hexTronik DT750 Brushless Outrunner 750kv - Page 102 - RC Groups
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Dec 27, 2012, 08:27 AM
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Fourdan's Avatar
Could you precise/measure the BB dimensions
** for L3010C
** for L3010B

L3010 stators (30x10 mm) are more square than DT750 34x7 mm ones
Maybe Peakeff could be better

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Dec 27, 2012, 10:08 AM
5,200 Led Lighted Bike-Bob P.
**neons**'s Avatar
Thanks for your help and explainations. I have not been following the Hex-DT series of improvements and variations. I was basically looking for the next step up from the 700 & 750 motors when I saw the DT-900 in HK. . I have my rewound DT-750 motors probably pumping out about 46oz. static thrust on my tester.

I am trying to find a more powerful DT-750 series motor that puts out closer to the 60oz. static thrust without rewinding. Even 50oz. thrust is better too. I thought the DT-900 would be a bigger motor and have more power. I know very little about the L3010B-C motors also. I did not realize the stators were smaller. I too like the big style DT-750 series like you say for easier winding also. It also is like a long stroke gas motor with more torque.

Looks like Maine is collecting a pile of snow today. my daughter lives up in Guilford,ME

**Neons** Bob
Last edited by **neons**; Dec 27, 2012 at 10:22 AM.
Dec 27, 2012, 02:59 PM
jackerbes's Avatar
I think the hexTronic D4023-850 would be a good choice for getting a DAT-750 style motor but with more power.

Getting 60 oz. of thrust out of a DAT-750 is a doable thing too though. The info below is a copy of the test info on one of Truglodite's Half Parallel dLRK rewinds. Look at his results, 38 oz. on 3S and 68 oz on 4S. The wind on that was 20 turns of 21 AWG, Half Parallel dLRK and terminated Wye or Star.

Weight: 93gm (w/mount & prop nuts/washers)
Kv = 783 RPM/V
Io @ 11.34V = 1.502 A
Io @ 15.33V = 1.797 A
Rm = 0.046 ohm (measured directly @ 1A)

3-cell Data===================================
No Load

APC 10x4.7sf (@ 29m alt, 19.7C temp): Zippy-R 3s2000
6901RPM/10.35V/13.49A/30.1oz/78.2% effy

APC 11x7e (@ 29m alt, 19.7C temp): Zippy-R 3s2000
6626RPM/10.22V/15.10A/32.8oz/80.1% effy

APC 12x6e (@ 29m alt, 19.7C temp): Zippy-R 3s2000
6464RPM/10.13V/16.65A/39.3oz/79.9% effy

GWS 1280hd (@ 29m alt, 19.7C temp): Zippy-R 3s2000
6186RPM/10.03V/19.53A/43.4oz/77.8% effy

4-cell Data===================================
No Load

APC 10x5e (@ 29m alt, 18.8C temp): Impulse 4s3000
9502RPM/14.34V/16.66A/45.1oz/85.1% effy

GWS 1060hd (@ 29m alt, 18.8C temp): Impulse 4s3000
9481RPM/14.39V/17.16A/40.5oz/80.4% effy

APC 11x7e (@ 29m alt, 18.8C temp): Impulse 4s3000
8605RPM/13.88V/27.18A/58.1oz/77.5% effy

APC 12x6e (@ 29m alt, 18.8C temp): Impulse 4s3000
8370RPM/13.72V/28.73A/68.5oz/82.3% effy

The half parallel wind is not exactly a no-brainer to do, it just requires you pay attention and get it right. Some winds are a little easier but none are notoriously difficult.

The image the Half Parallel wind (also compliments of Truglodite) is attached.

Dec 27, 2012, 08:36 PM
5,200 Led Lighted Bike-Bob P.
**neons**'s Avatar
That is a very nice and lengthy response. I see the difference now in that motor that you recommend trying, the D4023-850. It is wider stator in measure and surely has more power than the DT-750 and maybe the DT-900 also. I was looking at them this afternoon on the HK site comparing measurements. I put 2 in my Cart and went into my garage and worked on a plane. I had supper and went back to order the motors and they sold them out. I guess I have to wait now.

I never checked the outputs of my DT-750's I am running in my seaplane. I am using 4 blade 10x6 APC props and they rev up good. They are using 4S batteries and do have lots of thrust. I have one in Steve Shumates foamy Fokker Triplane and was wound half parallel. It has great power on 2200mah 3S and throws a 13X4E prop with authority. Love the thrust. 15 turns of 23Awg wire. I am just thinking of the little more power I can get with the D4023-850. Thanks for the nice post here of info. I know what I want now.
**Neons** Bob
Dec 27, 2012, 10:15 PM
jackerbes's Avatar
The D4023-850weighs about 20 grams more than the DAT-750 and by our 3 Watts per gram rule of thumb should handle another 60 Watts of input power. I've only done the LRK wind on it so far but it would really surprise me if the half parallel wind did not improve it quite a bit.

My initial testing on the LRK wind on the D4023-850 was pretty encouraging. I need to run that up on 4S and see how it looks but just have not gotten around to it.

Jan 08, 2013, 02:22 AM
low'n'slow is the way to go
DeepEastKilla's Avatar
As one who hates to see repetitive posts or questions that have been answered multiple times Im going to post fairly cautiously and say sorry in advance for those regulars in this thread.

I did start off googling the issue and came up with a few results. Hoping to further understand the problem and how I might be able to fix it I came to the logical place and found this thread. I never have had much success with the thread search tool and that didnt change this time, so once again, sorry if this question has been answered 1,000 times.

I decided to finally break and try my hand at getting into the multirotor world. I went with FliteTest Hquad plans which called for dt750's, but ended up getting 700's as the 750's were out of stock. Seeing as these motors are very similar I dont think my question will have any problem being answered here.

Anyway, like many others I seem to have messed up one of the 4 motors as it is much more stiff to turn than the other three. I had completed multiple test flights without issue and now cut the excess length off of my shafts. Before doing a post-op test flight I let the motors spin at low speed for a while just to check it out. Luckily for me a prop flew up then, rather than in flight a minute later. I tightened all the nuts down a bit more and put a drop of locktite on each. After re tightening the nuts I went back to fly and noticed one motor was very stiff.

I did some searching to find that I, like many others, had bent the motor bell by over tightening the nut with a prop directly pushed to the motor rather than another nut. I had hoped that simply loosening the overtightened nut a bit would undo the problem, but it seems the damage has been done.

The question now becomes what I can do to correct the problem from here. Mind you it doesnt seem to affect flight performance, but its one of those things that really bugs the crap out of my OCD side. Is the bell indeed bent and the motor ruined? could it be fixed by taking the motor apart and attempting to move the shaft up? First day with my quad in the air and it seems I may have taken it out of commission without even crashing!?

Hope there's hope for me! Thanks.
Jan 08, 2013, 08:08 AM
jackerbes's Avatar
There is a chance that you have not actually bent anything, you might have just pulled the shaft forward in the inner races and now the bearings are pulled together too tightly.

Look at these two sequences to see what I mean:

The right way to mount a prop:

end of shaft---> nut + washer + prop + washer + nut <---magnet housing top{

The wrong way to mount a prop:

end of shaft---> nut + washer + prop + washer <---magnet housing top{

The only difference in those two methods is that the nut that is closest to the magnet housing has been left off. That nut would normally be bottomed out where the threads end and the shaft becomes unthreaded.

In the wrong method prop is resting on the housing and as the nut is tightened it can pull the shaft forward through the inner bearing races. The pulling forces on the shaft is restrained at the back of the motor by a Circlip and that pulls the bearings towards each other and that is probably creating the drag you feel.

You may be able to relieve the pressure on the bearing by removing everything from the shaft, loosening the grub screw at locks the magnet housing to the shaft. That grub screw, incidentally, has probably slipped downwards on the shaft a short distance as the over-tightening happened.

Use a close fitting straight shank (not! ball ended) hex wrench to loosen the grub screw, if you use a ball ended hex wrench or loose fitting wrench it will probably strip the hex socket in the grub screw.

Just loosening the grub screw may provide some relief on the drag. If it does not, put the motor back in the mount, rest the mount on a block of wood that has a hole in it that is large enough to clear the Circlip. A hole that is about 5/16"/8mm or so is about right.

That will put the shaft point upward and the motor restrained on the block of wood. Put two nuts on the very end of the shaft and lock them together to protect the threads on the end of the shaft. Now use a small brass hammer and give the nuts a gentle tap. If that relieves the drag you are done. In a normal motor there will be a slight amount of play that will let the magnet housing move up and down, like one or two thousandths of an inch 0.025-0.050mm) or so.

Now you can replace the grub screw and you should put blue (not red!) Loctite on it when you do that. It is not a bad idea to upgrade the headless (1.5mm socket) grub screw with a button head screw that has a 2mm hex socket and the same 3-0.5mm thread. You can see one of those here:


And you can find them at the LHS in the Traxxas car replacement parts assortment or on eBay.

I never mount props on the DTA-750 motors by clamping them to the shaft with nuts. It is just a poor choice for getting adequate clamping force on the prop hub. I use wobbly prop savers and Thera-Band prop- saver bands as seen in the attached photos. And the full story on fiitting and using prop savers and making the bands is in this thread:

Prop Savers - Fitting, Using, Testing, & Making Thera-Band Bands - https://www.rcgroups.com/forums/show....php?t=1419378

I have hundreds of hours of flying time with prop mounted with those bands (using two or even three bands) and have not once ever lost a prop in flight. I hear the silliest stories from multi-rotor guys about how prop savers cannot be used because they cause vibrations, are not reliable or strong enough, and other silly reasons. Those are simply lame excuses.

If you fit a prop saver as shown at that link, use two or three Thera-Band bands, and have a balanced prop, the chances of losing a prop in flight are very remote. The bands are cheap (a fraction of a cent to a few pennies at the most) and can be replace occasionally for further insurance.

You have my sympathy on the lack of success on the search engine here. If you use it in the Advanced Search mode and make sure to set the date range for the search to Any Date... it will work a little better. But for most searches you will get better search results from google by using a search like "rcgoups.com dt700".

If the above does not fix your problem, you may have actually damaged the magnet housing by deforming the bell. That will be harder to deal with. If you need help on getting the motor apart this thread will help:


Last edited by jackerbes; Jan 08, 2013 at 03:37 PM.
Jan 08, 2013, 12:56 PM
Registered User
manuel v's Avatar
Quadracopter and HXT750.

By Crackup007.
Vuelo Quad Isra (5 min 5 sec)
Jan 09, 2013, 01:02 AM
low'n'slow is the way to go
DeepEastKilla's Avatar
New question now becomes, Whats worse? A tight motor or a lost e-clip... Yes, I managed to loose the e-clip. I took it apart and put it back together one time with much success, but wanted to tinker more so I took it apart again... Hopefully the LHS has some e-clips that will substitute the one lost on the floor somewhere.
Jan 09, 2013, 07:40 AM
jackerbes's Avatar
Originally Posted by DeepEastKilla
New question now becomes, Whats worse? A tight motor or a lost e-clip... Yes, I managed to loose the e-clip. I took it apart and put it back together one time with much success, but wanted to tinker more so I took it apart again... Hopefully the LHS has some e-clips that will substitute the one lost on the floor somewhere.
A tight motor would be the worst situation. If the sliding resistanceof the shaft in the inner bearing races is not too much, you'll notice that when the magnet housing is placed over the hammer heads (restrain it so it seats gently, don't let the magnets slam it into place or that can damage a bearing) it will find a location where it wants to be. That is the optimum position for it to be in when the motor is running, and I call it the "sweet spot".

You can measure where the sweet spot is by using feeler gauges in the gap between the base plate and the lower edge of the magnet housing. So when you mount the magnet housing you want to have that gap right and at the same time, (for a firewall mounted tractor motor) you want the Circlip to be up against the inner race (or against the washer/spacer that is on the shaft between the Circlip and inner race). That will prevent the pulling forces of the prop from pulling the magnet housing forward and out of it's optimum location.

Are we done tinkering yet? No! Of course not. With the motor set up as described above you may be able to push the shaft to the rear and displace it from the sweet spot. To prevent that from happening you have to place washer/spacers on the shaft inside the magnet housing so as to fill that small gap between the front bearing's inner race and the cylindrical boss inside the magnet. With that gap filled, you now have a motor that has a magnet housing that will stay in the sweet spot in either a pusher or puller configuration.

The final consideration is that when the motor heats up in use all of the various metals (aluminum and steel for the most part) will expand in all directions. The shaft will get longer, bearing tube will get longer, etc., etc. Carefully established tolerances will get larger and smaller as the different metals expand at different rates. And you need to set the motor up so that the bearings do not become too tight when the motor warms up.

Now the consideration is clearance or free play. Imagine that both the bearing tube and the shaft are going to get longer as they warm. But the aluminum will gain more length than will the shaft because that is the nature of the expansion rates in the two different metals. So, with a goal of having enough free play for the shaft to not cause the ball bearings to be pulled tightly against the sides of the bearing races, you want the magnet housing to have a small amount of fore and aft sliding movement in the races when the motor is at the ambient temperature. That will allow the motor to warm up without causing any bearing binding. That clearance will be seen as small amount of travel that changes that sweet spot gap when the housing is pushed in or pulled out.

I consider a free play of 0.001-0.002" (0.025-0.050mm) to be about the right amount for these motors.

Why do I worry myself about these kinds of details? Because once you are aware of them it is nearly impossible for an old machinist to not want to know what the clearance situation is on the bearings. And once you have learned what it is, it is impossible for an old machinist to not want to make it right.

Jan 15, 2013, 01:16 PM
Registered User
I have a little question about motor disassembly. How the bearing tube is connected to the stator? Is it glued or press fit? I'm thinking of machining a new tube with a different mount in it to make the motor shorter in height.
Jan 15, 2013, 06:14 PM
jackerbes's Avatar
Originally Posted by z4m1
I have a little question about motor disassembly. How the bearing tube is connected to the stator? Is it glued or press fit? I'm thinking of machining a new tube with a different mount in it to make the motor shorter in height.
It is anywhere from a slip fit to a light pressed fit and is also glued during assembly. On most of mine a bead of a clear epoxy like adhesive is usually visible around the tube on the top or bottom.

If you remove the bearings and use a butane micro torch to apply heat on the inside of the bearing tube you can usually soften the adhesive and twist the stator off. The problem on these motors is usually that of getting a good grip on the tube to do that. I would probably put the mount on the tube and attach the mount to a metal plate with a hole in it that allows the heating. Clamp the plate in a vise and use a gloved hand on the stator. When it will rotate slightly slide it off.

If you get a chance, show us your mount. it will be interesting.

Jan 16, 2013, 02:11 PM
Registered User
I'll post photos when it's coming together if it ever will. The project is still in design and "can it be done stage". I think I need to order few more motors or some enamel wire cause i dont think those windings will like heating that much. But for gripping i could use lathe chuck and use turning tool to keep the stator still and rotate the chuck while heating. And all if the heating thing works.
Jan 16, 2013, 04:01 PM
jackerbes's Avatar
If you heat the inside and quit as soon as it loosens it won't normally put much heat into the windings.

But most of the time when I do that the windings are either already gone or going to be stripped for rewinding.

You're a lucky guy if you have a lathe to use.

Do you have the newer motors with the 9mm bearing tubes? On those I think you could move the shoulder on the 9mm portion a little closer to the motor to take a little bit off of the height. I only have the original version moto with the 8mm tube. You can see them both here:


Jan 18, 2013, 05:22 PM
Registered User
Fourdan's Avatar
I tested recently two DT750 (new 2012 with tube 9mm and flat magnets)
For info:
Stock windings
1) Kv 757 rpm/V Rm 0.0711 ohm Io = 1.435A @11.06V
2) Kv 763 rpm/V Rm 0.0710 ohm Io = 1.470A @11.04V
Running smoothly
I will rewind in 2013 (probably!) for lower Kv

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