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Author Topic: Help with indoor duration helicopter  (Read 9535 times)
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PiperCub49
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« Reply #150 on: March 15, 2011, 07:35:10 PM »

The camera batteries were dead (Murphy's Law), so I decided to go ahead and build another set of rotor blades. These ones should be plenty strong. It's heavy, but what's the worst that can happen -- I get close to my required weight? Once the batteries charge, I'll start taking pictures and videos so that I can start documenting my changes and results and so that you guys can see what's going on. Hopefully the stronger LE, TE, and rotor spar will help me out.
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ykleetx
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« Reply #151 on: March 15, 2011, 09:49:43 PM »

OK. Good luck.

What do you think might be the problem with the helicopter?

Are the rotors turning "really fast", moderately fast, or "really show"?

Actually, let me ask more quantitatively:

- how many turns do you wind to get to .65 in-oz
- after 2 minutes of it unwinding (in the air, not in your hand -- you can keep picking it up and releasing it), how many turns are left?
- exact length and weight of motor

From this, we can get an idea of your RPM and compare with other helicopters. This is at least a start. I'll supply some numbers from other helicopters in a little bit.

-Kang
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PiperCub49
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« Reply #152 on: March 27, 2011, 04:37:52 PM »

Actually, let me ask more quantitatively:

- how many turns do you wind to get to .65 in-oz
- after 2 minutes of it unwinding (in the air, not in your hand -- you can keep picking it up and releasing it), how many turns are left?
- exact length and weight of motor

From this, we can get an idea of your RPM and compare with other helicopters. This is at least a start. I'll supply some numbers from other helicopters in a little bit.

I did some more testing yesterday, this time with an experienced duration flyer. I'm only slightly closer to where I need to be.

-Turns to .65 in-oz: 1200
-# of winds left after two minutes of unwinding: 720
-Length and weight of motor respectively: 322mm, 1.7g
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ykleetx
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« Reply #153 on: March 27, 2011, 05:01:35 PM »

Kody,

From you information, I calculate that your motor is too thin. (If your weight and length measurements are correct, your motor is around .095")

You should be using .125" motor. Start at around 1.2g. This motor would only be a 7.2" loop.

You can wind a .125" motor to 1.2 to 1.4 in-oz with the following max winds.

1.2g: 720 max turns
1.5g: 900 max turns
1.8g: 1180 max turns

A helicopter I'm familiar with, using 1.4g motor, that lasts around 2:30, turns at around 300 RPM over the course of the flight.
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PiperCub49
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« Reply #154 on: March 27, 2011, 06:15:49 PM »

I measured the rubber and you are absolutely right. The rubber is cut thin.

I grabbed some mystery rubber (on the left) and tried that. It takes 440 winds to get to .65 in-oz. The helicopter will "go up" for maybe 100 winds, but that's it. I need to try messing with the blades again.
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PiperCub49
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« Reply #155 on: March 27, 2011, 06:56:09 PM »

Shout-out to Bill- What is the distance between your rotors?
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ykleetx
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« Reply #156 on: March 27, 2011, 08:55:02 PM »

Kody,

Why are you winding only to .65 in-oz? As I posted, you can wind a .125" motor to 1.2 or 1.4 in-oz. There are more turns and torque in the motor that you are not using.

Next, if you are landing with too many turns, that means there's not enough power to sustain flight: The motor is too thin, the rotor's pitch is too high, or the model is too heavy, or all those.

-Kang
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« Reply #157 on: March 27, 2011, 09:02:45 PM »

Kody,

Take two 2-4" loops of the rubbe that you are using. Break in the loops. Then wind one until it breaks and note the breaking torque. Do this again until you are comfortable and trust the experiment and the observed breaking torque.

-Kang
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Olbill
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« Reply #158 on: March 27, 2011, 10:11:18 PM »

Shout-out to Bill- What is the distance between your rotors?

Kody
I don't have any helicopters in my possession to measure. On the one that I built I used an 18" motor stick. The ones that Sebastian used were Freedom Flight helicopters built exactly per the plans except that Harlan bearings were substituted for the Ikara bearings that came in the kit. I think the motor stick is around 12" long.

BTW Sebastian won the Georgia State finals on Saturday. His team finished fourth in the overall competition so they will not go to the nationals.

I went to a practice session last Thursday where Sebastian was testing his second helicopter for the first time. It flew even better than the first one. He launched it at torques up to 1.4 in-oz with no problems at all. It was very sensitive to motor weights with the best flights on motors of about 1.3g. Heavier motors did less time. The best flight I saw was 1:55.
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PiperCub49
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« Reply #159 on: March 28, 2011, 01:27:53 AM »

Kang,

Sorry for being frustrating. I was trying to match Bill's results, but why? I went up to .8 oz-in an she flies at last. Geez, I feel so foolish...just not thinking straight at all. No times have been recorded yet. It has all been casual experimentation until now.

I'll have a gym to myself all day today, so I hope to make some more progress. I'll experiment with rotor blade angle and torque the most. The vertical CG is about right.

Bill,

Great for Sebastian!

Just a couple of questions: 1) When Sebastian went with a lighter motor, would he make up for the lower weight with clay? 2) Do you think that my 1/32" MS can handle 1.4 oz-in? It's just something that I would rather not figure out the hard way if you already have some insight.



I thought that I'd end with some pictures. I forgot about posting pictures of my mystery rubber (left in first picture) earlier. Note the change in width also!
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Olbill
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« Reply #160 on: March 28, 2011, 11:40:51 AM »

Kody
The helicopter needs to weigh 4 grams WITHOUT rubber. You never want it to weigh more than that. The whole point of using less rubber is to reduce the TOTAL weight of the copter plus the motor.

One point about your torque meter - The distance from the main shaft to the contact point on the weighing platform needs to be one inch measured HORIZONTALLY from the main shaft. I don't know what the length of the pressure arm is on your meter but if it's one inch actual length then the scale readings are going to be higher than the actual torque.

Here's the explanation:

For a torque of 1 in-oz if the arm length is 1 inch then the force required to resist the torque will be 1 ounce. If the distance to the contact point measured horizontally from the shaft centerline is .9 inches then the force required to resist a 1 inch-ounce torque will be 1/.9 or 1.11 ounces. Thus your scale would read 1.11 when the actual torque is 1.00. I have found this distance to be critical on the torque meters I sell. I've built a calibration device that puts a 1 inch-ounce load on the meter. I then adjust the arm length so the scale reads between .98 and 1.02 oz at the 1 in-oz load.

Also, make SURE that your scale mode is set to ounces (oz) and NOT troy ounces (ozt).

edit: I just looked at your scale picture and see that you have the units set correctly.

edit #2: I missed the motor stick question. If the stick has a bracing wire or thread then it should be okay. Without bracing I doubt it would stand the load. Make sure the bearing and the hook are REALLY well attached. I flew my F1M with 1.2 in-oz of torque last weekend and both the bearing and the hook came loose.

Also, if you're using a 1.2 or 1.3 gram 1/8" motor you may have to use a spacer wire. Sebastian was able to get a fully wound 1.3g motor on his copter without a spacer but if he had gone much shorter with the motor it probably wouldn't have worked. My F1M is designed for motors about 15" long. Last weekend I was flying on 10 1/2" motors and needed a spacer. The spacer I used was an .012 wire about 2" long with closed loops at both ends. One of the loops needs to be around the front end of the motor and the other hooks onto the prop shaft. It's easiest to just make up the spacer with the motor and put the spacer on the motor instead of the front o-ring.

The spacer wire on my F1M was actually winding up a turn or two under 1.2 in-oz of torque. It might be necessary to go a little heavier with the wire for your copter. I think the letter of the rules would permit you to consider the spacer wire as part of the 4 gram minimum model weight. One way to make this obviously legal to the usually uninformed judges would be to make a prop shaft that stuck out 2" (or whatever distance was necessary) farther from the back of the bearing and then use a normal motor with 2 o-rings. Considering how badly copters handle any extra load you want to make sure that any spacer or prop shaft extension doesn't add to the minimum weight.
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PiperCub49
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« Reply #161 on: April 02, 2011, 01:00:00 AM »

Bill- Thank you for explaining the flaws in my torque meter. I am always interested in the math behind such things. I had seen the FliteTork before, but I didn't realize that it was made by you!...I'm can only blush when I compare ours. Embarrassed The proper adjustments have been made to my torque meter.

Can I get some help figuring this one out? I have been making the hole in my rotor spar with a pin and so far it's been done by eye. I was forced to make a new rotor spar when the hole began to wear and create wobble. Now, when I use the old method or my new quasi-jig, my rotor blades end up wobbling up to 1/4"! My setup is the exact same as the one in my last post (except that I have moved the Teflon bearing so that it's actually effective).

I've also tried putting a bearing on top of the rotor. I did this thinking that the clutch/brake on the wire was pulling down on one rotor, making it lean to one side, but this was not the case. I can't think of anything else to try. How do you gentlemen attach your rotors?

-Kody
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PiperCub49
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« Reply #162 on: April 09, 2011, 08:49:50 PM »

The competition was today. I've been testing non-stop for a week. Last night, I had a 50+ second flight on a .9 oz-in motor. Then, for undetermined reasons, the top rotor began wobbling horribly before I ever got to full torque. I looked at everything and rebuilt the top rotor three times. By sheer luck, I got the top rotor to spin flat enough to get some 30 second flights at the competition. Still, it wobbled until it came down sideways at 22 seconds. I was the last flight, so I just picked the helicopter up off of the ground and tossed it up again without any more winds and got a 30 second flight time! All of these flights were made on a completely new helicopter.

There was some time after the helicopter competition where I was able to keep testing. This resulted in a 35 second flight on an estimated .7 oz-in wind (this would have gotten me a bronze medal). I will keep flying the helicopter, since I'm oh-so close to getting good flight times.

I'm not sure how many people followed the discussion on Yahoo! Groups about stopping the top rotor, but we hit that problem today. A Freedom Flight kit got stuck in the rafters. Another competitor told the coach that it should be disqualified, as the helicopter was no longer being supported by it's own power, but the judge said that it was and let the clock tick. About five or so minutes later, the bottom rotor stopped spinning and the helicopter did not fall, so it was eventually disqualified.

Bill- You had it on the nose about the usually uninformed judges. We had two huge fans that were blowing air down on either side of the flight arena. It pushed my helicopter around all day and contributed a great deal to my unstable flights. In fact, there was so much air coming down, bouncing off the floor, and coming back up and hitting my helicopter blades that they were lifted and pulled free from my pigtail bearing every time I left the helicopter unpowered.

All of the helicopters that were above mine were kits. Three of the four were the Freedom Flight kits. None of the helicopters below mine were even close to being competitive. I was disappointed that there were no half-decent home built helicopters. I thought that at least somebody would tackle the rolled motor stick; boy, was I wrong. It's disappointing that I lost to laser cut, kit built helicopters, but I'm proud of myself for taking on the most engineering of us all. This is not a jab at Sebastian though. The winning time here in Maine was only about 1:30!

All-in-all, it was an "okay" day, taking bronze in Mission Possible, missing gold by literally half of a millimeter.

I also have to say that this project has inspired me. I didn't think that I would leave that gym with a positive attitude toward my helicopter, simply because I would be burnt out. That thought couldn't have been further from the truth and I can't wait to get back to it. In addition, during the test flying with the club member of mine, I discovered the Mini-Stick. Now I can't wait to build one. It should provide plenty of a challenge. Do you think it would be a decent build for me?

-Kody
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« Reply #163 on: April 10, 2011, 12:32:25 PM »

Kody
I'm proud of you for sticking with it and doing as well as you did. Will you be flying helicopters again next year? If so I'm sure you'll do better thanks to the effort you put into it this year.

I'm also happy the stuck helicopter didn't come down. That's a sad way to win a competition.

Almost every time I've traveled with a partner to an out of town competition we've gotten in the car for the trip home completely exhausted and sick of flying. And then we spend the whole trip dissecting what happened and making plans for the next time. So welcome to the club!
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PiperCub49
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« Reply #164 on: April 10, 2011, 03:04:37 PM »

Bill,

Thank you for your comments and all of your help. I don't think that it would have turned out the same way without you. Heck, I "borrowed" your design and ended up using it for the contest!

I am also making plans for next year. If Helicopters is an event next year, I will have a guaranteed spot in it and I will be back at it again in a heartbeat. This hobby is one of frustration, but it's a fun frustration and there is no way that I'll miss it.

Again, this isn't the end of helicopters for me. I'll fly my helicopter whenever I get the opportunity. I don't know when that will be, but it'll come along some time or another.

EDIT: I forgot to mention that no one competitor brought a torque meter. Puzzling...
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« Reply #165 on: April 10, 2011, 07:48:19 PM »

Good effort Kody. You will have learned a lot.

Cheers
John
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Olbill
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« Reply #166 on: April 10, 2011, 09:05:59 PM »

EDIT: I forgot to mention that no one competitor brought a torque meter. Puzzling...

Well next year you can tell everyone where to get one!
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PiperCub49
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« Reply #167 on: April 10, 2011, 09:18:41 PM »

EDIT: I forgot to mention that no one competitor brought a torque meter. Puzzling...
Well next year you can tell everyone where to get one!

Bill- Oh, duh! I'll make it a point to spread the word next year!

John- Thank you. I have learned a lot. I knew so little about rotary wing aircraft and vertical propulsion. My flight events in my three SO years (bottle rockets the first two years and helicopters this year) have taught me quite a bit and so I can say that I really have expanded my horizons in that sense.
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« Reply #168 on: March 24, 2012, 05:22:06 PM »

I spent an hour today watching 100% of the attempted helicopter flights hang up on sprinkler piping at the Georgia Science Olympiad state finals. It would be hard to imagine a worse place for them to fly. A classroom with an 8' ceiling would have been better.
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« Reply #169 on: March 24, 2012, 11:06:24 PM »

Bill,

Hey!  Long time, no talk.

My brother and I have been pinched for time with college applications this year and our own building has been practically cut off.  Out of interest, we bought a Freedom Flight kit and have been testing it with 1/8" and 5/32".  We managed a 1:39 second flight today.  I still can't grasp the concept behind the blade design (why it's so darn stable), but if there is anything good about it, it's that these blades are light and very strong because of the geometry.  The weight of this helicopter is in the motor stick, whereas most of the weight in my helicopter last year was in the main spars.

Anyways, our state flying site is a mine field too.  Girders are everywhere, along with an A/C system that is always on.  I am trying to downsize the width on this rubber until I can get a slower climb and descent.  Maybe that way I can get some more control on the climb.  Right now, it just takes off in any direction.

Here's one seemingly simple question that my brother and I can't agree on.  With the Freedom Flight kit, the helicopter rockets to the ceiling and pushes up against it.  Is it wasting energy doing this?  I think that it would be more efficient to put that energy into a slow climb, hover, and descent.

-Kody
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« Reply #170 on: March 25, 2012, 08:24:03 AM »

Kody
I guess that it's possible to hover a freedom flight copter but in my limited experience they either have enough power to go up or they come down. Sebastians #1 copter was an approximate copy of Maxout's design and was pretty stable in hover. He could have done better on lower power had he known how bad the site was going to be but he only had one practice session and that was spent flying the usual stick it on the ceiling pattern. Even if staying off the ceiling had cut his time in half it would have been good for a high placing.
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« Reply #171 on: March 26, 2012, 10:25:28 AM »

I have yet to test the 3/32", but if it proves less efficient than the 1/8", I can always strip some rubber in between the two sizes and see if the longer climb helps.  It will be interesting to see.
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« Reply #172 on: September 03, 2020, 03:00:21 PM »

Hi all,

Found this ten-year-old thread, and resurrected it in case it came in handy. For some unknown reason I volunteered to coach Helicopters at the local High School Science Olympiad this year. Due to Covid they want it done "virtually", on computer screens maybe using Zoom, emails etc. Being an old diabetic fat guy, that's about the only way I could do it too. Even the coming tournament will be virtual - students will fly their helicopters and report the results. Pretty good chance I'll never meet the students face to face, even through the tournament.

Two flies in the ointment: Though I've done model planes since age 6, and having recently coached Wright Stuff, Elastic Launched Gliders, and Electric Wright Stuff, I've never had anything to do with rotary-wing craft, outside of studying them in college. No practical experience, no real interest till now, and frankly no clue.

Rules include 20cm cm rotor diameter (dinky), min weight of 2.5g without motor, unlimited motor mass, up to three rotors, unlimited blade count. Average ceiling height of about 8 feet, which is typical for the inside of an ordinary house's living room or bedroom. BUNCHES of unpleasant restrictions there.

The other fly in the ointment: I just found out about doing this day before yesterday, and the tournament is Oct. 10, 2020. Five weeks.

Setting up a jig to build rotors now, already ordered a bunch of stuff from Freedom Flight and the local hobby shops. That 2.5g min weight will be providential. These will simply be really little copters, but proportionately somewhat balanced.

Will start with somewhat-balanced rotors, prototype will have ground-adjustable pitch though contest models probably won't (for weight purposes), once the prototype gets us into the ballpark. Building pitch twist into the blade might be the toughest part, I hear some folks simply make flat-blade rotors with constant spanwise pitch angle. That might be lighter, and may be the way to go, though it sounds inefficient. An extra month or two would certainly be welcome, but ain't gonna happen.

This tournament is supposed to be an experiment to see if a "virtual" tournament (or season) is even possible. That's why it's so early. I seem to have stupidly signed up for the most difficult event to do that in, they tell me it will be the only flying event.

Anybody got any guesses about how thick the rubber motor should be for something like this? I don't want to spend the flight bouncing off the ceiling, at least not very hard. That says to me that I'd be wasting energy. But getting a constant flow of power, enough to simply hover for a long time without hitting anything, might be impossible for a rubber motor.

Sigh.

Any suggestion or words of wisdom? Other than "Quit Now", I've already heard that one.
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