Huntsman Powerplant

[Dean Pritchard 1Participant @deanpritchard1]

Looking to install powerplant to allow final completion of build

[Dean Pritchard 1Participant @deanpritchard1]

I have a 42" Hull from a 31' Huntsman, in GRP. I have the bulkheads in, and the prop tubes in. I also have a pair of MFA 850 Torpedo motors which I intend to match up with a pair of 55mm 3-blade racing props. My question is, what speed controllers would you advise for this model, and also, which type of battery pack? I am looking to get this project finished over winter, as it has been delayed long enough! When finished, it will represent "Fordsport, no 707".

[ashley needhamParticipant @ashleyneedham69188]

Dean. Nimh battery pack , 12V and of 5000mAh would suit this application.

​Some would advise a Lipo pack, but I would say this depends if you already have boats that use Lipo batteries, or whether this boat is going to see a lot of use. Nimh`s last much longer.

​Others will advise dump the 850 and fit brushless, but I like the 850 motor and you already have some!

​The motors will be taking a good 10-12A each, so an ESC of at least 25A will be required. My experience of esc`s taking 20+ amps for a while is that they get warm/hot and need cooling if poss, a fan or water-cooling. . I would not like to voice to definite an opinion on the forum as to which ESC to buy but the M`tronics ones are ok…a 40A one with a small computer fan mounted above should do the trick (can get some nice small fans and they run on 12v a lot of them….Maplins etc.
​Ashley

[Dave MilbournParticipant @davemilbourn48782]

Dean

An 850 on 12v with a 3-blade 55mm prop will draw A LOT MORE than 12A. I've seen many 20A ESCs burned out running one of these. All I can advise in that respect is not to be tempted by any of the fantastical Chinese E-bay offerings. The current-handling capability of most of them is not just suspect but definitely wrong – in many cases by a factor of ten. Avoid these at all costs. Frankly I'd go for brushless but, as Ashley says, you're already down the road with the 850's.

I don't have any experience of MTroniks 40A ESC but I can recommend from personal use both the ACTion P98 and the Microgyros FR40.

The only other two pieces of advice I'd offer would be not to use sealed lead-acid batteries (much too heavy) and to fit one battery pack and one ESC for each motor i.e. the boat has two of everything. It's expensive but much easier to trace faults, easier on the electronics and batteries and you'll get twice the running time than by just using one pack.

BTW 'Fordspeed 707' was a Huntsman 31 so it's most likely the hull you have is 1/8 scale i.e. 46" long.

'Tintarf a biggun, mester!

Dave M

[ashley needhamParticipant @ashleyneedham69188]

MFA specified X50 props for these motors and this is what I always fit. mfa also gave a 10A figure presumably when fitted with an x50, so.. But I am not as experienced as DM

​twin esc is a good idea at this level of power to stop overheating issues if not using watercooling

Ashley.

[Paul TParticipant @pault84577]

Dean

From bitter experience I can testify that a pair of 850s in a 5ft Huntsman drew 30Amps during a high speed run and melted the Chinese 80Amp speed controller (and most of the wiring) I was also using a pair of SLA batteries for power and ballast which were simply not up to the job and were seriously hot when I finally recovered the boat.

At the time I had been given some very sage advice involving twin battery packs and twin P98 ESCs which I foolishly ignored.

Hard lesson to learn.

Paul

[Ian GardnerParticipant @iangardner62867]

Hello Dean,

I have had a little experience in these matters and I feel it is worth buying a watt meter so that you can get some idea of what current your 850s will be drawing on your chosen props. Needless to say the measured current will be somewhat higher as you will be testing the boat whilst stationary. I think you will be surprised at the amount of current drawn.

I have used MTroniks 40amp esc's and Electronize esc's and would always choose the latter. They are rugged and simple to use and enable you to go higher than 12v if you decide you need a bit more oomph- which is quite likely using 850's. They are large , but that isn't a problem in your case. These are the ones I have experienced. However the 30 amp esc may not be sufficient- hence the wattmeter.

If you are going down this route I would also suggest one controller and battery for each motor and use a Y lead to the rx. There is a lot of information about this stuff around, much of it written by Dave Milbourn whose advice should certainly be heeded.

Making a boat of that size go well will never be cheap but I would urge you to look at Lipo's. HIMH batteries just don't give up the current you want- it's something to do with internal resistance. When I used 12v NIMH and measured what was going on they dropped to 9v at full throttle- this was using Graupner 700's. I changed to 3s Lipo's and the difference was amazing- they are also much lighter.

Good luck.

Ian

[Byron Rees…(Ron)Participant @byronrees-ron]

Hi Dean and all,

Like Dave Milbourn I have a long and happy list of Fairey Marine craft under my belt including quite a few of Dave's own designs as well as Philip Connelly's and also my own designs.

As Dave clearly states in his two part build of the Huntsman, January and February Model Boats Mag 2016. These boats were initially offshoots of racing boats and are strong and light. Small versions of them sail exceptionally well with small brushless motors, they are fast, responsive and beautiful. But they MUST be kept light.

As the models get bigger the problems of powering them at their correct speed and attitude grows exponentially and a large version (Which I originally built around an HP 61 marine 2 stroke engine when they first came out) like the one you are doing, needs to be kept light with the best and most powerful motors you can afford. You cannot afford to use 12 volt Gel Cells, they do not give up their power quickly enough and weigh just too much.

These days we are blessed with the advent of newer technology and even though you have 2 new MFA motors ready to go, I would put them into something else at a later date, bite the bullet as they say and invest in two Brushless motors of at least 35mm to 50mm diameter, they are lighter,cooler and much, much more powerful than a brushed motor as well as 90% efficient. Li-Po batteries are also lighter and can really deliver the power when you need it, I would consider 2x 11.1volt. 5000mAh. and two speed controllers to match, Hawk 60s are expensive but very good.

Having seen a few of these models mooching around the lake and the disappointment on the face of the builder a few times, I wouldn't even consider for one moment using a brushed/Gel Cell/standard Escs. set up for a model like this. ((I've also seen the transformation when it is refitted with a brushless set up!)

Purely my own thoughts on the subject. (Sorry Ashley!)

Ron Rees.

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