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[victorian]

I'm just testing out the setup for a 1/96 light cruiser (Pelorus, 1897) with two unbranded 385 motors and two micro Viper 10A ESC's.

The problem is that the motors emit a strong whining noise, loud enough to be irritating in a scale model. I don't know how much it will be attenuated by the superstructure because there isn't one yet!

The mechanical arrangement is OK with no undue loading, binding, etc. The current at full power with 8.4v battery is 1.5A in total, eg 750 mA for each motor. The noise is worse when throttled back.

Mtronik say the ESC works at 3.3 Khz and this appears to be the source of the noise, possibly being transduced by the motor windings. They can't help with any advice about suppressing the noise.

These are very neat little ESC's and it will be a shame to have to change them. There's no room for bigger motors but perhaps all 385's are not equal? Any advice would be appreciated.

[wombat]

I'm afraid there is nothing you can do about the noise - the whine is generated by the switching of the ESC when the motor is stalled because the pulses are too short to overcome the losses of the motor, or at very low speeds when the efficiency is very low.

I wouldn't worry too much though, the noise will only be at low speeds and will be damped out by the water.

Wom

[HS93 (RIP)]

Does this happen the same with five or more pole motors ??

Peter

[cdsc123]

I thought all 385s were 5-pole?

[wombat]

Does this happen the same with five or more pole motors ??

Peter

Yes - certainly my 755s whine quite well at stall and low speed. It is all down to vibration in the windings and the core as a result of the magnetic field generated by the inrush current. Because the motor is stalled or running at low speed, there is no or little back-emf so the current spikes are very high. The current produces a magnetic field which results in a mechanical shock pulse which gives the noise.

[malcolmfrary]

When you consider that a loudspeaker has all the same parts as a motor plus a flap to move air efficiently, it's not really a surprise to find that they behave like a loudspeaker, i.e. they whine when connected to a pulsed supply.
If you use an old type (pre-computer) ESC, the whine will be replaced by a hum, as they work at 50Hz.  These tend to be larher.  For silint operation, there is the resistane type such as a Bobs board, which control by dissipating unused power as heat, and tend to be a bit "steppy" in speed.  They also need careful matching to the motor and are not usually small.
Fortunately the whine gets damped by the enclosing superstructure and surrounding water.

[Tom@Crewe]

If only someone could come up with a modern controller, using old Technology. a modern bobs board! can you still get them? Even the old Electroniz were quiet.

[victorian]

Many thanks for the insightful replies gentlemen. I'm not sure to what extent the noise arises from vibration in the armature core, loose windings and other quality issues in the particular motors. It seems to me that 3Khz is quite a high frequency to be transmitted through the mass of the armature, motor frame and shaft.

Can anyone advise if there are better quality motors available in this form factor? The low speed behaviour of these motors is rather coarse compared with the 12 pole car heater motors I have used previously.

[DickyD]

Hi Victorian have you looked at the Deans Marine motors. I have a couple of them and they are excellent ,really quiet and smooth .

http://deansmarine.co.uk/order1/accp/Untitled-4.jpg

 

[CLANGER]

I think that the whining happens because when iron is magnetised it expands. The armature is magnetised on and off by the pulsating current from the ESC. Transformers hum for the same reason.
Alan

[wombat]

Well actually this is not the case - any change in the physical size of the iron due to magnetisation is negligable. The reason transformers hum is because there some flexibility in the laminations even when varnished and the windings are not perfecly solid. If you listen to an encapsulated transformer, it is typically far quieter than an open one.

I suspect in a motor, the main sources of whine are the windings on the armature shifting in the magnetic field, and the armature rattling in any play in the bearings

[Ghost in the shell]

my Vision 400 in the neptun I sail is hooked up to a marine 15 esc, and at low speed, it tends to whine at anything below 50% throttle, however on the water, its noise is negligable, dont worry about it, to deaden it perhaps some polystyrene in the hull around the motor to help muffle it?