11-25-2009, 02:10 PM
On a DLRK wind, do you count the winds on each stator tooth as the number of winds or is it the combination of each pair that makes up the count? Here is my delima…
An FB of mine gave me a fried AXI 2808/24 motor to rewind. I have yet to unwind it, but after an hour of searching I have found that it should have 12 winds per tooth of triple strand 28Ga wire. So, my guess is that it’s the combination of the pairs that makes the ‘/24’ in the nomenclature.
He has gotten into 3D and is looking for a 950kV from the rewind since the 1190kV is a little too high for this type of application. So, 1190kV / 950kV = 1.253 and 1.253 * 24 winds = 30 winds. The motor looks to be terminated Delta, but in order to pack that many winds and have good power handling, I will terminate ‘Wye’ with 30 winds / 1.73 = 17.3 winds (but round to 18 for the symmetrical pair). I think I can get 9 turns of 22Ga wire on each tooth. It may be tight, but that’s the goal. If not, then it will get 24 Ga. The 24Ga will have a higher final resistance than the three strands of 28Ga, but you gotta do what what ‘cha gotta do.
Am I off base here? Any replys are greatly appreciated.
11-25-2009, 07:54 PM
I don't have any idea what AXI's winding count convention is but I don't see anything wrong with your re-winding arithmetic to get the desired Kv.
11-28-2009, 02:07 PM
MM - Thank you for the encouraging words.
Does anyone know or understand the AXI nomenclature?
11-28-2009, 05:49 PM
Educated guess never having taken one apart. This is a common convention.
28 is likely stator diameter. 08-stator depth.
24 - # of winds.
If you are right about triple strand then I suspect 24/3 = 8 winds/tooth. That part would not be common convention. Usually the combined strands would be counted as a single strand.
That's seems pretty consistent with a 1190KV.
Is it glued together ugly? eFlites are terrible.
11-29-2009, 01:51 AM
flydiver - Hey, how's it going? After hours of searching on rcgroups this morning, i figured out that a 2808/24 means...
28mm diameter stator
8 mm stator depth
and 24 winds per pair of DLRK windings (12 winds per tooth).
My FB that gave me the motor, said that he has a P-39 ready for it, so I think I will go with 7 turns of 19Ga per tooth to get close to the original 1190kV.
12-18-2009, 09:31 PM
I have finally finished the rewind on the AXI 2808. As much as I hated to do it, I had to settle with a final 1000kV wind verses the 950kV my FB wanted – which he stated was a-ok. Even with using every trick in my winding bag, I could not fit 30 turns of 22Ga wire (Delta) or 17.5 turns of 20Ga (Wye). Finally, I settled on 16.5 turns LRK of 20Ga wire terminated Wye. The main problem was in dealing with constant shorting while trying to use minimal insulation to leave maximum room.
NOTE: Rewinding an AXI motor is not for the faint of heart. It is more of an Un-winding/stator-prep project than a rewinding project. Then once you get the motor unwound, you have a very messy, sharp and jagged edged stator to re-insulate. Details below.
As stated in the note above, the first big hurdle was removing the original windings from the stator. AXI glues their windings together and to the stator. To remove the original copper, I resorted to using a Dremel with cutoff wheel being careful not to scar up the stator in the process. By slicing the windings along the center of each tooth, both front and back, I was able to pry, pick, pull and scrape the wires and glue off of the stator. This took a considerable amount of time.
Once the stator was winding free, I had to clean off all of the leftover glue mess. This was somewhat easy to do with a small file set and Dremel. Another thing to note here is that the stator plates are not glued together on a keyed mandrel. They were simply ‘aligned’ and glued. I say ‘aligned’ as one can plainly see that the key-slots are unevenly distributed through the stator tube hole. This process left the hammerheads with very sharp and jagged edges – a nightmare for trying to prevent internal shorts while rewinding.
Before insulating the stator with epoxy, I did a quick test wind on a tooth to see what I could fit on the teeth.17.5 turns came with considerable effort, but possible. Unwinding the wire showed that the sharp edged stator needed some attention. After a thin epoxy coat, I could not for the life of me get 17.5 turns again. It’s amazing how losing a little room can make such a big difference. After a treatment with some small files, enough epoxy was removed to get the 17.5 turns, but the force needed to keep the wires tight (same as I use on powder coated stators with no issue) kept biting through the epoxy and shorting. Out comes the kapton tape. Using 1-2 layers of kapton and some fish paper on the stator ends cured the shorting problems and still allowed 16.5 turns. Not perfect, but close enough.
I hope to power tool test the kV and finish terminating it tonight. Time permitting, I’ll try to pull the Io and Rm as well. Pics of this whole process to come.
12-21-2009, 03:10 PM
The results are in. An AXI 2808/24 (1190kV) converted to a 2808/29.5 is now a 1000kV motor. Preliminary calculations projected a 1001kV, and the final result is 1003kV.
Wire Gauge: 20
Max Efficiency: 80.2% (P-Calc Electric Motor Calculator)
The original 24 wind had an Rm of 0.115, Io of 1.3 with max efficiency of 76.6% (P-Calc Electric Motor Calculator), so I feel very good about this outcome.
I haven’t run any propped tests since I do not have a behind-the-firewall mount setup on my test stand and the AXI is an original version, which does not allow an ‘X’ type mount. Another FB has a Medusa Analyzer Pro and said he would test it over the holidays if the owner of the motor allows.