Propellors

[Brian Porter 2Participant @brianporter2]

Hi, first thread so please make allowances! My son & I are picking up from where we left off in 2002 on a 1/32 93cm twin motors & rudders RC K. D. Perkasa P150. It was half finished so we’re keeping the hull but completely stripping out & starting afresh. We want to use a lead acid battery. We’ve been advised on two MFA 850 motors with twin MTronics Viper Marine 40s & an MTronics W Tail Mixer.

Questions – we have plastic twin blade propellors (40mm M4) – would triple blades be best? And if so, plastic or brass?

Although high speed is not our intention we do want to reflect the top speed (54 knots) & acceleration of these boats as I’m sure many of you know!

Our prop shafts are ok but need stripping down for a good clean & grease which, is easy.

We’d be so very grateful for any advice. We want to get this right & to that end have even found an authentic gas turbine sound system!

Brian

[Brian Porter 2Participant @brianporter2]

Advice needed in choice of propellors

[ashley needhamParticipant @ashleyneedham69188]

Hi Brian and welcome to the forum.

To grapple with a couple of points:

Have you purchased the motors and so on already? There is not a great following for the MFA850 on the forum for some reason, but I like them lots! No doubt they will produce sufficient power, however the downside is their weight. I would say that if you have the motors, use them, my personal opinion. Likely best performance with a pair of X40 plasticprops, but they don’t look as nice as three or four blade brass ones when out of the water.

Unfortunately if 10 people reply to your post there will be 10 different motor combinations offered. Brushless would be the “modern” way to go, but another minefield..

Whatever you do, using an SLA will NOT deliver any sort of performance due to the massive weight and the inability to provide a good current flow for the motors. I would buy a pair of high capacity (4300 or 5000 mAhr ) 6v Nimh battery packs (connected n series for 12v). Buying two allows you to position them as ballast more effectively, and if one dis, you can replace just 1/2 your 12v batt.

There will be other suggestions.

Finally, purchasing the current and previous MB issues will allow you to read our Colin’s excellent article on the subject.

Ashley

Edited By ashley needham on 26/03/2021 13:15:10

Edited By ashley needham on 26/03/2021 13:15:31

[Ray Wood 3Participant @raywood3]

Hello Brian,

Welcome to the forum Good that your getting back onto the Perkasa, I think you would be disappointed with the lack power and the weight of lead acid batteries, I also think the 850's are rather heavy for you hull, If your going brushed motors 600's size driving X40 nylon 2 blade racing props will give a good turn of speed with nickel metal hydried buggy packs on 7.2v and much lighter.

Or these days brushless motors and Lipos are the fastest method of propulsion by far, but not my field.

On a fast planing hull I cannot see any reason to have seperate motor controls? but the choice is your obviously.

Bugger, Ashley beat me to it !!! we must be telepathetic

Regards Ray

Edited By Ray Wood 2 on 26/03/2021 13:16:34

Edited By Ray Wood 2 on 26/03/2021 13:18:26

[Brian Porter 2Participant @brianporter2]

Thanks Ashley & Ray for your thoughts, it’s much appreciated. We’ll digest all this.

This weekend we’re removing the existing deck, should be fun as we fibre glassed it on & joked back then about ever having to remove it but it has to go. Original (1967) photos etc seem few & far between. But we have some & from them we intend to 3D print several deck fittings, the first & challenging item being the torpedo racks but I think we’ve managed it!

Lead acid was a choice based on stability (it originally had one), but I think we’ll do some testing & rethinking after both your comments.

As for the propellors, I view of your comments we’ll get plastic 3 blades and test them against the 2 bladed ones. Whichever proves the best perhaps we should swap them for brass versions, any thoughts?

Certainly not a cheap hobby!! Will be taking photos as we learn and go!

Brian

[Colin BishopModerator @colinbishop34627]

Picking up on what Ray and Ashley have said I agree 100% that you don't want an SLA battery. The NiMH packs that Ashley suggests will be plenty heavy enough and keep the weight lower down as well. They can also deliver the higher currents needed to get decent performance.

With regard to propellers, most plastic three bladed ones are scale type and won't deliver the thrust you need for this type of model. If you are sticking with plastic then the black two blade racing type are the ones to use as Ashley recommends. They are cheap and effective so you can try different sizes. You can always upgrade to the more expensive brass type when you have got the boat sorted. It probably won't go any faster but will look nicer.

The Mtroniks gear should be fine.

The articles I wrote for the magazine in the March and April issues of the magazine are aimed at people like yourselves looking for straightforward solutions to motor and prop setups. One of the examples quoted (with photo) is a 102cm PT boat which uses two Graupner Speed 700 motors powered from 9.6volt NiMH packs, one per motor, and driving 30mm three blade Rivabo standard brass props. The builder, Gareth Jones, originally had Speed 600s fitted but the 700s give better performance and run cooler..

Colin

[Brian Porter 2Participant @brianporter2]

Thanks so much for your input Colin.

We’re rapidly coming to the conclusion that NiMH (x2 6v) is the way. Ashley suggested the spec but is there any particular make you’d recommend? Not too worried by cost, most important is weight for ballast & we’d prefer to go high on the mAhr. Since my first post it seems we’re committed to the two MFA 850s.

Brian

[Colin BishopModerator @colinbishop34627]

Component Shop are a reliable source of NiMH batteries. Their website doesn't seem to be working properly with my Firefox browser but Mictosoft Edge seems to be OK. You can get 5000mAh packs. Get extra voltage, 7.2 or 8.4 packs as it is always best to have some power in hand.

**LINK**

Colin

Edited By Colin Bishop on 26/03/2021 19:43:28

[neil hpParticipant @neilhp]

thanks guys……….that info is just what i wanted for powering my Tyne lifeboat when i need to………

and i didn't even need to ask. thank you all.

[Brian Porter 2Participant @brianporter2]

HELP – Voltage, being new to this we are now getting confused. We made it clear to a dealer that we have a Carson 14ch receiver (we have a Carson 14ch Pro TX) This evening I’ve just realised it’s max voltage is 8.4 but some say 6v! The motors the dealer recommended & sold us are are 12v. Sure they run at a lower voltage & we can reduce the battery output but that must reduce their speed. Can someone offer an easy to understand guidance for two confused beginners please? Thanks

Brian

[Brian Porter 2Participant @brianporter2]

Sorted electrics – my fault. Thanks again for your help guys.

[ashley needhamParticipant @ashleyneedham69188]

Oops. Added post just after Brian so have erased! Ashley

Edited By ashley needham on 27/03/2021 09:21:29

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