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I teach robotics with technic parts and M motors. The motors I have bought on Ebay burn out quickly and fit axles poorly (either too tight or too loose). It is difficult to teach when students' motors burn out every 10 minutes!

Please, someone tell me: who sells a good replacement M motor that will last more than a couple of hours of use and fits axles properly?

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    M motors? Do you mean Power Functions M motors [8883](bricklink.com/v2/catalog/… Functions M-Motor&category=%5BPower Functions%5D#T=S&O=%7B"iconly":0%7D) or Powered Up Medium motors [88008](bricklink.com/v2/catalog/… Linear Motor&category=%5BPower Functions%5D%5BPowered Up%5D#T=S&O=%7B"iconly":0%7D)? And the motors you buy on EBay, are they original LEGO or a clone brand?
    – Phil B.
    Commented Jan 31, 2023 at 11:10
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    For GBC displays at various shows, we usually have to replace a couple of Power Function M motors in a weekend, but that's in a setup where we have a couple of hundred of them running. 10 minutes is very low in comparison. I can't rule out that they could die that quickly if you abuse them in some way, but my first thought was that you can't be using original LEGO to get that experience. To address your other point, in my experience original motors and original axles fit together quite good (I can't see how bad axles could turn into abuse, but I can't rule that out). A Commented Jan 31, 2023 at 12:04

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If I understand you question correctly, you are currently using the Power Functions M motors such as this one:

PF M motor

I did a quick search on eBay, and most of the listings I see are not genuine LEGO PF M motors. They are listed as "for LEGO", or LEGO compatible, but they are not original LEGO products. Here's an example of one of the third-party motors:

Third-party PF M Motor

It looks very similar, but has many subtle differences. The easiest difference to spot is the lack of the word "LEGO" on the studs.

These may be good quality, or they may be significantly worse than LEGO products, but in any case, they were not manufactured by LEGO and did not go through TLGs QA process. These products also likely violate TLG's IP in some way.

The reason that it is difficult to find genuine PF M motors is because the entire PF line has been discontinued and replaced by Control+ in Technic sets. The closest replacement for the PF M motor is what TLG currently calls the Simple Medium Linear Motor:

45303

Unfortunately, this motor is also retired as a standalone product on LEGO.com, although it was included in sets as recently as 2022.

If you are looking to something that you can buy today directly from LEGO.com, the Technic Large Motor is probably the best choice.

Technic L Motor

Transitioning to the Control+ system would also require purchasing new battery boxes, which are not especially cheap.

One approach is to purchase genuine PF medium motors on a secondary market such as Bricklink. Here's the listing for the PF M motor there. Most established Bricklink sellers take quality very seriously. They know how to identify non-LEGO products and will work hard to make sure you only get genuine parts.

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  • I suspect that high-quality third-party motors would fit the asker's needs better than genuine-Lego Control+ motors. Commented Feb 22, 2023 at 2:48
  • definitely i have 42140 with 2 motors like this
    – LKBricks
    Commented Mar 2, 2023 at 3:13

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