Model Boat Mayhem - Forum

Please login or register.

Login with username, password and session length.
Pages: [1]   Go Down

Author Topic: Propulsion advice please  (Read 3126 times)

colh107

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 41
  • Looking into getting back into it, after 35+ yrs!
  • Location: Lincoln
Propulsion advice please
« on: August 02, 2019, 06:11:27 PM »

I'm looking into resurrecting an old craft (35yrs+) - a Modav 'Sea Vixen' same as this
and hoping for helpful suggestions as to a suitable electric motor.
It is, in theory, a planing hull - hard chine with a chine rail on each side. LOA 64cm, beam 22cm, weight (without motor/batteries/RC) 1200g.
Any thoughts please for giving it a reasonable turn of speed? (I'd also be asking for appropriate prop ideas too).
Thanks.
Logged

RST

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 656
  • Location: UK
Re: Propulsion advice please
« Reply #1 on: August 02, 2019, 09:34:18 PM »

Hi,

Are you missing a picture on the post?  Does it already have a shaft and propeller (diameter and type, e.g no of blades)?
Do you want to stay brushed motor because I guess at some point soon you'll get allot af answers and some will say brushless and Li-Po.  Some folk's definition of a "reasonable" turn of speed is different from others.  I'm old school brushed and Ni-Mh so with the pic and propeller details it might help put something together.


Rich
Logged

colh107

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 41
  • Looking into getting back into it, after 35+ yrs!
  • Location: Lincoln
Re: Propulsion advice please
« Reply #2 on: August 02, 2019, 09:51:50 PM »

Hi Rich, I think 'this' in my msg is a link to a pic? (If I've posted it right). Or https://www.modelboats.co.uk/sites/2/images/member_albums/121166/old%20boat.jpg
The shaft is in there  - 8BA or 6BA thread, iirc. Yes, it's from that far back! I have a two-blade prop on there at the moment, 40mm but I guess that's easily changed as necessary.
Brushed/Brushless is more modern than my antique knowledge, but I would expect brushed would do me. I would probably be looking towards LiPo for the better energy vs. weight (and I have a charger for all types). I can dig into ESC etc once I know what motor/voltage/current I looking to.
Logged

canabus

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 761
  • Boats a hole in the water you pour money into!!!
  • Location: Tasmania,Australia
Re: Propulsion advice please
« Reply #3 on: August 03, 2019, 05:47:23 AM »

Hi colh107

Rock Crawler Brush motor(540(35mm) specs @ 7.2 volts(2S Lipo).

20turn 18400 rpm

27turn 15000 rpm

35turn 12500 rpm

45turn 9500 rpm

55turn 7700 rpm

65turn 7000 rpm

80turn 5500 rpm

The Raboesch prop chart recommends a maximum rpm for their props.

eg Two blade C Type 40mm is 11000rpm.

Other companies may have other ideas.

Plastic and CNC prop handle more rpm.

So a 35 turn brush motor should be OK.

On Lipo batteries a Turnigy 2650 mah 2S 30C is 136 x 43 x 12mm, connectors 4mm weight 139 grams.

Brush ESC I use the Hobbywing Quicrun 60 Amp 2-3S on all my brush motors.

Setup is by changing links for battery type and forward/reverse with NO BRAKE !!
Just straight forward into reverse.

It's simple and it works !!!

If you wish to change to brushless divide the voltage into the rpm require to get the KV rating.
eg 7.2 divide my is rounded up 1800kv.

Canabus
Logged

colh107

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 41
  • Looking into getting back into it, after 35+ yrs!
  • Location: Lincoln
Re: Propulsion advice please
« Reply #4 on: August 03, 2019, 02:34:23 PM »

Thanks for that Canabus.
Do you have views on what the Quicrun's BEC is like? I see from the manual that it's a switcher not linear. More efficient sure, but they can have their own problems (speaking from many experiences getting switcher-powered electronics through EMC regs!).
Would you advise an external BEC instead?

Logged

colh107

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 41
  • Looking into getting back into it, after 35+ yrs!
  • Location: Lincoln
Re: Propulsion advice please
« Reply #5 on: August 03, 2019, 03:34:04 PM »

You'd recommend I get rid of the existing speed controller then...??  {-) {-)
Logged

colh107

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 41
  • Looking into getting back into it, after 35+ yrs!
  • Location: Lincoln
Re: Propulsion advice please
« Reply #6 on: August 03, 2019, 05:00:20 PM »

I've taken a look at props. I have two, both 2-blade 45mm. One of them is a 'Radio Active' X type - I still have the bag it came in (50p, back then, from the Newcastle Model Shop!)[/size]One is coarser pitch than the other, so I guess I could try both? (I'll post pics if it would help anyone advise). They would also have the advantage that I wouldn't need to upgrade the shaft to M4 thread.
Logged

canabus

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 761
  • Boats a hole in the water you pour money into!!!
  • Location: Tasmania,Australia
Re: Propulsion advice please
« Reply #7 on: August 04, 2019, 07:35:20 AM »

Hi colh107

I have had no problems with the BEC's on the Quicrun ESC.
I got four and ordered another one last night.

Ran the Hellen fishing boat (14 pounds weight) for 2 hours and the 4000mah 2S Lipo only drop to 7.1 volts on a 3 blade 50mm prop.

The general pitch is 1.4, but you can get a finer 1.2 and a courser 1.6.

Canabus
Logged

colh107

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 41
  • Looking into getting back into it, after 35+ yrs!
  • Location: Lincoln
Re: Propulsion advice please
« Reply #8 on: October 06, 2019, 05:35:16 PM »

Hi colh107

Rock Crawler Brush motor(540(35mm) specs @ 7.2 volts(2S Lipo).
...


The Raboesch prop chart recommends a maximum rpm for their props.
...


So a 35 turn brush motor should be OK.
...
Canabus


So, within reason, the performance won't be so much affected by the number of turns, but the latter means selecting prop size/pitch suitable for the particular motor's optimum rpm?
Curious about your reference to 'rock crawler' - what's the characteristic of these types that made you refer to them? i.e. what's different about other styles. (Assuming this refers to the car type not a make!)
BTW, the kit [yeah, I still have the original box and plans  :-X ] says 'for 2.5cc or electric power' - so a non-fancy 540 would be about right?
Additional background - it has a 6V Decaperm in it at the moment, but that didn't give much speed. Might have just had wrong prop size, but I assumed it was because too low revs with the gear-down.

Logged

DaveM

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 347
  • Why on earth do I do this?
  • Location: Nottingham
Re: Propulsion advice please
« Reply #9 on: October 06, 2019, 06:04:51 PM »

This seems to be rather getting away from practicality. My advice would be to fit an MFA 540/1 motor, a 7.2v 4500maH Sub-C size NiMH pack, an MTroniks 15A speed controller and an S35 2- blade plastic prop.

Reasons? It's somewhere to start; you can buy it all from UK suppliers; it's relatively cheap, and it will provide a much better performance from the "get go" than what you currently have. You can then experiment with prop size/pitch and voltage until you're totally happy with it.
DaveM
Logged

colh107

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 41
  • Looking into getting back into it, after 35+ yrs!
  • Location: Lincoln
Re: Propulsion advice please
« Reply #10 on: October 06, 2019, 06:10:39 PM »

This seems to be rather getting away from practicality. My advice would be to fit an MFA 540/1 motor, a 7.2v 4500maH Sub-C size NiMH pack, an MTroniks 15A speed controller and an S35 2- blade plastic prop.

Reasons? It's somewhere to start; you can buy it all from UK suppliers; it's relatively cheap, and it will provide a much better performance from the "get go" than what you currently have. You can then experiment with prop size/pitch and voltage until you're totally happy with it.
DaveM


Thanks Dave. Certainly "UK, and relatively cheap" is something worthwhile. Some pointers to decent starting points is indeed what I'm after - some of my questions are just to try to get a better tech understanding of it all.  :-)



Logged

colh107

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 41
  • Looking into getting back into it, after 35+ yrs!
  • Location: Lincoln
Re: Propulsion advice please
« Reply #11 on: October 06, 2019, 08:35:00 PM »

This seems to be rather getting away from practicality. My advice would be to fit an MFA 540/1 motor, a 7.2v 4500maH Sub-C size NiMH pack, an MTroniks 15A speed controller and an S35 2- blade plastic prop.

Reasons? It's somewhere to start; you can buy it all from UK suppliers; it's relatively cheap, and it will provide a much better performance from the "get go" than what you currently have. You can then experiment with prop size/pitch and voltage until you're totally happy with it.
DaveM


Dave, what your was reasoning for suggesting NiMH rather than LiPo? No disagreement intended, just interested - as I say, I'm learning and gleaning as much experience as I can.
I know LiPos are tricky blighters - I've designed electronics with them so I know their dangers. (Though, from a tech point-of-view, the charging characteristic of a LiPo is actually way way easier to monitor and control than NiMH - it's just that the latter are less likely to burst into flames if you do it wrong....!)
But anyway, I have a balanced smart charger that I use on other projects. So the chemistry doesn't worry me - but if there's other advantages of NiMH in models then I'm interested to learn.



Logged

DaveM

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 347
  • Why on earth do I do this?
  • Location: Nottingham
Re: Propulsion advice please
« Reply #12 on: October 06, 2019, 08:52:52 PM »

I think you've answered most, if not all, of your questions about the choice of NiMH batteries.

I personally now use LiPo packs exclusively but there are many who are scared of them. If you're aware of, and happy with the particular needs of charging and maintaining LiPo cells then there is no reason I can think of to recommend NiMH batteries in preference to them.

Please don't lose sight of the fact that this forum is read and absorbed by many different people. Some them are technocrats while others are technoprats. It's often impossible to distinguish one from the other from a brief initial post so please forgive those of us who aim our replies more towards the latter than the former. As you say, no disagreement intended...

DaveM
Logged

colh107

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 41
  • Looking into getting back into it, after 35+ yrs!
  • Location: Lincoln
Re: Propulsion advice please
« Reply #13 on: October 06, 2019, 09:02:38 PM »

Please don't lose sight of the fact that this forum is read and absorbed by many different people. Some them are technocrats while others are technoprats. It's often impossible to distinguish one from the other from a brief initial post so please forgive those of us who aim our replies more towards the latter than the former. As you say, no disagreement intended...

DaveM


A fair and sage point indeed - I get what you mean. Thanks.  :-)) :-))

Logged
Pages: [1]   Go Up