I'm new to winding motors. For this application, using .16mm wire, what would be the suggested number of turns for a DT750 motor?

Thanks,
Brent

Originally Posted by dmsgodeep

I'm new to winding motors. For this application, using .16mm wire, what would be the suggested number of turns for a DT750 motor?

Thanks,
Brent

You might want to follow Jack's advice and look into the Electric Motor Design and Construction forum:
http://www.rcgroups.com/electric-mot...struction-361/

There are already several threads dealing with the DT750, i.e.
http://www.rcgroups.com/forums/showt...ighlight=dt750

Originally Posted by jackerbes

I'm just lurking here out of curiosity but I've been rewinding motors like the ones being used here for a couple of years now and have found it to be very rewarding. The folks on the Electric Motor Design and Construction forum here have brought me along very nicely and quickly.

I think to get the best advice on motor re-winding the best way to do it is to go to that subforum and start a thread with the motor you want to rewind in hand. They will walk you through the process of getting it apart, getting the old windings off, and deciding how you want to rewind it.

Jack

Jack, thanks for posting that. I think it would be prudent to start a topic about rewinding motors for Brushless gimbals over there. The ball is in the air - who will catch it?

Remember to post a link here, and I will put on page 1

Originally Posted by dmsgodeep

I'm new to winding motors. For this application, using .16mm wire, what would be the suggested number of turns for a DT750 motor?

Thanks,
Brent

0.16 is probably a bit too thin for a DT750, youd be approaching 170-180 turns with that. Another guy used DT750 with 100 and 130 turns of 0.2

You are aiming to get a resistance of between 5 and 15 ohms between two phases on the finished motor.

Hi people, really great thread!

keep it comin!

just one question, what could be a good motor for a GH2 / GH3 camera gimbal?!?

Originally Posted by kinderkram

You might want to follow Jack's advice and look into the Electric Motor Design and Construction forum.

There are already several threads dealing with the DT750, i.e.

I did. The DT750 thread is over 100 pages and seems to be discussing only winding with the intention of spinning props, not for winding for this specific and new application on a gimbal. So I just don't see that as being helpful information. Maybe I'm missing something. ?

I've been reading everything I can on how to rewind, and the process itself looks rather simple. It's deciding on the wire thickness and number of turns for various motors for this unique application that has stumped me.

Originally Posted by JussiH

0.16 is probably a bit too thin for a DT750, youd be approaching 170-180 turns with that. Another guy used DT750 with 100 and 130 turns of 0.2

You are aiming to get a resistance of between 5 and 15 ohms between two phases on the finished motor.

Ok. Thank you. I will try and find info on how to do that test to get in that resistance range.
That helps me get going in the right direction.

Thanks,
Brent

A simple test is to turn one slot and measure the resistance on that - them you multiply that resistance by 8 to get the resistance on 2 phases. (there is 4 slots per phase on a 12-slot motor)

Originally Posted by dmsgodeep

I'm new to winding motors. For this application, using .16mm wire, what would be the suggested number of turns for a DT750 motor?

Thanks,
Brent

I don't think you are asking the right question. The wire size is the last thing you will find out and the number of turns has to give you a motor turning at the needed or optimal speed.

I'll answer that here because the details and considerations apply to both the gimbal motor and the flight motors. But the considerations for the gimbal motors is quite different and also a relatively new area of work as far as rewinding knowledge.

The motors, as you buy them, are wound with multiple parallel strands of finer wire. The parallel strands (I call each of the three groups a "bundle" of strands) are effectively the same as a single larger strand as far as current capacity.

Using fine parallel strands allows the strand count in a bundle to be easily changed so as to adjust for how many turns will physically fit on a stator arm. And it also allows the winding shops in China to wind different motors without having to stock an large assortment of wire sizes. The fine strand bundles also will bend around the arms easier and fit closer to the arm than a single larger strand in some cases.

On average quality motors the most commonly used wire in the bundles measures about 0.25mm or so and we generally consider it to be equivalent to 31 AWG wire which is 0.227mm uncoated. And this table is often used for estimating wire sizing and surface areas: http://en.wikipedia.org/wiki/American_wire_gauge - sizes and specs there are for typical uncoated magnet winding wire.

One example is the DAT-750 motor. As you buy those they have 18 turns with 8 strands of 0.25mm wire in the bundle. Each strand has a surface area of about 0.0404 mm2 so 8 strands have an area of of 0.0404 x 8 or 0.3232 mm2. So (looking at the mm2 numbers in the table) a single strand of 22 AWG wire with an area of 0.326 mm2 will give you a little more current capacity than the original 8 strand bundle.

The Kv is determined by the turn count and termination, the current capacity is determined by the surface area. Copper is King for current flow! So for turning props we want the most amount of copper we can get in the motor.

The Kv that results from each collection of parts (stator, magnets, flux ring, bearings, etc.) and a given turn count is unique to that particular assembly. But a production run of motors made from the same parts will only vary the Kv for each motor by a small amount, a few percent or so. Similar quality motors with similar Kv's will have similar turn counts but we really need to measure the Kv for a given motor to get more accurate numbers. The results can vary widely from the advertised specs in some cases.

It is the miscounted and misplaced turns, crossing turns, and even broken strands in a bundle that all contribute to the variations in the Kv. And they cause disruptions in the quality and harmony of the magnetic fields as the motor runs. And we can rewind more carefully to improve things. This is where my technical knowledge runs out, I am a re-winder, not really a technical expert on motors.

For driving propellers the maximum RPM desired and battery voltage determine the Kv needed for a given prop. Battery voltage x Kv = no load RPM. No load RPM / battery voltage (taken at same instant in time) = "raw" Kv. A "raw" Kv is accurate enough for our purposes, it is within a few percent of what the motor lab will determine it to be.

Motors will run at about 75% of their no load RPM when running at their continuous current rating (input power). So we can estimate the needed Kv from the max RPM number and the battery voltage.

One quick example: Say a raw Kv with a fully charged and rested 3S pack is found to be 12,000 RPM at full throttle with the pack at 12V under load (no prop=small load, little voltage drop). That tells us the raw Kv is about 12,000 / 12V or 1000. We then find the prop that will let the motor run continuously at full throttle without overheating and measure the RPM and voltage at full throttle again. The 75% rule of thumb says that will be about 9,000 RPM.

If the prop in the final test above is smaller than you wanted to use, you will need a motor that can handle a higher input power to spin a bigger prop. That would be a motor that weighs more or that is of higher quality.

Another rule of thumb has proven reliable is that the input power on average quality outrunner motors, running at their continuous rating, will be about 3 Watts for each gram of the motor weight (bare motor with connectors, no mounts or accessories). So if the motor in the example above weighed 80 grams I would expect it to have an input power of about 240 Watts. And on a 3S pack at 11V under load (3.7V per cell, about as low as you should go) I would expect the motor to be drawing about 22A (240W / 11V = 21.8A).

As the quality of motors improves the 3 Watts per gram rule of thumb can go up and our rewinds can raise that value. And buying better motors can raise it too.

I think JussiH is right, that the 0.16mm wire is too small for this application. And I'm not even sure that a DAT-750 would be a good motor for the gimbals because it is the open back CD-ROM type. I suspect that the back plate type motors as he has will be a better choice for their size.

But if the question is still "..using .16mm wire, what would be the suggested number of turns for a DT750 motor?..." the answer would be that it is the number of turns that gives you the Kv you need. And if the stator arms were not well filled at that number of turns, you would be giving up some of the motor's input power potential.

I further suspect that motors with more stator arms and more magnets will be the motors that are best and have the lowest cogging effect for use on the gimbals. I think it will be that way because of the low Kv's (400 or so?? or even less??). I suspect that with lower Kvs and slower (compared to turning props) rotational rates, having more stator arms and more magnets will make for having more cogging steps and smaller increments of movement from one cog to the next best. That will be where the smoothest movement is found I think.

So maybe the new pancake style motors with 20, or 24, or even 28 arms will be the best motor in the long run. And maybe people will even want to increase the magnet counts on the pancake motors to get more steps and even smoother motion?

Jussih, do you know what the Kv is on the motors you are using now? And just out of curiosity, is your controller applying the magnetic braking when the movement is stopped?

And if you want to share the below listed bits of info, it will good for this project. I can give this thread a quick lesson on using a turn calculator spreadsheets to help decide the turn counts they need to have to get the motor rewound.

- Model of motor you are using
- Kv specification of original winding (or a raw Kv if it was measured)
- Turns used in original winding
- Termination method on original winding

If the original winding was dLRK, I can use that as an input on a spreadsheet (like the screenshot seen here for the DT750) and it will give the turn count predictions for doing the dLRK and other winds and terminations on the motor you used.

If you can measure the raw Kv of one of your rewound motors it will also give you a chance to confirm that the speadsheet's turn count predictions are valid and give these folks the Kv they need for their gimbal motor rewinds.

You mention needing a resistance between 5 and 15 Ohms on a phase, that is interesting and good to know. But it is the raw Kv that is most needed to predict the turn counts.

Wow! This is getting awful lengthy but I guess it all goes for the benefit of the project?

Jack

I have purchased the firts batch that came out and the merchant seems to be Aleksandrs Ivanovs on paypal receipt. I have a gh2 and tried to find out the guys working with cams that weigh about the same . All data I could salvage from the russian forum with google translate is about two projects one is for nex5 and the other is for canon 550
This is the latest video of canon 550

test Brushless Direct Drive Gimbal (3 min 21 sec)

As his post (495) in this forum
http://translate.google.com/translat...303611-13.html
He is using 3536 RCtimer motor on roll with 65 turns ,0.2 wire and dt 750 on tilt with 130 turns, 0.2 wire wathing the last video I decided to try with these ordered them for starters now it's time to build a gimbal

Originally Posted by jackerbes

I don't think you are asking the right question. The wire size is the last thing you will find out and the number of turns has to give you a motor turning at the needed or optimal speed.

I'll answer that here because the details and considerations apply to both the gimbal motor and the flight motors. But the considerations for the gimbal motors is quite different and also a relatively new area of work as far as rewinding knowledge.

The motors, as you buy them, are wound with multiple parallel strands of finer wire. The parallel strands (I call each of the three groups a "bundle" of strands) are effectively the same as a single larger strand as far as current capacity.

Using fine parallel strands allows the strand count in a bundle to be easily changed so as to adjust for how many turns will physically fit on a stator arm. And it also allows the winding shops in China to wind different motors without having to stock an large assortment of wire sizes. The fine strand bundles also will bend around the arms easier and fit closer to the arm than a single larger strand in some cases.

On average quality motors the most commonly used wire in the bundles measures about 0.25mm or so and we generally consider it to be equivalent to 31 AWG wire which is 0.227mm uncoated. And this table is often used for estimating wire sizing and surface areas: http://en.wikipedia.org/wiki/American_wire_gauge - sizes and specs there are for typical uncoated magnet winding wire.

One example is the DAT-750 motor. As you buy those they have 18 turns with 8 strands of 0.25mm wire in the bundle. Each strand has a surface area of about 0.0404 mm2 so 8 strands have an area of of 0.0404 x 8 or 0.3232 mm2. So (looking at the mm2 numbers in the table) a single strand of 22 AWG wire with an area of 0.326 mm2 will give you a little more current capacity than the original 8 strand bundle.

The Kv is determined by the turn count and termination, the current capacity is determined by the surface area. Copper is King for current flow! So for turning props we want the most amount of copper we can get in the motor.

The Kv that results from each collection of parts (stator, magnets, flux ring, bearings, etc.) and a given turn count is unique to that particular assembly. But a production run of motors made from the same parts will only vary the Kv for each motor by a small amount, a few percent or so. Similar quality motors with similar Kv's will have similar turn counts but we really need to measure the Kv for a given motor to get more accurate numbers. The results can vary widely from the advertised specs in some cases.

It is the miscounted and misplaced turns, crossing turns, and even broken strands in a bundle that all contribute to the variations in the Kv. And they cause disruptions in the quality and harmony of the magnetic fields as the motor runs. And we can rewind more carefully to improve things. This is where my technical knowledge runs out, I am a re-winder, not really a technical expert on motors.

For driving propellers the maximum RPM desired and battery voltage determine the Kv needed for a given prop. Battery voltage x Kv = no load RPM. No load RPM / battery voltage (taken at same instant in time) = "raw" Kv. A "raw" Kv is accurate enough for our purposes, it is within a few percent of what the motor lab will determine it to be.

Motors will run at about 75% of their no load RPM when running at their continuous current rating (input power). So we can estimate the needed Kv from the max RPM number and the battery voltage.

One quick example: Say a raw Kv with a fully charged and rested 3S pack is found to be 12,000 RPM at full throttle with the pack at 12V under load (no prop=small load, little voltage drop). That tells us the raw Kv is about 12,000 / 12V or 1000. We then find the prop that will let the motor run continuously at full throttle without overheating and measure the RPM and voltage at full throttle again. The 75% rule of thumb says that will be about 9,000 RPM.

If the prop in the final test above is smaller than you wanted to use, you will need a motor that can handle a higher input power to spin a bigger prop. That would be a motor that weighs more or that is of higher quality.

Another rule of thumb has proven reliable is that the input power on average quality outrunner motors, running at their continuous rating, will be about 3 Watts for each gram of the motor weight (bare motor with connectors, no mounts or accessories). So if the motor in the example above weighed 80 grams I would expect it to have an input power of about 240 Watts. And on a 3S pack at 11V under load (3.7V per cell, about as low as you should go) I would expect the motor to be drawing about 22A (240W / 11V = 21.8A).

As the quality of motors improves the 3 Watts per gram rule of thumb can go up and our rewinds can raise that value. And buying better motors can raise it too.

I think JussiH is right, that the 0.16mm wire is too small for this application. And I'm not even sure that a DAT-750 would be a good motor for the gimbals because it is the open back CD-ROM type. I suspect that the back plate type motors as he has will be a better choice for their size.

But if the question is still "..using .16mm wire, what would be the suggested number of turns for a DT750 motor?..." the answer would be that it is the number of turns that gives you the Kv you need. And if the stator arms were not well filled at that number of turns, you would be giving up some of the motor's input power potential.

I further suspect that motors with more stator arms and more magnets will be the motors that are best and have the lowest cogging effect for use on the gimbals. I think it will be that way because of the low Kv's (400 or so?? or even less??). I suspect that with lower Kvs and slower (compared to turning props) rotational rates, having more stator arms and more magnets will make for having more cogging steps and smaller increments of movement from one cog to the next best. That will be where the smoothest movement is found I think.

So maybe the new pancake style motors with 20, or 24, or even 28 arms will be the best motor in the long run. And maybe people will even want to increase the magnet counts on the pancake motors to get more steps and even smoother motion?

Jussih, do you know what the Kv is on the motors you are using now? And just out of curiosity, is your controller applying the magnetic braking when the movement is stopped?

And if you want to share the below listed bits of info, it will good for this project. I can give this thread a quick lesson on using a turn calculator spreadsheets to help decide the turn counts they need to have to get the motor rewound.

- Model of motor you are using
- Kv specification of original winding (or a raw Kv if it was measured)
- Turns used in original winding
- Termination method on original winding

If the original winding was dLRK, I can use that as an input on a spreadsheet (like the screenshot seen here for the DT750) and it will give the turn count predictions for doing the dLRK and other winds and terminations on the motor you used.

If you can measure the raw Kv of one of your rewound motors it will also give you a chance to confirm that the speadsheet's turn count predictions are valid and give these folks the Kv they need for their gimbal motor rewinds.

You mention needing a resistance between 5 and 15 Ohms on a phase, that is interesting and good to know. But it is the raw Kv that is most needed to predict the turn counts.

Wow! This is getting awful lengthy but I guess it all goes for the benefit of the project?

Jack

Great post Jack, thank you for taking the time.

Jack, thanks for taking time to explain in such detail, I really appreciate it, and this info will be highly useful for DIY´ers. The mentioned spreadsheets would also be a very appreciated tool to have available.

I am currently rewinding some suppo 2208-17. As indicated that means (in this case) a 22*8mm stator with 17 turns, 12 arms. 2 strands of 0.28 with isolation. Original spec is 1100KV.

I could squeeze in 70 turns of a single strand 0.16mm on those. Star configuration in 2 layers as per Alex´s recommandations.

The KDA´s are branded 2208 but the stator is only 5mm high (meaning that its more like a 2205 motor). We got them as kits, so I cant state any original specs on those. Sebastian managed to get 80 turns of 0.16 onto those, but it took a few tries...and it seriously screwed with his Zen more than once...

We are still prototyping, but I will make some KV measurements and post the data soon.

Felix is making tests with different windings, and we will also post data for that soon. I need to get past next week, before I can free up time to make new threads and write all the documentation needed. We are collecting data and photos as we go, and there is already a russian spreadsheet with results gathered so far. Alex will translate it so it can be posted here. Here is a link to the original:

https://docs.google.com/spreadsheet/...WWFl2Smc#gid=0

I did not design the controller or the software, so I have posted your question about magnetic braking back to Alex. I believe the techique is referred to as magnetic vectoring.

You are correct (as far as I know) about more poles and arms giving more cogging steps and thus more smooth movement. Some of the Dualsky and T-motor navigator series may very well be ideal candidates for larger rigs.

Another very important thing to consider is to terminate the phases onto some really thin and flexible wire. We made the first ones with some rather stiff servo wires and struggled a bit with those inhibiting motion in one direction. Same thing goes for the IMU.

With your permission, I will link from page one to your post above?

Thanks again

Jussi

Originally Posted by JussiH

Jack, thanks for taking time to explain in such detail, I really appreciate it, and this info will be highly useful for DIY´ers. The mentioned spreadsheets would also be a very appreciated tool to have available.

The spreadsheets can be downloaded here, they are shared freely. You can run them with the free OpenOffice Calc software. It is best to keep them in the *.xls format for the easiest sharing:

Turn calculators - http://www.rcgroups.com/forums/showp...&postcount=266

As the spreadsheets are now they only go to 40 turns as that is more than enough for propellers. But the Kv numbers progress linear to the turn counts. If 17 turns gives you a1100 Kv 34 turns will give you 550 and 68 gives 275, etc.

If you understand spreadsheets (I don't) you could extend the turn count range of course. The best one to use will be the Turn Calculator 5 as it shows more winds. The entries in the yellow boxes must be from a dLRK wind and most motors are sold that way. The Simple Turn Calculator will also work if you are going to do the same wind as you happen to have. It will also need to be extended for higher than 40 turn counts.

I am currently rewinding some suppo 2208-17. As indicated that means (in this case) a 22*8mm stator with 17 turns, 12 arms. 2 strands of 0.28 with isolation. Original spec is 1100KV.

I could squeeze in 70 turns of a single strand 0.16mm on those. Star configuration in 2 layers as per Alex´s recommandations.

The KDA´s are branded 2208 but the stator is only 5mm high (meaning that its more like a 2205 motor). We got them as kits, so I cant state any original specs on those. Sebastian managed to get 80 turns of 0.16 onto those, but it took a few tries...and it seriously screwed with his Zen more than once...

We are still prototyping, but I will make some KV measurements and post the data soon.

I ran the Turn Calculator 5 for the 2211-17 using the 17 turns and advertised 1100 Kv. If that was a dLRK wind terminated Delta, the numbers should be fairly accurate. As you can see in the image of the lower half of the page 35 turns gives a Kv of 534 in cell G42 for a dLRK Delta wind and 308 for a Star or Wye wind. So your 70 turns would be half of that or 267 for Delta and 154 for Star.

Do you have a data logger that will let you see the current as the camera move and as the magnetic vectoring takes place and fights inertia? I have an Eagletree eLogger and love it for the questions it answers.

Excuse me for any confusion I may have caused in my posts here when I talk about higher and lower Kv's and turns. I seem to often get them confused in my mind and mistate them sometimes. A lower turn count is always a higher Kv and a higher turn count a lower Kv.

And if you did not know it, for the same turn count, changing Delta to Wye lowers the Kv by a factor of 0.58 and changing from Wye to Delta raises it by a factor of 1.73.

Felix is making tests with different windings, and we will also post data for that soon. I need to get past next week, before I can free up time to make new threads and write all the documentation needed. We are collecting data and photos as we go, and there is already a russian spreadsheet with results gathered so far. Alex will translate it so it can be posted here. Here is a link to the original:

https://docs.google.com/spreadsheet/...WWFl2Smc#gid=0

I did not design the controller or the software, so I have posted your question about magnetic braking back to Alex. I believe the techique is referred to as magnetic vectoring.

You are correct (as far as I know) about more poles and arms giving more cogging steps and thus more smooth movement. Some of the Dualsky and T-motor navigator series may very well be ideal candidates for larger rigs.

Another very important thing to consider is to terminate the phases onto some really thin and flexible wire. We made the first ones with some rather stiff servo wires and struggled a bit with those inhibiting motion in one direction. Same thing goes for the IMU.

With your permission, I will link from page one to your post above?

Thanks again

Felix's work should be real helpful for this. I never use motors at this low a Kv or wind that many turns with a single strand so there is lot to be learned here.

You're probably right about the magnetic vectoring, I call it a brake because it stops the prop and that is the ESC setting. I think it is essential to countering movement from inertia and the camera weight. I think the gimbal is going to be in nearly constant motion, even though small and nearly nearly imperceptible sometimes, because of the motion of the aircraft.

The transition from solid to stranded wire is easier with our larger wires of course. Some type of winding terminator fixed to the bearing tube or in the backplate might be the best way to go. And from there go to a silicone sheathed stranded wire that is as small as possible. I think I've seen mention of stranded, silicone sheathed, wire that was down around 40 gauge or so. As long as it is as large or larger than the winding it would be pretty good.

In a perfect world the turns will lay side by side and layer on layer, the jamming point is always down in the bottom the "V" between the arms and when turns on adjacent arms meet. Not much you can do about it. Reducing the turn counts on succeeding layers and moving them away from the jam will let you fit more turns if you are not already doing that.

And any and all of it can be shared at any time and place, that is why it is here. I have learned so much from so many in the 5-6 years I have been dabbling with electric RC that I'm just paying back favors. And you needn't thank me again, I am retired, have the time and interest, and you are keeping me entertained for free! Thanks for that!

Jack

Originally Posted by kinderkram

Woah! Can it get any better?

Most amazing imo is the smooth transition when he tilts the gimbal - before he throws the MWC into the bush.

Yah, the waiting is killing me, too.
Please stop fueling the fire!

Maybe Alexei did it on purpose, Jussih I think you should send him an AQ board for his future tests

Originally Posted by apejovic

Maybe Alexei did it on purpose, Jussih I think you should send him an AQ board for his future tests

Hehe, maybe. But I doubt the AutoQuad would have reacted any better being flown backwards into a tree.

On the other hand I'm sure the AQ's POI feature and the vertical override in PH would have helped to keep the object in focus when he ascended over the other guy with the cam pointing downwards.

Lots of good motor info guys thanks. I am certainaly not the best person to start a thread on this as my motor knowledge is obviously zero after reading the past few posts.

When Someone starts a thread please post a link here and on page one of this threa as this is the only difficult part of this project.