Rubber Band snapping

[rebeccajk]

My group is having trouble with the rubber band snapping after 500 turns or after two or three tests. We have tried lubricating it with Elmer's Slide All. Can we have any other suggestions?

[bjt4888]

Rebeccajk,
Please supply this additional info: thickness and length of rubber, type of o-rings, desciption of what this elmers product is , are you refe r ring to wimder turns or actual turns, are you stretching the rubber to betwen four and s e ben times original length while w i nding, is the rubbee breaking at the knot or in the middle, what knot are using ang describe how you are tying, hae you read all info in the 2015 forum related to rbber motors?
Iwould be glad to help if you can supply some or all of this info.

Brian T.
AMA since 1972

[bjt4888]

Rebeccajk,
My apologies for the scrambled message. I am not the best at typing on my phone. Elmer Slide-All appears to be a "dry" household lubricant appropriate for use on squeaky hinges. I do not believe that this would be a good rubber motor lubricant based upon this description that I see online. The most readily available good-quality lubricant for Wright Stuff rubber motors is "Armor All". Armor All is a silicone-based spray treatment used most commonly on car interior vinyl (or on tires). You can buy Armor All at any good hardware store and most general purpose stores that have an "automotive" section. Target stores carry Armor All.
Spray three squirts of Armor All in a ziplock sandwich bag, drop the motor in and massage the lubricant into the motor for about 15 seconds; drop the motor onto a clean paper towel, fold the towel over onto the motor and pat "dry" gently once. Do not actually "pat dry", just pat once so that the motor is not dripping with Armor All. The motor should still appear very shiny and wet with Armor All. For testing, I would relubricate every other flight. When simulating competition during testing with new, broken-in, motors relubricate every flight.
If you respond to my request for additional info, I will be able to determine if there are other steps you should take to prevent motor breakage at such al low numbers of turns. John Barker's equation would predict that a Tan Super Sport 1.5 gram motor of .055grams/inch, total length of about 12.75", with black rubber O-rings such as those sold by Freedom Flight Models (this would be rubber of approximately .083" thickness) should take 1,775 turns before breaking. 3/32" (.09375" thick) rubber will make a motor about 11.2" long (with the same O-rings already mentioned) and should take about 1,467 turns before breaking. I'm guessing that although 3/32" rubber is readily available, but might be too thick for a competitive 7.0 gram airplane meeting this year's rules. Of course, this is your mission, to test many variations and determine an optimal solution for the 7.0 gram airplane and all of the ballast options.

Good luck and good testing! Great job getting an early start.

Brian T.
AMA since 1972 (off and on)

[rebeccajk]

Mr. Brian T...
I am sorry for taking so long to respond.

1. What is the mysterious o-ring item that I see in many places? Thank you for the information on where to buy it. Where does it go?
2. The motor approximately 1/16" and 26" with a mass of less than 2 grams.
3. The electric motor winder that we are using doesn't give a gear ratio so we have assumed (which is not necessarily good) that it is 1:1.
4. We changed to the armour all after reading another article. By changing, the motors are working better.

Thank you for your time and help...

[jander14indoor]

O-rings. These are not plumbing O-rings. They are plastic O-rings. You don't buy them you make them. Take the suction tube off a discarded spray bottle, the ink tube (empty) out of an old Bic ball-point pen. I use the push rod liners available at hobby shops. Just about any approx 1/8 to 3/16 external external diameter plastic tube. Stiff enough to hold its shape, but not brittle. Teflon, PTFE, poly ethylene etc. Slice off rings approx 1/32 inch thick. Place two on your motor. They are used to wind the motors OFF the plane. One ring hooks over your winder, the other to an anchor some place convenient and solid. Stretch wind motor to torque and turns. Then transfer to the plane without loosing any winds.

Motor size, note max is 1.5 gm this year, not 2.0. Not sure if you meant loop is 26 inches, hope so for that skinny a motor. Properly lubed and stretch wound you should get almost 2000 turns in that motor. And if you aren't winding to near breaking you are flying with a half empty gas tank. Turns are fuel, thickness is power. WIND that motor.

If you are using an electric winder with a counter that is probably actual rubber motor turns. Can you stretch wind with the electric motor? I've not seen one that will. You won't get near as many turns without stretch winding. Most flying coaches recommend a manual winder because you can stretch wind and feel the motor to better predict when it will break. A good 10 to 1 winder is just as fast as an electric. You can get 15 or 20 to one winders that are even faster.

Yep, Armor All will allow MANY more turns than the dry lube you started with.

Comment, I suspect a 1/16 motor will be TOO thin for this years planes. Much smaller wings this year will require higher speeds and PROBABLY more motor torque.

Jeff Anderson
Livonia, MI

[Less_Incidence]

I wholeheartedly agree with everything in the above reply. Electric motor winders are not a good choice in my opinion, and here's why:

1. Electric winders can be too fast. When a motor is wound too quickly (especially without sufficient lubrication), it heats up, and this can cause nicks and tears to develop in the motor, causing snapping during the wind, fewer flights form one motor, and even midflight breakage. A motor explosion on your plane in midair is not a pretty sight - I've had two F1Ds and one Wright Stuff model destroyed this way.

2. Electric winders lack fine control. It's hard to get the last very few turns (which contain a very large amount of energy) into a motor without being able to wind very slowly and feel the motor as it's being cranked up.

3. Electric winders are inconsistent. This seems counterintuitive, as they would seem to be more consistent than winding by hand, especially in speed and number of turns, but I have found no substitute for winding by hand and by feel in order to get the maximum energy out of a motor. Rubber itself is inconsistent, and even within one batch I've found rubber of consistent thickness to vary in turn capacity as much as ±5%, and even rubber stripped by consistent density can vary as much as ±3%.

4. Electric winders make stretch winding very difficult. I assume most first-timers don't know what I and mr. Anderson mean by stretch winding, so this would probably be a good place to discuss winding technique.

When winding, there's a certain procedure. This is my method, and some operate differently, but I've had good results.

First, take your motor (assuming it's FAI Tan Super Sport rubber), hook one end to your hook (preferably a torque meter) and the other end to your winder, and stretch it out to 5 times its relaxed length, holding the winder. This may seem like a lot of stretch, but trust me, the motor can take much more.

Next, begin winding your motor. It's not necessary to wind extremely slowly, but as I mentioned before, winding too fast can harm the motor as well. Keep it stretched until you have a little over half of your target turns in the motor - if you're going for 1900 turns on that 26-inch loop, put 1000 turns in the motor. Keep it stretched.

Now, hold the winder with one hand and feel your motor with the other. Firmly pinch the motor about 1/4 to 1/3 of the way along its length between your thumb and forefinger, and gently pull back and forth. If the rubber seems somewhat firm and you can feel the knots in the motor "clicking" and slipping over one another, it's time to start walking in. If the motor is still very springy and stretchy, keep winding at that stretched length. You will probably break a few motors doing this before you get the feel right, so don't worry.

Now comes the tricky part. You need to carefully continue winding while walking the motor in toward whatever it is hooked to. The goal is to have your motor hit its maximum number of turns just as it reaches the length of the hook-to-hook distance on your plane's motorstick.

In my experience this is not a linear process. You will walk in very, very slowly at first, and you will have to move in more quickly later in the wind. As you walk in, stop and feel your motor every few turns of your winder. Each time you feel the motor, make a judgment as to whether you should stop walking in and wind a few more turns at that length or if you should keep walking in. Again, you will inevitably break some motors during this phase. You'll get the hang of it, but it's a struggle at first.

You do not necessarily want to fly at full torque like this, especially in a school gym, as a 7-gram model with an Ikara plastic propeller trimmed down to 20cm can climb more than 100 feet at full torque. So now is the time to back off some turns.

Carefully, steadily dewind the motor until you are at the desired number of turns. Do not stretch the motor back out as you back off. Make an educated guess as to the amount of backoff you want for your ceiling height, and then gradually increase or decrease backoff on subsequent flights until your plane cruises just below the ceiling. If you have a smooth ceiling, great. If you fly in conditions like mine with lots of rafters and obstacles, it may be good to keep your model cruising 1-2 feet below the lowest obstruction.

Even having backed off, there will still be lots of tension in the motor. Be careful as you handle it and transfer it on to the model.

Assuming you're right-handed, do as follows to transfer the motor on to the plane (Missing any step in this process can result in broken planes, so be careful):

Hold the motor firmly by its O-ring and end with your right hand, and use your left hand to remove the winder from the motor. Hold the motor steady and put the winder down.

Pick up your plane by the prop shaft/bearing with your left hand.

Bring the plane's prop hook to the O-ring on the motor, not the other way around. It should be simple to hook the O-ring on to your plane at this point.

Next, keep holding the plane with your left hand, release your right, and remove the other end of the motor from the winding hook with your right hand. Bring this end of the motor to the rear hook on the plane's motorstick, not the other way around. Hook the O-ring to the rear hook, being careful not to let go of the motor until you have gradually let the motor stick bear the full load of the motor. Letting a motor "snap" on to the rear hook is a good way to get broken models.

Again, this is my preferred method of winding, and not everyone does it this way.

Also note that the winding procedure I mentioned, specifically the amount of turns put in the motor at full stretch and the guidelines for feeling when and when not to walk in, are geared toward a very aggressive winding method. Especially in lower levels of SciOly competition, it is still possible to achieve good results while being a little more conservative when winding (and breaking fewer motors).

I hope this helps anyone who reads, and best of luck!

~WW

P.S. You can get a good 10:1 or 15:1 plastic winder from lasercutplanes.com. Those winders are very inexpensive and work well for Wright Stuff.

[bjt4888]

RebeccaJK,

I also am in agreement with Jeff Anderson's comments. It is likely that the rubber thickness you will need will be between .081" and .087", depending upon the propeller and model. These rubber thicknesses will make motors around 14" to 12" in loop length.

"Less Incidence" gave you an excellent description of a typical winding technique. Here is a link to the 2015 forum topic "Winding (your rubber motors)". Included in this 2015 thread is a link (hip pocket aeronautics link in a post by Jeff Anderson last year) with pictures of how to tie the knot. Pictures of the o-rings on the motor (on this same link) and a video I posted of a world-class flier winding a motor.

Good Luck and keep testing and analyzing data.

Brian T.

[bjt4888]

Sorry, here's the link to the 2015 Wright Stuff forum topic "Winding (your rubber motors):

http://scioly.org/phpBB3/viewtopic.php?f=191&t=6247

Brian T.