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Thread: Pick me a Mosfet for a RC Boat

  1. #41
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    Quote Originally Posted by Skepticist View Post
    It's one of those things that spend most of their time at the back of the parts drawer but when you need it, you'll have it. Use it with your CRO & calculator and you can observe those very short spikes that will be shown as 0.75mV/amp.
    The trouble with me is I know I have something but I cant ever find it when I need it so I get piss off but whenever days weeks later I need to find something else I then find the First thing I need to find. I HATE THIS! and this has happened more since I had the Stroke or even I image that I purchased it from Ebay.
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  • #42
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    I have the similar problem misplacing things all the time
    Usually accidentally stumbling upon it sometime later while looking for something else

    You're doing OK

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  • #43
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    Quote Originally Posted by Skepticist View Post
    I have the similar problem misplacing things all the time
    Usually accidentally stumbling upon it sometime later while looking for something else

    You're doing OK
    I try to be tidy and put things away in the correct place but I forgot the Correct place or get confused where it should be.. Good you make feel normal again because I thought it was me only to do this.
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    While I am all for DIY, building a PWM speed controller that has to decode the pulse from the RC is not exactly that simple or even cost saving considering you could just use one of these for 11 bucks:

    or with fan and stronger wiring for less than $18:


    HOWEVER a more unique approach to avoid cavitation(which I compare to wheel spin on the F1 grid) could be a simple two stage switching which you could adjust to always provide the perfect 'take off' while being still a DIY project.

    The idea is one MOSFET switches on the motor in series with a 50W power resistor to get it spinning and start a good water flow without cavitation and maybe 20-100 milliseconds later the second MOSFET switches to full power using this simple adjustable timer module for $3:


    The included relay makes things very simple to switch the MOSFET. The adjuster has at least 20 turns so you should find reasonable adjustment in the millisecond range. The clicking of the relay will help you there. Once you found the perfect 'take off' timing and with the right resistor you will always have it perfect for the race and out smart the others who have to rely on their RC skills using a PVM controller.
    You will be the Hamilton of RC drag-boat racing

    These are resistors I am talking about:


    I would suggest to get two 1Ω resistors which gives you a sensible range between 0.5-2Ω to play around with (parallel, series or just one). So your start up current will hardly exceed 22A (0.5Ω) or only 5.5A(2Ω option). I am guessing 1Ω should be just right. Never mind that the startup pulse is about 120W on the single 1Ω resistor. They can handle that for the 100 milliseconds or even a bit more.

    All the links above are from Australian sellers so you should have it in 10 days or less.
    Don't say you are not in a hurry. It is life and there is never enough time for it.

    As for NOT finding things I am certainly in the same boat as you and Skepticist, have been all my life.
    It comes with the cost of being creative.
    I am more likely to find what I was looking for in a pile of junk than in thousands of boxes stored away in cupboards.
    I compare my mess with the Universe and it all belongs to my theory of "Chaotic Order"

    That said, I do have all my resistors and semiconductors sorted in trays like in a Jaycar store, it are those odd parts where you just don't know where to put them that end up in nomeat's "Universe" and are usually found at later event's or 1 hour after (re)ordered on Ebay.
    Last edited by nomeat; 09-02-19 at 12:15 PM.
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  • #45
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    Maybe consider a heavier duty relay for the switched resistor starting setup. Those automotive 'horn relays' are cheap & rated for 30A or more so are much less likely to suffer from welded contacts & erosion due to arcing.

  • #46
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    Quote Originally Posted by nomeat View Post
    While I am all for DIY, building a PWM speed controller that has to decode the pulse from the RC is not exactly that simple or even cost saving considering you could just use one of these for 11 bucks:

    or with fan and stronger wiring for less than $18:


    HOWEVER a more unique approach to avoid cavitation(which I compare to wheel spin on the F1 grid) could be a simple two stage switching which you could adjust to always provide the perfect 'take off' while being still a DIY project.

    The idea is one MOSFET switches on the motor in series with a 50W power resistor to get it spinning and start a good water flow without cavitation and maybe 20-100 milliseconds later the second MOSFET switches to full power using this simple adjustable timer module for $3:


    The included relay makes things very simple to switch the MOSFET. The adjuster has at least 20 turns so you should find reasonable adjustment in the millisecond range. The clicking of the relay will help you there. Once you found the perfect 'take off' timing and with the right resistor you will always have it perfect for the race and out smart the others who have to rely on their RC skills using a PVM controller.
    You will be the Hamilton of RC drag-boat racing

    These are resistors I am talking about:


    I would suggest to get two 1Ω resistors which gives you a sensible range between 0.5-2Ω to play around with (parallel, series or just one). So your start up current will hardly exceed 22A (0.5Ω) or only 5.5A(2Ω option). I am guessing 1Ω should be just right. Never mind that the startup pulse is about 120W on the single 1Ω resistor. They can handle that for the 100 milliseconds or even a bit more.

    All the links above are from Australian sellers so you should have it in 10 days or less.
    Don't say you are not in a hurry. It is life and there is never enough time for it.

    As for NOT finding things I am certainly in the same boat as you and Skepticist, have been all my life.
    It comes with the cost of being creative.
    I am more likely to find what I was looking for in a pile of junk than in thousands of boxes stored away in cupboards.
    I compare my mess with the Universe and it all belongs to my theory of "Chaotic Order"

    That said, I do have all my resistors and semiconductors sorted in trays like in a Jaycar store, it are those odd parts where you just don't know where to put them that end up in nomeat's "Universe" and are usually found at later event's or 1 hour after (re)ordered on Ebay.
    WOW. More Options. The Trouble is I'm limited with Spare room. Total length is 18 inches and most of it was filled with I think foam. The Boat is designed not to sink if it flipped over which happens easy.
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  • #47
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    No meat has it right here I would suggest to get two 1Ω resistors which gives you a sensible range between 0.5-2Ω to play around with (parallel, series or just one). So your start up current will hardly exceed 22A (0.5Ω) or only 5.5A(2Ω option). I am guessing 1Ω should be just right. Never mind that the startup pulse is about 120W on the single 1Ω resistor. They can handle that for the 100 milliseconds or even a bit more. And a second mosfet for full power , comon 555 timer is easy . frustration yes the cause of stress , my method to this end is not to give a fvck about any thing and classify everything out of ten in importance things below a five are ignored a six is a maybe seven is well ok some time , eight is will it hurt , nine yep tomorrow and ten is if i have to then theres no stress and lifes a breeze lol
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  • #48
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    Quote Originally Posted by Mr 672A View Post
    WOW. More Options. The Trouble is I'm limited with Spare room. Total length is 18 inches and most of it was filled with I think foam. The Boat is designed not to sink if it flipped over which happens easy.
    Well if you can place the resistor(s) right at the bottom it will assist in not flipping over by lowering the centre of gravity but they are not really that heavy. I have only got the 100W versions here and they weigh 30g, so the 50W maybe 20g.
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  • #49
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    Quote Originally Posted by nomeat View Post
    Well if you can place the resistor(s) right at the bottom it will assist in not flipping over by lowering the centre of gravity but they are not really that heavy. I have only got the 100W versions here and they weigh 30g, so the 50W maybe 20g.
    The trouble is WEIGHT!! I fitted a more Powerful motor (figures said this) and I could not wait until I test it and it was a FLOP because more weight made the boat sit deeper in the water, go slower and also drained the Battery faster.
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    Default dont think so

    having been involved in the real hydro i would say that your balancing of the motor is not correct and as a result the boat is not getting up to its planing effiency and looks like a flop
    this is a common mistake when adjustment of the parts stop cavitation and generate lift , most high speed craft sit real low in the water at rest and slow speed . hell i had a 8 foot hydro with 9 inch free board and a skoda 1250cc four cylinder engine. the flywheel was maybe 4 inches from the off spring generating plant with a leg either side of the bell housing where the steering wheel was attached and bum against the transom with the shaft & universal under the seat , to get it on the plane i had to slide myself over the rockercover untill it grabbed and then sit down while all hell broke loose and you were at 65mph half throttle and cannot see a bloody thing because of the spray and the rooster tail 20 yards behind where i though i was at some time , shit it was good fun washing down the crowd with it , so dont be down hearted just work on getting it right the funs just starting cheers don
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    Quote Originally Posted by hinekadon View Post
    having been involved in the real hydro i would say that your balancing of the motor is not correct and as a result the boat is not getting up to its planing effiency and looks like a flop
    Yes I think I need a New hull/boat from Hobbyking in the US. Argh well I have to re think about this as I have noticed the more stuff I put into the boat the slower it gets.
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    can you superglue a bit of string to the heaviest part in the boat and pick it up to see where your balance point is ?? may be the centre of the motor / battery ?? forward and aft port and starboard if your nose down you got a submarine nose up but still have hull in the water but not too much transom in the water is the right track . speed is proportional to waterline length ie longer the faster, then comes center of gravity which is about 3 tenths back and seven tenths forward so the hull is a counter lever for the propulsion and keeps the nose dry . But do you want to know about this stuff ????cheers don
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  • #53
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    Quote Originally Posted by hinekadon View Post
    can you superglue a bit of string to the heaviest part in the boat and pick it up to see where your balance point is ?? may be the centre of the motor / battery ?? forward and aft port and starboard if your nose down you got a submarine nose up but still have hull in the water but not too much transom in the water is the right track . speed is proportional to waterline length ie longer the faster, then comes center of gravity which is about 3 tenths back and seven tenths forward so the hull is a counter lever for the propulsion and keeps the nose dry . But do you want to know about this stuff ????cheers don
    The Motor is in the Middles as I have no Vbox or transfer box fpr the prop shaft so the Motor can be further back. The Batteries are in the Back so I would say most of the weight is in the rear. I think the boat is not long enough and too wide.
    Yes most modern one a sleek and narrow not wide like my one and this I think is the issue as it has to push more water out of the way.
    Yes More info is good for you as If I get another hull I would have to design it better.
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  • #54
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    Default specs

    this begs the question is it mono hull or stepped hydro hull , whats it made of ???? get your ruler out and lets see what youve got maybe a photo ?
    Last edited by hinekadon; 12-02-19 at 10:15 AM. Reason: more
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    Quote Originally Posted by Mr 672A View Post
    The Motor is in the Middles as I have no Vbox or transfer box fpr the prop shaft so the Motor can be further back. The Batteries are in the Back so I would say most of the weight is in the rear. I think the boat is not long enough and too wide.
    Yes most modern one a sleek and narrow not wide like my one and this I think is the issue as it has to push more water out of the way.
    Yes More info is good for you as If I get another hull I would have to design it better.
    Well the resistors might come in handy to better balance it.
    Try hot glueing(lightly) fishing sinkers or pebbles(20-40g) first and see how it goes.
    Last edited by nomeat; 12-02-19 at 11:02 AM.
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