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Old Apr 30, 2012, 06:06 AM
Jack
USA, ME, Ellsworth
Joined May 2008
16,924 Posts
I'm not much of a speed motor guy either, and the 6 magnets is something I've never messed with. All mine have been 14P and a few 9N12P.

Do you have any idea what the original Kv on the motor was? If so this formula should get you in the ball park:

winds_new = winds_old * Kv_old / Kv_new

So if you know the prop RPM you want and the battery you'll use that will let you work out the no load RPM, then 75% of the no load RPM will be the approx max RPM under load.

Say you want a 28,000 RPM prop speed under load, that RPM would be 75% of the no load RPM. So the no load RPM would be about 37,600 (75% of 37,600 = 28,200) .

And the Kv x voltaqe = no load RPM. So for a 3S at 12.2V you want a Kv of 37600 / 12.2 or 3081.

Getting back to the winds_new = winds_old * Kv_old / Kv_new formula if the motor was 3000 RPM motor with 6 winds it would be:

winds_new = winds_old * Kv_old / Kv_new

winds_new = 6 * 3000 / 3801 = 4.7 turns

So you could shoot for 4, 4-1/2 or 5 turns...

Or you can just pick a number of turns, do a wind, get a raw Kv, and work it from there with the Turn Calculator.

Jack
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Old May 01, 2012, 06:31 AM
Registered User
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Delta Hookup

How do I do it


Thanks
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Old May 01, 2012, 06:58 AM
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Joined Aug 2007
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Excuse me

For getting off the DT topic ,


I will get back on


here is the block I hogged 2 mounts for my DT
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Old May 01, 2012, 07:08 AM
Jack
USA, ME, Ellsworth
Joined May 2008
16,924 Posts
Quote:
Originally Posted by NX-687 View Post
How do I do it


Thanks
Is it a ABC wind on a 9N stator? I think the attached will work for you.

Jack
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Old May 01, 2012, 07:10 AM
Jack
USA, ME, Ellsworth
Joined May 2008
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Quote:
Originally Posted by NX-687 View Post
For getting off the DT topic ,


I will get back on


here is the block I hogged 2 mounts for my DT
Wow! A lot of waste in that material I think. How is the motor retained in the mount and kept from turning, that is always where the issue is with this motor.

Jack
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Old May 01, 2012, 01:59 PM
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United States, CA, Cupertino
Joined May 2012
7 Posts
I recently crashed my quad and unfortunately landed hard on my dt700 motors on asphalt. My problems include broken shafts, broken stator arms, broken windings, etc. After digging through google trying to find information about these motors, I stumbled across this great thread. While most of the information I've seen here is about rewinding these DT motors, I want to get some clarification on some past topics that came up.

1. The grub screws on the motor mounts seem like junk. They constantly loosen up and cause vibrations, or even worse completely pop off from the mount. Someone said that they replaced the grub screws with 2mm hex button head x 3mm grubs. Does this mean an M2 screw with 0.4mm pitch, and 3mm length? If the original grub screws were your typical M1.5 size, did the extra 0.5mm just cause a tighter fit? In any case, my solution was to thread lock the grub screws in, which leads me to my next problem...

2. I can't get the grub screws out! I've tried heating the thread lock with a heatgun and a soldering iron, but I'm afraid the process will probably mangle the plastic mount. I was willing to sacrifice the plastic motor mounts and just dremel them apart, provided I could find replacement mounts. The closest I could find are these 8mm mounts:

http://www.headsuprc.com/servlet/the...unt-for/Detail

However, when I measured with my calipers I saw that the inner diameter/shaft tube of the motor is 9mm. Do you guys have any solutions for motor mounts suitable for multirotors?
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Old May 01, 2012, 02:43 PM
Jack
USA, ME, Ellsworth
Joined May 2008
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Quote:
Originally Posted by yergacheffe View Post
I recently crashed my quad and unfortunately landed hard on my dt700 motors on asphalt. My problems include broken shafts, broken stator arms, broken windings, etc. After digging through google trying to find information about these motors, I stumbled across this great thread. While most of the information I've seen here is about rewinding these DT motors, I want to get some clarification on some past topics that came up.

1. The grub screws on the motor mounts seem like junk. They constantly loosen up and cause vibrations, or even worse completely pop off from the mount. Someone said that they replaced the grub screws with 2mm hex button head x 3mm grubs. Does this mean an M2 screw with 0.4mm pitch, and 3mm length? If the original grub screws were your typical M1.5 size, did the extra 0.5mm just cause a tighter fit? In any case, my solution was to thread lock the grub screws in, which leads me to my next problem...
The hex socket button head screws have a 2mm socket but are 3mm screws. If you have ruined or lost the 3mm threads you can retap those and use 4mm hex socket button head screws to improve the clamping forces.

Whatever you use, degrease the screws and threads and put them togehter with blue (#242) not red (#272) Loctite. The red is just too strong.

Never use ball ended hex wrench to loosen a tight screw, it is an invitation to a stripped hex socket. Use only straight shank hex wrenches that fit well.

Here is a post here about replacing the shaft on a DAT-750, if you use prop savers it will be much harder to bend a shaft:

http://www.rcgroups.com/forums/showp...postcount=1080

More on prop savers here:

http://www.rcgroups.com/forums/showthread.php?t=1419378

Quote:
2. I can't get the grub screws out! I've tried heating the thread lock with a heatgun and a soldering iron, but I'm afraid the process will probably mangle the plastic mount. I was willing to sacrifice the plastic motor mounts and just dremel them apart, provided I could find replacement mounts. The closest I could find are these 8mm mounts:

http://www.headsuprc.com/servlet/the...unt-for/Detail

However, when I measured with my calipers I saw that the inner diameter/shaft tube of the motor is 9mm. Do you guys have any solutions for motor mounts suitable for multirotors?
Plastic? All the DAT-750 mounts I have seen are metal. The early ones were 8mm then they went to 9mm I think. But I don't know of a source for 9mm mounts. I would look for a good 8mm mount and ream it out to 9mm probably if that is what I had to have.

You can usually force a 1/16" (0.0625") straight shank (not! ball ended) hex wrench down into a 1.5mm hex socket and it might be able to save the day. For additional help I take an old spare, used for nothing else, straight shanked 1.5mm hex and heat it until it is bright red hot. Then I stick it in the socket and keep it there for 10 seconds or so to soften any Loctite that may be there. Then I immediately try the 1/16" hex wrench while it is still hot.

After that it is a case of using a Dremel tool and a #409 cutting disc to cut a slot across the screw and take it out with a flat tipped screwdriver.

Jack
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Old May 01, 2012, 05:52 PM
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United States, CA, Cupertino
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Hi Jack,

Thanks for the reply. I've also been looking at those other posts of yours to plan out the next set of repairs once I manage to get my motors free from the blue thread locker I used. I'm still a little confused by the set of replacement grub screws you used though. When you say the grub screws are "2mm socket but are 3mm screws", does the 3mm refer to the length? Sorry if it seems like I'm being dense, but the mechanical end of things is all very new to me. I'm just trying to figure out a screw callout that I can look up at the hardware store and buy, which I'm assuming is M2-0.4 x 3mm at this point.

As for the plastic motor mount, I'm referring to the black plastic piece in this picture:



The inner diameter of the black motor mount is 9mm, which matches the 9mm shaft tube of the motor itself.

I have a 1/16" hex driver that's ball ended, but it doesn't seem to even fit into the grub screw. I've been trying to track down a 1.5mm hex driver, but these small RC tools are pretty tough to find. Assuming I can find it, what do you use to heat up your hex wrench? I don't have a blow torch or anything awesome like that, just a small bic lighter and heatgun haha. At this point I'm considering the easiest solution is just drilling out the grub screw and retapping with a bigger screw.
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Old May 01, 2012, 06:36 PM
Jack
USA, ME, Ellsworth
Joined May 2008
16,924 Posts
Quote:
Originally Posted by yergacheffe View Post
Hi Jack,

Thanks for the reply. I've also been looking at those other posts of yours to plan out the next set of repairs once I manage to get my motors free from the blue thread locker I used. I'm still a little confused by the set of replacement grub screws you used though. When you say the grub screws are "2mm socket but are 3mm screws", does the 3mm refer to the length? Sorry if it seems like I'm being dense, but the mechanical end of things is all very new to me. I'm just trying to figure out a screw callout that I can look up at the hardware store and buy, which I'm assuming is M2-0.4 x 3mm at this point.
OK, to a 69 year old machinist, there is a lot that is taken for granted about screws and threads and pitches at all of that.

The original screws are 3mm headless set screws, with a thread pitch of 0.5mm. They are about 5mm long I think.

The replacement is a Button Head Socket Cap Screw that is about 6mm in length.

Both screws have the same 3mm x 0.5mm pitch thread, the major difference is the larger 2mm hex socket on the button head screw.

Quote:
As for the plastic motor mount, I'm referring to the black plastic piece in this picture:

<SNIP IMAGE>

The inner diameter of the black motor mount is 9mm, which matches the 9mm shaft tube of the motor itself.
That mount looks the same as the ones on my DAT-750 motors but they are made of aluminum, not plastic, and anodized with a black finish. It is not the world's best mounting and the small bearing tube and screws loosening can be problematic. But if you like the motor you just have to work at it a little.

On most of my planes with the DAT-750 I used stick mountings using the E-Flite EFLM-1519 mount and attaching the DAT-750 mount to that as seen here:

http://www.rcgroups.com/forums/showt...3#post16925561

Not sure what you have on your quad what could be used there.

Quote:
I have a 1/16" hex driver that's ball ended, but it doesn't seem to even fit into the grub screw. I've been trying to track down a 1.5mm hex driver, but these small RC tools are pretty tough to find. Assuming I can find it, what do you use to heat up your hex wrench? I don't have a blow torch or anything awesome like that, just a small bic lighter and heatgun haha. At this point I'm considering the easiest solution is just drilling out the grub screw and retapping with a bigger screw.
The screw is too hard to drill, don't be surprised if that does not work.

The thing that is bad about the ball ended drivers is that they have a reduced contact area inside the socket so that they strip the metal inside socket instead of driving the screw. A straight hex wrench bears the full depth of it's engagement. Sets like these are fine:

http://tinyurl.com/dxmax4l

The 1.5mm hex wrench is just slightly smaller than the 1/16" (0.0625"/1.5875mm) so the 1/16" one can often be forced into the 1.5mm socket. Even if you have to tap it in with something.

I use typical home use propane torch (fits on the blue metal gas cylinders) or a butane micro torch. I have extra 1.5mm hex wrenches that came with motors and stuff and I just heat one of those until it is red hot (holding it in a pliers of course). I use an extra wrench because after you heat it to red hot it is not longer useful as a hex wrench (too soft).

Tools are a life long game. The winner is the guy that dies owning the most of them. I might be in the running for the title...

I have cut a slot across the headless set screws with a Dremel tool (#409 abrasive cutting disc) and gotten them out with a flat screw driver.

I do feel sorry for anyone in a tool poor environment, it is a battle that just needs to be fought and won one tool at a time.

Jack
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Old May 01, 2012, 07:39 PM
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United States, CA, Cupertino
Joined May 2012
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Quote:
Both screws have the same 3mm x 0.5mm pitch thread, the major difference is the larger 2mm hex socket on the button head screw.
Okay, I think I finally understand after your clarification and reading some more about the kinds of parameters used to describe screws. When you say 3mm X 0.5mm pitch, then the 3mm refers to the outer diameter of the threads, and the 0.5mm refers to the pitch, of course. I think I assumed that fasteners were all completely standardized at this point and was trying to find the matching ISO metric screw for this situation, ie M2-0.4 x 3mm.

Quote:
That mount looks the same as the ones on my DAT-750 motors but they are made of aluminum, not plastic, and anodized with a black finish
Now that I think about it, I think you're right. They looked plastic to me because of the black finish, and I've never had RC experience before so I assumed hobbyking would use plastic mounts to cut down on costs. One of my motors took the brunt of the quad's crash, bending the shaft and tearing the bolts attached to the motor mount out of the wooden boom of the quad. The black motor mount is completely bent out of shape, so I'm thinking that if it was plastic it would've snapped off entirely instead of bending.

I'll have to mull over what to do next regarding removing the thread locked screws if I can't drill through them. I'm contemplating filling the socket heads with solder, then dremeling out a slot for a flat head screw driver. I certainly wish I had better tools, but I'm still in my early 20's so I haven't had a lot of time to start a collection nor do I have a house of my own to store all of them in.
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Old May 02, 2012, 04:56 AM
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Joined Aug 2007
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Jack

Thanks for the Delta hookup

I made a couple more mounts , I use a single 3mm grub screw to retain the motor
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Old May 02, 2012, 06:42 AM
Jack
USA, ME, Ellsworth
Joined May 2008
16,924 Posts
Quote:
Originally Posted by NX-687 View Post
Thanks for the Delta hookup

I made a couple more mounts , I use a single 3mm grub screw to retain the motor
OK, you must have access to some good sources of aluminum scrap and a machine shop. I envy you that. I had a lathe and milling machine in my garage for 20-odd years and was gunsmith/machinist/tinkerer at large. But the machines went away when I made my last cross country move from CA to ME.

They look nice, I have some reservations about the adequacy of one grub screw on these motors but if you work at it a little you can get away with it.

Jack
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Old May 02, 2012, 06:48 AM
Jack
USA, ME, Ellsworth
Joined May 2008
16,924 Posts
Quote:
Originally Posted by yergacheffe View Post
Okay, I think I finally understand after your clarification and reading some more about the kinds of parameters used to describe screws. When you say 3mm X 0.5mm pitch, then the 3mm refers to the outer diameter of the threads, and the 0.5mm refers to the pitch, of course. I think I assumed that fasteners were all completely standardized at this point and was trying to find the matching ISO metric screw for this situation, ie M2-0.4 x 3mm.



Now that I think about it, I think you're right. They looked plastic to me because of the black finish, and I've never had RC experience before so I assumed hobbyking would use plastic mounts to cut down on costs. One of my motors took the brunt of the quad's crash, bending the shaft and tearing the bolts attached to the motor mount out of the wooden boom of the quad. The black motor mount is completely bent out of shape, so I'm thinking that if it was plastic it would've snapped off entirely instead of bending.

I'll have to mull over what to do next regarding removing the thread locked screws if I can't drill through them. I'm contemplating filling the socket heads with solder, then dremeling out a slot for a flat head screw driver. I certainly wish I had better tools, but I'm still in my early 20's so I haven't had a lot of time to start a collection nor do I have a house of my own to store all of them in.
Good for you! I didn't mention the ISO designators because they don't mean much to most people. And it is not common to find Home Depot or hardware stores describing them that way. Ask the average hardware store guy in North America if they have any M3-0.5 x 6mm screws and you get a blank look. I found mine in the parts bags for the Traxxas RC cars at the LHS, the wilds of Maine is not the best place for finding them either.

Jack
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Old May 02, 2012, 02:26 PM
Out of helis, sanity returning
Tallahassee, FL
Joined Feb 2009
2,080 Posts
What a great thread!

I'm a big fan of the of the DT7xx series- I have a quad with DT700 motors that flies really well, and I'm making another with DT750 motors.

Also, I've noticed that HK has DT850 motors available. Anybody tried these, or is there another thread for them?

I actually was intending to post so I could ask about a good source for replacement bearings and shafts for these motors, but I did some more browsing in the thread and saw the link pointing to HeadsupRC. Is that still the go-to place for these supplies? C-clips also?

Brushless motors are so cool- with a supply of bearings and shafts, you can pretty much keep them going forever.

Rick
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Old May 02, 2012, 06:41 PM
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Quote:
Originally Posted by 2400RDR View Post
What a great thread!
I actually was intending to post so I could ask about a good source for replacement bearings and shafts for these motors, but I did some more browsing in the thread and saw the link pointing to HeadsupRC. Is that still the go-to place for these supplies? C-clips also?
Rick
It seems to me that people are just using any old 4mm diameter shaft and modifying them as needed, ie cutting out grooves for circlips and flats for grub screws. If you want a threaded 4mm shaft that's similar to the stock DT, I've read somewhere that people have salvaged them from GWS size 400 power systems but I've no idea what that means or where to even source the part.

I've managed to remove my thread locked grub screws by finding a properly sized 1.5mm hex driver. Since I don't know anything about motors, I'm listing my findings on its construction for reference to other complete newbies and confirmation from others.

The pieces along the shaft are ordered as follows:
[circlip]-[1-3 washers*]-[bearing #1]-[stator]-[bearing #2]-[washer]-[bell/rotor]

* I say 1-3 washers because I'm seeing various different washers in the 5 DT700s I have. In some cases, there's 3 equally sized thin washers, or a single fat washer, or a thin washer with a medium washer...

I've assessed the damage, and I think I should be able to salvage 3 of the 4 motors. One is fine as is, and the other two have damaged shafts. The fourth one has a chipped magnet on the rotor and the bell seems to have been slightly deformed enough that it won't spin freely on any of the stators I have.

Picture of three salvageable motors. The bottom one is fine, the top two have damaged shafts. Notice that the top motor also had the shaft pressed further into the bell housing in the crash. You can tell by the shortened amount of unthreaded shaft sticking out compared to the other two motors.

Rotor with chipped magnet

Bonus picture of the motor mount that took the brunt of the fall.

At this point I'm thinking I can take the shaft from the fourth motor and swap it out for one of the motors that has a damaged shaft, likely the top most motor in my first image since that one took the most damage. How do people typically remove the shafts from outrunners? From this thread it seems an arbor press is used. I don't have access to an arbor press nor do I have the space for one in my home, but I think I might be able to use a drill press as an arbor press in conjunction with a bench vise to pull the shafts out. edit: This thread has an excellent method requiring just a vise and a shaft larger than the motor shaft to push against. I'm gonna go to the hardware store and find a pvc pipe for this.

I'm also concerned that for the two motors with bent shafts, they don't seem to spin as freely as the motor that took no damage. When I spin the motor by hand, there's a slight ratchet but it still spins pretty easily. The other two motors are a bit stiffer, and seem to come to a stop quicker if I give the rotor a good spin. I don't think it's the bearings since I've swapped the stators into my spare DT700 and had it spin freely, so I'm thinking the bell must have gotten deformed enough in the crash to cause the magnets to rub up against the stators arms.
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