Brushless tool motor ?

[sardine]

I have refurbished a Makita brushless Grinder, I haven't got the battery for it yet, the bearings are all good but I noticed the rotor isn't free to spin like a brush motor but magnetically locked in position and very hard to turn, can't be turned by hand , can be turned with a spanner, is this how they work or has it gone back together wrong ?

 

[Pete.]

That is normal.

 

[Screwdriver]

Brushless motors have powerful permanents magnets in the rotor (the opposite of brushed). When switched off, these align with high precision to the windings on the stator so that moving them by hand means you have to overcome a strong magnetic force holding them in alignment. Speed and power are controlled by sophisticated electronics whereas in a brushed motor they just run off whatever volts you give them.