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Mar 30, 2016, 02:14 AM
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jammied's Avatar
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Help!

cf2805 first rewind


Well this is my first rewind! It started out as a cf2805 1300kv. It originally had 25t of 32g now has 12t of 24g. Havn't tested it yet does every thing look ok? Well other than it looks like I could work in China at the factory lol that took some doin!! Any thought on the kv and amps? I want to turn 8" props with it on my 10oz foamy
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Mar 30, 2016, 05:34 AM
homo ludens modellisticus
Ron van Sommeren's Avatar
Quote:
Originally Posted by jammied
... Any thought on the Kv ...?
Original termination? New termination?
How did you choose the new number of turns? Why 25?

Vriendelijke groeten Ron
Last edited by Ron van Sommeren; Mar 30, 2016 at 05:49 AM.
Mar 30, 2016, 05:46 AM
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Yes original delta termination. I counted the turns as I un wound it and it was pretty much every pole had 25 turns of 2 strand. I have 24g and 26g on hand so I went with as much 24g as I could. Just to get a feel for winding. Figured I would rewind with something different after I tested this wind to see if it actually would run.

My tach and watt meter is ordered just hasn't been delivered yet
Mar 30, 2016, 05:49 AM
homo ludens modellisticus
Ron van Sommeren's Avatar
Going from wye to delta will increase Kv by factor √3, and vice versa.

Kv is inversely proportional to number of winds, e.g. double winds will halve Kv, one third of the original winds will triple Kv
Simple formula:
(Re)winding and building motors, tips & tricks, checks & tests
→ opening post
→ 14. Calculating number of winds for desired new Kv

Vriendelijke groeten Ron
Mar 30, 2016, 05:56 AM
I am a nice guy! Really!
If you keep the termination the same the kV will be around 2600 since you have essentially cut the number of turns in half. Of course that assumes that the original 1300 was correct. You may be able to turn an 8 inch prop on 2S but not likely on 3 if it is the size I am thinking it is. I do not recognize the maker by the description you have provided.

I see Ron and I must have started typing at the same time. If this is your motor: http://www.headsuphobby.com/Emax-CF2...otor-H-440.htm it looks like it was already wound for 8 inch props on 3S.
Last edited by Mike Dubovsky; Mar 30, 2016 at 06:03 AM.
Mar 30, 2016, 05:59 AM
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OH I see. Thanks for the help.

Well I tested it and then test ran it without a prop. Now to come up with a wind that will work for the 8" props?

Just practicing on rewinding with it. would like to be able to fly the foamy with it. The blue wonders this size have a lot more power. This one didn't have enough thrust or efficiency to fly it for more than 2 minutes. Had to be wot


Yes that is the motor I have. It over heated easily. and didn't have very good thrust like the blue wonders in that size range
Last edited by jammied; Mar 30, 2016 at 06:10 AM.
Mar 30, 2016, 09:45 AM
Jack
jackerbes's Avatar
If you have about half as many turns as the motor did with a Delta termination, it will, as others have said double the Kv rating. But if you change the termination from Delta to Wye it will lower the Kv by a factor of 0.58 and get it back down into a more useful range.

Do you have a link to the wind image you used? If so, we can probably tell you how to change that from Delta to Wye and it will be a pretty simple change. The windings stay the same, just the way the ends are soldered together will change it from Delta to Wye.

Jack
Mar 30, 2016, 01:00 PM
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https://static.rcgroups.net/forums/a...DLRK-DELTA.jpg
Thanks for the help. I only have 24g and 26g wire. I thought of doing a half parallel dlrk as in your dt750 thread . I un wound the 12t of 24g as it was kinda ugly lol but did run. Good practice!!

Would the half parallel dlrk be a good wind or would the dlrk wye be better? I tried to download the kv calculator but my computer freaks out and wont open it. so still working on that
t
Last edited by jammied; Mar 30, 2016 at 01:23 PM.
Mar 30, 2016, 01:37 PM
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http://www.tcrconline.com/documents/...s%20Motors.pdf

This is a very informative link also
Mar 30, 2016, 02:10 PM
I am a nice guy! Really!
There is a lot of good information in that document but you have to be aware that not all of it is accurate at face value. An Example is a line on the third page down:

"Watts: Watts = V * Iin, Alternately P=IČR (P = I x I x Rm)"

This, to myself, implies that both formulas will give you the same result but in actuality the first part before the word "Alternately" is how you would calculate the power going into your motor, or any other device for that matter. The second part,"P=IČR (P = I x I x Rm)"
is the formula used to calculate the resistive power losses in a motor. Not the same thing obviously.

I guess if you already understand a lot of the concepts discussed, that document is a good reference but it does not explain everything accurately.
Mar 30, 2016, 07:53 PM
Jack
jackerbes's Avatar
Quote:
Originally Posted by jammied
https://static.rcgroups.net/forums/a...DLRK-DELTA.jpg
Thanks for the help. I only have 24g and 26g wire. I thought of doing a half parallel dlrk as in your dt750 thread . I un wound the 12t of 24g as it was kinda ugly lol but did run. Good practice!!

Would the half parallel dlrk be a good wind or would the dlrk wye be better? I tried to download the kv calculator but my computer freaks out and wont open it. so still working on that
t
The half parallel dLRK wind is a very good wind. In my experience I have not found another wind that will get power increases better that wind provides when a 12N14P motor us changed from dLRK to half parallel dLRK.

Note that when half parallel is used it is almost always with a Wye termination because, at the same turn count, it will double the Kv rating of a motor and the Wye termination lowers that by 0.58 and gets it back done into a more usable range.

You say Kv calculator, is that the Turn Calculator? If so, that is a spreadsheet and it runs under M$'s Excel app but it will also run under the free OpenOffice Calc spreadsheet (that is the only thing I ever use to run Turn Calculator). I save the spreadsheets in the Excel format instead of the default OpenOffice format.

The attached image is the Turn Calculator 5 spreadsheet for your motor, there are later versions that are better than TC 5 but TC 5 is better for posting screen shots with. Let us know if you need more help in getting the Turn Calculator going.

Attached is a zoom in screenshot of Turn Calculator 5 set up for your motor with some notes added, it shows the 1300 Kv for the stock wind, the Kv you would get with your 12 turn wind, and the Kv you would get with a Half Parallel dLRK (2PdLRK) Y wind.

As you can see, you need to get some finer wire to get more turns on and get the Kv down if you want a Kv that is similar to what the stock wind was.

If you know what Kv you want tell me what it is. Or if you know what prop and battery you will use I'll show you how to choose a Kv that will go well with that prop and battery.

Jack
Last edited by jackerbes; Mar 30, 2016 at 08:12 PM.
Mar 30, 2016, 08:19 PM
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Thanks I will havto research on how to read the spread sheet.

Just got done winding it again for the 3d time I went back to 12t 14g dlrk and terminated it wye. without a prop it doesn't get warm at all. Like it did before in stock new out of the box. Seems like the rpm is a little on the high side. I will havto take it back apart and try the half parallel dlrk.
Mar 30, 2016, 08:31 PM
Jack
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That image is zoomed in on the spreadsheet so the number can be read in the screenshot, this is what it looks like when Open Office Calc is running.

The yellow boxes are where you enter the turns and stuff so it will calculate all the other winds.

It is a little busy on the eye and maybe even intimidating to the brain but, believe me, it is one of the best tools we have for motor rewinding! Thanks to Manuel Verdugo again!

Jack
Mar 30, 2016, 08:37 PM
Jack
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Quote:
Originally Posted by jammied
Thanks I will havto research on how to read the spread sheet.

Just got done winding it again for the 3d time I went back to 12t 14g dlrk and terminated it wye. without a prop it doesn't get warm at all. Like it did before in stock new out of the box. Seems like the rpm is a little on the high side. I will havto take it back apart and try the half parallel dlrk.
If you'll look at that first image I posted it shows that, for 12 turns dLRK Delta the Kv would be about 2708, that info is in is the column to the left of the Y termination which produces the 1564 Kv.

So you are right, it was humming along pretty good. a 2708 Kv on 12V full throttle no prop would be about 32,000 RPM or so!

Jack
Mar 30, 2016, 09:23 PM
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Got ya!!Now I should be in the 1564 kv range. I thought that's what it was showing Now terminated star it is a lot more usable.

Thanks for everyones help and advice sometimes it takes me awhile to learn new equations and theories. Now to practice winding it different ways and get warmed up for the dt750 rewinds.

I did just do a test hover in the living room wit it on the foamy. With a 9x3.8 sf apc prop it has way more power than the 24gram blu wonders now!! And I can grab the motor after 2 minutes of half to full throttle runs Before it almost melted the front off the plane on test flight. This was for sure worth the winding best 24gram motor I have now!!


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