Replacing Bearings in Axi Brushless Motor

[Andy-H]

I bought a used Axi 1420/14 motor a while back. Whist it ran smoothly on the test bench, it sounds noisy mounted in an airframe. It’s fitted in an Acrowot - bolted to to an aluminium backplate with M5 threaded rods fixing the plate to the firewall.

 

I’m wondering whether to replace the bearings. I’ve done this with a couple of 4-max motors but George sells the spares. Does anyone have experience of replacing bearings in an Axi motor - if so, can you suggest a supplier or will I have to get them from Axi ?

[Andy Gates]

There are many bearing suppliers who can probably source the bearings for you once you have them out so they can be measured.

However, if the motor is quiet and smooth on the bench, it sounds like the source is elsewhere.

Loose mount, off centre prop adaptor, unbalanced prop?

Harmonics with the length of the motor stand offs?

 

I would search the set up first rather than change bearings.

[PeterF]

I buy bearings from suppliers on ebay or bearing boys for my various motors. Strip the motor down, remove the bearings and measure them with a vernier / caliper, ID, OD and width then find suitable bearings on line.I

 

https://www.bearingboys.co.uk/Miniature-Bearings-1324-c

[Philip Lewis 3]

First off do not get them from Axi (or any other motor manufacturer for that matter), no one makes bearings apart from bearing companies, not even the big car manufacturers so you are simply wasting money paying their mark up.

 

Taks it apart, measure the OD and ID diameter of the three bearings (likely to be two at the front and a bigger one at the back and the thickness, those are the dimensions you will need, I use SMD Bearings in Oxford, no need to trawl through the website just give them a ring (far easier and they have always been really helpful), they will ask you whether you want branded (typically Eizo) or budget, the difference is pennies so go branded. 

 

The other thing they will likely ask is whether open shielded or sealed, these motors use shielded bearings but you can check by seeing that there is no rubber seal but that there is a metal shroud which shields the bearing meaning you can't see the individual ball bearings.

 

Whenever I have taken apart Axi motors I have always found the grub screws to be really tight because they use thread lock liberally so use a really good hex drive so as not to round it off.

 

Other than that, it's a really simple process, cheap and very rewarding to do.

Edited September 19, 2023 by Philip Lewis 3

[Andy-H]

Many thanks. I was wondering whether the bearings might have been bespoke spec but sounds like not. I have noticed the front grub screws are about 5mm longer than necessary so perhaps the motor isn’t quite “as new” as the seller alleged. If anything, I might change the bearings just for peace of mind.

 

Meanwhile, I’ll double check the rest of the installation, in case anything is loose. 

[EvilC57]

I’ve always found Simply Bearings to be good.

[Andy-H]

Follow on question, and many thanks for comments so far which have been very helpful. 
 

The motor looks to be an early version of the 4120/14. On inspecting more closely, the shaft appears to be retained at the rear by a collet with a single grub screw but no flat on the shaft. Also, there’s no spacer or shim washer between the rear bearing and the collet which means the collet is fouling the rear bearing circlip. My guess is the motor has been dismantled in the past and any washer/spacer has been lost.

 

The only option would appear to be to fit a large dia. shim washer between the circlip and the collet, otherwise the collet is going to wear down quite quickly. I’ll need a shim washer with OD c.16mm to fit inside the hole in the rear of the case. Shaft is 6 mm but I can only seem to find 16mm OD shim washers with 10mm ID but I guess it’s better than no washer. Does that sound a reasonable solution ?

[Mike T]

Can you pull the rotor/shaft away from the stator housing with that collet off?  If not, maybe it's not needed?  If the rotor does move (i.e. collet definitely needed) then it may be possible to machine a relief on the collet (it appears to have one already) which will enable it to bear on the inner race, while missing the circlip.

Edited September 20, 2023 by Mike T
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