Simple questions
 

I have brushed motor mid-drive 38v 450watt- here is a link to the kit
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1


the motor seems to be a very common motor- everything is working great- no complaints
i'm just curious, when it comes time to replace motor I see a lot of similar motors rates at 24 and 36 volts- is the rating more about the controller or is it in the motor windings?


where is a good source of replacement parts for things that will go bad, like the freewheeling crankset, the freewheel on the motor, the unique bottom bracket used in the kit, and the motor itself?

First, I would be surprised if it really was brushed, brushless is almost all of them.

Common as compared to what?

It is ALL the controller. Voltage is a speed regulation mechanism.

Spare Parts? Well, if you had purchased a recognized brand name sold by reputable dealers, such as Bafang, Cyclone, TSDZ, spare parts are somewhat available but can be hard to get.

When you buy the absolute cheapest thing you can find from a no-name supplier, you either find out what it really is and who sells it, or when it breaks you just buy a whole new kit.

Alibaba

Electric Bicycle Parts-Electric Bicycle Parts Manufacturers, Suppliers and Exporters on Alibaba.comElectric Bicycle

generally, dc motors (including brushless) don't care much about voltage. They mostly care about current. Having said that, the voltage rating of a motor can indicate that it will be lacking in low-end torque or high-end speed. So you want to be in the same ballpark as the motor you are replacing.

Thanks for the helpful responses, the technical expertise is very appreciated!
I'm learning quite a bit from here and endless sphere