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Author Topic: Transmission Noise  (Read 3104 times)

BreezyB

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Transmission Noise
« on: September 10, 2009, 04:04:21 PM »

I'm using a "piggyback" motor configuration where the motor sits above the prop tube and drives the shaft through a Graupner 2:1 nylon gearbox both mounted on an 1/8" plywood bulkhead.  I would expect gear noise with this setup but I felt that in this case it was excesssive. While checking a few things I replicated the driveset up on the bench and the result was that the motor/gearbox just gave an acceptabe whirrring.  O0
I also ran the motor on its own and it just gave a low unobtrusive "hum" BUT when I held it against the plywood bulkhead it amplified the motor noise alarmingly.  >:-o  Clearly the balsa hull is behaving like a perfect sound box but insulating the motor mounting point with rubber sheet hasnt really helped. I guess the inside hull surfaces need to be sound deadened?????. I wondered about using expanding PU foam or similar.
Ideas would be gratefully received.
Regards
Barrie.
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toesupwa

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Re: Transmission Noise
« Reply #1 on: September 10, 2009, 04:53:31 PM »

I'm using a "piggyback" motor configuration where the motor sits above the prop tube and drives the shaft through a Graupner 2:1 nylon gearbox both mounted on an 1/8" plywood bulkhead.  I would expect gear noise with this setup but I felt that in this case it was excesssive. While checking a few things I replicated the driveset up on the bench and the result was that the motor/gearbox just gave an acceptabe whirrring.  O0

Is this with the boat in the water or on the bench?. Remember that with the boat in the water, the noise will be deadened by the water surrounding the boat.

Yes, use some closed cell expanded foam in certain areas as sound deadening material, also doubles as floatation by the way...

Can you isolate the gearbox from the bulkhead?...
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Subculture

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Re: Transmission Noise
« Reply #2 on: September 10, 2009, 05:19:58 PM »

A chap I knew used to fix his motors in using silicone sealant. His boats were always exceptionally quiet.

BreezyB

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Re: Transmission Noise
« Reply #3 on: September 10, 2009, 08:49:58 PM »

Thanks for your input Chaps.
There is less noise in the water but I would say only marginally. I think the problem may be that I have made sure that nothing can move by screwing and epoxy'ing everything together which is ideal for transmitting the slightest sound and now it's too late to introduce any sound deadening between parts.
Thanks again,
Barrie.
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andygh

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Re: Transmission Noise
« Reply #4 on: September 11, 2009, 05:23:42 AM »

I have a Springer with one of those gearboxes in it. Out of the water it sounds like a chainsaw but when it's a couple of yards away from me on the water I can barely hear it
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HS93 (RIP)

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Re: Transmission Noise
« Reply #5 on: September 11, 2009, 07:04:17 AM »

swap for a toothed belt drive, much quieter, if its the standard Graupner 2:1 nylon gears I think the spacing is similar to mfa belt drives I would check first or just buy a belt and gears from http://www.hpcgears.com/    use this to check size   http://www.hpcgears.com/calc.htm.

Peter
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Greggy1964

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Re: Transmission Noise
« Reply #6 on: September 12, 2009, 01:56:54 PM »

My guess is that your empty hull is acting like a sounding box, rather like when a guitar string is plucked and the vibration through the instrument sounds through the guitar body.

Have you tried floating it in the bath? The water might dampen the hull and thus the sound.

I would also recommend supporting the rear of the motor by a structure fixed to the prop shaft and hull to prevent movement.
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BreezyB

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Re: Transmission Noise
« Reply #7 on: September 12, 2009, 04:38:38 PM »

Thanks to Andy,Peter and Greggy for your suggestions.
The more I look at this problem the more it comfirms my original thought in my first posting,  that the hull is amplifying the sounds (Greg's description is probably spot on) both in or out of the water.
I was tempted to go belt drive(Peter)  but as the motor on its own is quite noise when bolted in place, I suspect that the belt drive would only reduce the gear noise (which I guess would be worthwhile).
I'm reluctant to change things too much because generally the noise doesn't spoil the boat but I will experiment with trying to stop the hull reverberating.I'll let you know how I get on!!
Cheers everyone,
Barrie.
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Proteus

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Re: Transmission Noise
« Reply #8 on: September 12, 2009, 06:11:30 PM »

you cold try some sound deadening pads of cars the type you see in door panels and floors ,they are a mastic/rubber about 3mm thick and self adhesive and can be painted to seal them they would help if weight is not a desperate problem, but if you put them in the motor area it wont be to bad.

Proteus,
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Greggy1964

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Re: Transmission Noise
« Reply #9 on: September 12, 2009, 07:27:51 PM »

As Proteus says or you could go with that expanding insulating foam in area not used by radio gear and motor.

But be careful if you use it after your deck is on without decent escape areas for it, if forgot about this and made my escape ports too small and it blew the bl**dy deck off my boat! :o <*< <:(
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Proteus

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Re: Transmission Noise
« Reply #10 on: September 12, 2009, 08:30:10 PM »

No not foam , I am not a fan of foam in boats as it can cause rot in wooden boats and makes them very heavy this is the type of thing the top link , but try your good  local car factor , they sell them in small amounts or a body shop may have some of cuts

Proteus

http://www.passionauto.co.uk/products/car-audio/fitting-accessories/sound-deadening/2m-car-sound-deadening-proofing-sheet.php

http://www.caraudiodirect.co.uk/second-skin-damplifier-pack.html

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BreezyB

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Re: Transmission Noise
« Reply #11 on: September 14, 2009, 08:53:44 PM »

Many thanks to those who contributed offering solutions and advice.
I take the point about the dangers of expanding PU given by Greggy but the material described by Proteus ,sounds (Ooops Sorry!!) an interesting option which I will definitely investigate. I may try conversion to belt drive even if it reduces the noise by 50% it may be worth it.
Ah well ! something to do when the weather turns nasty!!
Thanks to all for your help  :-))
Barrie.
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cos918

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Re: Transmission Noise
« Reply #12 on: September 14, 2009, 09:59:17 PM »

Hi Barrie . In my ferry I had 2 gearboxes and they wined like hell . Try every thing apart from sound deadening   could not stop the wine. So I ripped them out and went for direct drive noise gone in an instant. That product suggested by Proteus does work well if fitted correctly but It does weigh a fair bit.

John   
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BreezyB

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Re: Transmission Noise
« Reply #13 on: September 15, 2009, 12:06:48 PM »

Thanks for sharing your experience, John, this all useful information.
After talking to my club members and Mayhemmers alike and judging by the results from my own experiments, this problem may be difficult to cure to an acceptable level ; your comments rather confirm that suspicion.
It dawned on me quite early on that direct drive would have been better and I will use it in future, but in this instance I'm not sure that there is enough room to reposition the motor so that it is in line.This may mean that I will have to pursue all other suggestions or wear ear plugs!!!.
Fortunately it is not all doom and gloom because the boat is so good in all other aspects and is a joy to sail. If I can fix the noise aspect it will be the icing on the cake!!!
Thanks John,
Barrie.

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HS93 (RIP)

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Re: Transmission Noise
« Reply #14 on: September 15, 2009, 12:31:06 PM »

If you need any info on belt drive or what you need and where to get it eather pm or on hear it Will make a very big difference just the belt drive

Peter
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andrewh

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Re: Transmission Noise
« Reply #15 on: September 15, 2009, 04:39:31 PM »

"Will make a very big difference just the belt drive"

True - the thing that excites the noise is the gear teeth both hitting each other (physically) and air being squooged out of the tooth area at noisy velocities. 

Both of these can be reduced by helical gears - but at the cost of end-thrust.  (Hence double helical or herringbone gears).

Breezy - I can see you are a thinker and experimenter :} 
You could try friction belt drive using turned pulleys from wood  and a belt cut from bicycle inner tube or similar!
Or you could use the same mount structure as for the gears but fit belt timing pulleys (about 1.7 to 1 ratios  - so long as they miss each other) and fit a third pulley (doesn't need teeth) to take up the tension (mounted somewhere out to the side)
Hard to describe - will sketch if it would help.  There is no need then to find a matched toothed belt
andrew
rob an old printer - they used to have them in the paper drive!


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malcolmfrary

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Re: Transmission Noise
« Reply #16 on: September 19, 2009, 01:08:31 PM »

To alter the resonance of a panel, stick something to a part of the panel.  Strip of wood, felt, heavy rubber, it all helps.  If the gears are enclosed, filling the void with light grease should help reduce the hammering effect that andrewh mentions without the gears coating the insides of the boat when the motor runs.
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BreezyB

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Re: Transmission Noise
« Reply #17 on: September 19, 2009, 04:42:43 PM »

Thanks to Andy (again) and Malcolm for your ideas. I am about to go down the belt drive route with the help of HS93 (Peter) who has a lot of experience with this type of drive. The bits only cost peanuts and I wont have to change the shaft/motor centres so it will be quite straight forward to try this option. I will still try the sound insulation suggestions once the belt drive is up and running.
Ironically, this conversion/sound insulation thing started as just a passing thought but as Andy has already sensed, I cant leave well alone and it has now become a challenge!!!!. However, I get a great deal of pleasure out of this type of exercise,after all this is what model boats is all about!!!!. Thanks to all,

Barrie.
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red181

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Re: Transmission Noise
« Reply #18 on: October 23, 2009, 12:14:39 AM »

belt drive is also more resiliant, and you can easily (and cheaply) experiment with different ratios. Direct drive will introduce other problems such as plastic universal joints etc. MFA are a good source of beltys and gears, and the link posted earlier

I think this is a similar set up to yours?

as for the car deadening material, visit any car insurance repairers, always old panels getting thrown away, with the sound deadening stuck to the panel, usually no problem getting it off for free! :-))
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Ghost in the shell

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Re: Transmission Noise
« Reply #19 on: October 23, 2009, 01:52:46 AM »

idea: mount the driveline on rubber pads, with rubber sandwiched between the washer and the plate, and pad the surrounding area with sponge or acoustic damping foam off an old car bonnet
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BreezyB

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Re: Transmission Noise
« Reply #20 on: October 23, 2009, 06:12:33 PM »

Its ironic that Ghost should post an idea today as I have just completed the conversion from gears to belt drive. It needs to be stripped down and more carefully refitted as this set up was just a trial. The result has been very worthwhile, the motor still generates noise but is , in fact, quite pleasing but the harsh "chain saw" scream has completely gone, hurrah!!!!!!. With the help of Peter (HS93) I was able to install the timing pulleys inside the Graupner gearbox shell which is epoxied to the bulkhead and would have been difficult to change. HPC gears were really helpful and gave very quick delivery times.
I think the outcome has exceeded expectations largely because of the interest, ideas and technical advice from those Mayhemmers who gave me a helping hand (loud applause to you all).
Thanks guys
Barrie.

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