Motor /Controller /Prop upgrade

[Dave Cooper 6Participant @davecooper6]

Hi Folks,

A few years ago my son and I built a small (16&quot RAF launch just for fun /experience of our own design. It had a 6v brushed motor and heavy dry cell batteries and a '40' prop. Performance was disappointing – ie it didn't plane !

Got it down from the shelf yesterday and decided to do a refurb' /upgrade…I've fitted a secondary 'stepped' fore hull (like a hydroplane), and now wish to go brushless as I've been very impressed with my brushless electric glider's performance..

A few questions :- what motor /controller combination to fit ? (even though it's a fast electric – hopefully – I'd like reverse as well).

What prop to fit. The Graupner rep was in the model shop when I bought the 40 and suggested a 2-blade racing prop. They didn't have one, so, I got a 30 3-blader instead. BTW do these numbers refer to Pitch ?

As a young lad I had an RAF fire tender fitted with a "Mighty Midget" motor. This was also slow !!! However, the motor pulley drove a twin prop system via a rubber belt and 2 further pulleys on each prop shaft. Quite neat and I wonder if this would be less trouble than a twin motor set-up ? Maybe belt slip is a potential problem with a fast electric.

Sorry, I seem to have gone on a bit here…

Dave

[Dave Cooper 6Participant @davecooper6]

[harry smith 1Participant @harrysmith1]

Hi Dave

What size, type, voltage and mah is the glider's battery.

You maybe to use that !!!

On motor is a 28mm brushless T2836-1200kv, 340watts on 4S,shaft 4mm.

Unloaded rpm on 3S 13320 and on 4S 177760.

ESC with reverse Hobbyking car HK-60A (2-4S) weight 91grams.

Program card required(HK Prog-Card).

The larger Amp ESC will handle both 3 and 4S, so only upgrade you battery.

Hobbyking have some small lipo batteries in 3and 4S.

eg Turnigy 3S 1500mah 25C(73x33x27mm) and Zippy Compact 4S 1300mah 40C,

This will increase you power and loss a lot of weight.

ESC settings

1 Cutoff Voltage for 3S=10.2 and 4S=13.6
2 Start Power Percent=5%
3 Advance Timing=4
4 Run Mode=2
5 Brake Force=1
6 Drag Brake Force=1
7 Neutral Range=1
8 Initial Brake Force=1
9 Reverse Force=1

Harry Smith

[ashley needhamParticipant @ashleyneedham69188]

Hi Dave and welcome to the forum.

Using the setup as advised by Harry would no doubt provide the best solution to your question, as Harry has a lot of experience. The boat would also be very, very fast…

Do you have other models, and thus batteries to use or will you be starting from scratch?

Dare I suggest it, but for this modestly sized vessel, as a bit of fun, a speed 400 brushed can motor on a 6-cell (7.2V) Nimh and a 35 or 30mm prop would likely propel the boat at a reasonable speed. If you are a Lipo user currently then by all means use a Lipo pack, 2s.

The can motor may well fit easily in place of the old. A 20A Mtronics Viper ESC would be suitable at about £28 ish, and provide reverse, as well as being reasonably small and light.

GENERALISATION: TO BE TREATED AS A GUIDE!…. Common 2 blade plastic props come in course "X" pitch or fine "S" pitch. The S pitch ones would be suitable for the motor, at 35mm (as 30mm ones seem to be not available). 3 blade "scale" props are not suitable for high speed work and give poor reversing thrust. HOWEVER it is worth trying these things out on the boat, plastic props being cheap.

A 28mm brushless of 1200 (ish) Kv would be another choice as Harry suggests. Possibly something of 80-100 Watts would give sufficient performance on 2s or 3s Lipo batts. This is not contradicting harry, just offering an alternative.

Ashley

[Malcolm FraryParticipant @malcolmfrary95515]

The prop numbers probably give the diameter in mm. Back then, electric motors were pretty dire, dry cell batteries were better at being ballast than supplying power. Almost any clockwork boat could outrun an electric one. The 40 was probably the best answer to matching up a poor motor with a battery of very limited capability, but back then they were the only games in town.

This changed with the introduction of Mabuchi and Kako motors – not very good by todays standards, but a vast improvement over everything that went before. Todays motors are generally better yet.

For simplicity in picking parts, I would go brushed – a 280 motor, a NiMh (or LiPo) of voltage to suit what the label on the motor says and probably a Marine Viper 10 to control it. On a 16" boat that started as an RAF launch, a very much smaller prop will give the speed wanted. Big props are good for discharging batteries rapidly, causing the motor to convert stored power into heat. Over powering any hull rarely ends well.

I'm not sure that making the hull into a stepped type wil actually help – the Italians and Russians tried – if it had worked well, everybody would be using them.

[Dave MilbournParticipant @davemilbourn48782]

I think that the motor and battery suggested by Harry would not only be too powerful for this small model but also too large to fit. My only experience with something similar was an all-balsa Swordsman I made some years ago. It was about 20" long and, like Ashley suggested, had a Speed 400 and 7.2v NiMH AA-size pack. The prop was a 25mm 2-blade bronze job from Propshop and it was pretty darned quick! A 15A ESC would be plenty to cope with that motor, which shouldn't be loaded to more than 10A.

Dave M

[Charles OatesParticipant @charlesoates31738]

I was about to post suggesting a 400 motor but Ashley has beaten me to it. Would I be correct in assuming that the model has a relatively narrow beam, I.e. not built like a racing model. If so too much power will be bad idea. To get some idea about small fast boats look on YouTube at club 500 boats. These are a little bigger than yours, but using not much more power than we are suggesting go very quickly. They were also designed to be stable, yours might not be.

A modest brushless set up will go much faster, is that a good idea?

Hope that helps a bit.

Chas

[Charles OatesParticipant @charlesoates31738]

Sorry, I missed part of your question. Pulley drives are great for plodding models, forget about them for a quick one. Twin drive is possible in a quick 16 inch boat, but will need care, skill, experience and luck. Forget about that too.

Chas

[Dave Cooper 6Participant @davecooper6]

Thanks for the very comprehensive replies everyone – obviously a wealth of experience here… some more data on the model and equipment currently available :-

Length = 16" , Beam = 4.5", Empty hull weight (with rudder and steering servo /linkage) = 236 gms.

Motor label says "380 /385S" and is 280mm diam. 6 volt (runs quite nicely both ways and is now suppressed).

Shaft diameter = 2mm (I think this was why I couldn't get a two-blade racing one originally ?).

Props = '40' and '30' both 3-blader's.

Controller = "Bob's Board" , Type PB2, rated at up to 2.5 amps – servo mounted.

Available LiPo's (from my aircraft stock) :-

2s 7.4 v 450 Mah 20c weight 31gms

2s 7.4 v 1500 Mah 25-35c weight 83gms*

2s 7.4 v 2200 Mah 20c weight 123gms

* Size for 1500 Mah is 70 x 35 x 18 mm

Yes, not sure about the stepped hull either. Maybe worth a try along with one of the above LiPo's and the existing motor as a first test ? The 'step' was installed a few years ago so would require 'surgery' to remove !

Going to a generic model show on Sunday so may be able to source a better shaft /prop etc. to experiment with…

Regards,

Dave

[Malcolm FraryParticipant @malcolmfrary95515]

My Lotse (about 22" long) performed quite indecently well on a Lightspeed 400 intended for, and run on, a 7 cell NiMH pack via a 24mm 2 blade prop. A 16" boat will weigh a bit under half a similarly shaped 22" boat. The Lotse, ready to go, weighed 1Kg, a 16" boat will be less in proportion, and will need less power to move it similarly, which is why I suggested a 280 and a 20mm prop. Maybe a 360, a largely forgotten motor capable of spinning quite fast but with quite modest current requirements.

A small prop spinning fast will create fast moving water which, since every action has an equal and opposite reaction, a fast boat. A big prop shifting the same volume of water will not move it as fast, but will try to spin the hull in the opposite direction.

Probably the most important way to getting performance from a small boat is to keep the weight down. Only needing, and therefore using, a smaller, lighter speed control is a good start, especally if this means a smaller battery.

[ashley needhamParticipant @ashleyneedham69188]

A 380 is similar to a 400, in that it is a revvy beast, and should be ok on a 2s Lipo. A 385 is a somewhat slower motor usually rated to 12v or so, but in both cases it depends on the manufacturer as to the actual spec. Luckily a swap to a “known” 400 or what have you should be simply a straight swap. A 480 is the same diameter but a few mm longer and is a bit more powerful. Those from JP products are rated at 9.6 v.

The shaft at 2mm is too weedy and needs changing to a 4mm one, as this is the most common size allowing a wide choice of props. Having dissed the 3 blade props for fast work, they are cheap and worth a go..35mm I would try.

ideally a wattmeter would be good to make sure the motor is not overloaded, but fitting a fuse and checking how hot the motor gets after a few mins thrashing about will do.

best way to fit a fuse is to use electrical female blade connectors, crimped on, and insert a car type blade fuse. An easy way to retro-fit.

Ashley

[Charles OatesParticipant @charlesoates31738]

Hi Dave, try the 380 as Ashley said, but as he also says, that motor can vary according to manufacturer, I have 1 rated at 6 volts maximum. Try it with a 30 mm prop first, if it burns out, nothing lost. ( in the bath so you don't lose the boat.) If it works, that's great, if not get a better motor. If you have an ammeter, you can test it all properly, if not stick to the above.

Ditch the bobs board, not up to the job at all.

chas

[Dave MilbournParticipant @davemilbourn48782]

I'd strongly advise against a 35mm prop on a 380 – either 2- or 3-blade. My 2836 750kv brushless motors run on 35mm props and they are seriously more powerful than a Speed 400/480.

25mm is more like the size to go for or you'll draw over the magic 10A and be rewarded with smell followed by smoke and then silence… Agree 100% with Mr Oates ref Bob's Boards, and the 1500maH LiPo should be about right.

You can buy a 4mm shaft which runs in a 6mm O/D tube – Model Boat Bits sell them.

Dave M

[Ray Wood 3Participant @raywood3]

Hi All

my contribution is 15" long Ferret, free plan in MB's last year, 280 size brushed motors 15amp Mtronics 25mm 3 blade prop brass, 2 cell Lipo 7.4v 1100mah, skips around on the plane for 6-7mins 😀

Regards Ray

[Dave Cooper 6Participant @davecooper6]

Hi Folks,

Thanks once again for all the techie advice. I think the 'must haves' are: larger diam. shaft, new speed controller, fuse, and a selection of props to play with (including 2-bladers).

Looking through my son's buggy stock, I've found a small collection of motors going from 280(ish) up to a 540 can-size, so, can afford to burn out a few in the bath on a trial and error basis !

Been thinking about the stepped hull. This is a shallow 'v' stationed at about 1/4 to 1/3 back from the bow. At mid-ships it is 8mm deep and tapers to 3mm outboard. If it doesn't work, and /or makes the model unstable, I can convert it from the shallow 'v' tapering aft to a flat bottom stern without too much bother ie by adding some extra sheeting (whilst watching the dreaded weight gain).

Dave

[ashley needhamParticipant @ashleyneedham69188]

Dave. I have been using blue styrofoam lately, and a 10m sheet would do nicely for filling behind the step if that’s what you decide. It would weigh nothing and actually add to the buoyancy.

The normal 3 blade plastic types normally have a very fine pitch (they look very flat) and I think are worth a try on a 380. I certainly would not try a brass 3 blade prop of that size however.

Ashley

[Chris EParticipant @chrise]

Posted by Ray Wood 2 on 05/08/2019 17:46:53:

Hi All

my contribution is 15" long Ferret, free plan in MB's last year, 280 size brushed motors 15amp Mtronics 25mm 3 blade prop brass, 2 cell Lipo 7.4v 1100mah, skips around on the plane for 6-7mins 😀

Regards Ray

 

Is this a case of different motor with a different specification or is something odd?

Your post says that your 1100mah LiPo runs Ferret on the plane for 6-7mins. That is roughly 1/10 of an hour which means that you are running at around 10x the capacity of the battery. That is a current of lets say 10 to 11amps. Graupner list the stall current of their 280 as 6.8amps at 6v.

I have never thought of the 280 as a particularly strong motor and certainly not one that shrugs off abuse.

Chris

Edited By Chris E 1 on 06/08/2019 14:36:31

Edited By Chris E 1 on 06/08/2019 14:37:26

[Ray Wood 3Participant @raywood3]

Chris,

The motor is a Robbe Slow Fly 280, must be magic I guess? I don't do technical it either works or don't 😀

Decent pictures of Ferret planing in Model Boats July 2018 as the free plan.

Regards Ray

[Dave Cooper 6Participant @davecooper6]

Hi Ashley, Chris, Ray.

Thanks also for your contribution. Current thinking is to change one thing at a time on the launch – that way I can see what's having what effect. I still don't know if the hull design is sound yet !

I'm staying 'brushed' for the time being even though a brushless set-up would, ultimately, "add lightness" (an old Colin Chapman aim for making racing cars quick).

Looking at the trim of the boat in the kitchen sink, I could do with shifting some weight aft. I've had to shorten the shaft by 12mm in order to fit the Huco coupling (1st job)…so, only the receiver will be in the bows. The 1500 Mah Lipo fits nicely in front of the rudder servo ie well aft.

Has anyone had to resort to using ballast to get a model to plane, or, is all this in the hull design ?

Regards, Dave

[ashley needhamParticipant @ashleyneedham69188]

Dave. Ideally you do not want to add ballast to a planing boat. The usual avenue is shifting the battery about.

Test first, alter later.

Ashley

[Dave Cooper 6Participant @davecooper6]

Thanks Ashley – that makes sense. Just finishing off a bit of bow shaping /rudder hatch access at present. As soon as I've got this in primer I'll post a few pic's for all to comment on…

Dave

[Dave Cooper 6Participant @davecooper6]

Hi Folks

I have a few images to share comments on, but, could not get any of the 'image' icons on the "Post a reply" window to work. Also, it's nearly 60 years since I studied any Latin, so, that window /frame wasn't much help either !

There must be an easier way !!!

Dave

[Charles OatesParticipant @charlesoates31738]

**LINK**

Hi dave, the above is a link to a section on the forum homepage about how to post pictures.

Ask if you have any problems with it.

Charles

[Dave Cooper 6Participant @davecooper6]

Thanks for the link Charles but one problem remains…

Re-sized 3 images in Paint (all jpegs), typically, these are now 150×113 pixels and around 166 Kb in size.

Then, created the album and uploaded the re-sized images. Using the camera symbol then inserts the image into the forum post box but the size is massive, fills the whole box and even needs scroll bars to view it !

Name of the Album is "Dave's RAF Launch" if you want a look-see.

Confused of Wiltshire…

[Ray Wood 3Participant @raywood3]

Hi Dave,

The photos look fine in your album to me 😀 all you need to attach them to your posts.

Regards Ray

Edited By Ray Wood 2 on 23/08/2019 21:30:00

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