A: There are two kind brushes we normally use: the metal brush and carbon brush. We choose based on the speed, current and lifetime requirements. For quite small motors, we only have metal brushes while for big ones we only have carbon brushes. Compared with metal brushes, the lifetime of carbon brushes are longer since it will reduce the wear on the commutator. But for low speed motor, the carbon dust might not be able to burn in time which will cause failure too.
Q: How much I should pay for samples?
A: For low cost samples with quantity no more than 5pcs, we can provide them for free with freight paid by buyer (if clients can provide their courier account or arrange courier to pick them up from our company, it'll be okay with us). And for others, we'll charge sample cost and freight. It's not our aim to earn money by charging samples.
If it matters, we can make a refund once got the initial order.