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Jul 24, 2009, 01:20 AM
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My first (sort of) successful rewind CF2805 - 3rd times a charm! See post #5


While waiting on my Gobrushless 24g newbie wire, I rewound a CF2805 with 13 turns of 22g craft store enamelled wire (seemed to work well). I wound it LRK (I know, not a good idea on this small of a motor), with Delta termination.

Unloaded it did spin after some initial stuttering, but was VERY noisy. It smoothed out at higher throttle settings. Unfortunately, I don't have any way to measure RPM, but it was really fast at full throttle!

I put a very small (3xsomething) prop on it and it won't spin at all, just stutters a little and quits.

I did check for shorts between the windings and between each winding and the stator. I attached the dremel and checked the voltage between each pair of windings. 2 of them read 2.4v, the other pair 2.6v.

So, I am guessing that I miscounted my winds and don't have the same number somewhere?
Last edited by adamdb; Jul 26, 2009 at 01:26 AM.
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Jul 24, 2009, 01:36 AM
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Last edited by adamdb; Jul 24, 2009 at 01:43 AM.
Jul 24, 2009, 07:29 AM
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FLOEY's Avatar
Quote:
Originally Posted by adamdb
.
.
motor), with Delta termination.
.
.
I always try star termination first and then delta
if star works flawlessly.

If I find Delta working without oveheat (too much)
I keep it in Delta.

If overheating in Delta I usually go back to star.

Recently I burnt up a 5g brushless, it will be tricky
to rewind it ... star only termination, most likely.

H.
Jul 24, 2009, 12:10 PM
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I'm still confused about the direction of winding around the stators. Different reference pictures seem to show different directions:

Looking at it from the point of view of starting the wind at the hub and going out, this one shows clockwise on both opposing stators: clockwise (Go to Articles, then Electric Motors, Part 3)

Whereas this page shows the opposite, clockwise on one stator and counter-clockwise on the opposing stator: counterclockwise

What am I missing here?
Jul 26, 2009, 01:33 AM
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Woohoo! My GoBrushless newbie wire got here so I rewound this motor (for the 3rd time) with 13 turns of 24g, delta terminated, dLRK. Checked for shorts between windings and the stator, checked AC voltage with the Dremel. Everything checked out okay (after redoing 1/2 of the first phase I wound, this newbie wire is GOOD STUFF). Attached a Tbird 18 controller and IT WORKS! Tried it without and with a small prop and it starts easy and doesn't heat up at all. I didn't spin it up to full throttle because it is late at night and I didn't want to wake up the whole house, so full testing will have to wait for tomorrow, but so far so good.

Now that I have one actually working, I can see why people bother to do this. It's really satisfying to see one actually spin after you spent all that time on it.

And a big thumbs up for the Gobrushless newbie wire!
Jul 26, 2009, 01:20 PM
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Okay, so I spun it all the way up today and everything still seems to be working fine. It is very amp hungry like the original. With a 4.75x4.75 prop it was using 19A at full throttle, (similar to original). I didn't measure the RPM, but I'm sure they were WAY up there. Got similar results with a APC 5.7x3, right around 19A at full throttle. It barely got warm in my bench testing. The APC 5.7x3 setup delivered 21oz of thrust at full throttle.

I did try it with both a Thunderbird 18 and a HobbyWing 25 ESC. On the HobbyWing I had to change the timing to HIGH. Should I be concerned about this? The Tbird handled it no problem with default settings.

I have another of these that stills runs, but I am afraid it is on its last legs. Any suggestions for rewinding that would lower the amp draw? I assume that I would need to shoot for lowering the KV in order to do this.
Adam
Jul 26, 2009, 11:55 PM
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Looks like I am having a conversation with myself.

I think I will do the same wind on the second motor, but terminate it wye instead of delta. That should bring the Kv down to around 1700 (2900 / 1.7 = 1705) right? Will this also decrease the amp draw assuming a reasonable prop selection?
Jul 27, 2009, 12:16 AM
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flydiver's Avatar
So you don't get freaked out by the echo you might drop in on this thread for a master winder's take on that motor.
https://www.rcgroups.com/forums/showthread.php?t=930163
Jul 27, 2009, 10:48 AM
homo ludens modellisticus
Ron van Sommeren's Avatar
Quote:
Originally Posted by adamdb
. I think I will do the same wind on the second motor, but terminate it wye instead of delta. That should bring the Kv down to around 1700 (2900 / 1.7 = 1705) right? ...
Almost right. Kv will go down by factor 1.8. That would give a Kv of 2900/1.8 =1600 rpm/Volt. Torque per Ampère (=Kt), not torque by itself!, would go up by the same factor.

Vriendelijke groeten Ron
Jul 27, 2009, 06:17 PM
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flydiver,
I have read through most of that thread and need to do so again. Definitely a lot of good information there.

Ron,
Thanks for the correction. Is there any way to estimate amp draw of the wye vs. delta termination?
Jul 27, 2009, 06:28 PM
homo ludens modellisticus
Ron van Sommeren's Avatar
Going from delta to wye will lower Kv and therefore your rpm too by factor 1.8 (theoretically sqrt(3)). Power needed to drive prop goes down cubed with rpm. Since voltage has not changed, current has to go down cubed. Therefore current_new = current_old / (1.8³) = current_old/(5.8).

Also note that current wants to go up squared with voltage.

Vriendelijke groeten Ron


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