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[chas]

My flower class has had a 385 in it for 15 years, with a 7.2 volt battery I run on half throttle. It's probably the ideal motor for these.

[HMS Invisible]

HI ALL just askin for some advise here as tiger sailed ok an a good trim an very stable but the old motors i have fitted in her need to come out as they keep blowin 40 amp fuses an i was tryin to save on dosh but im not goin to worry now so can anybody direct me to some good 7v to 15v brushed  motors as i need some powerfull motors as tiger is really heavy an its takin a lot of boost to get her movin ?
so can anybody help me ?
chrisb

Chris, I think I saw a photo of coarse pitched scale brass props on your build thread and I think I saw the figure 30mm mentioned somewhere.
On 12v the 555 would measure in the region of 3~3.5 amps at 3,000 to 2750 rpm. In my opinion the 555 is the optimum choice.

Question for those considering efficiency, endurance or optimum by a definition other than cost.
I have a 30mm scale brass prop sold by Radestock recommended the 1/72 Flower Class corvette. It was a near match to the plastic kit rendering. If it gives the same rpm and current measurements above then, to match the same rpm (or power output) an RE385 motor will draw what?

[Sealord]

   
    Hi mate , ship looks brilliant on the water, i hope to see it sailing soon.
         

[frogman3]

   
    Hi mate , ship looks brilliant on the water, i hope to see it sailing soon.
         

YES so do i m8 but got to get new motors first hope to get some at wings an wheels
chrisb

[unbuiltnautilus]

A RE 385 based on experience, but not science, is an ideal choice at say 7.2v/7.4v for a model such as a 1/72 Flower Class with a probable current drain between 2 and 3 1/2 Amps. I would argue that a 35mm prob would be a better choice though!
The drill motors in Tiger were from the start a terrible choice, especially at 12v. I use a pair on 5:1 reduction boxes and 60mm 3 blade brass props at 6v in a 74" landing craft to great effect. I also use a pair of them at 3.3:1 reduction and 14.8v in a 38" motor torpedo boat with 42mm Graupner handed hydro props, also to great and speedy effect. I would not exceed 35mm and 7.2v direct drive as the current will skyrocket due to the excess load. I would have chimed in earlier but it would have been to little effect, so I just waited till everything went pop instead..

[roycv]

Hi all, loads of information there, thanks for the 555 specs.
The RE and RS designations are R = round. E = metal brushes  S = carbon brushes.
For Mabuchi basic specs look up
 www.mabuchi-motor.com/product/knowledge/classification/designations.html
regards
Roy

[ballastanksian]

What a lovely looking model on a lovely looking pond! She looks majestic on water whatever the motors and fuses might have done to spoil things. Be proud of yourself Chris as you have worked so hard and the end is in sight even if through a small mountain of blown fuses    . But as previously mentioned, they stopped this masterpiece from melting or being damaged, and that will allow you to get her up and reliable so you can enjoy some cruises around that super looking pond.

[HMS Invisible]

If me bleating on about this seems familiar It's because I've said this all before. https://www.modelboatmayhem.co.uk/forum/index.php?topic=56555.0
The difference here is that Unbuiltnautilus has come up with a figure to work with.

Tabular data for the RE 385 is in pdf form https://www.mfacomodrills.com/pdfs/RE385.pdf  (It says Stall Current: RE385 at 12v = 5.55A)

Ignoring nonlinearity due to the presence of iron, 8 volt stall current (6x1.33v NiMH)will be (8/12) x 5.55 = 3.7 amp. For 7.2v it's 3.33 amp and 6.0v it's 2.8 amp 
Six freshly charged, cooled down NiMH cells has a no-load voltage of (6x1.33=) 8 volts. The voltage out the battery terminals drops under the motor load so take your pick of these three for a lower voltage. For simpicity's sake I'll assume it is measured at 7.2 volt.

Look at performance curves of https://www.google.com/search?q=dc+motor+performance+graph or look closely at and to the left of the 55 turn, 555 graph.

What you see is:-
* (drain) current at peak power output is half the stall current. (It is just above 50% because of iron loss)
* rpm at peak power is half the no-load rpm
* efficiency, because of iron loss at full load, is slightly under 50% at peak power
(In a coreless motor there is little or no iron loss and the efficiency peak is high and well to left of the graph but quickly drops off.)

If you increase prop load such that tacho measurement is below 50% of no-load figure or ammeter is greater than 50% of the stall current you pass the point of diminishing returns and larger or coarser props slow the model down to burn off most of your power as copper cosses in the motor.

In this theoretical case, the RE 385 at 7.2 volt is overloaded beyond 0.5x3.33= 1.67 amp. That is to say, if a 30mm prop actually gives a current drain of 2 to 3 1/2 amp then you would be well advised to drop to a smaller prop.
You could carry on with the larger prop and use an appropriate reduction gear to take it nearer the peak efficiency at (7.2/12 x 0.99)=0.6 amp then raise the voltage for more power and speed. You'd be even better advised to switch to a 555 motor instead.^*

If you still don't believe me then you will see it yourself in your results. The 555 and published data for the MFA com drills motors is correct and performance is referred up to 75 Celsius.

[frogman3]

What a lovely looking model on a lovely looking pond! She looks majestic on water whatever the motors and fuses might have done to spoil things. Be proud of yourself Chris as you have worked so hard and the end is in sight even if through a small mountain of blown fuses    . But as previously mentioned, they stopped this masterpiece from melting or being damaged, and that will allow you to get her up and reliable so you can enjoy some cruises around that super looking pond.

HI ballastanksian cheers yes i am proud of her but to me it was a big dissaponintment to have probs on her first voyouge  regarding blowin 40 amp fuses but she is a very heavy model an i can understand that yes there is a high current goin through to them motors  an hopefully new set of 4 motors will cure this prob an ive cured the rudder problem as it also had a faulty R/C PLUG that dint connect proberly on the signal wire but ive cut that off an soldered on a new plug an now the rudder is workin proberly an hope that the turning circle will be better so for now TIGER is U/S until i get the new motors an fit in but building her has been a quite enjoyable 4 yrs an many thanks for your nice comments on her an yes she does look good on the wet stuff at least she dint sink which i have seen some big models DO so thats something
ATB to you SIR
CHRISB

[chas]

Just to put in a couple of actual figures, measured in my snowberry corvette. Mfa 385 motor, 15 years old, 7.2 nimh pack, 35 mm s pitch 2 blade propeller. Very non scale but very effective. Current with boat held stationary in the water, 1.8 amps flat out. Current with normal cruising throttle, boat held stationary 1.4 amps.
  The battery is 3.3 ah, it powers the motor, rsdio, revolving guns and a home made mister smoke unit. I've never run the battery down in our Sunday sailing sessions.
    I also use 2 of these motors in my Deans Marine Emden, also from the same 7.2 battery with 35 mms prop shop props. It runs at a perfect scale speed on about 80% throttle.
  This is my actual experience with these motors. After 60 years of making models I rate them as being one of the most adaptable for scale boats.
   I also have a ferry model, the Ionic, similar to Vic Smeeds Bardic, this is a bigger heavier model and has a pair of 555 motors which are very well suited to the model.
  I've always found that other people's experience with equipment is helpfull, so I hope the above will help others.

[Akira]

Chris, She looks spectacular on the water. Sorry about your motor issues, but even the full size ones have issues, sometimes they never go away(think USS Zumwalt). I am sorry that you will prevail and she will be the envy of all who see her. If I may, when you swap out motors, make sure that your shafts spin freely, just a thought.Jonathan

[Phil22]

Huge congrats Chris, she looks stunning on the water! What a superb effort indeed.More pics please of the next sailing 
Cheers,Phil

[unbuiltnautilus]

Very helpful. Mine was a guestimate, yours we can take to the bank as they say!
For Tiger it looks like four 555 motors will be a perfect choice, as suggested by a number of well respected members (and Bob!). Still, the dance continues though

[frogman3]

Chris, She looks spectacular on the water. Sorry about your motor issues, but even the full size ones have issues, sometimes they never go away(think USS Zumwalt). I am sorry that you will prevail and she will be the envy of all who see her. If I may, when you swap out motors, make sure that your shafts spin freely, just a thought.Jonathan

HI Johnathan thank you an yes she looks good an yes i exspected some probs like you say on the real ships but for me not the motors an yes ive had others say do the prop shafts spin freely thinkin thats makin the motors work harder so drawin more amps but no they spin easy so that not the problem cheers for lookin in on the thread
chrisb

[frogman3]

Huge congrats Chris, she looks stunning on the water! What a superb effort indeed.More pics please of the next sailing 
Cheers,Phil

AN HI Phil yes im pleased at how she sailed all 3 mins of it before the fuses blew but hope to sort out the probs with new motors an yes there will be more pic an hopefully under power goin at flank speed
cheers ATB
chrisb

[Dan]

Hi Chris,


Just caught up on your thread. It looks fantastic on the water! You should definitely be happy with that. But I'm sorry to hear about your issues! Now you've found the motor issue, hopefully you can get that sorted relatively easily with your new motors. Fingers crossed for you. What sort of throw do you have on the rudder? Can it be increased?
I'm fully aware of how issues like that on the water can shadow the joy of completing a model like that and it's hard to see through it at the time. But it does look fantastic, and like others have said, many people think the same.

[frogman3]

Hi Chris,


Just caught up on your thread. It looks fantastic on the water! You should definitely be happy with that. But I'm sorry to hear about your issues! Now you've found the motor issue, hopefully you can get that sorted relatively easily with your new motors. Fingers crossed for you. What sort of throw do you have on the rudder? Can it be increased?
I'm fully aware of how issues like that on the water can shadow the joy of completing a model like that and it's hard to see through it at the time. But it does look fantastic, and like others have said, many people think the same.

HI YOUNG Dan thank you for your nice comments an yes im pleased with her how she sailed but oh so heavy she is but got to be to set her down in the water but motor drain like i had was totally unexspected an i was amazed at blowin 40 amp fuses as my nimitz an my norfolk all sailed ok on 30 amp fuses so hope 4 new motors will do the trick an rudder was not workin properly as a freind saw that the signal  wire in the rudder plug was not makin connection properly but it is now so one thing less to go wrong an the rudder goes as far as it can an its a big one but in scale of the ship an how goes your ocean ? as havnt seen much or is life gettin in the way
chrisb

[littoralcombat]

Chris, despite your electrical issues (which are part and parcel of any large Ship construction whether it be full-size or model variety), Tiger looks absolutely brilliant on the water. You should be rightly proud of your creation, I applaud you Sir.
Nige
 

[frogman3]

Chris, despite your electrical issues (which are part and parcel of any large Ship construction whether it be full-size or model variety), Tiger looks absolutely brilliant on the water. You should be rightly proud of your creation, I applaud you Sir.
Nige
 

HI Nige many thanks for your nice comments on my tiger have been to a model show W/W an bought 4 new motors so i hope they will do the job of getting her sailing properly fingers crossed
cheers sir
chrisb

[frogman3]

HI GUYS well i went to wings an wheels an bought 4 motors for tiger i bought 540 X  4 MOTORS but wheather they will be powerfull enough to move tiger i can only hope so will fit the in this comin week
chrisb 

[frogman3]

HI all well im not all that pleased with the new motors that i got at w/w as i was goin to buy some treble 555 motors but when i told the gent what ship i wanted to power he said they would be to low powered an sold me 4x MFA 540 motors but for now i have just fitted in two an left the rear johnsons motors in as the 540 motors dont sound to pokey so i am taken her up Nowich pond again tomorrow to try her out with the motors ive now fitted in her but im begininng to think i may need bigger motors an maybe a bit bigger props but will see how she goes tomorrow an linkpic to see new motors fitted in with yellow an black tags on the motors
https://ibb.co/ctkPtbt


chrisb 

[Rob47]

Good luck Chris
I just had a Mtronik esc go up in smoke for no reason, so you're not the only one with problems :)

[frogman3]

Good luck Chris
I just had a Mtronik esc go up in smoke for no reason, so you're not the only one with problems :)

OH DEAR Rob VERY SORRY to hear that an it seems to me the eletronics they make nowadays are rubbish an did you have a fuse in front of it wired into the ESC circut ? an my day was a disater as yes i sailed tiger at 9am this morn without the S/S on an i was not pleased with them motors as i thought it was slow an sluggish an still a 50 ft turning circle an then to make matter worst the flamein wind got up really high an blew my hat off an only a few small boats were able to sail in this wind but i dint dare put tiger on the pond as it would have been blown into the concrete sides of the pond an then to make maters worst i just left her on show for the day shootin off the guns an such an then when we were packin up i done a silly thing as i put the main S/S in a box to protect it in travel on my chair an that blasted wind blew it off onto the concrete so there is a little damage which can be rapaired but i think tiger is jinked im at a loss on what motors an maybe bigger props to to fit to get her movin OH DEAR chrisb

[Martin (Admin)]

Try four of these Chris! 

775 3500-9000RPM Large Torque High Speed Motor Gear Ball Bearings- DC12V-36V

eBay item number:404219043582
eBay item number:394369188645
Cheap enough at £9 quid each.

[frogman3]

HI Martin many thanks for the info an ive just oredered 4 motors so i'll try these out  i bet at the end i will have the biggest stash of motors anwhere lol
cheers chrisb