Helicopters C

[dhdarren]

Has anyone else experienced problems with the knot on their rubber motors? Sometimes when we're flying it looks like the knot gets stuck on the side of the motor stick and stops our bottom rotor from rotating freely (independent of the motor stick). Any advice / solutions?

I would check the straightness of your motor stick. Earlier in the season, I was having issues with the motor bunching up when the motor was near its max number of winds. I later found that the motor stick had a very slight warp inwards (towards the rubber motor), causing it to catch near the middle of the motor stick. I found that it's easiest to check its straightness by using the corner of a table; this is because you cannot put it directly in the middle of a table due to the two front hooks sticking out, but if you put it on the corner, you can compare the straightness of your motor stick to the flatness of the table. I had to rebuild mine from a new sheet of balsa because the cement I applied had permanently stuck it in that warped position. If you have a perfectly straight motor stick, these issues should be much reduced.

You also just might not be tying the knot tightly enough, or you might be leaving too much excess. I always make sure to pull fairly hard on the ends of the rubber when tying the 3-step knot to ensure that it is tight as well as small (but not pulling hard enough to begin damaging the rubber, of course). Also be sure to cut off as much excess as you can. If your knot is tied correctly, you should be able to cut it off right up to the knot with scissors and not risk the knot slipping.

[jander14indoor]

For Helicopters with both rotors free from the motors stick I'd put the knot in the middle of the motor. If you think about it the middle of the motor shouldn't be turning much anyway. At least with respect to the motor stick. If it hits and locks on the motor stick it won't have much effect on the rotors.
If one rotor is locked to the motor stick, of course put the knot near that hook.

As to my knot description, here's what I wrote in Wright Stuff. Note the comment about weight is because WS has a motor weight limit. Not relevant to helicopters.

No, no. If you use the right knot there is no "Guessing" where to tie it.
- I weigh my motors and o-rings before I tie them. To as close to 1.5 gms as I dare vs the judges scales. As others have said, have a selection of motors in the range of 1.45 to 1.50 gm. Oh, side note, the static in rubber motors messes up some electronic scales, causing them to be inconsistent. You might want to weigh the same motor multiple times to see if your scale is susceptible to this problem. Its one reason I use only a mechanical balance at competitions.
- Lube the motor, at least the area where you'll tie the knot. Temporary lube is OK here, water works.
- I then make the ends even and tie an overhand knot, fairly near the end but no precise location.
- Then, grab both ends of the rubber on the inside of the loop near the knot and pull apart slowly. The knot will slip outward, making the tails shorter. Take that as close as you dare, I typically leave tails around 1/16 of an inch. Too short and this knot (which will become the outer knot) will sometimes slip. But that is surprisingly short.
- If the tails are too uneven, I keep pulling and pull the knot apart to start over.
- Now, here comes the magic.
-- Tie a second overhand knot inside the first, but in the opposite direction. I'm right handed and tie an overhand knot by spinning it clockwise around my left index finger. So to tie it the opposite direction I just stop and think and spin it counter clockwise around my left index finger.
-- Now, grab both ends of the rubber again on the inside of the loop and pull apart. This second know will slip outwards again, UNTIL it hits the first knot. It stops there and WON'T move. Ever. MANY years of flying, many years of coaching others, I've never had this double knot slip in use, no glue needed.

Oh, don't forget the O-rings before you tie the second knot! It is possible to pick this knot apart, but frankly I find it easier to just start over.

Jeff Anderson
Livonia, MI

[BagelsMan]

Hello fellow Helicopter enthusiasts!

Spent a lot of time reading on the forums but have yet to post anything, so here's to a first.

I have a few questions to ask you experts that you can hopefully benefit me with answering. First of all, some info. We tried a 3 2 and then built a 4 2 configuration with the FFM kit, which we're currently using to get times of around 1:45. Really stable, doesn't move too much on the ceiling, not too many unused winds, so no issues in those regards. The main issues we're facing are minimizing a bit of weight and increasing winds.

Right now we're about 0.17g over 2.5 and we've got some really good parts and not a whole lot of time to build more (studying for AP tests and other stuff finishing this time of year has been difficult to balance with Scioly). I'm in a position considering that it might be possible to shave down enough weight without building new parts, even though that's usually the normal standard of minimizing weight, but I don't want to do anything stupid and possibly damage a good helicopter without asking around first. What do you all think would be the best way of shaving off 0.17g or less just to get those times a bit higher? I was considering replacing the rather heavy ceiling bumper with a fixed bumper, or rather just replacing the pin which ways 0.1g alone with something else. Perhaps a carbon fiber piece of equal length? (I'm not sure if that's a great idea, given that it might diminish the ability to rotate without the head of the pin) I also thought of sanding off the edges of the motor stick just a bit but not enough to weaken the strength, but again I'm not sure if that's advisable. If anyone has any more definitive suggestions, they would be greatly appreciated.

The other issue is winds. With the 15-1 winder we've got 100 turns using .094, sometimes a bit more, but that's about it before breaking. We're using lubricant and stretching to about four times the length, standard suggestions, but not quite getting the amount of winds that other people have been able to achieve on this forum. What would be some recommendations that you guys have in increasing this? What rate should we be winding? As fast as possible and slowing towards the end or is winding slower somehow advantageous? What could the length of the motor at maximum with .094 to get more winds in? Would using something better than WD40 as a lubricant have enough of an effect to warrant changing lubricant?

We've also tested 0.85, 0.102 and a bit thicker but we've consistently had the best times with .094 so we're going to stick with that.

Going to Ohio in two weeks, hopefully we can get in the range of 2:00 to 2:15, or higher! (we'll try). Any other helpful suggestions aside from assessing these issues would be greatly appreciated. This thread has been a great resource this year, I'll be sure to keep up to date reading the new posts here in the next two weeks.


Thanks, and good luck to others at Ohio!

//Callan W. Rhode Island

[DoctaDave]

Hello fellow Helicopter enthusiasts!

Spent a lot of time reading on the forums but have yet to post anything, so here's to a first.

I have a few questions to ask you experts that you can hopefully benefit me with answering. First of all, some info. We tried a 3 2 and then built a 4 2 configuration with the FFM kit, which we're currently using to get times of around 1:45. Really stable, doesn't move too much on the ceiling, not too many unused winds, so no issues in those regards. The main issues we're facing are minimizing a bit of weight and increasing winds.

Right now we're about 0.17g over 2.5 and we've got some really good parts and not a whole lot of time to build more (studying for AP tests and other stuff finishing this time of year has been difficult to balance with Scioly). I'm in a position considering that it might be possible to shave down enough weight without building new parts, even though that's usually the normal standard of minimizing weight, but I don't want to do anything stupid and possibly damage a good helicopter without asking around first. What do you all think would be the best way of shaving off 0.17g or less just to get those times a bit higher? I was considering replacing the rather heavy ceiling bumper with a fixed bumper, or rather just replacing the pin which ways 0.1g alone with something else. Perhaps a carbon fiber piece of equal length? (I'm not sure if that's a great idea, given that it might diminish the ability to rotate without the head of the pin) I also thought of sanding off the edges of the motor stick just a bit but not enough to weaken the strength, but again I'm not sure if that's advisable. If anyone has any more definitive suggestions, they would be greatly appreciated.

The other issue is winds. With the 15-1 winder we've got 100 turns using .094, sometimes a bit more, but that's about it before breaking. We're using lubricant and stretching to about four times the length, standard suggestions, but not quite getting the amount of winds that other people have been able to achieve on this forum. What would be some recommendations that you guys have in increasing this? What rate should we be winding? As fast as possible and slowing towards the end or is winding slower somehow advantageous? What could the length of the motor at maximum with .094 to get more winds in? Would using something better than WD40 as a lubricant have enough of an effect to warrant changing lubricant?

We've also tested 0.85, 0.102 and a bit thicker but we've consistently had the best times with .094 so we're going to stick with that.

Going to Ohio in two weeks, hopefully we can get in the range of 2:00 to 2:15, or higher! (we'll try). Any other helpful suggestions aside from assessing these issues would be greatly appreciated. This thread has been a great resource this year, I'll be sure to keep up to date reading the new posts here in the next two weeks.


Thanks, and good luck to others at Ohio!

//Callan W. Rhode Island

First off, .17g isn't a whole lot to be worried about. If you don't want to risk breaking your helicopter I would just let it be. 0.17g is only about 6% of the minimum weight so that's really all the performance you're losing. I would spend my time optimizing motor length/mass, which could lead to >10% increase in times very easily.

As for how hard you're winding, it's impossible to really tell how close you are to reaching the max potential of the motor without knowing the mass of the motor,as well as the length of the motor (prior to winding).
You should also be stretching to 6-7 times the motor length to really break it in and to pack in the turns.

WD40 is also a terrible lubricant. It's petroleum based which actually harms the rubber. Use Armor All or any silicon based oils. I know WD40 makes a silicone oil lubricant as well but I had no luck with that. I currently use treadmill lubricant from amazon which is 100% silicone oil, but Armor All works just as well; it just need needs to be reapplied more often because its very thin.

[JasperKota]

I have some .94" rubber on me, and using this equation (for 1.5 gram motor, minus 0.1 assuming you use two rubber orings): break point = 42.2 * L * sqrt(L/W), L - length in inches, W - Weight, it does look like the rubber is going to break around 100 winds. I'll tie and lube (with armor all) it later and report how much I'm getting out of it before breaking.

Go with what DoctaDave said, I got ArmorAll at Home Depot. Just relubricant your rubber basically after every flight where you stress the rubber (not necessary for short trim flights).

[jander14indoor]

I'm going to disagree on how important the weight is.
6% reduction in structure translates directly to free 6% increase in rubber and then directly to duration. You'll be able to use that immediately to increase times without any technique improvement.
But yes, be careful on modifying a good helicopter. The FF copters I've seen do have a lot of weight in that standoff and I suspect you are best to start there (besides its very high on the copter, won't unbalance it and make it unstable). Consider making it shorter, thinner wire, shorter wire, Maybe CF. BUT, make sure it can't fall off, would be terrible to get a great time killed because the disk fell off early!
Look at the balsa at the center of your top rotor, can you sand it hollow round instead of square?
Also check the axle wire. If it runs all the way through your rotor, that might be an opportunity. Could you run it halfway through and then out the side.
Frankly some of that stuff you should build OFF copter and try first. And rethink about whether it would be better to build a new top rotor to get that weight loss.

As already mentioned STOP USING WD40 as a lubricant. It really degrades the rubber.

You mention you are happy with .094 rubber. When you tried different widths, what did you do about mass? Keep mass same, keep length same, keep winds the same?
If you haven't already, consider setting up a designed experiment around your current width and mass and winds to make sure you are at the true optimum.

Winding technique, slower is better. There are discussions on how to pack on max winds if you look around at the hard core indoor airplane forums. I think there are some on scioly if you check the archives for Wright Stuff. Good winding makes a difference when you get to that level.
Here's one: viewtopic.php?f=212&t=8094&p=281726&hil ... ue#p281726
And another: viewtopic.php?f=191&t=6247

Jeff Anderson
Livonia, MI

[daydreamer0023]

Does anyone know if there is a team going into Nationals with a competitive heli with a single bladed rotor? I'm just curious.

[yash99]

I've tried two single bladed rotors, but it seems as if it doesn't generate enough lift. Best bet seems to go with one single blade if any at all.

[Bazinga+]

Anyone know winning times at Nationals?

[maxxxxx]

Anyone know winning times at Nationals?

viewtopic.php?f=246&t=9875&start=90#p314454