Model Boat Mayhem - Forum

Technical, Techniques, Hints, and Tips => BRUSHLESS Motors and Speed Controllers => Topic started by: barriew on September 06, 2010, 08:55:38 PM

Title: Looking for small brushless/ESC combo
Post by: barriew on September 06, 2010, 08:55:38 PM
I want to try a small brushless motor in my 46cm Huntsman 31. Its currently got a 385 (I think) on 7.2v, but its not as fast as I would like. I have been advised a small brushless of about 100watts would be ideal, but I cant seem to find anything in that range. Giant Cod seems to be out of stock of most of his marine equipment, and anything else I can find is too expensive. This is only an experiment - I dont want to spend hundreds.
Any suggestions?

Barrie
Title: Re: Looking for small brushless/ESC combo
Post by: Shipmate60 on September 06, 2010, 08:59:14 PM
Use a brushed motor in her.

Bob
Title: Re: Looking for small brushless/ESC combo
Post by: nick_75au on September 07, 2010, 06:45:42 AM
He wants to use a brush-less, so what sort of advice is that >>:-(

an out-runner in the 22mm or 28 mm size, I'm guessing that you want around 10,000-15,000 RPM and guessing  a 35 mm prop.
This calls for a 1300 to 2000 Kv motor using your 7.2 volt battery

http://www.giantcod.co.uk/keda-thumrun-283708-outrunner-brushless-motor-p-403686.html

http://www.giantcod.co.uk/keda-thumrun-283710-outrunner-brushless-motor-p-403685.html
couple of examples

http://www.giantcod.co.uk/hobbywing-seaking-marine-reverse-program-brushless-p-403646.html

though if you just want to experiment get a cheap 10-15 amp airplane ESC (no reverse)

http://www.giantcod.co.uk/18-amp-esc-c-21_88.html

Nick
Title: Re: Looking for small brushless/ESC combo
Post by: barriew on September 07, 2010, 07:21:11 AM
Bob - I have a brushed 385, but with a 7.2 volt pack its too heavy, therefore slow. I do intend to try it with a 6v AA pack.

Nick - thanks for the advice. I think I can find suitable motors at a reasonable price, it was the ESC that was defeating me. It might be an idea to try a forwards only if I can't find anything else. There is no great rush as I'm off on holiday for a couple of weeks - maybe GC will have re-stocked by the time I get back ok2

Barrie
Title: Re: Looking for small brushless/ESC combo
Post by: nick_75au on September 07, 2010, 08:38:16 AM
Ok weight is an issue.
The motors I linked to might actually be too big, they are the same weight as a 385/400. I would suggest the 22mm motors then.

like this

http://www.giantcod.co.uk/a220814-1450kv-brushless-outrunner-motor-p-402432.html
I've got a similar 1000 Kv driving a 8 lb springer so no problem with power, it will be able to overcome the weight of a 7.2 pack. there are quite a few reversing brushless escs out there, they are just a little harder to find, Pulso/X-power are good as they operate as a proper boat ESC without the annoying double tap to get reverse that most car based esc's seem to have.

http://www.pulso.co.uk/product_info.php?cPath=22_25&products_id=43

Nick
Title: Re: Looking for small brushless/ESC combo
Post by: HS93 (RIP) on September 07, 2010, 09:03:46 AM


Look at this for some ideas a tested setup so no risks.


http://www.modelboatmayhem.co.uk/forum/index.php?topic=25584.msg251308#msg251308

peter
Title: Re: Looking for small brushless/ESC combo
Post by: malcolmfrary on September 07, 2010, 10:21:28 AM
Quote
I do intend to try it with a 6v AA pack
That might not be able to deliver the current demanded by the motor.
Title: Re: Looking for small brushless/ESC combo
Post by: barriew on September 07, 2010, 01:02:17 PM
That might not be able to deliver the current demanded by the motor.

Yes _ I realise that, but I have the pack so there's no harm trying before I spend money on a brushless setup. I am after all a Yorkshireman (in exile) and I rather like the description of us given by a distinguished fellow Yorkshireman, as Scotsmen with all the generosity squeezed out of %%

Barrie
Title: Re: Looking for small brushless/ESC combo
Post by: Subculture on September 07, 2010, 08:06:50 PM
You could try fitting a lipo pack in place of nicads/NiMH that will reduce the weight drastically and provide more than enough oomph!
Title: Re: Looking for small brushless/ESC combo
Post by: barriew on September 07, 2010, 08:26:52 PM
Yes - that looks the next step after the AAs

Barrie
Title: Re: Looking for small brushless/ESC combo
Post by: triumphjon on September 07, 2010, 09:01:04 PM
if its too slow on 7.2 why not increase the voltage ?
Title: Re: Looking for small brushless/ESC combo
Post by: roycv on September 07, 2010, 11:41:34 PM
Hi I have a 30 amp bi-directional brushless esc cost about 23 with p&p from web site below.  You don't need a programme card as the default is 50 / 50 fwd and reverse.

http://www.r2hobbies.com/eng/proddetail.php?prod=rcps81707_30

I have just bought a cheap motor and they seem to go together very well.  I bought 2 and offered 11 and it was accepted, but they are about 6 each.  These are outrunners, go for the lowest XXXX / volt you can find. these are 1540 rpm / volt

 http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=120462710842

You do not get the low motor speed you can get for brushed escs but this combination looks OK and goes slower than I expected.  I have just mounted it into a boat and will test later in the week.
I am just running on 7.2 volts and there is more power there than I had previously with a good 540, and you can just up the voltage to 12 volts for more power! Although the motor is quite small it does need a careful solid fitting as mine gets quite excited on just 7.2 volts.  I think maximum power suggested is 200 watts, which will probably do!!!!  My little Bobby boat (20 inches loa) starts to turn over at 50 watts.
 I think the blurb said >75 % efficient  so that's at least 50% better than a brushed 540 and mine was a ball raced balanced armature 30 turn MRP motor.
Good luck
Roy
Title: Re: Looking for small brushless/ESC combo
Post by: Shipmate60 on September 07, 2010, 11:47:44 PM
My reason for staying brushed is simple, the speed 400 or deans black 5 are little screamers and can be substituted for the original motor.
It should solve the problem for less than a tenner, no need for complete new set up.

Bob
Title: Re: Looking for small brushless/ESC combo
Post by: barriew on January 30, 2011, 12:13:23 PM
Its a long time since I started this post, but its been winter %)

I tried a different 400 in the boat, with only slight improvement, so I bought a cheap brushless/ESC combo from Hong Kong - 15 including post. The ESC is forwards only but I figured it was worth a try. When I came to fit it, I couldn't get the 400 out, so I put it into my Deans Fireboat which had a Deans Black 400 on 7.2v and gave reasonable performance, but not really up on the plane.

Just back from trying it out and it is certainly a big improvement running on a 7.4volt 4000mah LiPo about half the hull is out of the water at full throttle in a straight line. The motor and ESC only get warm, not hot, without any water cooling, so I am very pleased. I have another 7.4v LiPo which I plan to try in the Huntsman 31, and will probably get another brushless combo for my Swordsman.

Barrie
Title: Re: Looking for small brushless/ESC combo
Post by: dodgy geezer on January 30, 2011, 12:47:11 PM

I tried a different 400 in the boat, with only slight improvement, so I bought a cheap brushless/ESC combo from Hong Kong - 15 including post. The ESC is forwards only but I figured it was worth a try....


Can you give a reference for your little brushless?  I have been using small Giant Cod motors in my Eezebilts very successfully now for a while - these sort of things...


(http://s3.postimage.org/12by54ikk/brushless.jpg) (http://postimage.org/image/12by54ikk/)
Title: Re: Looking for small brushless/ESC combo
Post by: barriew on January 30, 2011, 01:19:28 PM
Dodgy

It was this one - not sure if its still available or not.

Ebay item number  270666247108

Barrie
Title: Re: Looking for small brushless/ESC combo
Post by: dodgy geezer on January 30, 2011, 04:12:55 PM
Interesting - it can still be seen here: http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=270666247108&ru=http%3A%2F%2Fshop.ebay.co.uk%3A80%2F%3F_from%3DR40%26_trksid%3Dp5197.m570.l1313%26_nkw%3D270666247108%26_sacat%3DSee-All-Categories%26_fvi%3D1&_rdc=1

It's not available now, but there are lots more other brushless combos from about 10 upwards...

I note it is 1400 KV - I usually try to keep mine down to below 1000 KV. Do you have any problem with cavitation? if my experience is anything to go by, altering the prop size will produce a marked effect - smaller ones sometimes improve the performance a lot...
Title: Re: Looking for small brushless/ESC combo
Post by: Dekan on January 30, 2011, 06:01:19 PM
Dodgy is the one on the right of your picture one of these  http://robotbirds.com/catalog/product_info.php?cPath=56_325&products_id=880

Title: Re: Looking for small brushless/ESC combo
Post by: dodgy geezer on January 31, 2011, 12:16:05 AM
Er, no - actually it's an early one that I bought from Giant Cod - a 2408-21T-3A which has a KV of 1400. 
Exception that proves the rule..... :embarrassed: :embarrassed:
Title: Re: Looking for small brushless/ESC combo
Post by: barriew on January 31, 2011, 07:42:58 AM
I note it is 1400 KV - I usually try to keep mine down to below 1000 KV. Do you have any problem with cavitation? if my experience is anything to go by, altering the prop size will produce a marked effect - smaller ones sometimes improve the performance a lot...

Yes - I think the original advice was for something less than 1000KV, but this seemed worth a try at the price. No cavitation that I could see, and I'm running on the kit supplied prop. Think it may be 35mm, but not sure. Anyway, its plenty fast enough, and with 4000maH in the battery plenty of run time - I get bored quite easily %%. After about 30 mins total run time yesterday there was no sign of slowing down, but when I could no longer feel my toes I decided enough was enough {-)

The only problem I have is that there were  no instructions at all for the ESC, so no how to program it - if that is possible. Just using it out of the box - I wait to its stopped beeping, then it  seems to perform OK.

Barrie
Title: Re: Looking for small brushless/ESC combo
Post by: dodgy geezer on January 31, 2011, 10:37:38 AM

The only problem I have is that there were  no instructions at all for the ESC, so no how to program it - if that is possible. Just using it out of the box - I wait to its stopped beeping, then it  seems to perform OK.


If it beeps I suspect it programs - I have found various pages on the fly-boy forums which give general programing instructions for various unmarked escs - but if it works fine in default mode, great!  If you do get a chance to experiment with props I think the results will be interesting - as the revs go up I think that the prop you are using becomes more critical....
Title: Re: Looking for small brushless/ESC combo
Post by: Dekan on January 31, 2011, 05:30:09 PM
I have lots of brushless motor....

I'm still not sure how their power relates to bushed motor ie I have been told that a 6v graupner speed 400 "produces" about 20W...A tower Pro 2408-21T "produces" over a 70W on 7.4V using an APC 8x4 propeller on a model plane.

Does that mean my 22" cabin cruiser is going exceed warp speed or are there other factors that will keep things in check?
Title: Re: Looking for small brushless/ESC combo
Post by: malcolmfrary on January 31, 2011, 05:57:45 PM
Quote
Does that mean my 22" cabin cruiser is going exceed warp speed or are there other factors that will keep things in check?
How much water the prop can shove backwards before it becomes a stream of bubbles is one consideration, the hull shape will have a maximum speed before it becomes unstable or the cabin blows off, and then there is the strength of the motor mount to hull join.  Every action has an equal and opposite reaction.  The motor twirling one way and working against the resistance of the prop in water will try to take its mount with it.
Title: Re: Looking for small brushless/ESC combo
Post by: Dekan on January 31, 2011, 07:17:02 PM
Malcolm.... I think I can stop the motor and boat parting company...My main concert is the lack of diameter and pitch options compared to a model aircraft...
Title: Re: Looking for small brushless/ESC combo
Post by: dodgy geezer on January 31, 2011, 08:19:09 PM
Motor mount will probably be easy enough - these things are usually mounted in foam aircraft. I think your main issues will be:

1 - Heat. These motors are designed to run in the open air with a prop in front of them. I run mine very under-volted so it is no problem for me, but do provide some flow of air...
2 - Vibration. These things go like the clappers. Do a good join to your propshaft, support the propshaft well and keep everything balanced..
3 - Prop size. I find that smallish props can give a huge increase in thrust, compared to larger ones. Bit non-intuitive...
Title: Re: Looking for small brushless/ESC combo
Post by: Dekan on January 31, 2011, 09:01:17 PM
How small a prop on 22" cabin cruiser... 2 blade 25mm?
Title: Re: Looking for small brushless/ESC combo
Post by: nick_75au on February 01, 2011, 05:45:24 AM
Dekan,
The motor is only going to draw as much power as the prop requires, As an example a gentleman in our club has motors capable of 1800 watts in his boat (brought them on size only to be equivalent to a 700), with a 50 mm prop on 6 volts the motors only draw 5 amps which is 30 watts.

Nick
Title: Re: Looking for small brushless/ESC combo
Post by: dodgy geezer on February 01, 2011, 08:06:10 AM
How small a prop on 22" cabin cruiser... 2 blade 25mm?

I have 30mm and 25mm in several different makes, and there is quite a difference between all of them - pitch is important, of course, and different makes seem to have quite different pitches. A fine prop seems to do better....