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[pt109]

I hope someone on the forum can help me to r/c a static model of a 1:35 scale Handalan (Spica-M) class missile boat.

The fibreglass hull is I believe from Orion Mouldings, its 48" long and 8" wide, with a single propshaft, but what i cannot find is any information as to what size of motor to fit in her.
The Handalans had a top speed of 34.5 knots and I would like her to have a reasonable scale speed without being too over the top - its not a speedboat so no loopy sized motors please .
It needs quite a bit of ballast to get her to the waterline, so I'd like to use extra batteries which should give me a reasonable long running time.
Has anyone any info or advice regarding what to fit? I've searched for other models of this class of boat to see what the had, but found nothing, also any advice as to prop size ?

[andyn]

An MMB 900 for the go and as many NIMH cells as you like in paralell for weight at 12v 

[stallspeed]

Psst,Andy!      http://www.modelboatmayhem.co.uk/forum/index.php?topic=20603.msg211704#msg211704

You might be the only one left who doesn't know that another Mayhem forum member SKAZ (Sologolf Kaddy?) is offloading the motors individually on Ebay for a tenner
12 v electric motor.
Body:                           52mm dia  85mm long
Shaft:                           single end 5.0mm dia ballraced
Commutator:                 12 pole, low noise
Voltage:                       12v DC
No load RPM:               6700 1.2A
Max efficiency:             5250rpm, 1500g cm, 80w, 12A, efficiency 55%
Max power:                  3200rpm, 3500g cm, 115w, 24A


MODERATION

Link to web site and ebay removed

Brian
Global Moderator

[FullLeatherJacket]

Nope - they're different motors, matey. Looks can be deceptive, you know.

FLJ

[DickyD]

Nope - they're different motors, matey. Looks can be deceptive, you know.

FLJ

Steady on Dave, you know Mr Stallspeed is always right 

[stallspeed]

There was no reference by me to MMB 900,if that is what you are thinking.

The performance spec I quoted actually matches that of the Graupner 900 and Mark reckons his 900's are a near equivalent here

[pt109]

Thanks for the info regarding a suitable motor, just so that I can get it in the water for trials, any ideas on a rough size of prop to start off with and how many blades, I can always experiment from there afterwards.
My other boats were all bought already set up by the previous owners, so I've never had to work these things out before

[stallspeed]

If you start with the props then a suitable motor can be found.
The Graupner 900 motors equivalents (google lukethemonkey) have loads of power but probably way too much torque and insufficient revs for the exact scale props for that boat,you wouldn't go anywhere in a hurry.
An example of one with less torque and more rpm than a Graupner 900 would be something like a torpedo 800 or RS-775
Going with less torque and more rpm for even smaller propswould be a 550.

[pt109]

When the superstructure was put on the fibreglass hull, the idea was to only have one prop instead of the three that it should have - less to go wrong, and as long as it looks good on the water I'm happy with that.
So forgetting about having a scale prop, if I got one of these 900 or equivalent motors, what size of prop could I use to get the model to travell at 2ft a second (approx scale speed) or maybe slightly faster to allow for headwinds on the pond

[stallspeed]

The way I would go about it is to bath test a 550 to measure current drain in order to find out the load torque the immersed propeller places on the motor...then pick a motor that would be more torque.
Have you got an unused selection of motors or props?
This might help.

[andygh]

As has been said, the 900 type motors would be far too torquey and slow revving for that type of boat. Personally I'd start with a Graupner 700bb turbo or similar and experiment with that

[red181]

PT109, there really isnt any definite answer to your question, it really is a matter of testing for yourself, however, you dont really want to be dragging unessassary weight around if you can help it, this will cause increase amp draw, loss of performance and extra heat.

I would start with a graupner 700bb turbo, 8.4 or 9.6v, start with a 45mm "x" prop, and 12v nimh. Then progress to 50mm "x" prop, keeping an eye on temperature of esc and motor as you go. The esc will have to be sufficient amp rating, and unless you have some way of measuring this in a bath test as previous notes, its really trial and error, you could fit fuses with a blow rating just less than the esc. Nimh batteries will give up the amps much quicker than lead acid, but will then run out quicker, so its a real play off, and only testing will give the answers. Lipo will be best, but there is then an additional expense. At testing stage I would stay with nimh and lead acid.

I got great results with my heavy 48" Huntsman, 700bb turbo, 9.6v, 19.2v nimh, 52.5mm "x" prop, look at the recent build thread for more info