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Author Topic: Winders, winding stooge, torque meters, winding methods  (Read 40521 times)
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Olbill
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« Reply #50 on: April 26, 2010, 02:19:58 PM »

Jeff Hood photos from Kent. Many excellent shots with a number of different winder setups.

http://picasaweb.google.com/jeffrey.hood/Kent2010#
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Art356A
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« Reply #51 on: May 19, 2010, 01:28:29 AM »

I brought the torque meter to the session at Rockledge on the 15th and it was well received by my friends there. I got orders for 2. The first one ships tom'w, and the second is waiting on scale dimensions to come in.

They take about an hour to make from shop scraps. Mine are aluminum because that's what's here, but I can imagine a very elegant one in 1/16 ply.

Art.
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Tmat
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« Reply #52 on: May 19, 2010, 02:16:30 PM »

Art, I bought the exact same model scale that you have from Deal Extreme (cost me $13.00 incl shipping!!). I'm going to try and have at go at making one myself using 1/32" music wire and two Peck nylon bearings (with 1/32" hole). I've made a little center collar from brass rod with a 1/32" hole and another 1/32" hole at 90 degrees (to mount the cross wire). I'll drill and tap it for a 0x80 set screw like a mini wheel collar.

Did you see Ray Harlan's critique on the Indoor Construction group? Basically, he felt that the drawback to this type of torque meter was that there will be some friction at the front bearing because the shaft will be loaded in tension (compression load on the bearing). The thought was that this friction would be greater than that encountered from a conventional torque meter that has the torque wire secured at the back end so that the front bearing only sees a rotational friction force, not a compression load.

A good point, but I'd like to see for myself how it works, plus it looks fairly easy to do.

Tony
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Olbill
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« Reply #53 on: May 19, 2010, 05:08:53 PM »

Art, I bought the exact same model scale that you have from Deal Extreme (cost me $13.00 incl shipping!!). I'm going to try and have at go at making one myself using 1/32" music wire and two Peck nylon bearings (with 1/32" hole). I've made a little center collar from brass rod with a 1/32" hole and another 1/32" hole at 90 degrees (to mount the cross wire). I'll drill and tap it for a 0x80 set screw like a mini wheel collar.

Did you see Ray Harlan's critique on the Indoor Construction group? Basically, he felt that the drawback to this type of torque meter was that there will be some friction at the front bearing because the shaft will be loaded in tension (compression load on the bearing). The thought was that this friction would be greater than that encountered from a conventional torque meter that has the torque wire secured at the back end so that the front bearing only sees a rotational friction force, not a compression load.

A good point, but I'd like to see for myself how it works, plus it looks fairly easy to do.

Tony

Art and Tony:

The design that I was thinking of would nearly eliminate any friction at the bearings. Basically the rear attachment would be a wire fixed to the rear support. There could be a slight preload by winding up the wire a little and then zeroing the scale. There actually is no (or very little) rotation of the torque member in the front bearing because there is very little actual movement of the weighing pan. If there is no rotation then there would be no friction.

Where the wire is attached to the rear support there would be close to zero movement of the wire.

I've done a real crude hand held mockup and it seems to work fine. Here's an equally crude drawing.
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Tmat
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« Reply #54 on: May 19, 2010, 06:01:35 PM »

Interesting idea Bill. I think that's worth a try. What sort of wire diameter were you thinking of using for the torque wire?

Tony
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Art356A
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« Reply #55 on: May 19, 2010, 10:07:02 PM »

It makes no difference what you use for a thrust bearing (the ball type I used is way overkill) because experience shows that the torque force is a huge multiple of the the tension.

The third and fourth ones have Tefzel thrust bearings and they're fine...the scale reading bounces around as you wind, and as soon as you stop, the torque reading starts to decrease instantly. If the rocker was binding on the frame (or on anything) the reading would hold and then there would be a sudden release.

I made up a noose of fine nylon thread and wrapped one end around the rear frame at the shaft and the other end around the arm at the front, then pulled it tight till it released the thrust bearing from contact with the front frame. Now we had Zero friction. The behavior of the winding and relaxing motor was exactly the same as before.

All due respect to Mr. Harlan, but it's a non-issue. You guys are complicating a simple, effective and easy to build device to accomplish nothing.

As a couple of more get built and used, you'll see that.

Art.
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Olbill
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« Reply #56 on: May 19, 2010, 11:24:25 PM »

Interesting idea Bill. I think that's worth a try. What sort of wire diameter were you thinking of using for the torque wire?

I dunno. Maybe start with something around .020 inside a 1/16 tube and see what happens. I could probably put one together in less time than it took to do the drawing.
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Art356A
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« Reply #57 on: May 19, 2010, 11:58:33 PM »

What will happen is that you'll get a reading lower than the actual torque.

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« Reply #58 on: May 20, 2010, 12:01:34 AM »

What will happen is that you'll get a reading lower than the actual torque.

Why do you say that Art?

I'm not trying to complicate it, just passing on the comments I've read elsewhere. I think it's a great idea too.

Tony
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Art356A
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« Reply #59 on: May 20, 2010, 12:41:44 AM »

Because what Bill is building here is basically a common torque meter without the disc. The .020 wire will resist the twist and lessen the force of the arm on the tray. That was my immediate reaction.

But, now that I think on it more, he's not wrong, I am, because there's no measurable rotation of the shaft...it just changes twisting pressure to linear downward pressure without actually moving.

I think #5 will be a variation on his theme. I sort of like it.

Art.
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Art356A
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« Reply #60 on: May 20, 2010, 12:24:55 PM »

Good Olbill. Here's #2 modified into #5. 1/16 brass tube and 20# Stren fishing line.
Solder the arm onto the tube and bend and/or trim it to length. Dress the hook end of the tube smooth, because you'll be pulling the motors off it. Slip the string in and tie a knot at the hook end. Leave a few inches at the anchor end. Bend the hook... I thought this step would capture the string but it didn't so I pulled out a half inch or so, spread it with CA and pulled it back in. That did it. Then cut the knot off. The fwd hole had to be opened to 5/64 so the bent tube would pass thru it. You can see how I clamped off the back end of the string. Just pulled it up snug and tightened the screw on it. A tiny gap opens up between the tube and frame when the rubber pulls on it.

Thrust bearing fears eliminated!

a.
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Olbill
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« Reply #61 on: May 20, 2010, 01:52:23 PM »

That's pretty slick Art!
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Tapio Linkosalo
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« Reply #62 on: May 22, 2010, 07:56:20 AM »

Ok, my first attempt for a digital torque meter. I took apart a 100g/0.01g cheapo scale. Unattached the torque element, built a new rig to hold it. Seen at the back. The body of the meter is a U-shaped piece of aluminum, just as in the ones that we have seen before. To that, the torque sensing element, at the back side of the aluminum body in the picture, is attached, with screws to the bottom on the left end. The side arm from the torque rod pushes the right end of the element down. So far no fancy bearing to the torque rod, and the side arm if from a D-connector. Need to make a better one, but this one was just to test the concept. Taking the scale apart enables me to make the thing more compact, and to turn the meter face more horizontal to make it readable from further away. I'll have to saw the scale body apart next, it will make a good housing for the electronics. Then I need to get a compact battery holder to replace the current, also using the scale part.

First attempt of winding rubber on the scale indicated that the readability is good, and the scale reading does not vary too much, so I think this works as good as analog one, if not better. And what is best, "one size fits all". This has enough sensitivity to work for LRS, while the force element can handle SO sized models.
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Art356A
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« Reply #63 on: May 22, 2010, 09:49:16 AM »

Tapio, this one's beyond both my ability and comprehension.

To return to the thrust bearing question, I've been testing a couple of units that I made for friends to the original design, but with Tefzel bearings instead of the ball bearing. The performance is identical on all styles and the one with the string isn't any better (you can't improve on perfect). My criterion is: How fast does the torque start to slack off after you stop winding? With all of them it's instantaneous.

Art.
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Tapio Linkosalo
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« Reply #64 on: May 22, 2010, 12:01:32 PM »

Ok, reworked the thing somewhat. Now the framework holding the circuit board is sawn apart, a small battery holder for the two AAA cells. But most of all, the part from D-connector is discarded, instead there is a full length of 1mm id 2mm O.D. brass tubing holding inside the 1mm wire for the hook. This makes the thrust bearing, sliding against a teflon washer inside the aluminum frame. Over the tubing is a shorter piece of 2mm/3mm tubing, making a snug fit for a 3mm wheel collar. the two tubes are cut through and there is a flat surface on the wire, so that the collar locking screw locks the setup from rotating on the wire even under torque. And now comes the neat part: the screw is over-length, and there is a thin washer between two nuts, pressing against the sensing element of the scale. Thus moving the washer, I can fine-tune the moment arm -> fine-tune the readings of the scale.

The setup seems to work smoothly, the reading run but not too fast to get the big picture of the torque. If I stop winding, the readings start to drop, as they should, and also the pull/release of the rubber stretch affects the readings.

Next task. Order a couple of extra scales for replacement parts... :-)
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Tmat
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« Reply #65 on: May 22, 2010, 12:01:37 PM »

Very cool Tapio!

I can't see from the picture how the wire shaft is restrained in the U-shaped bracket. Is there an arm or something that stops it from being pulled out and what pushes on the torque element? You mention a side arm but it's not clear. Is the readout from the original scale, or one you had on hand?

Modified after seeing the second posting from Tapio:
Umm, isn't the photo the same? Grin
Where's all the cool new doodads?
O.k., now I see it!
Even cooler! Grin
What's the scale read for you, cm/grams?

Tony
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Tapio Linkosalo
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« Reply #66 on: May 22, 2010, 12:07:02 PM »

Yeah, goofed with file save, trying to recycle the file name.... But now the new pic is there, and we can forget about the temporary arm, that did not hold under TQ that good anyway....

I still need to think about a fancy attachment to the winding rod and keep the torque element, display and battery in one unit.
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Olbill
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« Reply #67 on: May 22, 2010, 12:40:56 PM »

Tapio
This is all very cool! I think your experiments are confirming what Art has seen in his meters - that the concept works.

Art
Yes it's normal for the torque to start dropping immediately when you stop winding. There's some disagreement about indoor winding technique but many believe that a very slow wind gives the best results. The rubber stretches as you wind it and a slow wind will allow the rubber to conform to do its stretching while the torque increases. Once the motor has stopped stretching it will hold the torque pretty reliably. Another factor calling for slow winding is heat buildup in the motor. When rubber gets warmer it contracts. This isn't a good thing when you're close to maximum turns and torque so letting the heat dissipate during winding is logical. Some F1D fliers are said to take 10 minutes to wind a motor.
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Art356A
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« Reply #68 on: May 22, 2010, 01:40:20 PM »

Let me tell you about my motivation and my general level of sophistication in this. My main flyers are a pretty good Hangar Rat, and two fair to middling Phantom Flashes, plus some Bill Brown and Dick Baxter fun flyers. The most sophisticated level I've reached is two parlor mites that fly beyond expectations and a 40% overweight Minislick. So I read and try to absorb the science of this but don't have much to apply it to as I've never flown under a ceiling higher than 26 feet. I'm just now trying to learn how to cut and wind rubber to maximize the times while not hitting the ceilings.

Motivation... I tend to be parsimonious. Everybody talks about torque being more important than turns, but I was happy with my 20-1 K&P winder until it turned out it was really 15-1 and I had to learn the 15 times table to be able to use it properly, or else spring for $220 plus frt for a proper one. I had made a couple of simple torque meters calibrated 10° apart and numbered 1,2,3, etc., and after reading Hepcat's opinion (he's like God to me) that we all need to work with the same units of measurement, I decided to try to make up a device to calibrate them properly. I felt this apparatus could and should be made from shop scraps and my $10 Communist Chinese 100 gram scale.

Somewhere during the process, the calibrator became the meter. No extra charge.

a.
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Art356A
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« Reply #69 on: May 26, 2010, 11:25:21 AM »

I played with the last version (the one with the string) for awhile and decided that it was just dopey, not worth the effort. Here's the final one. The hook and arm is one piece and the tail is the other. The solder joint is 3/4" long and doesn't need binding as there's no real stress on it. The tubes are nylon (Nyrod and Goldenrod work fine, too). It's loose as a goose and about as simple as it can get.

An alternative is to double the arm back on itself and bend it into a tail, thus eliminating the soldering job. I did one like that of .020 wire just to try it out. It works, but flexes a bit, which I don't think affects the accuracy. It'd probably be better with .032.
 
Also, why does the hook need to be a real hook? Just bend the wire 10 or 20° past 90 and leave it about a half inch long. The rubber won't jump off it and it's much easier to unload.

a.
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« Reply #70 on: May 26, 2010, 12:24:56 PM »

What's it look like installed Art?

What stops the wire from pulling out of the bracket?

Tony
-I should probably wait for the next picture, but inquiring minds.... Grin
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Art356A
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« Reply #71 on: May 26, 2010, 01:58:08 PM »

The two nylon tubes act as spacers, locators and thrust bearing. The one piece rocker is kind of rickety, but if it were made of stouter stock, with a metal tube on the arm instead of plastic, it would be just as good as the soldered up one.

I tried to get readings on them both to see if they matched, but the rubber relaxed a bit while I was doing the R&R. The value of the drop was consistent with the time lag, though.
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« Reply #72 on: May 26, 2010, 02:21:19 PM »

I see now. So the distance from the center of the shaft wire to the end of the torque arm is 1.0"? That way you get automatic readings in in/oz.

Looks good!

Tony
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« Reply #73 on: May 26, 2010, 02:38:54 PM »

I'm liking this more and more. As soon as USIC is over I've gotta have one.
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« Reply #74 on: May 26, 2010, 03:16:25 PM »

Here's a new gadget I picked up today for $50 from Office Depot. It's a folding aluminum hand truck. Since I still carry my models in cardboard boxes I extended the load platform at the bottom with a piece of thin plywood. The cutouts in the plywood are so the truck will still fold flat. Including the extension it weighs about 8 pounds.
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