PDA

View Full Version : Micro bl outrunner neurosurgery repair


Bill G
03-31-2012, 12:04 AM
Before tossing this little BP Welgard outrunner in the bin, I decided to attempt a repair. Removing the stator and rewinding is easier said than done. The windings were not properly strain relieved by the manufacturer, which cause 3 of the 6 to break, but looking at them the wrong way. Remaining at the break point was roughly 2mm of winding length, of which to solder repair leads onto. To do this, a pintle tip solder iron had to be inserted in the tiny windows in the motor cage, and solder on repair leads. The repair leads were tinned, and soldered to the broken winding ends, only slightly thicker than human hairs. I thought that the varnish may be a problem, but the solder took, although I had to resolder 2 of the 3, as they did not take well enough the first time, and broke away.

After the leads were soldered on, the winding sets were identified with an ohmmeter, and soldered to the correct motor lead. After completing the repair and testing, the exiting leads were potted with thick to the motor housing, to ensure that they don't break away again. I had thought about initially gluing them before the damage happened, as they were so delicate. In the future, I will do this if I come across a motor with poorly strain relieved leads.

You Tube video of the motor running:
http://www.youtube.com/watch?v=znvW_r9E-Fk

flydiver
03-31-2012, 02:00 AM
Thin fragile wire is very characteristic of those small motors.
Good job on repair. Most people couldn't or wouldn't bother.

kyleservicetech
03-31-2012, 02:38 AM
Before tossing this little BP Welgard outrunner in the bin, I decided to attempt a repair. Removing the stator and rewinding is easier said than done. The windings were not properly strain relieved by the manufacturer, which cause 3 of the 6 to break, but looking at them the wrong way. Remaining at the break point was roughly 2mm of winding length, of which to solder repair leads onto. To do this, a pintle tip solder iron had to be inserted in the tiny windows in the motor cage, and solder on repair leads. The repair leads were tinned, and soldered to the broken winding ends, only slightly thicker than human hairs. I thought that the varnish may be a problem, but the solder took, although I had to resolder 2 of the 3, as they did not take well enough the first time, and broke away.

After the leads were soldered on, the winding sets were identified with an ohmmeter, and soldered to the correct motor lead. After completing the repair and testing, the exiting leads were potted with thick to the motor housing, to ensure that they don't break away again. I had thought about initially gluing them before the damage happened, as they were so delicate. In the future, I will do this if I come across a motor with poorly strain relieved leads.



Yeah, very good job!

Been there, done that a few times. What helps is a good soldering iron station, like my Weller 40 watt temperature regulated unit with a 0.015 inch diameter tip, and 0.015 inch diameter solder. (They do make solder this small! Be prepared for sticker shock.)

Bill G
04-01-2012, 12:08 PM
Thanks for the comments all.
Kyle that's pretty much it. There's nice equipment out there for soldering, but not cheap. Thin .015" solder would be useful, as there's no way I would attempt to get in there and tin with what I had, as it would have made a mess. The wires had to be tinned and soldered, with only the solder film on the iron tip. I'd love to acquire a first class solder station with desoldering capability. This was done with a cheap 40W iron that was not overpowered for the task, but could have used a thinner tip. I could barely get in there with the tapered tip, and the entire task was exactly like a much tougher version of the game "Operation". I really could use an iron with temp adjustment, as you have to be careful not to damage components such as ICs with excessive heat. The small iron generally will do the job, but there are those odd situations where the 40W unit doesn't quite have enough power, but the high power iron is overkill. In those cases you just have to work fast. I'm a charter member of the HPIFAT (high power irons for all tasks) society. :D

I have another motor that was damaged due to excessively long mounting screws, which nicked the windings. They eventually failed at the nicks. The ends were pried up, scraped, and bridged. The motor has been tested at over 10A on 3s. That one was a much easier repair.