motor advice

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motor advice

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27 December 2009 at 22:22 #1935
Red Ken
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@redken
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27 December 2009 at 22:22 #24777
Red Ken
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@redken
HI,

I have scratch built a Tug, it is 900mm. bow to stern and has a 200 mm. beam, it displaces about 5 kg.

I contacted a well known Model Boat supplier as to which motor to use, they recomended a 5 pole 540 type, which I duly installed with a Mtronic E.S.C. running on 7.2 volts. using a 40 prop.

On it’s first ‘sail’ I found that I could only get a speed slow enough by using the Transmitter throttle trim’s only, anything on the stick was too fast, more like a MTB than a Harbour Tug.

Can anyone advise of a suitable motor choice please ?

Something that would allow me to control using the stick and a moving the Tug at a sensible speed.

Thanks for reading this, any advice welcome.

Regards to all, Ken.
27 December 2009 at 23:35 #24778
neil hp
Participant
@neilhp
try using a 3;1 reduction gearbox fitted to the motor…..these are readily available from the motor suppliers and screw onto the end of the motor.

draw less juice as well.

Edited By neil howard-pritchard on 27/12/2009 23:36:29
28 December 2009 at 00:34 #24779
60watt
Participant
@60watt
Ken,if you mean a 545 when you say a 5 pole 540,I am not the only one of the opinion that they are not so good in the low speed range while running direct drive at low voltage.

If you have alternative motors and smaller props then give them a try(or both)

Alternatives are 3-pole 540 or 5-pole 550 or a 5-pole 555 (requires a higher voltage)

A gear reduction should improve things too but it involves more work and probably more expense.
28 December 2009 at 08:55 #24780
Dave Milbourn
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@davemilbourn48782
Ken

I have sent you a private message about this.

Dave M
28 December 2009 at 09:01 #24781
ashley needham
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@ashleyneedham69188
A common or garden MFA 540/1 motor would be my choice. Its not a powerful motor and whereas a 40mm prop might be on the big side for it, it will load it up ok for slow speeds (which is what you want).

Although,a 555 on 7.2v might well do…but ultimately it wont go very much faster than “scale” speed, ie nothing much in hand for emergencies or towing etc.

Years ago I bought 4 gold painted plastic 4 blade props in assorted sizes (40-60mm) and these were a bit of a dissapointment, as the pitch is very shallow, and they are fairly useless…BUT…something like it on your tug might slow it down without changing gear?

Ashley
29 December 2009 at 22:30 #24800
Red Ken
Participant
@redken
Thank you all for your advice, to answer a few points raised by your replies, the motor recommended was a 545, I had gained a couple of motors ( from redundant ambulance rotating beacons) they are 540’s and well run in, very free!

All motors that I have tried seem to have a high threshold voltage to start them rotating, in the Tug it means that it takes off at speed and needs a prompt ‘de-throttle’ to make it behave it’s self.

However, I will try your suggestions as if I get a motor which does not work in the Tug it would come in useful for the next boat I construct.

So thanks Neil, David, Ashley and Sixty Watt for taking the trouble to reply to this string.

I will keep watch for any further advice from whom-ever may want to offer it.

Ken.
29 December 2009 at 23:09 #24801
60watt
Participant
@60watt
That says you have a problem beyond the motor.Free up the shaft or use a smaller prop and if you can change any setting on the speed control then try that too.Speed controller output is a measurable quantity.Ideally you want a fully proportional output,no soft start, and not some strange profile suitable for aircraft or cars.

A higher torque or geared motor would be better at overcoming shaft friction.
30 December 2009 at 20:01 #24813
ashley needham
Participant
@ashleyneedham69188
The sort of 540 you need on a tug should be turning over on just a couple of volts, and the ESc should be able to provide this.

The props on all my boats can be turned at very slow speeds, no matter what the vessel…and mostly i use the Viper marine ESC`s.

You should not have any appreciable shaft friction, beyond a bit of grease drag, and even then not too much.

Ashley
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