Topic: 1/24 scale Vosper MTB - Brushless? (Read 9208 times)

shadysadie · « **on:** May 26, 2015, 05:13:53 pm »

Your advice would be very much appreciated as I have no previous experience of brushless motors.
I am currently building a Vosper MTB Type 2 in 1/24 scale based on the Kingston Mouldings hull and I think that now is the time to bite the bullet and seriously consider brushless power. I intend only to power the two outer props and leave the centre one to freewheel so what would be the best size motors to use please? Battery power will be Nimh (still not ready to go down the LiPo route) and I am looking for scale speed and planing performance with 30min or so endurance.
I would seriously consider using 3 motors if you think that the freewheeling prop is going to cause too much drag.
Look forward to receiving your advice/comments.

Regards, David.

canabus · « **Reply #1 on:** May 27, 2015, 02:39:07 pm »

Hi Shadysadie
One nice boat ,but, go brushless motors, I have been the brush motor and NiCad road and never again.
The performance that the boat that size requires brushless motors or an IC motor.
Motors D3348/4 1100Kv on 3 or 4 S batteries with Hk-60A car ESC'S with two Y connectors on one channel or two ESC's on one channel and the middle motor on another channel for slow speed.
Batteries 5800mah with a 60C .
Props I use 2 blade 40mm x 1.4 pitch, if using 3 blade go done in size because of blade area.
Oversize props overload the motor, ESC and batteries.

shadysadie · « **Reply #2 on:** May 27, 2015, 03:35:36 pm »

Many thanks canabus but as I said before, I am a complete novice when it comes to brushless motors, batteries and ESC's.
I fully understand your advice about props and running the centre motor on a separate channel and can look up the motors and ESC's but I'm lost when it comes to your battery advice! Are we talking NiMh or do I have to use LiPo's ? Also, just to prove my complete ignorance, what is a 60C?

Regards, David.

canabus · « **Reply #3 on:** May 28, 2015, 04:50:56 am »

You will have to use Lipo batteries (eg 5800mah 3S (11.1volts) or 4S(14.8volts)60C(the current rating of the battery).
With nicads in that size boat you will not get to a scale speed and not get a good run time.
The brushless motors a very powerful (about 750 watts equals one horse power).
My first brushless motor was 550watts in a off road buggy as a replacement for a hot 540S brush motor, the 2650mah Lipo battery(about the same size and weight as the old NiCad battery.
The car is like a Mini with the power of a V8 and goes like hell!!!!!!!
The run time was about 10 minutes and with the new setup over a hour.
Is your boat the 57.5 inch or the 36.5 inch hull?

shadysadie · « **Reply #4 on:** May 28, 2015, 01:28:23 pm »

The hull is 36.5 inches and thanks to you, canabus, plus a lot more research on this excellent site I am now much happier about the brushless/LiPo scene. Batteries and speed controllers are no problem and you have kindly pointed me in the right direction regarding motor size and power but how do I choose the correct one? I have looked on several sites (Hobbyking, Component Shop, Cornwall Model Boats etc.) and the price range/specifications for 1100Kv - 1300Kv motors seems to be endless and (to me) very confusing.

canabus · « **Reply #5 on:** May 28, 2015, 02:38:13 pm »

As your boat is the 36.5 inch one, I can help you better.
One of our club members is building a PT boat about the same size using three motors.
Motors B28-57-17L, 1700kv, 630 watts, diameter 28mm,length 57mm, battery3-6S shaft 3.175mm.
Drive line kits (code BP22-S Prop and BP-22 Sleeve) these included 3 blade 30mm x 1.4 pitch prop and the collate 4mm to 3.175 mm(motor to shaft).
Hobbyking also have an alloy prop the same size.
I have installed one of these drive kits in a Sea Hornet and as the motor bolts onto the drive tube with a support bracket between the mount ring and the motor. No lining up problems, I bolted the support bracket to the drive tube ring and added the motor after gluing.
I had the shorten the shaft a bit, so I popped out the rear bearing cut the tube and shaft to the length I required.
ESC's car 60A with reverse (connect the 3 ESC's with two y servo leads(code AM1052-30)(5 connectors in the kit).
The motors do not require the 60A ESC but these handle 4S batteries as the small ESC's only handle up to 3S batteries.
So if you require a bit more speed you can change from 3S to 4S batteries(extra 6000RPM).
Total motor power 1890watts.

canabus · « **Reply #6 on:** May 29, 2015, 11:28:33 am »

We changed out the B28-57-17L's today(too, too, powerful) it was faster than the torpedos.
We install three 2836 1200kv 340w 3-4S motors(code T2836-1200).
Only a quick run but more scale speed(rain storm).

gra2 · « **Reply #7 on:** May 30, 2015, 06:02:26 am »

Hi David,

Have posted photo of my 1/24 scale 77ft Elco PT boat which is 38 inches in length.
Boat runs on a Turnigy 3639-1100KV outrunner motor mounted on the centre shaft the flank shafts are freewheeling.
Battery is a 3S Lipo 30-40C discharge.
I would use the Hobbyking 60a car ESC as suggested above.

Boat runs very well with this setup.
Original setup had three brushed motors and did not perform as well as one brushless motor.

Graham

gra2 · « **Reply #8 on:** May 30, 2015, 06:05:27 am »

Hi David forgot to say boat has a three blade 35mm brass prop.

Graham

shadysadie · « **Reply #9 on:** May 30, 2015, 11:55:25 am »

Thanks canabus and gra2, you have both helped me a lot.
What I have decided to do is to initially use two 2836 1200Kv 340W motors on the outer props and let the centre one freewheel. I shall use 60A ESC's and LiPo batteries thus leaving me the option in future to uprate the motors/batteries if required and feel that this would be a good starting point.
Just one more question, is water cooling for the ESC's the best option?

Regards, David.

gra2 · « **Reply #10 on:** May 30, 2015, 01:38:35 pm »

Hi David if you use the car esc indicated above they have inbuilt fan cooling.

Graham

shadysadie · « **Reply #11 on:** May 31, 2015, 05:00:08 pm »

Regarding car ESC's it seems that the fan cooled Hobbyking X-car 60A would be ideal but I am a little confused (again!) about the 6 pin sensor cable which this ESC has. Am I right in thinking that for use in boats I just forget about it and tape it up out of the way? Motors will be Turnigy 2830 1200Kv 340w..

David.

gra2 · « **Reply #12 on:** June 01, 2015, 07:03:08 am »

Hi David,

The Hobby King car ESC that I use is 60AMP with reverse P/N SKU.HK 60A .
No sensor cable with ESC.

Hope this helps.

Graham

Time Bandit · « **Reply #13 on:** June 01, 2015, 10:18:13 am »

I am always using the Robbe Roxxy 9xx ESC for these applications.
Small, leightweight, no need to cool externally and (with programmer card) very easy programmable.
I´ve never found any other ESC with smoother starting of the motor and lower revs (even if it´s still not comparable with a good brushed motor and ESC).

shadysadie · « **Reply #14 on:** June 01, 2015, 02:42:07 pm »

Hello Tobias.
I agree that the Robbe Roxxy 9xx ESC seems to be the best choice but the 60A version costs £73 (98 euros) here in the UK and I'm just not prepared to pay this price yet. The fan cooled 60A car ESC is about a third of the price so I will give these a try and be prepared to learn from the experience if I have made a mistake !

David.

Time Bandit · « **Reply #15 on:** June 02, 2015, 08:51:42 am »

Okay that´s a word.
Same ESC is ~55€ here in germany, so it makes still sense to use them.

I never had any good experience with the cheap ESC from HK (especially the blue "boat type ESC" killed the motors like fleas) so I wont make any experiments anymore.

Btw why are you looking for 60A ESC for such a small 2830 motor.
"real" 30A should be absolutely enough. If you run 15A through that motor it will overheat pretty quickly.
Even a larger 2836 can maybe withstand 20A for just a few seconds without active cooling.

In my experience all the "datasheets" are completely unrealistic if it comes to boats.
340W (or 22A on 4S) as the announce it just apply to airplanes (with very good cooling effect by air) and just maybe for 30-60s. After that the motor will burn.

shadysadie · « **Reply #16 on:** June 02, 2015, 04:24:50 pm »

Thanks again Tobias for your truly useful information. As I have said before, I am a newcomer to the brushless world and the reason I was considering 60A ESC's was to enable me to upgrade the motor/battery power if necessary without changing any other components. I shall in fact be using 2836 1200Kv 340W motors and not 2830's as I stated previously.
Your comments regarding the Roxxy ESC have led me to further research on these units and I must confess that the specifications are very impressive - I am tempted to buy them despite the cost!

Regards, David.

Time Bandit · « **Reply #17 on:** June 02, 2015, 08:47:46 pm »

I´m not trying to convince you, the HK ESC probably also will do their job pretty well.
Just beware of those blue Hobbyking watercooled Boat ESC, they really suck.

Try one of those shops, one will probabaly send to the UK.
Should still work out even with higher shipping costs.

http://www.hobbydirekt.de/product_info.php?refID=froogle&products_id=111755&gclid=CLOkjL7h8cUCFezKtAodB2wATg
http://www.d-edition.de/RC-Modellbau-Zubehoer/Elektronik/Regler/Regler-Flug/Robbe-Roxxy-Brushless-Control-Regler-940-6.html?utm_source=google&utm_medium=shopping&utm_campaign=gs&gclid=CNbf9L7h8cUCFcXLtAod_zQADg
http://www.smdv.de/products/1700/Roxxy-Brushless-Control-940-6.html?ref=43&products_model=A78546&gclid=CJ7ow8Dh8cUCFQnItAodoFEADg

And don´t forget the programmer card, I never tried, but I heard it´s a mess to program them without it.

40A is absolutely enough for a boat of this size and for scale boats anyways. I´d never use higher amps in applications other than real racing boats.
40A at estimated 4S Lipo or 12S Nimh batteries and 2 motors will give you 1KW power output. Your model could run 40mph++ with that power

By the way if you really want more power it´s always better to increase the voltage instead of the current.
Keeps everything smaller (cables, connectors....) and better controlable.

1 advice:
Brushless motors are much more sensitive regarding "too much rpm" than brushed motors due to their ability to always hold their rpm. If you overload a brushed motor the rpm will go down and the current will be controlable in most cases. Brushless motors always hold their rpm and get into currents that can be 10 times higher than what you think.
They die instantly or kill anything else (ESC, battery, cables...) due to current overshooting very fast.
In scale (planing) boats motors with kv > 2000 are in 99% of all cases absolute rubbish.
In displacing boats I thing anything above 500kv is in 95% of all cases very wrong.

You should always try to bring the rpm in order to the speed you want.
E.g. 1200 kv motor on 4S Lipo = 16.000 rpm under load (1200kv * 14,8V * 0,9)

If you use a 40 mm prop with a pitch ratio of 1.0 (usual brass prop, racing props tend to have 1.4 - 1.6) you´ll get a speed of ~ 28 km/h / 17,5 mph.
(calculation for km/h: 16000 1/min * 0,04 (prop pitch in m) *0,7 (usual slip of prop in the water) / 60 (to come to m/s) * 3,6 (to come to km/h))

Your boat is probably capable of over 15 mph but scale speed will probably be around 10 mph.
So depending on your prop and battery you should probabaly buy a motor with less kv.

canabus · « **Reply #18 on:** June 06, 2015, 11:32:49 am »

Programming the Hobbyking 45/60/100A ESC(codes HK-45A/60A/100A).
1 Cut off voltage 3S batteries 9.9 volts.
4S batteries 12.8 volts.
This is a bit higher than recommended but safer on the battery and gives you a bit more battery crawl home time(see text below).
Recommended use voltage alarm(code alarm-voltage) also shows voltage per cell on the battery.
These alarms handle 2s upwards.
If you boat cuts out wait a few minutes the Lipo batteries cool a bit and you can crawl back to shore!!

2 Start power precent 10% a good start point(good slow start speed for slow cruising).

3 Advance timing 4 (maximum kick at the top end of the throttle).

4 Run mode 2 limits the braking setup.

5 Brake force 1 (50% lowest setting).

6 Drag Brake force use default 0.

7 Neutral range use default 8%.

8 Initial brake force 5%.

9 Reverse force 1 (25%) with the start power at 10% it will give you a good reverse slow speed.

This is a starting point in general and feel free to change these to your boat setup.

If using twin motor setup in a boat set one ESC with a higher cut off voltage and if the goes to one motor head for the shore.

shadysadie · « **Reply #19 on:** June 06, 2015, 07:56:51 pm »

Canabus, gra2 and Time Bandit - thanks very much to the three of you for all your help and advice. I think (hope!) that I am now heading in the right direction.

David.

shadysadie · « **Reply #20 on:** October 29, 2015, 03:28:25 pm »

As everyone was so helpful with my quest to go brushless last May/June, I thought it only proper to share the results. Final set-up is 2 Turnigy 2836 1200Kv motors, 2 Robbe Roxxy 940-6 speed controllers, 2 4250 4s 30c lipos and 40mm brass props.. Centre prop. freewheeling.

Took the boat out for " sea " trials on the local boating lake today and all my doubts and apprehensions have now disappeared ! Performance is very impressive from low speed all the way to getting up onto the plane and there is still power in hand which I shall not be using as it well exceeds scale speed. Motors and ESC's stayed cool too.

Thanks again all from a dedicated brushless convert !

Regards, David

gra2 · « **Reply #21 on:** October 30, 2015, 03:35:57 am »

G/day David,

Glad all turned out okay brushless is the future.

Graham

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Author Topic: 1/24 scale Vosper MTB - Brushless? (Read 9208 times)