Pingpong balls for tether buoyancy??

Control Boards, Controllers, Tethers, Ect.
Post Reply
User avatar
Technoviking
Posts: 8
Joined: Nov 29th, 2014, 12:30 am

Pingpong balls for tether buoyancy??

Post by Technoviking »

Hi All,

I just wanted to see if anyone had tried ping pong balls for tether buoyancy? Looking at the math, they could be buoyant for up to 50 meters, and they are cheap, $2 for 10 balls.

Here is the math - http://physics.stackexchange.com/questi ... to-pressur

I think with a little modification, perhaps filling with expanding foam, drilling a 8mm hole through the ball and feeding the cat5 cable through the hole, zip ties to hold it in place, this may be viable for 50 meters+ ?
Thoughts?

(excuse the paint diagram)
Attachments
Untitled1.png
Untitled1.png (51.99 KiB) Viewed 4380 times
User avatar
KR2_Diving
Posts: 391
Joined: Aug 30th, 2012, 11:43 am
Location: Currently: NW Suburbs of Chicago. Originally: NE Wisconsin

Re: Pingpong balls for tether buoyancy??

Post by KR2_Diving »

Interesting concept!

For discussion sake... how would drilling holes in the balls affect the rigidity of the balls? Would a ping pong ball full of water or wet foam provide more drag then buoyancy?

What if you could attach the ball to the tether without compromising the integrity of the ball?
rossrov
Posts: 383
Joined: Feb 28th, 2013, 5:01 pm
Location: Australia

Re: Pingpong balls for tether buoyancy??

Post by rossrov »

Maybe a short piece of tubing shoved through one hole, squirt some foam in the other hole, then push the tubing through that. The foam will continue to expand, and then the cable can be fed through the tubing. The ball gives a very good hydrodynamic shape for low speeds - good idea. Depth test with sinker and fishing line.
User avatar
Technoviking
Posts: 8
Joined: Nov 29th, 2014, 12:30 am

Re: Pingpong balls for tether buoyancy??

Post by Technoviking »

Ross thats a great idea, I will have to do some testing when i start on the tether. KR2 - The other idea i had was pushing ping pong balls down the length of a 30mm expanding braided cable sheath http://www.ebay.com/itm/4-30mm-Expandin ... 0793356553 and running the cables in the same sheath then use cable ties to prevent the balls from moving. This should not only look neat, but would make unwinding the tether much easier and also snag free.
User avatar
sthone
Posts: 588
Joined: Nov 8th, 2010, 9:25 pm
Location: Connecticut
Contact:

Re: Pingpong balls for tether buoyancy??

Post by sthone »

I think once you drill a hole in the ball you are going to compromise the integrity of the ball and lose that 50m rating. Even if you fill it with expandable foam it isn't going to help as most expandable foam is open cell and will not be able to handle the pressure at depth. The tube through the ball might work but you would have to make sure the seal between the tube and the ball was strong enough.

On that note though I was thinking of something similar where I would make a mold to make custom sized tether floats out of poor-mans Syntactic foam. (hobby style micro balloons and epoxy) I have to stuff already to try it out (I was going to start with just making a square block for my main floatation pod) I just need to find the time to do it.

-Steve :sting:
rossrov
Posts: 383
Joined: Feb 28th, 2013, 5:01 pm
Location: Australia

Re: Pingpong balls for tether buoyancy??

Post by rossrov »

With you on the microballoons Steve. Would be neat if they came out of an aerosol can. The thing i like about the ping-pong ball is that it is a ready-made mould of about the right size and shape. No pressure-proofing value on it's own once the holes drilled but I think the balls undrilled a great idea for filling otherwise water-filled voids in my next ROV. If I need to go deeper then it's microballoons.
The PU foam in aerosol can sold by a major hardware retailer in Australia claims to be closed-cell, BUT semi-rigid. Experimentation will determine whether "semi-rigid" is rigid enough for 50 metres.
I should have noted in the earlier post that it may be a good idea to deliberately drill the holes a bit oversize so the excess foam has somewhere to go. We don't want exploding ping pong balls or floats that end up too heavy

Ross
Ian MacKenzie
Posts: 160
Joined: Jan 3rd, 2014, 10:04 pm
Location: Vancouver B.C. Canada

Re: Pingpong balls for tether buoyancy??

Post by Ian MacKenzie »

Please post your findings. I'm almost ready to build my tether and have no idea what to use.
User avatar
micoma
Posts: 18
Joined: May 14th, 2014, 4:16 pm
Location: Venezuela

Re: Pingpong balls for tether buoyancy??

Post by micoma »

I used 1/4" closed cell foam. With 16 cat5 wires, 16g speaker wires, and a small rope it was slightly buoyant. Someone said they tried it going deep and some of the closed cells collapsed. I don't plan to go deeper than 50' so I think it will be ok for me. I haven't gone that deep yet so I can't say for sure. Details are at http://micomarov.weebly.com/.
Post Reply