Balancing driveshaft and prop

Discussion in 'Propulsion' started by darkapollo, Apr 2, 2021.

  1. darkapollo

    darkapollo Well-Known Member

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    Does anyone balance their props and drive shafts? Mine has a pretty bad vibration so I don’t want to go full speed on it for fear it will self destruct (and send the prop through the rudders again..)
    It shakes the grub screws loose pretty quickly.
     

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  2. Beaver

    Beaver 2020 Rookie of the Year Admiral (Supporter)

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    What prop?
     
  3. darkapollo

    darkapollo Well-Known Member

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    Just a plastic 3 blade prop for now. I think the issue is more from the u-joints on the intermediate shaft.
     
  4. Anvil_x

    Anvil_x Well-Known Member

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    the more out-of-true the U-Joints are, the more vibration you're going to get. if you get the motor more in-line with the shaft, the vibration should be reduced. I personally prefer using geared systems for this reason.

    U-Joints aren't meant to handle huge angular changes, they're for addressing slight deviations. pull the mount, and do your best to re-align it to your shaft. you shouldn't need to balance your prop or shafts unless you're spinning a huge prop at (for our hobby) a very high rpm. For example, running a 2+ inch prop with a big brushless motor.
     
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  5. darkapollo

    darkapollo Well-Known Member

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    Beaver and I were discussing it at length last night. It is 100% the slop in the u-joints causing the vibration. Unfortunately the motor is where it has to be for clearance. The angle is less than 14* on the intermediate shaft. It is aligned as straight on as I can with the u-joints as close to in phase as I can to mitigate the vibration. It has helped somewhat (a lot actually. It went from sounding like a blender to a diesel at idle) though I am still going to hit the grub screws with blue loctite just to be sure.

    Belt or gear drive may be in the future if it grenades itself.
     

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    Last edited: Apr 3, 2021
  6. wdodge0912

    wdodge0912 Well-Known Member

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    Doesn't matter
    Not sure if/how much it would affect these ships, but what about the phasing of the u joints?
    If my memory from college days serves me right (which was 9 years ago and then I never went into the field I got my degree in) they look out of phase.

    Id just square up the ends on the center shaft. Maybe even just replace it with some square stock. that part is where you would want to phase it at, they need to be on the same side. If I'm remembering correctly anyways.

    EDIT: didn't see the newest picture when I looked, looks a lot more in phase than the first one
     
    Last edited: Apr 3, 2021
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  7. Anvil_x

    Anvil_x Well-Known Member

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    Oh my.

    Dude I build wooden hulls. you can fix that pretty easy. When you see Beaver next time, he can show you. your motor mount is way too high. with a wood hull, once you glass it, you can Blammo-out a huge chunk of the hull with a cutter, re-contour and glass the mount into the hull itself. All those ribs and such are secondary strength/structural members once the glass is on there, so you won't weaken a fully-built hull

    I literally just did this on my Texas this winter. it's not a hard task, just takes some time and patience.

    All things considered, if the boat runs, go with it, and do this in your first big refit.
     
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  8. darkapollo

    darkapollo Well-Known Member

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    We shall “sea” tomorrow when she hits the water for the first time (so long as the rudder servo mount holds. The epoxy is setting up right now)

    It is mounted to the dual keels that make up the water channel. I’m very leery about removing anything that was once or still is structural. My wood working skills leave much to be desired, anything that will help keep the ship together should probably be left alone . It is already glassed but I REALLY don’t trust that to keep the structural integrity
     
  9. Anvil_x

    Anvil_x Well-Known Member

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    it's fine. once you see how durable these boats are , you'll be much more amenable to aggressive work. It may take time, and that's fine. as long as you have a running boat.
     
  10. bsgkid117

    bsgkid117 Vendor

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    On my wooden Bart I removed 6" of both keels and 3 ribs almost completely and there was absolutely no change to the ships structural rigidity.

    Just giving you some real life "I've literally done this" advice. You would be fine.

    IMG_20200613_183232.jpg
     
    Last edited: Apr 3, 2021
  11. darkapollo

    darkapollo Well-Known Member

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    After a half dozen attempts to create a belt drive (which did work, I was just never happy with the tensioning system) I reverted to direct drive. Against my better judgement, I cut out the keel section under the motor mount. Everything is much closer in alignment now (only off the centerline by a mm each way) and it made a world of difference. There is still a harsh vibration at 100% throttle but I think that is just due to everything spinning at 10k RPM and the u-joints being top-quality china pieces. It runs very quiet up through 50% throttle.

    As far as the robustness, maybe the ships you guys build. Earlier this week the hull took a nasty fall from my deck railing, landing HARD and square on the prop. It shattered the fiberglass around the center prop keel, broke the keel in three places, the subdeck, broke two ribs, broke the motor mount free, and cracked the sheeting. So yeah, it is in bad shape now.
    The 3d printed prop almost survived though. The blade it landed on bent back and delaminated to the point it was unrepairable.

    The replacement prop creates a lot of airflow even at low throttle speeds.
     
  12. Xanthar

    Xanthar Well-Known Member

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    Glad to hear the vibration is better, that is a bummer about the crash damage though : (
     
  13. darkapollo

    darkapollo Well-Known Member

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    Gooped it full of 30min long set high-strength epoxy. It SEEMS to be holding together now.
     
  14. bsgkid117

    bsgkid117 Vendor

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    Yikes. Sorry to hear about the fall. No ship wants to drop and hit the ground, full skeleton of wood or no. I doubt my original Bart with it's full 3/8 plywood frame, 1/2 x 3/4" keels, and thick fiberglass bottom would've faired any better. Bigger they are, harder they fall, etc, etc.
     
  15. darkapollo

    darkapollo Well-Known Member

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    Thankfully the breaks were mostly clean and I was able to snap it back together and with the help of 30min epoxy, restore it to working order. The only area that needs replaced is the fiberglass around the prop. Im positive that shattered because I was a bit too aggressive with profile sanding and had thinned it too far around the prop and rudder area.

    I had it in the water last night testing propellers.