On 7/29/07, Andrew Wowk <[EMAIL PROTECTED]> wrote: > Chris, > Do you know any details on how to do this?
No. I know it's done regularly on wound field armatures, both on the windings and the commutator, to keep things from flying apart at high rpm. I see no reason it couldn't serve the same function here, assuming there is room for the Kevlar band. It's important to understand that I've never seen the insides of these motors except in some pictures. I don't know as much as you guys do. For example, Paul Compton says banding the armature will reduce cooling. He may be right - I assume the air goes across both faces of the armature and out the rim of the case, so if you fill the gap around the rim you might reduce cooling. Or perhaps you can provide an exit for cooling air that is not blocked by the banding? Or keep the band narrow and centered over the clips? > Have there been any other reports of wheel lockup so far? Only Dale Henderson's that I know of. For me, that's enough. There's nothing particularly unusual about his installation, nothing to suggest it couldn't happen to any other user. Dale said, "i had a PMG132 lock up but i was only doing 15mph at the time but it left a nice skid mark." and "i'm not sure on the technical terms but i think they are called the communicator the little metal blades spinning on the edges near the housing. a few of those came off and jammed there is a picture on my blog." The picture is the second photo down on this page: http://geocities.com/hendersonmotorcycles/blog.html?pg=2&cnt=5&t=a That's why I'm being so emphatic about this. We know these motors can shed their little clips when worked hard, and life on an EM is hard work for them. Dale's experience shows that what we would normally assume to be no more than an expensive failure can also be a deadly one. Dale's failure could just as easily have happened in traffic at speed. To answer your earlier question Dale, traveling at higher speed would probably not have prevented a lockup. Friction at the tire patch does not change with speed - the only advantage speed gives you is that the jam would have to overcome the higher rotational inertia of the armature and wheel. Not something I'd bank on with ~5:1 gearing. Dale was lucky. The next person to whom this happens might not be. > Can the etek or PMG be repaired by simple resoldering the clips? I don't know. What surrounds the tabs that the little clips are soldered to? Is it sensitive to heat? In other words, would it be easy to toast something that shouldn't be toasted if one of us tried a repair with a big iron in our garage? My guess is that the way these things are assembled during manufacture depends on some specialized equipment that can ensure good, repeatable joints. Understand though, that your question misses the point. Solder must not be relied upon to withstand a significant physical load. Designing these clips to do that was a mistake. Others have made the same mistake in various applications, including an engineering team I joined years ago. I discovered the mistake when I read up on solder and learned how it's supposed to be used and not supposed to be used. Subsequent testing proved the solder would fail when loaded and thermal cycled. Here's another thought. If banding is impractical, I wonder if you could create some sort of mechanical interlock between the tabs on the armature and the clips. Maybe a small dimple that gets pressed into a mating hole? Crimp them together so that even with no solder at all you could spin the motor beyond its rated speed and not lose any clips. The subtle but critical issue here is that solder with no mechanical load on it works just fine, even with lots of thermal cycles. If you apply a mechanical load to a solder joint while it's going through those thermal cycles, you are begging it to fail. That's exactly what is happening to those little clips. If you can take the mechanical load off the solder joints, everything is fine. Again, you guys are the experts, I'm just on the sidelines. But based on what I've heard from you, there is no way I would use this style of motor on an EM unless I could make sure those clips could not lock my wheel. There are a variety of paths to a solution. I believe that simply monitoring temperature is not enough. Since the clips are always loaded by centrifugal force, even "normal" operating temperatures might ultimately result in failure. Chris
