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Hi Graham, There have probably not been any answers so far because we are most possibly speechless. If you go back and read through the comments above you will see that most of the problem has been the large overpowering of your boat (1690 Watts - according to info provided by DaveM), coupled with an inadequate drive train. So with all this knowledge available you have asked our opinion of the Graupner 500ECO - one of the largest motors in that range. This is quoted at 1440 Watts. This may not rip the drive train out as quickly as the other motor did but has enough torque to do so. In my opinion I think you could try a motor producing under 500 Watts and see how that goes - with a 5mm shaft.
Thanks Dave, Eventually we will have put together a body of knowledge that model boat builders can use with some certainty. At present the information is sketchy, hard to find and sometimes ambiguous. The motor designers and manufacturers have not been very helpful. For my La Combattante iii missile boat I used two Hobbyking Keda 720kV motors rated at 215 Watts and 19.3amps max. They were the first brushless motors I tried. I was not sure how many amps they would draw, so I connected an ammeter and fitted my video camera so it read the amps whilst operating. At full speed they used only 8 amps each. Each of the batteries is from 12V made from 9 x NiMH 9Ah D Cells. I easily get over an hour run time at good speed. The boat is 1605mm long so not small. This information may help someone.
Graham, I have attached the same table that Doug sent me. This has the relevant information you seek. According to the table attached the Graupner 500 kV ECO has a specified output of 1440 watts and 80Amps. Strangely the 400 kV ECO has a specified output of 2010 Watts. So the 1440Watt output is questionable and may be a typo based on the other entries in the table. more likely to be 2440Watts In any case you need a 5mm diameter propeller shaft. For shaft alignment i use a brass tube that slides snugly on the propeller shaft and then on the motor shaft. When the tube rotates/slides well on both then the shafts are aligned. I then fit the motor mounts, check and tweak the alignment if necessary, remove the tube and replace with a universal coupling. If the motor or propeller shafts are a different diameter then I insert the relevant size smaller tube inside the larger of the tubes. This method is simple and has served me well, including for larger IC engine powered boats belonging to friends. Haig
Thanks Dave, In common car language that is a V12 in a Ford Fiesta, with the Fiesta drive train. In some ways I believe the brushless motor manufacturers/sellers are responsible for the confusion. Mostly we see the kV, physical size and the number of Lipo cells required. You need to dig deeper to find out the Watts. The kV basically gives the RPM only. No mention of amps and power. We don't buy cars and motorcycles based on the engine RPM do we? Typically if you look at the reputed Graupner Speed Brushless range, they have low kV specs, but the differences between a 400kV 7.4V, 400kV BB 11.1V and a 400kV ECO 14.8V are 130W, 1100W and 2010W respectively. A huge difference. When viewing the on-line retail sites, including Graupner, they all look the same (maybe the same photo), but they are all very different motors. Without the rated amps and Watts (not published) the buyer is left unclear as to what they should buy. Brushed motors are more clearly defined. I must thank Doug for helping me out with Graupner brushless specs when I required assistance.
I get my Raboesch propellers from Cornwall model boats - and I am in Australia. It would be very interesting if there was a video made at the start of this post. How many Watts of power is that motor producing. That is the question I would have asked at the time.
[Score: 8/10] 64" HS Smitzopoulos Twin Propellors (3 Blade 35mm) Direct Drive to a 2 x 720kV (3 Blade) Powered by NiMH (12v) 9Amp/h Batteries Controlled Through 2 x Turnigy 30A (15Amps) ESC - Comments: La Combattante IIIB Class Guided Missile boat of the Hellenic Navy. It has two brushless motor systems (each described in the table, drawing 8 amps max). All four gun turrets can rotate and the main guns can also elevate. Radars both rotate. LED running lights. Hull is from balsa and marine ply with a fibreglass skin. Deck and superstructure is balsa. Masts are from brass tube.
Vosper 73ft Type 1 MTB - Scratchbuilt. Now running two brushless motors and NiMH batteries. Photos previously posted. 1/24 Scale Fairmile D MTB623 belongs to a good friend. This boat was also featured in a previous video with my Fairmile D. The lake was a bit choppy with realistic sea conditions.
Scratchbuilt WW2 1/24 Scale Vosper 73' Type 1 MTB. Built in 2016, in company with a friend's 1/24 scale BPB MGB. The Vosper hull is built from balsawood and fibreglass. The upper deck and superstructure is from balsawood. The weapons and fittings are from brass, aluminium and plastic. The 20mm and gunner can rotate.
1/35 Scale model of the La Combattante IIIB Class Fast Missile Boat of the Hellenic Navy. The boat is scratchbuilt. It is 1606mm long. It has 2 brushless 720Kv motors and NiMH batteries. The 76mm guns can traverse and elevate. The 30mm guns can traverse. Both radars rotate and there are LED running lights.
I tried a few different grades of oil and found that if the inside end of the prop tube is close to or below the waterline then some water always seemed to enter the boat, as well as leaving an oil slick in the lake. You also need an oiler tube. Light grade marine grease - whilst offering some friction initially soon eases off on the friction (via a quick run-in), whilst offering a good seal. I have ships, patrol boats and submarines and they all have marine grease. I re-grease the prop tubes/shafts once a year for the frequently used models and others once every few years. I also tried Lithium grease, but it always remains sticky and so does the friction load. In most cases this is great grease except for prop shafts. Choose what ever you are happy with.
Hi Seafarer, I have a few ships with rotating radars I have a few of these motors per the link below. They rotate quite well with one cell (1.4 volts) Gear Motor 3 - 224:1 90 Degree Shaft https://solarbotics.com/product/gm3/ I also have some of these, but they require a bit more vertical space. MFA 951 Series Motor and Gearbox 298:1 6volt (from CMB in the UK). I run these on 3 volts. Both are quite small. I have also used old servos in a couple of places.
Richard, If as you said each blade from shaft centreline to tip of blade is 30mm then it would not matter if you had two blades or ten. If the radius (your measurement) is 30mm then the diameter is 60mm. Perhaps you can remove the prop and place it on a flat surface so you can see the swept circumference when rotated.
Hi Richard, If each blade is 30mm from the shaft centre, it is a 60mm diameter propeller and is far too big for that size motor. For performance you need a larger motor say a Graupner 700 and I would still recommend a smaller propeller.
Hi John, Have you contacted Mtroniks about this at all. I have never received any answers to my email queries, but a friend of mine telephoned them with a query and they helped him. I agree with Dave and Doug too, but you have not yet told us if you have tried with a separate power supply to the Rx instead of the BEC.
John, Before you get any more ESCs here are a two basic things to try. 1. At the water's edge (on the stand) start the motors (both). Check their rotation. Then lower the boat into the water and see what happens. Either it should continue in the forward direction or it will stop and then go into reverse. Separately 2. Plug ESC into one radio channel and plug the other into another channel. This is a test - each ESC will be totally independent. Also we don't want use the BEC. I have had problems of a similar but slightly different nature with my Fairmile D previously, except that one of the motors would just stop after 15 or 20 seconds. Now I have each ESC running off a separate channel on the radio and the two channels are mixed so there is a master and slave channel and I use the single throttle stick to operate it. It works fine.
Hi Tica, From the question posed it was a sensible proposal. Please don't give up on offering help. I was not aware that RC gear needed to be set up for brushed motors or otherwise. I use mine for both brushed and brushless applications and I also have electronic ESCs as well as the old variable resistor types.
Another thought - The main difference between the bench and the water is the load on the system - ie increase in amps. This load may cause the reduction in signal and into failsafe? What size propellers are in use? Maybe a test with smaller props. I would also test without the BEC.
Hi John, I have a several MTroniks ESCs. If you have the Plug & Play type, then when you first start you need to move the stick forwards and then back. I find that sometimes they refuse to go forward and prefer reverse when the stick is moved forward, so I move the stick backwards first. This usually works (although I don't know why). I do not use the BEC (my choice). I have also had issues with using a single 30Amp Tio ESC running two 12V motors via the single ESC in my Vosper MTB. No answers from MTroniks. Regards
Both Fairmile D boats 1/24 scale and are scratch built. They have both been about 6 years in operation. MGB623 is an MGB, flying the Norwegian flag and belongs to a good friend. Mine is MTB741. It is powered by 2 Graupner Speed 700 12V motors with NiMH batteries. The 6 pdrs and 20mm guns can rotate. It has a balsa planked hull and fibreglass skin. Decks and superstructure are also balsa. Guns are from tinplate and brass.