Mounting Propellers

[Pilikia]

Bigbellydude commented in the Bilge Blower Thrusters thread that the discussion had wandered off-topic a bit, discussing how to mount propellers on the shafts of bilge pump motors. So, if you are interested in how to mount propellers on these motors you should first check out Steve's detailed discussion to be found near the bottom of the first page of Bilge Blower Thrusters.

I've had good luck with a simpler, but possibly riskier, approach shown in the attached photo. First, I bought a 1" long machine screw whose threads matched the propeller. I don't recall exactly the size and thread count, except I recall it was metric. (The nice thing about hunting for such things at Ace Hardware stores, compared to say, Home Depot, is they have "open stock" trays, allowing you try this one and that one, until you find what you need.)

I screwed this into the propeller very tightly, then I cut off the head of the screw. I used a flat file to file down the treads into a cone shape at the cut end, so that at the very tip there were almost no threads left, sloping gently up 1/4" or so to where the threads remained untouched. This made it into a "self-tapping" screw, which I screwed into the end of a 1-1/4" length of 1/8" ID brass tube (also from Ace).

Next, I used a wooden match stick to pack epoxy clay into the open end of the tube. I then SLOWLY pushed the tube onto the shaft of the motor. This shaft has a chamfer (flat spot) along one side, which provided a path for the excess clay to be squeezed out. I scraped away the excess clay as it emerged, so as to not allow it into the motor housing. I then left it for the epoxy clay to set.

Maybe I was just lucky. I've done it only this once. But the prop spins nice and true, and I'm sure it's not coming off anytime soon.

--Pilikia

[bigbellydude]

That looks like it might work. The only thing insecure I can see about it is that other than epoxy, there isn't anything holding the shaft and the prop together. However, I suppose that side screws and other things would off set the balance quite a bit!

I am going to look into this. It might work reasonably well. The only thing is that it might be expensive, especially with four or five props to deal with! But we do have an ACE in town, so that won't be a problem. Thanks for the tip!

[Pilikia]

Well . . . maybe Rambo could pull it apart. I sure can't.

Be sure you don't confuse epoxy adhesives with epoxy clay. http://www.amazon.com/Magic-Sculpt-Lb-E ... 606&sr=8-1. But be careful. It's very addictive.

As for cost, I can't imagine what could be cheaper.

[sthone]

Yeah, I've found out the hard way that if you just screw the prop onto a threaded shaft (no matter how tight) it will eventually spin off when the motor goes in reverse. The easy fix though is to just thread a nut onto the shaft first, next screw on the prop and then just back the nut off back against the prop. I haven't had one spin of using this method yet.

-Steve

[Pilikia]

Cool!

Thanks . . . I'll do it.

--Pilikia

[rabies]

Hi guys.

I'm working on my first ROV. I purchased a few of the Robbe 50 mm props that Steve recommended on his site. Along with the props, I purchased a few different prop adapters, in the hopes that one of them would work out. Unfortunately, none of them quite match up with the thread size on the props.

How has the epoxy method worked out for you guys? Can I use regular hardware store epoxy, or will I need something more specialized?

I would really like to find a less permanent solution so I can swap out different props if I want to. Has anyone been able to find off-the-shelf adapters that work with these Robbe props?

Thanks!

[Nautilus]

rabies,

I'm in the same boat (haha...no pun intended). I'm trying to avoid epoxy and I've bought a couple adapter pieces but don't have the props yet to try them out. Steve has posed a link to great schematic of his adapter in the "How to" section of his home built rov page. I haven't been to the hardware store yet to see if I can find all the pieces but it might be the best bet. Good luck and keep me posted. I'll do the same.

Bret

[sthone]

See THIS THREAD on how to make adapters for the Robbe props (or any threaded prop).

-Steve