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[Stavros]

Right I have this MTB dont know what hull it is built from it is in plywood with a solid balsa bow it is 48ins long and 10ins wide now I had it out today for the first time with twin MFA800 Motors driving 2 three bladed 50mm props the performance could only be decibel as snail like suggestions please.Would I be better off fitting 2xMFA850's or what other motors would you suggest cheers Stavros

[boatmadman]

What voltage does it run on?

Also, try using twin blade racing props, I know its not scale but it worked for me. I had a similar thing years ago with a 36" Brave Borderer. It now runs at scale speed on electronize 550 motors and plastic race props

Ian

[Stavros]

Either one or two 12v 7amp gell cells dont want to go down the road of power packs need sailing duration of approx Ihr!!
Also tried it on 40mm twin bladed racing props but no better

[John W E]

Hi Stavros

Any chance of you posting a pic of your mtb on this thread?  Just so we can see how its made up.

Aye
John E
BLUEBIRD

[Shipmate60]

Stavros,
Yes I would go for the 850's, they rev at about twice the speed of 800's.
I use 800's in large warships, not MTB's.
Also try going down to 1 battery to reduce the weight.

Bob

[Stavros]

Will take photos tomorrow Bob tried single batt but no difference oh Bob pm m8

[Stavros]

Photos as promised,general construction is plywood with Balsa bow,at present it does not have rudders due to an action mixer being used but it is getting rudders instead,this is due ot me not being to get 2 blade props of opp rotation so go back ot baisics the oly other mod I have to do is to remove rear bulkhead to get the batts furhter back 2 batts cause it to go along nose down so move them further back is the only cure Stavros

[John W E]

Hi there Stavros

wor lass reckons its time you had your garden borders dug over 

Anyway, I think you are caught between the devil and the deep blue sea - it looks a fairly heavy hull with superstructure - and ifyou actual want this hull to come onto the plane I dont think you would get the duration and sailing time because I think you would have to go down the Nicad route unless you did some major surgery inside the hull to try and lighten it.  Having said that, our friend RIGGERS on this forum has a Static build RAF crash tender - its been in the water on trials - and in it, bear in mind this only had the bare hull and its power supply was a large 6v 10 amP battery - driving (I think it was 2 x 850s or 2 x 800s).   I cant remember the size of the props, but, this did put a good performance on - not quite on the plane but near enough.

The other way is go the PsShips has suggested because I have done this on an mtb - only mine is 3 motors - and the power supply is 2 x 6 volt 4 amP batteries powering 3 MTronicks 550s - and I am sorry to say this but flat out - I am lucky if I get 10-15 minutes outof her, but by hell she shifts.  Speed controllers are Electronize (heavy duty ones - 15 amP) and on a sunny day the thermal overload on the speed controllers cut in and shut them down 'just like that'.

Aye
John E
Bluebird


hope this is of some help  :)

[johno 52-11]

There was a thread some time back about getting a rttl to run it might be worth looking at that.

http://www.modelboatmayhem.co.uk/forum/index.php?topic=850.0

John

[Shipmate60]

For interest, to get large models going VERY well a friend of mine uses:-

Hi Bob,
For my fast crash boats and torpedo boat I use Graupner 700BB turbo's with
Electronize 30 amp. FR30HX speed controller, I use props from the Prop Shop,
they are good.
Hope this helps.
By the way, the battery's are Ni-MH 13amp cells bought from Eurobatteries,
this is bought online, as these motors are thirsty for power a good set of
batteries are required, the drawback is that they are VERY expensive.
Best regards
Marshall

These are in large heavy planing hulls and look superb.
But
The batteries are over £100-00

Bob

[johno 52-11]

Hi stavros

Looking at your pictures I would say that the 50mm props are about the bigest diameter you are going to be able to fit on there. do you have some statistics for your boat Length, beam, weight. I have been helping a friend with his Severn class lifeboat for a number of years and its taken us a long time to get it to perform at scale speed. http://www.lifeboatmodels.co.uk/severnatspeed.htm It now running two large electric motors on 18V speed controllers are Electronize FR30HX props are four blade 75mm diameter and the battries are a 12V 12A and a 6V 12A sealed lead acids this gives a performance at full power for about 20 Min's.

I think you would find a better performance from the bigger Graupner motors and I would also consider changing the props to brass and possibly even 4 blades.

At the end of the day it comes down to taking advice and a bit of  trial and error.

But from what I have seen in the past there should be a way to get the performace you want.

John

[malcolmfrary]

Looking at the "Freelance MTB" article in the Your Models section of the main part of the site, someone has had the almost exact same problem to solve, and got a working answer.  Well worth a look.

[Stavros]

Well after much thiught I decided to remove the rear bulkhead so hte batt could be placed 4ins further back in the hull,changed props to 55mm 2 blade,put new rudders on instead of the mixer,she now planes no probs with a running time of 30 mins.Now going to experiment wiht 2x 540 race cans and 2 6v3amp batts just to compare worht a try!

[Shipmate60]

So what motors are in her?

Bob

[antuk]

that looks like black marauder . (part of the brave border family ) i built one from just plain balsa for my neighbour it had a standard 540 motor from maplan in it and ran on a standard 6cell pack 7.2 volts  on a 35x plastic prop i went scale speed and ran for around 20 mins on a full charge . i hope this is of use to you  . :)

[Stavros]

Now fitted with Mfa 850 and boy does it now fly