Bismarck and a DD

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Bismarck and a DD

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12 January 2016 at 19:04 #62673

Max Cormick

Participant

@maxcormick

hi, guys ,

I'm planning to convert my Bismarck 1/200 trumpeter to an RC model

what I need is an help about :

which motor I have to use ?

I have 3 propshaft 2mm dia long 230mm, 3 raboesch propellers 25mm L,R,R

3esc for brushed lelectric motors …..but which motor I have to use

Consider I have an RX working at 7.2v and I would like to use 6v or at least 7.2v as battery unit with about 3800MA

second kit is DD fletcher 1/125 where I planned to use MFA Re-280/5 6v motors

are these motor ok for this type of warship or…..?

any suggestion will be appreciated

best regards

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12 January 2016 at 19:04 #2544

Max Cormick

Participant

@maxcormick

13 January 2016 at 09:55 #62681

Malcolm Frary

Participant

@malcolmfrary95515

Doing some basic arithmetic for Bismark at 1:200 says that the motors need about 20 watts total, about 3.5 amps on 6 volts. 3 of your 280s should be fine.

Repeating for the Fletcher (Lindberg Blue Devil?) says that the 280s should be good on 7.2 volts. If there is room, a pair of 380s might be better. It was a fast boat.

Arithmetic. Original power in HP times 750 to convert to watts, divide by the cube of the scale for model watts, add about 50% to allow for the HP figure being power out of the engines and the model power being power in to the motors.

13 January 2016 at 13:53 #62684

Max Cormick

Participant

@maxcormick

thank you mate,

Arithmetic:

Bismarck: power 46000hp

scale 1/200

watt_scale (Ws) = (46000*750)/(200^3)

watt scale 50(ws50)=ws+ws*(50/100)=6.46 watt

single motor should be 6.46/3=2.15

mfa Re-280/5 has as features: 1.99 watt ->2watt

is that right?

I would like to understand better please

regards

Maurizio

Edited By Max Cormick on 13/01/2016 13:58:05

Edited By Max Cormick on 13/01/2016 14:11:43

13 January 2016 at 14:32 #62685

Dave Milbourn

Participant

@davemilbourn48782

Maurizio

I agree that your calculations are correct (sorry, Malc!) but I also agree that, according to those calculations, three MFA 280/5 motors run on 6 volts should do the job @2W each.

Dave M

13 January 2016 at 14:54 #62687

Max Cormick

Participant

@maxcormick

@ dave Milbourn

oh yes the result was only per single electric motor

regards

Maurizio

14 January 2016 at 09:38 #62702

ashley needham

Participant

@ashleyneedham69188

Having had a quick surf. it seems this is a fair size kit and moderately heavy with it ballasted up to the waterline. Deans marine sell "Kyte" Motors for this if motorising is required (no tech spec). I am wondering if the 280`s are big enough. The MFA 280`s are a bit weedy, the Graupner/other Speed 280`s are more the job, but possibly a 385 or even 380 might be appropriate. I don't think there is a space or weight issue, and slightly larger motors would give more flexibility.
Ashley

14 January 2016 at 10:21 #62707

Max Cormick

Participant

@maxcormick

I have found:

MFA RE – 360/1

operating range 6v ——->what does it mean? —–> it work ONLY AT 6V like a light bulb works at 220V?

nominal 6v CONSTANT

no load : rpm10450 0.31A

max efficency 8706rpr 1.55A

wat= 5.66

MFA RE – 380

operating range 3.0 – 7.2v

nominal 7.2v CONSTANT ——->what does it mean?

no load :1A, 26000 rpm

max efficency 19000 rpm , 4.41A

watt: 19,68

which could be the right electric motor for bismarck?

14 January 2016 at 10:41 #62711

ashley needham

Participant

@ashleyneedham69188

The 360 is a bit weak. The beauty of the 300 can size is there are several models to choose from all offering various qualities, is revs (380), torque (385), .low current consumption (360) or max power (speed 400) etc, and are interchangeable as same shaft size/can diameter, no fiddling with adaptors.

I unfortunately subscribe to the heretical view that it is better to overpower a model rather than underpower it. After all, you have a throttle available, and it is always handy to have a bit extra in case of emergencies.

If I were making a 4 foot warship I might use a pair of larger 540/1 motors, but you have three shafts and small props, so these smaller motors are more suitable.

The constant bit means that this is the recommended voltage to run the motor at for maximum motor life (basically). The 360 will run at anything up to 15v, same for the 385…but only 7.2V for the 380/400, as these are higher performance motors, or at least, configured to deliver their maximum at 7.2V.

My Titanic is 4 foot long, and runs nicely on 3x 385 motors. using 2x 35mm and 1x 30mm props, on 6v. Goes really well on 12V.

Ashley

14 January 2016 at 12:13 #62714

Malcolm Frary

Participant

@malcolmfrary95515

Anybody remember when motors were sold as "suitable for boats ** inches long"? Oddly, it worked quite well before we discovered technical specifications.

Yes, the 280s would probably need to be at the top end of their voltage capability and revving their bits off I had a bit of a mental block regarding the size of this thing – 385s would be much better, and the availability of a bit of reserve warp speed is never a bad thing. The power figures were based on the information in a Janes for the period, and quoted as 150,000HP for the ship. However, it was a warship, and therefore owned by a government, so the figure could be open to considerable interpretation either way. Same with the displacement.

14 January 2016 at 12:21 #62715

Max Cormick

Participant

@maxcormick

anyway I made a Mistake:

Arithmetic:

Bismarck: power 150000hp effective

scale 1/200

watt_scale (Ws) = (150000*750)/(200^3)

watt scale 50(ws50)=ws+ws*(50/100)=21 watt

3 motors

single motor should be 21.093/3=7.0 watt

single mfa Re-280/5 has as features: 1.99 watt ->2watt ——> so No good for Bismarck

Fletcher: power 60000hp

scale 1/125

watt_scale (Ws) = (60000*750)/(125^3)

watt scale 50(ws50)=ws+ws*(50/100)=34 watt

2 motors

single motor should be 34/2=17.0 watt

than 2 re-380/1 ….???

14 January 2016 at 13:53 #62721

Dave Milbourn

Participant

@davemilbourn48782

I have used and can recommend this motor on 12v **LINK**

(or rather three of them) for the Bismarck.

Tony Hadley will bear me out as he fitted one to his 'Guardsman' and found the same as I did – it has plenty of torque; it's quiet and draws very little current. Incidentally the Nominal voltage is the one used as a basis for the subsequent statistics such as RPM, current etc. The Voltage Range (e.g. 6v to 12v) shows the lowest and highest recommended voltages suitable for the motor.

14 January 2016 at 17:26 #62734

Max Cormick

Participant

@maxcormick

Model

Voltage

NO LOAD

AT MAXIMUM EFFICIENCY

STALL
TORQUE

OPERATING
RANGE

NOMINAL

SPEED

CURRENT

SPEED

CURRENT

TORQUE

OUTPUT

EFF

RPM

oz – in

g – cm

oz – in

g – cm

RE – 385LN

6.0 – 12.0

12v CONSTANT

7300

0.15

5950

0.9

–

110

–

660

I have a ******pack Nimh 7,2V-2700 mah

my RX is powered at7.2V

which Amper value I have to consider to properly power my boat ? No load speed current is it?

14 January 2016 at 17:30 #62735

Dave Milbourn

Participant

@davemilbourn48782

I would recommend that you buy a 12v NiMH battery pack, because those motors will not produce much power if you use only 7.2v.

If you use speed controllers with battery eliminator circuitry (BEC) then you will not need a separate battery for the receiver. Have a look here for more information on BEC. **LINK**

Dave M

Edited By Dave Milbourn on 14/01/2016 17:31:03

14 January 2016 at 18:26 #62737

Max Cormick

Participant

@maxcormick

ok I will have:

3 Esc with BeC

1 rx at 7.2V….must be powered alone?

3 motors 385LN

3 small servos: 1 for rudders, and 2 for turret guns

? 12v NiMH battery pack …..

how many Amper do you suggest for at lest half hour endurance

what I have to consider to dimensioning the amper battery pack? no load amper current or Max efficency current?

regards

Maurizio

14 January 2016 at 19:01 #62740

Dave Milbourn

Participant

@davemilbourn48782

Maurizio

You should aim to fit the largest capacity of battery pack which will go inside the model without making it too heavy. The standard size of each cell is generally a Sub-C type so the difference between say a 3300maH and a 5000maH pack is very small in terms of size and weight. The Max Efficiency current value has more relevance to the battery capacity because it more closely resembles what will happen when the model is in the water.

Your receiver will work on the BEC from just one of the speed controllers so you should disable the BEC in the other two like this **LINK**

You should not connect another battery pack to your receiver; the BEC will power it via the main battery pack.

Dave M

14 January 2016 at 19:08 #62741

Malcolm Frary

Participant

@malcolmfrary95515

What kind of RX needs 7.2 volts? Some have a BEC built in that allegedly lets them run on up to 7.2, but all the ones that I have run across are intended for 4.8 to 5 volts to run on 4 rechargeable cells or a BEC. If using multiple ESCs each with a BEC, t is generally a good idea to disable all but one to stop them arguing over which should supply the 5 volts.

The general rule for battery packs is to measure the space then figure out how much weight the boat can carry, then fit the biggest that will still allow the boat to float. It should be well able to carry 10 cells at 3700mAH which should see you well over your 1/2 hour. When trying to figure out consumption, forget the no load numbers, look at the "max efficiency" ones to get nearer to reality.

14 January 2016 at 19:14 #62743

ashley needham

Participant

@ashleyneedham69188

Max. Others may disagree, but I would only have one ESC, of about 20A, and this will run all 3 motors in parallel easily, it will not even get warm. the Rx will be powered by the BEC (battery elimination circuit) in the ESC, unless you buy an ESC that does not have this facility.

Generally I would say get the largest capacity you can, but even a bog standard 3700mAhr Nimh will run the boat for probably an hour I would say. The no-load current rating has no relevance practically speaking. The motors are at their most efficient at the manufacturers max efficiency current rating and thus produce the most power at this value from the battery supply, and if you were mucking about with props and so on you could possibly get the motors running at max efficiency, but you have a set size prop, so the motors will draw what they draw. About oooo….2A possibly, bit more, or more likely a lot less.

SO. 3 motors at 2A is 6 amps …..a 4200mA battery supplies 4.2A for an hour, 8.4A for 30 mins and so on…there is no set formula for the run time, the more throttle you use, the less the run time, but with small motors like this even with mostly full throttle it will run and run.

HOWEVER, you will not be running the Bismark at full throttle for very long, it will be running at 1/2 throttle or even less, and so the motor current draw will be..oooooo….probly only2A or so….thus even a standard sort of battery will last well over an hour, at least.. My Titanic can be on the water for 2 hours and not run flat, but consider that the boat will not be moving all the time.

Ashley

14 January 2016 at 21:11 #62750

Max Cormick

Participant

@maxcormick

just to understand better ( it is my first RC model)

I have

an RX range 4-10v) and

385LN 6.0 – 12.0 with max efficency current : 0.9A

Every engine consumes 0.9 A / hour then 3 ampere / hour

IF I give max power for 10 seconds I will have 0,49A= 3*(0,99a*10s/60s)

SO I must have:

1.a power supply for the 'rx (range 4 to 10v), servos and ESC (working ar 5V)

and

2.a power supply for my motors 12v as well as Lipo 3S 5200mAh

doing so

I should have an hour of battery life as endurance

is that correct?

Maurizio

Edited By Max Cormick on 14/01/2016 21:14:02

14 January 2016 at 23:05 #62751

Dave Milbourn

Participant

@davemilbourn48782

Malcom/Ashley

Over to you boys…

Dave M

15 January 2016 at 09:36 #62754

ashley needham

Participant

@ashleyneedham69188

Max. You are thinking too hard here. All these theoretical calculations are just that, and are rarely valid due to a host of other factors.

Fit one 20A ESC, with BEC facility, a 5000 mAhr 12v Nimh battery and you will get well over an hour running time, probably two hours..the battery will last to supply all the motors, ESC and servos, no problem.. This setup will work just fine, it may not be the absolute best but it is always the right thing to keep a build simple.

Ashley

15 January 2016 at 09:57 #62756

Dave Milbourn

Participant

@davemilbourn48782

Exactly like this:

15 January 2016 at 10:19 #62757

Malcolm Frary

Participant

@malcolmfrary95515

What Ashley and Dave said. Simple is good, especially on a first build.

The arrangement shown controls all three motors together, and in this case, as drawn, all three motors will turn the same way. If one of the motors needs to turn the other way, just reverse the connections to that motor. This is one of the few cases where fuses between ESC and motor makes sense – the fuses act as a handy test point as well as allowing for a misbehaving motor to not affect the other two.

If you feel the need to have independent control of the motors, then you will need three ESCs, and a rather different wiring diagram because there are many possible different arrangements. But probably it is best to keep it simple for now.

15 January 2016 at 15:51 #62769

ashley needham

Participant

@ashleyneedham69188

DM> Thank you, nice clear diagram, of the sort you do so well.

Malcolm. Thank you also, the reversing of the motors will probably have to be taken into account as I would imagine the props are left and right handed.

An easy way of fitting fuses is to simply crimp in a pair of 1/4" or whatever the metric is female blade connectors and fit car type flat blade fuses into one of the motor wires. Again, not fancy, but cheap and easy. 3 or 5A fuses will be more than sufficient.

Ashley

15 January 2016 at 16:01 #62771

Max Cormick

Participant

@maxcormick

I see it is easy

the power unit 12v Nimh work only for motors and I will use an other unit ( 7,2v as I have) for my receiver

thank you

For the fletcher I cannot use 2 385LN

I saw a Dumas 4.8V Motor 2021 but I dont know any tecnical features except 4.8v…..

an other one is MFA re360/1 ( I'm not able to show the Link sry)

looking at : http://www.cornwallmodelboats.co.uk/acatalog/JP-Motors.html