Tiny DC Motor Repair - Page 1
Forum section: electronics / repair

author: vidarr
author_rank: Frequent Contributor
timestamp: October 20, 2018, 02:10:34 pm
content: I have this tiny DC motor that the end broke off. Online, there are lots of pictures of the motor, but I cannot find what the inside looks like. I know one wire (GND) goes to the housing and the other wire touches the metal contacts around the axle. But, how to repair that? Do I make a cap for the end and then dangle some wires into the end of the motor to hit those contacts? What keeps them from bending up? How to keep them always in contact (I mean pushed down touching the contacts, not when it is spinning).Thanks

author: Gyro
author_rank: Super Contributor
timestamp: October 20, 2018, 02:46:29 pm
content: That's a coreless 3 pole brushed motor. There would have been two brushes in the end cap , one each side of the three metal contacts on the shaft (the commutator), each connected to a supply lead. Neither of the supply connection wires would have gone to the housing. The brushes would have been lightly sprung metal strips, possibly precious metal plated to maintain good contact as the motor turns.When you say "broke off" do you mean that the plastic end cap is lost, or do you still have it? If it is lost then I think you have nearly zero chance of a satisfactory repair.EDIT: A 5 pole version (with a damaged brush):

author: vidarr
author_rank: Frequent Contributor
timestamp: October 20, 2018, 03:44:16 pm
content: Thank you very much for that picture!I have the little cap that goes on the end, but the sprung, metal strips are gone (I don't know where). There is a possibility I can fix this.Maybe.Thank you!

author: Audioguru
author_rank: Super Contributor
timestamp: October 20, 2018, 04:16:50 pm
content: Small model airplanes and quadcopters use little motors like that. They are inexpensive but their brushes and commutator wear out soon.A local hobby store will have many replacement motors and one might be exactly the same as yours.

author: Gyro
author_rank: Super Contributor
timestamp: October 20, 2018, 04:24:01 pm
content: Yes, that would be a better bet, depending on whether gears or whatever are involved at the other end. From what I can see, there is a black plastic assembly attached but that might just use a push-fit plastic pulley and belt.If you have the plastic end bit then at least you havesomemechanical framework to work with. Maybe you can find some phosphor bronze strip that would glue into the slots. It's definitely a long-shot though.

author: vidarr
author_rank: Frequent Contributor
timestamp: October 20, 2018, 04:58:36 pm
content: Unfortunately, there are no stores like this anywhere near me.My plan is to fasten the commutator and instead the housing will spin. I am going to solder little fins to the housing and set inside another housing to create a tiny water pump.edit: Oh Yeah --- Thanks! Any comments on the water pump feel free. I'll post a pic when done. It is for liquid cooling an IC. This should be fun and cool.

author: Gyro
author_rank: Super Contributor
timestamp: October 20, 2018, 05:26:00 pm
content: Unfortunately that won't work - whichever is stationary, the electrical connections to the commutator need to rotate with the housing (magnet), hence the brushes.The only way to drive it would be with a brushless motor driver (ESC). You'd be better finding a different motor for the task.P.S. Water and electricity don't mix. Even at a few volts you will get electrolysis and corrosion.

author: vidarr
author_rank: Frequent Contributor
timestamp: October 20, 2018, 07:07:54 pm
content: I was going to put a little spring on the outer, stationary housing (the new one I make), that pushes onto the outer housing. Does that make sense? I am making a prototype now.

author: Gyro
author_rank: Super Contributor
timestamp: October 20, 2018, 07:48:07 pm
content: I don't think you're fully understanding my me regarding the brushes. Here's an animation from Wikipedia search "electric motor".The magnet is part of the housing, as are the brushes. The same brush-commutator action as shown in the animation must take place, regardless of whether the rotor is turning or the housing....https://en.wikipedia.org/wiki/Electric_motor#/media/File:Electric_motor.gifIf you make the housing rotate then your supply wires will twist up very quickly!

author: vidarr
author_rank: Frequent Contributor
timestamp: October 20, 2018, 08:39:02 pm
content: Oh, I think I get it. I understand how the DC motor works, I am having a hard time seeing how it is constructed. With a larger motor, there is a brush on either side pushing into the commutator. I thought that one of those "brushes" was attached to the housing somehow and the other was coming through the "top" (the side that opens).So, what is really built, is two brushes pushing down onto the end of the commutator? Is that right?edit: I just put my glasses on and looked at my pic again and I re-read your first post. I see it now. I cannot see up close without reading glasses, but my glasses don't magnify enough to see that detail. I had to zoom in on my picture. LOL. Thanks for all your help!!!

author: Gyro
author_rank: Super Contributor
timestamp: October 20, 2018, 08:59:18 pm
content: Yes, you've got it now. two brushes, one each side of the commutator.

author: vidarr
author_rank: Frequent Contributor
timestamp: October 20, 2018, 10:04:26 pm
content: Look what I saw now. I didn't even see the brushes. I took a picture and zoomed in. I have no idea how I can fix this without new glasses, or a magnifying glass, or something like that.

author: james_s
author_rank: Super Contributor
timestamp: October 20, 2018, 10:20:25 pm
content: Those brushes are completely mangled and twisted. Sorry but there is no reasonable way to repair that motor, you would be better off to throw it away and buy another one online, they're not expensive.

author: m3vuv
author_rank: Super Contributor
timestamp: October 20, 2018, 10:32:47 pm
content: sounds like a lost cause!,fancy posting such a stupid post,its a total no brainer in my opinion!!,m3vuv

author: CatalinaWOW
author_rank: Super Contributor
timestamp: October 20, 2018, 11:58:28 pm
content: I am not quite as negative on the possibility of repair for this. It will be difficult, but if you are at the end of a very long supply chain it may be easier than replacement. You will need a steady hand, fine tweezers, a microscope and much patience. No guarantees but it can be done. You will have to figure out how to install the cap with brushes onto the commutator without mangling the brushes. This can involve things like very careful shaping of the brushes, fixtures and multiple tries.Before you embark on this think about why it failed in the first place. The small cavity under the brushes captures the end of the motor shaft and forms a bearing. Most likely it has worn to a much larger diameter than its original. So the motor did strange gyrations and bent the brushes and threw the end off. A repair would have to correct this problem also. Depending on the tools you have access to this would range from tricky to impossible.A purchase may look much more attractive after thinking all of this through. Small motors like this are inexpensive at their source, and might not be that bad after they make their way to you.Finally, your concept for supplying one side of the power to the motor through a spring contacting the case is feasible. Since the end cap is non-conductive you could put another metal cylinder on the other side with a second spring to get the other side. This is very different from normal brush design and will have life, friction, contact resistance and other problems but might well serve a non-demanding application. That does not solve the problem that this motor is not design for or compatible with underwater operation. It might work in a non-conductive fluid like a light oil.

author: vidarr
author_rank: Frequent Contributor
timestamp: October 21, 2018, 12:09:58 am
content: Yeah, long end of a supply chain for sure. Not just that, but I have to pay $15 tax right of the bat. The shipping from China is always another $8 minimum (usually $12-20). So, this $0.50 motor is already at least $23.50. It wouldn't be here until next year around April, or May. It would be stupid not to at least give it an hour of trying. It is fun for me, constructive and relaxing, so it beats, say, reading other peoples' posts and making stupid comments.It broke by getting smashed in a toolbox. I think I can fix it. I'll give it a solid hour try.Thanks guys!

author: Gyro
author_rank: Super Contributor
timestamp: October 21, 2018, 10:03:53 am
content: Well, at least you found those brushes!Yes they are mangled but given your cost and time issues, there's nothing to be lost in trying.Eachbrush usually comprise parallel strips (looks like two in your case) to ensure that they make good contact - if one doesn't make good contact then you have a reserve. If you snap one, it probably isn't quite the end of the world.You clearly need some optical assistance (don't we all these days), but try to bend them straight again with fine tweezers. When refitting the cap, push the rotor up so that you can see the commutator andslidethe cap on sideways, watching out that the brushes don't snag, rather than just trying to push it onto the end which is sure to mangle them again. Then slide the rotor and cap together back into the housing. As CatalinaWOW says, it may take multiple tries.

author: TurboTom
author_rank: Super Contributor
timestamp: October 21, 2018, 11:48:09 am
content: Similar motors can often be found to drive the "vibrators" of older mobile phones. If you can get a scrap cell phone, preferably >10 years old, there's a good chance you'll find a motor inside that you can use as a replacement.