Drive shaft vibration in Trumpeter SeaWolf WTC

[dwi116]

Ah, the bane of Submariners, a noisy driveshaft. HMS Venturer detected and sank U-864 in the closing days of WWII due to a noisy driveshaft. The only successful sub on sub underwater engagement of WWII, I believe. Ok, I digress. On to business.


I have the prebuilt Sub-driver for the Trumpeter Seawolf and it turns out my driveshaft is a bit out of true. When I spin up the motor, I can feel the shaft “tingle” against my finger. Put one end of the dog-bone coupler on the shaft and its vibrating hard enough to confuse the ADF, even at low throttle. I imagine if I put it in the water the seals would leak from the shaking.

I pulled out the battery tray and disconnected the servo arms for a peak inside. First, the good news: The drive shaft which exits the WTC has a much larger diameter than that of the motor. There has to be a coupler/sleeve in there, and I would say it is very likely that my problem lies right where the shaft from the motor mates with this larger shaft. Should be no big deal, if I could just get at it. Anyway, the bad news is that a clever way to get at it to diagnose and repair eludes me at the moment. Hard to tell, but the electric motor looks to be pressed into place and also held in with silicone or maybe epoxy or some other adhesive. Any thoughts on how should I proceed?

Thank you,

Dwight Eyrick

[He Who Shall Not Be Named]

Dwight,

A stainless steel drive-shaft is press fit to the motor shaft -- the bore of the drive-shaft could be a bit off, but not much. The bad ones never leave this shop alive.

A bit of vibration is fine. The question is, does it leak or not. Your unit went out of the shop after completing the normal QA steps: Leak check of all seals (in water), run and break in of the assembled running gear, function test of all servos and ESC, and check-out of the gas portion of the ballast sub system. In water operation of the system will damp things out. Don't sweat the ADF jumping of the stern planes.

Don't sweat the vibration!

To get at the motor -- which is secured to the motor bulkhead by two machine screws -- you first have to pop off the drive-shaft seal foundation off the wet-side of the motor bulkhead. Doing so reveals the two motor securing machine screws. Remove the screws, pull the motor away from motor bulkhead and inspect away.

Unless something went terribly wrong between my shop and your hands, the SD is fine.

David,

[dwi116]

Hi David,

I've no doubt it was fine when you built it.

I popped the shaft seal off to take a look. The shaft is visibly out of true and shakes even worse without the dampening effect of the seal siliconed over it. Separating the motor from the bulkhead is proving to be a bit of a challenge. No screws holding the motor on mine in place, it seems to be press fit with a bead of silicone around it to hold it in place. I've trimmed away the silicone and tried firm pressure, but not too much, to try and get the motor to separate from the bulkhead. I can certainly put more English on it, but wanted to check in first. Anything I might be missing? Is there adhesive inside the mounting ring that I can't get to?

Thanks,

Dwight Eyrick

[He Who Shall Not Be Named]

Sorry, Dwight, I hit the 'edit' key by mistake. Nothing was changed.

OK, you got the seal/bearing unit off the shaft. And, yes, the shaft will vibrate even more without that support bearing in the line of fire. You're missing the two screws set beneath the RTV on the after (wet) face of the motor bulkhead -- those are exposed by digging out the RTV. You then remove them, and the motor comes right out.

Once you get the motor out, send it to me -- you'll never get that intermediate drive-shaft off without wreaking the motor bearings. Send me your address and I'll mail you a replacement motor and shaft.

David,