Strange noise from HXT motor on scooter

I ordered this motor, http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=3890&Product_Name=HXT_63-74_200kv_Brushless_Outrunner_(Eq:5240), and put it on my scooter. After time, I've noticed that it's developed an increasingly annoying "clacking" sound. Having trying to observed it, I noticed these things...

-It only seems to happen when the belt has significant tension. It seems to be barely there when rotating the motor when the belt isn't attached.
-The belt is centered on the pulley (Not unusual, just mentioned).
-It seems to happen about once a rotation of the motor, however, it doesn't seem to happen in "the same place" of rotation. I would hear the sound, roll slightly backwards before the sound came, rolled forwards and it wouldn't happen at that same place of rotation - It happened about one rotation after the forward rotation happened.
- When rotating very slow, it slows down into an elongated "clacking" sound that's stretched out, suggesting something that rubs more than "hitting".

So, any guesses as to what it might be? I don't really know that it's the motor, but I heavily suspect it probably has something to do with it. Maybe its the pulley? The pulley is attached to the shaft by a single-set screw.

Sounds like it could be a bad ball-bearing - you might see if you can get a stethoscope on Craigslist - might be able to help pinpoint which bearing needs to be replaced.

Caveat: I have no experience with this motor.

mrgarci1 said:

Sounds like it could be a bad ball-bearing -

Click to expand...

I second that

So, if it is a bad ball bearing, would replacing the entire "bearings thingamobob" solve it?

I was under the impression I'd need to upgrade the ball bearings eventually, anyways, so it probably wouldn't hurt to do it sooner. If it eliminates the problem, excellent! If not, I can rule out the ball bearings. But, gahhh.... I wanted to do the whole shebang of upgrades when my first magnet fell out so I could justify resecuring those, too. :/ I think the current ball bearings are merely "shielded" as opposed to sealed(Better for weather?), so that's why I would've liked to upgrade the bearings eventually.

The motor's casing/bell/can/skirt/whatever-it's-called also does seem abnormally hot for only pushing 50 amps (around 140-150 degrees) so it seems there's something creating extra heat. Since the windings are only .03 ohms, it seems that's only 75 watts of heat generated in the windings.

If my experience with two cheap Chinese RC motors is anything to go by, then I'd say it's very likely to be the bearings. Both of my motors had bad bearings, the primary problems being excessive assembly/locking adhesive having found its way inside the shielded races and a distinct lack of lubricant. The bearings had no makers name and seemed to be pretty poor quality.

Replacing the bearings is pretty straightforward, but you will probably find that they are glued in to the boss, so may need some persuasion to remove. My TowerPro motors have two small bearings next to each other at the "bell" end and a single, larger, bearing at the drive shaft end. I found that the bearings were standard sizes, readily available from SKF, NSK etc. You will probably have to make up some custom-sized drifts to drive the old bearings out. It might help to gently heat the centre of the motor (avoiding getting the windings too hot), as this will help soften the locking adhesive. I found that pointing a hot air gun down the bearing hole, with a narrow nozzle fitted to it, did the job for me.

I replaced my bearings with standard SKF shielded ones, as I didn't want the extra drag of using sealed bearings. Sealed bearings might be a good idea if you think it's likely that your motor may get very wet, otherwise I'd stick with shielded ones, as they'll keep out 99% of stuff, and run a bit more freely as well.

Jeremy

seems like a seal on a high speed shaft would get too hot from friction. that is why seals fail at low speeds too i think.

Okay, do you know available bearings of this type are at the local level or would I most likely have to order it in? I'm in Seattle so I'd think there'd be something, but it doesn't seem like Seattle has an equivalent to "Digi key" as far as electronic components go, so I'm not getting my hopes up.

Any good bearing shop should stock them, as they are standard, off-the-shelf, ball races. If you can't find a "real" bearing shop local to you, then a google should show up a virtual one in your neck of the woods.

I got mine from a UK on line bearing supplier, www.bearingboys.co.uk, but there must be somewhere like this more local to you.

You may need to search for miniature bearings to find the size range you need, as not all bearing stockists have these smaller sized bearings in stock.

The bearings may be marked with their part number, but if not you'll need to take the old ones out and measure the outside diameter, inside diameter and width, in mm, as they'll be metric. Bearing part numbers are fairly universal, for example the drive side bearing in the TowerPro 5330 is a 608Z, which is a standard 8mm inside diameter, 22mm outside diameter, 7mm width double shielded ball race and the bell end bearings are two 688Z bearings that are 8mm inside diameter, 16mm outside diameter and 5mm width, with shields.

You'll find the bearings will be sized in whole numbers of mm, so should be easy enough to identify.

Jeremy