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Old Jan 19, 2013, 07:38 AM
Jack
USA, ME, Ellsworth
Joined May 2008
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I'm looking forward to your results on the rewinds.

Did you happen to notice the results I got when I did a 19 turn LRK Wye terminated wind on this motor? I used that winding and termination to get a Kv that was similar to the motor's original Kv and I was really curious to see how the LRK wind would work on this motor.

Original post on 19 turn LRK wind - http://www.rcgroups.com/forums/showp...postcount=1409

Ignorance is bliss of course, and I was quite happy with that wind. I even went so far as to make this claim for it's performance as compared with the original wind but with only a single propeller:

"..this LRK wind give me an 8% increase in full throttle RPM, a 48% reduction in current draw, and a 15% increase in thrust..."

As the discussion continued it seemed that everyone saw nothing but a very inefficient motor. But I was still not unhappy with it. There was quite a bit of discussion as to my having made some mistakes or that there was something wrong with the ESC I was using. But nothing was ever found to be in error.

Eventually the motor developed a short during a test at 4S voltages and with a larger prop it and I wound it the same way again. And I got similar results again.

re-wound and retested data - http://www.rcgroups.com/forums/showp...postcount=1483

So all of this has remained sort of inconclusive because I have not gotten around to putting the motor on a plane and flying it. That has been my plan but I just haven't gotten to it. I don't know where the year went and now it is winter again so it will be on the agenda for the next flying season.

I'm not suggesting you to try the wind I did but it will be interesting to see what you do with your motors.

These motors have some of the worst looking factory winds I have ever seen. I think it is because of their size and winds being so visible on the open back. How did your motors look?

This image is of one of the worst I have seen, it was re-wound Half Parallel dLRK-Y and has been used a lot.

Jack
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Old Jan 25, 2013, 01:54 PM
Registered User
Finland
Joined Jan 2013
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I have now ordered some motors from HK for that new mount/tube project. But in the mean time I got intrested of winding and running on 4s. So would it boost efficency or what would happen if I rewind the motor for lesser Kv to counteract the increased voltage of 4s? The winding target would be to have same no load RPM with stock wind + 3s and new wind + 4s... ? Hard to explain with my english skillz..
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Old Jan 26, 2013, 12:51 PM
Jack
USA, ME, Ellsworth
Joined May 2008
16,658 Posts
It should work fine with the change in Kv. To estimate the needed Kv you can use the battery voltages and estimated no load and under load RPMs.

If you assume a cell voltage of 4.1V for the no load the no load RPM would be:

3S - 12.3V x 750 Kv = 9225 RPM no load

And assuming 75% of the no load for the continuous under load RPM

9225 x 75% under load = 6919 RPM

To get the Kv from a 4S pack the math would be:

9225 RPM / 16.4V = 563 Kv

And the 75% under load RPM would be the same as before:

9225 RPM x 75% under load = 6919 RPM.

You can look at the Turn Calculator 5 output for the DAT-750 to see what winds will get you a Kv down around 560:

http://www.rcgroups.com/forums/attac...mentid=5231461

As I see that, the high turn counts needed for that that low a Kv from the Half Parallel and LRK winds would lead me to trying the dLRK wind terminated Star (or Y or Wye). That shows a Kv of 557 for a 14 turn wind.

That would allow you to use a wire that has more surface area than the original 18 turn wind and that would increase the current handling ability some.

The original wind has 8 strands of 0.25mm wire. Looking at the wiki AWG page that makes the surface area in the original wind to be 8 x 0.040 mm2 or 0.3232 mm2,

The table shows the surface area of 22 AWG as 0.326 mm2 so if you can get the 14 turns on with 22 AWG wire or larger you should be able to handle the same kinds of input power as the original wind did. I had no trouble getting 18 turns of 22 AWG wire on this stator so you should be able to use a larger wire than 22. if you have 21 or 20 or even a little larger it would be worth trying. As I sure you know, the largest wire size that will allow you to get the 14 turns on is the wire that will give you the highest current capacity.

There will be some difference in the performance between the dLRK Delta and dLRK Star winds in use. You'll really just have to wind it and fly it to decide if the Star terminated wind is as good for you as the Delta was.

Just out of curiosity, what prop do you plan to use?

Jack
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Old Jan 28, 2013, 12:51 PM
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Finland
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Thanks for the reply. I'm thinking 12" APC SF props, or maybe bigger. I think the Kv could be even less cause of the max rpm of these size props. The goal would maybe to have 1000-1200 + grams of thrust at minimal amperage.

Mr. Ohm says that Voltage x Current = Power, so more voltage would give the same power with less Amps.
This is why I tought of 4s.
But on the other hand 4 cell battery weights more than 3 cell. So maybe 3s with more capacity would give about the same flight time than 4s and fewer amps.

I need to think that winding again.
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Old Jan 28, 2013, 12:58 PM
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Finland
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And I forgot to ask.
Is this the right dLRK winding scheme what you mentioned? But with Wye termination?

http://forum.flitetest.com/attachmen...8&d=1338560953
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Old Jan 28, 2013, 07:28 PM
Jack
USA, ME, Ellsworth
Joined May 2008
16,658 Posts
Quote:
Originally Posted by z4m1 View Post
Thanks for the reply. I'm thinking 12" APC SF props, or maybe bigger. I think the Kv could be even less cause of the max rpm of these size props. The goal would maybe to have 1000-1200 + grams of thrust at minimal amperage.
There is little thrust to RPM data for the big APC SF props at flybrushless.com, you can see that here:

APC SF 12 x 6 - http://www.flybrushless.com/prop/view/49

APC SF 12 x 3.8 - http://www.flybrushless.com/prop/view/49

Those make it look like your expectations are realistic enough for those props. The static testing data there never exceeds the RPM limits and the motors are not tested beyond the point where they are reaching their heat limits.

The APC SF props are rated for a max of 65,000 RPM / Diameter (inches) so the 12" SF prop max would be 5416 RPM. They won't, of course fall apart immediately if that is exceeded a little. So if I want a Kv that will let me take a prop to the RPM safety limit at full throttle I usually shoot for one that will or may give me a little more RPM than that at the starting voltage.

I rely on my knowledge and self control to keep track of where things are and when I am starting to push or exceed limits. And I'm a geezer at heart, I don't push things hard just for the heck of it.

For 3S I would probably assume a voltage of 12V shoot for a max of 6000 RPM. That works out to a Kv of 500 but I would probably take a little higher Kv than that knowing that I rarely launch at full throttle and seldom fly at it either.

If you did that at 560 and used it on 3S (12V) it would give you a theoretical full throttle RPM of 6720 and on 4S (16V) 8960 RPM. The 4S RPM would be well into the danger zone and I would find a throttle limit in static testing that kept me down around the 6000 or so area.

You obviously cannot pick one Kv for both 3S and 4S and the same prop so you have to settle for coming up short on 3S or setting a self imposed limit for 4S. I like the latter approach best and if 4S turned out to be more to my preference I might wind again later and fine tune the Kv down a little for 4S at that time.

Quote:
Mr. Ohm says that Voltage x Current = Power, so more voltage would give the same power with less Amps.
This is why I tought of 4s.
But on the other hand 4 cell battery weights more than 3 cell. So maybe 3s with more capacity would give about the same flight time than 4s and fewer amps.

I need to think that winding again.
It is not unusual to find that motors can be used on 4S even when their specs say they are 3S motors. And our rewinding efforts often contribute to allowing that. And you can prop down a little too better accommodate the higher voltage if necessary.

I should probably warn you that you are exploring new territory here to some extent. One of the regulars here has a spreadsheet with a list of the results of many of the winds that have been done on this motor:

http://www.rcgroups.com/forums/showa...2&d=1274343368

You can download that and run it under Excel or OpenOffice.org Calc and see a lot of info about the past rewinds. But there is no record in there of anyone having done a dLRK wind with a Wye termination. So my saying it will work is more based on my results with doing dLRK-Wye winds on other motors.

Most of the winds on this motor were more for 3D and speed or aerobatic flying and the dLRK-Delta and Half Parallel-Wye wind are the most used. I like the Wye winds I have done but part of that may relate to what I fly and how I fly. I prefer bigger props and slower planes and fly more at mide to three quarter throttle whereas many of the others were winding for more "sporting" types of flying.

I chose the dLRK-Wye primarily because of the lower Kv you want. And would not hesitate to try it if it looked like it was what I needed too. I just haven't needed a lower Kv on it yet, I'm usually happy in the 800 to 900 or so range.

Jack
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Old Jan 28, 2013, 07:38 PM
Jack
USA, ME, Ellsworth
Joined May 2008
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Quote:
Originally Posted by z4m1 View Post
And I forgot to ask.
Is this the right dLRK winding scheme what you mentioned? But with Wye termination?

http://forum.flitetest.com/attachmen...8&d=1338560953
There are at least two ways to do the dLRK wind, the one in the image you posted the link in valid as far as I know (have not used it). If you terminated that as Wye instead of Delta, as far as I know it will work. But have not done it that way yet and am not sure as to how to change it from Delta to Wye.

The two images attached are the references I normally use for dLRK wind and I use the dLRK for Delta image when I know I am going to terminate Delta. The dLRK for Delta winding bring the wires that will be joined out side by side for the easiest and neatest termination.

Jack
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Old Jan 30, 2013, 09:43 AM
Out of helis, sanity returning
Tallahassee, FL
Joined Feb 2009
1,948 Posts
Bearing wear question

Glad to see that this thread is still humming along since the last time I looked.

I'm wondering about bearing wear in this style of motor: when the bearings begin to wear out, which goes first- upper (in the bell) or lower (in the mount), or both.

I think in terms of upper and lower because I use DT700s on my quadcopter I guess it could just as well be front or rear.

Thanks-

Rick
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Old Jan 30, 2013, 12:48 PM
What goes up must come down..
Canada, QC, Saint-Laurent
Joined Jan 2002
1,718 Posts
Rick,
Once I was there, I changed both bearings so they should wear and tear normally.

Roger
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Old Jan 30, 2013, 01:18 PM
Out of helis, sanity returning
Tallahassee, FL
Joined Feb 2009
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Quote:
Originally Posted by rodair View Post
Rick,
Once I was there, I changed both bearings so they should wear and tear normally.

Roger
Yup- I intend to do that. I guess I'm interested in knowing which one takes the worst beating in normal use

I'd guess that it'd be the one on the bell end of the shaft.

Rick
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Old Jan 30, 2013, 01:22 PM
Jack
USA, ME, Ellsworth
Joined May 2008
16,658 Posts
The front bearing will usually show the wear first, it has the highest side loadings and also more vibration if there is any. I usually replaced them both when I did but the front one would usually feel rougher. If you stick a shaft into and bearing and rotate and feel any roughness at all it is a good time to replace them.

I kind of like these rubber sealed bearings best as they keep the lube in better and the seals fit a little closer. There will be more bearing drag because of the rubber seals but we cannot measure or feel the difference. They are like these (about $1.50 each):

http://www.ebay.com/itm/4x7-x2-5mm-B...-/251038843964

And here is my drill for lubricating them in this post: http://www.rcgroups.com/forums/showp...8&postcount=17

Too small, very cheap, it all balances out in the long run...

Jack
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Old Mar 23, 2013, 11:40 PM
What goes up must come down..
Canada, QC, Saint-Laurent
Joined Jan 2002
1,718 Posts
Another one..to be rewind.

In an attempt to fly at an early stage of the season still in the snow I took my courage my bipe that was equip with a stock DAT-750 somehow at the low outside temperature the motor was coffing..so I beleive it was one lipo's that was cycled to heavily last season, my friend suggest to let him fly and we install a 2200 3s almost new Lipo's full charged and with an GWS 11 x 8 Sf prop using Jack perfect method i.e. a prop saver with the tetra band to sucure that one.
Gee I was surprice loops hammer head a bit of inverted etc.. then a what was suppose to be a low pass end up as a crash and from far smoke could be observed..burnt ESC? or the DAT-750? ..

My friend told me after the flight that most of wasn't intentionally done but he was only trying to bring back the plane as it was going away for a while..
Also in his excitement to run at the plane to unplug the battery we found out the trootle was still at 75% throotle more

Anyway here are the picture of the damage motor + a fast rewind this time DLRK with whit the only wire I had on hands #23 AWG (16 turns) so I can go back in the air if weather permit ( above freezing + sun = good enough).

I am now ready for the terminaison what should I use Y or Delta?

I am ordering some bigger wire this time either AWG #21 or #22 I am looking at the champion's rewinder chart see what I have on hands (lipo wise) and check for best ones from the chart for 3S 1300 mAh or soon to come 2200 mAh lipo's.

Actually most of them look good some are out of the ordinary!

Jack, did you ever finish the one with more copper and LRK winding?

I wonder how much different thrust is from a prop in motion compare to static( loads torque effecincy at RPM etc)?

Anyway, the prop was fine the plane is the hangar as well as the motor getting a small fix for the time being..

Happy flying (rewinding) again Thanks to Jack for the tip about the prop bands!

Roger
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Old Mar 24, 2013, 06:50 AM
Jack
USA, ME, Ellsworth
Joined May 2008
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"..I am now ready for the terminaison what should I use Y or Delta?..."

The turn calculator for the stock motor shows 19 turns dLRK as producing a 711 Kv Delta and a 410 Kv Wye so I'd think you want to use the Delta term unless there is a bigger prop or a 4S or more battery in the plan.

"..Jack, did you ever finish the one with more copper and LRK winding?..."

The motor is still ready to go but I have not gotten to building a plane for it yet. I was going to build a 48" flying wing (scaled up KFm4 Zagnutz) but have spent the entire winter avoiding my chilly basement for the most part...

I still think that LRK wound motor has some potential for a 4S wind even though eveyone tells me the efficiency sucks. I got a little bit interested in building a tri or quad copter and FPV over the winter but never got beyond lurking on threads and studying the details.

A FPV flying wing with a good motor and electronics on it and two good cameras (one for the FPV pilot and a second for video capture) can chew a good part of $1000 if you don't shop it around some. The costs have been part of my slow down, I'm just not sure the interest is there as far as getting into quads or FPV.

Jack
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Old Apr 07, 2013, 07:09 AM
Life is such a brainfart.
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Melbourne Australia
Joined Aug 2004
406 Posts
Just a quick question....

I recently received 4 DT750 motors from HK and they seem to run fine. However, I have noticed there is a lot of drag if I spin the motors with my hand.

With my older DT750 motors, if you spin the motors by hand, they feel quite free and will spin around a half dozen times. With these new ones, they virtually stop straight away.

I removed the bell as I thought the bearings might be a bit dodgy. However, the top and bottom bearings in each motor are fine. Then I thought the stators might be rubbing a bit on the magnets, but there are not rub marks and a sheet of paper can fit in the air gap. I also thought it might be the E-clip that keeps the bell on the shaft. But even with that removed it made no difference.

So just wondering if anyone else has noticed this with their motors, and is it something I should be worried about?

Cheers,

Andy
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Old Apr 07, 2013, 10:02 AM
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Antony (France)
Joined Sep 2003
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Snaggers
Don't worry.
On mine I can launched a rotation between two fingers.
Stop after around 60 .. 90 deg (only)
(and three wires ends in open circuit, no touching)
Louis
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