Thread Tools
Feb 01, 2016, 06:54 PM
Registered User
Thread OP
Discussion

Knots in rubber motors


Well it was a beautiful still morning up here, I decided to do a bit more trimming on the stick-UP, being the expert I am I thought I would lube the motor with the liquid soap / gelatine / castor oil (although I used canola oil) mixture ......... well you guessed it, the square (reef) knot + overhand knot just slips apart, I tied the rubber before the lube was applied but I guess the lube properties are far greater than my knot tying abilities

Any suggestions here would be greatly appreciated.

Regards,
John .......
Sign up now
to remove ads between posts
Feb 01, 2016, 07:04 PM
B for Bruce
BMatthews's Avatar
I'm laughing with you because it's happened to me as well....

First off clean the motor in lukewarm water to wash away the lube.

Next is to clarify your use of the word "gelatine". The proper second ingredient to go with the liquid soap is "glycerine" and not Jello powder.

With the rubber wet tie the proper reef knot to start out. As you're pulling on the four ends of the knot to draw it tight putting it in your mouth and getting a bit of spit on it will aid in lubing the knot to tighten up really small and snug. Then as safety knots I like to tie off a single overhand knot in each of the two free ends. Draw these down snug to the reef knot as you tighten them. It's a bit of a trick to get them in snug to the knot but with a bit of practice you'll get the hang of it.

It's almost one of those times where you can honestly say "pull until it snaps and then ease off" You want to really stretch and pull that original reef knot tight. If you break the strand a time or two learning just how tight to make it that's maybe not (knot? ) a bad thing to learn. To stay in place I probably pull the rubber to up around 80 to 90% of its breaking stretch.
Feb 01, 2016, 11:15 PM
Registered User
Thread OP
Quote:
Next is to clarify your use of the word "gelatine". The proper second ingredient to go with the liquid soap is "glycerine" and not Jello powder.
Oops, I guess I was "knot" paying attention here, on second look I used Jel-it-in, a vegetarian gelling powder ...... what that was doing in the pantry is anybody guess but the mixture is still very slippery so I will use that until I can get some "glycerine".

Thanks again for the tips, I will go and practice your methods for a slip free knot.

Regards,
John ......
Feb 02, 2016, 10:00 AM
Registered User
Pat Daily's Avatar
After I tie knots in the rubber, I put a tiny drop of CA on the knots. Then I lube it with Dow 33. No failures so far.
Feb 02, 2016, 10:09 AM
Kansas is windy.
pburress's Avatar
Ditto what Pat Daily said! I use a simple overhand knot, wetted and pulled tight, then a drop of CA; never a failure.
Last edited by pburress; Feb 02, 2016 at 10:40 AM.
Feb 02, 2016, 01:40 PM
B for Bruce
BMatthews's Avatar
I'll have to try that lil' dot of CA. Never thought of gluing the knot.

The thin watery stuff I suppose?

I've tried a couple of the fancy products like Dow 33 over the years. But in the end I keep coming back to the basic soap and glycerine with a dash of castor. There's no doubt that the Dow and other things are great lubes. And likely better by far. But I like the old classic stuff because I can use a bottle of water to wash off my hands after handling the motors and get rid of the sticky feeling. Also when the motors have picked up some grit that was blowing around I can swish the motors in a sink of water when I get home to wash away the grit.

I know it still flies off and speckles the insides of the model. But I like the ability to easily wash it away so I live with the downside.
Feb 02, 2016, 01:52 PM
Kansas is windy.
pburress's Avatar
Yep, thin CA, but I bet thick would do the job just fine.

Being able to easily wash the lube off your hands is mighty appealing! Dow 33 definitely hangs around and can cause aggravation when handling a wound motor for example. I lube inside a plastic baggie which minimizes the handling and lube exposure.

Another lube that comes recommended by Don Deloach is pure silicone oil. I haven't tried it but Don sure wins a lot of contests so I'm sure it's good stuff.
Feb 02, 2016, 03:23 PM
B for Bruce
BMatthews's Avatar
Even with my soap and glycerine I still massage it into the motor inside a bag. But eventually the time to remove it and install in the model arrives.... and then it gets messy. Aside from wearing disposable gloves I don't see any way around that. And that's a bit of a bother at the field as well. I just find it easier to slightly open my water jug valve and wash the stuff off my hands after loading it into the model.

All of which is why I guess I prefer and continue to use the old old classic soap and glycerine lube. Is it the BEST lube? Absolutely not. But it's close enough and does the job well enough and I just like the ability to wash it off my hands and the rubber so easily.

Comes in handy when I need to tie up a snapped strand as well. I don't think I'm exagerating when I say that those other wonder greases or oils make tying and securing a knot pretty well impossible without some sort of de-greaser being used.
Feb 02, 2016, 05:17 PM
Intermediate Multi
Trisquire's Avatar
Where do you guys typically locate the knot once you've created the band? Near the front hook? Near the rear peg? At the CG? At the widest point of the fuselage? (assuming its an internal motor)
Feb 02, 2016, 06:37 PM
Kansas is windy.
pburress's Avatar
At the rear peg is the most common spot. As always you will get different opinions.
Feb 02, 2016, 07:00 PM
B for Bruce
BMatthews's Avatar
I put the knot at the rear peg as well. If it were in the middle of the motor it might cause one or more of the strands to stretch over it and fail by being stretched in that one bump to more than it will take.

The nose hook would work as well other than the tag ends flipping around would catch on stuff up front. So it's just best to put it at the back.

You mentioned "at the CG". But the rubber in the knot is so slight an amount that it's not an issue.
Feb 02, 2016, 07:53 PM
Intermediate Multi
Trisquire's Avatar
Got it. Thanks.
Feb 03, 2016, 12:26 AM
Diesel Danny
danny mz's Avatar
If you try this knot, the rubber has to be lubed first or it won't tighten up.

Best knot that I ever tried (I think that it came with a kit).

* Danny M *
Feb 03, 2016, 01:20 AM
B for Bruce
BMatthews's Avatar
I believe that you'll find that it's a"blood knot" or a variation of it. I've seen a similar knot but where the tag ends pass through the open eye from opposite sides. It's a great knot for re-tying broken winch lines for RC glider winches because the loaded lines are not all turned over which weakens them.


Quick Reply
Message:

Thread Tools