Proboat Miss Bud Bent Prop Shaft Help

[wkelly]

I am have converted my Proboat Miss Bud 1/12 scale from nitro to electric and have bent two prop shafts (almost 90 degree bend) in a matter of seconds. I have used the Y535 with the nitro and never had this problem and I am a bit perplexed as to why this is happening. My only thought is that the motor is spinning much much faster (32K RPM's) than the old nitro set-up and the 3/16th prop shaft just can't take the added stress.

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Is there a upgraded strut system that is recommended as an upgrade for this boat? Or is the motor/battery too much for the old proboat prop shaft? I've spent some time on the forums, but there is almost too much information to sort through and haven't found a solid answer.

Any info or suggestions you all can give would be great. I really have enjoyed this boat and want to take the guess work out of this.

My set-up is a Dynamite A3650 2000Kv motor, stock/new flex shaft, new/prop shaft and a new/balanced/sharpened Octura Y535 prop with one Gen's Ace 3300 4S 35C Lipo (see attached pic).

[1coopgt]

I must be blind. Where's the pictures of the prop shaft ? Showed everything but. Just wondering ... why are there set screws in the strut. Also it looks like the stuffing tube isn't aligned to the strut. Is the strut adjustable or fixed ?

[wkelly]

1coopgt, nope you are not blind, did not upload. There is an extra bend in the middle that wasn't originally there from me trying to see how straight I could get it, however not even close. The hole in the strut is a grease port, no threads. Strut is fixed.

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[fweasel]

That's not a 3/16" propshaft. It's 1/8" I believe. Is the prop balanced and sharpened?

[wkelly]

fweasel, indeed you are correct, it is 1/8". Yes, prop was balanced and sharpened. Hooked up the battery, quick text of the throttle to make sure everything was working and watched it bend before I even got it in the water, like it was melting. Didn't have a chance to see much if any vibrations as it happened all to quick. Otherwise I wouldn't of have ran it.

I am leaning towards replacing the bushings, but being fairly new to rc boating and working with and an older/discontinued boat, makes finding OE replacement parts challenging, hence why I am posting here looking for recommendations.

[leonard feeback]

I would get rid of that prop nut, way to big and maybe out of balance. Us a wheel collar to hold the prop on the shaft. You can make propshafts out of drill rod from the hobby shop.

[1coopgt]

How far was the prop shaft sticking out of the strut on the prop side ? Is the strut designed for 1/8" prop shaft. Sorry about all the questions. If I'm understanding the design . The prop dog should be almost against the strut and the ferrule on the other end of the propshaft the same right? You're running a drive shaft instead of a flex shaft right. I've never seen one of these setups before.

[leonard feeback]

Hi Paul, I think you said you were having trouble getting parts. Us an 1/8th" drill rod for your stub shaft, put your drive dog from the bent shaft on a piece of drill rod you cut the same length as the bent shaft. Drive dog in same spot on new shaft. Install prop and slide wheel collar up to prop and tighten to shaft. Ferrule the same as it was before. Be sure to put flat spots on the new shaft where needed. Then do a test run as before to see if shaft holds up.

[1coopgt]

Hi Paul, I think you said you were having trouble getting parts. Us an 1/8th" drill rod for your stub shaft, put your drive dog from the bent shaft on a piece of drill rod you cut the same length as the bent shaft. Drive dog in same spot on new shaft. Install prop and slide wheel collar up to prop and tighten to shaft. Ferrule the same as it was before. Be sure to put flat spots on the new shaft where needed. Then do a test run as before to see if shaft holds up.

I think you mean WKelly, Leonard unless his name is Paul too. This is good info for sure.

[Dr. Jet]

From what I read/see, it appears that you ran the motor/prop at full speed while it was out of the water. It also appears there may have been a space between the aft end of the strut and the face of the drive dog as 1coopgt stated.

A prop will spin at a MUCH higher RPM when it is out of the water. ANY imbalance in the prop will be amplified by the square of the RPM, so there was no doubt considerable side loads on the shaft, especially if it were cantilevered some distance beyond the support of the strut bearing. As it started to bend, that amplified the imbalance and Voil?! The bent shaft you have.

Others have mentioned 1/8" drill rod. I have found some issues when using that, and generally it's diameter issues. At 0.1250" diameter, most Octura and similar props won't slide on, it's often a tight fit in stuffing tubes, and it doesn't always fit into ball bearing races. I have found that a 0.1247" precision-ground shaft is MUCH better. The extra 0.0003" (REALLY SMALL) clearance makes all the difference in the world. See: https://shop.sdp-si.com/catalog/?cid...ned&view=table

[wkelly]

Thank you all for the info. Dr. Jet I believe you are on point with your assessment. Being that this is an older Proboat and difficult to find replacement parts, I will be updating to a Medium Offset Catamaran Strut and Rudder System https://www.offshoreelectrics.com/pr...rod=tfl-502b35 with a .150 flex shaft with 3/16th to 1/8th setpdown. I will need to make a few modifications to mount the the new system, however shouldn't be all that difficult. Found a youtube video of that I am going to do with the prop strut and rudder https://www.youtube.com/watch?v=na0hufZvBvQ

This should handle the torque and power output of the electric motor/batteries much better. No more "testing the throttle" out of the water either.

[1coopgt]

What size batteries are you planing on running? Where is the cg with the batteries in the boat. This will be interesting to watch. Whens the video coming?

[wkelly]

1coopgt, I am running one Gen's Ace 3300 4S 35C Lipo placed in the nose of the boat, see pic at the beginning of the post. COG is very close to the original COG when I had the nitro engine and fuel in it. Just a tad it forward of the original bulkhead, maybe a 1/4" to 1/2" at the most. With the new strut and rudder assembly installed, it will be hanging further off the back of the boat than before and I suspect that the COG will move back slightly.

Waiting for parts to arrive hopefully by Wednesday, and once installed, should be able to post a video by end of the week.

[1coopgt]

I watched the video in your other post . That was what raised my questions.

[wkelly]

We have success! After removing the stock strut mount and installed a new medium offset catamaran strut and rudder system with a new .150 flex shaft with 3/16th to 1/8th setpdown, no bent prop shafts or props, had two successful runs on the local pond. Didn't get an actual speed, but looked close to 35ish to me. Many onlookers enjoyed it just as much as I did. Thank you all for the great advice and sharing your wealth of knowledge. Watch the videos here:

https://www.youtube.com/watch?v=9wO3nuCmblY

https://www.youtube.com/watch?v=f9BObLcs9Ws