Turnigy produces a line of motors called “NTM”. Those are low cost brushless motors that are suitable for medium sized multicopters. At the time of this writing, these motors sell for around $15 each on HobbyKing. Since I’ve seen quite contradictory comments at various fora, I’ve decided to add this post to the confusion.
I’ve been playing with these motors for a while now and they work well. While not the best constructed motors, they allow very inexpensive builds that won’t break your bank when a flip turns bad. In fact my experience has been that these motors are pretty survivable and tough.
Overall, there are some tricks used to keep costs down on these motors. Here are the ones I’ve discovered:
The motor wires come with the bullet connectors soldered, but instead of flexible silicon wire, these are simply the same copper wrapped inside the motor, with some rubberized isolation and thermal shrink wrap. This solder joint is a stress point that can break easily with vibration or mechanical stress. Be careful how you unplug the motor from your ESC!
The motors do not include any mounting hardware. That is part of an accessory kit that adds another $2 to $3 to the total price. The kit includes the prop adapter, spinner, a flimsy aluminum mounting plate and all required screws.
The shaft is kept in place with a small clip on its bottom. While I’ve not experienced bells parting ways with the rest of the drone, this is certainly something that requires frequent inspections to make sure the assembly is safe.
That said, the bells on all my motors have dabs of epoxy on the inside that give the impression that these are factory balanced. In fact, after properly mounting them, there’s no vibration on the quad’s arms.
My work-horse NTM motor is the NTM 28-30S 800Kv. I fly these with 4S and Afro ESCs running SimonK with custom parameters. These motors have 4 M3/0.5 mounting screws in the bottom where the mounting plate is attached. The mounting plate provides 4 positions for M3 screws that would attach to your multirotor’s arms.
I like very much the fact that the motor mount is a separate, easily replaceable piece. It’s designed to break and absorb energy, saving the motor and presumably, other parts as well. However the design needs a few tweaks as in my experience, the material does not seem to hold up well over extended use.
The bearings in these motors are not the highest quality, but they are good for a few tens of hours of operation. Some of mine have been in the air for more than 50 hours with no issues. Because of the motor’s price point, it’s unlikely that replacing the bearings with high quality ones is really worth it. Some bearings will cost more than a new NTM motor, and then you need two!
All said and done, the NTM motors should be good for 3S and 4S midsize, low cost models. I would simply keep a couple of them in my stock, as spares.