Author Topic: Motor noise (Read 1071 times)

John Witt · « **on:** April 04, 2010, 11:35:39 AM »

During the first flights of the Jenny, I noticed that the motor made a turbine-like whine, which, when associated with the wind noise of the wire bracing made a very un-characteristic sound like the Jenny was powered by a turboprop. Not at all like an OX-5.

After thinking about this, I decided that the sound was likely a resonant noise from the steel magnet shell, since that was the only motor part that would give nice ring when tapped.

I wrapped the shell with two layers of electrical tape, taking some care to keep the tape thickness consistent around the shell, wrapping so that the lay of the tape was with the rotation and not against it. This worked very well. I estimate that something like 90% of the ringing has been damped out.

The motor still doesn't sound like an OX-5, but at least it's not pretending to be a gas turbine.

If you try this, keep an eye on the tape to make sure that motor heat isn't loosening the adhesive. You don't want a loose end beating your plane to death from the inside.

John W

Dennis Adamisin · « **Reply #1 on:** April 04, 2010, 12:24:00 PM »

That is a pretty amazing result. Mind the motor heat, as that tape could act like a blanket.

PLAN B: Look for some large shrink wrap - like they use on battery packs & such. That would prempt loose tape ends flapping away.

John Witt · « **Reply #2 on:** April 04, 2010, 08:42:24 PM »

Yes, that's a concern, Dennis. I wouldn't try it on a motor that runs warm/hot. The 1800 watt motor in the Jenny is mostly running at 1/3-1/2 throttle and is near the ambient temperature after landing.

Heat shrink would be better, for sure, but hard to find in 2 inch diameter, I suspect. Little motors might be easier.

John W

Dennis Adamisin · « **Reply #3 on:** April 04, 2010, 09:19:08 PM »

I used to buy it on large sizes for custom sailplane battery backs & such. What size motor are you using?

Dean Pappas · « **Reply #4 on:** April 05, 2010, 08:33:55 AM »

Yes, please.
Let us help you, and educate ourselves.
Provide all details: motor, RPM, prop, battery etc.
Please estimate the note frequency, too! Musician flying buddy, maybe?

The fact that you are running right at 1/2 throttle suggests that you may be hearing the switching or chopping rate.
Is it a high-note whine? That would be about right. Try raising the switching frequency to something above 20 KHz. If it disappears, then we have a winner.

If the motor is cool, try gluing a thick soft rubber ring cut from 1/4" sheet like a harmonic damper on a car crankshaft.

later,
Dean P.

TDM · « **Reply #5 on:** April 05, 2010, 10:05:03 AM »

I was worried about the destruction of our motors during flight due to high G loads in the maneuvers and how do some of us cope with this problem. I am not sure that we are addressing the problem in the first place simply because most of us are mounting the motor from the back on a fire wall.
Think about the point of mounting and weight distribution around this point. If you mount the motor from the back then you have the entire motor spinner and prop on one side of this mounting point and during the hard G loads on the motor all of this weigh is pressing against the bearings and forces the thin shaft to bend then the outer housing is hitting the magnets and Waaaaaammmmmm. On the opposite side if you mount the motor on a nose ring you have the prop and spinner on one side and the motor on the other side thus it has a much better balance. You still have the same load on the motor but the weight distribution evens up the load. So I advocate a front motor mounting on a nose ring.

Paul Walker · « **Reply #6 on:** April 05, 2010, 01:18:10 PM »

Quote from: Dorin Morosanu on April 05, 2010, 10:05:03 AM

I was worried about the destruction of our motors during flight due to high G loads in the maneuvers and how do some of us cope with this problem. I am not sure that we are addressing the problem in the first place simply because most of us are mounting the motor from the back on a fire wall.
Think about the point of mounting and weight distribution around this point. If you mount the motor from the back then you have the entire motor spinner and prop on one side of this mounting point and during the hard G loads on the motor all of this weigh is pressing against the bearings and forces the thin shaft to bend then the outer housing is hitting the magnets and Waaaaaammmmmm. On the opposite side if you mount the motor on a nose ring you have the prop and spinner on one side and the motor on the other side thus it has a much better balance. You still have the same load on the motor but the weight distribution evens up the load. So I advocate a front motor mounting on a nose ring.

I completely understand your concern, and logic. I thought the same.

However, after approcimately 600 electric flights, it has not proven to be an issue with the motors I use (Plettenberg). They are all rear mounted. To date, no issue.

Paul Walker

Dennis Adamisin · « **Reply #7 on:** April 05, 2010, 03:17:35 PM »

Quote from: Paul Walker on April 05, 2010, 01:18:10 PM

I completely understand your concern, and logic. I thought the same.

However, after approcimately 600 electric flights, it has not proven to be an issue with the motors I use (Plettenberg). They are all rear mounted. To date, no issue.

Paul Walker

NOW ya dunnit!

Dean Pappas · « **Reply #8 on:** April 05, 2010, 03:40:10 PM »

Dorin, you should have seen any of the several threads where we beat this one to death.
Your concer is valid, but only on a by-brand of motor basis.
The Pletty's have that big-end of the bell ring bearing.
The 40 series and up Hacker outrunners do as well.
This is very good!
Dean P.

Kim Doherty · « **Reply #9 on:** April 05, 2010, 09:04:49 PM »

Quote from: Dorin Morosanu on April 05, 2010, 10:05:03 AM

I was worried about the destruction of our motors during flight due to high G loads in the maneuvers and how do some of us cope with this problem. I am not sure that we are addressing the problem in the first place simply because most of us are mounting the motor from the back on a fire wall.
Think about the point of mounting and weight distribution around this point. If you mount the motor from the back then you have the entire motor spinner and prop on one side of this mounting point and during the hard G loads on the motor all of this weigh is pressing against the bearings and forces the thin shaft to bend then the outer housing is hitting the magnets and Waaaaaammmmmm. On the opposite side if you mount the motor on a nose ring you have the prop and spinner on one side and the motor on the other side thus it has a much better balance. You still have the same load on the motor but the weight distribution evens up the load. So I advocate a front motor mounting on a nose ring.

Dorin,

Mounting the motor from the rear allows you to reduce the amount of mass in the nose since you do not need to carry the structure all the way to the ring. I run the same motors as Paul and have never had an issue with a rear mount. You get what you pay for. (even if some people can't stand the thought of others purchasing quality products.)

Kim.

Keith Renecle · « **Reply #10 on:** April 05, 2010, 10:58:34 PM »

Hi John, To get back to your noise problem. My MVVS 6,5/910 motor sounds like a turbine on take-off as well. I set my timer gadget to start up slowly and this makes for a nice take-off. Right in the middle of the rpm range is where the harmonic noise comes in, so I reckon that Dean is spot on.......as usual. I think that it sounds great, but then my model is not a Jenny. Just an idea, you could add one of those sound generator cards with the aircraft sounds on them and make the Jenny sound like a real airplane. The demo's that I've listened to sound awesome, and I believe that this is the way that all scale models will eventually go.

Keith R

John Witt · « **Reply #11 on:** April 06, 2010, 02:01:52 PM »

The Jenny setup is listed here:

http://stunthanger.com/smf/index.php?topic=12044.msg150566#msg150566

This probably isn't too pertinent for most, since it's running with throttle control, but there you are.

The main thing about sound generators is the cost and of course the motor noise is still in the background. I think there is a German one that costs plenty, and just does the WWII engines. An OX-5 actually sounds about like a Cessna 150, since it's a V-8 and turning pretty slow. Don't recall what RAM has for sound, I know they have some boat stuff.

The tape wrapping took off the edge of the noise. I reckon it's about a 5-6 kHz note, probably from the chopping rate as Dean suggests, makes it about E8 (I'm a fiddler). The biggest realism problem is getting Cap't Eddie to run around front and pull the prop through.

The only motor I've had a bearing issue with was from a cart wheeled landing and that caused some dented bearing races. The motor had doubled 10mm bearings at the prop end and didn't bend the shaft. It was a rear mount and there are pictures here:

http://stunthanger.com/smf/index.php?topic=14560.msg131550#msg131550

John W

Dean Pappas · « **Reply #12 on:** April 06, 2010, 09:16:19 PM »

Hi John,
years ago, I was audio-tach'ing my planes with a tape recorder and a visit to my buddy the piano tuner's place.

later,
Dean P.

Author Topic: Motor noise (Read 1071 times)

John Witt

Motor noise

Dennis Adamisin

Re: Motor noise

John Witt

Re: Motor noise

Dennis Adamisin

Re: Motor noise

Dean Pappas

Re: Motor noise

TDM

Re: Motor noise

Paul Walker

Re: Motor noise

Dennis Adamisin

Re: Motor noise

Dean Pappas

Re: Motor noise

Kim Doherty

Re: Motor noise

Keith Renecle

Re: Motor noise

John Witt

Re: Motor noise

Dean Pappas

Re: Motor noise