Motor keeps breaking

[Fnfancy]

I have a problem, on my second outing with my mt410 the housing on my arrma blx 4075 2000kv motor breaks where the 4 screws holding the end cap are. Basically the material where the screw goes through breaks off at the skinny part towards the front of the housing. It was brand new so I called horizon and they are replacing it free of charge. So, not wanting to wait for it to show up, I pulled the motor out of my E-Revo 2.0 (which runs the same motor, arrma 4075) and basically rebuilt it with the stator and end caps from the broken new motor. Well yesterday I took her out for a very mellow bash, nothing like the last time (where I blew the rear shock pistons and broke the motor) just cruzing. Some decent little jumps, a few tumbles, still getting to know the truck type stuff. Got home blew her off and was brushing it down when I noticed that the second motor was starting to break at the same place. It didn't get all 4 screws yet, one completely and a second started. Now, what's a guy to do? Does this arrma motor just have a design flaw? Never had a problem with it before in both my E-Revos it's been ran in. Moving forward, I'm looking for some motor suggestions to pair with a hobbywing ez run max8. Also, I think I'm going to drill and tap some additional mounting holes in both arrma motors, maybe that or fashion some type or motor brace/ rear support to keep it from flexing. Thank you all for your time. Remember, keep having fun!

 

[Cmbscx10]

That sucks to read. All my motor cases do not have the slot cut in where the screws are. Odd Arrma does it that way.

Anyway, not sure of the screw size but if you have the ability to drill and tap I would make them 3mm, use a star washer and of course thread lock. If it breaks again then I would use it as a fishing weight.

 

[Fnfancy]

That sucks to read. All my motor cases do not have the slot cut in where the screws are. Odd Arrma does it that way.

Anyway, not sure of the screw size but if you have the ability to drill and tap I would make them 3mm, use a star washer and of course thread lock. If it breaks again then I would use it as a fishing weight.

Haha, it would probably do well as a fishing weight. The slot is actually not supposed to be there, that's where the can keeps breaking. Normally there is material there. It's like the motor tries to flex and ends up ripping the aluminum right there. All four screws on one motor and two on the second. Though if I didn't stop when I did it probably would have claimed all four.

 

[Cmbscx10]

Haha, it would probably do well as a fishing weight. The slot is actually not supposed to be there, that's where the can keeps breaking. Normally there is material there. It's like the motor tries to flex and ends up ripping the aluminum right there. All four screws on one motor and two on the second. Though if I didn't stop when I did it probably would have claimed all four.

Don't know square about the Internals of a BL motor but I am sure the current screws only go in a few mm. Since this is a sacrificial motor in a way can you drill and tap 2 or 3 opposing holes and drill a hole in the can like a normal motor? Lots of work but could be fun to see if it works.

My guess is the motor TQ and chassis flex is just too much for that shitty can mounting.

 

[Fnfancy]

The tourque in this motor is actually pretty impressive, the magnets are intense. You can't spin it by hand unless you have a pinion on it. I will try to drill and tap some holes, probably move them down some so more material is in between the hole and the end of the can.

 

[cordell12]

I am wondering if maybe the motor mount screws are slightly to long and are somehow pushing, causing stress at the front endbell. Then a small tumble, with the stress it breaks at the only weak point. I've been all over ArrmaForum and Arrma Facebook groups and have never seen this happen, and for it to happen twice tells me something isnt right with the way it is mounted.

 

[Fnfancy]

I am wondering if maybe the motor mount screws are slightly to long and are somehow pushing, causing stress at the front endbell. Then a small tumble, with the stress it breaks at the only weak point. I've been all over ArrmaForum and Arrma Facebook groups and have never seen this happen, and for it to happen twice tells me something isnt right with the way it is mounted.

I agree with your thoughts of something not right. I was going through the truck yesterday and noticed a couple things. While pushing down on the rear of the motor, the whole motor mount and center diff housing would flex quite a bit, flipped her over and started checking if screws where tight. I guess coming from traxxas vehicles I was a little scared cranking down on screws, I tightened the motor mount and diff housing screws at least half a turn more and it removed most of that flex. When the first motor broke, I was able to remove the end bell with no problems, when taking apart the older one to rebuild it whith the new ones internals I had to put it in a vice and use channel locks and a hammer to get it off. Notices arrma pits some sort of adhesive to help hold the end bells on, so I took apart the two broken ones and added some gorilla glue and reassembled. We'll see how it goes, I guess my next move is to check screw lengths as suggested, the warranty replacement motor came the other day so I want to figure this out before I wreck another motor. Thank you for the help and suggestions from all.