• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.

DT700 motor and epoxy incident, am I screwed?

#1
So, I started my tricopter build today. Want to say it is my first RC anything other than the kids stuff when I was little, a glider that never worked, a minirobot, some airsoft guns right out of college, and a lawnmower.

I picked up DT700 motors because everything else in the DT range was out of stock except the DT850s which were not specified if brush less or not and I am assuming the differences in the 700 and 750 as used in the tricopter guide are minimal.

I got to the part where you put a bit of epoxy on the motor to secure the wire. Apparently, I had an issue with the nozzle of the two parts and what I thought was the right consistency was not.

On the first motor the thinner half of the liquid squished around the wires and between the magnets. Not a big deal because this must have been the drying agent and dried quickly without leaving residue. The second motor was more of a problem. This time the goo flowed between the magnets and actually began to harden. I quickly took the motor apart. The third motor was fine and still appears to be fine. The first motor seems fine like the third one.

When I took the motor apart I used a paper towel with mineral spirits to wipe both surfaces of the magnets together as listed under cleanup for the glue. This did absolutely nothing for the glue other than make bits of paper towel stick to the magnet surfaces. What crap.

Well the stuff is still semi sticky. Seems that it is actually 25minute - 24hour glue as listed on the back instead of 5 minute as listed on the front. I have peeled the papertowel off but there are still tiny globs of sticky glue on the magnets. I assume that when it dries I can scrape it off. As of right now when I insert the motor back together it is harder to turn when I turn it, imagine that.

Here is my question, how screwed am I. I dont remember too terribly much about motors from school many years ago other than this type takes three wires to make work. Kind of like the three phases of power produced by the big turbines at power plants. Assuming I can get the maginets clean will the thinner epoxy that is covering some of the weaves, maybe on one or two columns, screw me over. Also, is it even reasonable to think I can get enough of the epoxy off without damaging the magnets to make the thing work right again?

I know I regretted not getting DT850 after I determined they were bigger versions of the DT700s which officially support 4 cell lipo but I didnt want to have to buy new ones already. So, am I screwed???
 
#2
Ok after taking the time to type this, letting it dry some more, and taking a shot of vadka I dont think this as big of a problem as I thought. It is not nearly as sticky as it was and I think I can scrape it off when it ever finishes drying. Either way I guess it is only a $10 problem. Just be a pain to wait another four weeks for some more motors.

Still anyone think there will be any problems?
 

Liemavick

New member
Mentor
#3
If you can get the magnets clean and remove enough glue from the coils to where its not rubbing you may have a good chance to save the motor. Use caution around your wire coils as you dont want to bend,break, or cut any of them. Take your time and you may be OK.
Good Luck,

Brian
 
#4
Seems much better now I scraped some more off and it is only a little bit rougher to turn than the other two. Whats the chance of it smoothing out after I fire it up and run it a big. Or will it cause extra stain on the motor?
 

colorex

Rotor Riot!
Mentor
#5
Seems much better now I scraped some more off and it is only a little bit rougher to turn than the other two. Whats the chance of it smoothing out after I fire it up and run it a big. Or will it cause extra stain on the motor?
If it has some friction it will draw more current, if this current is too big it may overload and burn out your ESC. It will also drain your battery a tiny bit faster.
 
#6
Update. I am pretty sure it is fixed and will know when I solder on bullet connectors and wire it up this weekend.

Turns out the slightly gritty feel was because I was testing it without the bearing in place on the bottom of the shaft. So the whole wire assembly was wobbling inside of the magnet assembly. It is now back together and I am not even sure which motor it was.

Also, did I mention that I hate C-clips? I am having some major renovations in my house right now and stuff is everywhere. One particular room has the contents of both my wife's and my bedroom closets. I was trying to get the clip off quickly before the glue dried last night. When the c-clip popped loose it flew into that room. I later found the clip under one of my wife's shoes after about 30 minutes of searching.
 

earthsciteach

Moderator
Moderator
#7
Yes, C-slips are evil. I always struggle with them. I'm sure there is a proper tool out there for those tiny things. You were very lucky to find the darn thing!

Actually, I was just down in the basement cleaning up my RC workshop and ran across a small bag of C-clips. I got pretty excited because one of my motors is in need of one. Now, to just install the darn thing!
 

Cyberdactyl

Misfit Multirotor Monkey
#8
First, mixing the epoxy shouldn't be such an issue. I usually squeeze a bead of each beside each so I can visually see they are similar. Be very careful not touch the tip of the bottle to the other liquid. Then mix thoroughly. Use a different stir pattern every few seconds, and stir for at least 20-30 seconds, making sure you're capturing and mixing every bit of each blob.

But enough of that, I don't want to sound like I'm lecturing on something so simple. Much better for me to share my boner when I first dealt with my DT750s. :rolleyes:

The next few lines is lifted from another thread here at Flitetest. . .

"I used JB Weld for it's strength under temperature. I thought about hot glue, but the windings do occasionally get very warm, so I was a bit worried the glue might soften during heavy motor load. And the complete coating of the stator windings will accelerate heating. But I must mention, there's a HUGE caveat in using JB Weld.

JB Weld is magnetic.

I learned this the hard way. What you MUST do if you use it is to remove the stator from the bell housing, as the housing has the neodymium magnets and the JB Weld WILL propagate towards the magnets and bridge the gap between the bell and the stator. When I checked on the progress about an hour later, I was horrified to learn the motors were locked solid! I thought I had trashed $45 worth of electronics. :mad: Luckily there's enough gap (~0.7mm) to work something thin in between. I spent roughly 15 minutes per motor with an exacto blade chipping the away that bridge."
 
Last edited:
#9
Yeh I dont think I let it sit long enough after mixing. Third motor worked out great. Also, saw JB weld at the store and it seemed like it was a bad idea because I thought it might have some sort of conductor in it.

Next time I think I will try hot glue since reading the temps on the stuff last night and it seems the wax that holds the maginets on melts at a much lower temp even than low temp hot glue. As for high temp hot glue it looks like it might actually damage the wires. I will do more research or just mix the epoxy better and let it sit longer next time.
 

Cyberdactyl

Misfit Multirotor Monkey
#10
No, JB Weld is perfect for the application. Non-conductive, Very strong, High heat tolerant.

If there's anything other than the precautions during application I would mention is it's slightly more brittle than something like Bob Smith's 2-part epoxy.
 

Liemavick

New member
Mentor
#11
This may be to simple of an idea. Why not disassemble the motors before applying any adhesive? That way you can see exactly where its going and if its getting where it shouldn't. Aside from the dreaded disappearing C clip it takes like 30 seconds to take a motor apart.
 

colorex

Rotor Riot!
Mentor
#12
This may be to simple of an idea. Why not disassemble the motors before applying any adhesive? That way you can see exactly where its going and if its getting where it shouldn't. Aside from the dreaded disappearing C clip it takes like 30 seconds to take a motor apart.
It is what I do! I was afraid the epoxy would run down towards the bearings so I took them apart first.
 

Cyberdactyl

Misfit Multirotor Monkey
#14
I've had the C-ring pop off and it took me 10 minutes scanning carpet with my head 12" from the floor to find it. Now I take a dry cleaner bag and put over my hands and motor when I remove and attach.