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Thread: Need help to power my 65" long "Klondike"

  1. #1
    Join Date
    Feb 2008
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    Default Need help to power my 65" long "Klondike"

    Back in 2008, I poste 2 threads looking for help before starting to build my scaled model of the Glen L Marine 50' cabin cruiser. In the Glen L catalog it's called the Klondike.
    Needless to say, since this was not to be a "Speed Boat" that would achieve 40+ MPH, not too many people asswerd the threads. One even suggested to use a "trolling motor"

    Well I ended up building my model at a 1/9 scale. It is about 65" long and weight in at 43#.
    Since this semi-displacement hull, I can't use the "power calculator" that I found before writing this thread.

    I have attached 4 pictures. One shows the hull under construction, one show the final product, one shows the motor I used to power up the boat and one shows the original installation with an old 1969 Kraft RC unit and rheostat speed control I was using at first

    The prop that I am using is a 3 blade 2 1/2" diameter. I can't remember what pitch it is. I can only guess at 2.25 buy roughly calculating the angle of the blade.

    The motor is a 12V motor out of an automotive emergency pump and light unit. I gutted the pump and kept the motor and the gear that was driving the pump. It as a 1:5.8 ratio.
    then made a shaft to joint the gear assembly to my prop shaft, As for power, a 12V gel cell battery out of a computer UPS pack

    After using it a few years things got a bit hectic and I had to shelve the boat for a while. When I took it back out last year, my radio system had seized up and was not longer usable.
    So my son in law, which had just started into RC cars and truck, passed me one of his radio system which had a "receiver/ESC' unit, a servo and the transmitter. Unfortunaly i was not getting the speed I had before, which was not very fast to start off with

    doing a few test runs last fall, I was getting 1.8 Knots with the 7.2V and 2.8 Knots with my 12V. base on a "hull speed calculator" I found on line, base on my waterline length, my semi displacement hull should reach 4.7 Knots to mimic the wake of the full size boat at 14 Knots.

    I kneed some input as to weather I should stay with a brushed motor but going to a smaller gear ration, or going to brushless with direct connection to prop, not gear reduction.


    Michel Paquette
    Attached Images Attached Images

  2. #2
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    Feb 2008
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    Default

    The speeds you are after can easily be attained with both brushed and brushless power systems, but if you are <2 knots under your target speed, and it is noticeably slower than it used to be, it seems likely that you can achieve your target by getting your existing stuff running as it should, without spending anything.

    My first step would be to try to get back the lost speed that it used to have, take out the shaft clean it, oil the bearings and check it spins freely, if not the bearings may need replacing. Clean the gears and oil the bearings in the gearbox, lightly grease the gears, spray the motor down with brake/carb cleaner and oil the bearings. Then test for speed again.

    If speed has not recovered with that done, it is likely the ESC calibration with the radio that lost the speed, you say it is an "receiver/ESC' unit" which implies a possibly toy grade all in one unit which I am not familiar with does it have any markings that you could search online to find a manual (or post photos here)? Most stand alone ESCs have a setting to calibrate them to the radio. Does the radio have end point adjustments or a throttle trim? Adjusting those can help if the ESC is not seeing full throttle when you apply it. Some ESCs even have a handy LED that comes on at full throttle so you can check the calibration.
    Paul Upton-Taylor, Greased Weasel Racing.

  3. #3
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    Feb 2008
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    Default

    Thank you for your reply
    First my loss of speed is due to going from 12V to 7.2V. Second, my test in the fall with my 12V was not going thru the radio system, so not a radio system problem. BTW, the Receiver/ESC is a "Dramada RE18v2" (2 in 1 Waterproof 2-Channel 2.4 GHz Reciver/ESC) Yes it comes from a Dramada car, I believe a 1:18 scale. Not a toy grade, but also not an advance grade.
    As for cleaning and oiling the shaft, I have done that a few weeks ago. As it is for the "gear reduction" system I had, I removed it as I was not confident that I could get more speed as there was a lot of "play" in the gears and I believe the ratio was too high.
    So my other son in law (he is a boilermaker and has a lathe) built me an extension shaft to go directly from my motor (1/8? shaft) to my prop shaft (4mm), eliminating the gear reduction.
    Here are some results of a bunch of test I made within the last few weeks using an amp meter and a tachometer. The ?motor alone? is the motor with the extension shaft on it, ?on the bench? is the assembly connected to prop shaft and ?in the water? is with the tail end of my boat in the bathtub. I relies that my bath tub results do not reflect what I will be getting on the water since it is harder to push water with the boat standing still than it is pushing the boat thru the water (at least this is my assumption).
    These are some of the results I was getting:
    With my gear box still in the boat (di not have my tachometer at this point)
    With the 7.2V battery: on the bench 1.8 amp
    In the water 4.0 amps
    With the 12V battey On the bench 1.8 amp
    In the water 7.9 amp

    After removing the gear box:
    With 7.2V battery motor alone 1.0 amp 9000RPM
    On the bench 2.9 amps 7000 RPM
    In The Water 8 amps 1800 RPM
    With 12V battery Motor alone 1.0 amp 16400 RPM
    On the bench 4.1 amp 13300 PPM
    In the water 18+ amps 3000 RPM (test was very short as I was getting heat on my wire connection and I was overloading my amp meter)

    Here are a couple of interesting facts that I have discovered with these test:
    1) A graph of RPM versus amperage is an almost a straight line, so I can estimate RPM for a given amperage
    2) I have also discovered with subsequent test that my motor start to vibrate under 5000RPM
    3) Using the graph, I estimated that when I had my gear reduction, my motor was at 9900RPM with my 12V battery putting my prop at 1707 RPM. And with my 7.2V, motor was at 6000RPM putting my prop at 1034 RPM
    4) The loss between Motor alone and on the bench, could be from one of 2 things. The motor shaft and prop shaft are not quite in line, or also due to the 1/8? hole in the shaft extension beings slightly over drilled as the case usually is when using a drill bit. I had to put 1 layer of aluminum duct tape to make it a bit more ?snug? for these 2 reason I want to use a couple of U-joint between the prop shaft and the motor shaft. I am just waiting for my 3.17 x 4 U-joint to arrive. Then I plan on doing a few more tests to see if there is any improvement.
    5) One more interesting fact. With either 7.2 or 12 volts, my moto runs at around 1390 RPM/Volts in the motor alone setup
    Attached are a few more pictures: one showing my setup to test ?motor alone?, one showing the setup in my boat and one is showing the prop.
    I would appreciate any comments or advise on what I have done so far.

    Michel Paquette

    PS: Spring is coming and I am anxious to get water in the drainage ditch beside my place to do actual water test.
    Attached Images Attached Images

  4. #4
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    Well, it looks like this will be another dead end post. Maybe my replies were just too long and too much useless info.
    So here is my last attempt to get some feedback.

    I am getting a new transmitter/Receiver and a 480A ESC good for up to 80A continuous forward and 60A continuous in reverse. Supported voltage is 2-4S Lipo or 5-12 NiMH.

    I am taking out my 5.8:1 gear reducer and going direct drive with my 12V motor and using a 12V battery.
    If I don’t get to my goal speed, is it worth putting in a 2:1 gear box, or am I better to just go straight to a brushless? My other concern about direct drive is the amperage might be too high in which case I know gearing down will help that situation.

    I am thinking of a Surpass Hobby 3660 3500KV brushless with a 90A ESC. Would this be better than trying to gear down on my Brushed

    Michel Paquette

  5. #5
    Join Date
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    ny
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    so, for brushless, KV is just how many rpm it spins per volt. so, given the 12v, a 3500kv motor will spin way too quickly for what you are looking for, at 31080 rpm not under laod, unless you want to run the 5.8:1 gear box still... your replies were not too long, nor filled with useless info, this forum in general plays with fast electric boats, with displacement hulls somewhat taking a back seat to the racing craft, it may take more than a few days to get the answers you seek.

    my personal opinion, i would try a 1000kv in a 2:1 gear box, at 12v , given the rough dimensions of your prop in the first post, that "should" put your top speed at roughly 7 mph, 6.6 knots, if the prop pitch of 2.25 is correct. you can use the calculator on here as long as you know all the variables. that takes converting your standard measures to metric for the prop, and approximating the battery voltage, i used a 3s battery, 11.1 nominal, 12.6v charged)

    Annotation 2020-03-25 084322.jpg

  6. #6
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    BoogieBoy
    Thank you for your reply and I apologies for my impatience.
    This gives me something to ponder on.
    From what I can see, you have filed out the information on that form already. I do need some clarification on some of these figures.
    I might try to fill in this form for my brushed motor.

    Were does torque constant come from?
    What about the 800 RPM/volt under load?
    And the estimated loaded RPM?
    Is slippage also an estimate? Does hull configuration and weight come into effect on this one?

    Would the test I have done help me to know some of these figures that I need to put in this form?

    I will be patiently waiting for a response this time.

    Michel Paquette

  7. #7
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    Michel, the calculator is a general output indicator designed around mono or catamaran style hulls, the slippage i calculated with is the standard calculation for a mono hull, but i estimate the submerged drive you have on your boat would be similar slippage to a surface piercing prop style of a mono hull due to the blades never coming out of the water and always having a clean supply of water

    . as for how they calculate the torque constant, i dont know. LOL.

    the loaded rpm/volt and total estimated loaded rpm comes from the motor efficiency box, if the motor is 100% efficient, it will spin the exact rpm/volt that it is rated for. if theres a lack of efficiency, that number will be lower...

    the yellow shaded areas are what i input, the rest of it the form calculates for you.


    as for filling the form out for your brushed motor, that's easy. take all the info i had input, and only change the first box to what you have found for your brushed motor, which if i read correctly was 1709rpm/volt, and change the motor efficiency box to 70% for brushed motors. that should let you know about what it would do. you can also play with the gear box section, i set it up as a 2:1 reduction, you can change the spur gear teeth number to what ever ratio you want, i.e, 5.8, 2, 3, and as long as the pinion still says 1, it will calculate that ratio.

  8. #8
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    Cool

    A few comments here.

    The calculator is for small planing hulls, not for large displacement bulls. Prop ?slippage? will be much higher than 25%. The OP doesn't have enough information to complete filling it out without a lot of guesses.

    Today there is no reason to use a gearbox in an electric boat. Twenty years ago sure, we had very limited motor choices then. Today a large, low Kv BL motor will be cheaper and easier, with fewer parts to break/wear out. If he wants to use brushed he has fewer options.

    Because few here on OSE have much experience with large scale boats like the OP?s, he will get more/better answers on a scale boat forum. He should try the sites below, where the posters have actual experience with boats just like his and don?t have to guess at what might work.

    https://www.rcgroups.com/scale-boats-55/

    https://www.rcuniverse.com/forum/rc-scale-boating-103/


    .
    ERROR 403 - This is not the page you are looking for


  9. #9
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    Boogieboy
    I appreciate your efforts, but Fluid is bringing up a good point.

    Fluid
    I will check out the suggested forums. Thanks for the info

    Michel

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