[PSUBS-MAILIST] Motor Suggestion?

Thu May 17 02:58:53 EDT 2018

Thanks Steve,
will pass the esc info on & post on the motor tests when I eventually
get into full swing.
Cheers Alan

Sent from my iPad

> On 17/05/2018, at 12:08 PM, Stephen Fordyce via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> 
> Hi Alan,
> My comment about continuous duty was more in relation to heat dissipation, but that's really interesting to hear about the mechanical limitations (my ambient housing includes the prop shaft and bearings already, so I just have to mate the motor to the shaft and mount it).
> 
> The good thing about the VESC is you have full control of all the parameters, and you can also run a detection of the motor settings.  So cogging should be fixable.
> 
> Regarding bluetooth/Android, I'm not sure whether your friend is trying to reinvent the wheel.  Buy the bluetooth module from https://metr.at/shop
> (no, the cheap Chinese alternatives don't work) and download the Metr (monitoring) and Perimetr (changing parameters) apps on Android.  You'll be up and running on bluetooth in minutes (works on the latest stock firmware).  Limited to PPM/UART control, but I can lend a hand with firmware changes if you're trying to do some other control method.
> 
> Setup instructions here: https://metr.at/setup
> 
> For anyone else that's interested, the VESC can control DC motors as well.
> 
> Cheers,
> Steve
> 
>> On Thu, May 17, 2018 at 7:17 AM, Alan via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>> Steve,
>> re your comment on the rc motors not being designed for continuous use.
>> Most motors of the 6374 size don't have a can/bell bearing. My Saite
>> motor didn't. All the torque from the rotating can is transferred through a
>> small area where the propeller shaft is press fitted & secured with a couple
>> of grub screws.  I made a stainless propeller shaft & put in an extra grub
>> screw to secure it but in time (30 hrs) the end of the can would pull against
>> the magnets when the motor came to a stop. So a slight bit of wear or bad
>> press fit caused a slight tilt of the can & because of the small air gap a tiny
>> bit of error has a large effect on the other end of the can.
>> The Turnigy SK3 aero drive 6374 has a can bearing. I had one that I crudely
>> tested in the pool initially (149kv). Just stuck a prop on it & lowered it in without 
>> a housing. It was cogging on very slow speeds & that is why I have gone for
>> sensored motors. There have been improvements in escs since then & the
>> Vesc may be better on sensorless mode.
>> Do you know who makes the Turnigy SK3? I would like to try one with 60kv.
>> I am suspending my motors between two housing bearings that take all the 
>> lateral load & are happy with the construction of the motors apart from the
>> lack of a can bearing! The 8085 looks to have one!
>> BTW the Saite motor was US $60-.
>> Cheers Alan
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> Sent from my iPad
>> 
>>> On 16/05/2018, at 1:21 PM, Stephen Fordyce via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>> 
>>> Hi James & Alan,
>>> My trials with the Maytech 6374 brushless motor did not go well, although the VESC is amazing and I cannot recommend it highly enough.  Bit of a learning curve, but I can now change all the parameters and monitor everything (temperatures/voltage/current/RPM) via bluetooth and Android smartphone.
>>> 
>>> Maytech recommended the 6374 motors based on the specs I gave them, and promised they would have certain resistance, etc.  Well, they arrived and didn't, so were only running at 50% efficiency with the propellor loads (roughly 27V, max 20A, ~500W, 800RPM) I put on them, and quickly triggered overheating protection as a result.  So if anyone wants a 6374 60Kv or 70Kv (I have one of each) let me know - I'm hoping to try the 8085 which is the next size up, but may have to go elsewhere if Maytech don't want to take the 6374s back or refund me on them.
>>> 
>>> It's critically important to match (at least ballpark) the motor and prop - and both are highly variable (just think about the infinitely variable number of coils and prop pitch).  Otherwise a huge chunk of your electrical input power is turning to heat and you may not even realise (I suspect this may have been happening to Alan with some of his issues).  Just because a motor is rated to however many volts, amps or watts, doesn't mean it will perform well outside of the sweet spot.  Efficiency is difficult to determine because it's hard to measure power out - but a good approximation can be found from the motor curves.  I have a spreadsheet/calculator if anyone is interested - email me direct at stephen.fordyce at tfmengineering.com.au .
>>> 
>>> The prop has a performance curve and so does the motor and matching them scientifically is a bit of an art form.  But apparently a good rule of thumb is to start with your prop RPM and torque under desired load.  To find nominal unloaded motor speed, multiply loaded RPM by 1.25.  Use this with your battery voltage to determine the Kv of the motor.  Then use the required prop torque to determine motor current and size.
>>> 
>>> I'm finding that often the RC motors are not well designed for continuous operation and the associated cooling, so they need to be derated significantly, or better cooled.
>>> 
>>> Cheers,
>>> Steve
>>> 
>>> 
>>> 
>>>> On Wed, May 16, 2018 at 9:01 AM, Brian Cox via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>>> Yes I am a proponent of golf cart motors as well.   If you can find a place that repairs them you can find some good deals.  Best plan is to just make multiple back up motors and switch them out if you have any problem.
>>>>  
>>>> Brian
>>>>  
>>>>  
>>>> 
>>>> --- personal_submersibles at psubs.org wrote:
>>>> 
>>>> From: hank pronk via Personal_Submersibles <personal_submersibles at psubs.org>
>>>> To: Alan via Personal_Submersibles <personal_submersibles at psubs.org>
>>>> Subject: Re: [PSUBS-MAILIST] Motor Suggestion?
>>>> Date: Tue, 15 May 2018 22:15:05 +0000 (UTC)
>>>> 
>>>> James, for an inboard motor, you can't go wrong with golf cart motors.  They are available in 48 volt and up to 8 hp I think.  These motors are extremely durable and cost effective.  Gamma has a 2 hp traction motor from a tenant sweeper, same as golf cart.  At full load it barely gets warm.  
>>>> Hank
>>>> 
>>>> On Tuesday, May 15, 2018, 3:28:36 PM MDT, Alan via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>>> 
>>>> 
>>>> Hi James,
>>>> just had a look at the motor & it's a bit of a beast.
>>>> Looks like an in-runner. It says elsewhere it is cooled with a fan but has
>>>> the option in the check box for air or water cooling.
>>>>    If you have a look at the Dragon submersible, they have gone with some
>>>> large diameter but short motors that resemble the high torque direct drive
>>>> bicycle hub motors that are popular. On the Dragon submersible it looks
>>>> like they have developed thier own propeller so that the thrust isn't hitting
>>>> the body of the thruster.
>>>> The cooling system on your motor isn't going to work if you put it in a water/
>>>> pressure proof enclosure. With the in-runner the coils are on the outside
>>>> & can dissipate their heat through the can, so there would be the option
>>>> of fitting the motor tightly in to a housing & letting the heat go through the
>>>> housing into the water; but the fins on the motor won't let that happen in
>>>> this case. Maybe grind them off. It has a temperature sensor so there is the
>>>> option of monitoring the temperature & running it at a suitable power. Some 
>>>> escs can drop the power automatically if the temperature gets too high.
>>>> The motor is very expensive. There is this Maytech motor designed for electric
>>>> surfboards that is rated at 600W
>>>> http://www.michobby.com/product/electric-surfboard-skateboard-e-bike-brushless-motor-8085-160kv-motor/
>>>> It is an 8085 160 kv out-runner & priced at $188- US. I am wanting to test 
>>>> one of these but will test my smaller motors first to get a better idea of what 
>>>> kv winding I should have. Maytech will wind to your specifications; I think you 
>>>> have some knowledge of the RC world so you will understand this.
>>>> This motor being an out-runner has the coils on the inside & so I am relying
>>>> on oil for cooling. 
>>>> You will need to replace the propeller shaft with a longer stainless shaft.
>>>> Your motor is designed to drive a pulley & you would have to check
>>>> what axial load the bearings take. In my thruster design I have my motors
>>>> suspended between two bearings in the thruster housing that take the
>>>> forward & reverse axial load.
>>>> Alien Power in England have some large brushless motors & motor controllers.
>>>> I think he's a small operator & he will respond to questions. Got an idea he's
>>>> in Birmingham.
>>>> I am focussed on my thruster testing at the moment, but could not put a 
>>>> time on when I will test the 8085 motor. You can keep an eye on my progress
>>>> if you want to hold off your thruster build.
>>>> There is an electric surfboard site that are using large DC motors, that may be
>>>> of help, but these boards are doing 40kph, so are more like planning boats
>>>> rather than submarines that fall in to the work boat category.
>>>> Good luck.
>>>> Alan 
>>>> 
>>>> 
>>>> 
>>>> 
>>>> Sent from my iPad
>>>> 
>>>> On 16/05/2018, at 3:51 AM, James Frankland via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>>> 
>>>> hi all
>>>> 
>>>> I am thinking about what motor I should use for my main thruster on
>>>> Skadoc.  Its got to be big.
>>>> 
>>>> All these ideas are just thoughts at the moment, as I am working on
>>>> battery pods now.
>>>> 
>>>> Expecting delivery of pipe from UK today.
>>>> 
>>>> So I have time to think how motor configuration is going to work.
>>>> 
>>>> What do you guys think about this motor choice here?  As a possibility.
>>>> 
>>>> https://www.miromax.lt/en/m-6/c-39/c-45/product-500-bldc_motor_hpm-5000b_-_nominal_power_5-86kw
>>>> 
>>>> I have room for 12 x12v batteries, so all voltages are a possibility.
>>>> 
>>>> I am also thinking of running an inverter and working at 120v AC.
>>>> investigating this.
>>>> 
>>>> Regards
>>>> James
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