Vibration & Noise

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Vibration & Noise

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10 June 2013 at 18:18 #41514
Howard
Participant
@howard79726
Hello;

A relative beginner, I thought I'd try building from scratch and have reached 'sea trials' stage on a 1:32 Higgins PT boat from Peter Miller's plan in MB. With hull sealed & painted, 7.2v Speed 600, 32mm Prop Shop fast electric prop (as suggested), 12", 4mm fineline propshaft,

2s Lipo + servo, ESC etc., I tried a few runs. She runs & handles straight & true, sits well in the water, but is rather noisy above half throttle.

By testing and eliminating the components in stages I found that the vibration comes from the propshaft, and if I take the actual shaft from the tube and roll it over glass it makes an eccentric tapping noise. Is this a regular problem? I could buy another shaft and replace the inner, fill it with grease, or simply concede that I won't solve it and complete the model as a freelance fire tender or something, and run it at more sedate (quieter) speeds. musing over experience gained as I twiddle the controls.

Any suggestions anyone, or is this an 'old chesnut' that one encounters now and then?

Edited By Howard on 10/06/2013 18:21:29

Edited By Colin Bishop, Website Editor on 21/06/2013 12:17:40
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10 June 2013 at 18:18 #2270
Howard
Participant
@howard79726
Noisy scratchbuilt Higgins
10 June 2013 at 21:25 #41516
ashley needham
Participant
@ashleyneedham69188
Howard.My personal opinion is;- 12 inches is on the long side for a 4mm propshaft, and the fineline ones have a thin tube and there is not much of a gap between tube and shaft. Any slight imbalance or the slightest..er..untrueness..of the actual shaft would give problems in the vibration department..

I favour "normal" size tubes, nylon bearings/stainless shafts..as sold by Marks models (perhaps as one supplier) and for a 12 incher I would only look at a 5mm shaft size.

Others will disagree, but thats my penn`orth of input.

ALSO..have you tried a different prop?? I would try this first..my TBD had a severe vibration nissue at speed (only at speed) and this was miraculously silenced (after, like you, I changed and beefed up other bits) by a simple change of prop. Plastic ones are cheap and a good old plastic two blade S or X prop will drive almost anything.

How is your motor mounted?? Those metal brackets can wobble somewhat using a single coupling..despite feeling solid in the boat. It is not unknown for the plastic/brass u/j`s to be less than concentric. I have used a plastic coupling (from Marks models) on the last couple of boats and they appear to work very well, and are capable of transmitting fairly reasonable power outputs and do not transmit vibration frome motor to shaft and vice versa.

Ashley.

Ashley
11 June 2013 at 09:47 #41521
Dave Milbourn
Participant
@davemilbourn48782
I would try and straighten or change the bent shaft as the first option, because keeping it as it is will never help the sitiuation. At best you'll be introducing another source of vibration (e.g. an unbalanced prop) to cancel it out. Grease will not dampen the vibration much but it will create drag on the shaft and increase the current drawn dramatically, especially in cold weather when the grease is less fluid.

I'll go along with Ashley ref MMB's flexible (silicon) couplings although there should be no vibration from the motor itself.

DM
11 June 2013 at 14:49 #41528
Howard
Participant
@howard79726
Gentlemen. Thank you for the suggestions; all helpful, none of them too time consuming or expensive. I will follow them up and add any items replaced to my ever-filling spares box, a testament to things that 'didn't quite work out'!

I did make up a motor mount for this model that incorporates a sleeve that fits over and hopefully aligns the propellor shaft (pics).

Howard
11 June 2013 at 22:35 #41533
Malcolm Frary
Participant
@malcolmfrary95515
A shaft that long and thin must be totally straight. Any curvature will cause it to flex when spun at speed, and no amount of alignment will solve it. Straighten it first, then you probably wont need any of the other cures. An extra bearing halfway could help, but might be difficult to arrange.
12 June 2013 at 07:14 #41536
Paul T
Participant
@pault84577
Howard

I would agree with the comments relating to a long 4mm shaft and I would suggest changing it for one with a larger diameter.

Regarding your model the frame looks superb and I compliment you on the quality of your joinery work.

Paul
21 June 2013 at 10:59 #41688
Howard
Participant
@howard79726
Gentlemen

I have replaced the coupling with a silicone rubber/ali composite one from MBB and fitted a plastic 2 blade X prop. Everything much smoother and quieter now – thanks for the help!

Howard
22 June 2013 at 09:58 #41711
ashley needham
Participant
@ashleyneedham69188
Howard. See, go for the cheap easy options first!! Did you swap both at the same time or was it just a combination of the two that stopped the buzz?? As I said, a change of prop did it for me.

Ashley
22 June 2013 at 23:41 #41754
Howard
Participant
@howard79726
Hi Ashley. I changed the prop first, and that really was the 'magic bullet' solution, but I had ordered the coupling also, largely because it seemed a bit mean on my part just to spend under 2 quid on a prop! So, on the 'don't knock it till you've tried it' principle I swapped the coupling, and I must say it seems a bit smoother and less 'slappy' than the plastic/brass one, and a good option for higher revs. Thanks once again.

Howard
23 June 2013 at 17:21 #41767
ashley needham
Participant
@ashleyneedham69188
Howard. I was amazed at the difference on my TBD. From an ear piercing sawmill buzz to relative quiet…all for £2 worth of prop. I would not have believed the difference.

I am sure the coupling will pay for itself, cutting down bearing wear in both shaft and motor.

Ashley
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