Silent Power!

[Graham DaviesParticipant @grahamdavies40622]

Hi All,

 I’m new to the forum, so hi to all!

 I need a bit of advice regarding powertrains. I’m building a fishing baitboat (my 3rd now, they are getting steadily more refined and it’s heading for a commercial enterprise) and have a couple of little issues that I ought to resolve at this stage:

1. Noise. My current incarnation has a 600 sized motor driving a 60mm prop through an 80mm M5 shaft via a universal coupling. This is glued into a fibreglass hull and is rediculously noisy! The motor is tie-wrapped to a balsa mount, but this is not the problem. The UJ appears to clamp to the motor shaft slightly off centre and this transfers vibration to the shaft. The next generation will be a moulding of solid hard polystyrene (the really hard, indestructible stuff) so I need to have a quiter solution. Can anyone suggest a reliably drivetrain and how o attach it to the boat so it is deathly quiet?

2. Grunt vs Battery life. I don’t need massive speed, but a bit of pulling power. At the moment it’s pretty much OK, but is there anything better? I need to keep the costs as low as possible, but need excellent reliability. Would a gearbox be a better move? I run 6V lead acid batteries.

Very many thanks in advance!

Graham

[Malcolm FraryParticipant @malcolmfrary95515]

I have replaced the plastic U/J part with silicone rubber tube over the splined fittings.  The first try worked loose too easily, but clamping it down with heatshrink tubing cured that problem.  The motor might benefit from mounting on rubber bushes.  I usually use the servo mout rubbers that I dont use for servos.

[Graham DaviesParticipant @grahamdavies40622]

Thanks Malcom,

This sounds like a sensible plan; a piece of tubing is likely to find it’s own concentricity.

I’ll give it a go

 Graham

[Charles OatesParticipant @charlesoates31738]

You could try bedding the motor in silicon sealant, that stuff you put around the bath edge. It works for me  and stops the sound conducting to the hull. The hull act as a kind of resonator for motor noise. Also you need to align motor and shaft as accuratly as possible to keep noise and power loss down, that makes the bearings last a lot longer too. Bedding into silicon helps here too.

 Gearboxes are fine but usualy very noisy, belt drives are better, but still not as quiet as a direct drive.

[Graham DaviesParticipant @grahamdavies40622]

Thanks Charles,

 I think its the shaft that is transferring the noise. I can hold the motor by hand and run it and it is still quite noisy. A major refurb is probably in order, I think…

 Graham

[Malcolm FraryParticipant @malcolmfrary95515]

You could have gained some play in the bearings.  I had a shaft that was noisy, and the bearings were OK but the steel shaft had worn.  As Charles says, alignment is important.

You could do worse than look at the how to pages on

http://www.modelboatmayhem.co.uk/

Silicone sealant is a good motor mount, but some brands give of acetic acid (vinegar smell) while curing, which is not good for any metal parts.  I have started using hot glur gun glue instead.  Non-corrosive and sets a lot quicker.

[Charles OatesParticipant @charlesoates31738]

Malcolm is dead right about the how to pages, well worth a look, and I bet he’s right about the shaft, a short time running with miss-alignment will spoil it. As to hot glue for the motor bed, I’m not keen, if the motor stars to get warm it can move quite easily. Is the shaft properly suported? a short length without suport can ‘whip’ that would give you a lot of noise.

[Graham DaviesParticipant @grahamdavies40622]

Thanks guys,

 I had a look at the pages and learnt more in a coffee break than in years on my own!

 Alignment seems to be the issue, along with the fact that everything is a bit rigidly mounted so vibration is transferred directly to the hull. One big area of misalignment is the motor end of the UJ. The hole is a fair bit larger than the motor shaft so when the grub screw is tightened it pushes the whole lot off centre. I will open this out and turn a bush on my lathe to fit and take out the freeplay. I expect this to make a big difference.

 Cheers all

 Graham

[ManxmanParticipant @manxman]

Hi Graham,

I known its a little on the late side (only just joined the club) You mentioned the noise was being transfered by the prop shaft.  I had a similar problem with my Loyal, unbearable noise – all down to being too eager to get on the water and forgot to pack the propshaft with a light grease ! – cured the problem with mine.

Cheers – Ken

[Graham DaviesParticipant @grahamdavies40622]

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