[PSUBS-MAILIST] Brushless Thrusters

Wed Sep 10 07:53:12 EDT 2014

AC induction motors can run off a VFD with the DC bus directly supplied - in this case, you only need the inverter stage and not the rectifier stage of the VFD, but there are caveats: the DC bus connections must be available (rare in small VFDs), and the bus voltage must be high (sqrt(2)×nominal motor voltage). This would require either a battery bank offering hundreds of volts DC, or some sort of DC-DC converter to step up the DC voltage into the VFD bus.

Sean

On September 10, 2014 4:04:59 AM MDT, Alan via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>Hi Brian,
>I don't know a lot about them, but I believe you can't run them off DC
>& they are generally heavyweight industrial units.
>Alan
>
>Sent from my iPad
>
>> On 9/09/2014, at 10:48 pm, Brian Cox via Personal_Submersibles
><personal_submersibles at psubs.org> wrote:
>> 
>> Why not just use an AC induction motor then?  
>> 
>> --- personal_submersibles at psubs.org wrote:
>> 
>> From: Alan via Personal_Submersibles
><personal_submersibles at psubs.org>
>> To: Personal Submersibles General Discussion
><personal_submersibles at psubs.org>
>> Subject: Re: [PSUBS-MAILIST] Brushless Thrusters
>> Date: Tue, 9 Sep 2014 22:24:04 +0700
>> 
>> Hi Alec,
>> not sure what motivated me down this path, but eventually it will add
>more to the psub
>> knowledge pool.
>> The brushless motors are used successfully on a lot of rovs &
>expensive submersibles,
>> so I assume the pros out way the cons. Just a matter of learning how
>to put together
>> a good package. The Haswing Protruar brushless Chinese trolling motor
>that Emile uses
>> was a very cheap unit. I made enquiries a few years ago & they
>offered me an ex factory 
>> sample thruster for I think a couple of hundred dollars. 
>> The motors I'm looking at are used on model trucks for racing on
>short courses; so should be able to wind them up quickly. One problem
>is that a lot of motor controllers for them
>> don't have reverse.
>> The motors are so small, you could probably use a standard peice of
>aluminium pipe
>> to house them, & machine the propellor shaft & bearing housing end
>out of a solid tube of
>> aluminium.  
>> Alan
>> Sent from my iPad
>> 
>> On 9/09/2014, at 8:30 pm, Alec Smyth via Personal_Submersibles
><personal_submersibles at psubs.org> wrote:
>> 
>> That is remarkable power for the size, very interesting for that
>reason alone. But it seems to me like quite a challenge to adapt as a
>thruster. I recall Emile's comment that the high-RPM Chinese brushless
>trolling motor he was using required something like ten seconds to wind
>up when you gave it juice. The efficiency makes it great for surface
>runs but not useful for submerged maneuvering. You might have the same
>issue with this if you need to gear it down.
>> 
>> Best,
>> 
>> Alec
>> 
>> On Tue, Sep 9, 2014 at 12:35 AM, Alan via Personal_Submersibles
><personal_submersibles at psubs.org> wrote:
>> Update,
>> Am still Googling away in pursuit of a home made brushless thruster.
>> I am set on using an in-runner motor as they have the coils on the
>outside & will be able
>> to transfer heat through the can.
>> The problem with in-runners is they have higher revs than
>out-runners, however either will 
>> require a planetary gearbox. I am looking at reducing the revs down
>to below 3000 rpm. 
>> This is based on other brushless thrusters I have looked at but might
>not be right ( any recommendations)?
>> Another problem is that most seem to draw huge amps.
>> Here is a 1200W motor for $30-. Of course there is the price of the
>controller & planetary gear that are needed.
>>
>http://www.hobbyking.co.uk/mobile/viewproduct.asp?idproduct=17720&type=&idparentcat=364
>> Most of the suitable motors seem to be found at places like Hobby
>King, and are used on RC trucks, or found on E bike sights. The
>aircraft motors aren't as robust.
>> These motors are tiny, but hugely powerful, so there is the potential
>to make a small streamlined
>> powerful unit.
>> I haven't had much luck with a matching gearbox. Some of the
>planetary gearboxes recommend
>> oiling (no good to me unless I oil compensate) while others don't. I
>am looking for a cylindrical unit to match my motor, preferably with
>thrust bearings.
>> If anyones got any advice or experience in this realm I'd be pleased
>to hear it.
>> Regards Alan
>> 
>> 
>> Sent from my iPad
>> 
>> On 7/09/2014, at 8:43 pm, Alan via Personal_Submersibles
><personal_submersibles at psubs.org> wrote:
>> 
>> Hi Hank,
>> the kort nozzle on the Indonesian thruster looks a bit Naff. 
>> ( I am designing an art work here.)
>> I could get a price for the unit without kort nozzle, but
>> I'm wondering if I could build something for 1/2 that price.
>> There are some reasonably priced brushless motors about.
>> I don't know that I could just retro fit a thrust bearing inside the
>can of the motor.
>> I tried to put a thrust bearing for reverse inside my brushed
>thrusters, but
>> couldn't find one with a thin enough section to fit.
>> Also the motors are a bit expensive to just buy & hope you can fit
>one.
>> How did you fit the thrust bearing on Gamma?  Did the propellor shaft
>extend out the back
>> of the motor?
>> Alan
>> 
>> 
>> Sent from my iPad
>> 
>> On 7/09/2014, at 7:22 pm, hank pronk via Personal_Submersibles
><personal_submersibles at psubs.org> wrote:
>> 
>> Allan
>> Dont worry about thrust bearings to much. They are aesy to get, I
>bought one for Gamma , real heavy duty for 80 dollars. Personally I
>would just use a good quality bearing and replace it once a year for 8
>bucks, if it is a small thruster. Are you not happy with the Indonesia
>thrusters? Or to pricey?
>> Hank
>> 
>> From: Alan via Personal_Submersibles
><personal_submersibles at psubs.org>; 
>> To: Personal Submersibles General Discussion
><personal_submersibles at psubs.org>; 
>> Subject: [PSUBS-MAILIST] Brushless Thrusters 
>> Sent: Sun, Sep 7, 2014 11:58:56 AM 
>> 
>> Hi people,
>> I've spent several hours today looking at brushless thrusters &
>wonder if anyone else has looked at them or got any ideas. There is the
>Indonesian thruster I posted a few weeks back at US 2,200. There is
>also the Haswing Protruar 2hp that Emile has; however they state that
>it's for fresh water only, & I think Emile said it was a bit noisy.
>> The inrunner motors that have the winding on the outside, seem a good
>option as they cool through convection to the can. They also need
>higher revs for torque & require a planetary gear box or similar. (
>which a lot have built in)
>>   I was looking at the option of making my own thruster, however the
>motor would require a thrust bearing & I don't
>> know of any that would have one other than maybe a high powered
>battery operated drill.
>> Any thoughts, suggestions thanks.
>> Alan
>> 
>> Sent from my iPad
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-- 
Sent from Kaiten Mail. Please excuse my brevity.
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