Model Boat Mayhem

Technical, Techniques, Hints, and Tips => BRUSHLESS Motors and Speed Controllers => Topic started by: Tug Fanatic on March 29, 2013, 12:43:21 PM

Title: Can a Brushless Outrunner be too Powerful?
Post by: Tug Fanatic on March 29, 2013, 12:43:21 PM
I am looking at using a brushless outrunner in a towing tug where big props, low revs and fine very low rev throttle control rule.
 
To get the low revs I need a low kv - 350kv is OK but lower is better - motor. I cannot find such a motor unless I go for a much bigger size than I really need. The higher the kv the lower the voltage that I would need. At 350kv I could use 12v. I know that this will give the motor an easy life but what will I loose? Obvious examples might be:
 
1) very low speed throttle control
2) motor efficiency
 
What do you think?
I have seen this motor as an example:
 
  http://www.hobbyking.com/hobbyking/store/__36825__Turnigy_Aerodrive_SK3_4250_350kv_Brushless_Outrunner_Motor_UK_Warehouse_.html (http://www.hobbyking.com/hobbyking/store/__36825__Turnigy_Aerodrive_SK3_4250_350kv_Brushless_Outrunner_Motor_UK_Warehouse_.html)
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: Mad_Mike on March 29, 2013, 03:43:03 PM
Im not sure if i read your post right but if so then your examples of losses are completely the reverse of what to expect. a 350kv motor on 12v would have quite a varied throttle range and on a small prop be extremely efficient. What kind of size prop are we talking about here?
sensorless brushless motors have a low rev limit, so theres only a certian rpm they can go down to before they stop giving back emf feedback, at this point they run lumpy or even stall. This rpm depends on the motor.
 
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: Tug Fanatic on March 29, 2013, 04:07:56 PM
Prop size 65mm or perhaps slightly larger.
The back emf problem is what I meant. With a lightly loaded motor I was wondering how low it might be. I am used, in model boats, to car heater motors that will run extremely slowly - less than 1 rev second & draw 3-4amps.
 
PS I know that 12v x 350kv = 4200rpm which is far too fast for a 65mm prop but to get a lower kv involves an even bigger motor. I could always try 6v!
 
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: Mad_Mike on March 29, 2013, 04:18:00 PM
if thats too fast then use belt reduction dont drop the voltage otherwise youl lose the rev rang. The belt reduction will will keep the rpms up so the motor has no back emf issues, plus it will lessen the load of the motor and increase efficiency.
You could look into sensored types brushless motors and esc's but the only type of sensored motor i know of are car inrunners types and they have usually have quite a high kv. It is possible to fit sensors to outrunners but youd need to look further into this:
https://www.youtube.com/watch?v=XVX5T7JkBDA&NR=1&feature=fvwp (https://www.youtube.com/watch?v=XVX5T7JkBDA&NR=1&feature=fvwp)
If you are getting car heater motors to work why the change? If it aint broke....
 
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: Tug Fanatic on March 29, 2013, 04:47:37 PM
If you are getting car heater motors to work why the change? If it aint broke....

The world has changed. I used to go to the scrap yard with a battery, a tachometer & a wattmeter & have a mooch around & come out with a motor of my choice that was in good condition & which I knew was a match for 1 - that was only a couple of years ago.
 
Now they won't allow the public into the yard and want 25 for one that they have removed especially for me. I can get a new one on ebay for less but I have no idea of the sizes or specs.
 
I note that the cheap 755 & 900 motors have disappeared.
 
Just chewing the fat for alternatives but it appears that ebay pot luck will have to do although I am also looking at the scooter motors which seem to be a reasonable size, 24v 2800rpm and 80-200watt. They are also widely used in the ride on 5" gauge trains.  24v lead acid is however unfortunate and 1400rpm on 12v doesn't sound enough. Wrong forum however.
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: Subculture on March 29, 2013, 06:52:02 PM
Ronne do a small motor rated at 300KV. Also Hi-model do a 225kv motor of reasonable proportions that is used in the Multiplex Funcopter.

For lower than that, you will either have to go for a large motor, or use some reduction, or wind your own.

For very low RPM's I find sensorless motors aren't terribly good, sensored is much better. I'm afraid there isn't much of a market for motors designed for scale boat use.
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: nick_75au on March 30, 2013, 10:13:50 PM
There is no problem running them on lower voltage, the torque is lower but it is still sufficient to drive the prop. Looks like the multi rotor models are using motors now that are a good match


http://www.himodel.com/electric/SUNNYSKY_V3508_380KV_Outrunner_Brushless_Motor_for_Multi-rotor_Aircraft.html (http://www.himodel.com/electric/SUNNYSKY_V3508_380KV_Outrunner_Brushless_Motor_for_Multi-rotor_Aircraft.html)


Cheers
Nick
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: Mad_Mike on April 01, 2013, 11:42:38 AM
The problem here though nick is this guy wants the brushless motor to have a smooth operation right threw entire rev range. From roughly 60 rpm right up to 3000rpm. I dont know weather the motor you have chosen can run down to 60 rpm but as far as im aware to get a brushless motor to run this slow it would need to be sensored, which to my knowledge noone does a sensored esc for boats. I think this is one of those rare situations where the pros of a brushed motor outweigh those of a brushless.
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: Tug Fanatic on April 01, 2013, 12:01:04 PM
I have decided to stick with brushed.
I fly with brushless but have no experience of the very low kv motors.
Thanks for your help.
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: nick_75au on April 02, 2013, 07:47:22 AM
Hi Tug Fanatic, No problem,


Mike
 I have found even with 1000kv motors on 6 volts the RPM is low enough to count revs by eye, your boat wont move with this low RPM unless its a big prop, you do get a slight kick when the motor starts  so the ESC can sense the RPM, some ESCs are better than others at low RPM as well.


Nick
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: Mad_Mike on April 02, 2013, 07:38:06 PM
Ill take your word for it then as you know scale and brushless better than i do. Tug fanatic is talking about a prop 65mm in diameter, Ive never had a boat with a prop that big so i dont know what rpms it would need before it starts to push.
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: essex2visuvesi on April 02, 2013, 11:36:17 PM
if you need around 24v then you could consider 6 cell lipo packs.
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: More Coffee on April 05, 2013, 01:57:43 AM
Ive had pretty good luck so far bench testing brushless..pushing air.
Loaded of course is going to be different....There wasn't that much kick ..most of the low rpm range can be solved by messing around with the ESC settings... however to pull a 90mm prop ..I will need belt reduction on the model .. power, isn't so much the problem as inertia I figure  spinning such a large wheel.  I mean ..you can only do so much with a certain mass before things get ...errr..strange....over coming it and getting rid of it...
http://www.hobbyking.com/hobbyking/store/__36825__Turnigy_Aerodrive_SK3_4250_350kv_Brushless_Outrunner_Motor_UK_Warehouse_.html (http://www.hobbyking.com/hobbyking/store/__36825__Turnigy_Aerodrive_SK3_4250_350kv_Brushless_Outrunner_Motor_UK_Warehouse_.html)
You do realise this motor can produce 1.5 horse power right.
 
 
 
 
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: Tug Fanatic on April 05, 2013, 12:22:14 PM
I know that it can produce 1.5bhp but that doesn't mean that it will unless I load it to the point where it need to.
I would welcome suggestions about a smaller cheaper motor that has a similar kv rating and which will turn a 65-75mm 4 blade kort nozzle prop without complaint. At least this won't get hot! The examples that were suggested above seem to be more expensive than this bigger motor. 
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: Subculture on April 05, 2013, 12:25:18 PM
This one-

http://www.hobbyking.com/hobbyking/store/__26957__Turnigy_Multistar_4822_390Kv_22Pole_Multi_Rotor_Outrunner.html

Slightly larger KV, but not much. Cheaper, will swing that prop easily, and a more suitable power rating, plus loads of poles, which will give very good slow speed running.
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: More Coffee on April 05, 2013, 07:01:50 PM
there 9 on back order {:-{
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: Subculture on April 05, 2013, 07:08:07 PM
Might have to wait a couple of weeks then. Never mind.
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: Mad_Mike on April 05, 2013, 07:25:25 PM
I know that it can produce 1.5bhp but that doesn't mean that it will unless I load it to the point where it need to.
I would welcome suggestions about a smaller cheaper motor that has a similar kv rating and which will turn a 65-75mm 4 blade kort nozzle prop without complaint. At least this won't get hot! The examples that were suggested above seem to be more expensive than this bigger motor.
I dont think you you will find a smaller motor than this with a similar kv. Why does the motor need to be smaller anyway? its still smaller than a scooter motor or maybe even a fan motor, not sure about the latter i cant recall ever handling one. Is it just a cost thing?
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: Tug Fanatic on April 05, 2013, 07:29:14 PM
This one-

http://www.hobbyking.com/hobbyking/store/__26957__Turnigy_Multistar_4822_390Kv_22Pole_Multi_Rotor_Outrunner.html (http://www.hobbyking.com/hobbyking/store/__26957__Turnigy_Multistar_4822_390Kv_22Pole_Multi_Rotor_Outrunner.html)

Slightly larger KV, but not much. Cheaper, will swing that prop easily, and a more suitable power rating, plus loads of poles, which will give very good slow speed running.

Missed that one. Thank you. It just doesn't look big enough but the numbers suggest that it is.
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: Tug Fanatic on April 05, 2013, 07:44:14 PM
I dont think you you will find a smaller motor than this with a similar kv. Why does the motor need to be smaller anyway? its still smaller than a scooter motor or maybe even a fan motor, not sure about the latter i cant recall ever handling one. Is it just a cost thing?

Cooling fan & heater fan motors are truly great motors for big propellers. They pull little current & can generate large amounts of thrust. They are made to run for thousands of hours and many are open motors so you can easily see the condition. I have no hesitation in recommending them for tugs & the like.
 
I am not worried about the size of the motor - it is just that I was asked if I was aware of 1.5bhp. Smaller didn't seem to be an option even though I had no need of such a powerful motor. The 26975 motor is interesting as its size opens up a number of possibilities but I am not convinced - probably my ignorance - that such a small motor will equal a fan motor.
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: nick_75au on April 06, 2013, 01:59:47 AM
Ive used one of these in a test and in my my Axe bow


http://www.hobbyking.com/hobbyking/store/__6246__hexTronik_DT700_Brushless_Outrunner_700kv.html?strSearch=dt700 (http://www.hobbyking.com/hobbyking/store/__6246__hexTronik_DT700_Brushless_Outrunner_700kv.html?strSearch=dt700)


results
55mm 4 blade prop, on 6volts[/size]2200 rpm10 amp peak about 8 amps averageabout 50 watts average,


on 12 volts any of the low KV Multi Rotors motors will have enough power me thinks

Nick
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: Tug Fanatic on April 06, 2013, 11:40:31 AM
This one-

http://www.hobbyking.com/hobbyking/store/__26957__Turnigy_Multistar_4822_390Kv_22Pole_Multi_Rotor_Outrunner.html (http://www.hobbyking.com/hobbyking/store/__26957__Turnigy_Multistar_4822_390Kv_22Pole_Multi_Rotor_Outrunner.html)

Slightly larger KV, but not much. Cheaper, will swing that prop easily, and a more suitable power rating, plus loads of poles, which will give very good slow speed running.

$31 is the international price & it is not available from the UK warehouse. Does anybody know what this will cost by the time I get it in the UK. A guess would be $31 + carriage + import duty + VAT + handlers fees which might add up to a lot more than the 20 price would suggest.
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: essex2visuvesi on April 06, 2013, 11:55:22 AM
Postage on that from HK international warehouse would be $4.99 using the cheapest method


Customs duty is pot luck when it comes to Hobby King..... I have had $300 orders from them that didn't attract customs duty and then $40 ones that have


Best suggestion is be prepared to pay duty and be happy if you don't!
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: Tug Fanatic on April 06, 2013, 12:26:30 PM
Postage on that from HK international warehouse would be $4.99 using the cheapest method


Customs duty is pot luck when it comes to Hobby King..... I have had $300 orders from them that didn't attract customs duty and then $40 ones that have


Best suggestion is be prepared to pay duty and be happy if you don't!

If you do get caught the 20% Vat is obvious but what extra charges do you incur. I am trying to figure a worst case price.
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: Subculture on April 06, 2013, 12:52:19 PM
Never paid any charges on stuff from HK. Pay attention to the checkout process and you can see how you can avoid this sort of thing.
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: essex2visuvesi on April 06, 2013, 01:20:09 PM
Never paid any charges on stuff from HK. Pay attention to the checkout process and you can see how you can avoid this sort of thing.


Yes there is.... and also try to avoid any service that uses DHL or Parcel Force
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: More Coffee on April 07, 2013, 11:41:06 PM
I know i'm in Canada but , generally I keep my orders below $50 , even if it means breaking up the order over a week ..
However its been my experience that every thing Ive had that come in over $100 I get hit.
 
DHL,UPS,FedEx .. it depends ,find out if your shipping charges include the brokerage fee , Ive had various items delivered by all of them , usually with no extra charge or I knew I would have to pay brokerage fee's ..
Good luck.
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: More Coffee on April 07, 2013, 11:51:42 PM
how about these .
http://www.hobbyking.com/hobbyking/store/__23521__NTM_Prop_Drive_50_60_Series_380KV_2665W.html (http://www.hobbyking.com/hobbyking/store/__23521__NTM_Prop_Drive_50_60_Series_380KV_2665W.html)
 
http://www.hobbyking.com/hobbyking/store/__22036__NTM_Prop_Drive_50_60_270KV_2400W.html (http://www.hobbyking.com/hobbyking/store/__22036__NTM_Prop_Drive_50_60_270KV_2400W.html)
 
http://www.hobbyking.com/hobbyking/store/__18539__Turnigy_L4255_500_Brushless_Motor_1100w_.html (http://www.hobbyking.com/hobbyking/store/__18539__Turnigy_L4255_500_Brushless_Motor_1100w_.html)
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: kinmel on April 08, 2013, 07:53:25 AM
These are a popular low reving motor with plenty of torque

http://www.giantshark.co.uk/xyh5055-400kv-brushless-outrunner-p-403284.html
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: Tug Fanatic on April 08, 2013, 02:40:53 PM
Thank you for the suggestions - these are still big motors..
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: Mad_Mike on April 08, 2013, 08:25:58 PM
found a brushed 900 motor:
http://www.ebay.co.uk/itm/MODEL-BOAT-MOTOR-900-HIGH-TORQUE-LOW-REV-12v-24v-CALDERCRAFT-/200912606867?pt=UK_ToysGames_RadioControlled_JN&hash=item2ec7531693 (http://www.ebay.co.uk/itm/MODEL-BOAT-MOTOR-900-HIGH-TORQUE-LOW-REV-12v-24v-CALDERCRAFT-/200912606867?pt=UK_ToysGames_RadioControlled_JN&hash=item2ec7531693)
775:
http://www.ebay.co.uk/itm/NEW-775-Hobby-Motor-18V-36V-2000RPM-Great-for-R-C-Boat-Apps-DIY-/281052956575?pt=LH_DefaultDomain_0&hash=item41700fc79f (http://www.ebay.co.uk/itm/NEW-775-Hobby-Motor-18V-36V-2000RPM-Great-for-R-C-Boat-Apps-DIY-/281052956575?pt=LH_DefaultDomain_0&hash=item41700fc79f)
i think if you want to get the really low rpms but still cheap, id consider buying a cheap motor be brushed or brushless and rewind it to suit your needs, that or a gearbox. Im looking for car fan motors on ebay. Are we talking about the radiator fan or the heater matrix fan?
 
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: Tug Fanatic on April 09, 2013, 09:16:55 PM
Either.
 
I traditionally used the heater matrix motors because they were often protected from the weather but still easy to get at. I then found a very cheap source of new Smiths heater motors but they are now all gone. Unfortunately heater motors have increasingly become buried in the dash but if buying new then that is not a problem. This is a Smiths motor that I used to get but these have a lower stall current than the previous ones that I used - but it does look the same.
http://www.distel.co.uk/asps/details1.asp?ID=NQ34 (http://www.distel.co.uk/asps/details1.asp?ID=NQ34)
or
http://www.ebay.co.uk/itm/Ford-Transit-Heater-Blower-Motor-Dash-Fan-10-until-end-of-March-2013-/251248736080?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item3a7f977750 (http://www.ebay.co.uk/itm/Ford-Transit-Heater-Blower-Motor-Dash-Fan-10-until-end-of-March-2013-/251248736080?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item3a7f977750)
 
Others have used the radiator cooling fan motors which is what I think that I will move over to using as if nothing else I can go round some garages to have a look at them! They vary considerably is shape & size. This is an example only as I haven't even seen a City Rover cooling fan.
http://www.ebay.co.uk/itm/City-Rover-RADIATOR-COOLING-FAN-AND-MOTOR-NEW-/251256081387?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item3a80078bebize (http://www.ebay.co.uk/itm/City-Rover-RADIATOR-COOLING-FAN-AND-MOTOR-NEW-/251256081387?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item3a80078bebize).
 
 
The other motors that have now arrived are the scooter motors which are used in the ride on model railway world but again I haven't tried one. Most are about 2800rpm apparantly:
http://www.ebay.co.uk/itm/Kids-Electric-Scooter-Replacement-Motor-120w-24v-/120633881162?pt=UK_Sporting_Goods_Scooters_LE&hash=item1c1656f24a (http://www.ebay.co.uk/itm/Kids-Electric-Scooter-Replacement-Motor-120w-24v-/120633881162?pt=UK_Sporting_Goods_Scooters_LE&hash=item1c1656f24a)
 
http://www.petrolscooter.co.uk/spare-parts/all-parts-by-type/electric-motors-parts.html?p=1 (http://www.petrolscooter.co.uk/spare-parts/all-parts-by-type/electric-motors-parts.html?p=1)
 
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: Mad_Mike on April 09, 2013, 10:29:34 PM
why is the lower stall current on this motor:
http://www.distel.co.uk/asps/details.asp?ID=38018NQ34&ER=0.673&CY=USD&AP=21.92 (http://www.distel.co.uk/asps/details.asp?ID=38018NQ34&ER=0.673&CY=USD&AP=21.92)
an issue? If you were to stall the motor then it would have a good chance of still working rather than burning out itself and/or the esc.
They seem to be at the same going rate as brushless motors.
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: Tug Fanatic on April 10, 2013, 08:46:27 AM
It isn't an issue except that I ran mine at about 5 amps which is above the stall current of this one. Mine stalled at nearer 10 amps. It suggests that there are at least 2 different power versions of this motor.
At 5 amps they don't get above tepid - although to be fair in a tug you don't use full power very much at all + I always measure the load static so it is probably a lot less at speed.
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: Mad_Mike on April 10, 2013, 07:53:34 PM
this lower stall current would suggest that the motor has more turns and lower kv that your usual motor.
regaurding the static test and im probably wrong but although there is a drop in amperage when the boat is moving i dont think the drop is much unless its a steep pitch propeller. Besides weather the tug is static in the domestic tank or pulling a load in the lake in both circumstances it is subject to propslip. Anyway do you know what you want to do then?
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: Tug Fanatic on April 10, 2013, 09:37:11 PM
As I understand it a scale prop has a pitch 1 to 1.5 times the diameter. The motor in question turns a 80mm prop at around 2500 rpm.
 
2500rpm x 60 minutes x 0.08metres(80mm) x say 1.4 (pitch) = 16.8kph or 10.4mph. I would have thought that say 4mph of model speed would have reduced the load on the motor considerably - but I am probably wrong as well.
I do know what I am going to do. Thanks you.
 
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: Subculture on April 11, 2013, 08:15:13 AM
Most model props are pitched to the ratio of 1-1.5 times diameter. I'd say for electric power you're better going for the lower figure, as you get less slip. Steam models are usually lower in RPM so they need a coarse pitch prop to get the best out of torquey, but slow revving engines.

Even good model props slip a lot more than their 1:1 counterparts, so the model will probably go a good bit slower than 10.4mph at that shaft speed.
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: Mad_Mike on April 11, 2013, 09:48:50 AM
As I understand it a scale prop has a pitch 1 to 1.5 times the diameter. The motor in question turns a 80mm prop at around 2500 rpm.
 
2500rpm x 60 minutes x 0.08metres(80mm) x say 1.4 (pitch) = 16.8kph or 10.4mph. I would have thought that say 4mph of model speed would have reduced the load on the motor considerably - but I am probably wrong as well.
I do know what I am going to do. Thanks you.
so erm... what motor you going with then?
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: Tug Fanatic on April 11, 2013, 10:47:05 AM
I am going to go & measure some of the cooling fan motors that are available new on ebay at local car dealers both to measure them & to look at the fans that they are driving to get some idea of their characteristics. I expect to buy the best (I hope) of them.
 
I would be very tempted with one of the scooter motors but 24v is a bit of a killer and 1400rpm unloaded on 12v is not enough.
 
I am looking at brushless for a smaller model that I am contemplating as I was very surprised to be told by Nick75_au above that some of the motors that I already own + their cell packs (3S 2200mah) will work for such as model. That way I will get a bit of experience of brushless in boats.
 
   
 
Title: Re: Can a Brushless Outrunner be too Powerful?
Post by: Mad_Mike on April 11, 2013, 11:16:18 PM
Ill probably be picking your brains on your findings then %) :D