever possible (produce more torque than inrunners). Use ESCs with a ratings comfortably in excess of the motor ratings, fit fuses to supplement any ESC protections. Ensure the ESCs are programmed to “soft start” characteristics. Also, the obvious check of making sure shaft alignment is correct is even more important with the higher speed capability of brushless motors. In spite of the trails, cost and tribulations of getting here. Have enjoyed the challenge and the end result does justify the means. Also, do not finally fit the deck until you are satisfied with the performance. Making the changes described with limited access would have been very difficult and frustrating.
Will be posting a blog update shortly describing my trials and tribulations with brushless motors. By using the "softest" start programmable ESC settings have found the squeal is largely eradicated. If you have not tried them, it is worth the trouble. The slipping coupling will not help, but am sure that will be corrected. I am using solid universal joints, which although noisy, give a positive drive. Your boat looks to go well, but hard to judge from onboard pictures.
Thanks, plenty to look at! Will work though the system and see where improvements can be made. Right now the squeal is intermittent and can be lived with. Once it happens returning the lever to neural and trying again seems to resolve it.
Adjusted the transom flaps and reprogrammed the ESCs to the softest start settings, retested. Until now, the test runs did not have the duration or stability to really examine what was happening. Using 3 S batteries acceleration is rapid and a is plane quickly achieved. However, as the acceleration continues and speed increases, the bow digs in. A cloud of spray then surrounds the model as the plane is lost. Brushless motors do not modulate as smoothly as brushed and adjusting power tends to be erratic or exaggerated. This is a scale model and the propeller shaft angles are per the plans. The thrust from the propeller has two components, horizontal and vertical. The horizontal propels the vessel forward. However, the vertical component forces the stern upwards and, correspondingly, the bow down. Have moved as much weight as possible towards the stern to counteract this, limited by maintaining the correct displacement and waterline. The easiest solution is to reduce motor power, decreasing both speed and the lifting component. Decided to retry the 2S batteries as they give reduced power. A plane is again achieved, but as the motor response is more docile, it can be controlled. If the speed gets too high the bow lowers, as before, but the motor output can be more easily adjusted. Spent a pleasant half hour or so with the vessel accelerating onto and off a nice, controllable plane. Much less spray and drama than with 3S and much more controllable. Have now decided to revise plans and use 2S rather than 3 batteries. A further advantage is the motor noise is muted and now sounds more like a gas turbine than a dental drill! Finally feeling comfortable with the model. Will thus shelve further building until the late fall when sailing in Canada concludes. Want to enjoy the rest of my fleet in the meantime! Will summarize my experiences with brushless motors in another blog shortly for the benefits of others contemplating their use. After restarting the model will resurrect periodic build blogs to advise progress.
Doug, Am sure it can do both of those! So far, have not had a high speed run long enough to really test the brass shafts. I hope to only need to use it for a couple of test runs shortly before will dismantle, make those upgrades and then finish the model over the winter. Rowen
Thanks Colin, will check as intent to strip down and lubricate this winter as the build progresses. Plans are to replace the two outer shafts with Stainless steel, currently brass rod anyway. Not holding out much hope though as have been been through all the obvious mechanical issues already. Rowen
Been researching the squeal and stutter on other websites and conclude RFI is probably not the major contributor. Others attribute it to a mismatch in the ESC / motor timing, which seems more likely. Whatever caused it, resulted in the affected motor failing. Which came first, the failure causing squeal or squeal causing failure is open to conjecture. Much to my surprise the manufacturer has decided to replace the motor under warranty. In the meantime, the motors I had planned to use originally (2800kV Outrunners) came into stock, so purchased a couple. Until now have had to use the ESC default settings as did not have a programming card. This also arrived with the motors. Following advice from another contributor reprogrammed the motors with “softer” start and acceleration settings. Fitted and tried the new motors and settings. On the bench, the squeal and stutter have almost gone. The motors are also more tractable. As the brushless motors are now going to be used for high speed operation only, with slow on the centre brushed, thought could simplify the controls by putting the brushless ESCs on one control system using a “Y” lead. However, this introduced inconsistent and erratic motor responses. Reverted to the two previous separate controls, port and starboard. On the water the performance is fine, as is the reliability. The 2S battery gave almost half an hours operation. The bow lifts nicely with both 2 & 3 S Batteries; plenty of spray. Hopefully resembling a 50 knot vessel! Another adjustment is needed to the transom flaps to try to hold the bow down later as she accelerates. Feeling now to finally be making progress with this model. The squeal has not gone, nor has erratic motor operation. The squeal is high pitched screech, rather like treading on a budgie! When it happens, bringing the control back to neutral and advancing it again almost always overcomes it. The erratic operation happens also when starting and is rather like the motors are not getting a signal to react to the control. Again, returning through neutral briefly seems to correct it. The revised motors and ESCs have increased the weight to 6lbs for the hull including all running gear, excluding batteries and superstructure. Whilst still trying to control weight have concluded this figure is satisfactory as the performance certainly is.
Decided to separate the two power systems; one to the port ESC and motor and the other the starboard. Hope this will reduce interference between the motor systems. Have also reverted to a remote battery powered Rx rather than the BECC system, again to reduce possible interference. The modifications did not resolve the problems. The squeal and stutter are still present, but much reduced. Sounds rather like a slipping coupling, but as these have been checked many times they can be eliminated. Apart from the squeal and the stutter, everything works well. The squeal /stutter occurs at start up, when it happens the control is returned to neutral, If the motor is immediately reselected, usually the problem goes away and the motor runs up cleanly. It only occurs when both motors are selected at the same time. Either runs up cleanly when selected individually. Interestingly enough, did some research on various Model Boats site and found some references to RF interference, no specific solutions though. Also examined some Aero modeling sites as they use powerful brushless motors with ESCs. There is some history of the problem there. Evidently when the mosfets (?) of the ESCs convert DC to AC, RF interference is generated. It can often be addressed by using ferrite rings on the ESC control leads. My latest ESCs actually have ferrite rings, so the problem must have been anticipated. This might account for the latest reduction in squeal and stutter levels. Am at a loss to think of any other modifications, so decided to conduct a water test. Maybe it is a characteristic of brushless motors, but their control response seems “ragged”, not smooth as with a brushed. Anyway, the squeal and stutter seemed reduced yet again, perhaps the water load damped them down. Was able to start exploring both the performance envelope and the viability of the brushed centre shaft motor. First impressions are that on a 2S battery the performance is fine, but it sparkles on 3S. On 3S the stutter and squeal are more pronounced though. Intend to do further trials but, unless something unexpected occurs, now plan to use 2S power. The centre brushed motor idea works well, this layout seems a good compromise. Will design a simple switching circuit to ensure the brushless motors can selected separately. This will avoid the inadvertent operation of both brushed and brushless unintentionally as they are on the same control stick. The brushed can then be used for low speed operation. Returning to the problem of squeal and stutter – has anybody else experienced this and how was it resolved?
Blog 4 update – Adjustable transom flap using metallic tape did not work. Think the vibration caused flexing and fatigue, so it finally split. Fortunately had established the correct angle, so reproduced the flap arrangement with a fixed thin alloy plate. Much more robust. Have installed the new brushless motors and ESCs. The current layout is brushless motors on the outer propellers and brushed on the centre, all powered by a single 3S Li-Po battery and Rx. Am hoping to commence water trails this week, but have found an issue which was also present with the original brushless motors. When either brushless motor is powered up it operates nicely, however, as soon as the second motor is started either motor “stutters” and a pronounced “squeal” can be heard. The brushed motor is unaffected. Have now tried several ESCs but to no avail, the issue remains. It can be cured though by powering each brushless motor with it's own battery. When this is done everything powers up cleanly and quietly. The obvious solution is to use two Li-Po batteries and abandon the single battery approach. Am reluctant to do this as the model weight will increase yet again. Has anybody experienced this when using twin brushless motors and, if so, how was it resolved?
This hobby gives countless opportunities for changing ideas! After some thought, have decided to try another approach. Whilst brushless motors give fantastic performance; so far have had poor experience of system reliability. As more information and advice from other modelers is gathered, suspect have been using undersized ESCs, accounting for many of the problems. However, whilst still waiting for the new brushless motors an idea developed. To instal a brushed motor on the centre shaft, whilst retaining brushless on the outers. My thinking is this could provide several advantages such as; a better slow speed performance more suitable for manoeuvring, lower current draw, improved fuse life and a reliable BECC output. It will also operate at below the Li-Po cut-off voltage, giving a “get home” facility in the event the brushless ESCs cut-offs operate. However, there is a slight weight penalty as brushed motors and ESCs are heavier than brushless. Fitted a brushed motor of the same O/D and mounting arrangement as the previous brushless to minimize installation issues. With a reliable Mtroniks ESC from my stock and suitable fuses, fitted these items along with the ballast and battery used earlier. Now, back to the pool. The system worked well. The vessel speed is much less than with a brushless motor on the centre shaft, but control-ability greatly improved. With the triple rudders she steers nicely. The thought of using a brushed motor on the centre shaft, with a brushless motor on each of the outers is attractive. It is hoped the additional operation of the outers in conjunction with with the centre shaft, will provide the expected performance. The centre shaft would then also provide manoeuvring and reliability with the outers shut down. If this works, think this power-train combination could be ideal. Once the new brushless motors and ESCs arrive will instal and report. On the attached pictures, the first shows the ballasted model sitting with the brushed centre shaft motor, the second with a brushless. The difference in draft is imperceptible, the bow sits slightly high in both cases. The third shows the model with the brushed centre shaft operating only at “full” speed.