Feb 16, 2013, 05:21 AM Registerer Used Paris Joined May 2010 714 Posts Ok, thanks Apache74, that answer is cristal clear! In fact, it's your pic that brought me to ask And it's true that when you've never imagine that a day you would rewind a motor, well... A lot of questions arise! "80 turns of .15mm copper wire gives 10 to 12 Ohms resistance per phase (4 slots)" This is a valuable information for me. I'm about to receive some .15mm wire and some 5010 rctimer motors; if I understand correctly, you mention 4 slots (and 3 phases of course), meaning that this info is ok for a 12 arms motor, amarite? Similar to the one on your pic (and the ones I've ordered). So it's all good for me, I know now that I have to make 80 turns at least per arm to obtain per phase 10 to 12 Ohms. Maybe I should give some more turns and then measure the resistance, to approach the bottom resistance limit (5 Ohms)? given the result is "more torque". I've read in the other thread that 0.15 mm wire for the 5010 is overkill, and 0.20mm would be ok... Despite the fact that 0.15mm means more turns (and more sweat lol) to achieve the same resistance result, there's not anything else about it? thanx again for the infos, this thread is a gold mine for blindfolded guys like me!
Feb 16, 2013, 05:58 AM
Registered User
France, RA, Bossey
Joined May 2011
50 Posts
Quote:
 Originally Posted by milouze Maybe I should give some more turns and then measure the resistance, to approach the bottom resistance limit (5 Ohms)? given the result is "more torque".
Nope, keep the resistance between 10 and 16 Ohms. Don't go below 10.
Otherwise there is a risk to burn the ESC's of the controller
As I wrote more turns=>more resistance=>more torque with lower amps, so if you increase the number of turns you will increase the resistance, not lower it.
Why are you speaking of 5 Ohms? Its far too low anyway, will draw too much Amps and will burn the power line/the ESC's
The main reason why we rewind is to increase the resistance and to draw less Amps under 12V (abt only 2-2.5 Amps...) and nevertheless keep an acceptable value of torque.
If you want to learn more you can read the link on brushless motors which Jack has given in one of the first posts.
 Feb 16, 2013, 06:39 AM Jack USA, ME, Ellsworth Joined May 2008 19,847 Posts If you are involved in electric RC you have to understand the basics of electricity. And to troubleshoot electrical systems you have to have a watt meter. A good watt meter to have is one called the Watt's Up watt meter. And the online manual for the Watt's Up will also teach you the basics of electricity. You can get it here: Watt's Up User's manual - http://www.rc-cars-planes.com/docs/w...ser_manual.pdf On page 9 (Chapter 4) that manual has a BASICS OF ELECTRICITY lesson that will give you what you need to know in simple terms. If you are new to all this, it will make you head hurt a little at first. But read it a couple of time and move on. Eventually it will stick and you'll be better for it. The Watt's Up is about \$50-\$60 or so, you can buy cheap Chinese copies of it for 1/3rd or half of that and those may or may not be just as good... Jack Last edited by jackerbes; Feb 16, 2013 at 07:35 AM.
Feb 16, 2013, 08:01 AM
Jack
USA, ME, Ellsworth
Joined May 2008
19,847 Posts
Quote:
 apache74 wrote: ..Why are you speaking of 5 Ohms? Its far too low anyway, will draw too much Amps and will burn the power line/the ESC's..."
That may be my fault. I think I am the one that said that. I am used to thinking that less resistance in a motor's windings is a good thing. And it is a good thing when I am rewinding motors for turning props and flying planes. But winding these gimbal motor is different and I am still learning and coming to grips with it.

When JussiH said the DC resistance of the windings, measured across any two connectors, needs to be in the 5 to 15 Ohms range I assumed that having less resistance (5 Ohms) would be better than having more (15 Ohms). If is not the case for this particular application, I will not say that any more.

In a typical motors like these, if you make the same DC resistance measurement before you strip the motor for rewinding as a gimbal motor, you will find a resistance of less than one Ohm across the ESC connectors. To measure it accurately you really need a milliohm meter that can measure resistance down to one thousandth of an Ohm. Those are very expensive, very few of us will have meters that can measure in milliOhms. The cause of the lower resistance it because of the shorter length of larger with and the difference in the way the motor is terminated (Delta instead of Wye).

I am conditioned to think that less resistance in the winding can be a good thing. I'll explain why I think that way with an example.

The rewound DAT-750 in the photo above has 3.33 feet of 23 AWG wire in each phase, that piece of wire will have a resistance of about 0.068Ω according to the calculator here:

http://www.cirris.com/testing/resistance/wire.html

That motor is terminated Wye so the DC resistance across two connectors would be about double that or 0.136Ω.

That motor, at full throttle with a Great Planes 10 x 4.5 slow fly prop, runs at an input power of 204 Watts. It is drawing 17A at 12V, Amps x Volts = Watts, 17A x 12V = 204W. And the motor is running at 7,000 RPM, giving me about 1000 grams of thrust, and the winding temperature is steady at about 90F/32C.

If I had wound that motor with 26 AWG wire the resistance in the 40" piece of wire in each phase would go from 0.068Ω to 0.136Ω. When I ran it at full throttle with the same load (the same prop) the motor would be drawing more current because of the increased resistance in the wire, the voltage would be drop lower, input power would probably drop, the motor would be running and a lower RPM, and the windings would be getting much hotter.

On the Ultrasky motor I used for this example, if I rewind it with 84 turns of 32 AWG wire each phase will have about 17 feet of wire and that will have a resistance of 2.79Ω. And when the motor is terminated Wye and I measure the resistance across two of the connectors, I will be measuring two phases (i.e., two lengths of wire) and the resistance will be doubled or about 5.58Ω

These gimbal motors are not turning continuously against a load. I am not sure exactly what is going on but I think that the three phases in the motor all have current in them and that is balanced so that the magnetic forces act as a brake to keep the motor from turning and in in one position. This is how the "Brake On" setting on most ESCs works for stopping propellers. The gimbal motors are thing to keep two gimbals pointed in the same direction so it must relax the magnetic braking and drive the motor to another location and put the brakes on again. This would be a relatively small movement and I have no idea what the current draw or other considerations are in this as it works.

The attached image is the eLogger data from static tests on the DAT-750 motor above. It shows me what is going on with that motor as it runs. But I have no idea what i would see from the gimbal motor. Maybe I should get back down into my cold basement, finish up the rewinding on it, and then see what it will do if I make it move around some.

Jack

# Images

Feb 16, 2013, 04:09 PM
checkout my Blog
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472 Posts
Quote:
 Originally Posted by jackerbes These gimbal motors are not turning continuously against a load. I am not sure exactly what is going on but I think that the three phases in the motor all have current in them and that is balanced so that the magnetic forces act as a brake to keep the motor from turning and in in one position. This is how the "Brake On" setting on most ESCs works for stopping propellers. The gimbal motors are thing to keep two gimbals pointed in the same direction so it must relax the magnetic braking and drive the motor to another location and put the brakes on again. This would be a relatively small movement and I have no idea what the current draw or other considerations are in this as it works. Jack
Hi Jack,

To be honest, I don't know for sure how the various implementations of the hobby brushless motor gimbals work, but there really would be no need at all for braking. Let me explain. In theory, a perfectly balanced gimbal with frictionless bearings needs no motor to maintain its position. Its inherent moment of inertia obeys the laws of physics and wants to remain stationary. Since no gimbal is perfectly balanced; and bearings, cables, etc add friction; and people actually want to purposely slew a gimbal; motors are needed. However, braking would only serve to couple accelerations tighter to the gimbal rather than isolate them. Also, it is better for power utilization if no brakes are used.

I'm not saying that these guys don't utilize braking, just that there is no need. I'd like to know the answer too.

Dan
 Feb 16, 2013, 07:05 PM Jack USA, ME, Ellsworth Joined May 2008 19,847 Posts I remember that JussiH mentioned "magnetic vectoring" one time when I said something about braking. And I think that is a term for what the control concept is or omething like that. And I agree that a perfectly balanced camera on a gimbal would need little or no motor power to stay aimed at one point. But there always going to be some imbalance with the rapidly changing attitude and effects of inertia, wind pressure, and other things like that. And I guess that is what the motor is correcting, that and maintaining the constand point of aim. I have no idea how these gimbals are actually operated, I came here to help with the motors and out of curiosity. I may be quad guy some day and may use a controller but have had no contact with them at all yet. As a quad is flying with one the these controllers and gimbals, does the pilot have like a PTZ control and then an option to lock the PTZ to an visual aiming point? Are there two cameras? One for the FPV and the second (the gimbal mounted one) is just for video capture? Maybe there is a manual I can read that would help me understand how these are used? Jack
Feb 17, 2013, 07:57 AM
Multicopter Nut
Romania, Bucharest
Joined Dec 2011
429 Posts
Quote:
 Originally Posted by milouze I'm about to receive some .15mm wire and some 5010 rctimer motors; [...] I've read in the other thread that 0.15 mm wire for the 5010 is overkill, and 0.20mm would be ok... Despite the fact that 0.15mm means more turns (and more sweat lol) to achieve the same resistance result, there's not anything else about it?
I'm finishing rewinding a 5010. Ended up using 2 strands of 0.20 mm and 131 turns on each arm. 3.5 ohm per phase, 7 ohms per circuit once connected in wye. And the arms are full, there's no space left between the coils.
I even believe I'll have to press the tops of the coils a bit, since there's little tolerance between the coils and the rotor.
 Feb 17, 2013, 01:59 PM Praying for better weather Joined Dec 2007 4,505 Posts Hi guy, interesting info. I have done one set of motors for my gimbal, but wanting to upgrade them to RCTimer 4215 630kv http://www.rctimer.com/index.php?gOo...9&productname= How do I work out the correct diameter wire and windings for these pancake motors being that the stators totally different ? I used 0.18mm wire and 60 turns on the 2830`s I have already done. Any help gratefully received
Feb 17, 2013, 03:38 PM
Jack
USA, ME, Ellsworth
Joined May 2008
19,847 Posts
Knowing the length and diameter of the wire will let you work up a good estimate. The image of that motor at RCTimer shows the stator arms pretty well, I zoomed in and cropped that to the attached image. It is a 12 arm stator and the arms look to have a typical amount of room for turns as for as the length.

Then you can just play with some wire and the numbers...

If you still have some of the 0.18mm wire (used is OK) you can wind one full layer on the and count the turns. Then mark it or cut it at the start and end and measure the length. Divide the length by the turns and that will tell you the length per turn.

And then you also know the number of turns you can expect to get in a layer on those stator arms.

If you look at 0.18mm wire on the wiki AWG table it has a resistance of 678.8 Ω/km.

If your turns worked out to be 12mm per turn and you had 60 turns per arm, the length of the wire in one phase would be 240 turns or 240 x 12mm or 2880mm.

2880mm = 0.00288km so the resistance in one phase would be 678.8Ω x 0.00288km or 2.954Ω

And the DC resistance measured across two connectors (two phases) would be 2.954 x 2 = 5.908Ω.

As you wind the test turns you can probably see if there is room for two or three layers on two adjacent arms. Or you can wind two adjacent arms and make sure if the layers will clear each other.

From that point on it is just a case of playing with the resistance for small or larger wire and varying the turn count until you get the DC resistance across two connectors in the 5-15Ω range.

As you increase and decrease the wire size it will also change the number of turns that will fit on an arm. If you have to add a few extra turns or remove a few turns from a layer to get a good number that is OK.

It would be nice if people reported the turns per layer and length per turn numbers for these various motors. And even the estimated resistance. We could get a list of what works for various motor here.

Jack

# Images

 Feb 17, 2013, 03:50 PM Praying for better weather Joined Dec 2007 4,505 Posts Thank you for the detailed reply. My last motor the RCTimer 2030 750kv had 60 turns and was 10.4 ohms over 2 phases for reference. The reason I ask is because I would like to get the most torque possible so its capable of moving a Nex5r with ease. On the databases I`ve looked at for brushless gimbal motors : https://docs.google.com/spreadsheet/...WWFl2Smc#gid=0 https://docs.google.com/spreadsheet/...tR2QwN0E#gid=0 Some of the 40 size motors are wound to over 35 ohms and reported to work well which contradicts the 5-15 ohms so I was wondering if the higher resistance is for the higher torque required for larger cameras
 Feb 18, 2013, 02:54 PM Registered User Joined Feb 2008 49 Posts Anyone tried to rewind a Turnigy 4206? Stripped mine today and rewind it with 0.15mm wire. Got 14.8 ohm between the phases with 75 turns. Runs slow and good with servo tester but just shutter with the Alexmos control? Will receive some 0.20 wire tomorrow. Calculated that with 80 turn I will get 7 ohm between the phases. Last edited by Fredrik R; Feb 19, 2013 at 06:39 AM.
Feb 19, 2013, 03:58 AM
Registered User
Norway Haugesund
Joined Jun 2010
329 Posts
This is my first test

Motor: Hextronik D2730 - 3000Kv
http://hobbyking.com/hobbyking/store...er_3000kv.html

13,2ohm between the phases with 70 turns (0,15 wire)

 SBGC AlexMos (4 min 5 sec)

The controller I used : http://www.csgshop.com/product.php?id_product=139
Last edited by culexus; Feb 19, 2013 at 04:20 AM.
Feb 19, 2013, 08:54 AM
Registered User
United States, TX, Austin
Joined Jun 2012
217 Posts
Quote:
 Originally Posted by culexus This is my first test Motor: Hextronik D2730 - 3000Kv http://hobbyking.com/hobbyking/store...er_3000kv.html 13,2ohm between the phases with 70 turns (0,15 wire) http://www.youtube.com/watch?v=ZndhH81iXyw The controller I used : http://www.csgshop.com/product.php?id_product=139
Have you actually received the controller from CSG shop? They said mine was shipped Feb 4 and I still have not received it. This is well over the 10 working days they quoted and I am getting concerned about CSG shop as I have heard they have a mixed rating from previous customers
Feb 19, 2013, 09:05 AM
Registered User
Norway Haugesund
Joined Jun 2010
329 Posts
Quote:
 Originally Posted by Rod Cole Have you actually received the controller from CSG shop? They said mine was shipped Feb 4 and I still have not received it. This is well over the 10 working days they quoted and I am getting concerned about CSG shop as I have heard they have a mixed rating from previous customers
Yes one week ago...
Don't you have a tracking nr on it?

The only thing to comment was that the sda scl on the mpu was reversed. But no problem just uploaded the latest firmware from alexmos and did a test
Now I need to find a good engine to rewind and build a gimbal I have a cnc mill also to build so I can mill some parts for the gimbal.
Feb 19, 2013, 10:58 AM
Registered User
United States, TX, Austin
Joined Jun 2012
217 Posts
Quote:
 Originally Posted by culexus Yes one week ago... Don't you have a tracking nr on it? The only thing to comment was that the sda scl on the mpu was reversed. But no problem just uploaded the latest firmware from alexmos and did a test Now I need to find a good engine to rewind and build a gimbal I have a cnc mill also to build so I can mill some parts for the gimbal.
They did send a tracking number. When I plugged it in to the USPS tracking site, it said the vendor had not shipped the package. I just checked again and it said the vendor is preparing to ship the package. What tracking site did you use?

I saw elsewhere that the sda dcl on the MPU was reversed.

I too am trying to find the ideal motor to power a gimbal for the Sony NEX-5N camera. It appears that either JussiH or Bricobrac may have some custom motors available soon so I am waiting on that announcement as I would prefer to not have to wind motors.
Last edited by Rod Cole; Feb 19, 2013 at 11:06 AM.