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[Biggles]

Hi Guys
Managed to pick up a Mk2 MFA Piranha unstarted kit, looking for electric motor suggestions? I have a spare Absima 10T brushed motor - 36.500 rpm, 170 watt, 7.2- 7.4 volt, 540 size. Any other suggestions please, I want it fairly fast but not too stupid!
Thank You for your help.

[Martin (Admin)]

 That looks like a 'standard' sized 540 /550 motor.
 Try that motor first, as it's a 'standard' size, you can always swap it out after-the-fact.

Also, be prepared to try several different props, to find one that matches the motor properly...


  https://www.absima.shop/pp/absima-electric-motor-thrust-b-spec-10t.htm?shop=absima_en&SessionId=&a=article&ProdNr=2310071&t=19114&c=19131&p=19131

 

[Subculture]

Go brushless. Better efficiency, no brushes to wear out, lighter etc.

[Biggles]

Any idea what size brushless and voltage, running a 35mm prop?
Thank you

[Subculture]

I would go for 3s (11.1v) minimum as that's kinder to the batteries. A 28mm or 35mm outrunner will be more than up to the job, and I would go for something rated around 1700-2500kv, which will give you a lively sport boat.

e.g. cheap as chips set-up, but these are pretty decent.

https://tinyurl.com/49e3ysyy

[Biggles]

Thank you for your help and advice, it’s greatly appreciated!
Happy New Year 2023 to you!

[chas]

Can someone educate me. How normal is it to run good but old model designs with a prop speed of 25,000 plus revs? My fastest models are 12-15,000 revs and they seem very quick to me. I'm betting on me getting too old and out of date.
Chas

[Subculture]

https://youtu.be/lMvlav39ouU

[Biggles]

Does anyone know if it’s possible to fit a KMB 28mm jetdrive to a Piranha?
Might be interesting!

[Subculture]

Sure, but a submerged drive works very well. Keep it simple.

[Martin (Admin)]

Anyone know what the differences are between the original & the MkII ?

[Fastelectrics]

Your 10 turn motor is a bit too hot for direct drive. Hook it up to a 3:1 gearbox to run it comfortably into a 30-35mm prop. The other option is to go brushless.

[Fastelectrics]

Here is a video of a similar boat running on 3 LiPo cells rated at 2200mAh. The motor is a 1800KV 2212 brushless. The boat went well but the motor ran too hot despite being water cooled. I have since swapped it for a larger motor rated at 1350KV. I am now just waiting for the local boating pond to be refilled so that I can test it.   https://www.youtube.com/watch?v=Aqt-Pq3QHD4

[Subculture]

What diameter and pitch of prop were you using with the 1800kv motor.
I tend to go for about 1.2x diameter pitch on my props.

[Subculture]

You may find this thread helpful.

https://www.modelboatmayhem.co.uk/forum/index.php/topic,29654.msg292647.html#msg292647

[Fastelectrics]

I think the prop on the video boat was a 1.4 pitch 30mm diameter.