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[Lord Bungle]

Running a 12volt 7amp hour battery
a MFA Barracuda motor
single 50mm 2 bladed plastic prop
mtrontiks viper 20amp esc.
this is flat out, thought it should plane a bit, or is it just me?
http://www.youtube.com/watch?v=4X4RUDtnmOA


will have to get it sorted soon as I got my next project in the post (top tip never go on ebay when your are off work ill, it can end up costing money  )
another Fairey Boat, this time a Huntsman style one, with twin 540 motors, Brass 4 vaned propellers, and a single large rudder,
I will probably be asking silly questions about this at a later date. 

[Martin (Admin)]

You're right, not very impressive. 

[Lord Bungle]

any ideas ?
I know the motor only does 3000 rpm but it has loads of torque. (the perkins m6's in my old seaplane tender red lined at 1500 rpm)
the battery is at the back end so the weight should help it.
should I change the motor for an MFA 850? (this is what MFA now recommend for the spearfish)

or should I be happy that I have a boat that will run all day without need to recharge the battery?

[Islander1951]

I believe that the barracuda motor only runs at 3000 rpm at 12v, and you say that you are using a 12v/7ah battery; that sounds like a gell cell lead acid unit, and they are HEAVY.

The motor doesn't rev enough to get that hull up onto the plane, you would do better with a higher revving motor and a smaller prop, and 12v NiMH
cells - Look here:  http://www.component-shop.co.uk/ 

Build as light as you can to get up onto the plane easily, and add plenty of (lightweight) power.   

Edward.

[50mm]

you need to be looking at 755 size motors (im assuming these baracuders are 555 size correct me if im wrong) to pull it on the plane running of 12v should give you at least 45 mins to an hour of run time if running twins, solo motor easily 3 hours +

also change the prop to a 40mm 3 blade, your speed is decreased do the other over sized prop (your cavitating thats why your slow) its pulling torque but you need speed. 3 bladed smaller prop will do the job 50mm twin blades are just killing your motors

[Lord Bungle]

you need to be looking at 755 size motors (im assuming these baracuders are 555 size correct me if im wrong) to pull it on the plane running of 12v should give you at least 45 mins to an hour of run time if running twins, solo motor easily 3 hours +

also change the prop to a 40mm 3 blade, your speed is decreased do the other over sized prop its pulling torque but you need speed. 3 bladed smaller prop will do the job 50mm twin blades are just killing your motors

ok think I have a 40 and a 45 mm twin blade props somewhere, will give that a go and see what happens. would the 755 motors be a better choice than an 850 motor (mfa recommend an 850 for the spearfish 2 )

[Lord Bungle]

I believe that the barracuda motor only runs at 3000 rpm at 12v, and you say that you are using a 12v/7ah battery; that sounds like a gell cell lead acid unit, and they are HEAVY.

The motor doesn't rev enough to get that hull up onto the plane, you would do better with a higher revving motor and a smaller prop, and 12v NiMH
cells - Look here:  http://www.component-shop.co.uk/ 

Build as light as you can to get up onto the plane easily, and add plenty of (lightweight) power.   

Edward.

yep they run at 3000 rpm at 12 volt.

(will probably use the NiMH batteries on the next project at twin  540 engined huntsman I just got.

[50mm]

not a 45,,, a 40mm 45 is still 2 big and it should be a 3 bladed prop, trust me i know what im on about when it comes to going fast!

i said 755 but you may need a better esc maybe 35A, check the motor rating i can't be sure. 850 will be more powerful but maybe to much for that boat

[Lord Bungle]

Thanks Marty, Pay day on Tuesday guess where all my money will be going  
blokes down at local model shop will be getting rich on me I think  
will probably go for the 850 as thats what MFA suggest for the hull, I can allways drop power down if its to much :)
will take on board what you said about the prop size, I will look to see what props I have (think they may be 2 blade one) and order some 3 blade ones 40mm,
or would a 4 blade prop be better? sorry if that sounds a silly question but I am still feeling my way with boats of this size.

[Islander1951]

I found this:

Robbe Power 755/40
Robbe Power 755/40. Powerful electric motor with integral cooling fan for single-motor/multi-motor direct-drive power systems in large multi-function model boats.

Operating voltage: 12-18 Volts
Diameter: 47.00 mm
Weight: 286 g
Length: 83 mm
Current Amps at max. efficiency: 4.50 A
max power: 8.00 A
Part No: R4491

Price: £16.38 (Including VAT at 17.5%)
Euros: €18.84 (Inc VAT) / US Dollars: US$21.75 (Tax Free)

Edward.

[Lord Bungle]

I found this:

Robbe Power 755/40
Robbe Power 755/40. Powerful electric motor with integral cooling fan for single-motor/multi-motor direct-drive power systems in large multi-function model boats.

Operating voltage: 12-18 Volts
Diameter: 47.00 mm
Weight: 286 g
Length: 83 mm
Current Amps at max. efficiency: 4.50 A
max power: 8.00 A
Part No: R4491

Price: £16.38 (Including VAT at 17.5%)
Euros: €18.84 (Inc VAT) / US Dollars: US$21.75 (Tax Free)

Edward.

Thanks Edward 

[50mm]

yup thats what you need you should just need the motor by the rating of it the ESc being 20A should be good male sure you fuse the positive connector on the motor with a 10A fuse so you don't get a blow out

[Lord Bungle]

learnt that well earlier on  :
I now run a fuse between then motor and the esc and one between the esc and the battery, Overkill? maybe but fuse holders and fuses are cheaper than escs 

[50mm]

or would a 4 blade prop be better? sorry if that sounds a silly question but I am still feeling my way with boats of this size.

3 bladed 40mm prop is needed 4 blades are designed for torque applications normally such as tugs etc, speed boats require 3 blades generally, in your case 3 blades will be perfect and also looking at the Fairey boat, they all run 3 blade props

[Islander1951]

This is the other one:


MFA Torpedo 850 Marine Electric Motor
MFA Torpedo 850 motor designed specifically for high performance medium size (30" - 48") model boats. It gives planing' type performance and is ideal for fast cruisers, off-shore type powerboats etc. Comes complete with mounting bracket and connecting leads.

Operating Voltage 12 volts.
Current approx. 10.82A at max efficiency.
RPM at 12.0v - 9778 at max efficiency.
Weight 595g (approx)
Shaft Diameter - 6.35mm (1/8")
Supplied complete with mount & connecting cables
Part No: 1115/1

Price: £24.95 (Including VAT at 17.5%)
Euros: €28.69 (Inc VAT) / US Dollars: US$33.12 (Tax Free)

More than twice as heavy!

Edward.

[TomTheKraut]

G'day,
... and please, Lord Bungle, check the props. If they are plastic and you can bend the prop-blades by hand - throw them away as far as they will fly!
Soft Prop-blades will invariably flex under load, thus changing their rake from anything they might have had before right down to near-zero.
If you want to run plastic props, use Graupner K-series. Better still: brass props from Simon's Prop Shop (http://www.prop-shop.co.uk/)

[red181]

Hi LB, I have a number of scale boats, that are very fast, Hunts, Aerokits Fireboat etc, so my input is from experience. If you want to stay brushed motor, get a Graupner 700 BB Turbo. 2 reasons, very well made,and  thrive on big volts. Your current set up will only ever be put putting around the lake

Go 8.4v, and run on 12volts nimh, my Aerokits Fireboat is 3 feet, its 8.4v motor on 19.2volts and goes mental, I also did a lot of work with a 12v BB Turbo (my preference) and the 9.6v, but has to be the BB Turbo.

Now I am not talking ballistic speed, but certainly scale and plenty in reserve on 12v. You will need a good quality esc, and electronise supply these, the good news is they are repairable, and UK based, get the biggest 35amp one, as you progress to faster and more amp draw them your equipment progress' with you

I run a gearbox, but direct drive will be fine, hence 12v not 19.2v like mine. It will need to be lubricated, and an oiler tube is the best way imo, the oil will coat the shaft and prevent the surface becoming tarnished from standing water and moisture after use. I know some peeps like to stuff grease up the tube, thats fine, but on a fast rev prop the grease "funnels" and could cause drag.
With props, I use a 3 blade cleaver propshop prop on my Fireboat, but this was after a great deal of testing with cheap 2 blade "x" props, you don't want to go buying an expensive prop first time and get it wrong, there is nothing wrong with the plastic 2 blade "x" props for your application, see my Huntsman videos, I doubt there is a faster scale boat on this forum, and it uses a plastic 52.5mm "x" prop. When you have some test figures, you can then invest in a better prop, I will eventually get a 3 blade cleaver from propshop for the Huntsman, they are very well made, not soldered together, and balanced,
the batteries need to bbe high mah, the lead acid cannot give up the juice quick enough, compoment shop do some really nice nimh stick packs, get 3000mah or upwards, then watch the boat fly! hope that helps




pre gearbox video

http://www.youtube.com/watch?v=xLOkqBsCoi8&feature=player_embedded

[Lord Bungle]

Thanks for all your help folks I am off this weekend to make my local model shop owner a rich man 

[offshore1987]

Iv got this model and have 850mfa init and on the same batt, she planes alday long :)

[triumphjon]

ive the same hull in double , 1 as the spear , the other is going to be a huntsman 31 , the spear is awaiting a pair of brushless motors ! while the 31 has a pair of 777 s brushed motors which may get swapped for brushless later ! . need to change the motor and lead gell battery in that one lb .

[Lord Bungle]

was playing with the Spear on Christmas day as my loverly Fiance Heather treated me to 1x MFA 850 motor 2 x Speed 600 7.2 and 2x speed 600 8.4 and a few sheets of balsa for Christmas 

While doing a general tidy up I was looking at the prop, I thought It looked a bit larger than 50mm so I used Heathers dress making tape to measure it, 60mm    hunted around in bits box and found all my spare props bar 1 were m4 threads only 1 in m5 thread is 35mm so put that on. As I am in west London today I may pop down to the Grand union canal at Brentford and give it a spin if its not to icey.

(might look into building a springer type tug now as I will have a spare Barracuda motor and 60mm prop, I know this works  )

[Nige52]

I have a Spearfish, into which I put a Hobbyking water-cooled brushless 3600 motor and 120a esc....it fly's...

[triumphjon]

whats your set up nige ?

[Nige52]

All the running gear is exactly what came with the kit, without fetching it down to look, I'm not sure what the prop size is but I will later. I used a Huco coupling and a water-cooled motor mount with either a 3 or a 4 cell Lipo. She planes no problem with the 3 cell, but funnily enough, hardly any difference with the 4 cell? Either way I'm very happy with the performance. The only thing I changed was the hatch lock, I utilised a proper one which I bought off the bay, a 1/4 turn alloy one.

Here is a photo of all the internals fitted and the deck and hull joined with wet fiberglass tape. I'll dig some more photo's out in a bit.

[Nige52]

A closer view