Motor Coupler VIBRATION

[detox]

Today I tested two of my Octura 5mm .187 couplers for balance. I simply bolted a coupler onto motor shaft then spun it under full power while holding motor in hand. One of the two couplers was so out of balance I could hardly hold motor in hand. The other coupler (the good one) caused LOTS LESS vibration...so that is the one I will be using. I will test the rest of my other different size couplers and mark them good or bad. The machined aluminum couplers should do very well I hope.

Before testing your coupler I think it is best to clamp a small piece of the same size cable or wire to the inside of coupler. Cut cable or wire even with coupler's end then tighten coupler to acheive a more accurate test

Also the Octura 5mm .187 collet has two allen set screw locations that bolt to motor shaft, be sure to try both of those locations on motor shaft before discarding coupler as out of balance.

BTW ...has anyone ever tried balancing a coupler or collet?


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[hydromaddicted]

Yes you can balance them and some of them come way out of balance, heck I've had a few that were slightly off center.

[detox]

The stock coupler on my UL-1 was WAY OFF CENTER. The stock coupler on my SV27 was OK.


...

[properchopper]

Another thing I've encountered, since we're talking about balance, is the out-of-balance drive dog. After balancing a prop to the max, an out-of-balance drive dog makes that effort somewhat futile, at least I think. This has become most apparent with my latest wire drive/ball bearing strut installation. I plan on working out the drive dog balance by installing another setscrew opposite the first one but haven't gotten there yet.

[detox]

Maybe I could assemble the propeller, drive dog, allen screw, and nut to a prop shaft and then balance before attaching drive wire or cable. I think could rig up the Grimracer style balancer to do this?

Hughey .150 assembled cables use a pin in place of a allen set screw. The pin goes all the way thru drive dog. This method looks more uniform well balanced to me.

[Fluid]

Before you go to the trouble of trying to balance a drive dog, think for a minute. The major cause of vibration in an FE boat is the huge disruption caused by the prop blades slapping the water 2 or 3 times each revolution. The magnitude of that force is so much higher than any tiny vibration caused by a drive dog that it makes minor imbalance of driveline parts inconsequential. Trying to get a prop perfectly balanced on a static balancer is again silly, since much more vibration is caused by prop blades of slightly differing sizes slapping the water.

I'm not saying you should not balance your prop or not make certain that your couplers are straight - just that trying to make everything "perfect" is a futile effort. It doesn't matter.



.

[Gerwin Brommer]

I finally agree with Jay.
Better put the effort in shaping the prop right.

[properchopper]

Before you go to the trouble of trying to balance a drive dog, think for a minute. The major cause of vibration in an FE boat is the huge disruption caused by the prop blades slapping the water 2 or 3 times each revolution. The magnitude of that force is so much higher than any tiny vibration caused by a drive dog that it makes minor imbalance of driveline parts inconsequential. Trying to get a prop perfectly balanced on a static balancer is again silly, since much more vibration is caused by prop blades of slightly differing sizes slapping the water.

I'm not saying you should not balance your prop or not make certain that your couplers are straight - just that trying to make everything "perfect" is a futile effort. It doesn't matter.



.

Jay, that's exactly what I thought, and haven't balanced the drive dog after coming up with the same realization.

[Jeff Wohlt]

If your coupler is too far off and you are running brass only then watch where it may slap on the stuffing tube edge. Octura would replace this for you. Some a little time ago also were not as true as could be. Some batches just do not come out as straight....the balance is a different issue.

Coupler alone is not as big of deal unless it is visible BUT then hooking it to something like flex and causing wobble just carries that wobble to a much harder weight on the motor bearing and can shorten the life of it.

[detox]

If your coupler is too far off and you are running brass only then watch where it may slap on the stuffing tube edge. Octura would replace this for you. Some a little time ago also were not as true as could be. Some batches just do not come out as straight....the balance is a different issue.

Coupler alone is not as big of deal unless it is visible BUT then hooking it to something like flex and causing wobble just carries that wobble to a much harder weight on the motor bearing and can shorten the life of it.

Jeff, Can you attach a custom drive dog to prop shaft using a pin like some Hughey brand cable drives use? Maybe Hughey can make me a custom .187 cable with drive dog attached using pin.

[Jeff Wohlt]

I never have but should be easy to drill and use a roll pin to hammer thru. Ed does sell these if you need any. I can buy the Dogs from Ed and get the pins if that is what you are asking. These are great until you need to move the dog in or out...most do not need that.

[sundog]

Because of tolerances and different manufacturing methods, most couplers are not balanced. If you fit a shaft into the hole and it turns freely, when you tighten down one side (flat of shaft) it will be off center. This can be a critical problem on a jet drive where a small vibration or wobble will be noisy and even damaging at high rpm.

IF the coupler has 3 or 4 (3 preferred) screws spaced evenly around the perimeter of the coupler, you can spend some time adjusting it and get it straight and (usually) vibration free. I have asked Jeff to make me some custom couplers just for jet drives because of this problem. And I second the statement about trying different screws on the flat - it can make a noticeable difference.

[Mike Caruso]

Because of tolerances and different manufacturing methods, most couplers are not balanced. If you fit a shaft into the hole and it turns freely, when you tighten down one side (flat of shaft) it will be off center. This can be a critical problem on a jet drive where a small vibration or wobble will be noisy and even damaging at high rpm.

IF the coupler has 3 or 4 (3 preferred) screws spaced evenly around the perimeter of the coupler, you can spend some time adjusting it and get it straight and (usually) vibration free. I have asked Jeff to make me some custom couplers just for jet drives because of this problem. And I second the statement about trying different screws on the flat - it can make a noticeable difference.

All parts need to be balanced once you have done that, then work on reducing vibration which is a separate subject. One item that will screw up your balance jobs is TOO BIG of through hole size. I found great service from this company Ithink they are small CENCO GRINDING ( www.cencogrinding.com ) that will sell you 1 or 35 drill blanks you pick the sizes
Std and Metric sizes. They are so inexpensive average $2.50 each that I now have had to buy an empty drill index box Ha. I have .185, .187 + .189" which allow me to get a good fit for correct spot on the prop center line. Agreed try different screws and lengths plus always have a short section of shaft inside coupler Not hanging out where it can effect the balance. Look around this site ( www.ghbalancer.com ) Gary and I met in 1970 he was in school for electronics and building the SW balance. I was just hired to be trained how to balance at a Race engine building shop in Chicago man I was 20 years old a long time ago....... Mike

[Mike Caruso]

Because of tolerances and different manufacturing methods, most couplers are not balanced. If you fit a shaft into the hole and it turns freely, when you tighten down one side (flat of shaft) it will be off center. This can be a critical problem on a jet drive where a small vibration or wobble will be noisy and even damaging at high rpm.

IF the coupler has 3 or 4 (3 preferred) screws spaced evenly around the perimeter of the coupler, you can spend some time adjusting it and get it straight and (usually) vibration free. I have asked Jeff to make me some custom couplers just for jet drives because of this problem. And I second the statement about trying different screws on the flat - it can make a noticeable difference.

All parts need to be balanced once you have done that, then work on reducing vibration which is a separate subject. One item that will screw up your balance jobs is TOO BIG of through hole size. I found great service from this company I think they are small CENCO GRINDING ( www.cencogrinding.com ) that will sell you 1 or 35 drill blanks you pick the sizes
Std and Metric sizes. They are so inexpensive average $2.50 each that I now have had to buy an empty drill index box Ha. I have .185, .187 + .189" which allow me to get a good fit for correct spot on the prop center line. Agreed try different screws and lengths plus always have a short section of shaft inside coupler Not hanging out where it can effect the balance. Look around this site ( www.ghbalancer.com ) Gary and I met in 1970 he was in school for electronics and building the SW balance. I was just hired to be trained how to balance at a Race engine building shop in Chicago man I was 20 years old a long time ago....... Mike

[sundog]

All parts need to be balanced once you have done that, then work on reducing vibration which is a separate subject.

Hi Mike. When I was speaking of balancing, I was talking about the elimination of vibration. Please explain the difference. Thx, Sdg.